Conventional Polarization-maintaining Fiber Research Articles

Performance analysis of the fiber coils combining hybrid polarization-maintaining fiber designs and symmetrical winding patterns.

Research on the performance of polarization-maintaining fiber (PMF) for fiber coils is significant for the precision improvement of an interferometric fiber optic gyroscope (IFOG) working in harsh environments. In this paper, we firstly report analytical models of the fiber polarization theory and present two types of hybrid PMF structures by a collaboration of geometry and stress effects: a Panda-type horizontal-elliptical core PMF (Panda-type HE-PMF) based on a superposition of geometry and stress, and a Panda-type longitudinal-elliptical core PMF (Panda-type LE-PMF) with geometry offset stress effect, achieving enhanced and suppressed modal performance by adjusting geometric anisotropy of elliptical-core in different directions. Then, the influence mechanisms of the geometric birefringence on the modal performance of both PMFs as the variation of fiber structural parameters are investigated via numerical simulations to determine the target fiber designs. The other significant attribute, including effective mode area (Aeff), nonlinear coefficient (γ), and chromatic dispersion (D), and their tolerance to PMF parameter fluctuations are also evaluated. Finally, both target PMFs with structural optimization are practically fabricated and wound into four fiber coils with quadrupolar (QAD) and 16-polar symmetrical winding patterns, respectively. The polarization ability and thermal performance are further demonstrated by experiments conducted on both PMFs, wound fiber coils, and built IFOGs under static and dynamic environments (over a wide temperature range of -40 °C to 70 °C), and compared with a conventional PMF. The testing results suggest that designed HE-PMF coils both achieve high birefringence, static extinction ratio (ER) values of up to 30.80 dB and 31.93 dB, respectively, corresponding to an almost one-fold increase over conventional coils. Remarkably, the ER property of the HE-PMF coil by combining this HE-PMF design and a 16-polar winding pattern consistently remains above 29.5 dB with a minimal fluctuation in ER of only 3.0 dB across the entire variable temperature conditions. The bias stability of the IFOG assembled with this coil is strongly enhanced to 0.0019 °/h and 0.082 °/h under static and dynamic conditions, respectively, which is a significant improvement over conventional coils of 0.136 °/h. Also, the static angle random walk performance of the improved IFOG is reduced to 0.000624 °/√h. In contrast, the LE-PMF as a comparison is shown to limited polarization characteristics with a low birefringence and ER due to the suppression effect of the geometric birefringence, and the applied IFOG output also exhibits larger drift, indicating a poor thermal ability. Experimental results show great agreement with theoretical analysis and numerical simulations, confirming the validity of design principles. The advances in both designs are instructive for the engineering applications of PMFs for IFOGs and for improving the accuracy of fiber sensors.

Retracted: Interferometric Air-Core Anti-Resonant Fiber Optic Gyroscope With Enhanced Thermal Stability

The use of a quadrupolar-wound coil of conjoined-tube anti-resonant fiber (CTF) in an interferometric air-core fiber optic gyroscope (FOG) is proposed and demonstrated. The CTF coil has low transmission loss and high modal purity, resulting in a long-term bias stability of 0.016 deg/h for the integration time of 1000 s. Furthermore, when compared to a gyro operated with conventional polarization-maintaining fiber (PMF) coil of the same length and diameter, the conjoined-tube anti-resonant fiber optic gyroscope (CTFOG) has an 11.2-fold reduction in thermal sensitivity, rendering the CTF a promising technological approach to efficiently improve the thermal stability of FOG in the future.

