WO2006038674A1

WO2006038674A1 - Optical transmission apparatus

Info

Publication number: WO2006038674A1
Application number: PCT/JP2005/018552
Authority: WO
Inventors: Toshihiko Yasue; Satoshi Furusawa; Masaru Fuse
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2004-10-07
Filing date: 2005-10-06
Publication date: 2006-04-13

Abstract

An optical beam output part (10) modifies an output light from a light source with a signal and outputs the modified output light as an optical beam signal. A spatial light modulating part (13) modulates the optical beam signal from the optical beam output part (10), in accordance with a predetermined unit spatial region or in accordance with a predetermined system (such as spread code or the like) for each of oscillation and longitudinal mode, to perform an optical encoding process. A spatial light demodulating part (15) demodulates the optical modulated signal from the spatial light modulating part (13) with a system corresponding to the predetermined system (such as despread code or the like) to perform an optical decoding process. A light receiving part (17) subjects the signal from the spatial light demodulating part (15) to a photoelectrical conversion to provide the converted signal as an output signal.

Description

Specification

Optical transmission equipment

Technical field

TECHNICAL FIELD [0001] The present invention relates to an optical transmission device that optically transmits a signal, and particularly to an optical transmission device that optically transmits a signal via free space or an optical fiber.

Background art

Conventionally, as an optical transmission device that optically transmits a signal, there are an optical transmission device that transmits an optical signal through a free space and an optical transmission device that transmits an optical signal through an optical transmission path.

Patent Document 1 describes an optical transmission device that transmits an optical signal through free space (FIG. 7 of Patent Document 1). FIG. 17 is a diagram showing a configuration of a conventional optical space transmission device described in Patent Document 1. In FIG.

In FIG. 17, the conventional optical space transmission device described in Patent Document 1 includes an optical transmission unit 700 and an optical reception unit 710. The optical transmitter 700 and the optical receiver 710 are installed so as to face each other. The optical transmitter 700 includes a light source 71 and a condensing optical system 72. The light receiving unit 710 includes a condensing optical system 74 and a light receiving element 75.

[0005] In the optical transmitter 700, the light source 71 is composed of a semiconductor laser, for example, and modulates the output intensity of the output light (oscillation light) based on the input signal (data signal) and outputs it as a light beam signal. . The condensing optical system 72 is composed of, for example, a lens or the like, expands the light beam diameter, converts the light beam signal into parallel light, and emits it to the free space 73.

[0006] In the light receiving unit 710, the condensing optical system 74 is constituted by a lens, for example, and condenses the light beam signal propagated through the free space 73. The light receiving element 75 photoelectrically converts the collected light beam signal and outputs it as an output signal. Thus, according to Patent Document 1, an optical signal can be transmitted through a free space.

On the other hand, Patent Document 2 describes an optical transmission device that optically transmits a signal via a large-diameter optical fiber (FIG. 1 of Patent Document 2). In the conventional optical transmission device described in Patent Document 2, the optical transmitter and the optical receiver are connected via a plastic fiber. The conventional optical transmission device described in Patent Document 2 is the same as the conventional optical transmission device described in Patent Document 1. Similarly, the optical transmission unit converts the input signal into an optical signal and transmits it. The receiving unit receives an optical signal transmitted through a large-diameter optical fiber as an output signal. Thus, according to Patent Document 2, an optical signal can be transmitted through a large-diameter optical fiber.

Patent Document 1: JP-A-7-221710

Patent Document 2: Japanese Patent Laid-Open No. 2000-22643

Non-Patent Document 1: JY Law and GP Agrawal, “Mode—Partition Noise in Vertical -Cavity Surface” Emitting Laser), I Tripley 'Photo Nitas' Technology' Letters (IEEE Photonics Technology Letters), VOL. 9, no. 4, April 1997, p43 7-439

Disclosure of the invention

Problems to be solved by the invention

However, in the conventional optical transmission device described in Patent Document 1, the modulated light beam signal is radiated into free space. Therefore, since it is relatively easy to intercept and decode the input signal by receiving the light beam signal propagating in space, there is a problem that the secrecy is poor. Also in the conventional optical transmission device described in Patent Document 2, the original input signal can be decoded if a part of the optical signal propagating through the optical transmission line is branched and extracted.

Therefore, an object of the present invention is to provide an optical transmission device that is excellent in secrecy.

Means for solving the problem

[0010] The present invention is an optical transmission device for transmitting an optical signal modulated by a signal to be transmitted, wherein the output light of the light source is modulated with the signal to obtain an optical beam signal, and the optical beam signal is converted into the optical beam signal. Output light beam output unit and light beam output unit power The output light beam signal is modulated according to a predetermined method (modulation Z demodulation code and control parameters described later) and output as an optical modulation signal. And a spatial light modulation unit that demodulates the output optical modulation signal by a method corresponding to a predetermined method and outputs it as an optical demodulation signal, Interferometric light demodulating power The optical light demodulating signal is photoelectrically converted and output as an output signal. The spatial light modulating section outputs an optical beam signal for each predetermined unit space according to a predetermined method. Modulate. Preferably, the light beam output unit outputs an optical beam signal comprising a plurality of oscillation modes, and the spatial light modulation unit modulates the light beam signal for each oscillation mode according to a predetermined method.

[0011] According to the present invention, the light beam signal is modulated and transmitted by a predetermined method for each unit space. Thus, in order to normally reproduce the optical modulation signal, it is necessary to demodulate the optical modulation signal by a method corresponding to the method used for the modulation of the optical modulation signal. Therefore, even if a third party who cannot grasp the method held by the proper receiver intercepts the optical modulation signal, the optical modulation signal cannot be reproduced normally. Therefore, it is possible to provide a highly confidential optical transmission device that prevents eavesdropping by a third party. Furthermore, in the multimode light that is output from the multimode light source, unpredictable fluctuations occur in the mode distribution ratio distributed to each mode. Since an eavesdropper cannot grasp the mode distribution ratio of multimode light, it cannot reproduce normally even if an optical modulation signal is intercepted. Therefore, the confidentiality can be further improved by matching the optical code processing with the multimode light in which the mode distribution ratio fluctuates unpredictably.

As an example, the light source may be a multimode light source that outputs light having a plurality of oscillation modes.

[0013] As another example, the light beam output unit may include a plurality of light sources, and output light beam signals by modulating output light output from the plurality of light sources.

As another example, the light beam output unit may include a multimode fiber that emits a light beam signal as a light beam signal composed of a plurality of propagation modes.

[0015] Further, the spatial light modulation unit may radiate a light modulation signal to free space, and the spatial light demodulation unit may demodulate the light modulation signal propagating in the free space. As a result, the optical modulation signal can be transmitted through free space.

[0016] The spatial light modulator and the spatial light demodulator may be connected via an optical transmission path. Thereby, an optical modulation signal can be transmitted through the optical transmission line.

[0017] For example, the light source may be a surface emitting laser, or a Fabry-Perot resonator laser. There may be. The light source may be a light emitting diode.

[0018] Further, the spatial light modulation unit includes a longitudinal mode separation unit that separates the light beam signal into a plurality of longitudinal modes and outputs the separated light beam signal to the spatial light modulation unit. The spatial light modulation unit includes a longitudinal mode multiplexing unit that inputs the output optical decoded signal and multiplexes the longitudinal mode, and the spatial light modulation unit follows a predetermined method for each longitudinal mode separated by the longitudinal mode separation unit. You can modulate the light beam signal.

