We constructed a temperature-controlled Fourier domain mode locking (TC-FDML) laser capable of high-speed wavelength sweeping and developed a real-time fiber Bragg grating (FBG) measurement system. The TC-FDML laser can perform high-speed wavelength sweeping at a sweep frequency of 50.7 kHz with a scan range of ∼60 nm in the 1.55-μm band. This system uses a data acquisition system mounting an analog/digital converter and field programmable gate array that enables real-time FBG measurement at a sampling frequency of 250 MHz. Using bidirectional wavelength sweeping by the TC-FDML laser, the system has a measurement time resolution of 9.9 μs. We show that the developed system can measure high-speed vibrations of several kHz and perform simultaneous and continuous measurements of multiple FBGs for a period of one hour.
We developed a high-speed wavelength-swept laser prototype using Fourier domain mode locking (FDML) and a reflection wavelength measuring system that could rapidly measure a fiber Bragg grating (FBG). The prototype FDML laser incorporated a temperature-controlled optical tunable filter and had a sweep bandwidth of 40 nm in the 1.55 μm wavelength band. This system was able to perform high-speed wavelength sweeping with a sweep frequency of 50.7 kHz and had a temporal resolution of 9.9 μs, which was equivalent to half of the laser’s sweep cycle, due to the FDML laser’s bidirectional swept-wavelength. In this paper, we report on high-speed vibration measurements of several kHz by this system using FBGs.
The purpose of this research is the development of a system for fabricating high-speed and long-time measurements of wide-band vibration using fiber Bragg gratings (FBGs) to determine the health of structures. We developed a real-time FBG interrogation system using wavelength swept laser. This system can perform real-time measurement of reflected wavelength from a multiple FBG at a temporal resolution of 0.1 ms. The authors also constructed a database system for managing the data obtained from high-speed and long-time measurement. This database system manages data using a relational database and transfers information on FBG reflected wavelengths obtained from this measurement system via the local network. We have demonstrated that this system is able to measure reflected wavelengths from a multipoint FBG at a temporal resolution of 0.1 ms over 24 hours, it was shown that this system could also monitor instantaneously applied high-speed vibrations.
The objective of this research is the construction of a structural health monitoring system that uses fiber Bragg grating (FBG) to determine the health of structures. We develop fast FBG interrogator for real-time measurement of the reflected wavelength of a multipoint FBG to monitor the broadband vibration of a structure. This FBG interrogator, which combines a wavelength-swept laser and a real-time measurement system is capable of measuring wavelength within a standard deviation of 2×10<sup>-3</sup> nm or less. We have demonstrated that the FBG interrogator is able to measure vibration that has a resonance frequency of 440 Hz at intervals of 0.1 ms with a multipoint FBG.