Birefringence Of Polarization-maintaining Fiber Research Articles

Performance improvement of a distributed temperature sensor with kilometer length and centimeter spatial resolution based on polarization-sensitive OFDR

A method to improve the performance of distributed temperature sensors with kilometer sensing distance and centimeter spatial resolution is proposed based on polarization-sensitive optical frequency domain reflectometry (OFDR). This approach records the temperature change along polarization maintaining fiber (PMF) from the Rayleigh backscattering (RBS) spectral difference between two orthogonal polarization axes using the distributed autocorrelation algorithm, where PMF is used as the sensing fiber. In addition, a technique to calibrate population birefringence and local birefringence, and a method to calibrate the initial birefringence inhomogeneity of PMF are proposed to enhance the performance of the sensor. The birefringence of PMF is used for temperature sensing, which is distinct from the traditional cross-correlation method of single-mode optical fiber temperature sensing, providing us with an innovative scheme to solve real-world engineering problems. The final sensing performance is achieved, with a sensing distance of 1.5 km, a spatial resolution of 5 cm, and a temperature measurement uncertainty of ±0.2 °C, subject to environmental noise and system random noise.

Mitigation of transverse mode instability by modal birefringence in polarization-maintaining fibers

The effect of transverse mode instability (TMI) poses a fundamental obstacle for a further scaling of diffraction-limited, high-power fiber laser systems. In this work we present a theoretical and experimental study on the mitigation of TMI by modal birefringence in a polarization maintaining (PM) fiber. With the help of comprehensive simulations, we show that the thermally-induced refractive index grating responsible for TMI can be modified and washed out when light is coupled with a polarization input angle detuned from the main axes of the fiber. To confirm the theoretical predictions, we have designed and manufactured an Yb-doped large-mode-area PM fiber. Using this fiber, we have systematically investigated the dependence of the TMI threshold on the polarization input angle of the seed laser. We experimentally demonstrate that when the polarization input angle of the seed is aligned at 50° with respect to the slow-axis, the TMI threshold increases by a factor of 2, verifying the theory and the numerical simulations. A high speed polarization mode-resolved analysis of the output beam is presented, which reveals that at the onset of TMI both polarization axes fluctuates simultaneously.

Revisiting the Stress-Induced Birefringence in Polarization-Maintaining Fibers

Two conventional errors in the stress-induced birefringence (SIB) of polarization-maintaining fibers (PMFs) are revealed and corrected. The first issue refers to the fundamental expression and its calculation of the SIB, which depends on the selection of stress components. There were obvious inconsistencies in two pioneering reports, while both were widely applied in subsequent works. The second issue is the basic form of the Airy stress function (ASF) in the cross-section plane of the PMF, which dominates the complexity of the stress calculation for SIB. The ASFs in two early pioneering works were different, which led to two different expressions of SIB. Both expressions cannot be reproduced, and calculated results were just around 1/2 of the corresponding measurements. In this paper, both issues have been fixed by revising the definition of SIB and proposing a new ASF form for PMFs. The developed theory is simple and does not have any mathematical contradiction in the calculation process, compare to reported works. Results of the revised SIB based on the developed theory achieve a good agreement with the practical experimental measurements.

Application of Crossed Polarizer Method in the Measurement of Differential Group Delay of Optical Fibers

In this paper, we report the use of crossed polarizer technique to measure the differential group delay (DGD) of few-mode optical fiber (FMF). The windowed Fourier transform (WFT) is applied in the analysis of beat length measurement in the spectral domain to obtain the dependence of DGD as a function of wavelength. The birefringence of polarization-maintaining fiber (PMF) and the DGD of FMF are measured by applying our method. We discuss the noise background, the width of DGD peaks, and the possible errors introduced in the optical path in the modified crossed polarizer technique.

Fiber-optic simultaneous distributed monitoring of strain and temperature for an aircraft wing during flight.

We applied a fiber optic distributed simultaneous strain and temperature measurement technique to the structural monitoring of the main wing of a middle-sized passenger jet aircraft during flight. We used 40 10cm long fiber Bragg gratings (FBGs), inscribed in a highly birefringent polarization-maintaining fiber. The FBGs were interrogated by optical frequency domain reflectometry, which could measure Bragg wavelength distributions at a sampling rate of 151Hz. The simultaneous measurement technique could detect structural behaviors of the wing during flight under temperature-changing conditions. In addition, we discuss the effect of the polarization mode-coupling and the apparent position shift of the FBGs over time, which occurred during flight.