Thereby, the light beam signal can be separated into a plurality of different longitudinal modes. Therefore, an eavesdropper cannot normally reproduce the intercepted light modulation signal unless it understands both the separated longitudinal mode and the method for demodulating the intercepted light modulation signal. Therefore, confidentiality can be further improved.

[0020] In addition, a mode dispersion detector that detects a mode dispersion characteristic of the optical demodulated signal is provided, and the spatial light demodulator is a characteristic opposite to the mode dispersion characteristic based on the result detected by the mode dispersion detector. Add correction with.

[0021] Thus, by detecting distortion due to mode dispersion, it is possible to compensate for distortion during demodulation of the optical modulation signal. Therefore, the authorized receiver can accurately reproduce the received light modulation signal.

[0022] As an example, the mode dispersion detection unit may detect a delay amount due to mode dispersion.

[0023] Further, the spatial light demodulator may add a predetermined delay amount for each oscillation mode so as to correct the delay amount due to mode dispersion detected by the mode dispersion detector.

[0024] As another example, the mode dispersion detection unit may detect the amount of loss due to mode dispersion.

Furthermore, the spatial light demodulation unit may add a predetermined loss amount for each oscillation mode so as to correct the loss amount due to mode dispersion detected by the mode dispersion detection unit.

[0026] Thereby, it is possible to adjust the optical power density of the light modulation signal output from the spatial light modulation unit. Therefore, for example, by adjusting the modulation parameter so that the optical power density of the optical modulation signal is constant with respect to the radiation angle, high eye safety can be obtained. [0027] The spatial light modulation unit may modulate the light beam signal based on a predetermined code, and the spatial light demodulation unit may demodulate the light modulation signal based on a code corresponding to the predetermined code. .

[0028] Further, a predetermined code (modulation code) for the spatial light modulation unit to modulate the light beam signal, and a code (demodulation code) corresponding to the predetermined code for the spatial light demodulation unit to demodulate the optical modulation signal ) And a sign changing unit for changing.

[0029] Thereby, the modulation code and the demodulation code can be changed every time. Therefore, compared to the case where these codes are always constant, it becomes difficult for an eavesdropper to grasp a method for normally recovering the optical modulation signal, so that the confidentiality can be improved. .

[0030] The spatial light modulation unit and the spatial light demodulation unit may be configured by a liquid crystal spatial light modulation element, or may be configured by a micromirror device.

[0031] Further, the spatial light modulator and the spatial light demodulator may be configured by a spatial light modulator using a magneto-optic effect, or by a light modulator using a multiple quantum well effect. Well, okay.

[0032] Further, the spatial light modulation unit and the spatial light demodulation unit may be configured by a light modulation element using an acousto-optic effect.

[0033] Further, the spatial light modulation unit may control the intensity of the light beam signal as an example of the control parameter, and the spatial light demodulation unit may control the intensity of the light modulation signal.

[0034] Further, as another example of the control parameter, the spatial light modulation unit may control the phase of the light beam signal, and the spatial light demodulation unit may control the phase of the light modulation signal.

[0035] The spatial light modulator may control the polarization state of the light beam signal, and the spatial light demodulator may control the polarization state of the light modulation signal.

The invention's effect

[0036] According to the present invention, an optical transmission apparatus excellent in secrecy is provided.

Brief Description of Drawings

FIG. 1 is a diagram showing a configuration of an optical transmission apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of the optical transmission apparatus shown in FIG. FIG. 3A is a diagram showing the light intensity of the light beam signal output from the multimode light source 11 for each oscillation mode.

[3B] FIG. 3B is a diagram showing an example of a modulation code (spreading code) used for optical modulation processing.

[3C] FIG. 3C is a diagram showing an example of a demodulated code (despread code) used in the optical demodulation process.

FIG. 3D is a diagram showing a mode distribution ratio in an optical demodulated signal output from the spatial light demodulator 15.

FIG. 3E is a diagram showing the sum of the spreading code and the despreading code for each mode.

FIG. 3F is a diagram showing, for each mode order, the light intensity of the light modulation signal when the light modulation signal radiated from the spatial light modulation unit 13 to the free space 14 is directly received.

FIG. 4 is a diagram showing an example of a noise distribution (frequency characteristic) of an output signal output from the light receiving unit 17.

FIG. 5A is a diagram showing the optical power density of a light beam signal output from a general light source.

FIG. 5B is a diagram showing a configuration of the nth-order mode modulation element 13-n according to the present embodiment.

FIG. 5C is a diagram showing the optical power density of the optical modulation signal output from the optical spatial modulation unit 13.

[FIG. 6A] FIG. 6A is a diagram showing a configuration of the spatial light modulator 13 when the modulation elements are two-dimensionally arranged.

[6B] FIG. 6B is a diagram showing a configuration of the spatial light modulation unit 13 in the case where the modulation element power corresponding to each oscillation mode is used.

[7A] FIG. 7A is a diagram showing a configuration of the multimode light source 11 described in the present embodiment.

FIG. 7B is a diagram showing a configuration of a light source when the light source is composed of a single mode light source 51 and a multimode fiber 52.

[FIG. 7C] FIG. 7C is a diagram showing a configuration of a light source when the light source also has an array type light source power. is there.

FIG. 8 is a diagram showing a configuration of an optical transmission device 2 according to the second embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of an optical transmission apparatus according to a third embodiment of the present invention.

FIG. 10 is a block diagram showing a configuration of the optical transmission apparatus shown in FIG.

FIG. 11A is a diagram showing the light intensity of the light beam signal output from the single mode light source 21.

FIG. 11B is a diagram showing an example of a modulation code (spreading code) used for optical modulation processing.

FIG. 11C is a diagram showing an example of a demodulated code (despread code) used for optical demodulation processing assigned to each spatial region.

[11D] FIG. 11D is a diagram showing the light intensity of the optical demodulated signal output from the spatial light demodulator 15.

[11E] FIG. 11E is a diagram showing the sum of the spatial regions of the spreading code and the despreading code.

FIG. 11F is a diagram showing the light intensity of the light modulation signal for each spatial region when the light modulation signal radiated from the spatial light modulation unit 13 to the free space 14 is directly received.

FIG. 12 is a block diagram showing a configuration of an optical transmission apparatus according to a fourth embodiment of the present invention.

[13A] FIG. 13A is a diagram illustrating an arrangement example of the n′m-order mode modulation elements 13-nm when the longitudinal mode separation unit 22 separates and outputs the light beam signal in the lateral direction.

[FIG. 13B] FIG. 13B is a diagram showing an arrangement example of n′m-th order mode spatial light modulation elements 13-nm when the longitudinal mode separation unit 22 separates and outputs the light beam signal.

FIG. 14A is a diagram showing the light intensity of the light beam signal output from the longitudinal mode separation unit 22 for each mode.

FIG. 14B is a diagram showing an example of a modulation code corresponding to the optical modulation processing performed in each mode.

FIG. 14C is a diagram showing an example of a demodulation code corresponding to the optical demodulation processing performed in each mode.

[FIG. 14D] FIG. 14D shows the mode components in the optical demodulated signal output from the spatial light demodulator 15b. It is a figure which shows a distribution ratio.

FIG. 14E is a diagram showing the sum of the spreading code and the despreading code for each mode.

