Liquid Crystal Microdisplay Research Articles

Microscope projection photolithography based on liquid crystal microdisplay

We developed a microdisplay-based microscope projection photolithography (MDMPP) technique in which a liquid crystal (LC) microdisplay is used as a reconfigurable photomask for a microscope projector. The LC microdisplay provides a significant advantage in terms of cost and speed since patterns can be generated through software instead of redesigning and fabricating glass photomasks. The constructed MDMPP system could produce line patterns as narrow as 2.4 µm, smaller than that specified by the diffraction limit, with the aid of a 4× objective lens. The achievement of a linewidth smaller than the theoretical limit may be ascribed to a combination of overexposure and the underetching effect, in addition to the good optical performance of the system. In a diffraction experiment performed with fabricated slits, the application of the MDMPP technique helped provide various patterns of the slits, demonstrating the potential usefulness of the MDMPP system in undergraduate optics courses. We expect that MDMPP can contribute to the field of physics education and various areas of research, such as chemistry and biology, in the future.

An optical tweezer in asymmetrical vortex Bessel-Gaussian beams

We study an optical micromanipulation that comprises trapping, rotating, and transporting 5-μm polystyrene microbeads in asymmetric Bessel-Gaussian (BG) laser beams. The beams that carry orbital angular momentum are generated by means of a liquid crystal microdisplay and focused by a microobjective with a numerical aperture of NA = 0.85. We experimentally show that given a constant topological charge, the rate of microparticle motion increases near linearly with increasing asymmetry of the BG beam. Asymmetric BG beams can be used instead of conventional Gaussian beam for trapping and transferring live cells without thermal damage.

Optical trapping and moving of microparticles using asymmetrical Bessel-Gaussian beams

We study the optical trapping, rotating and moving of 5-mm polystyrene microspheres in asymmetrical crescent-shaped Bessel-Gaussian laser beams that carry the orbital angular momentum. The beams are generated by a liquid crystal microdisplay and focused by a microobjective with a numerical aperture of NA = 0.85. It is shown experimentally that while the topological charge of the beam remains unchanged, an increasing asymmetry of the beam causes a near-linear increase in the microparticles velocity. This serves to confirm that the orbital angular momentum (OAM) of the beam depends in a linear manner on the beam's asymmetry. The use of crescent-shaped beams can reduce the thermal exposure of biological objects during optical micromanipulation.

Novel FLC- Materials Open New Possibilities for FLCoS Based Microdisplays and Video Projectors

A video projector with liquid crystal microdisplay based on FLCoS- structure is considered, and the new low-voltage ferroelectric liquid crystal (FLC) with a compensated helix as an electro-optical material providing physically realizable continuous gray scale hysteresis-free modulation characteristic is proposed to use in FLCoS.As light sources in RGB color channels the laser diodes of red, green and blue light are proposed to use. To prevent the interference of light beams resulting in the speckle noise appearance in output images it is proposed to input a despeckler – single FLC cell into an optical unit of information readout, in order this cell implemented fast electrically controlled spatially- inhomogeneous phase light modulation with a depth of ≥π. To form on a screen the large data blocks with information capacity of 108…109 pixels and with different geometric configuration a two-dimensional scanner is proposed to use, which is optically coupled to a screen and optical unit of information readout.Possible technical results - increasing the frame rate up to 600Hz as a minimum, the color gamut expansion, increasing a brightness of images, suppression of the speckle noise, - can be used not only in new devices of information visualization and displaying, but also in systems of data storage and processing and others.

Flexible structured illumination microscope with a programmable illumination array

Structured illumination microscopy (SIM) has grown into a family of methods which achieve optical sectioning, resolution beyond the Abbe limit, or a combination of both effects in optical microscopy. SIM techniques rely on illumination of a sample with patterns of light which must be shifted between each acquired image. The patterns are typically created with physical gratings or masks, and the final optically sectioned or high resolution image is obtained computationally after data acquisition. We used a flexible, high speed ferroelectric liquid crystal microdisplay for definition of the illumination pattern coupled with widefield detection. Focusing on optical sectioning, we developed a unique and highly accurate calibration approach which allowed us to determine a mathematical model describing the mapping of the illumination pattern from the microdisplay to the camera sensor. This is important for higher performance image processing methods such as scaled subtraction of the out of focus light, which require knowledge of the illumination pattern position in the acquired data. We evaluated the signal to noise ratio and the sectioning ability of the reconstructed images for several data processing methods and illumination patterns with a wide range of spatial frequencies. We present our results on a thin fluorescent layer sample and also on biological samples, where we achieved thinner optical sections than either confocal laser scanning or spinning disk microscopes.

