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Spatial light modulators
Published in Neil Collings, Fourier Optics in Image Processing, 2018
The surface micromachining of a silicon wafer is the basis of the grating light valve (GLV) technology. A layer of silicon oxide followed by a layer of silicon nitride is deposited on the silicon wafer. The silicon nitride is patterned into narrow strips, followed by the etching of the silicon oxide layer. Finally, aluminium is evaporated onto the active area of the device. The etching of the silicon oxide releases the silicon nitride ribbons from the silicon substrate so that an applied voltage can move them down towards the substrate. The thickness of the oxide layer is designed to be one quarter of the wavelength of light which is to be used, so that, when the ribbon is pulled down onto the substrate, the path length of the light reflected from the ribbon is changed by one half wavelength. The interference between light reflected by the ribbon and light reflected from the substrate mirrors, in between the ribbons, changes from one of constructive interference, when no voltage is applied beneath the ribbon, to one of destructive interference, when a voltage is applied. In the state of destructive interference, the light is diffracted at an angle given by the spatial frequency of the grating multiplied by the wavelength of the light.
Electro-Optical and Acousto-Optical Devices
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
Section 11.2 introduces the concepts of photoconduction. It is followed by Section 11.3, where we discuss design, characteristics, and applications of p–n and p–i–n photodiodes, avalanche photodiodes, vacuum photodiodes, and photomultipliers. The concept of metal oxide semiconductor (MOS) capacitor and its application in the design of charge-coupled device (CCD) structure, MOS read-out scanner, and CCD imager are introduced in Section 11.4. Next, in Section 11.5, we describe cathode-ray tube (CRT) technology and various imaging tube technologies, such as vidicon, plumbicon, and image intensifier. Section 11.6 introduces the physics of electro-optic (EO) modulation. Section 11.7 discusses the working of EO amplitude modulator, EO phase modulator, Pockels read-out optical modulator, Kerr modulator, liquid-crystal light valve, spatial light modulator, and liquid-crystal display devices. Finally, in Section 11.8, the concept of acousto-optical modulation and its application to a few hybrid systems are elaborated.
Technology and applications of spatial light modulators
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
The origin of these devices occurred after various attempts in the late 1970s to use continuous membrane mirrors, locally deformed under the application of local electric fields, as a means to modulate the reflectivity or the phase of the reflected optical beam [118]. This concept was expanded in the early 1980s to include the first MEMS-type structures in silicon [119,120]. This MEMS structure is essentially an array of silicon-based pixel-level metallized cantilevers which tilt in response to an electric potential applied to the pixel electrode. This MEMS structure which started with analogue tilt response design was later refined by the Texas instruments developers as a binary (digital) device with only two states. This recent design, combined with a complex driving circuitry to allow grey scale operation based on a PWM scheme, is the basis for today’s high-brightness, high-resolution projectors aimed at such ambitious goals as electronic cinema [121]. The other principal MEMS-type SLM is based on the pixels constructed in a shape of interdigitated fingers. In this configuration, the application of an electric field across this digitated finger structure results in the formation of a diffraction grating with a variable field-dependent depth. Thus diffraction of the incoming optical readout beam, rather than its deflection, constitutes the novelty of this MEMS structure. This “grating light valve” (GLV) device [122,123], conceived and developed by Bloom, is now under development.
Review on development and performance of shape memory alloy/polyimide thin-film composites
Published in Materials and Manufacturing Processes, 2023
Dhiraj Narayane, Ravindra V. Taiwade, Khemraj Sahu
Jayachandran et al.[2] studied the optical reflectance of Ni-Ti SMA film for various wavelengths of light and observed its high reflectance in the visible spectrum. Based on observations, they proposed a potential application of Ni-Ti SMA/PI composite as an optical mirror in interferometry measurement. The composite can reflect the refracted light from the beam splitter and adjust the path length of reflected light by electrically actuating it to generate interference fringes. These composites can also be used as a light valve or on-off optical switch for spatial light modulators.[161] Geetha et al.[37] presented the conceptual design of low voltage operated closed-type electromechanical switch based on Cu-Al-Ni-Mn/PI composite in which actuation of composite intercepts the contact between input and output. Further, they expected its possibility as an ultra-wideband antenna for wireless communication in military applications.
Liquid crystal light valves as optically addressed liquid crystal spatial light modulators: optical wave mixing and sensing applications
Published in Liquid Crystals Reviews, 2018
S. Residori, U. Bortolozzo, J. P. Huignard
The liquid crystal light valve, as schematically depicted in Figure 1(a), is an optically addressed spatial light modulator made by associating a nematic liquid crystal (LC) layer with a photoconductive (PH) material cut in the form of a thin plate (a mm or less thickness, a few transverse section). The PH is one of the confining wall of the LC cell, while the other wall is a glass window. The thickness d of the nematic layer is typically in between 10 and 50 mm. Transparent (Indium-Tin-Oxide, ITO) electrodes are deposited over the outer face of the PH layer and the interior side of the glass wall, allowing the application of an external voltage across the device. The effective voltage transferred to the LC layer depends on the electrical impedance of the PH material, hence, can be controlled by illuminating the photoconductor at the appropriate optical wavelength.