Variable-spun fiber wave plate can be used to change the polarization state in fiber optic sensing systems. However, the beat length of the birefringence fiber may variation with different operating wavelength, which further leads to the instability of the polarization transforming performance. Based on the relation between the beat length and the operating wavelength, the wavelength sensitivity is simulated for the variable-spun fiber wave plate with different structural parameters (fiber length, spun rate profile and maximum spun rate). The achromatic bandwidth of the qualified fiber plate is discussed. The results have certain reference value for the design, fabrication and evaluation of variable-spun fiber wave plate.
Fiber wave plates are usually used for the transformation of polarization state in fiber sensing systems. Environment temperature and operating wavelength may influence the beat length of the birefringence fiber, inducing the instability of fiber wave plates on polarization transforming. As for the variable-spun fiber wave plate with different structure parameters (fiber length, spun rate profile and maximum spun rate), this paper describe the effect of beat length on the equivalent phase retardation. The proper range of the beat length for the qualified fiber wave plate is calculated by the differential phase retarder cascade model. The results are of referential value to the design, fabrication and evaluation of the variable-spun fiber wave plate.
A variable-spun birefringence fiber, as long as the spun rate changes slowly enough and the maximum spun rate is large enough, can realize the conversion between linearly polarized light and circularly polarized light. Environment temperature may affect the beat length of the birefringence fiber, which leads to the instability of the polarization of the fiber wave plates. According to the relation between the beat length of the fiber and the temperature, we discuss the thermal stability of variable-spun fiber wave plates with different structural parameters, and give the temperature range for qualified operation. The research results are of referential value to the design, fabrication and evaluation of the variable-spun fiber wave plates.
Influence of splicing the highly birefringent photonic crystal fiber (HB-PCF) with single mode fiber (SMF) under two
different experimental conditions is studied in details. The result shows the birefringence of the HB-PCF can be either
increased or decreased significantly, depending on the connection conditions of the HB-PCF end, which are classified as
case I (the end is closely butted by another fiber) and case II (the end is in open air). From the experiment and
theoretical analysis, it has shown that in case I the retardation change of the spliced section of HB-PCF with 0.2mm in
length can be 3.2 times larger than the original value. However, in case II the retardation may be reduced to 72.12% of
the original one. The obtained result is important for the design and fabrication of optical fiber devices and sensors based
on HB-PCFs.
The deviation of cores' shape in dual-core fiber may affect the coupling characteristics between the two cores. For the
same given cores' area in three kinds of dual (circular, elliptical, egg-shaped) core fiber, the relationship of the coupling
length with the cores' shape is calculated at different wavelength It is found the coupling length of dual-circular-core
fiber is the longest and dual-elliptical-core fiber is the shortest while dual-egg-shaped-core fiber is in the middle.
Two asymmetric structures are combined together in holey cladding of microstructure fiber. One is the rectangular lattice
of holes elongated in y-axis. The other is a pair of holes with enlarged diameters near the fiber core oppositely along xaxis.
The influence of structural parameters on relation between birefringence with wavelength is calculated. Their
interaction at different wavelength can make the beat length insensitive to wavelength. By optimizing the lattice pitches
and the holes diameter, 10mm stable beat length with relative bandwidth 12% are obtained in 1310nm and 1550nm bands.
This holey fiber is suitable for fabricating wideband fiber-optic wave-plate.
Compact samples of quarter wave plate have been fabricated respectively by cutting holey birefringent fiber and
conventional birefringent fiber into different length of short sections. The temperature instability and wavelength
sensitivity of these samples are analyzed and measured. The influence of fiber length and fiber prototype on the
retardation variation is compared. The retardation deviation almost linearly increases with the fiber length of samples.
Compared with the sample made of conventional birefringent fiber, the temperature stability of the sample made of holey
birefringent fiber is greatly improved by one order, but the wavelength bandwidth needs to be further expanded by
optimizing the holey cladding structure.
The influence of extension lead at both sides and input polarization state on polarization transform performance of
increscent-spinning birefringent fibre is calculated and examined. In the extension lead, the output polarization state is
fluctuating with period relevant with the max-spin-rate or the beat length of birefringent fiber. It is found, the optimal
input polarization state for the best output linear polarization is not the ideal circular polarization but a elliptical
polarization related with the maximum spin rate, the optimal input linear polarization orientation is not in line but has a
slight divergence angle with the birefringent axes of fiber, and if the input linear polarization is not perfect linear
polarization, the output circular polarization would be nonlinearly degraded. These results have advisable meaning for
the design, test and evaluation of the quarter wave plate made by the increscent-spinning birefringent fibre.