Polarization-independent quasi-flat-top comb filter using an in-line Sagnac interference

We propose a novel all-fiber quasi-flat-top comb filter based on an in-line Sagnac interference. The transmission function of the proposed filter is theoretically analyzed using Jones transmit-matrix. And the influence of several factors on the output spectrum is experimentally demonstrated, such as the length of the two polarization-maintaining fibers (PMFs), the birefringence of PMFs, the rotatable angle of polarization controllers (PCs) and the temperature subjected to PMFs. A well-defined flat-top interference pattern as theoretically expected is achieved. The measured extinction ratio and free spectrum range (FSR) of the proposed filter are 25dB and 16nm, respectively. In addition, it has the advantages of good flattop transmission passband, high channel isolation, fully compatible with optical-fiber system and low cost. This kind of filter can be widely used in dense wavelength division multiplexing (DWDM) systems.

Temperature-independent fiber inclinometer based on orthogonally polarized modes coupling using a polarization-maintaining fiber bragg grating.

A reflection fiber inclinometer is proposed and experimentally demonstrated based on two linearly polarized (LP) modes coupling. The configuration consists of a section of polarization-maintaining fiber (PMF) containing a fiber Bragg grating (FBG) splicing with single mode fiber (SMF). Bending the PMF in the upstream of FBG can induce an additional birefringence of PMF, which results in the intensity changes of two LP modes owing to orthogonal polarization coupling. The experimental results represent that the device shows different bending responses at the angle range from 0° to 40°and from 64° to 88°, respectively. Moreover, the temperature change just shifts the wavelengths of LP modes reflected and does not influence their intensities, which effectively avoid the temperature cross-sensitivity and make it a good candidate for measuring inclinometer and temperature simultaneously.

Compensation of temperature and strain coefficients due to local birefringence using optical frequency domain reflectometry

We demonstrate a high precision simultaneous temperature and strain measurement by means of polarization sensitive optical frequency domain reflectometry (OFDR). In the measurement, a high birefringence polarization maintaining (PM) fiber was used as sensor. It was confirmed that the thermal and strain coefficients of birefringence in PM fiber were position-dependent parameters, which can be used to compensate the errors of temperature and strain measurement. High accuracy simultaneous measurement of temperature and strain within errors 0.8°C and 7με was achieved with spatial resolution of 6.5mm over 170m fiber in this report.

高精度双折射可控保偏光纤光栅研究

高精度双折射可控保偏光纤光栅研究

Influence of birefringence dispersion on a distributed stress sensor using birefringent optical fiber

Distributed stress sensor with a white-light scanning interferometer is used to detect stress distribution by analyzing polarization mode coupling caused by forces exerted on PMFs (polarization maintaining fibers). In measurement of polarization coupling, the birefringence in sensing fiber is usually considered to be wavelength independent. Sensitivity and spatial resolution of the distributed stress sensor are constant for a given optical source spectrum. In practical measurement, however, the birefringence in PMFs is related with optical wavelength. In other words, birefringence dispersion exists in PMFs. Due to birefringence dispersion, the relationship between stress and coupling strength varies with different positions of external forces, and spatial resolution of the distributed stress sensor descends obviously with transmitted distance. In this paper, influences of external-force positions and optical source spectrum on distributed stress sensor are analyzed in consideration of birefringence dispersion and validated with experiments. A method for compensating birefringence dispersion in the sensing system is proposed in the end.

Spectral-domain measurement of phase modal birefringence in polarization-maintaining fiber

We report on a new and simple method for measuring the wavelength dependence of phase modal birefringence in a polarizationmaintaining fiber. The method is based on application of a lateral pointlike force on the fiber that causes strong coupling between polarization modes and utilizes their interference resolved as the channeled spectrum. The change of the phase retrieved from two recorded channeled spectra that are associated with the known displacement of coupling point is used to determine the phase modal birefringence as a function of wavelength. A windowed Fourier transform is applied to reconstruct precisely the phase change and the phase ambiguity is removed provided that we know the phase change of the spectral fringes at one specific wavelength. The measured wavelength dependence of phase modal birefringence is compared with that resulting from the group modal birefringence measurement.

