An Improved Wire Grid Polarizer For Thermal Infrared Applications
By admin · Core Tech · 30/01/14
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 μm, our 144 nm pitch LWIR polarizers transmit better than 70% of the passing polarization state and have a contrast ratio better than 40 dB. Transmission and reflectance measurements from a Fourier Transform Infrared spectrometer show qualitative agreement with optical modeling results from a rigorous coupled wave analysis package. Preliminary laser damage threshold (LDT) testing and sample analysis indicate that damage is initiated at defects in the silicon AR coating. In the blocking state, the wires can withstand 110 kW/cm2 of continuous wave CO2 laser radiation at 10.6 μm wavelength (360 μm spot size), while the parts show an order of magnitude lower laser damage threshold of the passing polarization state. Removing the AR coating defects should improve LDT performance in the thermal IR and may also result in an increased transmittance in the passing configuration. Moxtek has also developed a MWIR polarizer which shows high contrast (>35 dB) between blocking and passing states and an exceptionally high passing state transmission (>95% between 3.3 and 5.7 μm). The Moxtek MWIR polarizer has an improved AR coating and does not show the same LDT damage initiation mechanism.