Projection imaging device for eliminating DMD stray light

Abstract

The present invention relates to a projection imaging device, specifically a projection imaging device for eliminating DMD stray light. The purpose of the present invention is to provide a projection imaging device suitable for a DMD with a small volume and a long wavelength and capable of eliminating DMD stray light, comprising a laser light source, wherein the laser light source emits a surface light source incident on a relay system, and the light source passing through the relay system is incident on a microlens array in parallel, and the surface light source is shaped by the microlens array into a point light source and then incident on a TIR prism, and then incident on a DMD after passing through the TIR prism, and the image is projected onto an imaging system after being reflected by the DMD, thereby making the DMD diffraction-free. The present invention reduces the incident light spot of the DMD through a microlens array, eliminates the diffraction of the DMD blazed grating from the source, shields the stray light generated by the diffraction outside the DMD in advance, improves the imaging quality and image contrast of the projection imaging device, and has a significant and simple effect.

Description

Technical Field

[0001] The invention relates to a projection imaging device, in particular to a projection imaging device capable of eliminating DMD stray light. Background Art

[0002] The projection imaging device includes a laser light source, a relay system, a digital micromirror array, a TIR prism, and an imaging system including a projection lens. The laser light source emits a surface light source that is incident on the relay system, is collimated by the relay system, and then is incident on the TIR prism in parallel. Then, it is incident on the digital micromirror array after passing through the TIR prism. After being reflected by the digital micromirror array, the image is projected onto the imaging system including the projection lens. The digital micromirror array (DMD) (for the convenience of description, the digital micromirror array is replaced by DMD in the following text) is a reflective spatial light modulator composed of many micro-reflective lenses, which is widely used in digital lithography technology. The micromirror of the DMD has three states: a non-working state with a deflection angle of 0°; an "on" state with a deflection angle of +12° along the diagonal line, and all the reflected light passing through the micromirror enters the projection system and presents a bright state; an "off" state with a deflection angle of -12° along the diagonal line, and the reflected light deviates from the projection system and is absorbed by the absorption device to present a dark state, thereby obtaining images with different grayscales. When the micro-lenses of the DMD are arranged at intervals, grid diffraction will occur like a grating, generating stray light, and there is an opening in the center of the micro-mirror, and the aperture ratio (light-transmitting area) is less than 100%, which seriously affects the imaging contrast of the projection imaging device. The prior art limits the resolution of the projection lens behind the DMD by designing various parameters (such as adjusting the numerical aperture) to filter out high-frequency diffraction components and optimize the imaging contrast of the projection imaging device. However, in the application process, many companies have proposed design requirements for reducing the volume and increasing the wavelength of the DMD, but such a structural design will make the stray light phenomenon of the DMD more serious. The original method of optimizing the imaging contrast of the projection imaging device by adjusting the resolution of the projection lens behind the DMD can no longer meet the requirements of its imaging contrast. Therefore, at this stage, it is urgently necessary to design a projection imaging device that is suitable for a DMD with a smaller volume and a longer wavelength and can eliminate DMD stray light. Summary of the invention

[0003] The object of the present invention is to provide a projection imaging device which is applicable to a DMD with a smaller volume and a longer wavelength and can eliminate DMD stray light.

[0004] The present invention is implemented by adopting the following technical scheme: a projection imaging device for eliminating DMD stray light, comprising a laser light source, a relay system, a microlens array, a DMD, a TIR prism, and an imaging system. The laser light source emits a surface light source that is incident on the relay system, which is collimated by the relay system and then incident on the microlens array in parallel. The surface light source is shaped by the microlens array into a point light source and then incident on the TIR prism. Then, the point light source is incident on the DMD after passing through the TIR prism. After being reflected by the DMD, the image is projected on the imaging system, thereby making the DMD diffraction-free.

[0005] The principle description steps are as follows: 1) According to the DMD structure and its working principle, the DMD is equivalent to the structural model of a two-dimensional blazed grating, and the blaze angle is the working state deflection angle θ c = ±12°, the grating constant d corresponds to the pixel period of the DMD, that is, the DMD grating constant d is equal to the sum of the DMD pixel size a and the pixel gap b. For example, the DLP9500 series DMD products developed by TI in the United States have a pixel size a of 10.8μm×10.8μm, a pixel number of 1920×1080, and a pixel gap b of 1μm, which is equivalent to a blazed grating with a grating constant of 11.8μm; 2) According to the grating theory, the DMD diffraction characteristics are analyzed, and the grating is the single slit diffraction factor Multi-slit interference factor As a result of the modulation, the reflective blazed grating can shift the zero-order of single-groove diffraction and inter-groove interference, thereby concentrating the light energy on the required first-order diffraction spectrum. i ,θ r Respectively represent the angles between the incident light, the outgoing light and the normal line of the DMD surface, θ i '、θ r 'represent the angles between the incident light, the outgoing light and the normal line of the grating plane, where θ i '=θ i -θ c ,θ r '=θ r +θ c The total intensity distribution of the emitted light is I, and the intensity of the point is I P .

[0006]

[0007] The grating equation is obtained from formula (1) and formula (3): mλ=d(sinθ' i +sinθ' r ) (4) Therefore, for a blazed grating with a certain wavelength λ and grating constant d, the distribution of the diffraction order m is determined by the incident angle θ i and the deflection angle θ of the DMD c The increase of diffraction order m will lead to stray light phenomenon and affect the imaging contrast.