A photoelectric measurement system for measuring the beat length of birefringence fiber is set up including a set of
rotating-wave-plate polarimeter using single photodiode. And two improved cutback methods suitable for measuring
beat-length within millimeter range of high birefringence fiber are proposed through data processing technique. The cut
length needs not to be restricted shorter than one centimeter so that the auto-cleaving machine is freely used, and no need
to carefully operate the manually cleaving blade with low efficiency and poor success. The first method adopts the
parameter-fitting to a saw-tooth function of tried beat length by the criterion of minimum square deviations, without
special limitation on the cut length. The second method adopts linear-fitting in the divided length ranges, only restrict
condition is the increment between different cut lengths less than one beat-length. For a section of holey
high-birefringence fiber, we do experiments respectively by the two methods. The detecting error of beat-length is
discussed and the advantage is compared.
Examined is the influence by input state of polarization and analyzing scheme on sensitivity in the measurement system of beat length that relies on magneto-optic modulation technique in which the magnetic gap and intensity of magnetic field have been given. Through theoretic analysis and experimental study, it is found that there are three experiment schemes getting maximum sensitivity. First, the polarization direction of the input linearly polarized light is at θ = 00 or 900 to the birefringence fast axis of e fiber, at the same time, the two analyzing axes of Wollaston prism are at γ = 450 to the birefringence fast or slow axis of fiber. Second, the polarization direction of input linearly polarized light is at θ = 450, and γ = 00 or 900. Third, the input light beam is circular polarized light, at the same time, γ = 00 or 900. The sensitivity under three cases is approximately equal, but the third scheme needn't pinpoint the direction of birefringence axis of fiber, which makes the experiment more convenient and avoid the measurement error caused by the adjustment of angle.
Based on the analysis on the variable coupled-mode equation, we proposed an optimal profile of variably spun rate Q(z) = 0.5tan{arcsin[(z/L)sin(arctan2Q(L)]} to get better performance for all-fiber polarization transformer (AFPT), where Q(z) is normalized spun rate by beat length LB along the fiber length L. Then, in accordance with the intrinsic structure of AFPT, and in consideration of considering the phase-difference effect, we calculated the Jones vector from point to point along fiber to simulate the evolution of state of polarization (SOP) in AFPT with this optimal spun rate profile. For comparison, calculations are also made with other two kinds of spun rate profile (linear, cosine) often used in the AFPT fabricating process. The Influence of spun rate variation profile on the polarization transforming performance of AFPT is discussed and compared in detail. It is found that both in the case of linear-in/circular-out where the extinction ratio of output light is required as small as possible and in the case of circular-out/linear-in where the extinction ratio of output light is required as large as possible, the AFPT with optimal spun-rate profile presents best performance, and the linear spun-rate profile is the worst. The analysis and calculation results have referential values to the design, fabrication and evaluation of AFPT samples.
An all-fiber polarization transformer made of variably twisted holey birefringence fiber is proposed to decrease the
temperature instability. After reviewing the beat length (or modal birefringence) variation of holey birefringence fiber
with temperature and wavelength, the model for simulating the polarization transforming ability of the variably spun or
twisted birefringence fiber is set up based on the mode-couple equation with variable coupled coefficients. Compared
with the conventional polarization transformer made of variably spun stress birefringence fiber, the temperature
instability from -20°C to +80°C and wavelength sensitivity from 1200nm to 1600nm of their polarization transforming
performance are simulated and discussed.
The variably coupled-mode equation in all-fiber polarization transformer (AFPT) is theoretically analyzed and an
optimal profile of variably spun rate to get better performance for AFPT samples is proposed as Q(z) =
0.5tan{arcsin[(z/L)sin(arctan2Q(L))]} where Q(z) is the normalized spun rate by beat length LB along the spinning
section of AFPT with total length L. Then, in accordance with this specific intrinsic structure of AFPT, we found that
there exists a set of strictly analytic solution for the variably coupled-mode equations of AFPT. It is also found that the
linear polarized exact eigen-modes of AFPT at the un-spun end are not parallel but with a slight angle relative to the
birefringence axes of the un-spun fiber. The difference of phase factor and amplitude between the exact analytic solution
and the asymptotic solution is compared and discussed. The analysis has referential values to the design, fabrication and
evaluation of AFPT samples.
Spun optical fibers with different structure and different spinning rates are fabricated and their spectral transmittance is measured. It is found that the transmittance of spun stress-type fiber drops down in a certain long wavelength band as the spinning rate is increased, while this phenomenon is not found in the spun conventional fiber or un-spun stress-type fiber. We suggest it due to the micro-bending-loss induced by the spinning eccentricity of the fiber core.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.