Phase conjugation driven by orthogonal pump waves in birefringent fibers

Phase conjugation driven by orthogonal pump waves in birefringent polarization-maintaining fibers is studied analytically and numerically. For typical parameters, the gain bandwidths and polarization sensitivities associated with orthogonal-pump waves are comparable to those associated with parallel-pump waves. However, the maximal gains are significantly lower.

Dispersion of birefringence and differential group delay in polarization-maintaining fiber

We present an interferometric technique for measurement of the dispersion of birefringence in polarization-maintaining fibers. The approach yields measurements over a broad spectral range from analysis of single interferograms obtained in a tandem inteferometer. The technique is demonstrated to measure first-, second-, and third-order dispersion of the differential propagation constant, corresponding to differential group delay (DGD) and its dispersion to second order; measurements are immune to asymmetry in the interferomgram that is being processed. The technique is further applied to measurement of the temperature dependence of DGD and its first-order dispersion.

Wavelength Tunable Ultrashort Pulse Fiber Laser.

Compact system of wavelength tunable ultrashort soliton pulse generation has been demonstratedusing modelockedfemtosecond fiber laser and polarization maintaining (PM) fiber. The wavelengths of generated pulsescan be changed continuously by merely varying fiber input power. The generated pulses are almost transformlimited ideal soliton pulses. Two-colored soliton pulses can be generated simultaneously usingthe birefringenceof PM fibers. Using the dispersion shifted PM fibers, in addition to the soliton pulse, the anti-stokespulse is generated at the shorter wavelength side. Using the diameter reduced PM fibers and dispersion shiftedPM fibers, the wavelength tunable ultrashort pulses can be generated in the wide wavelength region of 1.3-2.0μm. In this paper, the characteristics of wavelength tunable soliton pulse are described withthe principles and applications.

Full characterization of polarization-mode dispersion with random-mode coupling in single-mode optical fibers

Theoretical expression has been derived for polarization-mode dispersion with random-mode coupling in optical fiber by simple means. The square-root dependence of polarization-mode dispersion not only on a fiber length but on a mean-coupling length has been experimentally verified for the first time. This characterization became possible only by the use of highly birefringent polarization-maintaining fiber and introduction of fusion splices with desired coupling lengths.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spectral signal processing in intrinsic interferometric sensors based on birefringent polarization-maintaining optical fibers

The straightforward spectral signal processing technique is applied in intrinsic strain, temperature and distributed linear position interferometric fiber optic sensors based on birefringent polarization maintaining fibers. The method provides nonincremental absolute measurements of external physical parameter affecting the sensing fiber. Simultaneous interrogation of sensors in a network is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Frequency-derived remote measurement of birefringence in polarization-maintaining fiber by using the optical Kerr effect

A technique to measure remotely the birefringence of polarization-maintaining fiber is described. The method uses a pump-and-probe scheme that employs the optical Kerr effect together with a small wavelength difference between the sources to allow a measurable derived frequency to be generated. The frequency depends on the birefringence of the fiber and the source wavelength offset. This latter feature provides a tunable frequency and hence an extra degree of freedom in the system design.

Results of Experimental Investigation into the Birefringence of Polarization-Maintaining Fibers with Stress-Applying Parts by Means of Photoelasticity

Results of Experimental Investigation into the Birefringence of Polarization-Maintaining Fibers with Stress-Applying Parts by Means of Photoelasticity

Long-length low-loss polarization-maintaining fibers

Long-length low-loss polarization-maintaining fibers are useful for coherent optical transmission systems, active transmission lines with optical nonlinear effects, and other long-length optical transmission systems, such as those for bidirectional optical transmission. Design, fabrication, and characteristics of highly birefringent polarization-maintaining fibers with long length and low loss, especially polarization-maintaining and absorption-reducing (PANDA) fibers, are reviewed and discussed in this paper. Application of the fibers is also discussed.

Ultimate limit of polarization cross talk in birefringent polarization-maintaining fibers

Direct measurement of the ultimate limit of the polarization cross talk of the birefringent fibers caused by anisotropic Rayleigh scattering (ARS) is presented theoretically and experimentally by using polarization optical time-domain reflectometry (POTDR). With POTDR, ARS appears as the bias existing in the backscattered power ratio between the cross-coupled and excited modes. A value twice that of the bias corresponds to the depolarization ratio representing the anisotropy of the fiber core material. The biases measured by birefringent polarization-maintaining fibers are all within 3% of the mean value 0.048.