WO2016150095A1

WO2016150095A1 - Method and device for inhibiting laser speckles

Info

Publication number: WO2016150095A1
Application number: PCT/CN2015/088045
Authority: WO
Inventors: 夏军; 杨磊; 张晓兵; 夏欢林
Original assignee: 中兴通讯股份有限公司
Priority date: 2015-03-20
Filing date: 2015-08-25
Publication date: 2016-09-29
Also published as: CN106033148A

Abstract

A method and device for inhibiting laser speckles. The method comprises: collimating and expanding a laser light source (100); converting the collimated and expanded laser light source into linearly-polarized light (101); and modulating phases of the linearly-polarized light according to one or more random phase diagrams (102). Phases of modulated linearly-polarized light are randomly distributed, the coherence of a laser light source is reduced, and when the modulated linearly-polarized light is used as a light source of a projection display system, inhibitions to laser speckles are simply achieved.

Description

Method and device for suppressing laser speckle

Technical field

This application relates to, but is not limited to, laser projection techniques.

Background technique

The laser has the advantages of good monochromaticity, strong directivity, high brightness, large chroma triangle, etc. It is used as a light source for projection display, with high color saturation and clear image, which can achieve high quality of large screen and small portable projection. image. These make laser displays an advantage that is unmatched by other light source display technologies.

For the display system, the intensity of a point on the observation surface is superimposed by the reflected light from the surface of the screen. Since the roughness of the screen surface is greater than the wavelength of the light wave, the laser forms a diffuse reflection on the surface of the screen, and the wavelet emitted from each point of the object reaches the observation point. The phases are randomly distributed, but due to the high coherence of the laser, the wavelets are coherently superimposed to form a laser speckle, which is a granular speckle pattern with spatial intensity fluctuations.

Laser speckle is the noise on the imaging light field, causing energy loss; and the strong speckle pattern on the screen reduces the resolution and contrast of the image, which seriously affects the image quality; while the presence of laser speckle is visible to the viewer. The glare flashes, causing discomfort to the audience. These shortcomings have become the bottleneck restricting the development of laser display technology. Therefore, suppression of laser speckle has become the key to the further development of laser display technology.

The related art methods for suppressing laser speckle can be roughly divided into two categories:

One is to modify the laser source to reduce its temporal or spatial coherence, including using different wavelengths of light source illumination, using temperature effects to cause laser wavelength drift, etc., to reduce temporal coherence; or, using the same wavelength of laser array illumination , using a superposition of pulsed lasers to reduce its spatial coherence method. However, these methods require relatively complex design and modification of the laser source. For example, in a method of attenuating laser speckle by using laser array illumination of the same wavelength, M mutually incoherent laser light sources (ie, laser light source arrays) are respectively incident on the screen at different incident angles, and incident angles of the respective laser light sources are used. The contrast of the speckle can be reduced to the original when it is larger than the imaging angle.

In this way, the projection display system needs to be considered when designing the laser light source array. Different projection display systems may require different laser light source arrays, which obviously leads to a complicated design of the laser light source array.

The other is a method for forming a boiling speckle pattern on the screen based on the principle of statistical optics, including moving scatterers, moving aperture diaphragms, vibrating screens, rotating optical fibers, etc., using mechanical motion devices to drive the optical devices to move quickly on the screen. A method of forming a speckle boiling pattern. However, there are certain problems in the manufacture and maintenance of the device because mechanical devices are required for mechanical operation. For example, in a method of using a vibrating screen to attenuate the laser spot, the vibrating screen needs to be specially customized, and a driving device such as a motor needs to be provided, and the driving device needs to be configured with a corresponding power source, and needs to have a mechanical arm and a vibrating screen fixed. The vibrating screen needs to select the appropriate vibration amplitude and vibration frequency to make the effect of weakening the laser speckle better, without affecting the normal viewing of the image. However, different vibration amplitudes and vibration frequencies may be required for different image sources. For dynamic image sources, the vibration amplitude and vibration frequency need to be adjusted in real time, so that the implementation of the driving device is complicated, and the volume of the driving device is also Larger, this runs counter to the miniaturization and portability of the projection system.

Summary of the invention

The following is an overview of the topics detailed in this document. This Summary is not intended to limit the scope of the claims.

This paper proposes a method and device for suppressing laser speckle, which can easily achieve the suppression of laser speckle.

A method of suppressing laser speckle, comprising:

The laser source is collimated and expanded;

Converting the collimated and expanded laser light source into linearly polarized light;

The linearly polarized light is phase modulated according to one or more random phase diagrams.

Optionally, the method further comprises: displaying the modulated linearly polarized light as a light source of the projection display system.