FIG. 14F is a diagram showing the light intensity of the light modulation signal for each mode order when the light modulation signal radiated from the spatial light modulation unit 13b to the free space 14 is directly received.

FIG. 15 is a block diagram showing a configuration of an optical transmission apparatus according to a fifth embodiment of the present invention.

FIG. 16 is a block diagram showing a configuration of an optical transmission apparatus according to a sixth embodiment of the present invention.

FIG. 17 is a diagram showing a configuration of a conventional optical space transmission device described in Patent Document 1.

1, 2 Optical transmission equipment

9 Data input section

10 Light beam output section

11 Multi-mode light source

12, 16 Condenser

13 Spatial light modulator

14 Free space

15 Spatial light demodulator

17 Receiver

18 Data output section

21 Single mode light source

22 Vertical mode separator

23 Longitudinal mode multiplexing section

24 Distortion adjuster

25 Parameter change section

51 Light source

52 Multi-mode file 53 Array type light source

60 optical fiber

100, 700 Optical transmitter

110, 710 Optical receiver

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0040] (First embodiment)

FIG. 1 is a diagram showing a configuration of the optical transmission device 1 according to the first embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration of the optical transmission device 1 shown in FIG. Hereinafter, the configuration of the optical transmission device 1 will be described with reference to FIG. 1 and FIG.

The optical transmission device 1 is an optical space transmission device that optically transmits a signal through the free space 14.

In FIG. 2, the optical transmission device 1 includes an optical transmission unit 100 and an optical reception unit 110. The optical transmitter 100 and the optical receiver 110 are installed in a state of facing each other. The optical transmission unit 100 includes a data input unit 9, a light beam output unit 10, and a spatial light modulation unit 13. The light receiving unit 110 includes a spatial light demodulating unit 15, a light collecting unit 16, a light receiving unit 17, and a data output unit 18. In FIG. 1, the data input unit 9 and the data output unit 18 are not shown. In FIG. 2, the light condensing unit 16 is not shown.

In the optical transmission unit 100, the data input unit 9 outputs a data signal to be transmitted to the optical reception unit 110 to the optical beam output unit 10.

The light beam output unit 10 includes a multimode light source 11 and a condensing unit 12. The multimode light source 11 is composed of, for example, a surface emitting laser. The multi-mode light source 11 modulates output light composed of n different oscillation modes (n: an integer equal to or greater than 0) based on a data signal (input signal) input from the data input unit 9 to generate a light beam signal. Output as. In the present embodiment, the case where the multimode light source 11 has four different oscillation modes will be described as an example. In this case, the multimode light source 11 outputs a 0th-order to third-order mode light beam signal.

[0044] The condensing unit 12 is an optical system including, for example, a lens. The condensing unit 12 outputs the light beam signal output from the multi-mode light source 11 as parallel light. The spatial light modulation unit 13 modulates the light beam signal output from the light collecting unit 12 for each unit space (space 1 to N + 1 in FIG. 2) by a predetermined method. Specifically, the spatial light modulator 13 performs light modulation processing based on a predetermined code (hereinafter referred to as a modulation code or a spread code) for each oscillation mode (spatial region) of the light beam signal, and performs light modulation. Radiates to free space 14 as a signal. The spatial light modulator 13 includes a plurality of n (n is an integer from 0 to N) order mode modulation elements 13-0 to 13-N. These n-order mode modulation elements 13-0 to 13-N are collectively referred to as n-order mode modulation elements 13-n when it is not necessary to distinguish them.

[0046] The n-order mode modulation elements 13-n are spatial light modulation elements that are made of, for example, liquid crystal, and are spatially arranged. In FIG. 1, the spatial light modulator 13 has 0th-order to 3rd-order mode modulation elements 13-0 to 13-3 as modulation elements corresponding to light beam signals in the 0th-order to third-order mode. . In the present embodiment, the description will be made assuming that the code used for the light modulation processing represents the transmittance (that is, the parameter for controlling the light intensity). A predetermined code is assigned to each nth-order mode modulation element 13-n. In FIG. 1, for example, the 0th-order mode modulation element 13-0 (white), the third-order mode modulation element 13-3 (dot pattern), and the second-order mode modulation element 13-2 (hatched) in descending order of transmittance. The primary mode modulation element 13-1 (black) is obtained. Thus, the optical code processing by the spatial light modulator 13 is realized by performing optical modulation processing by a plurality of n-order mode modulation elements.

In the optical receiver 110, the spatial light demodulator 15 demodulates the optical modulation signal by a method corresponding to the modulation method used by the spatial light modulator 13, and outputs it as an optical demodulated signal. The spatial light demodulator 15 performs an optical demodulation process on the optical modulation signal based on a predetermined code (hereinafter referred to as a demodulation code or a despread code) for each unit space described above. The spatial light demodulation unit 15 includes a plurality of n (n is an integer from 0 to N) order mode demodulation elements 15-0 to 15-N. These n-order mode demodulation elements 15-0 to 15-N are collectively referred to as n-order mode demodulation elements 15-n when it is not necessary to distinguish them.

[0048] The nth-order mode demodulating elements 15-n are spatial light modulation elements made of, for example, liquid crystal, and are spatially arranged. The spatial light demodulator 15 uses the corresponding nth-order mode demodulating element 15-n for each oscillation mode of the optical modulation signal that has propagated through the free space 14, and based on the despread code corresponding to the spread code. Demodulated and output as an optical demodulated signal To help. In the spatial light demodulating unit 15, the n-order mode demodulating elements are arranged so as to correspond to the arrangement of the n-order mode modulating elements in the spatial light modulating unit 13. In FIG. 1, the spatial light demodulator 15 has 0th to 3rd mode modulation elements 15-0 to 15-3. Each demodulating element has a predetermined transmittance. As described above, the optical demodulation processing is performed by the spatial light modulation unit 15 by performing the optical demodulation processing by the plurality of n-order mode demodulation elements.

[0049] The condensing unit 16 is a condensing optical system including, for example, a lens. The condensing unit 16 condenses the optical demodulated signal output from the spatial light demodulating unit 15. The light receiving unit 17 is, for example, a light receiving element such as a photodiode. The light receiving unit 17 photoelectrically converts the optical demodulated signal output from the light collecting unit 16 and outputs the result to the data output unit 18 as an output signal.

[0050] Next, the principle of the present invention using mode distribution noise and optical code processing will be described. FIG. 3 is a diagram showing the light intensity and modulation / demodulation code of each signal according to the present embodiment.

FIG. 3A is a diagram showing the light intensity of the light beam signal output from the multimode light source 11 for each oscillation mode. Here, it should be noted that even if the total light intensity of all modes of the light beam signal output from the multi-mode light source 11 is kept constant in time, each mode is set at time tl and time t2. The ratio of the distributed light intensity (mode distribution ratio) fluctuates.

FIG. 3B is a diagram illustrating an example of a modulation code (spreading code) used for optical modulation processing.

In the spatial light modulator 13, the 0th to 3rd mode modulators 13-0 to 13-3 are connected to the 0th to 3rd modes based on the modulation codes f (0) to f (3) shown in FIG. 3B. Light modulation processing is applied to the light beam signal.

FIG. 3C is a diagram showing an example of a demodulated code (despread code) used for optical demodulation processing. In the spatial light demodulator 15, the 0th to 3rd mode demodulating elements 15-0 to 15-3 are used to convert the optical modulation signal into an optical signal based on the demodulated codes g (0) to g (3) shown in FIG. 3C. Demodulate.

