Monolithic focal-plane arrays of photodetectors capable of imaging the same scenes simultaneously in multiple wavelength bands in the visible and infrared spectral regions have been proposed. In prior visible/infrared imaging systems, it has been standard practice to use separate optical trains to form images in visible and infrared wavelength bands on separate visible- and infrared-photodetector arrays. Because the proposal would enable the detection of images in multiple wavelength bands on the same focal plane, the proposal would make it unnecessary to use multiple optical trains. Hence, multispectral imaging systems could be made more compact and the difficulties of aligning multiple optical trains would be eliminated.
Each pixel in an array according to the proposal would contain stacks of several photodetectors. The proposal is a logical extension of prior concepts of arrays of stacked photodetectors for imaging in two or three wavelength bands. For example, such an array was described in “Three- Color Focal-Plane Array of Infrared QWIPs” (NPO-20683), NASA Tech Briefs, Vol. 24, No. 5 (May 2000), page 26a.
In one proposed design, (see figure), each pixel would be divided into four subpixels, one being dedicated to a visible and near-infrared (V) band, one to a combination of the V band and a very-long wavelength infrared (VLWIR) band, one to a combination of the V band and a long-wavelength infrared (LWIR) band, and one to a combination of the V band and a medium-wavelength infrared (MWIR) band. For this purpose, each subpixel would include a GaAs-based positive/ intrinsic/negative (PIN) photodiode for detection in the V band stacked with three quantum-well infrared photodetectors (QWIPs), each optimized for one of the aforementioned infrared bands. The stacks of photodetectors in all the subpixels would be identical except for the electrical connections, which would be configured to activate the various wavelength band combinations.
This work was done by Sarath Gunapala, Sumith Bandara, John Liu, and David Ting of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free online at www.techbriefs.com/tsp under the Electronics/Computers category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
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Refer to NPO-30541, volume and number of this NASA Tech Briefs issue, and the page number.
This Brief includes a Technical Support Package (TSP).
Photodetector Arrays for Multicolor Visible/Infrared Imaging
(reference NPO-30541) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory, focusing on advancements in photodetector arrays for multicolor visible and infrared imaging. It is associated with NTR Number 30541 and is part of NASA Tech Briefs, which disseminate aerospace-related technological developments with potential wider applications.
The core innovation discussed is the proposed 4-color Quantum Well Infrared Photodetector (QWIP) focal plane array. This technology aims to enhance imaging capabilities across multiple wavelengths, including visible, near-infrared (NIR), mid-infrared (MWIR), and long-wave infrared (LWIR). The design features a layered structure comprising semi-insulating GaAs substrates and various doped regions, which facilitate the detection of different infrared wavelengths. The document includes detailed diagrams illustrating the configuration of the photodetector layers, including the isolation layers and intrinsic regions necessary for optimal performance.
The proposed QWIP array is designed to operate at specific voltage levels, with configurations that allow for the detection of signals across the specified spectral ranges. The document emphasizes the importance of these advancements in applications such as remote sensing, environmental monitoring, and various scientific research fields, where multicolor imaging can provide critical data.
Additionally, the document outlines the potential commercial applications of this technology, suggesting that the innovations could lead to improved imaging systems in both civilian and military contexts. The integration of visible and infrared detection capabilities into a single device represents a significant step forward in sensor technology, enabling more versatile and efficient imaging solutions.
The Technical Support Package also serves as a resource for researchers and industry professionals interested in the latest developments in photodetector technology. It encourages collaboration and innovation through the NASA Innovative Partnerships Program, which aims to foster partnerships that can leverage NASA's research for broader technological advancements.
In summary, this document presents a comprehensive overview of a cutting-edge photodetector technology that promises to enhance multicolor imaging capabilities, with implications for various scientific and commercial applications. It highlights NASA's commitment to advancing aerospace technology and its potential impact on a wide range of fields.
