Application of QWIP FPA Technology to the Integrated Multispectral Atmospheric Sounder (IMAS)
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infrared detector quantum well photodetector QWIP ↗
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Results for “microlens array”
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Theory of dispersive microlenses
A dispersive microlens is a miniature optical element which simultaneously focuses and disperses light. Arrays of dispersive mircolenses have potential applications in multicolor focal planes. They have a 100 percent optical fill factor and can focus light down to detectors of diffraction spot size, freeing up areas on the focal plane for on-chip analog signal processing. Use of dispersive microlenses allows inband color separation within a pixel and perfect scene registration. A dual-color separation has the potential for temperature discrimination. We discuss the design of dispersive microlenses and present sample results for efficient designs.
Herman, B.↗
Multiple fiberoptic probe for several sensing applications
A multiple fiber-optic particle sizing probe which uses a linear array of 11 optical fibers positioned in the focal plane of a graded index microlens is presented. The probe, a compact optical spectrum analyzer, provides simultaneous filtering of the angular spectrum of an extended quasi-monochromatic source. Active and passive configurations provide accurate measurements of the particle size distributions. The multiple fiber-optic probe together with processing electronics is a particle sizing sensor which yields the size distribution within 1-2 min.
Dhadwal, Harbans S.↗
Measurements of microlens performance
We present results of laboratory evaluations of several microlens types that have been designed and fabricated at the Lockheed Research and Development Division. The microlenses include wideband and dispersive types, in isolation and in arrays, and fabricated with binary or grayscale methods. Different lens pixel geometries are considered, including square, hexagonal, and skewed microlenses. We describe our micro-optics laboratory testbed which has been designed for the evaluation of individual lenslets or 2D arrays at selected spectral wavelengths. Measurement capabilities include focal length, point-spread functions, wavefront quality, and modulation transfer functions. Our present effort focuses on the results of point spread function measurements and their comparison with design predictions.
Shough, D.↗
Campaign 9 of the K2 Mission: Observational Parameters, Scientific Drivers, and Community Involvement for a Simultaneous Space- and Ground-based Microlensing Survey
K2ʼs Campaign 9 (K2C9) will conduct a approximately 3.7 sq. deg survey toward the Galactic bulge from 2016 April 22 through July 2 that will leverage the spatial separation between K2 and the Earth to facilitate measurement of the microlens parallax Pi(sub E) for approximately greater than 170 microlensing events. These will include several that are planetary in nature as well as many short-timescale microlensing events, which are potentially indicative of free-floating planets (FFPs). These satellite parallax measurements will in turn allow for the direct measurement of the masses of and distances to the lensing systems. In this article we provide an overview of the K2C9 space- and ground-based microlensing survey. Specifically, we detail the demographic questions that can be addressed by this program, including the frequency of FFPs and the Galactic distribution of exoplanets, the observational parameters of K2C9, and the array of resources dedicated to concurrent observations. Finally, we outline the avenues through which the larger community can become involved, and generally encourage participation in K2C9, which constitutes an important pathfinding mission and community exercise in anticipation of WFIRST.
K2s Campaign 9 (K2C9)↗
Increasing Linear Dynamic Range of a CMOS Image Sensor
A generic design and a corresponding operating sequence have been developed for increasing the linear-response dynamic range of a complementary metal oxide/semiconductor (CMOS) image sensor. The design provides for linear calibrated dual-gain pixels that operate at high gain at a low signal level and at low gain at a signal level above a preset threshold. Unlike most prior designs for increasing dynamic range of an image sensor, this design does not entail any increase in noise (including fixed-pattern noise), decrease in responsivity or linearity, or degradation of photometric calibration. The figure is a simplified schematic diagram showing the circuit of one pixel and pertinent parts of its column readout circuitry. The conventional part of the pixel circuit includes a photodiode having a small capacitance, CD. The unconventional part includes an additional larger capacitance, CL, that can be connected to the photodiode via a transfer gate controlled in part by a latch. In the high-gain mode, the signal labeled TSR in the figure is held low through the latch, which also helps to adapt the gain on a pixel-by-pixel basis. Light must be coupled to the pixel through a microlens or by back illumination in order to obtain a high effective fill factor; this is necessary to ensure high quantum efficiency, a loss of which would minimize the efficacy of the dynamic- range-enhancement scheme. Once the level of illumination of the pixel exceeds the threshold, TSR is turned on, causing the transfer gate to conduct, thereby adding CL to the pixel capacitance. The added capacitance reduces the conversion gain, and increases the pixel electron-handling capacity, thereby providing an extension of the dynamic range. By use of an array of comparators also at the bottom of the column, photocharge voltages on sampling capacitors in each column are compared with a reference voltage to determine whether it is necessary to switch from the high-gain to the low-gain mode. Depending upon the built-in offset in each pixel and in each comparator, the point at which the gain change occurs will be different, adding gain-dependent fixed pattern noise in each pixel. The offset, and hence the fixed pattern noise, is eliminated by sampling the pixel readout charge four times by use of four capacitors (instead of two such capacitors as in conventional design) connected to the bottom of the column via electronic switches SHS1, SHR1, SHS2, and SHR2, respectively, corresponding to high and low values of the signals TSR and RST. The samples are combined in an appropriate fashion to cancel offset-induced errors, and provide spurious-free imaging with extended dynamic range.
Pain, Bedabrata↗