Optical fibre sensor using frequency beating technique

Abstract

In this paper, a new method to realize the optical fibre sensor using an optical heterodyne technique (OHT) is proposed and numerically demonstrated. In this method, the bandpass filter (BPF) was utilized as a reference element and fibre Bragg grating (FBG) served as a sensing element. The wideband light is equally split and launched to sensing and reference elements. The reflected light of sensing element coherently interferes with the output of BPF inside 3-dB coupler. A photodiode detects the interfered signal and the beat frequency can be determined to achieve a high-resolution. To examine the proposed method, the scheme for temperature sensing is investigated. The Fabry-Perot narrow-bandpass filter type (F7 glass) serve as BPF. The results reveal that a good and fast response to temperature change with the sensitivity of 1.152 GHz/ oC can be obtained.