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.

We propose an interrogation-system with automatic recognition and delay correction functions of fiber Bragg gratings (FBGs) by pulse modulation with a wavelength-swept laser. By pulse-modulating the light of a wavelength-swept laser, light with an arbitrary wavelength bandwidth can be extracted as the pulsed light. In the automatic recognition function of FBGs, the pulsed light is sequentially controlled to match the wavelength bandwidth of each FBG. This recognition method enables the selection and detection of a reflection signal from a single FBG. Therefore, reflection signals from multiple FBGs can be recognized individually. When multiple FBGs are installed at long distances, the reflection signal of each FBG is affected by the propagation time (delay). In the interrogation system with the wavelength-swept laser, the delay lowers the measurement accuracy. Therefore, a delay correction function using bidirectional sweeping of the wavelength-swept laser is used. The wavelength-swept laser using Fourier domain mode locking (FDML) is driven at a sweep frequency of 50.7 kHz with a sweep bandwidth of ∼60 nm. This study demonstrates that pulse-modulated FDML laser can automatically recognize reflection signals from multiple FBGs installed at arbitrary long distances. When the recognition process is complete, the interrogation system can perform real-time measurement with a time resolution of 9.9 µs, without being affected by delay that occurs when installing at a long distance.

We developed a real-time spectroscopy system for continuous measurement using a Fourier-domain modelocked (FDML) laser. The FDML laser was driven at a sweep rate of 50 kHz in the near-infrared region of 1550 nm. To achieve robust real-time measurement, the spectroscopy system properly designs the pulse modulation of the FDML laser and the length of the reference optical path. The intensity fluctuation of the FDML laser was corrected by introducing a reference optical path. We demonstrated that the spectroscopy system performs continuous measurements for 1 min or more with a time resolution of 20 μs.