CN1645183A - Raster optical modulator with translational reflective mirror and array thereof - Google Patents

Abstract

Mirror translational grating optical modulator and array, the optical modulator includes: a substrate; an insulating layer and an electrode layer formed on the substrate; a movable plate on the electrode layer supported by a support beam, which is applied to the electrode The bias drive is driven to move vertically downward; the fixed grating fixed to the base is covered on a plurality of structural units formed by the above components to form an array, and the space gap between the fixed grating and the electrode layer is the space for the movable plate to move. When no voltage is applied to the grating light modulator, the plate is located in the first plane, and the light intensity is concentrated at the zero order of diffraction; driven by voltage, the plate moves vertically up and down, and is located in the second plane, and the light intensity is concentrated at the first order of diffraction, thus realizing Different modulation of the incident light beam to provide different distributions of diffracted light energy. The modulator has the advantages of enlarging the effective area of the device, realizing the surface array structure of the light modulator, improving the optical diffraction efficiency of the device, simplifying the processing technology of the device, and the like.

Description

Instructions Mirror translational grating light modulator and array

technical field

The present invention relates to a light beam modulation device, in particular, the present invention relates to a reflector translational grating light modulator and array, which realizes different modulations of light beams based on a movable plate and a fixed grating, so as to provide different The distribution of diffracted light energy meets the requirements of projection display systems.

Background of the invention

The prior art has disclosed a variety of optical modulators based on MEMS technology that can be used alone or together with other modulators, and these modulators include digital micromirror devices (DMDs) and grating light valves (GLVs).

Among these devices, digital micromirror devices (DMDs) and grating light valves (GLVs) are represented, and their commercial applications have achieved great success. DMD is a modulator composed of millions of deflectable reflective micromirrors manufactured by MEMS technology. The tight gap of the DMD micromirror makes the projected image produce a more detailed and seamless picture with high analytical power.

But the defect of DMD is that its complex multi-layer structure leads to complicated manufacturing process and low yield

Grating light valve (GLV) is a typical micro-optomechanical system, used for optical switches or optical attenuators, etc. The GLV device switches or attenuates the light beam through the diffraction effect, instead of using mirror radiation or polarization modulation. The device is constructed on a silicon base with multiple parallel microstrips suspended on the substrate. These strips are electrically coupled. When a voltage is provided to them, the movable strips will bend toward the substrate, thereby Forms a very good diffraction grating. The light valve array of the diffraction grating specifically includes a row of parallel-aligned, spaced, movable elongated reflective parts, and each movable reflective part can move independently relative to the fixed reflective part in parallel and spaced planes. The movable and fixed reflective elements are arranged such that the respective movable and fixed reflective elements together cause reflection and/or diffraction of light incident thereon in different states. When the offset is λ/4, the incident beams reflected by different ribbons produce a phase difference of π/2, so the maximum light intensity is obtained at the first level of the diffraction image; The light intensity is also different, so that the purpose of beam modulation is achieved.

The difference between GLV and DMD is that it uses the principle of grating diffraction to realize beam modulation, which has higher response speed, simple circuit, simple manufacturing process and high yield. But GLV devices also have the following problems:

1. If the incident light wave is not exactly λ, then the so-called black pixels will show a certain bright color, but the so-called bright pixels will not show a completely bright color. Therefore, the contrast obtained by the display based on the above principle is inferior to the theoretical result.

2. It must be ensured that when no voltage is applied, that is, the device is in the off state, and the strips are in the same plane to achieve the purpose of completely reflecting the incident light, otherwise, if the strips are not in the same plane, a grating will also be formed. It will produce diffracted light that we don't want to get, which will reduce the contrast of the device display; and when the bias voltage is applied, that is, the device is in the open state, and it must be ensured that the movable strips in a pixel are all lowered to the same height, these High requirements are placed on the manufacturing precision and technology of the device.

