640×512 InGaAs focal plane array camera for detecting 1.58μm absorption spectra of CO2

Abstract

This Paper introduces a 640×512 InGaAs focal plane array (FPA) camera integrated into a grating spectrometer for measuring 1.58μm absorption spectra of CO2. To gain atmospheric CO₂ concentration by detecting short wave infrared of reflective sunlight from the earth surface has been demonstrated to be an effective way. A hyperspectral spectrometer is designed to detect 1.58μm absorption spectra of CO₂. The spectrometer is a grating spectrometer which is optimised to respond to the spectral range from 1.562 ~ 1.592μ with spectral resolution of 0.1nm. For high sensitivity, F-number is determined to be 1.8. We designed a 640×512 InGaAs FPA camera system which can be coordinated with the grating spectrometer. The camera integrated a 640×512 InGaAs FPA with 25 μm pixel pitch. The 640×512 InGaAs FPA is sensitive to 0.9μm-to-1.7μm short wave infrared (SWIR) band and features a 298 K temperature detectivity, D^*, greater than 5×10¹² cm-1√Hz∕W. The 640×512 InGaAs FPA has characteristics of quantum efficiency no less than 70% at wavelength of 1.58 μm, pixel operability more than 99.91%, two gain modes and three integrat ion modes. The camera features 3Hz rate (exposure time) and 14-bit output. The FPA’s embedded TEC module is controlled to keep the detector core at proper temperature. The detector core temperature could be adjusted to below 263 K for lower readout noise and dark current. A Universal Series Buses 2.0 (USB2.0) has been used to transmit spectral data and commands. Commands of window size, position, gain mode and integration time per frame can be sent by the USB2.0 interface.