Device and method for reducing speckle in projected images

An image projector includes a light source for displaying light and a diffusing screen coupled to an in-plane vibrator. The diffusing screen is positioned to receive the display light from the light source and generate phase-modulated display light. The image projector also includes a collimating element positioned to receive the phase-modulated display light. The image projector further includes a display panel positioned to receive the phase-modulated display light after being collimated by the collimating element. The display panel is configured to generate a projectable image using the phase-modulated display light.

TECHNICAL FIELD

This disclosure relates generally to optics, and in particular but not exclusively, relates to image projectors.

BACKGROUND INFORMATION

Many conventional projector displays include a display that modulates an illuminating light beam. The illuminating light beam may be a white light provided by a light source, such as metal halide lamps, xenon lamps, or mercury lamps. On the other hand, the illuminating light beam may include three separate color light beams, which are red, green, and blue light beams. Each color light beam may be separately provided by a light emitting diode (“LED”), a laser diode, or other types of laser such as gas laser, solid state laser, etc. The display panel may be a digital micro-mirror device (“DMD”) or micro-electro-mechanical system (“MEMS”) such as in a digital light processing (“DLP”) display system. The display panel may also be a liquid crystal display (“LCD”) or liquid crystal on silicon (“LCOS”) display.

Lasers have some advantages over other light sources. For example, their lifespan is about 10,000 hours in contrast to an approximately 1,500 hours of lifespan of mercury lamps. The brightness of lasers can be as high as 10,000 lumens, or more. In contrast, an LED projector lamp may provide approximately 1,000 lumens. A home theater projector may require at least 1,000 lumens. Lasers may also provide a wider color gamut as compared with traditional light sources.

In addition, a laser light source is compact in size, which may be more suitable for a pico projector. A pico projector is a projector used in handheld devices such as mobile phones, personal digital assistants, digital cameras, etc, which have little space to accommodate an attached display screen. Thus, a displayed image is projected onto any nearby viewing surface such as a wall.

The coherent nature of laser light can cause undesired laser speckles. A coherent laser beam incident on a non-specular reflecting surface such as a display screen or a wall, may be scattered with random phase by the surface. The random phase is caused by the random microscopic profile of the surface. When an observer looks at the projected image on the display screen or wall, the scattered light with random phase will interfere to form a speckle pattern in the retina of the observer. A speckle pattern is characterized by some spots appearing blacked out in a supposedly bright area. The blacked out spots appear to sparkle when there is relative movement between the scattering surface and the observer. Thus, the observer may perceive a projected image corrupted by a speckle pattern. Accordingly, a method or apparatus for reducing speckles is desirable.

DETAILED DESCRIPTION

As will be appreciated, a speckle reducing device and method for reducing speckles in a projected image may provide for the reduction or elimination of laser speckles in a projected image produced by laser light illumination. In addition, examples of the disclosed speckle reducing device may provide a light source that has high brightness, long lifespan, wide color gamut, and compact size, which are advantageous for a pico projector.

It is appreciated that the teachings of the disclosure are applicable to all types of projections display panels including DMD, MEMS, DLP, LCD, and LCOS. Additionally, if a laser is used as a light source, the laser used may be laser diodes (semiconductor lasers), gas lasers, solid state lasers, and other types of lasers such as fiber lasers. However, for illustration, only a pico projector using an LCOS display panel and laser diodes will be described.

FIG. 1is a block diagram of a typical pico projector20using an LCOS panel. Light beams24A,24B, and24C are emitted by a red laser diode22A, a green laser diode22B, and a blue laser diode22C, respectively. Light beams24A,24B, and24C are collimated by collimating lenses26A,26B, and26C, respectively. The green laser diode may be replaced with a green IR-pumped solid state laser. The collimated light beams may be combined using a dichroic combiner cube (“X-cube”)28and become a combined light beam30. Beam30passes through a first magnifier lens32and a second magnifier lens34, and is reflected by a polarizing beam splitter (“PBS”)36toward an LCOS panel38. The incident light is polarization-modulated by LCOS panel38. The polarization-modulated light is reflected by LCOS panel38, passes through PBS36(thus becomes intensity-modulated) and passes through a projection lens40to arrive on a screen42. When an observer looks at the image projected on the screen, the scattered laser light with random phase from the screen may interfere producing an undesired speckle pattern in the retina of the observer. The observer may perceive the projected image as corrupted by the speckle pattern.

FIG. 2illustrates an example block diagram of a pico projector120using LCOS panel38, in accordance with an embodiment of the disclosure. Light beams24A,24B, and24C from a red laser module with despeckle device122A, a green laser module with despeckle device122B, and a blue laser module with despeckle device122C, are collimated by collimating lenses26A,26B, and26C, respectively. Each laser module includes a despeckle device that includes a diffusing screen. Each collimating lens collimates laser light after being phase-modulated by the diffusing screen. In the illustrated embodiment, a dichroic combiner cube (X-cube)28combines the collimated light beams into combined light beam30. Beam30passes through a first magnifier lens32and a second magnifier lens34, and is reflected by a polarizing beam splitter (“PBS”)36toward an LCOS panel38. The incident light is polarization-modulated by LCOS panel38. The polarization-modulated light is reflected by LCOS panel38, passes through PBS36(thus becomes intensity-modulated) and passes through a projection lens40to arrive on a screen42.