Optionally, converting the collimated and expanded laser light source into linearly polarized light comprises: converting the collimated and expanded laser light source into the linearly polarized light by using a polarizer.

Optionally, the polarizer is a linear polarizer.

Optionally, the phase modulating the linearly polarized light comprises: phase modulating the linearly polarized light with a spatial light modulator.

Optionally, the diameter of the collimated, expanded laser source is greater than or equal to the window diameter of the spatial light modulator.

Optionally, the polarization direction of the linearly polarized light is the same as the polarization direction of the spatial light modulator when no voltage is applied.

Optionally, the spatial light modulator is a reflective spatial light modulator;

After converting the collimated and expanded laser light source into linearly polarized light, before the phase modulating the linearly polarized light by the spatial light modulator according to one or more random phase diagrams, the method further comprises:

Changing the direction of propagation of the linearly polarized light;

The phase modulating the linearly polarized light by the spatial light modulator according to one or more random phase diagrams includes:

The reflective spatial light modulator is used to phase modulate the linearly polarized light after changing the propagation direction according to one or more random phase diagrams.

Optionally, the changing the direction of propagation of the linearly polarized light comprises: changing a propagation direction of the linearly polarized light by using a beam splitting prism.

A device for suppressing laser speckle, comprising:

The collimating beam expanding module is set to: collimate and expand the laser light source;

The conversion module is configured to: convert the collimated and expanded laser light source into linearly polarized light;

The modulation module is configured to phase modulate the linearly polarized light according to one or more random phase diagrams.

Optionally, the conversion module is a polarizer.

Optionally, the polarizer is a linear polarizer.

Optionally, the modulation module is a spatial light modulator.

Optionally, the spatial light modulator is a reflective spatial light modulator.

The device also includes:

The module is changed to be set to change the propagation direction of the linearly polarized light.

Optionally, the changing module is a beam splitting prism.

Compared with the related art, the embodiment of the invention includes: collimating and expanding the laser light source; converting the collimated and expanded laser light source into linearly polarized light; according to one or more random phase diagram pairs Linearly polarized light is phase modulated. In the solution of the embodiment of the present invention, the linearly polarized light after changing the propagation direction is modulated according to the random phase diagram, so that the phase of the modulated linearly polarized light is randomly distributed, thereby reducing the coherence of the laser light source, and using the modulated line. When polarized light is used as a light source for a projection display system, suppression of laser speckle is simply achieved.

In addition, the polarization direction of the linearly polarized light is the same as the polarization direction of the spatial light modulator when no voltage is applied, so that the linearly polarized light after changing the propagation direction is incident on the spatial modulator and only phase-modulated, thereby ensuring image quality.

Other aspects will be apparent upon reading and understanding the drawings and detailed description.

BRIEF abstract

1 is a flow chart of a method for suppressing laser speckle according to an embodiment of the present invention;

2 is a schematic structural view of a device for suppressing laser speckle according to an embodiment of the present invention;

3 is a schematic structural view of a device for suppressing laser speckle according to a first embodiment of the present invention;

4 is a schematic structural view of a device for suppressing laser speckle according to a second embodiment of the present invention;

FIG. 5 is a schematic structural diagram of a projection system according to a third embodiment of the present invention; FIG.

FIG. 6 is a schematic structural diagram of a projection system according to a fourth embodiment of the present invention.

Embodiments of the invention

Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that the embodiments in the present application and the various manners in the embodiments may be combined with each other without conflict.

Referring to FIG. 1, an embodiment of the present invention provides a method for suppressing laser speckle, comprising:

Step 100: Perform collimation and beam expansion processing on the laser light source.

In this step, in order to improve the utilization efficiency of the spatial light modulator, the diameter of the collimated and expanded laser light source may be greater than or equal to the window diameter of the spatial light modulator.

Step 101: Convert the collimated and expanded laser light source into linearly polarized light.

In this step, in order to ensure image quality, the polarization direction of the linearly polarized light may be the same as the polarization direction of the spatial light modulator (such as the alignment direction of the liquid crystal molecules) when no voltage is applied.

In this step, a collimator (such as a linear polarizer) can be used to convert the collimated and expanded laser light source into linearly polarized light.

Step 102: Perform phase modulation on the linearly polarized light according to one or more random phase diagrams.

In this step, the spatially polarized light can be phase modulated by the spatial light modulator.

The spatial light modulator may be a reflective spatial light modulator (such as a liquid crystal pure phase spatial light modulator) or a transmissive spatial light modulator.

When the spatial light modulator is a reflective spatial light modulator, step 101 and step 102 further include: changing a propagation direction of the linearly polarized light.

