Fiber Laser And Sensing Application Based On Sagnac Loop

In the field of optical communication,fiber lasers and become a hot topic in recent years.With the advantages of high gain,simple structure,low insertion loss and many output wavelengths,multi-wavelength erbium-doped fiber lasers are widely used in optical fiber sensing,instrument testing,microwave photonics and precision spectroscopy However,the existing optical fiber lasers have many drawbacks,such as less output wavelength and instability.Therefore,how to further improve the multi-wavelength erbium-doped fiber laser to achieve stable multi-wavelength output has important research significance.Fiber optic laser sensor can realize the integration of laser output and sensing.And the optical fiber laser sensing system combines the advantages of fiber sensors of high sensitivity,less susceptible to electromagnetic interference and distributed measurement capability,with the advantages of fiber lasers of high optical signal to noise ratio and narrow linewidth,so it is widely used in geological exploration,earthquake prediction,hydroacoustic measurement and safety detection and so on.In this paper,a multi-wavelength erbium-doped fiber laser and fiber laser sensor based on Sagnac loop filter is proposed.The properties of the proposed multi-wavelength fiber laser and sensor are analyzed in detail.The detailed contents are as follows:(1)The transmission functions of polarization-maintaining fiber,polarization controller,coupler and other related devices are derived by using the transmission matrix method.Theoretical analysis and simulation of fiber Sagnac ring filter are carried out.The polarization independence,transmission and reflection properties of Sagnac ring are obtained.Then the transmission function of double Sagnac ring filter based on polarization-maintaining fiber and few-mode fiber is derived.(2)A switchable multi-wavelength erbium-doped fiber laser based on double Sagnac loop filter is proposed.The parallel double Sagnac loop filter is consisted of polarization-maintaining fiber and few-mode fiber.The structure is simple.And the multi-wavelength output of erbium-doped fiber laser is realized by the comb filter property.When using the double Sagnac comb filter in linear cavity laser system,a switchable multi-wavelength fiber laser with stable single-,dual-,and triple-wavelength outputs can be obtained at room temperature by adjusting the polarization controllers and changing the polarization state in the cavity.At the same time the lasing wavelength locations also can be switched.The results show that the side mode suppression ratio(SMSR)of the output wavelength is more than 34dB and the maximum wavelength shift of output wavelength is less than 0.05nm,which can be applied in fields such as wavelength division multiplexing and all-optical communication systems.(3)A stress fiber optic laser sensor is proposed.The polarization-maintaining fiber in Sagnac loop are used as the sensor heads of the laser sensor to measure the stress.A complete optical fiber laser sensor system is built in the lab.The stress is detected by the change of laser wavelength output,and the strain sensitivity is 2.38 pm/??.