[0054] As the control parameter expressing the modulation code and the demodulation code in the above, for example, light intensity information can be used. For example, when a liquid crystal spatial modulation element is used as the modulation element, the modulation / demodulation code can be expressed by controlling the transmittance of the liquid crystal spatial modulation element. [0055] FIG. 3E is a diagram showing the sum of the spreading code and the despreading code for each mode. The spreading code shown in Fig. 3B and the despreading code shown in Fig. 3C are complementary to each other, and the transfer function h (n) = f (n) X g (n) of the entire optical modulation / demodulation is Is set to be constant. That is, as shown in FIG. 3E, the sum of the spreading code and the despreading code in each mode is a constant level for all modes. When spreading codes and despreading codes are expressed in terms of transmittance, the transfer function h (n) is a force set so that f (n) X g (n) is constant for all n. When the code and despread code are expressed in decibels (dB), the transfer function h (n) is set so that f (n) + g (n) is constant for all n.

FIG. 3D is a diagram showing a mode distribution ratio in the optical demodulated signal output from the spatial light demodulator 15. As shown in FIG. 3D, the mode distribution ratio of each mode of the optical demodulated signal output from the spatial light demodulator 15 is the same as the mode distribution ratio of the optical beam signal output from the multimode light source 11 (FIG. 3A). It becomes. As shown in FIG. 3C, the legitimate receiver has a despread code complementary to the spread code shown in FIG. 3B, so that the input signal can be reproduced normally.

FIG. 4 is a diagram showing an example of the noise distribution (frequency characteristics) of the output signal output from the light receiving unit 17. In FIG. 4, the vertical axis represents relative intensity noise, and the horizontal axis represents frequency. The solid line indicates the noise distribution of the output signal obtained by the authorized receiver, and the dotted line indicates the noise distribution of the output signal obtained by the eavesdropper. As described above, since the legitimate receiver can reproduce the input signal normally, the relative intensity noise in the output signal becomes smaller than the output signal obtained by the eavesdropper.

Next, a case where an optical modulation signal propagating in the free space 14 between the spatial light modulator 13 and the spatial light demodulator 15 is illegally received (wired) will be described. Here, it is assumed that the eavesdropper does not have the spatial light demodulation unit 15 held only by the authorized receiver and does not know the information regarding the spread code. For example, FIG. 3F is a diagram showing the light intensity of the light modulation signal for each mode order when the light modulation signal radiated from the spatial light modulation unit 13 to the free space 14 is directly received. The optical modulation signal received by the eavesdropper is obtained by multiplying the light beam signal shown in FIG. 3A by the spreading code shown in FIG. 3B. In other words, the optical intensity of the optical modulation signal received by the eavesdropper is significantly different from the optical beam signal shown in FIG. No.

[0059] As shown in FIG. 3F, when the mode distribution ratio of the multimode light is changed to a state different from that at the time of oscillation, the noise component when the optical signal is photoelectrically converted (received) is shown in FIG. As shown by the dotted line, there is a phenomenon in which the number of subscribers increases significantly compared to the case of regular recipients and is distributed over a wide band. In this way, the signal received by the eavesdropper is superimposed with the unpredictable mode distribution noise based on the physical phenomenon, so that it is extremely difficult for the eavesdropper to reproduce the signal normally. Even when an eavesdropper receives only a specific mode, the light intensity of each oscillation mode is constantly fluctuating, so that the received signal is highly noisy with the level constantly fluctuating. Therefore, even in this case, the eavesdropper cannot reproduce the signal normally.

[0060] As described above, according to the present embodiment, the optical transmission device uses the fluctuation of the mode distribution ratio of the light beam signal output from the multimode light source and the optical code processing by the optical spatial modulation unit. To transmit an optical modulation signal. As a result, the eavesdropper cannot grasp the mode distribution ratio of the multimode light and the demodulation code corresponding to the modulation code, and thus cannot normally demodulate the signal. Therefore, highly confidential optical space transmission can be realized.

[0061] Furthermore, by using the optical transmission apparatus according to the present embodiment, it is possible to ensure eye safety (eye safety) by controlling the modulation code. 5A to 5C are diagrams showing the optical power density of the optical beam signal and the optical modulation signal, and the configuration of the modulation element. FIG. 5A is a diagram showing the optical power density of a light beam signal output from a general light source. As shown in FIG. 5A, the optical power density of the light beam signal output from the light source generally has a Gaussian distribution with respect to the radiation angle, and has a property of exhibiting a peak at a specific radiation angle. /! Depending on the light source, the distribution may be biased in either the XY direction (perpendicular to the optical axis Z direction shown in Fig. 1). However, as shown in FIG. 5A, a light beam having a peak with respect to a specific radiation angle with a constant optical power density is likely to have a negative effect on the eye.

Therefore, in the present embodiment, the optical power density distribution of the optical beam signal output from the multimode light source 11 and the ideal (flat) optical power density to be radiated to the free space 14 The modulation code used in the optical spatial modulation unit 13 is controlled in consideration of the distribution. FIG. 5B is a diagram showing a configuration of the nth-order mode modulation element 13-n according to the present embodiment. As shown in FIG. 5B, in the n-order mode modulation element 13-n, the transmittance of the region through which the light beam signal with high optical power density passes is lower than the transmittance of the other regions. In this way, by controlling the modulation code in the region through which the light beam signal having a high photoelectric density passes, the optical power density of the light beam signal can be set to a predetermined threshold value or less.

FIG. 5C is a diagram showing the optical power density of the optical modulation signal output from the optical spatial modulation unit 13. As shown in FIG. 5C, it is ideal that the light modulation signal radiated to the free space 14 has a flat photoelectric density distribution and does not show a peak at a specific radiation angle. By controlling the modulation code used in the light spatial modulation section 13, the light modulation signal radiated to the free space 14 has little influence on the eyes, that is, high eye safety can be ensured. Note that the aspect ratio of the optical modulation signal (optical power density ratio in the XY directions) is preferable to a force close to 1. This ensures high eye safety regardless of the characteristics of the multimode light source 11. Thus, by controlling the modulation code, the optical modulation signal radiated into free space has a flat optical power density distribution and does not exhibit a peak at a specific radiation angle. Therefore, safety for human eyes can be ensured.

In this embodiment, for simplification of description, the n-order mode modulation element and the n-order mode demodulation element are arranged one-dimensionally in the X direction as shown in FIG. The case was explained as an example. Here, when a multi-mode light source is used, the first-order to n-order mode light is emitted concentrically around the zero-order mode light. Therefore, the n-order mode modulation element and the n-order mode demodulation element may be arranged in the X direction and the Y direction and arranged two-dimensionally. 6A and 6B are diagrams illustrating an example of the configuration of the spatial light modulator 13. FIG. FIG. 6A is a diagram showing the configuration of the spatial light modulator 13 when the modulation elements are arranged in a two-dimensional manner. As shown in FIG. 6A, when the modulation elements are arranged two-dimensionally, the number of combinations of modulation codes increases, so that the secrecy is further improved.

