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Phase-only liquid crystal on silicon (LCOS) devices are relatively new but are becoming core optical engines in a number of significant application areas such as holographic projection and telecommunications switches.
This thesis details the investigation into the fabrication and characterisation of these devices. The objective is to make 'proof-of...
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... to traditional liquid crystal devices, the pi-cell has same direction of alignment (see Figure 2.7) on the two substrates rather than having opposite directions as in the traditional ECB cells. In OCB, the pre-tilt angle has to be larger (>8°), and it only operates between the bend deformation and homeotropic state [16] . ...
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... assembly process flow is a complicated multi-step procedure including mechanical and thermal treatments, and optical inspection of the individual substrates. The overall generic phase-only LCOS assembly process can be developed in several steps as follows in Figure 2.2. ...
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... of which the peak-valley (PV) is 583nm (A) and a 7 x 12 mm glass substrate with ITO side up of which the PV is 294nm (B). In Figure 2.4, the dimensions of both the silicon and glass substrates are larger than that of ...
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... alignment rubbing is performed using the AZ-LCD MF7 rubbing machine (Figure 2.6). The rubbing process requires experience to operate. ...
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... (planar) alignment means that the long axes of the molecules are parallel to the glass substrate, whilst vertical alignment means that the long axes of molecules are perpendicular to the glass substrate, and tilted alignment produces an acute angle between the long axes of the molecules and the glass substrate. The parallel-aligned device (Pi-cells, Figure 2.7_A) creates an undesirable splay state when voltage is applied, which is hard to eradicate with the limited voltages available on the silicon backplane. ...
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... a phase-only LCOS device, the device structure is anti-parallel with small tilted alignments, as shown in Figure 2.7_B. The high birefringence nematic liquid crystals are used in thin antiparallel tilted aligned devices. ...
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... a phase-only LCOS device, the glue should be deposited as indicated in Figure 2.9. Glue should never touch the pixel array in order to avoid the contamination of the active area of the device. ...
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... have fabricated a variety of LCOS test devices with different cell geometries. A second cell using 2.4μm spacers is shown in Figure 2.19 (A). ...
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... second cell using 2.4μm spacers is shown in Figure 2.19 (A). The assembly is simplified in this case because of the absence of circuitry on the silicon backplane, and there are no positional constraints on the glue line (green line in The third set of LCOS devices shown (the two 23.3 x 14.1 mm LCOS devices in Figure 2.20) are one batch of the largest LCOS devices that can be assembled at this moment. ...
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... for the assembled LCOS device on the right in Figure 2.20 using the glass and silicon in Figure 2.4, the thickest area is 2.45μm and the standard deviation of the uniformity is worse than that on the left figure, which was made from the glass and silicon of Figure 2.5. and the cell construction is neat and robust. ...
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... for the assembled LCOS device on the right in Figure 2.20 using the glass and silicon in Figure 2.4, the thickest area is 2.45μm and the standard deviation of the uniformity is worse than that on the left figure, which was made from the glass and silicon of Figure 2.5. ...
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... for the assembled LCOS device on the right in Figure 2.20 using the glass and silicon in Figure 2.4, the thickest area is 2.45μm and the standard deviation of the uniformity is worse than that on the left figure, which was made from the glass and silicon of Figure 2.5. and the cell construction is neat and robust. ...
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... the die-level assembly process is able to achieve the required spatial uniformity for a phase-only LCOS device. In Figure 2.21, the size of the liquid crystal filling hole is controlled to within 2mm in order to maintain the device uniformity and guarantee an efficient material filling process. The glue line needs to be wide enough to seal the device firmly without bringing the contact with the pixel array. ...
Citations
... In general, the assembly process of LCOS devices is divided into two methods, wafer level assembly and die-level assembly. [79] The wafer-level assembly has been widely used in commercial amplitude modulating LCOS devices. [85][86] The wafer-level assembly technique origins from the high-volume production lines. ...
... The tilted alignment produces an acute angle between the long axes of the molecules and the glass substrate. [79] For the phase-only LCOS SLM device in this project, as shown in Figure 2.9, the alignment method adopted is anti-parallel with tilted alignment. ...
... When LCOS SLM devices are designed to perform phase-only modulation, to maximize the phase modulation efficiency, the polarization state of input light must be parallel to the alignment direction of liquid crystal molecules. This is mainly because liquid crystal modules in the most current LCOS SLM configurations can only provide the change of effective refractive index of light in one plane [79,104,105,106,107]. Therefore, the direction of the liquid crystal alignment is also considered as the operating direction of a phase-only LCOS device. ...
