Study on Aided Optical Alignment by Programmable Spots Array Generated by Off-Axis Parabolic Phase Based on LCoS-SLM

A high quality and high performance 2D Spatial Light Phase Modulator has been developed for wide range of basic and practical applications. We will discuss how LCOS micro‐display device is developed into LCOS‐SLM for various important non‐display applications ranging from basic and applied researches such as singular optics and fluorescence microscopy to industrial applications in laser processing and machining.

In 3‐D display system based on opto‐electronic reconstruction of digitally recorded hologram, the field of view of such a system is limited by the spatial resolution of the liquid crystal on silicon (LCOS) spatial light modulator (SLM) used to perform the opto‐electronic reconstruction. In this article, the spatial resolution limitation of LCOS SLM associated with fringe field effect and interpixel coupling is determined by liquid crystal director simulation and Finite Difference Time Domain (FDTD) simulation. The diffraction efficiency loss associates with the imperfection in phase profile is studied with an example of opto‐electronic reconstruction of an amplitude object. A high spatial resolution LCoS SLM with wide reconstruction angle is proposed.

This work describes the steps necessary for a holographic pattern projection of high quality with a phase-only Liquid crystal on silicon spatial light modulator (LCoS-SLM). The aim is high-throughput optical lithography on nonplanar surfaces. Aspects of diffractive optical element calculation as well as aspects of aberration compensation are needed to increase the uniformity and fidelity of intricate patterns.

This work presents the application studies of holographic techniques using LCoS-SLM (Liquid Crystal on Silicon - Spatial Light Modulators) to replace the masks in photolithography process. Computer-generated holograms obtained from two images with known dimensions, simulating a Clear Field Mask and a Dark Field Mask, were applied to one LCoS-SLM connected to an holographic optical setup capable of reducing the reconstructed images, allowing the survey of the most relevant parameters of the photolithography process for the manufacture of fine structures and from their characterization identify the limits imposed by LCoS-SLM in the process. The results are good and presents excellent possibilities of a holographic system applied to processes of Maskless Photolithography.

Liquid-crystal on silicon spatial light modulators (LCOS-SLM) with pixel size as small as few microns enable the implementation of programmable diffraction gratings with large deflection angles (small period). We study triplicator phase gratings at the limit of the LCOS spatial resolution, where the binary phase profile is the only alternative. First, we show the effect of the sinc envelope that unavoidably arises from the LCOS pixelation. Then, we use the Fourier transform theory to analyze the binary phase grating in a pixelated device in terms of the pixel size, fill factor and phase difference between the two levels in the grating. The experimental diffraction pattern of a binary triplicator grating displayed on the SLM with a period of 2 pixels reveals that pixel crosstalk becomes relevant. Its effect on the conditions to render a triplicator and on the diffraction efficiency is analyzed.

Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLMs) are used as programmable adaptive optical elements1,2,3 in many applications involving high power lasers. In some cases, LCoS SLMs may be exposed to laser radiation that can cause permanent, irreparable damage to the SLM. The damage arises from a number of parameters including laser wavelength, pulse duration, pulse repetition rate, beam diameter, spatial profile, temporal profile, and even angle of incidence. This paper is an introduction and practical guide to understanding laser damage mechanisms and expected damage threshold levels for LCoS SLMs.

Surface-stabilized antiferroelectric liquid crystals (AFLCs) and V-shape smectics share the spontaneous generation of intermediate transmission states, i.e. analogue grayscale. On the other hand, liquid crystal on silicon (LCOS) appears to be a promising alternative to thin-film transistors (TFTs) in the preparation of reflective microdisplays and spatial light modulators (SLMs). The feasibility of preparing LCOS SLMs using AFLC and V-shaped LCs has been analyzed. A comparative study of a number of AFLC and V-shape materials as candidates for LCOS SLMs has been carried out. Test cells below 1 µm have been prepared using an ITO-coated transparent glass plate and an aluminized silicon back plate mimicking the actual LCOS device. AFLC waveforms compatible to low-voltage operation of the silicon backplane have been demonstrated. V-shape waveforms have been designed and demonstrated as well. The results show that both LC families may be employed in this specific application. Dynamic behavior, with frame rates over 200 Hz, is especially remarkable.

