Helical-core fibers have been widely utilized for various applications such as orbital angular momentum manipulation, optical filtering, and sensing. In this work, we demonstrate the sensitivity enhancement of a helical-core fiber by tailoring the resonance wavelength towards the dispersion turning point (DTP) utilizing a post chemical etching process. When the sensor works at different dispersion points, the responses of the device on external parameters, including mechanical torsion, temperature, strain, and external refractive index are investigated and compared. Tailoring the resonance wavelength of the helical-core fiber towards the dispersion turning point in the post chemical etching process significantly enhances the sensitivity to various kinds of parameters, which provides an avenue for modifying and optimizing performances of optical devices.
A fiber-optic Doppler velocimeter based on a dual-polarization fiber grating laser is demonstrated. The fiber grating laser produces two orthogonally polarized laser outputs with their frequency difference proportional to the intra-cavity birefringence. When the laser outputs are reflected from a moving targets, the laser frequencies will be shifted due to the Doppler effect. It shows that the frequency difference between the beat note of the laser outputs and the beat note of the reflected lasers is proportional to the velocity. The proposed fiber-optic Doppler velocimeter shows a high sensitivity of 0.64 MHz/m/s and is capable of measurement of wide range of velocity.
The beat frequency dependence of the sensitivity for a Faraday-rotation based heterodyning fiber laser magnetic field sensor is studied, which shows that lower beat frequency results in higher sensitivity. By lowering the beat frequency to 2 MHz, the maximum sensitivity of about 43 Hz/μT to magnetic field has been achieved for a heterodyning fiber laser inscribed on an Erbium doped fiber. It also shows that the beat frequency is dependent on the polarization of the 980 nm pump. Therefore, dynamical tuning of the sensitivity optically has also been demonstrated by tuning the polarization of the 980 nm pump.
We investigate the spectral characteristics of Brillouin scattering in micro-scaled silica fibers with diameter of ~2μm. A multiple-peak structure in contrast to the conventional counterparts is observed. The measured temperature and strain sensitivities are ~0.8MHz/°C and ~0.05MHz/με, respectively, corresponding to a fiber diameter of 2.01μm. A comparison with the conventional single-mode fiber is made in our manuscript.
The noise performance of the beat note generated by a dual-polarization fiber grating laser is very critical for sensing applications. To reduce the noise of the beat note, external optical feedback is employed with a fiber Bragg grating as a reflector. It then shows that a longer feedback time results in larger noise reduction. With a 50 m single mode fiber as the delay line, more than 20 dB phase noise reduction has been achieved for a dual-polarization fiber grating laser which shows a phase noise of -92 dBc/Hz @ 10 kHz offset with external optical feedback applied.
We carried out distributed measurements of the parametric Brillouin gain using a sensing technique based on an
Brillouin optical time-domain analysis. Using this distributed technique, we study the influence of the polarization mode
dispersion (PMD) of the single mode fiber (SMF) to the Brillouin parametric gain spectrum. It is found that the shape of
the obtained spectrum depend on the local birefringence of the fiber.
This paper gives an experimental study on Brillouin scattering property in an all solid photonics bandgap fiber (ASPBGF) using tapering technique. There are four Brillouin resonance peaks, one from the pure silica core and three from microstructure cladding of the AS-PBGF. We report Brillouin frequency shift and linewidth of the fiber. Because these four peaks show the different temperature and strain dependence, the simultaneous measurement of temperature and strain can be achieved.
The Brillouin scattering spectrum of a photonic crystal fiber was measured experimentally by core-offset splicing to a
single mode fiber. One main peak and five sub-peaks due to Brillouin scattering were identified and their frequency and
intensity dependences on strain and temperature were investigated in detail. Besides the frequency shift, the intensity of
the Brillouin scattering was also found to vary with strain and temperature changes. It is then expected to solve the
problem of cross sensitivity in the conventional single-mode fibers.
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