Among them, a spectroscopic prism can be used to change the propagation direction of linearly polarized light.

In step 102, the linearly polarized light after changing the propagation direction is phase-modulated by a reflective spatial light modulator according to one or more random phase diagrams.

When the spatial light modulator is a transmissive spatial light modulator, there is no need to change the direction of propagation of the linearly polarized light.

Wherein, using a computing device (such as a computer) to generate one or more random phase maps, the generated random phase map is loaded into the spatial light modulator to change the polarization state of the spatial light modulator, when the direction of propagation is changed When the linearly polarized light is incident on the spatial light modulator, the spatial light modulator phase modulates the linearly polarized light that changes the direction of propagation.

The method also includes:

Step 103: Projecting and displaying the modulated linearly polarized light as a light source of the projection display system.

In the method of the embodiment of the present invention, the linearly polarized light after changing the propagation direction is modulated according to the random phase diagram, so that the phase of the modulated linearly polarized light is randomly distributed, and the coherence of the laser light source is reduced, and the modulated line is used. When polarized light is used as a light source for a projection display system, suppression of laser speckle is simply achieved.

Referring to FIG. 2, an embodiment of the present invention further provides an apparatus for suppressing laser speckle, comprising:

The collimating beam expanding module 201 is configured to: perform collimation and beam expansion processing on the laser light source;

The conversion module 202 is configured to: convert the collimated and expanded laser light source into linearly polarized light;

The modulation module 203 is configured to phase modulate the linearly polarized light according to one or more identical random phase diagrams.

In the apparatus of the embodiment of the invention, the conversion module 202 can be a polarizer.

In the device of the embodiment of the invention, the polarizer may be a linear polarizer.

In the apparatus of the embodiment of the present invention, the modulation module 203 may be a spatial light modulator.

In the apparatus of the embodiment of the invention, the spatial light modulator may be a reflective spatial light modulator.

The device may also include:

The changing module 204 is configured to change the propagation direction of the linearly polarized light.

In the apparatus of the embodiment of the invention, the changing module 204 may be a beam splitting prism.

The apparatus of the embodiment of the present invention will be described in detail below.

First Embodiment, FIG. 3 is a schematic structural view of a device for suppressing laser speckle using a reflective spatial light modulator. As shown in FIG. 3, the collimated and expanded laser light source 1 passes through the linear polarizing plate 2, and the polarization direction of the linearly polarized light is the same as the liquid crystal molecule alignment direction of the reflective spatial light modulator 4 when no voltage is applied. The linearly polarized light is deflected and incident on the reflective spatial light modulator 4 through the dichroic prism 5. The computer 3 generates a series of random phase maps that are loaded onto the reflective spatial light modulator 4 over time. The reflective spatial light modulator 4 phase-modulates the deflected linearly polarized light, and the phase of the modulated linearly polarized light is randomly distributed, thereby reducing the coherence of the laser light source.

Second Embodiment, FIG. 4 is a schematic view showing the structural composition of a device for suppressing laser speckle using a transmissive spatial light modulator. As shown in FIG. 4, the collimated and expanded laser light source 1 passes through the linear polarizing plate 2, and the polarization direction of the linearly polarized light and the liquid crystal molecules of the transmissive spatial light modulator 6 are arranged without applying a voltage. To the same. The linearly polarized light is incident on the transmissive spatial light modulator 6. The computer 3 generates a series of random phase maps that are loaded onto the transmissive spatial light modulator 6 over time. The transmissive spatial light modulator 4 phase-modulates the linearly polarized light, and the phase of the modulated linearly polarized light is randomly distributed, thereby reducing the coherence of the laser light source.

Third Embodiment FIG. 5 is a structural diagram showing the structure of a projection system in which linearly polarized light is directly used as a light source. As shown in FIG. 5, the collimated and expanded laser light source 1 passes through the linear polarizing plate 2, and the polarization direction of the linearly polarized light is the same as the liquid crystal molecule alignment direction of the reflective spatial light modulator 4 when no voltage is applied. The linearly polarized light is deflected and incident on the reflective spatial light modulator 4 through the dichroic prism 5. The computer 3 generates a series of random phase maps that are loaded onto the reflective spatial light modulator 4 over time. The reflective spatial light modulator 4 phase-modulates the deflected linearly polarized light, and the phase of the modulated linearly polarized light is randomly distributed, thereby reducing the coherence of the laser light source.

