Monolithic tunable single source in the mid-IR for spectroscopy

Abstract

We present a scheme for the realization of high performances, large tuning range, fully integrated and possibly low cost mid infrared laser source based on quantum cascade lasers and silicon based integrated optics. It is composed of a laser array and a laser combiner. We show that our metal grating approach gives many advantages for the fabrication yield of those laser arrays. We show the results of such a fabrication at 1350 cm-1 with 60 cm-1 tuning range. The silicon is a low cost option for the size consuming combiner. In the development of the SiGe platform, we present the loss measurement set up and we show losses below 1dB/cm at 4.5µm.The need for broadly tunable sources for Mid-Infrared spectroscopy has been identified for years. In order to detect a complex molecules or a set of simple molecules, one needs a source with a small line width and tunable over a few tens of wave numbers. External cavity sources are already available but with limited performances and cost reduction potential. Distributed Feedback (DFB) Quantum Cascade Lasers (QCL) is one of the favored sources for the Laser Spectroscopy ]. We propose here a monolithic tuneable source which is very appealing because of the compactness, the robustness and the usability. A single DFB QCL has a limited tuning range, the two main leverages being the temperature via external temperature control (slow tuning) and via the current (Fig. 1 right).

Application of a ring cavity surface emitting quantum cascade laser (RCSE-QCL) on the measurement of H_2S in a CH_4 matrix for process analytics

“…Processing different, individually addressable, ridge type DFB-QCLs on a single chip as an array allows to produce a laser source [24], [25] covering several tens of wavenumbers that still features a spectral resolution smaller than 0.01 cm −1 . A further refinement of this concept concerns fusion of an optical coupler to the monolithically produced DFB-QCL array to achieve emission from a single spot [26].…”

Implementation of a quantum cascade laser-based gas sensor prototype for sub-ppmv H2S measurements in a petrochemical process gas stream

“…Implementation of new QCL designs, such as multiple DFB chips [49–51], RCSE arrays [52], or Vernier-effect QCLs [53, 54], will allow for a further extended spectral coverage. Thus, other ro-vibrationally accessible analytes of particular interest can be measured as well.…”

Multi‐wavelength quantum cascade laser arrays

“…In addition to the developments on arrays of QCLs with buried refractive index gratings in our group, efforts on the realization of arrays based on metal‐plated surface gratings have been recently reported in conference contributions by Carras et al The DFB gratings of the laser elements in this approach feature a complex coupling coefficient and do not require an additional cladding growth step after grating definition. While cw operation with 20 mW of single‐mode output power was reported for individual QCLs based on surface gratings by the same group at the III‐V Lab , no performance characterization of an array has been published up to now.…”