FIG. 3illustrates a laser module122that includes a transmissive diffusing screen, in accordance with an embodiment of the disclosure. Laser module122is an example laser module that could be used as red laser module122A, green laser module122B, and blue laser module122C. Laser module122includes a laser diode124(which could be a variety of colors) and a transmissive diffusing screen126. For a green laser module, a green IR-pumped solid state laser may replace a green laser diode. Transmissive diffusing screen126may be a transmissive micro-lens array screen, a transmissive micro-fly-eye lens array screen, a transmissive screen with nano particles, or any type of transmissive diffusing screen. InFIG. 3, transmissive diffusing screen126is illustrated as a micro-lens array screen. Although transmissive diffusing screen126is illustrated as a micro-lens array screen in the disclosure, it is appreciated that a diffusing screen may also be a micro-fly-eye lens array screen, a screen with nano particles, or any type of diffusing screen.

A single beam128from laser diode124is converted into multiple beams130from a plurality of virtual sources by transmissive micro-lens array screen126. In other words, laser beam128is phase-modulated by transmissive micro-lens array screen126. Although multiple beams130appear like a single beam132, they are different beams from separate virtual sources. InFIG. 1, the viewed speckle pattern is generated by a single beam. InFIG. 2, the viewed speckle is generated by multiple beams130. Accordingly, there is more interferences among beams having random phases taking place inFIG. 2than inFIG. 1. As a result, the speckle size inFIG. 2may be less than the speckle size inFIG. 1.

When micro-lens array screen126moves in-plane as shown by an arrow134, the light paths from the virtual sources to the display screen and to the retina, which are involved in the interferences, change, and the generated speckle pattern accordingly changes. The change is faster for the speckle pattern having smaller speckle size. However, the projected image does not change as the position of micro-lens array screen126changes. Thus, if micro-lens array screen126is vibrated in-plane fast enough (i.e. faster than the response time of the eye), as shown by arrow134, the viewed speckle pattern may be washed away, while the projected image is unchanged.

Micro-lens array screen126is secured on an in-plane vibrator136having vibration shown by arrow134. The vibrated micro-lens array screen126may cause the viewed speckle pattern to be reduced or even disappear (as perceived by a human eye), while the projected image is unaffected. Laser light128is phase-modulated by vibrated transmissive diffusing screen126.

FIG. 4illustrates a lens140positioned between laser diode124and transmissive diffusing screen126, in accordance with an embodiment of the disclosure. Laser module142is an example laser module that could be used as red laser module122A, green laser module122B, and blue laser module122C. Laser module142includes lens140positioned between laser diode124and transmissive diffusing screen126, which may better control the area illuminated by the laser light. Lens140may also collimates the laser light emitted by laser diode124. Laser light128is phase-modulated by vibrated transmissive diffusing screen126.

FIG. 5shows an embodiment that may share similarities toFIG. 3. Instead of using a transmissive diffusing screen126, laser module162includes a reflective diffusing screen146, in accordance with an embodiment of the disclosure. Laser module162is an example laser module that could be used as red laser module122A, green laser module122B, and blue laser module122C. Reflective diffusing screen146may be a reflective micro-lens array screen, a reflective micro-fly-eye lens array screen, a reflective screen with nano particles, or any type of reflective diffusing screen. For illustration, a reflective micro-lens array screen146is illustrated inFIG. 5. In this manner, a single beam128from laser diode124is reflected into multiple beams130from a plurality of virtual sources by reflective micro-lens array screen146. Laser light128is phase-modulated by vibrated reflective diffusing screen146.

FIG. 6illustrates a lens148positioned between laser diode124and reflective diffusing screen146, in accordance with an embodiment of the disclosure. Laser module182is an example laser module that could be used as red laser module122A, green laser module122B, and blue laser module122C. Laser module182includes lens148positioned between laser diode124and reflective diffusing screen146, which may better control the area illuminated by the laser light. Lens148may also collimates the laser light emitted by laser diode124. Laser light128is phase-modulated by vibrated reflective diffusing screen146.

FIG. 7illustrates an example block diagram of reflective diffusing screen146. In the illustrated embodiment, reflective diffusing screen146includes a transmissive diffusing screen126and a reflecting substrate150. Other configurations or constructions of reflective diffusing screen146are possible.

