Elliptical-core Polarization-maintaining Fiber Research Articles

Bow-tie holes-aided elliptical-core polarization-maintaining fiber with high birefringence

We present a Bow-tie holes-aided elliptical-core polarization-maintaining fiber (PMF) comprised of an outer elliptical-core, with three circular holes of silica material inside it, and two symmetrical Bow-tie stress-applying parts (SAPs), creating a fiber with a superior polarization-maintaining ability by superimposing geometric birefringence on the stress birefringence. The overall modal birefringence of this exceptional fiber design is capable of as high as 8.54 × 10-4 at a wavelength of 1.55 µm, corresponding to an almost onefold increase compared to a conventional Panda-type PMF. The other significant attribute of the PMF, effective mode area, is also evaluated comprehensively over wavelengths ranging from 1.25 µm to 2.05 µm. Furthermore, we also discuss the sensitivity of the modal properties to fluctuations in the structural parameters of the fiber during the fabrication process to demonstrate that the design has excellent tolerance to deviations in practical fabrication. In summary, the PMF with fine modal properties proposed in this study is a promising candidate for widespread use in high-precision fiber-optic sensors and fiber communication systems.

Helical Long Period Fiber Grating Inscribed in Elliptical Core Polarization-Maintaining Fiber

A high-quality helical long period fiber grating (HLPFG) in elliptical core polarization-maintaining fiber (PMF) was experimentally demonstrated by using the hydrogen-oxygen flame heating technique. Such a single HLPFG with a length of 6.5 mm could be used to generate orbital angular momentum (OAM) modes, i.e., OAM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">±2</sub> . The secret of the successful generation of the OAM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">±2</sub> mode is that the elliptical core PMF has two-fold symmetry in the cross-section. The resonance dip of the coupling attenuation and wavelength was strongly dependent on the length and helical pitch of the HLPFG. The HLPFG also exhibited a higher strain sensitivity of 30.7 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> . The proposed method opens a new way to generate a higher-order OAM mode by using multiple-fold symmetry fiber.

Group-Birefringence-Dispersion Measurements for Polarization-Maintaining Fibers Using a Kerr Phase-Interrogator

A method which utilizes a Kerr phase-interrogator to measure the group birefringence dispersion (GBD) of a polarization-maintaining fiber (PMF) is systematically studied in this paper. The differential group delay of two sinusoidally modulated optical signals (SMOSs) polarized along the principal axes of the PMF is measured by a Kerr phase-interrogator, which leads to the group birefringence of the PMF. As the laser wavelength of the SMOSs varies, the group birefringence as a function of the laser wavelength is obtained, and the GBD is calculated as the derivative of the group birefringence with respect to the laser wavelength. The proposed method is experimentally demonstrated by characterizations of a Panda PMF with high GBD and an elliptical core PMF with low GBD, and its performance is analyzed. The proposed method eliminates the impact of the laser coherent length and allows for characterizing the GBD of PMFs that are tens of kilometers long.

Ultra-sensitive high temperature sensor based on a PMPCF tip cascaded with an ECPMF Sagnac loop

We propose a sensitivity magnified polarization maintaining photonic crystal fiber (PMPCF) Fabry-Perot probe cascaded with a Sagnac loop (SL) for high temperature measurement (up to 1000 °C). The Fabry-Perot interferometer (FPI) fabricated by fusion splicing a PMPCF tip with a single mode fiber works as a sensing interferometer. The cascaded SL consisting of a temperature insensitive elliptical core polarization maintaining fiber (ECPMF) is applied as a reference interferometer. The free spectral range of the SL is easily tailored by adjusting the ECPMF length, making it similar to that of the sensing FPI, to generate Vernier effect. Experimental results show that the temperature sensitivity of the single FPI is 13.71 pm/°C, and the sensitivities of cascaded FPI-SLs are 143.52 pm/°C, 418.7 pm/°C and 1.15 nm/°C. The measured magnification factors are about 10, 35 and 91, which are consistent with theoretical results. The linearity of temperature response is 99.94 % from room temperature to 1000 °C. The proposed ultra-sensitive sensor has promising prospects for high temperature measurement.

Temperature-strain discrimination in distributed optical fiber sensing using phase-sensitive optical time-domain reflectometry.

A method based on coherent Rayleigh scattering distinctly evaluating temperature and strain is proposed and experimentally demonstrated for distributed optical fiber sensing. Combining conventional phase-sensitive optical time-domain domain reflectometry (ϕOTDR) and ϕOTDR-based birefringence measurements, independent distributed temperature and strain profiles are obtained along a polarization-maintaining fiber. A theoretical analysis, supported by experimental data, indicates that the proposed system for temperature-strain discrimination is intrinsically better conditioned than an equivalent existing approach that combines classical Brillouin sensing with Brillouin dynamic gratings. This is due to the higher sensitivity of coherent Rayleigh scatting compared to Brillouin scattering, thus offering better performance and lower temperature-strain uncertainties in the discrimination. Compared to the Brillouin-based approach, the ϕOTDR-based system here proposed requires access to only one fiber-end, and a much simpler experimental layout. Experimental results validate the full discrimination of temperature and strain along a 100 m-long elliptical-core polarization-maintaining fiber with measurement uncertainties of ~40 mK and ~0.5 με, respectively. These values agree very well with the theoretically expected measurand resolutions.

High-sensitivity distributed transverse load sensor with an elliptical-core fiber based on Brillouin dynamic gratings.

A high-sensitivity distributed transverse load sensor based on Brillouin dynamic gratings (BDGs) is proposed and demonstrated experimentally for the first time, to the best of our knowledge. The principle is to measure the transverse-load-induced birefringence change through exciting and probing a BDG in an elliptical-core polarization-maintaining fiber. A distributed measurement of transverse load is demonstrated experimentally using a 10 m sensing fiber, which features high sensitivity to a transverse load with a measurement accuracy as high as 0.8×10(-3) N/mm at a 20 cm spatial resolution.

基于椭圆芯保偏光纤模间干涉的光学电压互感器

基于椭圆芯保偏光纤模间干涉的光学电压互感器

Intermodal beat lengths in birefringent two-mode fibers

We use an accousto-opitc method to measure the beat lengths between the LP(01) and the LP(11) modes propagating both in an elliptical-core polarization-maintaining fiber and in a bow-tie high-birefringence (Hi-Bi) fiber for a wide range of optical wavelengths. The Hi-Bi fiber exhibits considerable polarization splitting in the measured beat lengths at all measured wavelengths. According to theory for circular-core fibers, the beat length should have a minimum at the wavelength at which the two modes have the same group velocity in the fiber. We find that for the elliptical-core fiber such a minimum does not exist in the two-mode region. Based on our measurements we discuss the use of different fiber types in various two-mode devices.