FBG wavelength demodulation based on a radio frequency optical true time delay method

Abstract

A new fiber Bragg grating (FBG) wavelength shift demodulation method based on optical true time delay microwave phase detection is proposed. We used a microwave photonic link (MPL) to transport a radio frequency (RF) signal over a dispersion compensation fiber (DCF). The wavelength shift of the FBG will cause the time delay change of the optical carrier that propagates in an optical fiber with chromatic dispersion, which will result in the variation of the RF signal phase. A long DCF was adopted to enlarge the RF signal phase variation. An IQ mixer was used to measure the RF phase variation of the RF signal propagating in the MPL, and the wavelength shift of the FBG can be obtained by the measured RF signal phase variation. The experimental results showed that the wavelength shift measurement resolution is 2 pm when the group velocity dispersion of the DCF is 79.5 ps/nm and the frequency of the RF signal is 18 GHz. The demodulation time is as short as 0.1 ms. The measurement resolution can be improved simply by using a higher frequency of the RF signal and a longer DCF or larger chromatic dispersion value of the DCF.

Coupled optoelectronic oscillator based strain sensor with extended measurement range

“…With the development of microwave photonics (MWP) technology, the interrogation scheme of optical fiber sensor using MWP has attracted wide attention [15,16] . The basic principle of the MWP-based interrogation method is mapping the optical change to the change of the electrical signal, such as the change of the frequency transmission response of the microwave photonics link [15] , intensity change [17] or phase shift [18] of the microwave signals [19] . Optoelectronic oscillator (OEO) can produce high-frequency microwave signals with high spectral purity, high stability and low phase noise.…”