Novel silicon-based liquid crystal spatial light modulator

Abstract

The utility model relates to the field of laser processing, in particular to a novel silicon-based liquid crystal spatial light modulator, which is characterized by sequentially comprising a complementary metal oxide semiconductor (CMOS) silicon-based back plate (100), a central symmetry aluminum pixel electrode layer (101), a medium reflecting layer (102), a lower orientation layer (103), a liquid crystal molecular layer (104), an upper orientation layer (105), an indium tin oxide (ITO) electrode layer (106), a glass substrate (107) and an anti-reflecting layer (108) from bottom to top. According to the utility model, the reflectivity, the diffraction efficiency and the phase flatness of the silicon-based liquid crystal spatial light modulation device are improved, the electric field is uniformly distributed, the fringe field effect is reduced, the switching speed of phase modulation is effectively improved, the laser processing efficiency and quality are greatly improved, and more laser processing modes are realized. The technical scheme provided by the utility model can be applied to multiple fields of invisible cutting, laser marking, laser welding and the like.

Description

Technical Field

[0001] The utility model relates to the field of laser processing, in particular to a novel silicon-based liquid crystal spatial light modulator. Background Art

[0002] Liquid Crystal on Silicon (LCOS) spatial light modulator is a reflective liquid crystal device based on CMOS technology. Usually, a single LCOS chip consists of millions of pixels, and the size of each pixel ranges from a few to tens of microns. By adjusting the voltage of each pixel, the deflection of the liquid crystal molecules can be changed, thereby achieving control of the phase or intensity of the incident light.

[0003] Initially, LCOS was mainly used in the display field. Compared with other display technologies, display devices based on LCOS have higher resolution, lower energy consumption and excellent color performance. With the continuous deepening of research on spatial light modulators, the application scope of LCOS is also gradually expanding. In particular, in recent years, as a new type of spatial phase modulation of optical engines, LCOS has been widely used in the fields of laser processing and optical communications, including phase optical shaping, multi-point parallel processing, and wavelength selective switches.

[0004] As a new type of spatial light modulator, silicon-based liquid crystal can achieve pixel-level phase control of spatial light, thereby realizing corresponding functions according to the application scenario. The physical structure of the traditional silicon-based liquid crystal spatial light modulator includes, from bottom to top: CMOS silicon-based backplane, aluminum pixel electrode layer, lower orientation layer, liquid crystal molecule layer, upper orientation layer, ITO electrode layer and glass substrate. When a voltage is applied between the aluminum pixel electrode layer and the ITO electrode layer, the liquid crystal molecules will deflect under the action of the electric field. Different voltage intensities or ways of applying voltage will cause the liquid crystal molecules to have different deflection angles and working modes. Due to the optical anisotropy of liquid crystal molecules, different deflection angles will result in different refractive indices and optical phases. Therefore, when the incident light irradiates different positions of the liquid crystal layer, different optical phase delays will be generated due to the different applied voltages, which will in turn induce a diffraction effect, thereby achieving spatial phase modulation of the incident light.

[0005] In recent years, in order to improve the accuracy and efficiency of laser processing, some manufacturers have used diffractive optical elements such as DOE or silicon-based liquid crystal to modulate the phase and intensity of the processing light, thereby achieving more sophisticated laser processing, such as multi-focus invisible cutting, beam shaping, 3D processing, parallel processing, etc. The use of solid-state DOE devices has a relatively single function, and can only produce one light field distribution for a surface structure, and cannot be dynamically adjustable, and the cost remains high. Although pure phase-type silicon-based liquid crystal devices can achieve dynamic and efficient regulation of laser beams, because the pixel size is equivalent to the thickness of the liquid crystal layer, and the number of pixels reaches millions, the edge field effect between adjacent pixels will cause the light field distribution to fail to reach the ideal state. In order to reduce the edge field effect, a certain space (gap area) must be left between adjacent aluminum pixel electrodes. Therefore, when the incident light propagates to the silicon-based liquid crystal backplane, the reflectivity of the light incident on the aluminum electrode is close to 100%, and only a small part of the light incident on the gap is reflected, and they will be absorbed and lost through the silicon-based backplane. When silicon-based liquid crystal is used in laser processing, the lost light energy will lead to a decrease in the efficiency of light utilization. At the same time, the light absorbed by the CMOS backplane will cause the backplane circuit to heat up, thereby reducing the effect of spatial light modulation. Increasing the area fill rate of each pixel aluminum electrode (the ratio of the electrode area to the pixel area) can reduce the loss of incident light and improve the reflectivity. However, increasing the area of ​​the aluminum pixel electrode will increase the size of the device, and reducing the area of ​​the gap area will lead to fringe field response, increase crosstalk, and reduce the performance of the device.

