Polarization properties of birefringent fibers with stress rods in the cladding

The polarization properties of fibers with high-expansion aluminum-doped stress rods in the cladding are described. Polarization beat lengths and polarization-holding parameters comparable to those of state-of-the-art high-birefringence fibers are obtained. The diameter of the outer cladding is not sufficient to provide optimum constraint on the stress rods. Increasing the diameter of this region should significantly reduce both the beat length and the polarization-holdingh- parameter. No anomalous behavior or thermal hysteresis is observed in the temperature dependence of the fiber birefringence below 600°C. Above 600°C, a permanent hysteresis which reduces the fiber birefringence is observed.     

非对称应力结构单模光纤偏振特性

本文通过理论分析,得出了非对称应力结构单模光纤,不管其应力结构如何,其本征传导模必定是线偏振的,在这种光纤中只存在线双折射,而没有任何形式的圆双折射。这一结果得到了实验证实。     

Polarization in optical fibers

Recent research on fibers with very small or very large birefringence for polarization-dependent applications is reviewed. The nature of random coupling between normal modes of polarization is analyzed and discussed in connection with various applications.     

Polarization characteristics of side-pit and side-tunnel fibers using the effective index method

The effective index method has been used to determine the polarization characteristics of side-pit and side-tunnel fibers. The results obtained by the present method compare quite well with those reported by using the finite element method.     

Polarization anisotropy in optical reflection spectra of structures with open nanowires

The optical reflection spectra of structures with open nanowires created from ZnCdSe/ZnSe heterostructures are investigated. A significant polarization anisotropy of the reflection is observed over a wide spectral range, including the exciton resonance regions of the wire, the barrier, and the substrate. The effect of additional laser pumping on the reflection spectrum is examined. The observed effects are interpreted in terms of a model of an effective anisotropic layer. A numerical simulation of the reflection spectra based on this model is in good qualitative agreement with experiment. Fiz. Tekh. Poluprovodn. 33, 1080–1083 (September 1999)     

Polarization measurements on single-mode fibers

An overview of current measurement techniques on conventional and polarization maintaining single-mode fibers is presented. The various methods are discussed and classified with respect to the relevant polarization parameters. Applicability ranges and resolution are pointed out for different types of fibers     

Polarization properties of randomly-birefringent spun fibers

The spinning of single-mode telecommunication fibers is a technique currently and widely used to reduce polarization mode dispersion. Yet, this technique was originally envisaged as a way to produce fibers with arbitrarily low birefringence, to be used in sensor applications. In spite of their applicative significance, spun fibers are still not completely understood. In this paper, we report an extensive analysis of the polarization properties of spun fiber. Both unidirectional and periodic spin profiles are considered. It is shown that very high polarization maintaining capabilities may be achieved by properly tuning the spin parameters.     

Polarization coupling in kinked single-mode fibers

When a fiber is stretched over a small ridge on a drum, the modifications of the distributions of curvature and of lateral force near the ridge induce extra birefringence in the fiber. Many such kinks, distributed randomly along a high-birefringence fiber, degrade the polarization-holding quality of the fiber. A theoretical analysis of these effects and pertinent experimental results are presented.     

Polarization holding in elliptical-core birefringent fibers

Polarization holding in high-birefringence elliptical-core fibers is evaluated for the fiber birefringence spatial frequency range 1.5 cm^-1< beta_{i} < 40cm^-1, corresponding to beat lengths from 1.6 mm to 4.2 cm. This range of spatial frequencies is spanned by making measurements with a broad-band light source on four fibers with different degrees of birefringence. In this way, the strength of the internal birefringence perturbations is mapped to give the first experimental measure of their power spectrum. It is shown that commonly available fiber jackets can significantly degrade the polarization holding. For low spatial frequencies, the strength of the perturbations decreases rapidly with increasing frequency, but this rate decreases by more than half over a one-and-a-half order of magnitude increase in spatial frequency. A possible origin of the perturbations is suggested and it is shown that the strength of these perturbations must be reduced if polarization holding to a very high degree is to be realized in elliptical-core fibers. Presently, internal perturbations limit the polarization holding to ≤ 14.4 dB over 1 km.     

Polarization behavior in multiply perturbed single-mode fibers

A general theory is presented for polarization evolution characteristics in anisotropic single-mode optical fibers to which plural perturbations of different kinds are applied simultaneously. This treatment is based on modified coupled-mode theory. Polarization performance in the system can be described by a simple projection rule when the birefringence caused by individual perturbation is known. Several examples of applications are classified according to their mode coupling properties in fused silica fibers.     

