Abstract
We present the development of an external cavity Bragg grating stabilized 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 characterization of its performance for the purpose of spectroscopic measurement of methane at this wavelength using a 25 cm path-length 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 = 8.3 × 10-5 AU was achieved, which is consistent with the performance of standard distributed feedback lasers. The new device exhibits a side-mode suppression ratio of -40 dB and a low RIN of <-150 dB/Hz, and thus avoids the high levels of noise or instability normally associated with larger, mechanically driven external cavity lasers. The silica-on-silicon platform has the potential for low-volume manufacturing of special lasers at the custom wavelengths required for gas detection, without the need for investment in foundry solutions.
Highlights
Tunable diode laser spectroscopy (TDLS) is an important technique for the detection and quantification of trace atmospheric gases [1]
We report for the first time the use of a tunable laser based on planar silica-on-silicon in gas detection, a demanding application requiring high wavelength precision, mode-hop free tuning and low noise
The limit of detection of a target gas species can be quantified as the noise equivalent absorbance (NEA, in units absorbance units (AU)) or the minimum detectable absorption coefficient, allowing instrumental techniques to be compared without reference to the specific target gas
Summary
Tunable diode laser spectroscopy (TDLS) is an important technique for the detection and quantification of trace atmospheric gases [1]. The result is that the cost of a single laser can depend on the size of the market for detection of each gas species, or that specific wavelengths are not available in this format. This presents a problem for the detection of unusual gases in specialist applications, or for research that requires only limited quantities. We report for the first time the use of a tunable laser based on planar silica-on-silicon in gas detection, a demanding application requiring high wavelength precision, mode-hop free tuning and low noise. Whether the precise wavelength required by gas sensing can be realized on demand, and whether the performance of the resulting laser is suitable for the application, considering tuning performance and stability
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