3. Due to structural and process limitations, there is a gap w _g between the two strips, which will affect the diffraction efficiency of the grating.

4. In order to obtain a suitable offset and a larger effective diffraction area, the length of the ribbon should be about 100 microns. In this way, the device can only be used for linear arrays. When it is used for display, it needs to use mechanical scanning, which cannot Form a seamless array structure like DMD.

Compared with the existing optical modulator technologies, each has its own advantages and disadvantages. Is it possible to have an optical modulator that not only has the advantages of the above-mentioned optical modulators but also avoids its disadvantages, so that the effective optical area of the pixel is high and easy to integrate? Area array, simple process and high yield rate, which became the original intention of our invention

Invention content:

Aiming at many problems existing in the prior art, and overcoming the disadvantages of complex DMD process and the low effective diffraction area of GLV, which is difficult to be integrated into an area array, the purpose of the present invention is to provide a mirror translational grating light modulator and array , expand the effective area of the device, realize the array structure of the light modulator, obtain the mirror translational grating light modulator system, improve the optical diffraction efficiency of the device, and simplify the processing technology of the device.

The technical solution adopted by the present invention to solve its technical problems is as follows

The present invention designs a mirror translational grating light modulator, which modulates the incident light beam. The light modulator includes the following components:

base;

an insulating layer and an electrode layer formed over the substrate;

A movable plate located at a certain distance above the electrode layer and supported by a support beam. The movable plate has a reflective surface and is driven to move vertically downward by the electrostatic force generated by the bias voltage applied to the support beam;

The support beam used to support the movable flat plate, the lower part of the support beam is supported on the base, and is coated with a metal film as a positive electrode, so that a movable capacitor plate is formed between the same electrode layer.

A fixed grating, the fixed grating is covered on the structural unit composed of the above components, and is fixed to the base, and there is a space gap between the fixed grating and the electrode layer for the movement of the movable plate; and

The driving circuit connects the electrode layer and the supporting beam through the electrode lead-out wire.

To obtain an array of optical modulators, the fixed grating is integrally covered on a plurality of structural units composed of the above-mentioned components arranged side by side to form an array, and fixed to the base to form an array of optical modulators.

The optical modulator and its array can work in the switch state. When no voltage is applied, that is, in the "OFF" state, the height difference between the movable plate and the fixed grating is nλ/2, which meets the requirements of the incident beam reflected by the grating and the plate. The two beams of light have a phase difference of 2nπ, and the light intensity is concentrated at the zero order of the diffraction image after meeting and interfering; after applying the bias voltage V ₁ , that is, in the "ON" state, the vertical downward displacement of the plate is (2n-1) λ/4, satisfying that the phase difference of the reflected beam obtained by the reflection of the incident beam through the fixed grating and the movable plate is (2n-1)π/2, and the diffracted light intensity is almost zero at the zero order, and at ±1 The maximum light intensity is obtained at the level.

The grating light modulator and its array can also work in an analog state to control the distance between the upper fixed grating and the lower movable plate. If n=1, when the applied voltage range is between 0-V ₁ , the height difference is between It is linearly adjustable between λ/2 and λ/4, and the diffracted light intensity will change with the distance the plate moves, thus forming different gray levels; it can also be achieved by keeping the time in a certain working state. grayscale levels.

The advantage analysis of the present invention compared with prior art is as follows:

1. Since the fixed grating in the present invention does not need to participate in mechanical movement, the gap (the gap between the two slender beams) that must exist in the structure of the GLV is effectively solved, and the optical diffraction efficiency of the device is improved.

2. The reflective part participating in the mechanical movement is in the form of a flat plate, which is easy to ensure that the flat plate is in a parallel state during the pull-down process, and the displacement that the flat plate needs to move down is very small, and its mechanical fatigue and adhesion effect have little influence on the structure , so it can basically ensure that the phase difference of multiple reflected light beams is constant when the device is in the on state or in the off state, and the contrast of light modulation can be improved.

