Monolithic, Optically Coupled, Multi-Section Mid-IR Quantum Cascade Lasers

Kamil Pierściński,Piotr Gutowski,Dorota Pierścińska,Grzegorz Sobczak,Katarzyna Krajewska,Aleksandr Kuźmicz,Krzysztof Chmielewski

doi:10.3390/photonics8120583

Abstract

Mid-infrared (mid-IR λ ≈ 3–12 μm), single-mode-emission Quantum Cascade Lasers (QCLs) are of significant interest for a wide range of applications, especially as the laser sources are chosen for laser absorption spectroscopy. In this work, we present the design, fabrication and characterization of multi-section, coupled-cavity, mid-IR quantum cascade lasers. The purpose of this work is to propose a design modification for a coupled-cavity device, yielding a single-mode emission with a longer range of continuous tuning during the pulse, in contrast to a 2-section device. This effect was obtained and demonstrated in the work. The proposed design of a 3-section coupled-cavity QCL allows for a single-mode emission with 35 dB side-mode suppression ratio. Additionally, the time-resolved spectra of the wavelength shift during pulse operation, show a continuous tuning of ~3 cm−1 during the 2 μs pulse. The devices were fabricated in a slightly modified, standard laser process using dry etching.

Highlights

In our previous paper [13], we described a singlemode emission from 2-section CC Quantum Cascade Lasers (QCLs) fabricated by focused ion beam (FIB) milling or by inductively coupled plasma reactive ion etching (ICP-RIE)
The selected modes are separated by the free spectral range (FSR) of the short cavity
In this work we introduced a modified, coupled-cavity device, consisting of three sections, with two optical gaps

Summary

Introduction

QCL [8] or photonic crystals resonators [9] All of these solutions are possible to implement experimentally; they either require additional or external elements (e.g., external cavity), leading to systems sensitive to mechanical vibrations, or to the high cost of a single device due to the complexity of processing technology (e.g., DFB). In our previous paper [13], we described a singlemode emission from 2-section CC QCLs fabricated by focused ion beam (FIB) milling or by inductively coupled plasma reactive ion etching (ICP-RIE) These devices were characterized by a stable, single-mode operation and relatively high optical power.

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Conclusion