The modulated linearly polarized light is incident on the projector 7 through the dichroic prism 8. The projector 7 projects an image onto the screen 9. Since the reflective spatial light modulator 4 performs random phase modulation on the laser light source, the speckle pattern on the screen 9 changes with time, and when the two adjacent loadings into the reflective spatial light modulator, the human eye sees the speckle superposition. The time-averaged effect, which achieves a reduction in laser speckle.

Fourth Embodiment FIG. 6 is a structural diagram showing the structure of a projection of linearly polarized light after spatial filtering as a light source. As shown in FIG. 6, the collimated and expanded laser light source 1 passes through the linear polarizing plate 2, and the polarization direction of the linearly polarized light is the same as the liquid crystal molecule alignment direction of the reflective spatial light modulator 4 when no voltage is applied. The linearly polarized light is deflected and incident on the reflective spatial light modulator 4 through the dichroic prism 5. The computer 3 generates a series of random phase maps that are loaded onto the reflective spatial light modulator 4 over time.

The modulated linearly polarized light passes through the lens 10 to become a spherical wave, and is spatially filtered by the small hole 11 placed on the back focal plane of the lens 10. The emitted light is incident on the projector 7 through the dichroic prism 8. The projector 7 projects an image onto the screen 9. The reflective spatial light modulator 4 randomly modulates the linearly polarized light, and the laser passes through the lens 10 to become a divergent spherical wave, and spatial coherence is further reduced. The light beam converges to a point on the back focal plane of the lens 10, passes through the small hole 11, performs spatial filtering, and is incident on the projector 7 through the dichroic prism 8 for projection, suppressing the speckle effect of the screen 9.

The projector 7 in the third embodiment and the fourth embodiment may be a general laser projector or laser holography projector.

Industrial applicability

In the solution of the embodiment of the present invention, the linearly polarized light after changing the propagation direction is modulated according to the random phase diagram, so that the phase of the modulated linearly polarized light is randomly distributed, thereby reducing the coherence of the laser light source, and using the modulated line. When polarized light is used as a light source for a projection display system, suppression of laser speckle is simply achieved. In addition, the polarization direction of the linearly polarized light is the same as the polarization direction of the spatial light modulator when no voltage is applied, so that the linearly polarized light after changing the propagation direction is incident on the spatial modulator and only phase-modulated, thereby ensuring image quality.

Claims

A method of suppressing laser speckle, comprising:

The laser source is collimated and expanded;

Converting the collimated and expanded laser light source into linearly polarized light;

The linearly polarized light is phase modulated according to one or more random phase diagrams.
The method of claim 1 further comprising: projecting said modulated linearly polarized light as a source of a projection display system.
The method according to claim 1 or 2, wherein converting the collimated and expanded laser light source into linearly polarized light comprises: converting the collimated and expanded laser light source into a polarizer by using a polarizer The linearly polarized light.
The method of claim 3 wherein the polarizer is a linear polarizer.
The method of claim 1 or 2, wherein said phase modulating said linearly polarized light comprises phase modulating said linearly polarized light with a spatial light modulator.
The method of claim 5 wherein the diameter of the collimated, expanded laser source is greater than or equal to the window diameter of the spatial light modulator.
The method of claim 5 wherein the polarization direction of the linearly polarized light is the same as the polarization direction of the spatial light modulator when no voltage is applied.
The method of claim 5 wherein said spatial light modulator is a reflective spatial light modulator;

After converting the collimated and expanded laser light source into linearly polarized light, before the phase modulating the linearly polarized light by the spatial light modulator according to one or more random phase diagrams, the method further comprises:

Changing the direction of propagation of the linearly polarized light;

The phase modulating the linearly polarized light by the spatial light modulator according to one or more random phase diagrams includes:

Using the reflective spatial light modulator to change the transmission according to one or more random phase diagrams The linearly polarized light after the broadcast direction is phase-modulated.
The method of claim 8, wherein the changing the direction of propagation of the linearly polarized light comprises: changing a direction of propagation of the linearly polarized light with a beam splitting prism.
A device for suppressing laser speckle, comprising:

The collimating beam expanding module is set to: collimate and expand the laser light source;

The conversion module is configured to: convert the collimated and expanded laser light source into linearly polarized light;

The modulation module is configured to phase modulate the linearly polarized light according to one or more random phase diagrams.
The apparatus of claim 10 wherein said conversion module is a polarizer.
The device according to claim 11, wherein the polarizer is a linear polarizing plate.
The apparatus of claim 10 wherein the modulation module is a spatial light modulator.
The apparatus of claim 13 wherein said spatial light modulator is a reflective spatial light modulator;

The device also includes:

The module is changed to be set to change the propagation direction of the linearly polarized light.
The apparatus of claim 14 wherein said changing module is a beam splitting prism.