WO2010099707A1

WO2010099707A1 - Laser optical engine

Info

Publication number: WO2010099707A1
Application number: PCT/CN2010/070156
Authority: WO
Inventors: 权星泽; 金东侠; 金城守
Original assignee: 上海三鑫科技发展有限公司
Priority date: 2009-03-06
Filing date: 2010-01-13
Publication date: 2010-09-10
Also published as: JP3174810U; CN101825832B; CN101825832A

Abstract

A laser optical engine in portable micro-projection device is disclosed. In order to reduce the interference of the laser and decrease the laser speckle, the frequency of modulation is more than KHz when laser sources are driven in real time. The laser sources which do not need frequency-doubling are modulated by high frequency 300MHz, and the green laser source which has been frequency-doubled is modulated by 2KHz, and the result is that the laser speckle is reduced and the output of the green laser is increased.

Description

Laser optical engine

Technical field

The present invention relates to portable pico projectors, and more particularly to light source technology for portable pico projectors.

Background technique

In order to practicalize a portable pico projector that is smaller than a palm or a projector that is embedded in a notebook or the like, it is necessary to develop an optical engine for a small projector.

One of the important components that determine the size of an optical engine is the light source. The laser is representative of a light source with a small volume and high light output capability. The laser chip has a size of about 2000 μm, but can output light of 1 W or more, and is an excellent light-emitting element. However, the disadvantage of lasers is the presence of Speckle.

technical problem

Speckle is an intrinsic property of lasers and is an interference phenomenon caused by the high coherence of lasers with the same wavelength, phase, and amplitude. Speckles appear as spots on the screen, which can damage the quality of the image and give the viewer a flickering feeling.

Technical solution

It is an object of the present invention to provide a laser optical engine capable of reducing the coherence characteristics of laser light and attenuating speckle.

To solve the above technical problem, an embodiment of the present invention provides a laser optical engine, including:

At least one laser source;

a light modulator that generates an image using light emitted by a light source;

The projection lens magnifies and projects the image generated by the light modulator, and further includes:

A modulation drive unit for modulating the input load of the light source during the on time to a load that varies at a frequency above one kilohertz.

Beneficial effect

Compared with the prior art, the main differences and effects of the embodiments of the present invention are as follows:

KHz at the On time of the laser source The modulation drive of the above frequency reduces the coherence of the laser and weakens the speckle phenomenon.

Further, 300Mhz is applied to a laser light source that does not require frequency multiplication. The high-speed modulation has a significant effect on speckle reduction caused by wavelength fluctuations. This is because the resonance phenomenon unique to the laser diode fluctuates the magnitude of the charge density existing in the active field of the laser diode, which causes a change in the tortuosity in the resonator to cause wavelength fluctuation.

Further, the green laser generated by the frequency doubling is performed at 2 kHz. The modulation of the frequency repeat switch not only reduces the speckle, but also increases the total light output of the green laser.

Further, by introducing a diffuser, the speckle can be diffused, and the interference between the lines caused by the laser light source can be weakened.

Further, the laser speckle can be further attenuated by the vibrating beam shaper.

DRAWINGS

1 is a schematic view showing the structure of an optical engine to which the technical solution of the present invention is applied;

2 is a schematic diagram of a driving signal for synchronously driving each light source and a light modulator;

3 is a schematic view showing a driving method of a laser light source in an embodiment of the present invention;

Figure 4 is a simplified diagram of the green laser generation process;

Fig. 5 is a diagram showing changes in light output of DPM according to changes in input load in the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following description, numerous technical details are set forth in order to provide the reader with a better understanding of the present application. However, those skilled in the art can understand that the technical solutions claimed in the claims of the present application can be implemented without these technical details and various changes and modifications based on the following embodiments.

The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

The structure of an optical engine to which the technical solution of the present invention can be applied is as shown in FIG. 1. The optical engine is of a reflective type, including: an R light source (10R), a G light source (10G), a B light source (10B), and a dichroic mirror 50R. , 40G, 50B, diffuser (20), beam shaper (Beam Shaper) (30), objective lens (40-1, 40-2), light modulator (60), projection lens (70), polarization beam splitter (80), where R stands for red, G stands for green, and B stands for blue .

