We show that 1-°C drift of laser temperature yields a strain error of ~8 με in Brillouin optical correlation-domain reflectometry. Under the assumption that the strain measurement accuracy is +/-20 με (severe requirement), +/-2.5-°C drift of the laser temperature can be permitted for proper system operation. We prove this prediction by performing distributed strain measurements at different laser temperatures. Our results indicate that, if we allow a strain measurement accuracy of approximately +/-100 με (or more), we can even remove the thermal control of the laser, leading to cost reduction and downsizing of the system. Distributed strain and temperature sensors are key tools for monitoring the conditions of various civil infrastructures. In particular, distributed sensing techniques based on Brillouin scattering in optical fibers have been the focus of attention because of their ability to detect sub-centimeter strained or heated sections along long optical fibers. 1) Based on the configurations of light injection to sensing fibers, Brillouin sensors can be divided into twoend-access "analysis" and one-end-access "reflectometry". The former includes Brillouin optical time-, frequency-, and correlation-domain analysis (BOTDA, 2-5) BOFDA, [6][7][8] and BOCDA), [9][10][11][12][13] whereas the latter includes Brillouin optical time-, frequency-, and correlationdomain reflectometry (BOTDR, [14][15][16] BOFDR,17) and BOCDR). [18][19][20][21][22][23][24][25] In general, analysis systems exhibit higher signal-to-noise ratios (SNRs) due to the use of stimulated Brillouin scattering. However, despite their lower SNRs, reflectometers based on spontaneous Brillouin scattering have higher degrees of freedom in embedding the sensing fibers into structures; in addition, measurements can be continued even when the sensing fibers are broken. Needless to say, each reflectometry has its own merits and demerits, and here, we focus on BOCDR.

We demonstrate that fiber Bragg gratings in polymer optical fibers can lead to reflection peaks in any wavelength range when exciting high-order propagation modes, which can enhance the design of sensing systems for specific applications.

We show that 1-°C drift of laser temperature yields strain error of ~8 με in Brillouin optical correlation-domain reflectometry. We do not require laser thermal control, leading to cost reduction and downsizing of the system.