In the present embodiment, the n-order mode modulation elements are arranged point-symmetrically with the 0-order mode modulation element as the center of symmetry. Here, the spatial light modulator is 1 for each oscillation mode. One n-order mode modulation element may be provided. FIG. 6B is a diagram showing the configuration of the spatial light modulation unit 13 in the case where there is one modulation element corresponding to each oscillation mode. The configuration of the spatial light modulation unit 13 shown in FIG. 6B is compared with the configuration of the spatial light modulation unit 13 shown in FIG. 1, and the primary to tertiary mode modulation elements corresponding to the primary to tertiary mode light beam signals. 13— 1 to 13 3 are different in that they are one by one. In FIG. 6B, the first-order to third-order mode modulation elements 13-1 to 13-3 are arranged below the zero-order mode modulation element 13-0. However, these modulation elements are It may be arranged above the mode modulation element 13-0.

[0066] In this embodiment, the mode order of the multimode light and the type of the mode modulation element correspond to each other on a one-to-one basis. It can be applied, or a certain mode of light can be assigned to multiple modulation elements.

[0067] When the n-order mode light beam signal is modulated using the spatial light modulator 13 shown in FIG. 6A or 6B, the configuration of the spatial light demodulator 15 provided in the optical receiver 110 is as shown in FIG. Complementary to the spatial light modulator 13 shown in 6A or 6B, the transfer function h (n) = f (n) X g (n) force of the entire optical modulation / demodulation is constant for all n In this way, the modulation code and the demodulation code may be set. Further, the nature of the mode distribution noise used in the present invention is described in detail in Non-Patent Document 1, taking a surface emitting laser as an example.

In the present embodiment, a surface emitting laser has been described as an example of the multimode light source. However, the multimode light source may be other than the surface emitting laser. For example, the multimode light source may be a Fabry-Perot resonator laser or a light emitting diode.

[0069] In the present embodiment, the force light source described in the case of using a multi-mode light source as an example of the light source is not limited to the multi-mode light source, and may be any configuration that can output a plurality of oscillation mode lights. Good. 7A to 7C are diagrams showing an example of a light source applicable to the present invention. FIG. 7A is a diagram showing a configuration of the multimode light source 11 described in the present embodiment. FIG. 7B is a diagram showing the configuration of the light source when the light source is composed of a single mode light source 51 and a multimode fiber 52. As shown in FIG. 7B, a plurality of oscillation mode lights can be output by connecting a single mode light source 51 and a multimode fiber 52. A multimode light source may be used instead of the single mode light source 51. Yes.

FIG. 7C is a diagram showing a configuration of the light source when the light source is an array type light source.

The array light source 53 is also configured with a force such as a plurality of surface emitting lasers. In this way, an array type light source 53 may be used to configure a pseudo multimode light source! /.

Further, in the present embodiment, the liquid crystal spatial light modulation element has been described as an example of the spatial light modulation unit. Here, the spatial light modulation unit may be a micro-mirror device or a spatial light modulation element using a magneto-optic effect, a multiple quantum well effect, and an acousto-optic effect. The configuration of the spatial light demodulator is the same as this.

Further, in the present embodiment, a case has been described in which light intensity information is used as an example of a specific control parameter used for light modulation / demodulation processing. Here, the control parameter used for the optical modulation / demodulation processing may be optical phase information (including optical delay information) or polarization state information. That is, instead of the spatial light modulator controlling the intensity of the light beam and the spatial light demodulator controlling the intensity of the light modulation signal, the spatial light modulator controls the phase of the light beam and the spatial light demodulator The phase of the modulation signal may be controlled, the spatial light modulation unit may control the polarization state of the light beam, and the spatial light demodulation unit may control the polarization state of the light modulation signal.

[0073] (Second Embodiment)

FIG. 8 is a diagram showing a configuration of the optical transmission device 2 according to the second embodiment of the present invention. In FIG. 8, the optical transmission device 2 includes a light beam output unit 10, a spatial light modulation unit 13, an optical fiber 60, a spatial light demodulation unit 15, a condensing unit 16, and a light receiving unit 17. The spatial light modulator 13 spatially arranges a plurality of n-order mode modulators 13-n. The spatial light demodulator 15 spatially arranges a plurality of nth-order mode demodulating elements 15-n. In FIG. 8, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.

[0074] The difference between the optical transmission device 2 shown in FIG. 8 and the optical transmission device 1 according to the first embodiment shown in FIG. 1 is that a large-diameter optical fiber 60 that is not a free space is used as a transmission line. This is the point used. The large-diameter optical fiber is, for example, a plastic fiber.

As shown in FIG. 8, the optical transmitter 100 and the optical receiver 110 are connected via an optical fiber 60. In the optical transmitter 100, the optical modulation signal output from the spatial light modulator 13 is transmitted via the optical fiber 60 and input to the spatial light demodulator 15 of the optical receiver 110. As described above, according to the present embodiment, similarly to the first embodiment, the optical modulation signal transmitted by the optical transmission unit is optically transmitted through the large-diameter optical fiber, and the optical reception unit Can be received as an output signal. Therefore, the present invention can also be applied to uses such as an optical transmission device using a large-diameter optical fiber.

[0077] (Third embodiment)

In the first embodiment, multimode light is output using a multimode light source. In contrast, in the third embodiment, single mode light is output using a single mode light source.

FIG. 9 is a diagram showing a configuration of the optical transmission device la according to the third embodiment of the present invention, and FIG. 10 is a block diagram showing a configuration of the optical transmission device la shown in FIG. . In FIG. 10, the optical transmission device la includes an optical transmission unit 100a and an optical reception unit 110. The optical transmission unit 100a includes a data input unit 9, a light beam output unit 10a, and a spatial light modulation unit 13. The light receiving unit 110 includes a spatial light demodulating unit 15, a light collecting unit 16, a light receiving unit 17, and a data output unit 18. The optical transmission device la shown in FIG. 10 differs from the optical transmission device 1 according to the first embodiment shown in FIG. 2 in the configuration of the beam light output unit 10a. Since the other configuration is the same as that in FIG. 2, the same reference numeral is given to the same configuration as that in FIG. 2, and the description is omitted.

The light beam output unit 10a includes a single mode light source 21 and a condensing unit 12.

The single mode light source 21 outputs a 0th-order mode light beam signal. The condensing unit 12 outputs the 0th-order mode light beam signal output from the single mode light source 21 as parallel light.

The spatial light modulation unit 13 includes a plurality of space n (n is an integer from 1 to N) modulation elements 13-1 to 13-N, and the light beam signal is transmitted to a plurality of spatial regions 1 to N. Modulate every N (integer greater than 1). These spatial n modulation elements 13-1 to 13-N are collectively referred to as spatial n modulation elements 13-n when it is not necessary to distinguish them. The spatial n modulation element 13-n has the same configuration as the nth-order mode modulation element 13-n in the first embodiment. In the present embodiment, the case where the spatial light modulator 13 has four spatial n modulation elements (space 1 to spatial 4 modulation elements) will be described.

In FIG. 9, the light beam signal and the light modulation element are illustrated in an enlarged manner. Single mode The output light output from the light source 21 corresponds to the 0th-order mode light output from the multimode light source shown in FIG.

The spatial light demodulation unit 15 includes a plurality of spaces n (n is an integer from 1 to N) demodulation elements 15-1 to 15 N. These spatial n demodulating elements 15-1 to 15-N are collectively referred to as spatial n demodulating elements 15-n when it is not necessary to distinguish them. The spatial n demodulating element 15-n has the same configuration as the n-th mode demodulating element 15-n in the first embodiment.

FIGS. 11A to 11F are diagrams showing the light intensity and modulation / demodulation code of each signal in the present embodiment.