The R/G/B light source sequentially illuminates the R/G/B light. Specifically, the time for irradiating one frame is set to T, the time of T/3 is irradiated to the R light source, and the time of the next T/3 is irradiated with the G light source, and then The next T/3 time illuminates the B source. It can be understood that the light source can also be sequentially irradiated in other orders, such as B/G/R.

The light source used in the micro projector requires a small volume and a large amount of light, so a laser light source is required. The three light sources (10R, 10G, 10B) are reflected by the respective

dichroic mirrors

50R, 50G, 50B or transmitted to the diffuser (20).

The dichroic mirror 50G functions to reflect the G light source (green laser light emitted from 10G) and transmit the remaining light. The dichroic mirror 50G can also use a general mirror that can reflect all of the ordinary visible light. The dichroic mirror 50R functions to reflect the R light source (red laser light emitted from 10R) and pass the light of the remaining wavelength range, and the dichroic mirror 50B functions to reflect the R light source (the blue laser light emitted from 10B) through the remaining wavelength. The effect of the range of light.

The diffuser (20) vibrates perpendicular to the optical axis, so the randomness of the light increases as it passes through the diffuser (20). This diffuser is a device designed to eliminate laser-specific laser speckles (Speckle) to reduce the coherence of laser light to reduce laser speckle.

Light passing through the diffuser (20) will transform the beam shape through the beam shaper (30). The reason for changing the shape of the beam is to shape the pattern of the beam to the shape of the incident surface of the light modulator (60) to improve the light efficiency.

In the example of Fig. 1, the beam shaper (30) uses a fly-eye lens composed of a small lens body on both sides, and two single-sided lenses may be used. On such two sides, or a plurality of small lens bodies each formed by aggregating them on one another, they are formed in one-to-one correspondence with each other. Such a light-speed shaper converts a laser incident at a diameter of 100 to 200 μm into a surface state and expands, which can alleviate the coherence characteristics of the laser and diffuse the light energy into a surface light, thereby reducing the specificity of the laser light generated by the concentration together. The danger.

The small lens body included in the fly-eye lens may have various shapes such as a quadrangular convex lens shape, a hexagonal convex lens shape or a circular shape, etc., but preferably conforms to the effective area shape of the light modulator. For example, when the effective area of the light modulator is quadrangular, the shape of the small lens body is also quadrangular to minimize light loss.

The diameter of the lenslet body is preferably 80-500 um, and the beam is more easily shaped at this size. This is because the diameter of the small lens is less than 80 um, and the lattice pattern is generated in the light beam due to the continuity of the laser, and it is difficult to make a lens configuration having a smooth surface smaller than 80 um in the prior art. When the diameter is increased, the effect of the beam shaper is weakened, and the uniform light source required for the ultra-small optical engine is not obtained, so it is preferable to use 500 um or less.

Each lenslet body is composed of a mixture of lens lenses of various sizes, thereby reducing laser speckle.

The objective lens (40) is a lens that bundles light shaped by a beam shaper by a light modulator (60), and generally consists of one to two sheets.

The light modulator (60) refers to an element that selectively passes incident light, blocks or changes the optical path to form an image. A typical example of a light modulator (60) is a digital micromirror device (Digital Micromirror Device ("DMD"), Liquid Crystal Display ("LCD") components, liquid crystal on silicon (Liquid) Crystal On Silicon, referred to as "LCOS" and so on.

DMD is used in digital light processing (Digital Light Processing, referred to as "DLP"), which uses the field timing (field) Sequential), using a digital mirror arranged in the same number of pixels as the number of pixels (DIGITAL MIRROR). DLP refers to a projector that uses light from a light source to adjust the optical path with a digital mirror and reflects it with a spacer to achieve Gradation or image formation.

