Application of High-Speed Quantum Cascade Detectors for Mid-Infrared, Broadband, High-Resolution Spectroscopy

Abstract

Broadband, high-resolution, heterodyne, mid-infrared absorption spectroscopy was performed with a high-speed quantum cascade (QC) detector. By strictly reducing the device capacitance and inductance via air-bridge wiring and a small mesa structure, a 3-dB frequency response over 20 GHz was obtained for the QC detector, which had a 4.6-μm peak wavelength response. In addition to the high-speed, it exhibited low noise characteristics limited only by Johnson–Nyquist noise, bias-free operation without cooling, and photoresponse linearity over a wide dynamic range. In the detector characterization, the noise-equivalent power was 7.7 × 10−11 W/Hz1/2 at 4.6 μm, and it had good photoresponse linearity up to 250 mW, with respect to the input light power. Broadband and high-accuracy molecular spectroscopy based on heterodyne detection was demonstrated by means of two distributed-feedback 4.5-μm QC lasers. Specifically, several nitrous oxide absorption lines were acquired over a wavelength range of 0.8 cm−1 with the wide-band QC detector.

Electrical flicker-noise analysis based on trapping and de-trapping model in quantum-cascade detectors

“…[27] This high-speed behavior is one of the outstanding features of ISB photodetectors that other types of IR photodetector cannot achieve. Mid-IR QC detectors that feature uncooled operation and high-speed response are promising candidates as photodetectors for high-speed spectroscopy, [28] broadband heterodyne detection, [29] and free-space optical communication in the mid-IR range. [30,31] Therefore, further improvement in performance is strongly desired through a better understanding of the operating characteristics of QC detectors.…”