[0008] According to the above analysis of the diffraction characteristics of the blazed grating of the DMD and the original method of optimizing the imaging contrast by adjusting the resolution of the projection lens behind the DMD, the requirements of imaging contrast can no longer be met. Therefore, we break the conventional thinking and start from the root of the problem, that is, adopt the idea of ​​eliminating diffraction. The surface light source from the relay system is shaped into a point light source through a microlens array and then incident on the DMD through a TIR prism, thereby directly eliminating the grating diffraction of the DMD, eliminating the stray light of the projection imaging device caused by the diffraction of the DMD, and improving the imaging quality of the projection imaging device.

[0009] The beneficial effects produced by the present invention are as follows: the present invention uses a microlens array to shape the surface light source incident on the DMD into a point light source, eliminates the DMD blazed grating diffraction from the source, shields the stray light produced by the diffraction outside the DMD in advance, improves the imaging quality and image contrast of the projection imaging device, and does not need to subsequently limit the resolution of the projection lens behind the DMD by designing various parameters to reduce the influence of stray light, and the effect is significant and simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0011] Figure 2 It is a schematic diagram of the structure of DMD;

[0012] Figure 3 The schematic diagram of DMD being equivalent to a blazed grating;

[0013] Figure 4 Schematic diagram of the structure of the microlens array.

[0014] In the figure: 1—laser light source, 2—relay system, 3—microlens array, 4—DMD, 5—TIR prism, 6—imaging system, 7—spherical lens. DETAILED DESCRIPTION

[0015] The projection imaging device for eliminating stray light of DMD4 includes a laser light source 1, a relay system 2, a microlens array 3, a DMD4, a TIR prism 5, and an imaging system 6. The laser light source 1 emits a surface light source that is incident on the relay system 2. After being collimated by the relay system 2, the surface light source is incident on the microlens array 3 in parallel. After being shaped into a point light source by the microlens array 3, the point light source is incident on the TIR prism 5. After passing through the TIR prism 5, the point light source is incident on the DMD4. After being reflected by the DMD4, the image is projected on the imaging system 6, thereby making the DMD4 diffraction-free.

[0016] The principle description steps are as follows: 1) According to the structure and working principle of DMD4, DMD4 is equivalent to the structural model of a two-dimensional blazed grating, and the blaze angle is the working state deflection angle θ c= ±12°, the grating constant d corresponds to the pixel period of DMD4, that is, the DMD4 grating constant d is equal to the sum of the DMD4 pixel size a and the pixel gap b. For example, the DLP9500 series DMD4 product developed by TI in the United States has a pixel size a of 10.8μm×10.8μm, a pixel number of 1920×1080, and a pixel gap b of 1μm, which is equivalent to a blazed grating with a grating constant of 11.8μm; 2) According to the grating theory, the DMD4 diffraction characteristics are analyzed, and the grating is the single slit diffraction factor Multi-slit interference factor As a result of the modulation, the reflective blazed grating can shift the zero-order of single-groove diffraction and inter-groove interference, thereby concentrating the light energy on the required first-order diffraction spectrum. i ,θ r Respectively represent the angles between the incident light, the outgoing light and the normal line of the DMD4 surface, θ i '、θ r 'represent the angles between the incident light, the outgoing light and the normal line of the grating plane, where θ i '=θ i -θ c ,θ r '=θ r +θ c The total intensity distribution of the emitted light is I, and the intensity of the point is I P .

[0017]

[0018] The grating equation is obtained from formula (1) and formula (3): mλ=d(sinθ' i +sinθ' r ) (4) Therefore, for a blazed grating with a certain wavelength λ and grating constant d, the distribution of the diffraction order m is determined by the incident angle θ i and the deflection angle θ of the DMD c The increase of diffraction order m will lead to stray light phenomenon and affect the imaging contrast.

[0019] From formula (3) and formula (4), we can get: Therefore, for a blazed grating with a certain wavelength λ and grating constant d, the distribution of the diffraction order m is determined by the incident angle θ i and the deflection angle θ of DMD4 c The increase of diffraction order m will lead to stray light phenomenon and affect the imaging contrast.

[0020] According to the above analysis of the diffraction characteristics of the blazed grating of DMD4 and the original method of optimizing the imaging contrast by adjusting the resolution of the projection lens behind DMD4, it can no longer meet the requirements of imaging contrast. Therefore, breaking the conventional thinking and starting from the root of the problem, the idea of ​​eliminating diffraction is adopted. The surface light source from the relay system 2 is shaped into a point light source through the microlens array 3 and then incident on the DMD4 through the TIR prism 5, thereby directly eliminating the grating diffraction of DMD4, eliminating the stray light of the projection imaging device caused by the diffraction of DMD4, and improving the imaging quality of the projection imaging device.

[0021] In a specific embodiment, the microlens array 3 is a square-arranged microlens array 3. The microlens array 3 is composed of a plurality of spherical lenses 7 with circular cross-sections, which improves light energy utilization and illumination uniformity compared to spherical lenses with square cross-sections.

Claims

1. A projection imaging device for eliminating DMD stray light, comprising a laser light source (1), a relay system (2), a DMD, a TIR prism (5), and an imaging system (6), characterized in that: The invention also includes a microlens array (3), wherein a laser light source (1) emits a surface light source which is incident on a relay system (2), is collimated by the relay system (2) and then incident on the microlens array (3) in parallel, is shaped by the microlens array (3) into a point light source and then incident on a TIR prism (5), and then incident on a DMD after passing through the TIR prism (5), thereby directly eliminating the grid diffraction of the DMD, and after being reflected by the DMD, an image is projected onto an imaging system (6), wherein the microlens array (3) is a square-arranged microlens array (3), and is composed of a plurality of spherical lenses (7) whose cross sections are circular.

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