FIG. 11A is a diagram showing the light intensity of the light beam signal output from the single mode light source 21. The 0th-order mode light beam signal output from the single-mode light source 21 is input to the space 1 to space 4 modulation elements 13-0 to 13-3 via the condensing unit 12. Here, the intensity of the 0th-order mode light beam signal output at time tl is constant.

FIG. 11B is a diagram showing an example of a modulation code (spreading code) used for the optical modulation processing.

In the spatial light modulator 13, the spatial 1 to spatial 4 modulation elements 13-1 to 13-4 perform optical modulation processing on the light beam signal using the modulation codes f (0) to f (3) shown in FIG. 11B. .

FIG. 11C is a diagram illustrating an example of a demodulation code (despread code) used for optical demodulation processing assigned to each spatial region. In the spatial light demodulator 15, the spatial 1 to spatial 4 demodulating elements 15-1 to 15-4 use the demodulation codes g (0) to g (3) shown in FIG. Apply processing.

[0088] FIG. 11E is a diagram showing the sum of the spatial regions of the spreading code and the despreading code. As in the first embodiment, the spreading code shown in FIG. 11B and the despreading code shown in FIG. 11C are complementary to each other, and the transfer function h (n) = f (n) X g (n) is set to be constant for all n.

FIG. 11D is a diagram showing the light intensity of the optical demodulated signal output from the spatial light demodulator 15.

As shown in FIG. 11D, the optical intensity ratio of the optical demodulated signal output from the spatial light demodulator 15 is the same as the optical intensity ratio of the optical beam signal output from the single mode light source 21 shown in FIG. 11A. Become one. As shown in FIG. 11C, the legitimate receiver has a despreading code complementary to the spreading code shown in FIG. 11B, so that the input signal can be reproduced normally. FIG. 11F is a diagram illustrating the light intensity of the light modulation signal for each spatial region when the light modulation signal radiated from the spatial light modulation unit 13 to the free space 14 is directly received. The optical modulation signal received by the eavesdropper is obtained by multiplying the light beam signal shown in FIG. 11A by the spreading code shown in FIG. 11B. That is, the optical intensity ratio of the optical demodulated signal received by the eavesdropper is significantly different from the optical intensity ratio of the optical beam signal shown in FIG. 11A, as shown in FIG. 11F. However, since the eavesdropper does not have the spatial light demodulation unit 15 held only by the authorized receiver, the eavesdropper cannot normally reproduce the received optical modulation signal.

As described above, according to the present embodiment, even when a single mode light source is used, highly confidential optical space transmission can be realized. Since the eavesdropper does not have a decoding code corresponding to the modulation code, the optical modulation signal cannot be normally reproduced even if the light modulation signal is received improperly. Therefore, it is highly confidential using the optical code Z decoding process.

V, optical transmission can be realized.

[0092] (Fourth embodiment)

In the first embodiment, a plurality of oscillation mode lights are separated into each oscillation mode and optical code processing is performed. On the other hand, in the fourth embodiment, each oscillation mode is further separated into different longitudinal modes and optical code processing is performed.

FIG. 12 is a block diagram showing a configuration of an optical transmission device lb according to the fourth embodiment of the present invention. In FIG. 12, the optical transmission device lb includes an optical transmitter 100b and an optical receiver 110b. The optical transmission unit 100b includes a data input unit 9, a light beam output unit 10, a spatial light modulation unit 13b, and a longitudinal mode separation unit 22. The light receiving unit 110b includes a spatial light demodulating unit 15b, a light collecting unit 16, a light receiving unit 17, and a data output unit 18.

Compared with the optical transmission device 1 according to the first embodiment shown in FIG. 1, the optical transmission device lb shown in FIG. 12 includes a spatial light modulation unit 13b further including a longitudinal mode separation unit 22, The optical demodulator 15 b is different in that it includes a longitudinal mode multiplexer 23. Since the other configuration is the same as that of the first embodiment, the same reference numeral is given to the same configuration as that of FIG. 1, and the description thereof is omitted.

The longitudinal mode separation unit 22 separates the light beam signal output from the multi-mode light source 11 into a plurality of hand longitudinal modes and outputs it. Specifically, the longitudinal mode separation unit 22 separates the n-order mode light beam signal into light components of different wavelengths of m (m: integer of 1 or more) order. Implementation In the embodiment, a case where the longitudinal mode separation unit 22 has two light component forces O-order and first-order will be described as an example.

[0096] For example, the longitudinal mode separation unit 22 separates the 0th-order mode light beam signal into a 0th-order and a 1st-order longitudinal mode and outputs them. Therefore, the 0th-order mode light beam signal is output from the longitudinal mode separation unit 22 as a 0 · 0th-order mode light beam signal and a 0 · 1st-order mode light beam signal. Here, light whose oscillation mode is η order and longitudinal mode is m order is expressed as n'm order mode.

The spatial light modulation unit 13b includes an n · m-th order mode modulation element 13-nm corresponding to the n′m-order mode light beam signal output from the longitudinal mode separation unit 22. When the oscillation modes of the light beam signal output from the multimode light source 11 are four modes from 0th to 3rd, the total number of modes of the light beam signal output from the longitudinal mode separation unit 22 is 0 · 0th to 3rd. · Primary 8

FIGS. 13A and 13B are diagrams showing the configuration of the n′m-order mode spatial light modulator 13-nm included in the spatial light modulator 13b. FIG. 13A is a diagram illustrating an arrangement example of the n′m-th order mode modulation elements 13-nm when the longitudinal mode separation unit 22 separates and outputs the light beam signal in the lateral direction. In FIG. 13A, the 0 · 1st order mode modulation element is arranged on the right side of the 0 · 0th order mode modulation element, and the 1 · 1st order mode modulation element is arranged on the right side of the 1 · 0th order mode modulation element. .

The 0th-order mode light beam signal output from the multimode light source 11 is separated into a 0 · 0th order and a 0 · 1st order mode by the longitudinal mode separation unit 22 and outputted. The 0 · 0th order mode space modulation element 13-00 performs optical modulation processing on the 0 · 0th order mode light beam signal output from the longitudinal mode separation unit 22. 0 · 1st-order mode spatial modulation element 13-01 is placed beside 0 · 0th-order mode spatial modulation element 13-00 and output from longitudinal mode separation unit 22 0 · 1st-order mode light beam signal Modulation processing is performed.

Note that the longitudinal mode separation unit 22 may separate and output the light beam signal in any direction.

FIG. 13B is a diagram showing an arrangement example of n′m-order mode spatial light modulators 13-nm when the longitudinal mode separation unit 22 separates and outputs the light beam signal in the vertical direction. In this case, as shown in FIG. 13B, the 0 · 1st mode spatial modulation element 13-00 is arranged immediately below the 0 · 0th order mode spatial modulation element 13-00. Returning to the description of FIG. 12, the spatial light demodulator 15b has an n · m-order mode spatial light demodulator 15-nm corresponding to an n′m-order mode optical modulation signal propagating in the free space. The n · mth-order mode spatial light demodulator 15-nm is arranged to have a complementary relationship with the n'mth-order mode spatial light modulator 13-nm.

