Multi-band multiplexing intra-cavity gas sensing system and method

An intra-cavity gas sensing system based on multi-band aliasing construction, consisting of a laser resonant cavity subsystem, a gas sensing subsystem and a detection-demodulation subsystem, wherein

• the first subsystem is a laser resonant cavity, consisting of the first beam splitter, two wavelength division multiplexers, two pump light sources, two doped optical fibers, two optical isolators, two tunable optical attenuators, a beam combiner, an optical circulator and an F-P tunable optical filter. Using optical fiber, the two output ports of the first beam splitter are connected with input ports of the first wavelength division multiplexer and the second wavelength division multiplexer, respectively. The other input ports of the first and the second wavelength division multiplexers are coupled with the output ports of the first and the second pump light sources. The first wavelength division multiplexer is connected with the first doped optical fiber, the first optical isolator and the first tunable optical attenuator in turn, whereas the second wavelength division multiplexer is connected to the second doped optical fiber, the second optical isolator and the second tunable optical attenuator in turn. The output ports of the first and the second optical attenuators are coupled with an input port of a beam combiner and the output port of the beam combiner is connected to the first port of an optical circulator, while the third port of the beam combiner is connected to the input port of the F-P tunable optical filter;
• the second subsystem is the gas sensing portion, consisting of a gas cell and an optical reflective mirror. The gas cell and optical reflective mirror are connected with the laser resonant cavity through the second port of the optical circulator. The optical reflective mirror reflects the signals output by the laser resonant cavity back to the same cavity so as to form laser resonance;
• and
• the third subsystem is the detection-demodulation portion, comprising the optical coupler. The input port of the optical coupler is connected with the output port of the F-P tunable optical filter. The output port of the optical coupler is coupled with the input port of the second beam splitter. The two output ports of the second beam splitter are connected with the input ports of the first and second optical detectors, respectively. The output ports of the first and second optical detectors are connected with an analog input port of a data acquisition module, respectively. The data acquisition module is connected to a computer. The analog output port of the above module is connected with an electrically-controlled input port of the F-P tunable optical filter.