[0006] Although the pixel size of silicon-based liquid crystal is getting smaller and smaller, the pixelated phase modulation cannot achieve smooth and continuous phase modulation. At the same time, the increase in the number of pixels increases the complexity of the driving circuit, increases the overall power consumption of the device and limits the available optical design space, and poses higher challenges to the driving method of silicon-based liquid crystal devices and the calculation of holograms. This in turn increases the manufacturing cost and ongoing operating cost of the device.

[0007] In the field of laser processing, existing technologies modulate the incident ultrafast laser into different light field distributions, such as vortex light, Bessel light, flat-top light, longitudinal multi-focus, etc., by loading CGI, blazed gratings or adding DOE in the optical path, to achieve different ultrafast laser processing techniques, such as invisible cutting and scribing of semiconductor wafers. However, the silicon-based liquid crystal itself divides the light irradiation area into millions of effective pixels and loads holograms, using the diffraction principle to generate patterns. The discrete phase modulation and edge field effect caused by the pixel distribution make it impossible to achieve the ideal light intensity distribution, limiting the performance of silicon-based liquid crystal devices and the efficiency of laser processing.

[0008] Therefore, the problem we need to solve is to reduce the edge field effect between pixels and the discrete phase distribution caused by pixels on the basis of dynamically modulating the laser using a silicon-based liquid crystal spatial light modulator, so as to achieve large-area 3D high-speed precision laser processing and improve processing efficiency. At the same time, we should simplify the structural design of silicon-based liquid crystals and reduce the number of optical path components, so as to achieve miniaturization and standardization of processing modules and make them suitable for various types of laser processing equipment. Utility Model Content

[0009] The utility model aims to provide a novel silicon-based liquid crystal spatial light modulator, which is used to improve the performance and yield rate of the spatial light modulator and simplify the device packaging.

[0010] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0011] A novel silicon-based liquid crystal spatial light modulator comprises, from bottom to top, a CMOS silicon-based backplane (100), a centrally symmetrical aluminum pixel electrode layer (101), a dielectric reflection layer (102), a lower orientation layer (103), a liquid crystal molecule layer (104), an upper orientation layer (105), an ITO electrode layer (106), a glass substrate (107) and an anti-reflection layer (108).

[0012] The electrode structure of the centrally symmetrical aluminum pixel electrode layer (101) is distributed in a fan shape.

[0013] The electrode structure of the central symmetrical aluminum pixel electrode layer (101) is distributed in a ring shape.

[0014] The electrode structure of the central symmetrical aluminum pixel electrode layer (101) is a combination of fan-shaped distribution and ring-shaped distribution.

[0015] The gap area of ​​the electrode of the central symmetrical aluminum pixel electrode layer (101) is 100-300nm, the radial period is 3-8μm, the number of periods is 500-2000, the circumferential period is 0.5o-1o, the number of periods is 360-720, and the duty cycle of the pixel electrode is greater than 95%.

[0016] The electrode surface of the central symmetrical aluminum pixel electrode layer (101) is prepared with a high refractive index dielectric metamaterial structure; the high refractive index dielectric metamaterial is Si, ZnSe or GaAs; the metamaterial is periodically arranged in the short axis and long axis directions of the liquid crystal, the period on the long axis is 300-800nm, the duty cycle is 50%-80%, the thickness of the high refractive index material is 100-500nm, the width of the dielectric material on the short axis is 100-200nm, and the period is 300-500nm.

[0017] The centrally symmetrical aluminum pixel electrode layer (101) can simultaneously enhance reflection and realize horizontal orientation of liquid crystal.

[0018] The ITO electrode layer (106) is photolithographically processed so that it is arranged periodically in the long axis direction of the liquid crystal molecules, the width of the ITO in each period is 6-8 μm, and the gap between adjacent ITOs is 200-300 nm; then a liquid crystal orientation layer is made on the surface of the ITO electrode layer (106); grooves are generated by rubbing a polyimide PI film, so that the liquid crystal material can be neatly arranged in the long axis direction when no voltage is applied.

