Fast Interrogation of Fiber Bragg Gratings with Electro-Optical Dual Optical Frequency Combs

Abstract

Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized sources for the interrogation of other sensors based on wavelength change or wavelength filtering, such as fiber Bragg grating (FBG) sensors. In this paper, a dual-OFC FBG interrogation system based on a single laser and two optical-phase modulators is presented. This architecture allows for the configuration of multimode optical source parameters such as the number of modes and their position within the reflected spectrum of the FBG. A direct read-out is obtained by mapping the optical spectrum onto the radio-frequency spectrum output of the dual-comb. This interrogation scheme is proposed for measuring fast phenomena such as vibrations and ultrasounds. Results are presented for dual-comb operation under optimized control. The optical modes are mapped onto detectable tones that are multiples of 0.5 MHz around a center radiofrequency tone (40 MHz). Measurements of ultrasounds (40 kHz and 120 kHz) are demonstrated with this sensing system. Ultrasounds induce dynamic strain onto the fiber, which generates changes in the reflected Bragg wavelength and, hence, modulates the amplitude of the OFC modes within the reflected spectrum. The amplitude modulation of two counterphase tones is detected to obtain a differential measurement proportional to the ultrasound signal.

Fiber Bragg grating sensors for monitoring of physical parameters: a comprehensive review

“…Active interrogation method involves comparatively more complex system than passive interrogators but gives better resolution. Many researchers have worked on various active interrogation methods such as using Fourier-domain mode locked laser fiber, 49 optical frequency comb, 50 Fabry-Perot filter, 51 and acousto-optic tunable filter. 52…”

A Fiber Bragg Grating Interrogation System with Self-Adaption Threshold Peak Detection Algorithm

“…The measured wavelength resolution could reach typically 0.5 pm for an interrogation system with four channels. Posada-Roman proposed a fast interrogator based on electro-optical dual optical frequency combs [ 25 ], which improved the minimum detectable ultrasound amplitude of the system to 50 . On-chip silicon photonic integration is a promising means to produce an integrated on-chip fiber Bragg grating (FBG) interrogator.…”

Electro-optic dual-comb interferometer for high-speed vibrometry

“…DCS has made significant contributions in other metrology applications beyond the realm of spectroscopy, such as laser ranging [6][7][8], vibrometry [9,10], optical arbitrary waveform characterization [11,12] or coherent Raman spectral imaging [13]. For measuring distances, DCS stands out due to its unique combination of high precision and large unambiguity range.…”

“…The analysis of the frequency modulated signal generated through this effect leads to a measure of the time-dependent velocity of the target and its vibration amplitude. An EO-DCS can alternatively be combined with a fiber-based sensor to read distributed vibrations [10]. Notwithstanding, the optical phase coherence of the DCS is not fully exploited in these two examples.…”