Sensitivity Improvement in Vernier-Effect Demodulation Based on Frequency Doubling of Sensing Spectrum

We propose that the sensitivity can be effectively improved by spatial-frequency doubling of the sensing signal before the signal processing assisted Vernier-effect demodulation via a single fiber interferometer, which has been proven to have the same effect as physically increasing the optical path difference (OPD) in an interferometer but keeps the sensor small in size and does not introduce any additional crosstalk and cost. In the proposed scheme, only one fiber interferometer is used for sensing. The sensing spectra are squared to double their spatial frequencies, and then, an artificial reference spectrum (ARS) is extracted from one of the squared spectra and multiplied by each squared spectrum to form the Vernier effect. To validate the principle, a widely used Sagnac interferometer (SI) with a conventional polarization-maintaining fiber (PMF) of only 10 cm in length is designed for temperature sensing. Significantly, by simply doubling the spatial frequency of the sensing signal, the magnification of Vernier effect is improved from 4.96 to 74.82, resulting in an ultrahigh sensitivity of 117.17 nm/°C.

Cascaded Sagnac Loops Embedded With Two Polarization Maintaining Photonic Crystal Fibers for Highly Sensitive Strain Measurement

A strain sensor based on cascaded Sagnac loops with two polarization-maintaining photonic crystal fibers (PMPCFs) has been experimentally demonstrated. Air holes distributed on the cross section of PMPCF go through the whole fiber, which makes the special fiber more sensitive to ambient force compared with conventional optical fiber. The lengths of the two PMPCFs are close, but not the same, to form envelopes on the total output spectrum and then obtain high resolution to the detected parameter by the Vernier effect. The influences of the difference in length of the two PMPCFS on spectral envelopes are discussed. As the length of the PMPCF in reference loop increases, free spectrum range of the cascaded Sagnac loops (or envelope period) and magnification decrease. The sensitivities of this strain sensor are calculated by tracking upper and lower envelopes. Results reveal that its average sensitivity is up to 45.15 pm/με and the corresponding resolution is 0.44 με as strain varies from 0 to 2000 με. Compared with a single Sagnac loop, the sensitivity magnification is about 28.94. The sensing characteristics of a conventional polarization-maintaining fiber (PMF) are studied to compare with the PMPCF. Moreover, reversibility has also been proved to possess low error rate. In short, the fiber strain sensor possesses high sensitivity and great reversibility.

Wavelength-Switchable Fiber Laser Based on Long-Period Fiber Grating Written on Polarization-Maintaining Photonic Crystal Fiber.

Here we propose a wavelength-switchable erbium-doped fiber ring laser using a temperatureinsensitive spectral polarization-dependent loss (PDL) element and two fiber Bragg gratings (FBGs). The fiber PDL element was fabricated by inscribing a long-period grating (LPG) on polarizationmaintaining photonic crystal fiber (PMPCF) with a 10.6 μm CO₂ laser. The LPG fabricated on PMPCF, referred to as PMPCF-LPG, has the characteristics of a fiber polarizer at two specific wavelengths due to the birefringence of PMPCF and the co-directional mode coupling of the LPG. The two wavelengths at which the fabricated PMPCF-LPG acts as a polarizer are two resonance wavelengths (~1528.58 and ~1555.90 nm) of the PMPCF-LPG, obtained for orthogonal input polarization states. By considering these two resonance wavelengths of the PMPCF-LPG, the Bragg wavelengths of two FBGs, which determine lasing wavelengths in our wavelength-switchable laser, were selected as ~1527.71 and ~1554.74 nm. As the temperature sensitivity of the PMPCF birefringence is 30 times lower than that of the birefringence of conventional polarization-maintaining fiber (PMF), the fabricated PMPCF-LPG could facilitate more stable switching operation between the two lasing wavelengths in comparison with a previous fiber laser employing an LPG inscribed on conventional PMF as a wavelength-switching filter. The lasing wavelengths of our laser could be switched by controlling input polarization of the PMPCF-LPG with a polarization controller, and temperature-insensitive wavelength switching operation was experimentally demonstrated over a temperature range of 25-100 °C.