[0019] The beneficial effects of the utility model are as follows:

[0020] The utility model improves the performance of silicon-based liquid crystal and simplifies the preparation process. The utility model combines the central symmetrical pixel electrode with the ITO periodic structure to reduce the impact of zero-order light. The utility model improves the reflectivity, diffraction efficiency and phase flatness of the silicon-based liquid crystal spatial light modulation device, evenly distributes the electric field, reduces the edge field effect, effectively improves the switching speed of phase modulation, greatly improves the processing efficiency and quality of the laser, and realizes more laser processing methods. The technical solution of the utility model can be applied to multiple fields such as invisible cutting, laser marking, and laser welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic structural diagram of the liquid crystal on silicon spatial light modulator of the utility model.

[0022] Figure 2 This is a schematic diagram of the ITO electrode layer of the utility model.

[0023] FIG. 3( a ) is one of the schematic diagrams of the centrally symmetrical distribution of aluminum pixel electrodes of the present invention.

[0024] FIG. 3( b ) is a second schematic diagram of the centrally symmetrical distribution of aluminum pixel electrodes of the present invention.

[0025] FIG. 3( c ) is a third schematic diagram of the centrally symmetrical distribution of aluminum pixel electrodes of the present invention.

[0026] Figure 4 This is a schematic diagram of the high refractive index medium metamaterial of the utility model being used as a reflection layer and a lower orientation layer.

[0027] FIG5( a ) is a hologram loaded onto a liquid crystal on silicon phase-type spatial light modulator.

[0028] FIG5( b ) is a schematic diagram of the light field intensity distribution generated after the laser beam passes through the hologram.

[0029] FIG6( a ) is a hologram loaded onto a liquid crystal on silicon phase-type spatial light modulator.

[0030] FIG6( b ) is a schematic diagram of the light field intensity distribution generated after the laser beam passes through the hologram. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] like Figure 1 As shown, a novel silicon-based liquid crystal spatial light modulator is a sandwich structure, characterized in that it includes, from bottom to top, a CMOS silicon-based backplane 100, a centrally symmetrical aluminum pixel electrode layer 101, a dielectric reflection layer 102, a lower orientation layer 103, a liquid crystal molecule layer 104, an upper orientation layer 105, an ITO electrode layer 106, a glass substrate 107 and an anti-reflection layer 108.

[0033] The electrode structure of the centrosymmetric aluminum pixel electrode layer 101 can not only evenly distribute the electric field and reduce the edge field effect, but also more effectively fill the pixel area and improve the light reflectivity and optical efficiency of silicon-based liquid crystal.

[0034] First, a silicon-based liquid crystal drive circuit is made on the surface of a single-crystal silicon substrate using a traditional CMOS process, and then a metal reflective layer and a low-refractive-index oxide protective layer are deposited in sequence. The metal reflective layer is then etched by micromachining methods such as photolithography and nanoimprinting. According to the design of the centrally symmetrical pixel electrode, fan-shaped and annular aluminum pixel electrodes are made to achieve pixel unit patterning. The gap area of ​​the pixel electrode is 100-300nm, the radial period is 3-8μm, the number of periods is 500-2000, the circumferential period is 0.5o-1o, the number of periods is 360-720, and the duty cycle of the pixel electrode is greater than 95%. A high-refractive-index dielectric metamaterial structure is prepared on the surface of the pixel electrode layer. The high-refractive-index dielectric metamaterial is Si, ZnSe or GaAs. The metamaterial is arranged periodically in the short axis and long axis directions of the liquid crystal, the period in the long axis is 300-800nm, the duty cycle is 50%-80%, the thickness of the high refractive index material is 100-500nm, the width of the dielectric material in the short axis is 100-200nm, and the period is 300-500nm. The structure can simultaneously enhance reflection and realize horizontal orientation of the liquid crystal (such as Figure 4 shown).

[0035] Secondly, an anti-reflection layer and an ITO electrode layer are plated on the surface of the glass substrate. In order to eliminate the influence of zero-order light, the ITO electrode layer is photolithographically processed so that it is arranged periodically in the long axis direction of the liquid crystal molecules. The width of the ITO in each period is 6-8μm, and the gap between adjacent ITOs is 200-300nm. Then a liquid crystal orientation layer is made on the surface of the ITO electrode layer. Grooves are generated by rubbing a polyimide (PI) film (about 20nm thick), so that the liquid crystal material can be neatly arranged in the long axis direction without applying voltage.

[0036] Finally, the silicon-based backplane is bonded to the glass substrate, and the spacer particles are evenly mixed in the frame glue. The thickness of the liquid crystal layer is controlled by the spacer. A glue dispenser is used to dispense glue and seal the upper substrate to frame the area where the liquid crystal is located, and an opening is left to inject the liquid crystal and seal it.

