JP3174812U - Optical engine for small projectors - Google Patents

Abstract

An optical engine for a small projector that can make full use of light from a light source.
An optical engine includes light sources 10G, 10R, and 10B, polarization splitters 50G, 50R, and 50B that separate light from the light sources, two light modulators 60 that convert light into an image screen, and an optical modulator. It includes at least two polarization splitters 80 that adjust the optical path after passing through.
[Selection] Figure 1

Description

  The present invention relates to a portable small projector, and more particularly to a small projector including an optical engine that can reuse polarized light that is not used under light from a light source.

  In order to commercialize portable small projectors that are smaller than the palm or projectors that can be put into notebook computers, it is necessary to develop small, low-power projectors. In order to reduce the size of the projector, it is necessary to use a light source with a small size and high brightness.

  In order to apply a portable small projector to a mobile phone, it should be able to be driven by a battery, so that a light source with relatively low power consumption and high efficiency must be used. The light source of such a low power consumption type small projector is preferably a laser light source or an LED (Light Emitting Diode) light source. Laser light sources are widely recognized as light sources with low power consumption and high luminous efficiency.

  A small projector converts light from a light source into an image screen by an optical modulator. At present, this light modulator is usually a projection / reflection type LCD (Liquid Crystal Display) and LCOS (Liquid Crystal On Silicon) using liquid crystal. However, since the light modulator converts the image screen using polarized light, before the light from the light source is incident on the light modulator, the light is usually converted into P-polarized light and S-polarized light by a polarizer. Choose one and discard the others. Here, the vibration direction of the S-polarized light vector (electric field intensity vector) is perpendicular to the incident surface, and the vibration direction of the P-polarized light vector is parallel to the incident surface. The incident surface is a plane composed of the interface normal and the wave vector direction of the incident light.

  Since the laser light source is originally linearly polarized light with the same phase, the light modulator is well suited.

  To display the video screen, lasers of the three primary colors of green / blue / red are required. Currently, blue and red semiconductor lasers already exist, but a solid state green laser has not yet been developed. In order to solve this problem, a frequency doubling technique (Frequency Doubling) can be used. Frequency multiplication is the conversion of a long wavelength laser to a short wavelength laser.

  Relationship between wavelength λ, velocity V, frequency f: V = λ * f

  Since the speed of light is constant, increasing the light frequency by a factor of two reduces the wavelength by half. In order to obtain green light of 532 nm, IR light of 1064 nm can be frequency-multiplied to obtain light having a wavelength of 532 nm that is halved. However, during frequency multiplication, the proportion of linear polarization of the laser is reduced to the original 70% -80%. As the proportion of linearly polarized light decreases, the amount of discarded light also increases. However, since green light is a primary color light that affects the amount of white light, it greatly affects the light efficiency.

  The light efficiency of the LED light source is worse than that of the laser light source. Since the LED light source is mixed light and not linearly polarized, all three primary colors green / blue / red filter almost half of the light through the incident polarizer at the light modulator tip, thereby achieving linear polarization.

  In order for existing optical engine structures to achieve linear polarization, a significant amount of light must be filtered, and the filtered light is gradually converted to heat, thus causing the optical engine to generate heat, and There is also a problem that power consumption is improved due to a decrease in light efficiency.

  An object of the present invention is to provide an optical engine for a small projector that can make full use of light from a light source.

In order to solve the above technical problem, an embodiment of the present invention provides an optical engine for a small projector. This optical engine
At least one light source;
A polarization splitter that separates light from the light source into two optical paths and different polarization modes of the two optical paths;
Two light modulators that convert the light of two light paths into a video screen,
And at least two polarization splitters for adjusting the two optical paths after passing through the two optical modulators to the same optical path.

  The main differences and the effects of the embodiments of the present invention compared with the existing technology are as follows.

  The light emitted from the light source is separated into two light paths with different polarization modes, and each light is modulated, and then adjusted to one light path, thereby making full use of the original filtered polarized light. The efficiency of the optical engine can be increased, and the power consumption and heat generation of the optical engine are reduced.

