JP2018180382A - Image projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image projector using a visible light coupler for multiplexing of rays of light of same color and same polarization capable of achieving high output even when a space modulation optical element having polarization dependency used.SOLUTION: Disclosed image projector includes: multiple visible light sources each of which outputs a lay of light of identical polarization, the multiple visible light sources including at least one set of visible light sources each of which outputting lays of light of identical color; a visible light coupler using a plane lightwave circuit configured to multiplex lays of light output from the multiple visible light sources to output the multiplexed light; and a space modulation optical element having polarization dependency, which is configured to input the multiplexed light output from the visible light coupler and output the multiplexed light as image output after spacially modulating the same.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image projection apparatus using a light source that combines and emits visible light such as red (R) light, green (G) light, blue (B) light and the like in the same polarization state.

  In recent years, development of a compact RGB light source using a laser diode (LD) that outputs light of three primary colors of R (red light), G (green light) and B (blue light) for eyeglasses-type terminals and pico projectors It has been done. Since the LD has high straightness compared to the LED, a focus-free projector can be realized. In addition, LDs have high luminous efficiency, low power consumption, high color reproducibility, and have attracted attention in recent years.

  FIG. 1 shows a schematic view of an image projection apparatus using a liquid crystal device. FIG. 1 shows an image projection apparatus including the LD 1 and the spatial modulation optical element 10. The spatial modulation optical element 10 includes an input side lens 2, a polarization beam splitter (PBS) 3, a polarizer 4, a liquid crystal on silicon (LCOS) 5, and an output side lens 6. FIG. 1 shows an example of an image projection apparatus using LCOS as a liquid crystal device.

  In an image projection apparatus as shown in FIG. 1, an image is projected by controlling the intensity of light for each pixel by changing the birefringence using the liquid crystal alignment of the LCOS 5. The mainstream of video projection using a liquid crystal device is a method of providing an RGB color filter for each pixel, and a method of time-dividing RGB light and irradiating the liquid crystal and superimposing each video as afterimage light. In any case, the light incident on the liquid crystal device needs to be polarized.

A. Nakao, R. Morimoto, Y. Kato, Y. Kakinoki, K. Ogawa and T. Katsuyama, “Integrated waveguide-type red-green-blue beam combiners for compact projection-type displays”, Optics Communications 330 (2014) 45-48 Y. Hibino, "Arrayed-Waveguide-Grating Multi / Demultiplexers for Photonic Networks," IEEE CIRCUITS & DEVICES, Nov., 2000, pp. 21-27 A. Himeno, et al., “Silica-Based Planar Lightwave Circuits,” J. Sel. Top. Q. E., vol. 4, 1998, pp. 913-924 J. Sakamoto et al. “High-efficiency multiple-light-source red-green-blue power combiner with optical waveguide mode coupling technique,” Proc. Of SPIE Vol. 10126 101260M-2

  Since the outputs of R and G are weaker than those of B in the LD, an RGB light source or the like in which R and G are polarization-multiplexed by two each may be used to increase the output. Since such RGB light sources are usually multiplexed using polarization multiplexing when light of the same color is multiplexed, the output light includes both polarization components of vertical polarization and horizontal polarization.

  However, a space optical element having polarization dependency such as a liquid crystal device is usually used in the image projection apparatus, and the polarization component of either the vertical polarization or the horizontal polarization of the output light is cut. Therefore, there is a problem that the output can not be increased when an image projection apparatus is configured using an RGB light source that performs such polarization multiplexing and a spatial optical element having polarization dependence such as liquid crystal. did.

  On the other hand, an RGB light source that performs such polarization multiplexing may be used in an image projection apparatus using a digital mirror device (DMD) or the like that operates independently of polarization, but the DMD is a liquid crystal. On the other hand, it is expensive and has problems such as the color braking phenomenon.

  The present invention is to increase the light output by using a visible light coupler that combines light of the same color and the same polarization in an image projection apparatus using a space modulation optical element having polarization dependency. An object of the present invention is to provide a video projection device realized.