Liquid crystal on silicon (LCOS) technology has initially been developed for imaging and display applications. This technology combines the unique light-modulating properties of liquid crystal materials and the advantages of high-performance silicon complementary metal oxide semiconductor (CMOS) technology through dedicated LCOS assembly processes. Phase-only LCOS SLM are becoming an important tool for laser processing in a range of systems. A recent breakthrough in laser-induced self-assembled nanostructure in glass has made it possible to store data in fused silica. The technology of 5D optical data storage in transparent materials paves a promising way to almost unlimited lifetime data storage for future cloud. The phase-only SLM has already shown its potential for this application in tailoring ultrafast lasers writing beam for optical data storage. In data writing process, a light filed of target data pattern (multi-beam arrays) with target linear polarization state is required to encode information onto the nanograting structure created by laser pulses. In data writing beam generation, phase-only LCOS SLM can generate arbitrary data pattern by using diffractive holographic imaging. However, the polarization control of output image is still achieved by using an external polarization modulator. This leads to the complication, bulkiness, and large delay in current methods. Therefore, this research aims to develop a phase and polarization modulation method based on phase-only LCOS SLMs to simultaneously control both the holographic image and its polarization state. Phase-only modulation of light can tailor the output image by using computer-generated holograms onto LCOS SLMs. This is very useful for generate arbitrary multi-beam data writing light field. To fully control the polarization state of the data writing light field, the amplitude and relative phase of two orthogonal polarization components needs to be independently modulated. However, the phase-only modulation cannot directly affect the polarization of light. Therefore, three methods are proposed to achieve the phase and polarization control using LCOS SLMs. Also, two customized LCOS SLMs were designed and fabricated by using in-house-developed die-level assembly technique. They are used in all experiments of this research. First method is parallel coding and two-beam combining. Two orthogonal input beams are parallelly and independently encoded with the same target image information but with the different amplitude information by using two phase holograms on two LCOS SLMs. Then, two modulated beams are now considered as two polarization components and be spatially superposed to form target polarization state. The first-order diffraction efficiency change controlled by using phase modulation depth on hologram is used to design a technique to encode amplitude information onto the hologram. This technique is used in all three methods for amplitude modulation of polarization components. This method requires high precision alignment process in beam combining. In the second method, to avoid beam combining in polarization control, instead of modulating two beams, the object of modulation is changed to two polarization components of a single input beam. By using the characteristic of polarization sensitivity of phase-only LCOS SLM, two polarization components of single beam are sequentially and independently coded with information target image and amplitude using two LCOS SLMs. Because the spatial status to components of single beam remain unchanged in the modulation, the phase and polarization control is achieved automatically. The third method is a compact system using only single LCOS SLM device. The principle of this method is two polarization components coding like in the second method, but the fundamental difference is in a polarization components rotation technique in compact system. Using this polarization rotation technique, two light components can be independently coded by separately using two holograms on the two halves of LCOS SLM. The prototype of the compact system is developed and fabricated, and the effectiveness of the system has been experimentally verified. To sum up, the phase and polarization modulation methods based on LCOS SLM has been explored and developed. They can provide dynamical control of both polarization sate and image of light field using only LCOS. The proposed methods can provide a more promising way to largely increase the data writing speed in the 5D optical data storage technology.
... With the DRAM addressing scheme, the switching time of the liquid crystal will not limit the number of lines which can be addressed, but will limit the frame rate. Pre-pulsing the drive waveform can introduce gains in switching performance [41]. ...
... The corresponding phase depth can be calculated for each measured power using Eq. (6), as shown in Fig. 4. It is noted that the valley points in Fig. 3 do not reach zero power, which is a direct result of spatial phase nonuniformity [27]. ...
A method to measure the optical response across the surface of a phase-only liquid crystal on silicon device using binary phase gratings is described together with a procedure to compensate its spatial optical phase variation. As a result, the residual power between zero and the minima of the first diffraction order for a binary grating can be reduced by more than 10 dB, from − 15.98 dB to − 26.29 dB . This phase compensation method is also shown to be useful in nonbinary cases. A reduction in the worst crosstalk by 5.32 dB can be achieved when quantized blazed gratings are used.
