Research On Time-Division Multiplexing Of Interferometric Fiber Optic Signals

As one of the simplest and most efficient schemes, time-division multiplexing (TDM) is applied to the design of fiber-optic sensor arrays widely. After the comparison of different TDM schemes, a system of interferometric fiber-optic hydrophone using TDM technique is designed and it's mainly components are a directional-coupler optical switch and delay coils. Based on this scheme, the number of hydrophones can be enlarged, and it's easy to hybrid with space-division multiplexing and wave-division multiplexing.In this paper, firstly the work mechanism of optical switch was described and the static performance testing was carried out. Then the 4-element TDM system was analyzed. After the high-speed optical switch driver circuit and detection circuit were designed, the generation and detection of multiplexing signals was accomplished. By the use of DSP to control the optical switch and PCI-9812 to be synchronous, the signals of different channels was sampled and correctly demultiplexed. In the end, the 4-element TDM signals were demodulated using phase-generated carrier (PGC) technique.The measurement results obtained show crosstalk levels of different channels was in the range -16dB to -20dB, and crosstalk arose chiefly due to incomplete extinction of the input pulse generated by the optical switch. On the basis of simulation, a conclusion that crosstalk coming from hydrophones in the border of array has deeper effects on array directional response than those in the middle was drew, and the result is useful for the layout of arrays. Another conclusion was that when the crosstalk levels of a 4-element array are less than -20dB, the -3dB width of main lobe decreases 0.172° and the effect can be ignored.