Abstract
In this work, two-section, coupled cavity, mid-IR quantum cascade lasers (QCLs) were characterized in terms of their tuning range and emission stability under operation towards potential application in detection systems. Devices were processed by inductively coupled plasma reactive ion etching (ICP-RIE) from InP-based heterostructure, designed for emission in the 9.x micrometer range. Single mode devices were demonstrated with a better than 20 dB side mode suppression ratio (SMRS). The fabrication method resulted in improved yield, as well as high repeatability of individual devices. Continuous, mode-hop-free tuning of emission wavelength was observed across ~4.5 cm−1 for the range of temperatures of the heat sink from 15 °C to 70 °C. Using the thermal perturbation in the lasing cavity, in conjunction with controlled hopping between coupled-cavity (CC) modes, we were able to accomplish tuning over the range of up to ~20 cm−1.
Highlights
Quantum cascade lasers (QCLs) are compact laser sources of infrared radiation in the mid-IR range (3–20 μm) and in the THz range (1–5 THz)
We have previously presented CC-quantum cascade lasers (QCLs) fabricated by means of focused ion beam (FIB) post-processing [22,23,24]
The temperature of the device was kept at 20 °C for all light
Summary
Quantum cascade lasers (QCLs) are compact laser sources of infrared radiation in the mid-IR range (3–20 μm) and in the THz range (1–5 THz). In this article an alternative approach to achieving single mode emission is presented: coupled-cavity quantum cascade lasers (CC-QCLs). The process developed in this work to fabricate devices is based exclusively on dry etching. It allowed the achievement of high throughput and high yield without further complications to standard QCL fabrication procedure. In order to overcome the disadvantages of the FIB process, gaps separating sections were defined by dry etching during the fabrication process [15] It is shown directly how the FTIR (Fourier transform infrared) spectrum of pulsed operated lasers becomes broadened due to in-pulse shift of the emission wavelength even for short (hundreds of ns) pulses
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