Photocurable three-dimensional (3D) printing is a stepwise layer-by-layer fabrication process widely used in the manufacture of highly specialized objects. Current 3D printing techniques are easily implemented; however, the build rate is slow and the surface quality is less than ideal. Holographic 3D display (3DHD) technology makes it possible to reform planar wavefronts into a 3D intensity distribution, which appears as a 3D image in space. This paper examined the application of holographic imaging technology to 3D printing based on photocurable polymers. The proposed system uses a 3DHD diffractive optics system based on a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM), wherein a 3D layered image is created in the optical near field, based on a computer-generated hologram (CGH) optimized using the iterative angular spectrum algorithm (IASA) and a circular IASA. From a single CGH, multiple 2D sliced images are created in space to form a 3D optical image used to initiate the photopolymerization of photocurable resin to form 3D objects. In experiments, the proposed 3D printing system was used to create five polymer objects with a maximum axial length of 25 mm and minimum feature width of 149 μm. The phase-only CGH reformed the incident light into a distribution of optical intensity with high diffraction efficiency suitable for photocuring. Despite limitations pertaining to fabrication area and axial complexity in this initial study, the proposed method demonstrated high light efficiency, high resolution in the lateral direction, rapid fabrication, and good object continuity.

Phase-only beam shaping with liquid crystal on silicon spatial light modulators (SLM) allows modulating the wavefront dynamically and generating arbitrary intensity patterns with high efficiency. Since this method cannot take control of all degrees of freedom, a speckle pattern appears and drastically impairs the outcome. There are several methods to overcome this issue including algorithms which directly control phase and amplitude, but they suffer from low efficiency. Methods using two SLMs yield excellent results but they are usually limited in the applicable energy due to damage to the SLM's backplane. We present a method which makes use of two SLMs and simultaneously gives way for high-energy laser applications. The algorithm and setup are designed to keep the fluence on the SLMs low by distributing the light over a large area. This provides stability against misalignment and facilitates experimental feasibility while keeping high efficiency.

Since the evolution of the ferroelectric liquid crystal (FLC) on silicon spatial light modulator (SLM)1, there have been improvements in resolution, speed and optical quality2,3. The SLM we are presenting here contains improvements to all these factors as well as improvements on fill factor, liquid crystal dynamics and fabrication techniques. The SLM has 320x240 pixels on a 34μm pitch and fits onto a 14mm square die. The silicon was designed for maximum fill factor as well as high speed operation with a suitable high speed FLC. To this end it is addressed using a 64 bit bus and the integrated circuitry includes facilities for a number of addressing schemes.

We have developed a high-resolution, multi-color retinal imaging system using liquid crystal adaptive optics. A liquid crystal on silicon (LCOS) spatial light modulator (SLM) is used to correct ocular aberrations. In order to compensate for the dependency of an LCOS SLM on optical wavelength and acquire aberration-corrected images at different color, we apply an open-loop technique. In the open-loop technique, the imaging light is separated from the sensing light and the optimal phase modulation is applied only to the imaging light while the sensing light is not phase-modulated. With the system, in vivo imaging of the human retina is achieved by using illumination light at wavelength of 655nm and 593nm and sensing light at 780nm. Photoreceptors are clearly revealed at each illumination wavelength with the liquid crystal adaptive optics.