Tunable and switchable triple-wavelength ytterbium-doped fiber ring laser based on Sagnac interferometer with a polarization-maintaining photonic crystal fiber

A tunable and switchable triple-wavelength ytterbium-doped fiber laser (YDFL) based on a polarization-maintaining photonic crystal fiber (PMPCF) Sagnac interferometer is proposed and experimentally demonstrated. Owing to the large inhomogeneity of gain profile and simple two-level system of ytterbium-doped fiber, a tunable triple-wavelength lasing output is achieved with a tuning range of 1.6 nm. At room temperature, the maximum wavelength shift and peak power fluctuation are less than 0.018 nm and 0.64 dB, respectively. Moreover, the output lasing can be switched to single-wavelength lasing or dual-wavelength lasing through adjusting polarization controller. A tunable single-wavelength lasing with the side-mode suppression ratio above 50 dB is achieved from the wavelength of 1034.276 nm to 1038.314 nm. Two kinds of tunable dual-wavelength lasing with the tuning range of 3.2 nm are obtained in our experiment. In addition, the temperature stability is discussed by constructing the YDFL with PMPCF and conventional polarization-maintaining fiber (PMF), respectively. Experimental results demonstrate that the measured temperature sensitivity for PMPCF-based YDFL is 0.014 nm/℃, which is five times lower than that for PMF-based YDFL.

Performance improvement of a resonant fiber optic gyroscope with a hybrid photonic crystal fiber ring resonator.

The photonic crystal fiber (PCF) with better thermal stability and polarization-maintaining performance is applied to the resonant fiber optic gyroscope (RFOG). A hybrid fiber ring resonator is fabricated using the conventional polarization-maintaining fiber (PMF) and PCF with close mode field diameters (MFDs) to reduce MFD-mismatch-induced splicing loss. Furthermore, the temperature-dependent birefringence coefficients of the PMF and the PCF are measured to differ almost four times in absolute value and be opposite in sign. The polarization stability of the hybrid PCF-PMF ring resonator is improved by a factor of 7 compared with the PMF ring resonator with the same length of PMF. The RFOG equipped with this hybrid PCF-PMF ring resonator achieves a bias stability of 1.67°/h.

A high-birefringent photonic quasi-crystal fiber with two elliptical air holes

A photonic quasi-crystal fiber (PQF) with high birefringence based on ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) is described. There are two elliptical air holes in the core to increase birefringence and the outer air hole array has a twelve-fold Stampfli-type quasi-crystal structure. ZBLAN reduces absorption loss in the infrared region resulting in higher birefringence. The birefringence and confinement loss of the PQF are analyzed numerically by the full-vector finite element method. Birefringence is higher than that of conventional polarization-maintaining fibers due to the two elliptical air holes in the center and reaches the maximum of 4.15×10−2 at a wavelength of 2 μm. The novel structure has great potential in high-performance optical devices.

Dodecagonal photonic quasi-crystal fiber with high birefringence.

A photonic quasi-crystal fiber (PQF) with high birefringence is proposed. A dodecagonal Stampfli quasi-periodic lattice of air holes constitutes the cladding of the PQF. The PQF maintains the properties of high birefringence and single-mode operation regime in a wide wavelength range from 1.2 to 2.0 μm by optimizing the size of the air holes around the core of the PQF. A birefringence with 3.86×10-2 can be obtained at 1.31 and 1.55 μm optical telecommunication windows. The birefringence is of the order of 10-2, which is two orders of magnitude larger than that of the conventional polarization-maintaining fibers and hardly affected by the incident wavelength. The proposed PQF also maintains a high nonlinear coefficient and low confinement loss. Our structure and simulation results are expected to provide a valuable reference and basic data to relative fabrication and experiments.

Distributed phase birefringence measurements based on polarization correlation in phase-sensitive optical time-domain reflectometers.