3. The entire movable plate is driven by electrostatic force to move vertically up and down as a whole, which expands the effective diffraction area of the device, reduces the gap between pixels, and can realize the area array structure of the light valve to obtain the area array grating light. modulator system.

4. The fixed grating structure is adopted, the processing of the fixed grating can be separated from the processing of the movable plate and other parts, it has nothing to do with the mechanical response, natural frequency and other characteristics of the whole structure, but only with the optical diffraction efficiency, so it can be more Effectively solve the optical diffraction problem and simplify the processing technology of the device.

5. When implementing the system array, it is not necessary to add a grating to each pixel, but only need to use packaging technology to fix the processed fixed grating on the substrate after obtaining the array structure, so as to ensure the height difference between the grating surface and the flat surface It only needs to meet the requirements, and the structure of the device is simplified.

6. The moving part of the present invention is only a movable plate, and it is driven by electrostatic force to move vertically up and down, instead of being driven by the hinge of DMD structure to deflect left and right. Its processing technology is simple and its mechanical stability is high.

7. There are many ways to drive the movement of the plate. Different support beam structures can be used to drive the plate to move up and down. In this way, different structures can achieve different response speeds of the plate movement to meet the light modulation requirements of different applications. The device can be widely used in display, projection, printing, optical communication and spectrometer.

Description of drawings

Fig. 1 is a structural diagram of a specific implementation of the mirror translation grating light modulator proposed by the present invention (only one pixel is shown);

Fig. 2 is a sectional view of Fig. 1;

FIG. 3 is a cross-sectional structure diagram of a second specific implementation of the mirror translational grating light modulator proposed by the present invention (only one pixel is shown);

FIG. 4 is a schematic diagram of a mirror translational grating light modulator array proposed by the present invention;

Fig. 5 is a schematic diagram of the state of the mirror translational grating optical modulator shown in Fig. 1 in the "OFF" state;

Fig. 6 is a schematic diagram of the state of the reflector translational grating light modulator shown in Fig. 1 in the "ON" state;

Fig. 7 is the diffraction efficiency distribution figure of two kinds of states;

Detailed ways

Referring to Fig. 1, the structure of a single pixel of the reflector translational grating light modulator includes a fixed grating 1, a reflective surface 2, a support beam 3, an insulating layer 4, a substrate 5, an electrode layer 6, a movable plate 7, and a drive circuit 8. Its production method is as follows: first deposit a layer of silicon oxide on the substrate 5 by using peroxidation technology to form an insulating layer 4, which plays an insulating role; the electrode layer 6 composed of polysilicon material is deposited on this oxide to form an insulating layer 4. into; Utilize sacrificial layer technology, make support beam 3 and movable plate 7; Form capacitive pole plate between support beam 3 and electrode layer 6, the optional material of support beam 3 is many, the present invention adopts silicon nitride plating In the way of double-layer structure of aluminum, single-layer structure of polycrystalline silicon can also be used as the material. The movable plate 7 is composed of nitrogen-doped silicon material, has high rigidity, is supported by support beams, is located at a certain distance above the electrode layer 6, and is driven to move vertically downward by the bias voltage applied to the electrode layer 6 , the movable plate 7 is coated with an Al reflective surface 2; the surface of the fixed grating 1 is also coated with an Al reflective surface, and the fixed grating 1 and the substrate 5 are fixed by packaging technology to form a pixel. The pixel units composed of the above components are arranged side by side to form an area array or a line array, forming a structure as shown in Figure 4. There is a space gap between the fixed grating and the electrode layer for the movement of the movable plate.