As the cost of photomasks for lithography processes becomes prohibitive especially for large size panel displays, researchers have been developing maskless alternatives using various physical wave sources. Despite the prominent overall manufacturing cost reduction benefit, the maskless lithography system has drawbacks in some respects. These issues include productivity, size of the system, and lithography hardware cost efficiency. One of the well accepted solutions is massive parallel exposure using multioptical heads. In order to implement the multi heads option, securing accurate alignment of the heads is essential. In this paper, an alignment algorithm of a spot array manipulated with serial mechanism is suggested. The suggested method enables to reduce the overall error using the genetic algorithm. Defining spot array error as fitness function of the algorithm is introduced. And correlation with kinematics of the optical system and spot array error will be represented. In addition, 4 DOF serial manipulator design and its kinematic analysis is presented. Finally, the developed system is tested and evaluated. The suggested algorithm allows spot array error to be reduced about 80 % with regards to random error. This paper contributes to accurate alignment of the heads by suggesting an alignment algorithm of a spot array manipulated with a serial mechanism.

A new method of making three-dimensional hologram is presented.On the basic principle of two-step rainbow holography,we obtain the Fraunhoer phase information of three-dimensional object by digital coding the wave front of multi visual angle images.Such images are divided into small blocks and coding individually.In the experiments,the phase information of blocks was inputted into phase only liquid crystal on silicon spatial light modulator,the voxel image was reconstructed at the focal plane of fourier lens with laser ilumination and recoded with interference on photoresists.The whole three-dimensional image was obtained by matrix stitching voxel images.The results proved this mehtod.It will be an important technology of three-dimensional display.

A liquid crystal on silicon spatial light modulator (LCoS SLM) with large phase modulation has been thoroughly characterized to operate optimally with several linear phase modulation ranges (π, 2π, 3π, 4π, 6π, and 8π) for an intermediate wavelength of the visible spectrum (λG = 530 nm). For each range, the device response was also measured for two additional wavelengths at the blue and red extremes of the visible spectrum (λB = 476 nm and λR = 647 nm). Multiorder diffractive optical elements, displayed on the LCoS SLM with the appropriate phase modulation range, allowed us to deal with some widely known encoding issues of conventional first-order diffractive lenses such as undersampling and longitudinal chromatic aberration. We designed an achromatic multiorder lens and implemented it experimentally on the SLM. As a result, the residual chromatic aberration reduces to one-third that of the chromatic aberration of a conventional first-order diffractive lens.

Straightness measurement is a very important technique in the field of Mechanical Engineering. A particular applicationwould be very high accuracy machining on a diamond turning lathe. In this paper a novel optical method for measuringstraightness of motion using reflection confocal optics is proposed. The advantage of this method in comparison with thetransmission optical systems used by Burch and Williams' is that the lateral displacements in the direction of the two axesperpendicular to the optical axis, and the rotation angles around all three axes, can be measured simultaneously. This can bevery useful for straightness measurement. Also, reflection optical systems are more compact in length.Keywords: straightness measurement, optical alignment, reflection confocal optical system, straightness measurement ofmotion, geometrical optics SUMMARY When a table moves along a guide way, lateral displacement occurs which often needs to be measured. There have beenseveral proposals to measure this displacement using optical, rather than mechanical methods. Optical methods are classifedaccording to the optical principle used: interference, Moire gratings, or geometrical optics. The optical methods offer theadvantages of being non-contacting and able to measure lateral displacements accurately over a long distance.Burch and Williams' (1974) developed a geometrical optical system using a transmission confocal design. Using theirmethod, lateral displacements in the direction of the two axes perpendicular to the optical axis can be measured, along withrotation angles around those axes. The method described here is based on reflection confocal systems. The advantage of thismethod is that lateral displacements in the direction of the two axes to the optical axis can be measured, along with rotationangles around all three axes. Also shorter length optical systems may be measured using a reflection optical system. Theaccuracy of the lateral displacement measurement is several micrometres for movements of the order of a metre. In thefuture we plan to improve the accuracy to better than one hundred nanometres using a position displacement magnifyingdevice that is being developed by our group.The figure shows top and side views of a table MT which moves along a guide way GW and an optical arrangement formeasuring its motion using a reflection confocal optical system. The light beam from a He-Ne laser HL is divided intotwo beams by a beam splitter BS and a mirror M .