Spectroscopic gas detection using a Bragg grating - stabilized external cavity laser, custom written in planar integrated silica-on-silicon

Abstract

We present the development of an external cavity Bragg grating stabilised laser for tunable diode laser spectroscopy (TDLS). Our design uses a planar integrated silica-on-silicon platform incorporating a custom written Bragg grating as the wavelength-selective element of the laser cavity. We have developed a prototype singlemode laser at 1651 nm and performed a detailed characterisation of its performance for the purpose of spectroscopic measurement of methane at this wavelength using a 25 cm pathlength single-pass cell. Mode hop-free tuning of 0.13 nm has been demonstrated at frequencies of up to 10 kHz. A single-point limit of detection for TDLS of ΔI/I0 = 8.3x10^-5 AU was achieved, which is consistent with the performance of standard distributed feedback lasers. The new device exhibits a sidemode suppression ratio of -40 dB and a low RIN of <-150 dB/Hz, thus avoiding the high levels of noise or instability normally associated with larger, mechanically driven external cavity lasers. The silica-on-silicon platform has potential for low-volume manufacturing of specialist lasers at the custom wavelengths required for gas detection, without the need for investment in foundry solutions.

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Identifiers

ORCID for J. Gates: orcid.org/0000-0001-8671-5987

ORCID for P.G.R. Smith: orcid.org/0000-0003-0319-718X

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