The above-mentioned grating light modulator uses the up and down movement of the movable plate to make the incident light beam diffracted by the grating to obtain different light intensity distributions at different positions of the diffraction image. See Figure 5, it is the off state, that is, the initial state without voltage applied. When no voltage is applied, when the movable plate is in the first plane shown in the figure, the height difference between the movable plate and the fixed grating is nλ/2, which satisfies the incident The two beams of light reflected by the grating and the flat plate have a phase difference of 2nπ, and after encountering and interfering, the light intensity is concentrated at the zero order of the diffraction image; see Figure 6, which is the open state. When a certain bias voltage is applied, the electrostatic force will Make the movable plate move vertically downward, when the descending displacement is (2n-1)λ/4, the phase difference of the reflected light beam reflected by the two is (2n-1)π/2, the diffracted light intensity obtained in this way , which is almost zero at zero order, and the maximum light intensity is obtained at ±1 order. The diffraction efficiency distributions of these two states are shown in Fig. 7 .

There are many existing technologies that can realize the vertical movement of the movable plate 2 , taking one pixel as an example, two of which are shown in FIG. 2 and FIG. 3 . Fig. 3 shows that the center of the movable flat panel 7 is fixed on the supporting beam 3, and there are four supporting beams; Fig. 3 shows that the four corners of the movable flat panel 7 are connected with the supporting beam 3. Regardless of the method, when a certain voltage is applied to the support beam or the electrode layer, the support beam is electrically coupled, and the support beam will be driven by the electric field force and bend downward, thereby driving the movable plate to move vertically downward.

The bias voltage applying device 8 adopts the existing mature technology in the field, and mostly adopts voltage driving. According to different array requirements, adopt active drive or passive drive. At the same time, the electrode lead-out wires of the driving circuit can be obtained while making the structure.

The present invention has been described above using the embodiments. Improvements and modifications that only become apparent to those skilled in the art after reading this disclosure document still belong to the spirit and scope of this application.

Claims (4)

1, raster optical modulator with translational reflective mirror is characterized in that photomodulator includes:

The a substrate;

Insulation course that forms on the b substrate and electrode layer;

C is positioned at a determining deviation on the electrode layer, by the movable flat board that brace summer supports, movable flat board has reflecting surface, and drives to do vertically and move by being applied to bias voltage on brace summer or the electrode layer;

D is used to support the brace summer of movable flat board, and this brace summer lower support and is coated with metallic film in substrate, have electric coupling, makes it with forming movable capacitor plate between the electrode layer.

Fixed grating of e, this fixed grating cover on the structural unit of above-mentioned parts composition, and fix with substrate, are the movable dull and stereotyped spatial joint clearance that moves between fixed grating and the electrode layer.

The f driving circuit is by electrode outlet line connection electrode layer and brace summer.Can produce the driving voltage of varying level, different frequency.

2, raster optical modulator with translational reflective mirror according to claim 1 is characterized in that: brace summer is positioned under the movable flat board, or is positioned at the outside, movable dull and stereotyped four limits, and with its parallel arrangement in same plane.

3, a kind of raster optical modulator with translational reflective mirror array, it is characterized in that: use the described photomodulator structural unit of a plurality of claims 1 to be arranged in array by row and column, the movable flat board of adjacent structure unit is arranged on the line alternately, fixed grating integral body covers in a plurality of structural units and forms on the array, and fix with substrate, form light modulator arrays, each photomodulator can independently apply bias voltage, spacing of reflecting surface is all adjustable separately about it, obtains the different diffraction effect.

4, according to claim 1,2 or 3 described raster optical modulator with translational reflective mirror and arrays, it is characterized in that: when making alive not, movable dull and stereotyped difference in height with fixed grating is n λ/2, satisfy incident beam and on phase place, differ 2n π, meet and interfere the back to concentrate on the zero level of diffraction image in light intensity through fixed grating and the two-beam line that movable flat reflective obtains; After applying bias voltage, dull and stereotyped displacement vertically downward is (2n-1) λ/4 o'clock, satisfying through incident beam is (2n-1) pi/2 through the phase differential of the fixed grating folded light beam that both reflections obtain with movable flat board, and diffraction intensity is almost nil at the zero level place, and obtains largest light intensity at ± 1 grade of place.

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