Measurement Of Arm-length Difference Of Fiberoptic Interferometric Hydrophone Based On Microwave Photonic Technology

With the development of ocean research, fiber optic hydrophone is invented as a new kind of Sonar sensor. It has good performance in sensitivity and frequency response. The base structure of fiber optic hydrophone is Michelson interferometer.So the length difference(dL) of interferometer’s two arm determines its performance. While there is no effective method to measure the dL. This paper makes a deep research to find out a way to measure the dL.Firstly.this paper introduce the development of microwave photonic technology and fiber op-tic hydrophone, which promote the modern communication technology and sensor measurement technology developing rapidly. Then give out fiber optic hydrophone’s base structure and discuss several dL measurements mentioned in literature. But they all don’t work well. Some fiber length measurements are also discussed is this paper, such as OTDR,OFDR,PCDR.Lastly,this paper give out two methods:one is PGC parameter estimation method based on laser modulation, the oth-er is the length difference of fiber optic hydrophone measurement based on microwave photonic technology.This paper gives out the theory of the two methods and use numerical simulation to proof their feasibility. Analyze how the SNR of input signal,MZM modulator bias shift and the unbalance of fiber optic hydrophone’s two arm influent the measure system. Based on the theory and simulation, a measure instrument is built.Many experiments are designed to test the measure instrument.8 fiber optic hydrophones are measured by OBR4400 and the instrument designed in this paper. The results are no difference in 0.01%. The measure range of the instrument is 10 cm to 1000m and its accuracy is 35μm(@ 10cm-60m), same as OBR4400. At last, random error of this instrument is discussed and the factors affecting random error are pointed out, which can give an advise to design more accurate instru-ment.