  An image projection apparatus according to an aspect of the present invention is a plurality of visible light sources that output light of the same polarization, and includes at least one set of visible light sources that output light of the same color. And a visible light coupler using a planar lightwave circuit that multiplexes the light output from the plurality of visible light sources and outputs the combined light, and the combined light output from the visible light coupler is incident, A spatial modulation optical element having polarization dependency, which spatially modulates the combined light and outputs it as an image output.

  According to the present invention, it becomes possible to combine and emit light of the same color with the same polarization by using PLC, so that a space modulation optical element having polarization dependency such as a liquid crystal device is used. Even in this case, high output can be realized.

  Further, according to the present invention, when performing multiplexing, interference is avoided without affecting the video quality by controlling the drive timing of the LD so that the light emission timing of the LD that outputs the light of the same color is different. It is possible to prevent signal deterioration.

It is the schematic of the imaging | video projection apparatus using a liquid crystal device. It is a figure which illustrates the imaging | video projection apparatus based on Example 1 of this invention. It is a figure which illustrates the imaging | video projection apparatus based on Example 2 of this invention. The relationship between the effective refractive index and the waveguide width of the light of the zeroth order, 1st order, and 2nd mode about each wavelength in the RGB coupler of the video projector which concerns on the Example 2 of this invention is shown. It is a figure which illustrates the imaging | video projection apparatus based on Example 3 of this invention.

Example 1
FIG. 2 illustrates an image projection apparatus according to a first embodiment of the present invention. In FIG. 3, a silica-based planar lightwave circuit (PLC) type optically connected to first to fifth visible light sources 101 to 105 and first to fifth visible light sources 101 to 105 is shown. An image projection apparatus 100 is shown that includes an RGB coupler 110 and a spatial modulation optical element 120 having polarization dependency, which spatially modulates the output light from the RGB coupler 110 and outputs it as an image output. The spatial modulation optical element 120 includes an input side lens 121 optically connected to the RGB coupler 110, a PBS 122, a polarizer 123, an LCOS 124, and an output side lens 125.

  The RGB coupler 110 includes first to fifth input waveguides 111 to 115 optically connected to the first to fifth visible light sources 101 to 105, and first to fifth input waveguides 111 to 115, respectively. And an output waveguide 117 for outputting the light multiplexed by the coupler 116 to the input-side lens 121. The output waveguide 117 is composed of a multimode waveguide.

  The first to fifth visible light sources 101 to 105 output, for example, green light G2 and G1, blue light B, and red light R1 and R2 in one polarization state of horizontal polarization and vertical polarization, respectively. Can. The lights R1, G1, B, R2 and G2 are lights of the same polarization state. In addition, light B, R1, and G1 are light having wavelengths in the wavelength range of 400 to 495 nm, 495 to 570 nm, and 620 to 750 nm, respectively, and G2 and R2 have wavelengths of 495 to 570 + β nm and 620 to 750 + γ nm, respectively. .Beta. And .gamma. Are small values of 0 or more and the line width or less, and the line width is approximately 1 nm or less depending on the light source of the incident light. The matters described above for the lights R1, G1, B, R2 and G2 are similarly applicable to the following embodiments.

  The lights G2, G1, B, R1 and R2 outputted from the first to fifth visible light sources 101 to 105 are incident on the RGB coupler 110 and are respectively transmitted through the first to fifth input waveguides 111 to 115. The light is multiplexed by the coupler 116 and emitted from the output waveguide 117. The emitted combined light is collimated by the input side lens 121 and enters the LCOS 124 through the PBS 122 and the polarizer 123, is modulated and reflected by the LCOS 124, and enters the output side lens 125 through the polarizer 123 and the PBS 122. The image is output by collimation.

  In the present invention, PLC type RGB couplers 110 are used to combine the light from each LD. In recent years, an RGB coupler module using a PLC has attracted attention (see, for example, Non-Patent Document 1). The PLC manufactures an optical waveguide on a planar substrate such as Si by patterning by photolithography and reactive ion etching, and a plurality of basic optical circuits (for example, directional coupler, Mach-Zehnder interferometer, etc.) Various functions can be realized by combining (see, for example, Non-Patent Documents 2 and 3).