[0037] Embodiment 1:

[0038] As shown in Figure 3(a), the electrode structure of the centrally symmetrical aluminum pixel electrode layer 101 is fan-shaped and is arranged on a CMOS silicon-based backplane. The pixel electrode has a fan-shaped structure of equal size, forming a circle, which is evenly distributed circumferentially in the effective area of ​​the silicon-based liquid crystal. A gap area of ​​a certain width is left between adjacent fan-shaped electrodes to reduce the edge field effect. Each fan-shaped pixel electrode can apply a voltage between the CMOS backplane and the ITO electrode layer to cause the liquid crystal molecules corresponding to the fan-shaped area to deflect, change the effective refractive index of the area, and modulate the phase of the incident light. According to the requirements of the application scenario, the structure can achieve linear or nonlinear distribution of the circumferential phase. In order to achieve continuous phase modulation, the number of the fan-shaped electrodes is sufficient (greater than 360).

[0039] FIG. 5( a ) and FIG. 5( b ) are schematic diagrams of using a circumferentially distributed linear phase to generate vortex light in Example 1 of the present invention.

[0040] A vortex light hologram is loaded on the silicon-based liquid crystal device prepared by the above steps, FIG5(a), and the hologram has a linear phase distribution in the circumferential direction. is the angle corresponding to the circumferential direction, l is the order of the vortex phase, and in this embodiment l=3. The phase of the hologram in the radial direction at the same angle is the same. The silicon-based liquid crystal device is connected to a water-cooling structure (not shown in the figure) to increase the processing threshold of the device. The laser incident on the silicon-based liquid crystal spatial light modulator will diffract, and after being focused by the lens, a hollow vortex light intensity distribution will be generated, Figure 5(b). The light beam with a vortex phase can be used for laser precision processing, optical tweezers, and increasing the bandwidth of optical communications.

[0041] Embodiment 2:

[0042] As shown in Figure 3(b), the electrode structure of the central symmetrical aluminum pixel electrode layer 101 is annularly distributed and is arranged on the CMOS silicon-based backplane. The pixel electrode has an annular structure of equal size, Figure 3(b), forming a circle, which is evenly distributed radially in the effective area of ​​the silicon-based liquid crystal. A gap area of ​​a certain width is left between adjacent annular electrodes to reduce the edge field effect. Each annular pixel electrode can be deflected by applying a voltage between the CMOS backplane and the ITO electrode layer, so that the liquid crystal molecules corresponding to the annular area are deflected, the effective refractive index of the area is changed, and the phase of the incident light is modulated. According to the requirements of the application scenario, the structure can achieve linear or nonlinear distribution of radial phase. In order to achieve continuous phase modulation, the number of the annular electrodes is sufficient (greater than 1000).

[0043] FIG. 6( a ) and FIG. 6( b ) are schematic diagrams of longitudinal multi-focus beam shaping in Example 2 of the utility model.

[0044] An axial multi-focus hologram is loaded on the silicon-based liquid crystal device prepared by the above steps, Figure 6(a), for the invisible cutting process of silicon wafers. The hologram has a nonlinear phase distribution with multiple focal superpositions in the radial direction, and is optimized by a holographic algorithm. The phase of the hologram at the same radius is the same. The laser incident on the silicon-based liquid crystal spatial light modulator will diffract, and after being focused by the lens, an axial three-focus light intensity distribution will be generated, Figure 6(b). It should be pointed out that the hologram with annular phase distribution can also be used to generate flat-top light, Bessel light and many other spatial light modes with centrally symmetric light field intensity, and it is dynamically adjustable, and has great application prospects in laser processing.

[0045] Embodiment 3:

[0046] As shown in Figure 3(c), an aluminum pixel electrode with a central symmetrical distribution is provided, which is arranged on a CMOS silicon-based backplane. Combining the first and second designs above, the pixel electrodes are uniformly distributed in the circumferential and radial directions in the effective area of ​​the silicon-based liquid crystal to form a circle. In the effective area of ​​the silicon-based liquid crystal. A gap area of ​​a certain width is left between adjacent electrodes. The size of each pixel electrode is not equal, and is individually controlled by the voltage difference between the CMOS backplane and the ITO electrode layer, so that the liquid crystal molecules in the corresponding area are deflected and the phase of the incident light is modulated. According to the requirements of the application scenario, the structure can simultaneously achieve linear or nonlinear distribution of radial and circumferential phases. In order to achieve continuous phase modulation, the number of pixel electrodes is sufficient (greater than 1000 in the radial direction and greater than 360 in the circumferential direction).