[0102] The longitudinal mode multiplexing unit 23 multiplexes the n'm-order mode optical demodulated signal output from the n'm-order mode spatial light demodulating element 15-nm, and supplies it to the light receiving unit 17 as the n-order mode optical demodulated signal. Output

14A to 14F are diagrams showing the light intensity and modulation / demodulation code of each signal in the present embodiment. In FIGS. 14A to 14F, the case where the oscillation modes (transverse modes) of the light beam signal output from the multimode light source 11 are two, ie, 0th order and 1st order will be described as an example.

FIG. 14A is a diagram showing the light intensity of the light beam signal output from the longitudinal mode separation unit 22 for each mode. The longitudinal mode separation unit 22 separates the 0th order light beam signal output from the multimode light source 11 into 0 · 0th order and 0 · 1st order modes and outputs the separated signals. Accordingly, as shown in FIG. 14 (b), the modes of the light beam signal output from the longitudinal mode separation unit 22 are four orders of 0 · 0th order, 0 · 1st order, 1 · 0th order, and 1 · 1st order. Similarly to the first embodiment, the ratio of the light intensity distributed to each mode (mode distribution ratio) fluctuates at time tl and time t2.

[0105] FIG. 14B is a diagram illustrating an example of a modulation code corresponding to the optical modulation processing performed in each mode. In the spatial light modulation unit 13b, the 0 · 0th to 1 · 1st order mode modulation elements 13-00 to 13-11 are represented by the spread codes 0'0) to; [(1'1) shown in FIG. Then, optical modulation processing is applied to the light beam signal.

[0106] FIG. 14C is a diagram illustrating an example of a demodulation code corresponding to the optical demodulation processing performed in each mode. In the spatial light demodulator 15b, the 0 · 0th to 1 · 1st order mode demodulator elements 15-00 to 15-11 have the despread codes ₈ (0'0) to ₈ (1'1) shown in FIG. In this case, the optical beam signal is optically demodulated.

FIG. 14E is a diagram showing the sum of the spreading code and the despreading code for each mode. As in the first embodiment, the spreading code shown in FIG. 14B and the despreading code shown in FIG. 14C are complementary to each other, and the transfer function h (n'm) = f (nm ) X g (nm) force All n • m are set to be constant! RU FIG. 14D is a diagram showing a mode distribution ratio in the optical demodulated signal output from the spatial light demodulator 15b. As shown in FIG. 14C, the legitimate receiver has a despreading code complementary to the spreading code shown in FIG. 14B, so that the input signal can be reproduced normally.

FIG. 14F is a diagram showing the light intensity of the light modulation signal for each mode order when the light modulation signal radiated from the spatial light modulation unit 13b to the free space 14 is directly received. The optical modulation signal received by the eavesdropper is obtained by multiplying the light beam signal shown in FIG. 14A by the spreading code shown in FIG. 14B. In other words, the optical intensity of the optical demodulated signal received by the eavesdropper is significantly different from the optical beam signal shown in FIG. 14A in the mode distribution ratio of the optical demodulated signal, as shown in FIG. 14F. However, since the eavesdropper has the spatial light demodulator 15b held only by the authorized receiver, the optically modulated signal cannot be reproduced normally.

[0110] As described above, according to the present embodiment, the optical transmission device, in addition to the fluctuation of the mode distribution ratio of the light beam signal output from the multimode light source, and the optical code processing by the optical spatial modulation unit, Further, the optical modulation signal is transmitted using the longitudinal mode separation of the light component. Thereby, compared with 1st Embodiment, confidentiality can be improved further.

[0111] (Fifth embodiment)

FIG. 15 is a block diagram showing a configuration of an optical transmission apparatus lc according to the fifth embodiment of the present invention. In FIG. 15, the optical transmission device lc includes an optical transmitter 100 and an optical receiver 110c. The optical transmission unit 100 includes a data input unit 9, a light beam output unit 10, and a spatial light modulation unit 13. The optical receiving unit 110c includes a spatial light demodulating unit 15, a condensing unit 16, a light receiving unit 17, a data output unit 18, and a distortion adjustment unit 24.

The optical transmission device lc shown in FIG. 15 is different from the optical transmission device 1 according to the first embodiment shown in FIG. 2 in that the optical reception unit 110c further includes a distortion adjustment unit 24. . Since the other configuration is the same as that of the first embodiment, the same reference numeral is given to the same configuration as that in FIG. 2, and the description thereof is omitted.

In the present embodiment, the optical transmitter 100 transmits a test signal for testing having a predetermined pattern to the optical receiver 110c prior to data transmission.

The light receiving unit 17 detects the optical intensity of the test optical demodulated signal demodulated by the spatial light demodulating unit 15. [0115] The distortion adjustment unit 24 stores in advance the light intensity when the test signal is received without being degraded by mode dispersion. The distortion adjusting unit 24 compares the light intensity detected by the light receiving unit 17 with the light intensity stored in advance. Thereby, the distortion adjusting unit 24 functions as a mode dispersion detecting unit that detects the mode dispersion characteristic of the optical demodulated signal. Then, the distortion adjustment unit 24 stores the light intensity force detected by the light receiving unit 17 in advance, and adjusts the demodulation code used by the spatial light demodulation unit 15 for demodulation so as to match the light intensity. For example, when a liquid crystal spatial demodulation element is used as the demodulation element, the distortion adjustment unit 24 adjusts the transmittance of the liquid crystal spatial demodulation element. As a result, the spatial light demodulator 15 can demodulate the optical modulation signal based on the result detected by the distortion adjuster 24. That is, the spatial light demodulator 15 demodulates the optical modulation signal by applying correction with a characteristic opposite to the mode dispersion characteristic based on the result detected by the mode dispersion detector.

As described above, according to the present embodiment, the loss can be compensated by detecting the loss due to mode dispersion (deterioration of light intensity) and adjusting the demodulation code. That is, the spatial light demodulator adds the loss amount for each oscillation mode so as to correct the loss amount due to the mode dispersion detected by the mode dispersion detector. Therefore, the optical modulation signal received by the authorized receiver can be accurately reproduced.

In the present embodiment, the distortion adjustment unit adjusts the optical intensity of the optical demodulated signal output from the demodulation unit. Here, when a plurality of oscillation mode lights are transmitted, the propagation time of each mode is different, so that a propagation delay due to wavelength may occur. In that case, the distortion adjustment unit may adjust the delay time of each oscillation mode due to mode dispersion. In this case, the distortion adjustment unit determines whether or not the delay time (delay amount) of the optical signal detected by the light receiving unit is correct. Then, the distortion adjustment unit adds a predetermined delay amount to the optical demodulated signals output from each n-th mode demodulating element so that the delay times of the optical demodulated signals output from the plurality of n-th mode demodulating elements match. give. That is, the spatial light demodulator adds a predetermined delay amount for each oscillation mode so as to correct the delay amount due to mode dispersion detected by the mode dispersion detector (distortion detector). In this way, by adjusting the delay due to mode dispersion, it is possible to accurately reproduce the optical modulation signal received by the authorized receiver. [0118] When the distortion adjustment unit adjusts the loss or delay of a signal due to mode dispersion, the distortion adjustment unit may be provided in the optical transmission unit. In this case, the distortion adjustment unit may give a predetermined loss or delay amount to the optical modulation signal output to each n-order mode modulation element force.

[0119] (Sixth embodiment)

FIG. 16 is a block diagram showing a configuration of an optical transmission device Id according to the fifth embodiment of the present invention. In FIG. 16, the optical transmission device Id includes an optical transmitter lOOd and an optical receiver 110d. The optical transmission unit lOOd includes a data input unit 9, a light beam output unit 10, a spatial light modulation unit 13, and a parameter change unit 25-1. The light receiving unit 110d includes a spatial light demodulating unit 15, a light collecting unit 16, a light receiving unit 17, a data output unit 18, and a parameter changing unit 25-2.

