Fiber distributed-feedback lasers used as acoustic sensors in air

Abstract

Contributions to the acoustic signal sensitivity of fiber distributed-feedback (DFB) lasers in air are investigated both theoretically and experimentally. The theoretical results show that the dominant contribution to the laser frequency shift comes from adiabatic temperature shifts in the surrounding air at lower frequencies and from pressure at higher frequencies. The transition frequency was found to be between 5 and 20 kHz, depending on the elastic boundary conditions of the fiber laser. The acoustically induced frequency shifts of two fiber DFB lasers were measured, and the sensitivities varied from 0.61 MHz/Pa at a 100-Hz acoustic frequency to 0.34 kHz/Pa at a 15-kHz acoustic frequency.

Frequency and Intensity Noise of Single Frequency Fiber Bragg Grating Lasers

“…The experiments show noise floors that are similar in shape to the theoretical prediction, but 1-3 dB above the theoretical predictions. On the other hand, the thermooptic coefficient of silica fibers generally accepted elsewhere in literature δn/ nδT + δε/δT ≈ 5 2 × 10 −6 K −1 [9,25] is about a factor of two smaller than the value used in [27,28]. [9,25] Numerical integration of T 2 rms f as expressed in (34) produces a value that is a factor of two smaller than the right-hand side of Eq.…”

“…Frequency noise densities that are believed to be dominated by spontaneous emission seeding (25) for f 3 kHz have been reported for a L c = 19 mm DBR single frequency fiber laser with relatively high cavity losses a rt M ∼ 0 05 [24].…”

“…The sensitivity of a fiber DFB laser to acoustical vibrations in air has been studied both theoretically and experimentally in [25] and was found to range from about 600 kHz/Pa at f = 100 Hz to about 2 kHz/Pa at f = 7 kHz. For instance, 60 dBA (200 µPa) acoustical noise at f = 100 Hz will cause a laser frequency noise amplitude of ν rms = 12 kHz.…”

High-temperature-resistant distributed Bragg reflector fiber laser written in Er/Yb co-doped fiber

“…Depending on the operation principle, fiber grating laser sensors are classified into two categories, namely wavelength encoding sensor and polarimetric sensor. The former converts a measurrand into a corresponding change in the operation wavelength of the laser [1,2], which is similar to that of the fiber grating sensors. The polarimetric sensor requires the fiber grating laser to operate in two orthogonal polarization modes and converts a measurrand into a corresponding change in the beat frequency generated by the two polarization modes of the laser [3,4].…”

Ultrasonic hydrophone based on distributed Bragg reflector fiber laser

“…Although acoustic sensors based on fiber grating laser were reported in [9] and [10], their operation principle is similar to that of the fiber grating hydrophone. Instead of modulating the relatively broad reflection signal (typically 0.2 nm) of the fiber gratings, acoustic pressure modulates the higher power and much narrower linewidth of the output of the fiber lasers.…”