Project 2.1

This project aims to provide a compact optical source that will be positioned inside the resonant fork, increasing the sensitivity and compactness of the intracavity QEPAS system by means of an evanescent waveguide mode of the laser. This provides a robust way to access the high intra-cavity power. This integrated configuration, that far exceeds the currently available technology for intracavity QEPAS applications in terms of size and robustness, will lead to the realisation of compact, lightweight and low-power sensors. The ESR research activity will focus on the fabrication of a hybrid laser situated on a silicon nitride cantilever showing a footprint 150 microns x 1 mm. The basic component (hybrid laser) will consist of a tunable resonant cavity, similar to the one developed in ESR Project 3.2 , that will be integrated with a gain chip for the realisation of an external cavity hybrid laser.

After wafer scale fabrication of the silicon nitride devices, the wafer will be cut using laser dicing into the required cantilever shape. In this framework, the preliminary designs from ESR Projects 3.2 and 1.3 will be adapted in order to let the resonant cavity fit inside the cantilever. Fabrication tolerances and technological limits will be taken into account in the design process in order to better identify the electromagnetic behaviour of the whole system. Particular attention will be given to the definition of a protocol for the mechanical assembly of the whole suspended system. In this regard, different approaches for the integration of the resonant cavity and the gain chip will be considered and investigated. The thermal behaviour of this hybrid source will be experimentally assessed, verifying its thermal stability over a wide range of temperatures.

Fabrication of the integrated source will be carried out at Tyndall National Institute and MTU by means of electron beam lithography and dry etching (this activity will be connected to Project 3.2). Characterisation of the fabricated prototypes will be carried out at both POLIBA and MTU. The silicon nitride chip and gain chip will be permanently connected using a UV curable epoxy process and transferred to a single heatsink. The bonding process will be optimised over the course of the project to reduce the coupling losses at this interface. Starting from these results, the ESR will then investigate/test the sensing performance of the new intra-cavity QEPAS system together with ESR1.1 for the measurement of ammonia (with absorption in the telecoms range) which is an important indicator of the quality of food.