[0120] In comparison with the optical transmission device 1 according to the first embodiment shown in Fig. 2, the optical transmission device Id shown in Fig. 16 includes an optical transmission unit lOOd further including a parameter changing unit 25-1. The receiving unit 110d is different in that it further includes a force parameter changing unit 25-2. Since the other configuration is the same as that of the first embodiment, the same reference numeral is given to the same configuration as that in FIG. 2, and the description is omitted.

[0121] The meter changing units 25-1 and 25-2 are connected via a transmission line (not shown). The parameter changing units 25-1 and 25-2 adjust the parameters of the modulation code and the demodulation code in the spatial light modulation unit 13 and the spatial light demodulation unit 15 in synchronization with each other. For example, when a liquid crystal spatial modulation / demodulation element is used as the modulation / demodulation element, the modulation / demodulation parameter corresponds to the transmittance. The parameter changing units 25-1 and 25-2 change the parameters of the modulation code and the demodulation code every predetermined time. That is, the parameter changing units 25-1 and 25-2 function as a code changing unit for changing a predetermined code and a code corresponding to the predetermined code. The parameter changing units 25-1 and 25-2 may change the modulation code and demodulation code meters in accordance with user instructions. In that case, a user instruction input unit that receives an instruction from the user may be provided in the optical transmitter lOOd and the optical receiver 110d.

[0122] As described above, according to the present embodiment, the parameters of the modulation code and the demodulation code can be changed. Therefore, compared with the case where the modulation / demodulation code parameter is constant, 'Gender can be improved.

[0123] In the third to sixth embodiments, the optical transmission device has been described as transmitting an optical modulation signal via free space. Here, as in the second embodiment, the optical transmitter and the optical receiver may be connected via a large-diameter optical fiber.

[0124] In the fourth to sixth embodiments, the light source provided in the optical transmission device has been described as a multi-mode light source. However, as in the second embodiment, the light source is a single mode. It may be a light source.

Industrial applicability

The present invention is useful as an optical transmission device having excellent secrecy.

Claims

The scope of the claims

[1] An optical transmission device for transmitting an optical signal modulated by a signal to be transmitted, which modulates the output light of the light source with the signal to form a light beam signal, and outputs the light beam signal And

A spatial light modulation unit that modulates the light beam signal output from the light beam output unit according to a predetermined method and outputs the modulated signal as a light modulation signal;

A spatial light demodulation unit that demodulates the light modulation signal output from the spatial light modulation unit in a method corresponding to the predetermined method, and outputs the demodulated signal as an optical demodulation signal;

A light receiving unit that photoelectrically converts the optical demodulated signal output from the spatial light demodulating unit and outputs the result as an output signal;

The spatial light modulation unit modulates the optical beam signal for each predetermined unit space according to the predetermined method.

Optical transmission device.

[2] The light beam output unit outputs a light beam signal having a plurality of oscillation mode light powers, and the spatial light modulation unit modulates the light beam for each oscillation mode according to the predetermined method. The optical transmission device according to claim 1.

3. The optical transmission device according to claim 2, wherein the light source is a multi-mode light source that outputs light having a plurality of oscillation modes.

[4] The light beam output unit includes a plurality of the light sources, and outputs the light beam signal by modulating output light output from the plurality of light sources.

2. An optical transmission device according to 2.

5. The optical transmission device according to claim 2, wherein the light beam output unit includes a multimode fiber that radiates the light beam signal as a light beam signal composed of a plurality of propagation modes.

[6] The spatial light modulation unit radiates the light modulation signal to free space,

The optical transmission apparatus according to claim 2, wherein the spatial light demodulation unit demodulates the optical modulation signal propagating in the free space.

7. The optical transmission device according to claim 2, wherein the spatial light modulation unit and the spatial light demodulation unit are connected via an optical transmission path.

8. The optical transmission device according to claim 2, wherein the light source is a surface emitting laser.

9. The optical transmission device according to claim 2, wherein the light source is a Fabry-Perot resonator laser.

10. The optical transmission device according to claim 2, wherein the light source is a light emitting diode.

[11] Further, the light beam signal is separated into a plurality of longitudinal modes and output to the spatial light modulator,

A vertical mode multiplexing unit that inputs the optical decoded signal output from the spatial light demodulation unit and multiplexes the vertical mode;

The optical transmission device according to claim 2, wherein the spatial light modulation unit modulates the light beam signal in accordance with the predetermined method for each longitudinal mode separated by the longitudinal mode separation unit.

[12] Further, a mode dispersion detection unit for detecting a mode dispersion characteristic of the optical demodulated signal is provided,

The optical transmission device according to claim 2, wherein the spatial light demodulating unit performs correction with a characteristic opposite to the mode dispersion characteristic based on a result detected by the mode dispersion detecting unit.

13. The optical transmission device according to claim 12, wherein the mode dispersion detection unit detects a delay amount due to mode dispersion.

[14] The spatial light demodulating unit adds a predetermined delay amount for each oscillation mode so as to correct a delay amount due to mode dispersion detected by the mode dispersion detecting unit. Item 13. The optical transmission device according to Item 12.

15. The optical transmission device according to claim 12, wherein the mode dispersion detection unit detects an amount of loss due to mode dispersion.

[16] The spatial light demodulator may be configured to detect the mode dispersion detected by the mode dispersion detector. 13. The optical transmission device according to claim 12, wherein a predetermined loss amount is added for each oscillation mode so as to correct the loss amount.

[17] The spatial light modulator modulates the light beam signal based on a predetermined code,

3. The optical transmission device according to claim 2, wherein the spatial light demodulating unit demodulates the optical modulation signal based on a code corresponding to the predetermined code.

[18] Further, the predetermined code for the spatial light modulation unit to modulate the light beam signal, and the code corresponding to the predetermined code for the spatial light demodulation unit to demodulate the light modulation signal The optical transmission device according to claim 17, further comprising: a code changing unit that changes

19. The optical transmission device according to claim 2, wherein the spatial light modulator and the spatial light demodulator are configured by a liquid crystal spatial light modulator.

20. The optical transmission apparatus according to claim 2, wherein the spatial light modulator and the spatial light demodulator are configured by a micromirror device.

21. The optical transmission device according to claim 2, wherein the spatial light modulator and the spatial light demodulator are configured by a spatial light modulator using a magneto-optic effect.

22. The optical transmission device according to claim 2, wherein the spatial light modulation unit and the spatial light demodulation unit are configured by an optical modulation element using a multiple quantum well effect.

23. The optical transmission device according to claim 2, wherein the spatial light modulation unit and the spatial light demodulation unit are configured by a light modulation element using an acoustooptic effect.

[24] The spatial light modulator controls the intensity of the light beam signal,

The optical transmission apparatus according to claim 2, wherein the spatial light demodulator controls the intensity of the optical modulation signal.

[25] The spatial light modulator controls the phase of the light beam signal,

The optical transmission device according to claim 2, wherein the spatial light demodulator controls the phase of the optical modulation signal.

[26] The spatial light modulator controls a polarization state of the light beam signal,

The optical transmission device according to claim 2, wherein the spatial light demodulator controls a polarization state of the optical modulation signal.