Polarization rotation in nonlinear bimodal optical fibers

The effect of nonlinear interactions on second-order modes in circular cross-section optical fibers is considered. In the linear case, analysis using the proper modes reveals that the fiber is a natural polarization rotator. An initial linearly polarized (LP) mode is actually a mixture of proper modes and recurs only periodically as the field propagates; at half-periods the input polarization and field pattern are rotated by 90°. Complete analytical expressions and numerical examples describing the modification of this phenomenon by nonlinearity are presented. For lower powers, the phenomenon persists with period increasing toward infinity at a transition point, beyond which complete polarization rotation is suppressed. At very high powers, the Kerr effect dominates: polarization is fixed in one direction and an LP mode does become a real mode of the system     

Polarization properties of stimulated Brillouin scattering insingle-mode fibers

The polarization properties of stimulated brillouin scattering (SBS) in low birefringent optical fibers were evaluated using Stokes calculus. It was found that the Brillouin gain for orthogonally polarized pump and probe wave is half (in dB) of the gain for identical polarization, and not equal as often mentioned in literature. Therefore the polarization factor is K=1_1/2 for complete polarization scrambling, and not K=2. The spontaneous SBS has the same state of polarization as the pump, and its degree of polarization is 33.3% for low pump powers and near 100% for high pump powers. The experimental results agree very well with the calculations     

Polarization and dispersive properties of elliptical-hole photoniccrystal fibers

We survey the properties of photonic crystal fibers with elliptical air holes, examining mode shapes, birefringence, group velocity walkoff and dispersion, and cutoff conditions. We find new types of behavior for each quantity and demonstrate the possibility achieving large birefringence with zero walkoff in the single-mode regime. We show that the dispersive properties of the vector modes are closely tied to those of the so-called fundamental space filling modes, and that at long wavelengths, the fibers exhibit a single-polarization single-mode regime of propagation without the presence of material anisotropy     

Polarization control on output of single-mode optical fibers

Polarization control of the light output from single-mode fiber systems is very important in order to connect it to polarization-dependent integrated optical circuits and applications using a heretodyne detection system. In this paper, automatic control of the polarization of light transmitted through the fiber was demonstrated by an electrooptical and electrical feedback system. In this system, we used a 1.6 μm long wavelength semiconductor CW BH laser, low-loss single-mode optical fiber with a loss of 0.2 dB/km, and two thinz-cut LiNbO3modulators tilted 45° relative to each other. The output light from this polarization controller was maintained to be linear while that from the single-mode fiber was unstable and elliptically polarized.     

Polarization dispersion measurement on twisted single-mode optical fibers

A new method for measuring polarization dispersion between two eigen polarization modes is presented. It utilizes the measured phase shift corresponding to birefringence difference between two adjacent wavelengths. This method makes it possible to measure small polarization dispersion by using a short test piece even when eigen polarization modes are elliptically polarized. A polarization dispersion of 0.4 ps/km in twisted single-mode fibers can be measured in an approximately 4-m-long fiber by using 1.152- and 1.161-μm lines in a He-Ne laser. Experimental data that polarization dispersion decreases with an increase in fiber twist ate in very close agreement with theoretical results.     

Polarization mode dispersion in spun fibers with different linearbirefringence and spinning parameters

This paper shows how the initial linear birefringence determines the necessary spinning parameters to produce spun fiber with optimum differential group delay (DGD) and polarization mode dispersion (PMD) properties. DGD measurements are reported on two pairs of fibers, each pair having been fabricated from a particular fiber preform. The fiber pairs each consist of a sample of spun and unspun fiber. These measurements are then compared with theoretical simulations for each fiber to determine the required range of spinning parameters for a given initial linear birefringence. These results should help in optimizing the spinning parameters for producing high-performance spun fibers     

Polarization mode dispersion of short and long single-mode fibers

Polarization mode dispersion (PMD) in short and long single-mode fibers was measured by a polarization-maintaining Michelson interferometer. A nonnegligible PMD was found in some standard fibers. The sensitivity enables PMD to measure the bend-induced PMD of a fiber rolled on a 28-cm diameter drum. A theoretical model for PMD with random mode coupling is developed, and an explicit equation for the time-of-flight distribution is presented. Comparison between measurements on short and long fibers with residual birefringence leads to an estimation of the coupling length on the order of 20-30 m     

Photochromic liquid-core fibers with nonlinear input-output characteristics

Photochromic liquid-core fibers were fabricated by using benzene or 2-propanol solution of spirobenzopyran. The fiber element consisting of a benzene-solution core and a silica-glass cladding exhibited variable transmittance that was controlled by ultraviolet irradiation. When a visible laser beam (532-nm wavelength) was used as input signal, output signal power increased nonlinearly with input power due to reversed photochromism. This nonlinear input-output characteristic was observed without ultraviolet light, when a fiber was constructed with 2-propanol solution and a polymer-coated glass tube. These experimental results agreed with the theoretical prediction that was based on a simple photochromic fiber model.     

Chromatic dispersion characteristics of fibers with opticalKerr-effect nonlinearity

Chromatic dispersions of optical fibers with Kerr-effect nonlinearity are investigated. Under high optical intensity, dispersion characteristics become different from those of the linear state (or weak optical intensity) since the refractive index profile changes in accordance with the intensity profile. Nonlinear dispersion characteristics are calculated for step-index and quadratic profile fibers with core-cladding, core, and cladding nonlinearity. It is shown that although the propagation constant of the step-index fiber increases substantially from the linear value, the group delay and waveguide dispersion do not increase as much