  Furthermore, for the three primary color laser light sources, the optical path separation process is performed only for the green laser, thereby setting the thickness of the polarization splitter and completely eliminating the phase difference due to the optical path difference of the different optical paths. Can be obtained only by frequency multiplication.

  Furthermore, by providing a diffuser between the laser light source and the light modulator, the influence of laser speckle can be significantly reduced.

  Further, for the LED light source, the light from the three light sources is matched to the same path, and then the optical path is divided by one polarizing device. Therefore, it can process uniformly with respect to various lights with few apparatuses, and is especially suitable when the light from an LED light source is mixed light.

  Further, in the case of an LED, the light of all wavelengths is separated into all polarized light, and the influence of green light is the largest in luminous intensity, and the thickness T of the polarization splitter is set to 2nπ times the wavelength of green light of 532 nm (n is It is best to adjust to an integer).

FIG. 1 is a schematic view of an optical engine of a small projector constituted by only one optical path. FIG. 2 is a schematic view using a laser light source as an optical engine in the first embodiment of the present invention. FIG. 3 is a schematic view using an LED light source as an optical engine in the second embodiment of the present invention. FIG. 4 is a schematic view using another LED light source as an optical engine in the second embodiment of the present invention. FIG. 5 is a schematic diagram of a structural diagram of a polarization splitter designed according to the present invention. FIG. 6 is a schematic diagram of an optical engine using only one light source in the third embodiment.

  In the following, a number of detailed techniques have been described so that the reader can better understand the present application. However, an engineer in this field realizes a technical scheme that requires protection of each utility model registration request of the present application without various changes and modifications based on these detailed technologies and the following embodiments. It is understood that it can be done.

  In order to clarify the objects, technical solutions, and advantages of the present invention, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

  One important novelty of the present invention is that the light from the light source is separated into two light paths with different polarization schemes, adjusted for each of these two light paths, and then adjusted to one light path. That is. For comparison, first, a technical scheme that does not use the novel features of the present invention will be described. This technical solution is as shown in FIG.

  This reflective optical engine includes the following.

  R light source (10R), G light source (10G), B light source (10B), splitter 50R, 50G, 50B, diffuser (20), beam shaper (30), objective lens (40), light modulator (60), projection A lens (70) and a polarization splitter (80). Here, R represents red, G represents green, and B represents blue.

  The R / G / B light source emits R / G / B light one after another. More specifically, if the time for irradiating one frame is T, the R light source is irradiated for the time T / 3, the G light source is irradiated for the next T / 3, and the next T / 3 time is irradiated. B light source is irradiated. It can be understood that the light source can be irradiated one after another in other orders, for example, B / G / R.

  The three light sources (10R, 10G, 10B) are reflected or transmitted to the diffuser (20) by the respective splitters 50R, 50G, 50B.

  The splitter 50G reflects the G light source (green laser from 10G) and transmits excess light. The splitter 50G can also be an ordinary mirror that reflects all normal visible light. . The splitter 50R plays a role of reflecting the R light source (red laser from 10R) and passing the light in the surplus wavelength range, and the splitter 50B reflects the R light source (blue laser from 10B) and surpasses the surplus wavelength range. Plays the role of passing light.

  Since the diffuser vibrates perpendicular to the optical axis, the light randomness increases when passing through the diffuser. Such a diffuser is a device installed to remove the laser-specific laser speckle (Speckle) and is used to reduce the characteristic of laser beam coherence, thereby reducing laser speckle. To achieve the objectives.

  The light that has passed through the diffuser changes the shape of the beam by a beam shaper. The reason for changing the shape of the beam is to shape the beam and adapt it to the shape of the entrance surface of the light modulator (60), thereby increasing the light efficiency. Typical examples of the beam shaper (30) are a compound eye lens (Fly Eye Lens), a light pipe (Light Pipe), and the like. Shown in FIG. 1 is a typical example of a beam shaper (30), which is a compound eye lens composed of a number of spherical or aspherical small lenses on a substrate.

