Broad and narrow-band wire grid polarizer (WGP) products suitable for MWIR and LWIR applications requiring high contrast were developed on antireflection (AR) coated silicon using Moxtek nanowire patterning capabilities. Accurate metrology was gathered in both transmission and reflection from the SWIR to LWIR using a combination of FTIR and dispersive spectrometers, as well as laser-based light sources. The WGP structures were analyzed using SEM, FIB, and STEM techniques and optical data was derived from IR VASE, transmission, and reflectance measurements. Modeling of device performance was achieved using rigorous coupled wave analysis. Laser damage thresholds were determined and various damage mechanisms identified.
High contrast wire grid polarizers on silicon suitable for mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) applications have been developed using wafer-scale aluminum nanowire patterning capabilities. The 144 nm pitch MWIR polarizer typically transmits better than 95% of the passing polarization state from 3.5-5.5 microns while maintaining a contrast ratio of better than 37dB. Between 7 and 15 microns, the broadband LWIR polarizer typically transmits between 55 and 90% of the passing state and has a contrast ratio better than 40 dB. A narrowband 10.6 micron polarizer shows about 85% transmission in the passing state and a contrast ratio of 45 dB. Transmission and reflection measurements were made using various FTIR spectrometers and compared to RCWA modeling of the wire grid polarizer (WGP) performance on antireflection-coated wafers. Laser Damage Threshold (LDT) testing was performed using a continuous wave CO2 laser for the broadband LWIR product and showed a damage threshold of 110 kW/cm2 in the blocking state and 10 kW/cm2 in the passing state. The MWIR LDT testing used an OPO operating at 4 microns with 7 ns pulses and showed LDT of 650 W/cm2 in the blocking state and better than 14 kW/cm2 in the passing state
Moxtek has developed a high contrast IR polarizer on silicon suitable for long wavelength thermal IR applications using our aluminum nanowire, large area patterning capabilities. Between 7 and 15 microns, our 144 nm pitch polarizers transmit better than 70% of the passing polarization state and have a contrast ratio better than 40 dB. Transmission and reflectance measurements were made using a Fourier Transform Infrared (FTIR) spectrometer with instrument accuracy verified using silicon and germanium reference standards. Results were compared to RCWA modeling of the wire grid polarizer (WGP) performance on antireflection-coated wafers. The FTIR instrument noise floor limited the maximum contrast measurement to about 40 dB, but high polarizer contrast was verified at 10.6 μm using a CO2 laser and pyroelectric detector. A continuous wave Gaussian beam from a CO2 laser was used for Laser Damage Threshold (LDT) testing and showed LDT values of 110 kW/cm2 and 10 kW/cm2 in the blocking and passing states respectively. Analysis of laser damage threshold test samples shows the damage propagating from defects in the anti-reflection (AR) coating. Removing these AR coating defects should improve LDT performance and transmission in the thermal IR.
This paper reports the development of the first Liquid Crystal Adaptive Lens (LCAL) with circular electrodes for imaging application. LCAL is an electro-optical device using a set of electrodes to grade the refractive index across its aperture. The principle of liquid crystal adaptive lens is briefly discussed. The special advantages and challenges in using circular electrodes are addressed. Numerical simulation is performed to predict the imaging performance. A prototype of LCAL was designed according to the requirements for application in a microscope imaging system with a diameter of 7.86 mm and a focal length adjustable from 0.2m to infinity. The structure of the LCAL with circular electrodes includes the top ITO ring electrodes and the connecting wires, insulating layer, ITO plugs, and the bottom ITO conducting wires. This prototype was fabricated on a glass substrate by using micro-fabrication process. The focusing performance of the LCAL with circular electrodes was presented. The experimental results agree well with the simulation results. The imaging experiment of LCAL is performed when LCAL focal length is 1m, 0.38m and 0.2m under incoherent source. The resolution of the images formed by LCAL combined with a fixed lens is indistinguishable from that of the image formed only by a fixed lens, while the contrast is lower.
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