: Traditionally, digital imaging systems rely on the use of dedicated photodetectors to capture specific wavelengths in the visible spectrum. These photodetectors, which are commonly made of silicon, are arranged as arrays to capture the red, green and blue wavelengths. The signal captured by the individual photodetectors must then be interpolated and integrated to obtain the closest color match and the finest possible resolution with reference to the actual object. The use of spatially separated detectors to sense primary colors reduces the resolution by a factor of three compared to black and white imaging. The FOVEON detector technology greatly improves the color and resolution of the image through its vertically arranged, triple well photodetector. This is achieved by exploiting the variation of absorption coefficient of silicon with wavelength in the visible spectrum. Hence, in a silicon detector, the shorter wavelength (e.g. blue) would be mainly absorbed at a shallow depth. A longer wavelength (e.g. red) would penetrate the material deeper than the shorter wavelengths and be primarily absorbed at a greater depth. By producing a layered silicon detector, all three primary colour wavelengths of red, green and blue can be captured simultaneously. This thesis aims to study the FOVEON camera's ability to image light from the near Infrared (NIR) to the Ultra-Violet (UV) range of the electromagnetic spectrum. The imaged obtained using a set of bandpass filters show that the camera has response both in the UV as well as NIR regions.

https://apps.dtic.mil/sti/pdfs/ADA429699.pdf

Detecting near-UV and near-IR wavelengths with the FOVEON image sensor

: In this thesis, the performance of a step quantum well infrared photodetector (QWIP), which was designed to detect a laser spot at 1.05 m and IR radiation between 9.5 m to 10.5 m, was evaluated. In the far infrared (FIR), the maximum responsivity of the test detector at 10 K was measured at 1.02 A/W with a peak wavelength of 10.3 m under a negative bias of 0.83 V. The D* at background limited infrared performance (BLIP) was measured at 8.0x10(9) cm square root Hz/W with 180 degrees field of view. The BLIP temperature was found to be about 55 K. In addition, the FIR detection wavelength found shift with the amount of bias across the device. The amount of shift observed was 0.21 meV/KVcm-1 which is due to linear Stark effect associated with the step quantum well. The quantum well infrared detectors made of square quantum wells found to have an order of magnitude lower Stark shift originated from second order effects. This suggests that the step well infrared detector can have applications in tunable wavelength infrared detectors.

High responsivity tunable step quantum well infrared photodetector

: This system was designed to evaluate the response characteristics of photodetectors operating at wavelengths in the 1 micron and 8-12 micron range. A Quartz-Tungsten-Halogen source was used for visible and near-IR energy, and a dedicated IR element provided gray-body radiation with a peak at 1150 Kelvin. A monochromator was employed in conjunction with a six-position filter wheel to provide precise control of energy incident on the photodetectors. Variations in the efficiency of components were compensated for through normalization based on the energy incident on the photo detectors. An intuitive, computer-based interface was developed to automate data collection, and provided numeric and graphic representations of data as it is being collected. At completion, data is exported to a spreadsheet file. A commercial silicon detector was successfully characterized, and accurate voltage response and responsivity curves were generated. A pyroelectric detector was used to verify proper operation of gratings and filters at infrared wavelengths. The system is suitable for its intended purpose, and will be capable of characterizing detectors designed to operate in the 3-5 micron range with the installation of appropriate filters and gratings.

https://calhoun.nps.edu/bitstream/10945/3782/1/02Dec_Herdlick.pdf

Bryan E. Herdlick

Papers

Computer-Controlled Photodetector Characterization System (Design and Construction)