High-Speed Interrogation System for Fiber Bragg Gratings With Buffered Fourier Domain Mode-Locked Laser

Abstract

We develop a high-speed interrogation system with a wavelength-swept laser for sensing multiplexed fiber Bragg gratings (FBGs). High-speed and multipoint sensing is achieved by means of a buffered Fourier domain mode-locked (FDML) laser, a recently proposed high-speed wavelength-swept laser. This laser increases the measurement rate several times by tailoring the laser output with a buffer stage. The developed buffered FDML laser successfully achieves a measurement rate of 202.8 kHz using a general FDML laser driven at a sweep rate of 50.7 kHz. In order to detect reflection signals of FBGs at the high measurement rate, the measurement system introduces digital signal processing using a field programmable gate array (FPGA). However, FBG measurements with wavelength-swept lasers are affected by the propagation time (delay) in the optical fiber connecting from the laser to the FBG sensor, which reduces measurement accuracy. To overcome this limitation, the developed system uses a delay correction method with bidirectional sweep of the buffered FDML laser. The interrogation system with the buffered FDML laser achieves a time resolution of 4.9 µs without being affected by the delay.

Real-Time Spectroscopy System for Continuous Measurement With Fourier-Domain Mode-Locked Laser at 1550 nm

“…To measure the wavelength sweep characteristics of the light extracted by the FSW, an experiment was carried out using a wavelength monitor (FB200, ANDO) [12], [14]. Fig.…”

“…1 shows a real-time spectroscopy system for continuous highspeed measurements using an FDML laser. The FDML laser uses an oscillator (OSC1, 33612A, Agilent) to operate at a sweep rate f m of 50 kHz [12], [14]. The output light of the FDML laser was injected into a fiber optical switch (FSW).…”

“…Measurements made using near-infrared lasers, such as microelectromechanical system-tunable vertical-cavity surface-emitting lasers, supercontinuum light sources, optical frequency combs, and wavelengthswept lasers, have been reported [7]- [10]. Several studies have focused on high-speed measurements obtained using a Fourier-domain mode-locked (FDML) laser, which is a type of wavelength-swept laser [11]- [14]. For spectroscopic measurements using an FDML laser, the time resolution is determined by the sweep rate of the laser [10].…”

Real-time measurement system for overlapping reflection signals of fiber Bragg gratings using high-speed wavelength-swept laser

“…32 To measure FBGs installed at a short distance, we have used a two-buffered FDML laser at a measurement rate of 202.8 kHz. 33 However, measurements using high-speed wavelength-swept lasers are affected by the propagation time (delay) of the optical fiber that relays the measurement system and FBG. In fact, the delay reduces the measurement accuracy of FBGs.…”

“…Thus, delay compensation has been developed using optical frequency combs, 34 fiber Fabry-Perot (FFP) etalons, 35 and bidirectional laser scanning. 33,36 On the other hand, for distant FBGs, their reflection signals are folded back within the laser sweep period, hindering their identification. Methods for modulation of the laser sweep frequency 37 and pulse modulation of the laser swept light 38 have been reported for identification.…”