Novel tunable laser sources with 1.5-μm and 1.57-μm cascaded DFB reflectors for in situ gas monitoring applications

Novel tunable lasers based on 1.5-μm and 1.57-μm cascaded distributed-feedback reflectors are realized for real-time monitoring of H₂O and CO gas mixtures immediately in multi-gas sensor systems. With simple fabrication procedures, the new design allows the realization of a widely tunable laser source that can cover the H₂O and CO absorption wavelength bands. With the temperature tuning of 0.1 nm/°C and current tuning of 0.014 nm/mA, the laser can be tuned to cover over 3 nm wavelength range in each wavelength band. Experiments verify that the lasers can have more than 38 dB SMSR over the tuning range. The characteristics of high power, excellent spectral purity, and simple wavelength switching control can simplify the analysis procedures of gas sensing and thus reduce the cost. By direct absorption method, the tunable laser has been successfully adopted in a diode laser sensor system for monitoring of water vapor concentration near 1.5 μm and carbon monoxide near 1.57 μm. Less than 15% error in the line strength is observed between the measured data and HITRAN database.