A combinative triple-well optical trap for three-species cold atoms or molecules

We propose a scheme to form a combinative triple-well optical trap for cold atoms or molecules in focus plane by using an optical system composed of a lens and a phase-type spatial light modulator (SLM) based on liquid crystal microdisplays illuminated by a plane light wave. The principle of forming a triple-well optical trap is analyzed and the characteristic parameters of optical potential are calculated. We also discuss the evolution between a tripe-well optical trap and a double-well one (or a single-well one). Additionally, the propotential applications of our triple-well trap and its novel optical lattices in four-wave mixing with matter waves, cold collision of three atomic species and so on, are explored.

Diffraction and fringing field effects in small pixel liquid crystal devices with homeotropic alignment

Reducing the pixel dimensions of liquid crystal microdisplays in search of high resolution has a fundamental impact on their electro-optic behavior. The liquid crystal director orientation becomes distorted due to fringing fields and diffraction effects influence the optical characteristics of the device once the structure features approach the wavelength of the incident light. Three-dimensional finite element simulation of the liquid crystal dynamics with a variable order approach is combined with a full-vector beam propagation analysis to investigate how elasticity and diffraction limit the resolution as a function of the pixel size for transmissive and reflective architectures with vertical liquid crystal alignment. The key liquid crystal properties are considered and the importance of materials with high birefringence is confirmed for small pixel devices as these improve the contrast for a fixed pixel size.

34.4L: Late‐News Paper: Polarization Independent Projection Systems Using Thin Film Polymer Polarization Gratings and Standard Liquid Crystal Microdisplays

AbstractWe report on our progress in using polymer Polarization Gratings (PGs) to enhance the brightness of standard Liquid Crystal (LC) microdisplays. By replacing conventional polarizers with PGs, high transmittance (>85%) and contrast ratios (>300:1) can be achieved with common LC modes and unpolarized input light. Using this approach, we demonstrate a polymer‐PG projection display prototype with double the brightness compared to a polarizer‐based system using the same illumination (input acceptance angles≥±15°).

Optical proximity correction for a versatile LCD based direct write maskless photoplotter

The digital simulation of a photoplotter’s direct write process, where the reconfigurable mask is a liquid crystal microdisplay, leads to the development of two proximity correction techniques. The first works by modifying dimensions and in adding serifs or assistant features to the original structure design. The second, more innovative and only exploitable with a grey level capable direct writing device, precompensates structures with a multilevel spatial modulation of the luminous energy. We also present the computer simulation used to develop these OPC techniques and confirm its performance by comparing modelled and experimental results.

18:3: Late‐News Paper: Polarization Independent Liquid Crystal Microdisplays

AbstractWe demonstrate a polarization‐independent, diffractive, liquid crystal microdisplay on a reflective 256×256 pixel silicon backplane using nematic liquid crystal polarization gratings. Striking results are observed in a single‐panel projector with remarkably simple optics, where the technology supports up to ∼75% throughput (reflectance) of unpolarized light, contrast ratios approaching 1000:1, and < 800 μs total switching time.

Versatile stepper based maskless microlithography using a liquid crystal display for direct write of binary and multilevel microstructures

A versatile photolithographic photoplotter based on a stan- dard photoreduction stepper, where the reticle is replaced by a commer- cial liquid crystal microdisplay, is reported. The microdisplay module is designed as a drop-in replacement, allowing the photoplotter to be sim- ply and quickly converted into a standard stepper, making it an extremely versatile, low-cost research and development tool. Binary and multilevel plotting are demonstrated with plot rates of several Mpixels/s and 1-m feature sizes into standard industrial photoresist. The limitations on plot rate and resolution are presented and techniques for overcoming them discussed. © 2007 Society of Photo-Optical Instrumentation Engineers.

Hypergeometric modes

A new family of paraxial laser beams that form an orthogonal basis is discussed. When propagated in uniform space, these beams preserve their structure to scale. The intensity distribution profile for such beams is similar to that for the Bessel modes, representing a set of alternating bright and dark concentric rings. The complex amplitude of these beams is proportional to the degenerate (confluent) hypergeometric function, and therefore we term such beams hypergeometric (HyG) modes. The HyG modes are generated with a liquid-crystal microdisplay.