  The compound eye lens (30) is composed of a number of small lenses on a transparent substrate, and these small lenses have various shapes, for example, a quadrangular convex lens, a hexagonal convex lens, and a circular shape. However, it is better to match the shape of the light modulator (more precisely, the effective screen picture of the light modulator). For example, if the effective screen of the light modulator is approximately square, the shape of the small lens should also be square. By doing so, optical loss is minimized.

  In the embodiment of FIG. 1, a double-sided compound eye lens having small lenses on both sides is used, but a single-sided compound eye lens can also be used.

  The objective lens (40) is a lens that focuses the light beam shaped by the beam shaper, and usually consists of two lenses, and achieves a more accurate alignment by adjusting the distance between the two lenses. Can do.

  The light modulator (60) is an apparatus that forms an image picture by selectively passing incident light, blocking, or changing an optical path. Typical examples of the optical modulator (60) include a digital micromirror device (abbreviated as “DMD”), a liquid crystal display (abbreviated as “LCD”) device, an LCOS (Liquid Crystal On Silicon). , Abbreviated as “LCOS”).

  The DMD is a device used for a digital light processing (abbreviated as “DLP”) projector, which uses a field sequential drive method and arranges in a matrix system with the same number of pixels. Used for digital mirrors. The DLP is a projector that adjusts an optical path of light from a light source by a digital mirror and achieves a gradual change by reflection of a reflector or forms an image.

  A liquid crystal display (LCD) is a device that selectively turns on / off liquid crystal to form an image. Projectors using an LCD device include a direct-view type, a projection type, and a reflection type. Direct-view projection is a method in which the background light on the back surface of the liquid crystal display device forms an image through the LCD panel and can be observed directly. Projection-type projection is a method in which an image formed by a liquid crystal display device is magnified by a projection lens, then projected onto a screen, and the image reflected from the screen is observed. The structure of the reflection type and the projection type is almost the same, and the distinction is that the reflection type has a reflection film on the substrate under the LCD, and the reflected light is magnified and projected onto the screen. It is in.

  LCOS is a reflective liquid crystal display, which operates in a reflective mode by changing the lower substrate of a conventional double-sided substrate at the liquid crystal display end from transparent glass to a silicon substrate.

  The projection lens (70) is composed of a number of lenses, and magnifies and projects the image formed by the light modulator (60) onto a screen (not shown).

  Since it is a reflection type light modulator, there is a polarizing beam splitter (abbreviated as “PBS”) (80) between the light modulator and the projection lens.

  There is also an incident polarizing plate (l10) between the PBS and the objective lens, and plays a role of performing linear polarization filtration on the light incident on the optical modulator. Such filtration reduces the light by 20% to 30% in the case of a laser light source, and reduces the light by approximately half in the case of an LED.

  The first embodiment of the present invention relates to a portable small projector, the structure of which is configured as shown in FIG.

  Light from the green light source (10G) is separated into P-polarized light and S-polarized light through the polarizing film (90). The same result can be obtained by reflecting P-polarized light and passing S-polarized light, or passing P-polarized light and reflecting S-polarized light. Here, a description will be given by taking an example of reflecting P-polarized light.

  The P-polarized light reflected through the polarizing film (90) enters the PBS (200) through the splitter (50R, 50B), the diffuser (20), the beam shaper (30), and the objective lens (40). The splitter (50R) has a characteristic of reflecting red light and allows other light to pass therethrough, and the splitter (50B) has a characteristic of reflecting blue light and allowing other light to pass through, both of which are green / red. / Plays the role of unifying the three primary colors blue into the same optical axis.

  The polarizing film (201) of the PBS (200), contrary to the polarizing film (90) located in front of the green light source (10G), transmits P-polarized light and reflects S-polarized light. Therefore, the P-polarized light that has passed through the objective lens enters the optical modulator (601) through the PBS (200). The light reflected from the reflective light modulator (601) is converted into S-polarized light by phase conversion. The converted light is incident on the projection lens by reflection of the polarizing film of PBS (200).

