Introduction of a four-step modulation used in PGC method

Yang Liu; Min Zhang; Yanbiao Liao

doi:10.1117/12.726466

5 March 2007 Introduction of a four-step modulation used in PGC method

Yang Liu, Min Zhang, Yanbiao Liao

Proceedings Volume 6595, Fundamental Problems of Optoelectronics and Microelectronics III; 65952D (2007) https://doi.org/10.1117/12.726466
Event: Fundamental Problems of Optoelectronics and Microelectronics III, 2006, Harbin, China

Abstract

Fiber interferometer sensors are widely used in sensor technology, and have considerably high sensitivity. PGC(Phase Generator Carrier) technology is the most useful modulation method. Traditional PGC methods have quite complex demodulation algorithm since they use sinusoid phase modulation. This complexity limits their use in large scale multiplexing. In this article, we will first introduce a two step modulation and its demodulation algorithm with two sample rates: one sample points per one step and two per one. Furthermore we will amend it to a four-step phase modulation. Also a method of modulation depth feedback is introduced. With this method we can control the modulation step to be exactly &pgr;/2 . An estimation for DC content required by the demodulation is introduced too. The demodulation algorithm requires 4 sample points for one demodulation output point. The most advantage of this modulation method is that it is quite easy to realize with AOM(Acoustic optic modulator) and has a very simple demodulation algorithm. For every output point we should do two additions and one arc-tangent calculation. With 8 sample points, with five additions and two multiples, we can have one modulation step feedback point( the output rate is 1/8 of input rate). Only the power estimation needs to be carried out every sample period, but it is only some additions. Also there will be no need for digital filters during demodulation.

Citation Download Citation

Yang Liu, Min Zhang, and Yanbiao Liao "Introduction of a four-step modulation used in PGC method", Proc. SPIE 6595, Fundamental Problems of Optoelectronics and Microelectronics III, 65952D (5 March 2007); https://doi.org/10.1117/12.726466

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KEYWORDS

Modulation

Demodulation

Feedback loops

Phase modulation

Interferometers

Phase shift keying

Sensors

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