DE2611011A1 - Optical fibre coupling esp. for repeaters - abuts monomode and gradient fibres for undirectional transmission by matching refractive indices of cores - Google Patents

Abstract

An optical coupling device is for use in communications equipment, in optical repeaters. For coupling in one direction an arrangement of monomode fibres and gradient fibres is used, with one end of the monomode fibre abutting one end of the gradient fibres. The fibres are so adjusted that the core of the monomode fibre meets a point on the core of the gradient fibre at which the refractive index of the core of each fibre is the same. The fibres are fixed in this relative position, in which the losses are a min. for the direction of transmission, but very great for transmission in the reverse direction. To suppress mantle waves, iris diaphragms may be fitted to one or both ends of the fibres.

Description

Keyword: optical coupling arrangement for systems

optical communications technology Keyword: optical Coupling arrangement for systems of optical communications technology Title: Procedures and Arrangement for the design of optical coupling arrangements in systems of the optical Communication technology, preferably in repeaters for optical transmission links The invention relates to a method and an arrangement for designing optical Coupling arrangements in systems of optical communication technology, preferably in Repeaters for optical transmission links. Such optical transmission systems serve to transmit electrical signals through suitable electrical-optical converters (e.g. semiconductor laser diodes) have been converted into light signals via optical fibers from a location A to a location B, at the end of the fiber optic link the light signals through suitable optical-electrical converters (e.g. photodiodes) converted back into electrical signals.

Prior art: It is known from DAS 1254513 that electrical Signals in the form of optical signals can be transmitted over glass fibers. For longer transmission distances of a few 100 m to a few km, the optical signals are so weakened and distorted that they are in a so-called.

Repeater need to be regenerated. With optical transmission links of this type optical coupling arrangements are often required for connecting pieces of fiber with each other and for connecting pieces of fiber with terminals or components within these end devices (e.g. repeaters).

Two designs have become known for repeaters. Repeater one first type convert the incoming optical signals into electrical signals, which are then regenerated electrically and then converted back into optical signals (H. Ohnsorge: New Possibilities for Message Systems on the Easis of Laser fiber optic channel. NTZ-Report 17, VDE-Verlag GmbH, Berlin, 1973).

Repeaters of the second type regenerate the optical signals on optical signals Ways, i.e. without the interposition of an electrical regeneration circuit (R. Th. Kersten: Optical communication and integrated optics.

Elektronik 1975, issue 6, 5. 72/77).

With both types of repeater, optical coupling arrangements are used for the connection the fibers of the transmission path to the components of the repeater. the peculiarities occurring in this case are explained using the example of a repeater of the first type. Such a repeater has an electro-optical converter in its transmitting part, preferably a laser diode, and in its receiving part an opto-electrical one Converter, preferably an avalanche photodiode or a pin photodiode. Repeater, using components of this type advantageously enable digital transmission of messages, whereby for high transmission rates of> 50 Mbit / s and distances of a few km currently mainly semiconductor lasers, avalanche photodiodes and single-mode fibers or gradient fibers come into consideration as a component combination.

For high transmission rates, single-mode fibers have the advantage that they the light pulses distort the least on the transmission path; your light-guiding Cross-section is very small (~ 3 µm), so that when coupled to a light source or a light receiver must be adjusted very precisely. Same accuracy Adjustment is required when two single-mode fiber pieces are coupled together will. For this purpose, it has been known that a double eccentric plug connection is advantageous here (O. Krumpholz; E. Pfeiffer: Coupling device connecting a glas fiber with an integrated optical circuit. Topical Meeting on Integrated Optics, New Orleans, January 1974.

J. Guttmann; O. Krurnpholz; E. Pfeiffer: A simple connector for glass fiber optical waveguides. AEO Volume 29 (1975), pp. 50/52).

The single mode fiber consists of a core with a refractive index n1, a Diameter dk and a jacket with a refractive index n2 X n1 and an outside diameter D ~ 100 - 200; him. If one sets the refractive index n of the fiber as a function of the radius r in cylinder coordinates, a step-shaped, rotationally symmetrical one is obtained Profile as shown in Figures 5 and 6, among others.

is shown.