  In PLC, a cladding layer and a core layer are deposited on a substrate of Si or the like to produce a waveguide, and therefore, the substrate is warped due to a stress difference caused by different materials, and thus has birefringence. For this reason, horizontally polarized light or vertically polarized light propagating in the PLC propagates in the waveguide while maintaining the polarization state on the same principle as the polarization maintaining fiber (inserting the wave plate in the waveguide, It is possible to perform polarization conversion by fabricating a waveguide such as a torsional waveguide). Therefore, when light is input to PLC by one polarization of horizontal polarization and vertical polarization and is multiplexed, the light multiplexed by PLC is emitted with its polarization state maintained. The combined light is emitted as one of the horizontal polarization and the vertical polarization, so that it can be handled even when a liquid crystal device is used.

  According to the video projector 100 according to the first embodiment of the present invention, since light is multiplexed using the PLC type RGB coupler 110, light of the same color is multiplexed with the same polarization and emitted. It becomes possible to realize high output even when using a space modulation optical element having polarization dependency such as a liquid crystal device.

  In the present embodiment, although red light and green light are combined to increase the light intensity, the present invention is not limited to this, and blue light may be combined. . Further, although an example using five visible light sources is shown in this embodiment, the present invention is not limited to this, and includes at least one set of outputting light of the same color among red light, blue light and green light. Thus, a plurality of visible light sources may be used. The same applies to the following embodiments.

(Example 2)
FIG. 3 illustrates an image projector according to a second embodiment of the present invention. In FIG. 3, PLC type RGB couplers 210 optically connected to first to fifth visible light sources 201 to 205, and first to fifth visible light sources 201 to 205, and outputs from RGB couplers 210 There is shown a video projector 200 including a polarization dependent space modulation optical element 220 that spatially modulates light and outputs as a video output. The spatial modulation optical element 220 includes an input side lens 221 optically connected to the RGB coupler 210, a PBS 222, a polarizer 223, an LCOS 224, and an output side lens 225. For example, an LD can be used as the first to fifth visible light sources 201 to 205.

  The RGB coupler 210 includes first to fifth input waveguides 211 to 215, first and second directional couplers 231 and 232 having the same waveguide width, and third and fourth directional waveguides having different waveguide widths. And directional couplers 233 and 234, respectively.

As shown in FIG. 3, the third input waveguide 213 is configured with a tapered waveguide structure so as to have _first and _second portions 2131 and 2132 with different waveguide widths. Also, the first, second, fourth and fifth input waveguides 211, 212, 214 and 215 are single mode waveguides, and the third input waveguide 213 is a multimode waveguide.

  Green light G2 and G1, blue light B, and red light R1 and R2 output from the first to fifth visible light sources 201 to 205 are incident on the first to fifth input waveguides 211 to 215, respectively. Be done. R1, G1, B, R2 and G2 are all zero-order mode light of the same polarization state.

  The first directional coupler 231 couples the light G1 incident from the second input waveguide 212 to the third input waveguide 213, and the light B incident from the third input waveguide 213 The waveguide length, waveguide width and gap between the waveguides are designed to couple to the two input waveguides 212 and couple back to the third input waveguide 213.

  The second directional coupler 232 couples the light R1 incident from the fourth input waveguide 214 to the third input waveguide 213, and the third directional waveguide 231 is configured to receive the third input waveguide. The waveguide length, the waveguide width, and the gap between the waveguides are designed to transmit the lights G1 and B coupled to the light source 213.

Third directional coupler 233 is disposed on the first portion 213 ₁ near the third input waveguide 213. Fourth directional coupler 234 is arranged in the second portion 213 ₂ near the third input waveguide 213.

  The third and fourth directional couplers 233 and 234 are mode couplers configured by asymmetric directional couplers having different waveguide widths (see, for example, Non-Patent Document 4). In the mode coupler, the effective refractive index of the light of the zero-order mode in the narrow waveguide with the narrower waveguide width matches the effective refractive index of the light of the high-order mode in the wider waveguide with the wider waveguide width. At the same time, the light of the zero-order mode propagating through the narrow waveguide can be 100% coupled to the adjacent wide waveguide while being converted to the light of the high-order mode. On the other hand, since the effective refractive index of the zeroth-order light propagating through the wide waveguide does not match the effective refractive index of the zeroth-mode light in the narrow waveguide, it is coupled to the adjacent narrow waveguide Do not pass through the mode coupler.

