Abstract
The study is aimed at selecting low-cost semiconductor laser emitters for fiber-optic sensors of systems that monitor the technical condition of mine workings, open pits and monolithic building structures. One specimen of each of the three commercial red laser emitters used in visual fault locators, Guangyan, YJ-550C and KFL-11M, with a rated power of 50 mW and a rated wavelength of 630 nm, was investigated. The optical power was recorded every 10 min during 240 min of continuous operation after a one-hour warm-up. The optical frequency was measured by heterodyning with the iodine-stabilized He–Ne laser of the national primary standard of length of the Republic of Kazakhstan, with a Renishaw XL-80 laser as a reference. The optical power decreased by 13.4%, 6.9% and 11.9%. The standard deviation of the optical frequency was 2.15, 10.78 and 1.17 MHz against 0.029 MHz for the reference laser, and the Allan deviation at 0.25 s was 43 to 132 times worse. Abrupt beat-frequency jumps were observed for the Guangyan and KFL-11M emitters. Among the tested specimens, YJ-550C showed the highest power stability and is preferable for intensity-based quasi-distributed sensors provided that a reference channel is used, whereas use in interferometric schemes must be assessed against the optical path difference and the allowable error.