Rapid-aging civil infrastructures have become social issues worldwide. Developed countries have faced difficulties e.g. cost increase in infrastructure maintenance, shortage of highly-skilled human resources. Thereafter, infrastructures have been inspected infrequently e.g. every 1~10 year. 3D mapping powered by light detection and ranging (LiDAR) platforms has recently been brought to public attention. In infrastructure maintenance, LiDAR having high-precision and long-measurement range is expected to enhance inspection frequencies and lower the maintenance cost. Time-of-flight (ToF) approach is generally utilized for long-range measurement, however it suffers from low depth resolution. Although development of dual-comb interferometry enabled high-precision ToF rangefinders, sophisticated stabilization is required for two lasers. On the other hand, frequency-modulated continuous-wave (FMCW) LiDAR can perform ranging with a single laser. However, its measurement range is limited by its receiver bandwidth. Although FMCW LiDAR with low-speed analog-to-digital converters can conduct long-distance ranging by reducing its wavelength-sweeping rate, the measurement refresh rate is sacrificed. In this article, we propose a long-range FMCW LiDAR employing wavelength-swept optical frequency comb which overcomes ranging limitation caused by its receiver bandwidth. In addition, the spectrum of such optical frequency comb is apodised to circumvent its inherent ranging ambiguity. We have performed proof-of-concept experiments using the proposed LiDAR. With optical fibers for emulating beam propagation, we have succeeded in ranging corresponding to 1,605-m free-space propagation with a 10-MHz FMCW receiver. Our proposal will make an important contribution to infrastructure maintenance.
A novel Erbium-doped fiber laser sensor based on a sigma-type cavity configuration using a double-pass cascadedchirped long-period fiber grating (C-CLPG) as a reflective sensor section is proposed for a real-time displacement sensor, in which the double-pass C-CLPG is provided by returning the transmitted light of the C-CLPG with a Faraday rotator mirror (FRM) in the σ-branch of the cavity. The σ-branch with FRM-reflection realizes a compensation effect for the polarization fluctuations in the sensor section, a stable oscillation output during the sensing operation, and a suitable arrangement for remote sensing. In the experiment, we have successfully demonstrated a real-time displacement measurement based on bending characteristics of the C-CLPG, taking advantage of laser-type sensors.
In this article, we review various fiber diagnostic methods based on distributed sensing such as optical timedomain reflectometry, optical frequency-domain reflectometry etc., fiber characterization schemes employing digital coherent receivers and various interferometric approaches. We also go through multiple industrialized fiber diagnostic instruments provided by leading manufactures in the installation and maintenance market.
Conference Committee Involvement (1)
29th International Conference on Optical Fiber Sensors
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