Curtis R. Hruska

Advances in miniaturized spectral sensors

Recent advances in the deposition of patterned thin film spectral filters have enabled a new class of radically miniaturized spectral sensors. This new technology enables numerically large arrays of spectral bandpass filters with unprecedented manufacturing economy. For example, a 64-channel array occupying two square millimeters and spanning 400-900 nm can be deposited with as few as eight coating steps. Mating this filter array to a photodiode array yields a tiny multispectral sensor with diverse applications. The bandpass filters are single-cavity Fabry-Perot designs with common top and bottom mirrors. The dielectric spacer layer between them determines the passband wavelength and is patterned to differing thicknesses using a binary scheme, i.e., each successive “sub-spacer” layer is half the thickness of the previous one. The technical challenge is uniformly patterning and depositing thinner and thinner sub-spacers, which can be only a few nanometers thick. We have demonstrated 64-channel arrays covering the spectral range of 400-900 nm and 775-1075 nm. These arrays have been mated to high-responsivity 2D silicon detectors, in much the same way that linear variable filters are mated to linear detector arrays. The resulting sensor is less than 3 x 3 x 1 mm in size and ideal for integration into mobile devices, wearable electronics, autonomous aerial vehicles, and countless industrial applications. Sensor performance is currently being evaluated for food quality and freshness measurement, drug identification, fuel quality measurement, explosives detection, colorimetry and illumination measurement, solar flux monitoring, remote sensing, and myriad other applications.

Inorganic Reflective Achromatic Quarter-Waveplate for Optical Pick-up Applications

This paper discusses the design, fabrication and application of a quarter-waveplate (QWP) element to address reliability, retardance achromaticity, small wavefront distortion and low-cost aspects of polarization controlling components in high definition, three-channel optical-pickup systems. The retarder is an all-inorganic reflective QWP that provides achromatic 90° retardance for the three laser wavelength bands. These 200-mm wafer scale fabrication parts show a retardance uniformity of about 3%. The surface distortion of these thin-film coated components has been measured to be less than 0.01 waves RMS over 4.5 mm square aperture at 633 nm wavelength. These all-inorganic reflective QWPs developed by JDSU are flexible in design, durable and highly reliable under high light flux exposure and adverse environmental conditions. Several prototype parts have been tested for damp-heat, thermal cycling, low and high temperature storage and the measured 0.5% retardance variations after 2300 h is comparable to the errors of retardance metrology.

50.3: Inorganic Trim Retarder Compensator for VAN‐Mode LCoS Projection Systems

We describe the design, fabrication and contrast measurement results of a high performance, all-inorganic, grating-based contrast enhancer for an LCoS-based projection display that has these attributes: complete A/C-plate compensation, accurate retardance targeting, excellent retardance magnitude and axis uniformity and environmental durability. An overall system contrast of more than 5500:1 with f/2.4 cone illumination has been obtained.