In order to function as a mode coupler, the third directional coupler 233 sets the effective refractive index in the zero-order mode of the light G 2 for the first input waveguide 211 and the first portion 213 of the third input waveguide 213. so that the effective refractive index equal at the high-order mode light G2 for _1, and the effective refractive index in the higher order modes of light G1, B, R1 to the first portion 213 ₁ of the third input waveguide 213 When light G1 for the first input waveguide 211, B, so that the effective refractive index not equal in R1 0-order mode, the first input waveguide 211 and first portion 213 ₁ of the waveguide width is set It is done.

Similarly, in order to function as a mode coupler, the fourth directional coupler 234 is configured to set the effective refractive index in the zero-order mode of the light R2 to the fifth input waveguide 215 and the second refractive index of the third input waveguide 213. so that the effective refractive index becomes equal with respect to the portion 213 ₂ of the higher order modes of light R2, and, in the higher order modes of light G1, B, R1 to the second portion 213 ₂ of the third input waveguide 213 The waveguides of the fifth input waveguide 215 and the second portion 213 ₂ so that the effective refractive index and the effective refractive index in the zeroth mode of the light G 1, B, R 1 for the fifth input waveguide 215 are not equal. The width is set.

  The operation of the RGB coupler 210 shown in FIG. 3 will be described. The zero-order mode light G1 incident from the second input waveguide 212 is coupled to the third input waveguide 213 in the first directional coupler 231 having the same waveguide width, and the third input waveguide The zero-order mode light B incident from the waveguide 213 is coupled to the second input waveguide 212 at the first directional coupler 231 and coupled again to the third input waveguide 213.

The zero-order mode light R1 incident from the fourth input waveguide 214 is coupled to the third input waveguide 213 in the second directional coupler 232 having the same waveguide width, and the third input waveguide The lights G 1 and B propagating through the waveguide 213 are transmitted by the second directional coupler 232. As a result, the lights G1, B, R1 incident on the first to third input waveguides 211 to 213 are multiplexed through the first and second directional couplers 231 and 232, and the third light is input to the first portion 213 ₁ of the input waveguide 213.

On the other hand, the zeroth-order mode light G2 propagating in the first input waveguide 211 is converted into a higher-order mode by the third directional coupler 233 functioning as a mode coupler, and the third directional coupler 233 Coupled to the first portion 213 ₁ of the input waveguide 213. Light G2 of bound higher-order mode, is the third input light G1 of the first order mode of a part 213 ₁ propagating in the waveguide 213, B, R1 and multiplexing, the third input guide is input to the second portion 213 ₂ of the waveguide 213.

Furthermore, the zeroth-order mode light R2 propagating through the fifth input waveguide 215 is converted to a higher-order mode by the fourth directional coupler 234 functioning as a mode coupler, and the third directional coupler 234 coupled to second portion 213 ₂ of the input waveguide 213. Light R2 of bound higher-order mode is further combined with the third of the second portion 213 ₂ and the propagated are multiplexed optical input waveguide 213. As a result, the combined light of the lights G 2, G 1, B, R 1 and R 2 incident to the first to fifth input waveguides 211 to 215 is output from the output port of the third input waveguide 213 to the space modulation optical element 220. It is output.

  As described above, high-intensity multiplexed light can be output by multiplexing the light of the same color different in the waveguide mode.

  FIG. 4 shows the effective refractive index and the waveguide width of the light of the zeroth order, the first order, and the second mode for each wavelength λ1 = 450 nm, λ2 = 520 nm, λ3 = 650 nm in the RGB coupler 210 according to the second embodiment. Show the relationship between The waveguide film thickness was 3.6 μm, and the relative refractive index difference Δ was 0.45%.

