Abstract
The optical gain spectrum has been investigated theoretically for various designs of active region based on InAs/GaInSb quantum wells—i.e., a type II material system employable in interband cascade lasers (ICLs) or optical amplifiers operating in the mid-infrared spectral range. The electronic properties and optical responses have been calculated using the eight-band k·p theory, including strain and external electric fields, to simulate the realistic conditions occurring in operational devices. The results show that intentionally introducing a slight nonuniformity between two subsequent stages of a cascaded device via the properly engineered modification of the type II quantum wells of the active area offers the possibility to significantly broaden the gain function. A −3 dB gain width of 1 µm can be reached in the 3–5 µm range, which is almost an order of magnitude larger than that of any previously reported ICLs. This is a property strongly demanded in many gas-sensing or free-space communication applications, and it opens a way for a new generation of devices in the mid-infrared range, such as broadly tunable single-mode lasers, mode-locked lasers for laser-based spectrometers, and optical amplifiers or superluminescent diodes which do not exist beyond 3 µm yet.
Highlights
An important class of semiconductor lasers operating efficiently in the spectral range of the first atmospheric window (2.9–5.3 μm), coinciding with the strongest absorption lines of many environmentally relevant gasses, utilizes a cascaded scheme of interband transitions in type II quantum well (QW) structures [1,2,3,4]
We first consider the influence of various modifications in an interband cascade lasers (ICLs)-like active region on the fundamental optical transition energy
We have theoretically studied various designs of ICL active region made of combinations of type II InAs/GaInSb materials in the context of maximizing the width of optical gain spectrum, as demanded by many optoelectronic applications in the mid infrared range
Summary
An important class of semiconductor lasers operating efficiently in the spectral range of the first atmospheric window (2.9–5.3 μm), coinciding with the strongest absorption lines of many environmentally relevant gasses, utilizes a cascaded scheme of interband transitions in type II quantum well (QW) structures [1,2,3,4] Such devices are called interband cascade lasers (ICLs) and they are usually based on a broken gap material system of InAs/GaInSb [2,3,5,6]. The usage of such materials, besides the natural band edge alignment which is necessary in ICLs, allows the emission in a broad range of the mid-infrared (MIR) [7] and the growth on GaSb or InAs substrates to remain in a relatively low strain limit range This assures the high structural and optical quality of epitaxially grown III-V materials and a good device performance. GaSb-based ICLs are ideal for MIR spectroscopy and gas sensing applications that rarely require Watt-level optical power [13]
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