Research On Strain Sensing Technology Based On Optoelectronic Oscillator

Microwave photonics is an emerging interdisciplinary combining radio frequency engineering and optoelectronics.It has broken through some unsolvable problems in traditional electrics and optics,and new theories and technologies are constantly being proposed,which makes the scope of application more and more extensive.As an important branch of microwave photonics,an optoelectronic oscillator(OEO)can generate microwave signals with a wide frequency range,high stability,low phase noise,and high tunability.Therefore,OEOs have received widespread attention since they were invented.In recent years,OEO-based sensors have quickly entered people's vision due to their unique advantages.By combining traditional optical fiber sensors with OEOs,the demodulation process is converted from the optical domain to the electrical domain.Thanks to mature and high-precision microwave monitoring methods,high-sensitivity,high-resolution,and high-speed demodulation sensing is realized.This article mainly conducts in-depth research on OEO-based sensing technology.By combining OEO with different optical fibers,two strain sensing solutions are proposed,a brief description is as follows:(1)By combining OEO with high-birefringence(Hi-Bi)fiber,a novel strain sensing method is proposed.By properly controlling the polarization state of the light wave sent into the Mach-Zehnder modulator,the strain-induced phase change between the two orthogonally polarized lights transmitted along the fast and slow axes of the Hi-Bi fiber is mapped to the frequency change of the oscillating microwave signal.Therefore,the demodulation of strain is achieved by monitoring the frequency change of the oscillating microwave signal.Both theory and experiment results show that the frequency of the oscillating microwave signal generated by OEO has a linear relationship with strain with a measurement sensitivity of 369.3 Hz/??,and the measurement range reaches 0-700 ??.In addition,when the frequency resolution is 1 Hz,the strain resolution can reach 0.0027??.(2)By using OEO based on linearly chirped fiber Bragg grating(LCFBG),a wide range of strain measurement method is realized.Strain will cause the wavelength of the LCFBG's broadband reflection spectrum to shift.Due to the high dispersion and delay characteristics of the LCFBG,the transmission time of the optical signal transmitted and reflected from the LCFBG will change,resulting in the change of total delay of the OEO loop.As a result,the frequency of the OEO oscillating microwave signal also changes,and the demodulation of the strain is achieved by monitoring the frequency changes.The theoretical analysis and experimental verification of the scheme show that the frequency of the oscillating microwave signal generated by OEO has a linear relationship with strain,the experimental result of strain sensitivity is 1.983 k Hz/??,and the measurement range reaches 0-5000 ??.