  The light emitted from the red light source (10R) passes through the splitter (50R, 50B) and enters the projection lens through the same path as the P-polarized light of the green light.

  The light emitted from the blue light source (10B) passes through the splitter (50B) and enters the projection lens through the same path as the red light. The red light source (10R) and the blue light source (10B) must be adjusted to the same P polarization as that of the green light.

  The light emitted from the green light source (10G) is reflected by the reflective film (80) through the polarizing film (90), and then passes through the diffuser (20), the beam shaper (30), and the objective lens (40), Incident at (100).

  Similarly, the polarizing film (101) and the polarizing film (201) of the PBS (100) reflect S-polarized light and allow P-polarized light to pass through. Therefore, the light incident on the PBS (100) is reflected through the polarizing film (101) and enters the light modulator (602). Then, the light reflected through the light modulator (602) is converted into P-polarized light, and enters the projection lens through the polarizing film (101).

  The light separated into polarized light is only green light, and the light modulator (602) converts only the image screen of the green light. Therefore, it is only necessary to perform light modulation according to the emission time of green light.

  FIG. 5 is a diagram for explaining the polarization splitter in more detail. As shown in FIG. 5, the light reflected through the polarizing film (90) travels a longer optical path than the light that has directly passed through, and the optical path difference is the length through the reflecting surface (80) ( 300).

  The length (300) is the thickness T of the polarization splitter. This optical path difference does not affect the phase of the separated light. In the case of a laser light source, since the polarized light is green light, the thickness T must be 2nπ times the wavelength 532 nm of the green laser (n is an integer).

  Importantly, the optical path difference between the two optical paths is 2nπ times the optical wavelength. Other than the method in which the thickness of the polarization splitter is 2nπ times 532 nm, other methods may be used. For example, one optical path difference adjusting component may be added to one optical path, and this component may be independent or a transparent film on the surface of the optical element having the optical path.

  For the three-primary-color laser light source, the optical path splitting process is performed only for the different polarized light of the green laser, thereby completely removing the phase difference due to the optical path difference of the different optical paths by setting the thickness of the polarization splitter. In particular, the current green laser is not obtained by frequency multiplication alone, and is adapted to the low proportion of linear polarization instead.

  The second embodiment of the present invention relates to an optical engine for a small projector. The second embodiment is almost the same as the first embodiment, and the difference is mainly as follows.

  In the first embodiment, the light source is a laser light source of three primary colors of red, green, and blue, and the polarization splitter separates only the green laser into two optical paths, and the red and blue lasers are in only one optical path. is there.

  However, in the second embodiment, the light source is an LED light source of three primary colors of red, green, and blue, and the light of these three light sources first combines one optical path, and then the two polarization methods by the polarization splitter. Separate into different light paths. Since the light from the three LED light sources is mixed light, the light of different polarization methods is modulated, and then adjusted to one optical path, thereby improving the light source efficiency by about one time.

  An actual example of an optical engine using one LED light source in the second embodiment is shown in FIG. In order to simplify the explanation, the polarizing film (90) is set to reflect the P-polarized light and pass the S-polarized light. The S-polarized light having passed through the polarizing film (90) enters the PBS (200) through the beam shaper (30) and the objective lens (40). The polarizing film (201) of the PBS (200) transmits S-polarized light and reflects P-polarized light. At the same time, the S-polarized light incident on the PBS (200) enters the optical modulator. Then, the light reflected through the light modulator (601) is converted into P-polarized light and enters the projection lens (70) through the polarizing film (201).

  In addition, the P-polarized light reflected through the polarizing film (90) enters the beam shaper (30), the objective lens (40) and the PBS (100) through the reflecting film (80).

  Similarly, the polarizing film (101) and the polarizing film (201) of the PBS (100) reflect P-polarized light and pass S-polarized light. The P-polarized light incident at the same time is reflected through the polarizing film (101) and then enters the optical modulator (602). Then, the reflected light converted into S-polarized light by the light modulator (602) enters the projection lens (70) through the PBS (100) and the PBS (200).