FIG. 8illustrates an example block diagram of a pico projector220using a transmissive diffusing screen, in accordance with an embodiment of the disclosure. In the illustrated embodiment, instead of having three separate laser modules with despeckle devices as shown inFIG. 2, three laser beams can first be combined using a dichroic combiner cube. More specifically, dichroic combiner cube228combines light beams from a red laser diode222A, a green laser diode222B, and a blue laser diode222C into a combined light beam230. The green laser diode may be replaced with a green IR-pumped solid state laser. Combined light beam230passes through a vibrated transmissive micro-lens array screen226. Thus, combined light beam230is phase-modulated by vibrated transmissive micro-lens array screen226. A collimating lens26collimates the combined light beam after passing through vibrated transmissive micro-lens array screen226. Lenses224A,224B, and224C may be optionally included between laser diode222A,222B, and222C and dichroic combiner cube228, respectively. An image projected by pico projector220may have a reduced speckle pattern compared to conventional pico projectors.

FIG. 9shows an example block diagram of pico projector240using a reflective diffusing screen, in accordance with an embodiment of the disclosure. Dichroic combiner cube228combines light beams from a red laser diode222A, a green laser diode222B, and a blue laser diode222C into combined light beam230. Combined light beam230is reflected by a vibrated reflective micro-lens array screen246. Thus, combined light beam230is phase-modulated by vibrated reflective micro-lens array screen246. Reflective micro-lens array screen246may be similar to reflective diffusing screen146shown inFIG. 7. A collimating lens26collimates the combined light beam after being reflected by vibrated reflective micro-lens array screen246. Lenses224A,224B, and224C may be optionally included between laser diode222A,222B, and222C and dichroic combiner cube228, respectively. An image projected by pico projector220may have a reduced speckle pattern compared to conventional pico projectors.

FIG. 10illustrates a micro-lens array screen166with four tethering beams (150,152,154, and156), in accordance with an embodiment of the disclosure. Micro-lens array screen166may be exemplary of micro-lens array screens126,146,226, or246. The tethering beams are configured to secure on an in-plane vibrator136ofFIGS. 3-6.

In-plane vibrator136includes a comb-drive actuator MEMS (micro-electro-mechanical system) and other types of actuators.FIG. 11illustrates an example block diagram of a comb-drive actuator MEMS300having micro-lens array screen166secured on it, in accordance with an embodiment of the disclosure. Comb-drive actuator MEMS300includes four fixed comb electrodes302,304,306, and308anchored to the substrate (not shown). Four moving comb electrodes310,312,314, and316are secured with micro-lens array screen166via tethering beams150,152,154, and156, respectively. Properly applying electric voltages to the comb electrodes will move micro-lens array screen166in-plane in the directions shown by arrows318and320. The tethering beams may be flexible and elastic to allow micro-lens array screen166to vibrate. Alternatively, the tethering beams may be rigid, and they are suspended by electro static field, which will also allow micro-lens array screen166to vibrate. In this manner, micro-lens array screen166is vibrated in a 2D movement, i.e., in directions shown by arrows318and320.

It is appreciated that a speckle is averaged out if its intensity varies from maximum to minimum in the integration time, i.e., the response time of the eye. Accordingly, a 1D vibration of micro-lens array screen166may be sufficient to reduce the laser speckles produced in the projected image, if the 1D vibration generates sufficient speckle intensity variation from maximum to minimum in the integration time. Furthermore, the 1D movement of micro-lens array screen166may not cause a corresponding 1D movement of the speckle pattern, instead, it may cause a random change of the speckle pattern.

FIG. 12illustrates an example block diagram of a comb-drive actuator MEMS330having micro-lens array screen166secured on it, in accordance with an embodiment of the disclosure. Comb-drive actuator MEMS330includes a fixed comb electrodes302anchored to the substrate (not shown). Moving comb electrode310is secured with micro-lens array screen166through a tethering beam150. Another tethering beam154secures micro-lens array screen166on an extendable support322. Properly applying electric voltages to the comb electrodes will move micro-lens array screen166in-plane in the directions shown by arrow318. Extendable support322allows micro-lens array screen166to vibrate. In this manner, micro-lens array screen166is vibrated in a 1D movement, i.e., in a direction shown by arrow318.

FIG. 13shows a flow chart of a method400for reducing speckles in a projected image, in accordance with an embodiment of the disclosure. The order in which some or all of the process blocks appear in process400should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in a variety of orders not illustrated, or even in parallel.

In process block405, display light is provided. Display light can include more than one color of light (e.g. red, green, and blue) or a combined beam (e.g. combine beam30). The display light is phase-modulated in process block410. The display light may be phase-modulated by passing the display light through a diffusion screen (e.g. diffusing screen126or146) coupled to a vibrator (e.g. in-plane vibrator136). If the display light includes more than one color of light, each color of light may be phase modulated individually, as shown inFIG. 2. In process block415, the display light is collimated. The display light may be collimated with a lens such as lens26,26A,26B, or26C. In process block420, a display panel (e.g. LCOS panel38) receives the display light after the display light has been collimated and phase-modulated and the display panel generates a projectable image with the display light. The display light may be directed toward the display panel by a polarized beam splitter.