A liquid crystal display element (LCD) refers to an element that selectively turns on/off a liquid crystal to form an image. Among the projectors using LCD elements, there are direct-view, projection, and reflection types. The direct-view projection is a method in which the background light behind the liquid crystal display element forms an image through the LCD panel and can be directly observed; the projection type projection is to enlarge an image formed by the liquid crystal display element by using a projection lens and project it onto the screen, and observe the slave screen. The way of reflecting the image; the reflective type is basically the same as the projected type, except that the reflective type is provided with a reflective film on the substrate under the LCD, and the reflected light is amplified and projected onto the screen.

LCOS is a reflective liquid crystal display, which converts the lower substrate of the two-sided substrate of the conventional liquid crystal display end from a transparent glass to a silicon substrate, thereby operating in a reflective manner.

The polarization beam splitter (80) is an optical element that functions to transmit incident light to the light modulator (60). The hexahedron of the glass material and the polarization separation film are distributed diagonally, which is necessary for the reflective optical engine. An optical component.

The incident light hits the polarization separation film of the polarization beam splitter, the S polarization is reflected by the polarization separation film to the light modulator, and the P polarization is transmitted through the polarization beam splitter and discarded. The light emitted by all the light source sections (10) is converted to a line parallel state at a certain point on the optical path to maintain the light efficiency. However, the output of the laser light source has a polarization ratio of several hundred to one, and does not require an optical component in which the conversion line is parallel, so it is very suitable for a light source of a micro projector.

In this way, the S-polarized light reflected by the polarization separation film is converted into P-polarized light during formation of an image by the light modulator, and the image light converted into P-polarized light is again incident on the polarization beam splitter (80) and hits the polarization separation film. The image light of this time is all P-polarized, so it is incident on the projection lens (70) through the polarization separation film.

The projection lens (70) is composed of a plurality of lenses, and an image formed by the light modulator (60) is enlarged and projected onto a screen (not shown).

Described above is a reflective optical engine, and the technical solution of the present invention is also applicable to a transmissive optical engine. The structure of the transmissive optical engine is similar to that of the reflective type, the main difference being that there is no polarization beam splitter (80), and the optical paths of the objective lens (40), the light modulator (60) and the projection lens (70) are the same straight line.

2 is a schematic view showing the principle of R/G/B three-color laser driving in the above-described pico projector. In order to miniaturize the optical engine of the pico projector, a light modulator is used to represent the color image. Use field timing (field A sequential liquid crystal display device (LCD) is a light modulator that conforms to this purpose. Such a field timing refers to a method in which the time zone is divided into three equal parts, and the green, red, and blue images corresponding to the three primary colors are sequentially displayed at respective times. The human eye will have a residual image, and when the image is displayed at a certain speed or higher, it will be regarded as a continuous picture. Movies or animations use this principle. The color image is the same. When the R/G/B primary colors are quickly displayed, the viewer will consider the three primary colors mixed white due to the afterimage effect. Similarly, when the amount of light of the three primary colors is different, a plurality of colors can be adjusted, so that the relative amounts of the three primary colors can be adjusted to achieve the purpose of displaying the desired color.

The field timing drive is to re-divide the 60 Hz image frame by three equal parts. An R/G/B sub-image corresponding to the amount of light of the three primary colors is generated for each video image, and then the above-described sub-image is driven at 180 Hz. According to the above-mentioned 180 Hz sub-image synchronously incident R/G/B light, a 60 Hz color image can be obtained. FIG. 2 illustrates the above-described driving signals for driving the three R/G/B light sources according to the 180 Hz sub-image.

As shown in Figure 2, the R source signal is 180Hz, there is an On Time interval. The interval between the light sources is used to transmit the light quantity data of each pixel to the light modulator, and there are three such intervals in each frame, and the sum is about 10% of the total load.

Control the On of each light source Time, in conjunction with the time signal corresponding to the light modulator, repeats the 180 Hz on/off action with a certain amount of light energy.

Embodiments of the present invention improve upon such simple light source driving to reduce the coherence characteristics of the laser.

