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.
Highlights
The good performance of fiber Bragg grating (FBG) sensors makes them useful in different environments and applications [1,2]
Electro-optic dual optical frequency comb (OFC) have been recently applied in spectroscopy to implemented in different instrumentation and measurement fields, as it allows for direct mapping of obtain compact and frequency portable signals systems forThe field applications
The new interrogation method proposed here take advantage of the dual-OFCs (DOFCs) to make smart use of the optical spectrum, exploiting its versatility and agile frequency configuration make smart use of the optical spectrum, exploiting its versatility and agile frequency configuration capabilities in order to enhance the sensitivity of a FBG sensor
Summary
The good performance of fiber Bragg grating (FBG) sensors makes them useful in different environments and applications [1,2]. Electro-optic dual OFCs have been recently applied in spectroscopy to implemented in different instrumentation and measurement fields, as it allows for direct mapping of obtain compact and frequency portable signals systems forThe field applications [12], as they provide optical more frequencies into radio [10]. Incorporation of dual-optical frequency combcoherent broadband sources with higher power per line and independent control of line spacing and comb techniques would allow for the detection of small changes in the spectrum of FBGs with a large bandwidth. They offer flexible and optimized sources for theapplied interrogation of other to sensors, dynamic range [11]. Measurements of vibrations and ultrasounds are demonstrated with this sensing system
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