The manufacture of single-mode fibers presents difficulties, in particular with regard to an exact adherence to the core diameter selected once longer fiber lengths.

In contrast, gradient fibers have far less stringent requirements with regard to an adjustment to light sources, since they have a larger light-guiding Cross-section (50-100 µm). The disadvantage of these fibers is the larger one Distortion in the transmission of optical signals, closely related to manufacturing tolerances depends on the refractive index profile in this fiber. The refractive index profile of the gradient fiber should very closely match the function n2 (r) = n02. (1 - 2 (g) 2) for O Z r z R suffice. In the formula, n (r) denotes the refractive index as a function of the radius r in cylinder coordinates naten nO the maximum refractive index of the core the relative difference in refractive index R der half the diameter of the core of the gradient fiber.

Given the current state of the art, it cannot be foreseen to what extent the manufacturing tolerances of the two fiber types mentioned are practically manageable and to what extent single-mode fibers before gradient fibers in broadband Transmission links are used once.

As already mentioned, possible solutions have been found to remove pieces of fiber one and the same type to connect with each other. Out of the uncertainty about the Future development of fibers results from the fact that each fiber type respectively requires its own repeater, with optical inputs and outputs that match exactly are adapted to the type of fiber used in the transmission path.

This makes it impossible, once the transmission system has been set up the fibers used there at a later point in time simply against fibers one exchange other type; if an exchange would nevertheless be necessary, this would be it with conversion work on the optical coupling arrangements for the terminals and repeaters tied together.

When light is irradiated into fibers, the desired wave types in the light-guiding fiber core also generates undesired wave types in the cladding of the fiber, which can lead to additional signal distortion, especially if the standing waves (e.g. in the case of shorter transmission paths) arrive at the receiving location with little attenuation. In the laboratory, the glass fibers are looped in order to suppress standing waves passed through a bowl with immersion liquid, the refractive index of which is equal to The refractive index of the fiber cladding is (mode stripping). For practical applications outside However, the laboratory has not yet known an adequate solution.

With a central light irradiation in gradient fibers are always stimulated a variety of wave types, causing the light pulses, especially at not exactly parabolic refractive index profile are more distorted than with a non-central light irradiation (Guttmann et al .: Dispersion measurements in new "Selfoc" fibers. Optical and Quantum Electronics 7 (1975) pp. 305/309).

With an eccentric light irradiation close to the kernmantle boundary the gradient fiber is excited a smaller number of wave types, creating a causes less signal distortion (runtime dispersion) on the upper tray path will. A practicable solution for using this effect is also so far not known.

Object of the invention: The invention is based on the object by an inventive design of optical coupling arrangements in systems of the optical communications technology, preferably in repeaters for optical transmission links, to circumvent the aforementioned disadvantages. In particular, the optical coupling arrangements be such that optical fibers of different types with different light-guiding diameter and refractive index profile without modification with one and the same Terminal or repeater are interconnected in optical transmission systems can.

Any sheath waves that may be present in the fibers should, if possible, not be Have an influence on the connected devices (e.g. receiver part of the repeater) and the coupling losses should be as low as possible.

On the other hand, the coupling devices should be of light-emitting Devices (e.g. transmitter part of a repeater) must be designed in such a way that, if possible, no Sheath waves are excited in the connected fibers and an optimal coupling of light is possible in different fiber types. The coupling losses here should be as small as possible and as few fashions as possible should be stimulated will. Furthermore, such a flexible coupling technique should not be any noticeable additional Cause signal distortion.

Solution: According to the invention, the tasks mentioned are achieved by a special one Arrangement and combination of different components in optical coupling arrangements, preferably for end devices and repeaters, solved: 1. For coupling purposes of light signals in one direction, among other things, an arrangement of single-mode fiber and gradient fiber is used used, with one end of the single-mode fiber butted to one end of the gradient fiber is set and the fibers are adjusted so that the core of the single-mode fiber meets a point of the core of the gradient fiber in which the core refractive indices both fibers match as closely as possible. For this purpose, the core refractive index n1 of the single-mode fiber must be meet the following condition: n (R) - n1 L nO By combining Single mode fiber / gradient fiber are at the transition from the small light-guiding Core of the single mode fiber in the large core of the gradient fiber the coupling losses low for light waves, but very high in the opposite direction. This results in the possibility of interconnecting fibers of different types, if it is guaranteed that the light transmission should only take place in one direction.