The laser is a collection of the same wavelength, the same amplitude, and the same phase of light, with strong coherence. Even if the beam shaper is used to shape and expand the surface light source, random interference image points will be generated. This interference image point is reflected as a speckle, called speckle. The inventors of the present invention believe that the following relationship exists:

Randomness = variable wavelength × variable phase × variable angle of incidence

Corresponding to the above formula, there are three representative methods to reduce the coherence of incident light.

The first method is that the incident angle is variable.

The diffuser (20) of Figure 1 is a method of variable angle of incidence. However, the light diffuser (20) cannot completely eliminate the speckle, and it is necessary to cooperate with other methods.

The second method is that the phase is variable.

The phase-variable method is to give a change in the polarization, and it is difficult to use it at the front end of the optical modulator.

The third method is that the wavelength is variable.

Variable wavelengths can be used as an important means other than diffusers (20).

Figure 3 is a schematic illustration of an improvement in light source driving in a case in which the present invention is applied.

The laser diode emits light of a single wavelength, but in both cases the wavelength can be varied.

The first is the change in temperature. The wavelength of the light emitted by the laser diode changes gradually as the operating temperature changes. This range of change is about 0.25 nm / C °. At -10 C°~+10 The wavelength will continue to change arbitrarily if the C° range continuously changes.

To control the operating temperature, it is necessary to increase the temperature of the laser diode, which has the disadvantage that the optical engine will become bulky.

The second is to turn on the light source as shown in Figure 3. Time) is divided into a plurality of intervals and modulated into a high speed load. The drawing is divided into nearly 10 sections for the convenience of explanation, but it is actually a high-speed modulation of 3Khz or more. In particular, when the high-speed modulation of 300 Mhz is performed, the speckle reduction effect caused by the fluctuation of the wavelength is remarkable. This is because the resonance phenomenon unique to the laser diode causes the fluctuation in the magnitude of the charge density existing in the active field of the laser diode to be large, which causes the variation in the tortuosity in the resonator to cause fluctuations in the wavelength.

In the case of modulation drive, the input load is adjusted to half the size in Figure 3. The minimum value of the input load during high-speed modulation can be any value between the maximum value and zero.

Red and blue lasers can be modulated into loads that vary by hundreds of Mhz, but green light is not. Because the green light is called the diode pump module (Diode Pumped) The optical component of the Module, referred to as "DPM" for short.

Since a solid green laser has not been developed so far, the green laser is generated by the second harmonic (Second) Harmonic Generation ("SHG" for short) multi-wavelength infrared laser (Infrared Laser) multiplier (Frequency Doubling) is converted to a green wavelength to use. Frequency multiplication is generally performed using an optical component such as DPM (90), the construction of which is briefly described in FIG.

The wavelength of about 800 nm emitted by the infrared laser (100) is converted into green light of 532 nm by DPM (90). Such DPM (Diode Pumped Module) consists of Nd:YVO4 (110, Nd-doped yttrium vanadate) and KTP (120). KTP (120) is KTiOPO4 (Potassium Titanyl) Phosphate Crystals is a nonlinear optical component that is used in the frequency doubling of lasers.

The 808 nm infrared laser (100) is converted into a long-wavelength light of 1064 nm by Nd:YVO4 (110), and the long-wavelength laser of 1064 nm is multiplied by a non-linear element KTP (120) to a green laser of 532 nm.

The above DPM (90) cannot accommodate the high-speed modulation of hundreds of Mhz, so it should be changed to a few degrees of khz. In a preferred embodiment of the invention, the light modulation of the green light described above can be up to 2000 KHz. Of course, it can also be modulated into other frequencies, such as 1500Hz, 2500Hz, etc., but the effect will be worse.

The above DPM (90) has an advantage in addition to the speckle reduction effect by driving modulation wavelength fluctuations as previously described.

