Gas detection system using intracavity fiber laser with loop cavity having saturated absorption fiber

A gas detection system with an inner ring cavity fiber laser using saturated absorption optical fiber, said system comprising:

• a ring fiber laser consisted of a pump source, a wavelength division multiplexer, a first active optical fiber, a first coupler, a fiber Bragg grating and a second coupler connected successively;
• an optical isolator coupled between said first active optical fiber and said first coupler, for preventing reverse light from transmitting in said active fiber, wherein said first coupler is used for dividing the laser light isolated by the optical isolator into a detecting beam and an intensity measuring beam according a certain power ratio;
• a second active optical fiber connected between said fiber Bragg grating and said first coupler as a saturated absorber;
• a detection gas chamber connected between said first coupler and said second coupler, which is introduced with the gas to be detected, and receives the detecting beam from said first coupler and makes it pass through the gas to be detected and then output to said second coupler;
• a first photoelectric detector connected to the output of the first coupler for detecting the laser intensity outputted from said ring fiber laser to generate a first light intensity signal;
• a second photoelectric detector connected to the output of the second coupler for receiving the intensity measuring beam passing through the detection gas chamber to generate a second light intensity signal;
• a feedback control unit for receiving said first and second light intensity signals and generating a feedback signal to adjust said pump source and said fiber Bragg grating.