[0047] Furthermore, in the above three designs, although the structure of the centrally symmetrical pixel electrode can effectively fill the pixel area, reduce the number of pixels and the complexity of the driving circuit, the gap area between the pixel electrodes still causes a small amount of light (less than 5%) to be unable to be modulated, thereby generating zero-order light. In another arrangement, the ITO electrode layer is processed into a grating structure and arranged periodically in the long axis direction of the liquid crystal molecules. The voltage loaded on the ITO electrode in each period can be individually controlled by the driving circuit, so that the liquid crystal molecules are arranged periodically.

[0048] Furthermore, a metamaterial structure composed of dielectrics is used to replace the dielectric reflective layer of the multilayer film. The incident laser light is incident vertically from top to bottom. When the polarization direction of the light is consistent with the periodic arrangement direction of the metamaterial, according to the Mie scattering theory, the electromagnetic wave will resonate in the high-refractive index dielectric material, thereby achieving the effect of super reflection (reflectivity>95%). At the same time, the periodic structure of the metamaterial's groove structure allows the liquid crystal molecules to obtain an initial orientation, thereby reducing the thickness and energy consumption of silicon-based liquid crystal devices and simplifying the manufacturing process of silicon-based liquid crystal devices.

[0049] In summary, the novel silicon-based liquid crystal spatial light modulator proposed in the utility model has the advantages of high reflectivity, small edge field effect, phase continuity, low preparation cost, etc. It can be used for different wavelengths and has universal and wide applications in laser processing.

[0050] The above shows and describes the basic principle, main features and advantages of the utility model. Those skilled in the art should understand that the utility model is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the utility model and are not used to limit the utility model. Without departing from the spirit and scope of the utility model, the utility model may have various changes and improvements, which fall within the scope of the utility model to be protected. The scope of protection of the utility model is defined by the attached claims and their equivalents.

Claims

1. A novel liquid crystal on silicon spatial light modulator, characterized in that: From bottom to top, it includes a CMOS silicon-based backplane (100), a centrally symmetrical aluminum pixel electrode layer (101), a dielectric reflective layer (102), a lower orientation layer (103), a liquid crystal molecule layer (104), an upper orientation layer (105), an ITO electrode layer (106), a glass substrate (107) and an anti-reflective layer (108).

2. The novel liquid crystal on silicon spatial light modulator according to claim 1 is characterized in that: The electrode structure of the centrally symmetrical aluminum pixel electrode layer (101) is distributed in a fan shape.

3. The novel liquid crystal on silicon spatial light modulator according to claim 1, characterized in that: The electrode structure of the central symmetrical aluminum pixel electrode layer (101) is distributed in a ring shape.

4. The novel liquid crystal on silicon spatial light modulator according to claim 1, characterized in that: The electrode structure of the central symmetrical aluminum pixel electrode layer (101) is a combination of fan-shaped distribution and ring-shaped distribution.

5. The novel liquid crystal on silicon spatial light modulator according to claim 1, characterized in that: The gap area of ​​the electrode of the central symmetrical aluminum pixel electrode layer (101) is 100-300nm, the radial period is 3-8μm, the number of periods is 500-2000, the circumferential period is 0.5o-1o, the number of periods is 360-720, and the duty cycle of the pixel electrode is greater than 95%.

6. The novel liquid crystal on silicon spatial light modulator according to claim 1, characterized in that: The electrode surface of the central symmetrical aluminum pixel electrode layer (101) is prepared with a high refractive index dielectric metamaterial structure; the high refractive index dielectric metamaterial is Si, ZnSe or GaAs; the metamaterial is periodically arranged in the short axis and long axis directions of the liquid crystal, the period on the long axis is 300-800nm, the duty cycle is 50%-80%, the thickness of the high refractive index material is 100-500nm, the width of the dielectric material on the short axis is 100-200nm, and the period is 300-500nm.

7. The novel liquid crystal on silicon spatial light modulator according to claim 1, characterized in that: The centrally symmetrical aluminum pixel electrode layer (101) can simultaneously enhance reflection and realize horizontal orientation of liquid crystal.

8. The novel liquid crystal on silicon spatial light modulator according to claim 1, characterized in that: The ITO electrode layer (106) is photolithographically processed so that it is arranged periodically in the long axis direction of the liquid crystal molecules, the width of the ITO in each period is 6-8 μm, and the gap between adjacent ITOs is 200-300 nm; then a liquid crystal orientation layer is made on the surface of the ITO electrode layer (106); grooves are generated by rubbing a polyimide PI film, so that the liquid crystal material can be neatly arranged in the long axis direction when no voltage is applied.

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