Quantum cascade lasers (QCLs) and Interband cascade lasers (ICLs) are promising new mid-IR sources for spectroscopic
applications. Desirable characteristics include extremely high brightness, broad emission, very high resolution, compact
size, and modest power consumption. For most spectroscopic applications, it is necessary to tune QCLs over a broad
emission wavelength range. The conventional approach for broad tuning is to use an external cavity (EC) which
incorporates a mechanically tuned diffraction grating within the laser cavity.
In this paper we will describe an alternative approach to EC-QCL tuning which utilizes miniature, thermally tuned, MEMS
fabricated filters, allowing for a very compact, simple, mechanically stable package with no moving parts. The system
is well suited for discrete measurements at multiple wavelengths as needed by many of the industrial spectroscopic
analyzers in use today. An accuracy of 0.02 cm-1 over the 50 cm-1 range of the test laser and a precision of 0.002 cm-1 over
a 15 cm-1 scan has been demonstrated. High resolution mode hop free CW scanning of a 0.5 cm-1 range at a scan rate of
200 Hz with a wavelength precision of 0.002 cm-1 has also been demonstrated. This makes the design an attractive
alternative to current Distributed feedback (DFB) QCLs for high resolution gas phase measurements due to the added
advantage of broad tunability for the detection of multiple gases, and the capability to select multiple gas lines of different
intensity to extend the dynamic range.
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.
KEYWORDS: Optical filters, Tunable filters, Electronic filtering, Tunable lasers, Signal detection, Signal attenuation, Sensors, Polarization, Semiconducting wafers, Control systems
The advantages of low cost amplifier solutions in single-channel link extender or loss compensator systems cannot be fully realized unless the ASE noise around the signal peak is removed. Doing so requires a cost-effective solution with high performance, including low insertion loss (<-2.5dB), low PDL (<-0.25dB), low power operation (<200mW), and fast tuning (<1sec). We have successfully fabricated and packaged a tunable ASE filter into a small form-factor 2-port package which meets these requirements. We obtain filter properties at both the chip and package-levels and examine filter performance operating under optically open and closed loop control.
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.
Thermo-optic layers of thin film semiconductors are deposited by PEVCD to create thermally tunable bandpass filters for WDM optical networks. Amorphous semiconductor films, adapted from the solar cell and display industries, are the primary ingredient. Single-cavity tunable filters with FWHM=0.085 nm, >40 nm tuning range, and insertion losses 0.2-4 dB are demonstrated. Key enablers for this new family of index-tunable thin film devices are PECVD deposition, large internal temperature changes >400C, high conductivity polysilicon heater films, and extremely robust film adhesion. Possible applications include optical monitoring, add/drop multiplexing, dynamic gain equalization, and dispersion compensation.
The emergence of wearable electronics is leading away form glass substrates for the display backplane, to plastic and metal. At the same time the substrate thickness is reduced to make displays lighter. These two trends cooperate toward the development of compliant substrates, which are designed to off load mechanical stress from the active circuit onto the substrate. Compliant substrates made the circuit particularly rugged against rolling and bending. Design principles for compliant substrates include: (a) Moving the circuit p;lane as close as possible to the neutral plane of the structure, and (b) Using substrate and encapsulation materials with low stiffness. Design principle (a) is demonstrated on thin-film transistors made on thin steel foil. Such transistors function well after the foils are rolled to small radii of curvature. Principle (b) of compliant substrates is demonstrated with bending experiments of a-Si:H TFTs made on thin substrates of polyimide foil. TFTs on 25-micrometers thick polyimide foil may be bent to radii of curvature as low as 0.5 mm without failing. The reduction in bending radius, from R-2 mm on same- thickness steel foil, agrees with the theoretical prediction that changing from a stiff to a compliant substrate reduces the bending strain in the device plane by a factor of up to 5.
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