For example, the gap between the waveguides in the first directional coupler 231 is 2 μm, the gap between the waveguides in the second directional coupler 232 is 4.7 μm, and the first input waveguide 211 and the first portion 213 ₁ When the fifth input waveguide 215 and a second portion 213 ₂ and each gap between the waveguides in the 2.5 [mu] m, 702Myuemu the coupling length of the first and second directional couplers 231 and 232, third The coupling length of the directional coupler 233 is 2380 μm, the coupling length of the fourth directional coupler 234 is 900 μm, and the waveguide width of the first and fifth input waveguides 211 and 215 is 1.5 μm. The waveguide width of the fourth through fourth input waveguides 212 and 214 is assumed to be 2 μm. In this case, based on FIG. 4, for each wavelength λ1 to λ3 Considering the waveguide width effective refractive index becomes equal, the first portion 213 ₁ of the waveguide width 7.15Myuemu, the second portion 213 ₂ It can be seen that the RGB coupler 210 according to the second embodiment can be realized by setting the waveguide width to 8.00 μm.

  According to the image projection apparatus 200 according to the second embodiment of the present invention, it becomes possible to combine and emit light of the same color with the same polarization, and a space modulation optical element having polarization dependency such as a liquid crystal device. It is possible to realize high output even when using

(Example 3)
FIG. 5 shows a video projector according to a third embodiment of the present invention. In FIG. 5, PLC type RGB couplers 310 optically connected to first to fifth visible light sources 301 to 305, and first to fifth visible light sources 301 to 305, and outputs from RGB couplers 310. There is shown a video projector 300 including a polarization dependent space modulation optical element 320 that spatially modulates light and outputs as a video output. The spatial modulation optical element 320 includes an input side lens 321 optically connected to the RGB coupler 310, a PBS 322, a polarizer 323, an LCOS 324, and an output side lens 325.

  The RGB coupler 110 includes first to fifth input waveguides 311 to 315 optically connected to the first to fifth visible light sources 301 to 305, and first to fifth input waveguides 311 to 315, respectively. And a multimode waveguide 316 optically connected thereto.

  According to the video projector 300 in the third embodiment, the simple configuration using the multi-mode waveguide 310 makes it possible to combine and emit the light of the same color with the same polarization, such as a liquid crystal device or the like. Even when a space modulation optical element having polarization dependency is used, high output can be realized.

(Example 4)
In the fourth embodiment, control methods of the first to fifth visible light sources in the video projector according to the first to third embodiments will be described.

  In general, polarization multiplexing is used for combining light of the same color, so that interference does not occur when combining light of the same color. On the other hand, in the video projection apparatus according to the first to third embodiments, in order to multiplex light of the same polarization, the lights of the same color interfere with each other if the wavelengths of the lights of the same color are aligned. Such interference causes the deterioration of the image.

  Usually, the oscillation wavelength of the LD is different depending on the individual, so even if the light of the same color is different in wavelength by several nm in many cases (it is also possible to make such a combination), the LD is affected by heat during driving. Since the central wavelength of the output light is shifted by about 5 to 10 nm, the wavelengths of the output light may match under a specific condition, and the light may interfere.

  Therefore, in order to avoid interference, the output light of the LD that outputs the light of the same color at a frequency high enough to be unrecognizable to the human eye is time-divisionally driven to drive the light of the same color not simultaneously. Interference can be avoided.

  Specifically, the frequency that human eyes can recognize is said to be about 20 Hz, and the modulation frequency of LCOS is generally about 100 Hz. Therefore, the first to fifth visible light sources of the video projector according to the present invention are driven so as not to simultaneously emit light of the same color using a time division modulation signal of about 1 kHz, which is sufficiently higher than 100 Hz. Thus, it is possible to avoid interference without affecting the video quality.

Claims (5)

A plurality of visible light sources outputting light of the same polarization, the plurality of visible light sources comprising at least one set of visible light sources outputting light of the same color;
A visible light coupler using a planar light wave circuit, which multiplexes the light output from the plurality of visible light sources and outputs the combined light.
A polarization dependent space modulation optical element which receives the combined light output from the visible light coupler and spatially modulates the combined light and outputs it as an image output;
An image projector characterized by comprising:   The apparatus according to claim 1, wherein the plurality of visible light sources are laser diodes.   3. The video projector according to claim 1, wherein the visible light coupler combines light beams output from the plurality of visible light sources by using a multi-mode waveguide.   3. The image projector according to claim 1, wherein the visible light coupler combines the light of the same color by using a mode coupler.   The plurality of visible light sources are driven so as not to simultaneously emit light from the set of visible light sources using a time division modulation signal having a frequency of 1 kHz or more. Video projection device.

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