Broadband and narrow band light coupling for QWIPs

Abstract

In this work, we will present a detailed study on the corrugated coupling scheme, which uses optical reflection at the angled sidewalls. In particular, we have investigated, both theoretically and experimentally, corrugated quantum well infrared photodetectors (QWIPs) with different cover materials over a wide range of spectral regime. We found that the coupling is insensitive to the wavelength but depends strongly on the optical properties of the cover material. We will also present the results of C-QWIP focal plane arrays (FPA) characterized so far. An important advantage of the corrugated coupling is its scalability to small pixel size. Based on one corrugation per pixel geometry, we have fabricated a 1024 × 1024 C-QWIP FPA with 99.5% connectivity. With the corrugated coupling geometry, many application restrictions on QWIPs can be eliminated. We will further show that the lack of normal incident absorption in QWIPs can actually be an advantage. It allows one to manipulate the absorption characteristics of QWIPs through different optical coupling structures and creates new detector functionality. The present example is an infrared spectrometer. It consists of a linear array of quantum grid infrared photodetector (QGIP) elements. Each QGIP element shares the same QWIP material but has different grid geometry. The QWIP is made of broadband materials such as the binary superlattices to give an extremely broadband (∼10 μm) absorption. The structure of the grid, on the other hand, determines the specific wavelength to detect at each detector element in the array. In the QGIP spectrometer, detectors with different line widths will detect different wavelengths simultaneously, thus yielding the emission spectrum of an object. A collection of QGIP spectrometers can form an adaptive FPA.