In this paper a technique to measure the distributed birefringence profile along optical fibers is proposed and experimentally validated. The method is based on the spectral correlation between two sets of orthogonally-polarized measurements acquired using a phase-sensitive optical time-domain reflectometer (ϕOTDR). The correlation between the two measured spectra gives a resonance (correlation) peak at a frequency detuning that is proportional to the local refractive index difference between the two orthogonal polarization axes of the fiber. In this way the method enables local phase birefringence measurements at any position along optical fibers, so that any longitudinal fluctuation can be precisely evaluated with metric spatial resolution. The method has been experimentally validated by measuring fibers with low and high birefringence, such as standard single-mode fibers as well as conventional polarization-maintaining fibers. The technique has potential applications in the characterization of optical fibers for telecommunications as well as in distributed optical fiber sensing.

Phase sensitivity to temperature of the guiding mode in polarization-maintaining photonic crystal fiber.

The propagating phase changing of a polarization-maintaining photonic crystal fiber (PM-PCF) caused by temperature variation is theoretically studied, as well as compared with conventional PANDA fiber. As to verifying numerical analysis, a platform based on a Michelson interferometer for phase versus temperature measurement was built for both kinds of fiber. Experiments show that PM-PCF has similar temperature sensitivity with conventional polarization-maintaining fiber. With optimized PM-PCF design (thinner coating layer and coating material with smaller thermal expansion coefficient), the sensitivity could be further reduced to about 80% of the present level.

짧은 센서부를 가진 편광유지 광자결정 광섬유 기반 편광 간섭형 스트레인 센서

In this paper we have implemented a temperature-insensitive polarimetric fiber strain sensor based on a Sagnac birefringence interferometer composed of a short polarization-maintaining photonic crystal fiber (PM-PCF), a 3-dB fiber coupler, and polarization controllers. The PM-PCF used as a sensor head was 2 cm long, which is the shortest length for a sensing element compared to other polarimetric fiber strain sensors using a PM-PCF. The proposed sensor showed a strain sensitivity of ~0.87 pm/μe with a strain measurement range from 0 to 8 me. The temperature sensitivity was also investigated and measured as approximately -12 pm/℃, when ambient temperature changed from 30 to 100℃. This temperature sensitivity is about 82 times smaller than that of conventional polarization-maintaining fiber (approximately -990 pm/℃). In particular, from a practical perspective we have experimentally and theoretically confirmed that the wavelength selected for the indicator dip location does not make a significant difference in the strain sensitivity.Keywords: Optical fiber sensor, Strain sensor, Polarization-maintaining photonic crytal fiber, Sagnac birefringence interferometerOCIS codes: (060.2370) Fiber optics sensors; (060.2420) Fibers, polarization-maintaining; (060.5295) Photonic crystal fibers; (350.2460) Filters, interference

Analysis of shupe effect in polarization-maintaining photonic crystal fiber-optic gyroscope

The Shupe effect in a fiber optical gyroscope with polarization-maintaining photonic crystal fiber was studied. The thermal sensitivitise of the polarization-maintaining photonic crystal fiber and conventional polarization-maintaining fiber were simulated and measured. Then the Shupe error in the gyroscope was analyzed. The contrast results showed that the Shupe error of the gyroscope with the polarization-maintaining photonic crystal fiber is quantitatively comparable to that using the conventional polarization-maintaining fiber.

Highly birefringent ZrF4-BaF2-LaF3-AlF3-NaF photonic quasi-crystal fiber with twin grapefruits holes

A novel design of highly birefringent photonic quasi-crystal fiber based on ZrF4-BaF2-LaF3-AlF3-NaF glass with twin grapefruit air holes near the core and twofold symmetry is proposed. The basic unit is composed of one square and its neighboring regular triangle. Using the finite element method, the birefringence and confinement loss are investigated simultaneously by changing the pitch of air holes and sizes of air holes. Numerical results show that the fiber maintains single mode operation in a wide wavelength range from 1.8 μm to 2.2 μm, and the birefringence is on the order of 10-2, two orders of magnitude larger than that of the conventional polarization-maintaining fibers, which is largest (around 2 μm) ever reported to our knowledge and the same order of magnitude as that obtained by fiber using elliptic air holes But this designed fiber is easy to fabricate compared with the fibers using elliptic air holes.