Diffraction and signal processing experiments with a liquid crystal microdisplay

In this work, we show some diffraction experiments performed with a liquid crystal display (LCD) that shows how useful this device can be to teach and experience diffraction optics and signal processing experiments. The LCD acts as a programmable pixelated diffractive mask. The Fourier spectrum of the image displayed in the LCD is visualized through a simple free propagation diffraction experiment. This optical system allows easy testing of different diffractive elements. As a demonstration we include experimental results with well-known diffractive elements like diffraction gratings or Fresnel lenses, and with more complicated elements like computer-generated holograms.

Electrical Response of Antiferroelectric Liquid Crystal Cells with Asymmetric Response

Liquid crystal microdisplays are heavily used in applications ranging from static and quasi-static images to video-rate displays. Antiferroelectric liquid crystals with asymmetric response exhibit good properties to be employed in this kind of devices, for example in mobile telephones. Asymmetric response arises from dissimilar surface conditioning onto the cell glass plates. The resulting asymmetric antiferroelectric devices feature multiplexed analogue grey scales with very simple driving schemes. In this work, a comparative study of properties of antiferroelectric liquid crystal cells with symmetric and asymmetric response is carried out. Asymmetric cells give rise dissimilar current peaks depending on the polarity of the applied waveform. This effect may stem from various contributions, such as ionic conductance and free charges accumulated superimposed to the symmetric antiferroelectric response.

Optimized Pixel Design to Remove Disclination Lines in a Homogeneously Aligned Liquid Crystal Microdisplay Driven by a Fringe-Electric Field

A fringe-field-driven homogeneously aligned liquid crystal (LC) [named fringe-field switching (FFS) mode] microdisplay which is free of disclination lines has been designed. With a pixel structure newly proposed in which the LCs with negative dielectric anisotropy aligns perpendicular to the horizontal field existing between pixels and the equipotential area is optimized, the LC director is not deformed at all by this disturbing field between pixels. Consequently, the disclination lines can be suppressed even with a distance of 1 µm for a pixel size of about 15 µm so that a high resolution and high contrast microdisplay can be realized.

Fringing-Field Effects on High-Resolution Liquid Crystal Microdisplays

Fringing-field effects on high-resolution liquid crystal microdisplay devices, including the reflection-type liquid-crystal-on-silicon (LCOS) and transmission-type poly-silicon thin-film-transistor liquid crystal displays are simulated by the beam propagation method. The electro-optic performances of six commonly used liquid crystal modes are analyzed by the two-dimensional optical simulator. The vertically aligned (VA) cell exhibits the highest contrast ratio, but its fringing-field effect is severe. A circularly polarized light illuminated LCOS device is presented to eliminate the fringing-field effect of the VA cell. Both simulated and confirming experimental results show that the long-standing problems of poor sharpness, low brightness, and slow transition time of the VA cell can be overcome by using a circularly polarized light.

Computer-generated holography as a generic display technology

Computer-generated holography technique is a powerful technology suitable for a wide range of display types, including 2D, stereoscopic, autostereoscopic, volumetric, and true 3D imaging. Computer-generated holography is an emerging technology, made possible by increasingly powerful computers, that avoids the interferometric recording step in conventional hologram formation. Instead, a computer calculates a holographic fringe pattern that it then uses to set the optical properties of a spatial light modulator, such as a liquid crystal microdisplay. The SLM then diffracts the readout light wave, in a manner similar to a standard hologram, to yield the desired optical wavefront. Although CGH-based display systems can be built today, their high cost makes them impractical for many applications.

High-definition vertically aligned liquid crystal microdisplays using a circularly polarized light

A high-definition vertically aligned liquid crystal (LC) microdisplay exhibits a excellent contrast ratio, but its fringing field effect splits the bright state unevenly and leads to a very slow response time. By utilizing a circularly polarized light instead of conventional linearly polarized light, we have overcome the long-standing problems of poor sharpness, low brightness, and slow response time. Confirming computer simulations agree with the experimental results well. This approach can be applied to both reflective and transmissive LC microdisplays.

Improving the flatness of silicon backplanes for high quality FLCoS microdisplays

The flatness of silicon backplanes for ferroelectric liquid crystal microdisplays is essential for their commercial success. The various factors affecting the flatness of liquid crystal on silicon backplanes are reviewed. A flattening technique is proposed based on a promising method that employs induced stress of thin films to control the deformation of silicon wafer. Limitations of this technique are discussed.

Two‐Dimensional Optical Simulation Tool for Use in Microdisplay Analysis

AbstractOptical performance of small pixel structures utilized in liquid crystal microdisplays may be affected by diffraction and multidimensional variations in liquid crystal director orientation. Modeling such structures may require more robust computational methods than existing one‐dimensional techniques. We present an implementation of the Finite‐Difference Time‐Domain method suitable for analysis of these structures.