Figure 5 is a schematic illustration of the operational characteristics of DPM (90) for an input load. Figure 5a is an output diagram of an existing drive method for inputting a load. Fig. 5b is an output diagram when the input load is modulated at a high speed. When the green light source is modulated to a number Khz repeatedly on/off, the light output during the entire load is increased. This is because the output capability of the DPM has a gradual attenuation characteristic when the load amount is increased. Therefore, the off interval between loads increases but the light output increases.

In Fig. 5, the input load of the infrared laser forming the green light source is modulated in an on/off manner, that is, the minimum value of the input load change is 0, and the embodiment of the present invention is not limited to this modulation mode, and the input load variation is minimal. The value can actually be any value between 0 and the maximum.

In this embodiment, the modulation of the light source can be accomplished by a modulation drive unit that modulates the input load of the light source during the on time to a load that varies at a frequency above one kilohertz. It can be understood that the modulation driving unit is a logic unit, which can be implemented as a separate physical unit, or can be part of one physical unit, or can be implemented by a combination of multiple physical units. The physical implementation of the modulation driving unit itself is not the most Importantly, the functions it implements are a key to solving the technical problems presented by the present invention.

Visible in the laser light source On When the time is driven, the modulation drive of several KHz or more is performed, which can reduce the coherence characteristics of the laser and weaken the speckle phenomenon. Especially in the case of green light, in addition to reducing the speckle phenomenon, the light output efficiency can be increased.

In addition to weakening the laser speckle by high frequency modulation of the laser source and introduction of the diffuser, elements for the vibrating beam shaper can be introduced, which are further attenuated by the vibrating beam shaper.

The above embodiments are directed to three laser light sources, but the technical solution of the present invention is not limited to the optical engines of three laser light sources, and may be one, two or more laser light sources, or may be laser light sources and light emitting diodes. Level tube (Light Emitting Diode, referred to as "LED"), is a hybrid light source, such as a red laser source, a green laser generated by an infrared laser source, and a blue LED source.

Although the invention has been illustrated and described with reference to the preferred embodiments of the present invention, it will be understood The spirit and scope of the invention.

Embodiments of the invention

Industrial applicability

Sequence table free content

Claims

1 . A laser optical engine that includes:

At least one laser source;

a light modulator that generates an image using light emitted by the light source;

a projection lens for magnifying and projecting an image generated by the light modulator, further comprising:

A modulation driving unit is configured to modulate an input load of the light source during an on time to a load that varies at a frequency above one kilohertz.

2 . According to claim 1 The laser optical engine is characterized in that the laser light source comprises a red laser light source and a blue laser light source;

The input load of the red laser source and the blue laser source varies between 3 kHz and 300 MHz.

3 . The laser optical engine according to claim 2, wherein the input load of the red laser source and the blue laser source has a variation frequency of 300 MHz Between.

4 . A laser optical engine according to claim 3, wherein said minimum value of said input load change is 1/2 of the maximum value .

5 . The laser optical engine according to claim 1, wherein said laser light source comprises an infrared laser light source;

The input load of the infrared laser source has a frequency of change of 2000 kHz.

6 . According to claim 5 The laser optical engine is characterized in that it further comprises a diode pumping module for converting the infrared laser generated by the infrared laser source into a green laser.

7 . The laser optical engine according to claim 6, wherein the minimum value of the infrared laser light source input load change is 0 .

8 . According to claims 1 to 7 The laser optical engine of any of the preceding claims, further comprising a diffuser disposed between the light source and the light modulator for reducing laser speckle of the light source;

The diffuser includes a diffusing element and a drive element that rotates or vibrates the diffusing element.

9 . The laser optical engine according to claim 8, further comprising:

a beam shaper disposed between the light source and the objective lens for converting a light beam emitted by the light source into an effective region shape of the light modulator;

And an element for vibrating the beam shaper.

10 . According to claims 1 to 7 A laser optical engine according to any of the preceding claims, wherein the light modulator is one of the following:

Liquid crystal display element, digital micromirror device, silicon-based liquid crystal;

The light modulator modulates a plurality of light sources in a field sequential manner.