  In the case of an LED, all light of all wavelengths is separated into polarized light, and the influence of green light is the largest in luminous intensity, so the thickness T of the polarization splitter is 2nπ times the wavelength of green light of 532 nm ( It is better to adjust n to an integer). If the light source is many LEDs, the polarization splitter need not be exactly 2nπ times 532 nm. A certain beneficial effect can be obtained as long as it is 2nπ times a certain wavelength near the center wavelength of visible light.

  The example shown in FIG. 3 may have other variations, but FIG. 4 shows one variation. 4 is different from FIG. 3 in that one reflection mirror 50G is provided, and 50G may reflect any light as long as it reflects only green light.

  The third embodiment of the present invention relates to an optical engine for a small projector. The third embodiment is almost the same as the second embodiment, and the difference is mainly that the second embodiment uses three light sources, but the third embodiment uses only one light source. There is to be. The structure of the optical engine in the third embodiment is as shown in FIG. A typical embodiment of the third embodiment is a mini projector that displays a black and white image. This mini projector uses one white light source 10 and one reflecting mirror 50. Although it is not necessary to use a white light source, a monochrome laser is used as the light source. The image at this time is a monochrome “grayscale image”, and can be applied when a color image is not required.

  The fourth embodiment of the present invention relates to an optical engine for a small projector. The fourth embodiment is almost the same as the first embodiment, and the difference is mainly as follows.

  In the first embodiment, three light sources are used, but in the fourth embodiment, a mixed light source is used, that is, the light source includes at least one laser light source and at least one LED light source. . Regarding the installation of the optical path, the first and second embodiments can be referred to, that is, a light source having a relatively low proportion of linearly polarized light (for example, an LED light source and a laser light source by frequency multiplication) is divided into two polarization methods. Are divided into different optical paths, adjusted respectively, and then combined into one optical path. A light source with a relatively high proportion of linearly polarized light, for example, a laser light source that is not frequency-multiplied, may appear in only one optical path, or may exit in two optical paths simultaneously.

  Although the invention has been illustrated and described with reference to several optimized embodiments of the invention, it will be appreciated by those skilled in the art that the spirit and scope of the invention has been described. It is possible to give various changes to this in terms of form and details, without prejudice.

Claims (10)

At least one light source;
A polarization splitter that separates the light from the light source into two optical paths and different polarization modes of the two optical paths;
Two optical modulators each used to convert the light of the two optical paths into a video screen;
At least two polarization splitters used to adjust the two optical paths through the two optical modulators to the same optical path;
An optical engine for a small projector.   2. The optical engine for a small projector according to claim 1, wherein there are a large number of the light sources.   The light source is a laser light source of three colors, red, green, and blue, and the polarization splitter separates only the green laser into two light paths, and the lasers of two colors, red and blue, are only in one light path. The optical engine for a small projector according to claim 2, wherein the optical engine is provided.   The optical engine for a small projector according to claim 3, wherein there is a speckle reduction diffuser between the light source and the light modulator.   The light modulator divides the time of one frame into three time slices and adjusts the image corresponding to the light source at each time slice, among which the light modulator in the green laser light path only corresponds to the green laser light source The optical engine for a small projector according to claim 3, wherein the image adjustment is performed only in the time slice to be performed.   The light source is an LED light source of three colors of red, green, and blue, and the light of the three light sources is first adjusted to one optical path and then separated into two optical paths by a polarization splitter. The optical engine for a small projector according to claim 2.   3. The optical engine for a small projector according to claim 2, wherein the light source includes at least one laser light source and one LED light source.   The optical engine for a small projector according to any one of claims 1 to 7, wherein the thickness of the polarization splitter is 2nπ times 532 nm, where n is an integer.   The optical engine for a small projector according to any one of claims 1 to 8, wherein the polarization axes of the polarization splitters are the same.   10. The optical engine for a small projector according to claim 1, wherein the light modulator is one of a liquid crystal display device, a digital micromirror device, and an LCOS.

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