On the other hand, such a coupling arrangement offers the possibility of to realize "optical valves".

2. With the inclusion of such a coupling arrangement can now build a repeater, which can be connected to transmission lines with single-mode or Gradient fibers can be switched on. For this purpose, in the receiving section of the repeater used a piece of gradient fiber with the one already described Refractive index profile that the light-receiving component (avalanche or pin photodiode) with an adjustable plug connection (preferably double eccentric plug connection) connects to the front panel of the device. In the transmission part of the repeater there is a piece Single-mode fiber at one end with the light-emitting component (e.g. semiconductor laser) and at the other end also with an adjustable plug connection (double eccentric) tied together. The two pieces of fiber - single mode and gradient fiber - are sufficient the conditions already specified. If you now use it on the transmission path Gradient fibers of the same type as they are present in the receiving part, so brings the coupling of the gradient fiber to the receiving part with no difficulties because fibers of the same type are connected to one another, whereas the Coupling to the transmitter part of the repeater from the option specified under 1 Makes use. The double eccentric plug-in connection facilitates this in an advantageous manner Way an exact adjustment. If a single mode fiber is used in the transmission link, the coupling of this fiber to the transmitter part of the repeater takes place in the usual way Way, because here two fibers of the same type are connected to one another, whereas the transition from single mode to gradient fiber is now at the coupling point to the receiving part of the repeater occurs.

3. To prevent sheath waves from being excited in the transmission fiber are, at least one end of the short single-mode fiber in the repeater end part covered with an iris diaphragm in the area of the surface of the fiber cladding. Likewise is achieved by attaching an iris diaphragm, e.g. B. in the form of a paint cover, on one At the end of the piece of gradient fiber in the receiver section of the repeater, the influence of standing waves reduced to the quality of the received signals. The iris diaphragms are preferred attached to the fiber ends of the short fiber pieces in the repeater, which are connected to the semiconductor laser or the photo diode are connected by an adhesive point.

Advantages of the invention: The advantages that can be achieved with the invention exist among others in that instead of a multitude of repeaters for different Fiber types a uniform repeater is used for single-mode or gradient fibers can be and that in existing transmission lines optionally fibers according to the state-of-the-art technology can be inserted. The repeater also stands out characterized in that the coupling arrangement according to the invention provides an optimal coupling, i.e. without large coupling losses, with the slightest distortion due to time-of-flight dispersion and guaranteed with optimal suppression of standing waves. When using Gradient fibers on the transmission path, the light is coupled in in the transmitting part of the repeater via a piece of single-mode fiber, which in this case also acts as a single-mode filter acts and a defined coupling of light into the edge zone of the core of the gradient fiber allows the delay time distortion of the signals on the transmission link can be reduced.

The invention is now based on an embodiment and the the following FIGS. 1-7 explained in more detail. They show: FIG. 1 the basic structure a repeater 'Fig. 2 shows the basic mechanical structure of a double eccentric plug connection (4), Fig. 3 shows the diagram of an optical transmission link consisting of one Transmitting part (3), a fiber link (29) and a receiving part (1), Fig. 4 shows the scheme the connection of semiconductor laser (9) and double eccentric plug connection (4) by means of a piece of single-mode fiber (10), FIG. 5 schematically shows the coupling of single-mode fiber (10) and gradient fiber (30) with central light coupling into the gradient fiber for low-loss adaptation with different light-guiding diameters and different refractive index profiles, Fig. 6 schematically shows the coupling of single mode (10) and gradient fiber (30) with eccentric light coupling into the gradient fiber for low-loss and low-distortion adjustment with different light-guiding Diameters and different refractive index profiles, Fig. 7 the scheme of the connection of double eccentric plug connection (4) and photodiode (6) by means of a piece of gradient fiber (5) and an iris diaphragm (13) in the form of a lacquer cover on the cross-section at Fiber end and Fig. 8 schematically the piece of single-mode fiber (10) with iris diaphragm (14).

