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Register a new userUltrahigh-Resolution Fiber-Optic Sensing Using a High-Finesse, Meter-Long Fiber Fabry-Perot Resonator
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Added by
Nabil Md Rakinul Hoque
Publication date
2019
fields
Physics
and research's language is
English
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Ultrahigh-resolution fiber-optic sensing has been demonstrated with a meter-long, high-finesse fiber Fabry-Perot interferometer (FFPI). The main technical challenge of large, environment-induced resonance frequency drift is addressed by locking the interrogation laser to a similar meter-long FFPI, which, along with the FFPI sensor, is thermally and mechanically isolated from the ambient. A nominal, noise-limited strain resolution of 800 f{epsilon} /sqrt(Hz) has been achieved within 1 to 100 Hz. Strain resolution further improves to 75 f{epsilon} /sqrt(Hz) at 1 kHz, 60 f{epsilon} /sqrt(Hz) at 2 kHz and 40 f{epsilon} /sqrt(Hz) at 23 kHz, demonstrating comparable or even better resolutions than proven techniques such as {pi}-phase-shifted and slow-light fiber Bragg gratings. Limitations of the current system are analyzed and improvement strategies are presented. The work lays out a feasible path toward ultrahigh-resolution fiber-optic sensing based on long FFPIs.
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Fiber-based optical microcavities exhibit high quality factor and low mode volume resonances that make them attractive for coupling light to individual atoms or other microscopic systems. Moreover, their low mass should lead to excellent mechanical response up to high frequencies, opening the possibility for high bandwidth stabilization of the cavity length. Here, we demonstrate a locking bandwidth of 44 kHz achieved using a simple, compact design that exploits these properties. Owing to the simplicity of fiber feedthroughs and lack of free-space alignment, this design is inherently compatible with vacuum and cryogenic environments. We measure the transfer function of the feedback circuit (closed-loop) and the cavity mount itself (open-loop), which, combined with simulations of the mechanical response of our device, provide insight into underlying limitations of the design as well as further improvements that can be made.
An all-fiber, micro-pulse and eye-safe high spectral resolution wind lidar (HSRWL) at 1550nm is proposed and demonstrated by using a pair of upconversion single-photon detectors and a fiber Fabry-Perot scanning interferometer (FFP-SI). In order to improve the optical detection efficiency, both the transmission spectrum and the reflection spectrum of the FFP-SI are used for spectral analyses of the aerosol backscatter and the reference laser pulse. The reference signal is tapped from the outgoing laser and served as a zero velocity indicator. The Doppler shift is retrieved from a frequency response function Q, which is defined as the ratio of difference of the transmitted signal and the reflected signal to their sum. Taking advantages of high signal-to-noise ratio of the detectors and high spectral resolution of the FFP-SI, the Q spectra of the aerosol backscatter are reconstructed along the line-of-sight (LOS) of the telescope. By applying a least squares fit procedure to the measured Q spectra, the center frequencies and the bandwidths are obtained simultaneously. And then the Doppler shifts are determined relative to the center frequency of the reference signal. To eliminate the influence of temperature fluctuations on the FFP-SI, the FFP-SI is cased in a chamber with temperature stability of 0.001 during the measurement. Continuous LOS wind observations are carried out on two days at Hefei (31.843 N, 117.265 E), China. In the meantime, LOS wind measurements from the HSRWL show good agreement with the results from an ultrasonic wind sensor (Vaisala windcap WMT52). Due to the computational expensive of the convolution operation of the Q function, an empirical method is adopted to evaluate the quality of the measurements. The standard deviation of the wind speed is 0.76 m/s at the 1.8 km. The standard deviation of the retrieved bandwidth variation is 2.07 MHz at the 1.8 km.
We build a resonant fiber optic gyro based on Kagome hollow-core fiber. A semi-bulk cavity architecture based on a 18-m-long Kagome fiber permits to achieve a cavity finesse of 23 with a resonance linewidth of 700 kHz. An optimized Pound-Drever-Hall servo-locking scheme is used to probe the cavity in reflection. Closed-loop operation of the gyroscope permits to reach an angular random walk as small as 0.004$^circ/sqrt{mathrm{h}}$ and a bias stability of 0.45$^circ$/h over 0.5 s of integration time.
A high-finesse Fabry-Perot cavity with a frequency-doubled continuous wave green laser (532~nm) has been built and installed in Hall A of Jefferson Lab for high precision Compton polarimetry. The infrared (1064~nm) beam from a ytterbium-doped fiber amplifier seeded by a Nd:YAG nonplanar ring oscillator laser is frequency doubled in a single-pass periodically poled MgO:LiNbO$_{3}$ crystal. The maximum achieved green power at 5 W IR pump power is 1.74 W with a total conversion efficiency of 34.8%. The green beam is injected into the optical resonant cavity and enhanced up to 3.7~kW with a corresponding enhancement of 3800. The polarization transfer function has been measured in order to determine the intra-cavity circular laser polarization within a measurement uncertainty of 0.7%. The PREx experiment at Jefferson Lab used this system for the first time and achieved 1.0% precision in polarization measurements of an electron beam with energy and current of 1.0~GeV and 50~$mu$A.
We report long-term laser frequency stabilization using only the target laser and a pair of 5 m fiber interferometers, one as a frequency reference and the second as a sensitive thermometer to stabilize the frequency reference. When used to stabilize a distributed feedback laser at 795 nm, the frequency Allan deviation at 1000 s drops from 5.6*10^{-8} to 6.9*10^{-10}. The performance equals that of an offset lock employing a second, atom-stabilized laser in the temperature control.
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