Finely tunable laser based on a bulk silicon wafer for gas sensing applications

Abstract

In this work a very simple continuously tunable laser based on an erbium ring cavity and a silicon wafer is presented. This laser can be tuned with very fine steps, which is a compulsory characteristic for gas sensing applications. Moreover the laser is free of mode hopping within a spectral range sufficiently wide to match one of the ro-vibrational lines of a target molecule. Here the proposed laser reached, at ~1530 nm, a continuous tuning range of around 950 pm (>100 GHz) before mode hopping occurred, when a silicon wafer of 355 μm thickness was used. Additionally, the laser can be finely tuned with small tuning steps of <12 pm, achieving a resolution of 84.6 pm °C−1 and by using a thermo-electric cooler (TEC) the laser showed a high wavelength stability over time. These tuning characteristics are sufficient to detect molecules such as acetylene in which the mean separation between two ro-vibrational lines is around 600 pm. Finally, it is shown that the tuning range can be modified by using wafers with different thickness.

Tailored Algorithm for Sensitivity Enhancement of Gas Concentration Sensors Based on Tunable Laser Absorption Spectroscopy

“…Here, in order to have repetitive tuning cycles, the laser line wavelength was tuned over time by driving the TEC with a Proportional-Integral-Derivative (PID) controller, which was implemented with LabVIEW software (PC DAQ). In this laser setup, a bulk silicon wafer of 85 m in thickness was used as a spectral selective filter [ 25 ]. Hence, the wafer acts as a Fabry–Perot Interferometer (FPI), and therefore, its reflection pattern can be shifted by varying the refractive index of silicon.…”

“…Hence, the wafer acts as a Fabry–Perot Interferometer (FPI), and therefore, its reflection pattern can be shifted by varying the refractive index of silicon. This can be achieved by taking advantage of the thermo-optical properties of silicon [ 25 ]. Consequently, this allowed us to tune the laser emission wavelength to scan one ro-vibrational absorption line of the target molecule.…”

Gas Sensor Design Based on a Line Locked Tunable Fiber Laser and the Dual Path Correlation Spectroscopy Method

“…Basically, this tunable laser is formed by a ring cavity in which a bulk silicon wafer of 85 µm thickness is used as a spectral selective filter [25]. Hence, the wafer acts as a Fabry-Perot interferometer (FPI) and therefore its reflection pattern can be shifted by varying the refractive index of silicon.…”

“…Hence, the wafer acts as a Fabry-Perot interferometer (FPI) and therefore its reflection pattern can be shifted by varying the refractive index of silicon. This can be achieved by taking advantage of the thermo-optical properties of silicon [25]. Consequently, this allowed us to tune the laser emission wavelength to match one ro-vibrational absorption line of the target molecule.…”

All Single-Mode-Fiber Supercontinuum Source Setup for Monitoring of Multiple Gases Applications

“…Many of these setups are based on a spectroscopic absorption principle since atoms absorb light at specific wavelengths [9]. There are different techniques that are based on this principle and are used for gas monitoring and sensing such as: Tunable Diode-Laser Absorption Spectroscopy (TDLAS) [10][11][12][13][14][15][16][17][18], Tunable Laser Absorption Spectroscopy (TLAS) [19][20][21], Cavity Ring-Down Spectroscopy (CRDS) [19,22,23], Cavity Enhanced Absorption Spectroscopy (CEAS) [24], Fiber Laser Intracavity Absorption Spectroscopy (FLICAS) [25,26], gas cell with coreless fiber optic [27,28], or measurement of the incident and transmitted intensity of light travelling through a medium [29,30]. Some of these techniques use laser diodes, lasers, or tunable lasers for their high output power, narrow wavelength, and high resolution, however the poor stability of these parameters and the narrow measurable bandwidth limit the applicability of devices based on these techniques since they are tuned to detect and measure only certain absorption peaks of the molecule.…”