Fig. 1 shows the basic structure of a repeater, consisting from a receiving part (1 ″, a power supply unit (2) and a transmitting part (3).

The receiving part (1) has an optical input in the form of a adjustable plug connection (4), a photodiode (6), a piece of gradient fiber (5), which connects the photodiode (6) with the connector (4) and at one end an iris diaphragm (13), and an electrical regeneration circuit (7) which regenerated the received signals, recovered the data clock and the received and Clock signals at the sockets (11) are available.

The light signals come from an incoming fiber via the plug connection (4) and the subsequent piece of gradient fiber (5) to the photodiode (6), in which the Optical signals are converted back into electrical ones and from there to electrical ones Regeneration circuit (7) are conducted.

The transmitter part (3) contains an electrical circuit (8) for laser control, the semiconductor laser (9) and the double eccentric plug connection (4 », which with the Laser is connected via a single mode fiber (10). The piece of single mode fiber possesses at one end an iris diaphragm (14) to prevent standing waves in the single-mode fiber (10) can be stimulated.

The electrical signals to be transmitted are clocked by the Sockets (12) to the laser control circuit (8) and from there to the semiconductor laser (9), which converts the electrical signals into optical ones. The light signals are generated by the semiconductor laser (9) via a piece of single-mode fiber (10), which acts as a single-mode filter, to the plug-in connection (4) headed.

The double eccentric plug connection (4) is shown by way of example in FIG. 2 shown. It allows a very fine adjustment, e.g. B. when coupling Single mode fiber to single mode fiber, if one is used as a transmission link will. In this case, the geometrical dimensions and refractive indices of the fiber piece (10) match those of the connected single-mode fibers. The double eccentric plug connection (4) consists essentially of an insert (19) which is inserted into the front plate (17) of the repeater housing and the two rotating bodies (18) of the double eccentric records. In the openings (21) and (22) are simple plugs that are attached to the connecting glass fibers are attached, introduced. A precise adjustment takes place by turning the two rotating bodies (18), which run in sliding fits (20).

Fig. 3 shows schematically an optical transmission path (29), wherein these contain both a gradient fiber (30) and a single mode fiber (35) can.

In the event that the transmission link (29) is a gradient fiber (2o), Fig. 4 shows the path of light from the semiconductor laser (9j via the piece of single-mode fiber (10) and the connector (4) in the gradient fiber (30). The coupling of the fibers in the plug connection (4) is illustrated in FIG. 5 and 6 explained.

To ensure a low loss of coupling during this transition, the arrangement is chosen so that firstly the light from a smaller one into one larger light-guiding cross-section and secondly the core refractive index of both Fibers at the point of contact match as closely as possible.

In Fig. 5 is also the refractive index profile (32) of the single-mode fiber (10) and the refractive index profile (31) of the gradient fiber (30) are shown. At central 5, the core refractive index n1 of the single-mode fiber must therefore be fed in according to FIG (10) be equal to the maximum refractive index n0 of the gradient fiber (30) (n1 = nO). In the case of non-central light feed according to Fig. 6, the core refractive indices must be at the point of contact of the light-guiding cross-sections also match, i.e.

nGrF (R) n1M0F GrF The corresponding refractive index profiles (33), (34) of the Gradient or single mode fibers are also indicated in FIG. 6. The type of coupling of single-mode fiber (10) and gradient fiber (30) according to FIG. 6 also offers the Advantage of the lower delay time distortion of the light signals in the connected Gradient fiber.

In the event that the transmission link (29) is a single mode fiber (35), the coupling technique described in FIGS. 5 and 6 only occurs in the plug connection (4) of the repeater receiving part (1), as shown in FIG. 7 shows. Here, too, the same considerations apply in this regard as for Fig. 4 to 6. FIG. 7 also shows an iris diaphragm (13) on the cross section of the gradient fiber piece (5).

8 accordingly shows an iris diaphragm (14) on the cross-sectional area of the Monomcdefaserstückes (10). These panels can be realized with lacquer covers will. Die'Faserenden with iris diaphragm are preferably with the appropriate Semiconductor components connected by adhesive technology.

