Polarization effects in optical fiber lasers and applications to gas sensing.

摘要

This work studies the application of fiber lasers for gas detection using a spectroscopic technique known as Laser Intra-cavity Spectroscopy. It is demonstrated that a compact and rugged spectroscopic device can be fabricated by using rare earth-doped silica fiber lasers. Experimental results using Fiber Laser Intra-cavity Spectroscopy (FLICS) with an Er3+-doped fiber laser and acetylene as the absorber show that, with this approach, an enhancement in sensitivity is obtained in comparison to the regular absorption spectroscopy method. Since the sensitivity is limited primarily by laser amplitude noise, the use of a dual beam noise-cancellation technique with FLICS would be of great advantage. This requires the fabrication of a de-coupled dual-output fiber laser cavity, for which the polarization control of the fiber laser is of great importance. Experiments with optical fiber laser cavities combining fibers with high and low birefringence show that, upon compensating the birefringence inside of the laser cavity, the polarization effects observed in optical fiber lasers can be tailored to meet the requirements of specific applications. As an example, the combination of FLICS with a high sensitivity detection technique called BRD (Balanced Ratio-metric Detection) is examined. An overview of this detection scheme and results comparing different experimental set-ups are presented.