We describe initial results from a module built using the Thermal Light ValveTM (TLV) - a diffractive thin
film spatial light modulator that provides high response to long-wavelength infrared radiation. In this paper
we briefly describe a differential-mode TLV device, its solid state structure, readout system configuration,
and performance parameters. We describe the architecture of an 80x60 OpTICTM thermal imaging module
based on the TLV, and give some early imaging results. We review the manufacturability of the
component and module and the implication for low-cost thermal imaging.
The Thermal Light Valve™ (TLV) is a diffractive thin film spatial light modulator that provides high response to long-wavelength infrared radiation. In this paper we describe the rationale for optical-readout thermal imaging arrays, and some of the challenges faced by past devices. We then describe the TLV device, its solid state structure, readout system configuration, and performance parameters. We show how the TLV overcomes key performance issues faced by previous optical-readout arrays to achieve a modeled system performance of 16mK NETD. In addition we describe the TLV's advantages from the point of view of manufacturing tolerances and wide ambient temperature operating ranges resulting in a TLV chip yield in excess of 95% - a critical cost advantage of RedShift Systems' OpTIC™ optical thermal imaging cores.
A novel uncooled long-wave infrared imaging technology with optical readout is proposed and developed targeted for low cost thermal imaging applications. This technology uses the thermo-optic effect in a semiconductor to detect infrared signals rather than the thermal-resistance effect used in traditional microbolometers. The key component of the imager, the focal plane array, is made up of thermally tunable thin film filter membrane pixels. Each thermal pixel acts as a wavelength translator, converting far infrared radiation signals into near infrared signals which are then detectable by off-the-shelf CCD or CMOS cameras. This approach utilizes optical filter and MEMS technologies, to build a low-cost passive long wavelength infrared focal plane array without electrical leads or active cooling. Within one year since the commencement, NETD values of 0.28K in a 160x120 array operating at 22Hz video frame rate have been achieved without temperature control.
A new family of miniature nano-tunable narrowband infrared filters has been developed based on the thermo-optic properties of thin film semiconductors. Originally developed for fiber optic telecommunications networks at 1.5 μm, the technology has now been extended to the 3-5 μm range, leading to very compact tunable filters with passbands on the order of 0.5% of center wavelength and tuning ranges up to 4% of center wavelength. Two applications are described. First, a prototype carbon monoxide sensor testbed based on a 4550-4650 nm tunable filter is shown to be capable of detecting less than 20 ppm of CO. Second, we show how nano-tunable thin film filters can be integrated with miniature blackbody sources to create a new family of ultra low cost integrated tunable IR emitters, which we have named Firefly. Packaged in TO cans, Firefly devices enable precision detection of gases including carbon dioxide, carbon monoxide, sulphur dioxide, hydrogen cyanide, water vapor, nitric oxide or methane.
Thin film interference coatings (TFIC) are the most widely used optical technology for telecom filtering, but until recently no tunable versions have been known except for mechanically rotated filters. We describe a new approach to broadly tunable TFIC components based on the thermo-optic properties of semiconductor thin films with large thermo-optic coefficients 3.6X10[-4]/K. The technology is based on amorphous silicon thin films deposited by plasma-enhanced chemical vapor deposition (PECVD), a process adapted for telecom applications from its origins in the flat-panel display and solar cell industries. Unlike MEMS devices, tunable TFIC can be designed as sophisticated multi-cavity, multi-layer optical designs. Applications include flat-top passband filters for add-drop multiplexing, tunable dispersion compensators, tunable gain equalizers and variable optical attenuators. Extremely compact tunable devices may be integrated into modules such as optical channel monitors, tunable lasers, gain-equalized amplifiers, and tunable detectors.
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