Polarization-maintaining photonic crystal fiber based quarter waveplate for temperature stability improvement of fiber optic current sensor

Fiber optic quarter waveplate (QWP) is widely used in all kinds of optical fiber systems such as fiber sensing systems. Specifically, in fiber optic current sensor (FOCS) system, which is now applied in power grids to measure current and monitor operation, fiber optic QWP is a key device and has serious impact on temperature stability and accuracy of the system. We fabricated a QWP using polarization-maintaining photonic crystal fiber (PM PCF), and studied its impact on the temperature characteristic of a home-made FOCS system. We also made a QWP with conventional polarization-maintaining fiber (PMF) for comparison purposes. The measured system error of the FOCS prototype using a QWP made of PM PCF between −40°C and 70°C was 8.45‰, which is five times smaller than with a QWP made of conventional PMF.

Low loss fusion splicing polarization-maintaining photonic crystal fiber and conventional polarization-maintaining fiber

An efficient and simple method of fusion splicing of a Polarization-Maintaining Photonic Crystal Fiber (PM-PCF) and a conventional Polarization-Maintaining Fiber (PMF) with a low loss of 0.65dB in experiment is reported. The minimum bending diameter of the joint can reach 2cm. Theoretical calculation of the splicing loss based on mode field diameters (MFDs) mismatch of the two kinds of fibers is given. All parameters affected the splicing loss were studied.

Temperature-insensitive polarimetric vibration sensor based on HiBi microstructured optical fiber

A new type of highly birefringent microstructured optical fiber has been tested for vibration measurements using a polarimetric technique. This technique takes advantage of the stress-induced phase shift between the two orthogonally polarized fiber eigenmodes. Comparison of three different fiber types shows that standard single-mode fibers do not provide stable measurements and that conventional polarization-maintaining fibers lead to a significant cross-sensitivity to temperature. However, for highly birefringent microstructured fibers specifically designed to provide a temperature-independent birefringence, our experiments show repeatable vibration measurements over a frequency range extending from 50 Hz to 1 kHz that are unaffected by temperature variations (up to 120 °C).

双倍光程的保偏光纤环及其在光纤陀螺中的应用

A novel polarization maintaining fiber (PMF) loop is proposed and used for an interferometric fiber optic gyroscope (FOG). By splicing a conventional PMF loop with two pigtailed polarization beam splitters, polarized light can be guided to propagate along the slow and fast axes of the PMF in sequence to double its effective optical length in the loop. In particular, the resultant optical length in the combined loop is partially self-compensated for some external disturbances, such as transverse strain. Primary experiments on the FOG using the proposed loop demonstrate that the average static bias deviation between –40 and +60 oC is less than 0.050 deg./h, and the average bias variation under conventional random vibration test is less than 0.10 deg./h.

Polarization-maintaining optical microfiber

We have successfully demonstrated a polarization-maintaining (PM) fused silica microfiber by adiabatically tapering a conventional PM fiber. Compared to standard single-mode microfibers, the proposed PM microfibers exhibit robust polarization, preserving characteristics under the presence of external perturbations, such as bending. A polarization-extinction ratio of 16 dB is typically obtained through the device with a corresponding excess loss of 0.2 dB.

Writing of Long-Period Gratings in Conventional and Photonic-Crystal Polarization-Maintaining Fibers by CO$_{2}$-Laser Pulses

We report the writing of long-period gratings in conventional and photonic-crystal (PC) polarization-maintaining (PM) fibers by high-frequency CO-laser pulses. We find that the writing efficiency depends on the irradiation direction of the writing beam with respect to the principal axes of the fiber, with the highest efficiency obtained when the irradiation direction is along the slow axis of the fiber. Such orientation dependence is much stronger for a conventional PM fiber than for a PC PM fiber. Using a conventional PM fiber, we demonstrate a grating that shows two clean polarization-splitting rejection bands with a separation of 33.4 nm and a contrast higher than 30 dB.