The methods and coupling arrangements described here for coupling and connecting optical fibers of different types to a repeater can go anywhere are used where optical fiber links with end devices, repeaters or other optical components (e.g. integrated optics) flexible or solid They are therefore not necessary on the first repeater Kind of limited, but much more generally applicable.

The same applies to the iris diaphragms used in this context for the suppression of standing waves, which is advantageous as a paint cover on the jacket area of a fiber cross-section can be realized.

Claims (16)

Claims: 1 .: Method and arrangement for the design of optical Coupling arrangements in systems of optical communications technology, preferably in Repeaters for optical transmission links, characterized in that for coupling purposes of light signals in one direction an arrangement of single-mode fiber and gradient fiber is used, with one end of the single-mode fiber butted onto one end of the gradient fiber is set that the fibers are adjusted so that the core of the Mor, omodefaser meets a point of the core of the gradient fiber in which the core refractive indices both fibers match as closely as possible that the adjusted fibers in this position are fixed and that by the combination of single-mode fiber / gradient fiber at Transition from the small, light-guiding core of the single-mode fiber to the large core the gradient fiber lowers the coupling losses for light waves, and vice versa Direction are very large and that the condition n (R) s nl = nO is met. 2. Method and arrangement for the design of optical coupling arrangements in optical communications systems, preferably in optical repeaters Transmission links, characterized in that for the suppression of standing waves when transmitting light signals via optical fibers, iris diaphragms on the fiber ends attached to one or both ends of a fiber that defines the fiber cross-section cover in the area of the fiber sheath. 3. Method and arrangement for the design of optical coupling arrangements in repeaters for optical transmission links, characterized in that the Receiving part of the repeater has an adjustable fiber connector that with the component receiving the light signals via a piece of gradient fiber is connected that the transmitter part of the repeater is an adjustable fiber connector has, which with the component emitting the light signals via a piece of Monomcdefaser is connected that the refractive index profile of the gradient fiber approximately the formula n2 (r) = n2o (1 - 2 - # - (r / R) 2) for 0 # r # R is sufficient and that the core refractive index n1 and the core diameter dk of the single mode fiber meets the conditions n (R) - n1 'nO and d meet 2 R. 4. The method and arrangement according to claim 2 and 3, characterized in that that the ends of the fiber pieces in the receiving and transmitting part of the repeater to each one end with an iris diaphragm. 5. The method and arrangement according to claim 1 and 2, characterized in that that the iris diaphragm is realized by a lacquer covering on the fiber cross-section will. 6. The method and arrangement according to claim 1 or 3, characterized in that that the adjustable fiber plug-in connections double eccentric plug-in connections are. 7. The method and arrangement according to claim 3, characterized in that that the component receiving the light signals is a photodiode. 8. The method and arrangement according to claim 3, characterized in that that the component receiving the light signals is a component of the integrated Optics is. 9. The method and arrangement according to claim 3, characterized in that that the component emitting the light signals is a semiconductor laser. 10. The method and arrangement according to claim 3, characterized in that that the component emitting the light signals is a component of the integrated Optics is. 11. The method and arrangement according to claim 1 and 3, characterized in that that gradient fibers are used as transmission fibers on the transmission link that are similar to the piece of gradient fiber in the receiver section of the repeater. 12. The method and arrangement according to claim 1 and 3, characterized in that that single-mode fibers are used as transmission fibers on the transmission line that are similar to the piece of single-mode fiber in the transmitter part of the repeater. 13. The method and arrangement according to claim 1, characterized in that that the adjusted fibers are fixed in place with an adhesive with a refractive index n1 be connected to each other. 14. The method and arrangement according to claim 1, characterized in that that the adjusted fibers in their position by a detachable, adjustable double eccentric plug connection are connected to each other. 15. The method and arrangement according to claim 1, 3, 14, characterized in that that the core of the single mode fiber on the core of the gradient fiber in its edge zone meets. 16. The method and arrangement according to claim 1, 3, 14, 15, characterized in that that an immersion liquid is used at the joint between the two fiber ends, which fills any gaps between the fiber ends and their refractive index is equal to the nuclear refractive index of the single mode fiber.