Abstract
In this work a hybrid gas sensor based on a tunable fiber laser and a correlation spectroscopy technique is presented. The laser is tuned by varying the temperature of a bulk silicon wafer of 85 μ m thickness and, once the desired wavelength is reached the line, is locked by keeping fixed its temperature. According to experimental results the wafer temperature variation was in the order of 0.02 K, which induced an estimated wavelength deviation of 0.12 pm, which satisfies the high wavelength position accuracy required for gas sensing applications. Additionally, it is shown that errors due to laser intensity fluctuations can be minimized by implementing a simple dual path correlation spectroscopy stage. As a proof of the suitability of our tunable fiber laser for gas sensing applications, a C2H2 sensor was implemented. By using a 10 cm gas cell at atmospheric pressure, it was possible to detect concentrations from 0 to 20% with a sensitivity of 521 ppm and sub-minute time response. Moreover, the experimental measurements and simulated results have a high level of agreement. Finally, it is important to point out that, by using doped fiber with different characteristics, other wavelength emissions can be generated.
Highlights
Gases are used in a broad range of applications and it is important to have sensors capable of measuring concentration with high precision
In order to carry out some numerical simulations, let us consider the ro-vibrational line of C2 H2 occurring at 1532.8302 nm [24] and use a laser line emission that has a Gaussian profile with 15 pm of full width at half maximum (FWHM) (Figure 2a)
The laser was tuned by changing the temperature of a 85 μm thickness silicon wafer with a PID control program
Summary
Gases are used in a broad range of applications and it is important to have sensors capable of measuring concentration with high precision. Diode lasers, as single-mode distributed feedback laser diodes (DFB), are quite popular for this application Another light source option for LL-TLAS sensing in the near infrared (NIR) region are fiber lasers, since these can provide narrow line width emissions and are relatively low cost because these can be implemented with standard communication components [4]. These lasers can be used to detect gases such as acetylene (C2 H2 ), hydrogen iodide (HI), ammonia (NH3 ), carbon monoxide (CO). Experimental measurements supported by numerical simulations are provided demonstrating the suitability of the tunable fiber laser for the implementation of this type of sensing application
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