Acoustooptic modulators for single-mode fibers

The design of in-line acoustooptic modulators for single-mode fibers is discussed. The basic configuration consists of a cylindrically symmetric piezoelectric transducer fabricated on the fiber surface, so that the fiber itself acts as a cylindrical acoustic resonator. Depending on the fiber design, the acoustic wave can induce phase, birefringence, or polarization modulation of the light in the fiber. Pairs of the polarization modulators in series can be used to shift the optical frequency. Factors affecting the performance of all of these devices are discussed.     

Triple-clad single-mode fibers for dispersion shifting

A design procedure for triple-clad dispersion-shifted single-mode fibers is developed. Following this procedure, fibers are identified which have low dopant concentrations in the core compared to those of the previous dispersion-shifted fiber designs, a second-mode cutoff wavelength close to the operating wavelength, zero dispersion at 1550 nm, a small bending loss at 1550 nm (for a bend radius of 3.75 cm), and a spot size that is large enough not to compromise the splice loss. A significant advantage of these fibers is that low-dispersion is available over a wide wavelength band about the wavelength of zero dispersion     

Generalized Gaussian approximation for single-mode fibers

A variational method is presented that generalizes well-known Gaussian method for single-mode fibers. This method uses only simple elementary functions to approximate the fundamental mode fields. By applying it to practical cases such as step index and clad parabolic index fibers, where exact solutions can be found, it is demonstrated that the method is essentially simple and that it is accurate for the analysis of single-mode fibers and devices. This approximation provides much better eigenvalues and, in particular, evanescent fields than the traditional Gaussian. Significantly, the present approximation's range of applicability covers the whole single-mode range, while being only slightly more complicated than the modified Gaussian method     

Fusion splices for single-mode optical fibers

A practical low loss splicing method based on the discharge fusion for single-mode fibers was developed. Average splice losses of 0.4, 0.2, and 0.1 dB for fibers with 5.2, 7, and 10 μm core diameters, respectively, are obtained by a simple apparatus utilizing the self-alignment effect due to the surface tension of melted fiber ends. The surface tension effect is analyzed both experimentally and theoretically. Experimental splice losses, both after and during heating, coincide with the theoretical estimated values. It was found that the optimum heating temperature for low loss splices is near 2000°C at 8.5 W electric discharge power. Splicing loss causes are examined. The main cause of the practical splice loss is the residual core axis misalignment caused by an insufficient surface tension effect and core eccentricity with respect to cladding.     

Single-polarization single-mode optical fibers

Strictly speaking, an ordinary axially symmetrical single-mode fiber is a "two-mode" fiber because two orthogonally polarized HE11modes can be propagated in it. This fact results in the instability of the polarization state of the propagated mode when geometrical perturbation exists in the fiber, and also the so-called polarization mode dispersion. These are harmful in some applications of single-mode fibers to communication and measurement. To prevent these adverse effects, single-polarization single-mode (SPSM) optical fibers have been developed. Three basic types of the SPSM fiber are elliptical-core fiber, stress-induced birefringent fiber, and side-pit fiber. This paper describes the principles of these three types, performance obtained experimentally, theoretical approaches, and measurement techniques related to the SPSM fibers. Finally, relevant technical tasks in the future are mentioned.     

Extended Gaussian approximation for single-mode graded-index fibers

A new trial function which extends the generalized Gaussian method for the study of weakly guiding single-mode fibers is presented. This function uses only simple elementary functions to approximate the fundamental modal fields. In many cases of study, we show that the present trial function gives a significant improvement over the existing trial functions, and it is very useful in the analysis of fibers and related devices     

Bend loss in single-mode fibers

In this paper, we present the results of extensive single-radius bend loss measurements for two different fibers over wide ranges of wavelength (800-1600 nm) and curvature radius (13.5-27.5 mm). A new bend loss formula is also derived, allowing a good fit of experimental data over the whole range of both parameters. Using an equivalent step-index (ESI) approach we obtain a good agreement between estimated and real parameters: e.g., cutoff wavelengths are within 1%     

Single-polarization single-mode photonic crystal fibers

A new structure of single-polarization single-mode (SPSM) photonic crystal fiber (PCF) is proposed and analyzed by using a full-vector finite element method with anisotropic perfectly matched layers. From the numerical results it is confirmed that the proposed fiber is low-loss SPSM-PCF within the wavelengths ranging from 1.48 to 1.6 /spl mu/m, where only the slow-axis mode exists and the confinement loss is less than 0.1 dB/km.     

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     

Birefringence in bent single-mode fibers

Changes to field properties when an optical fiber is bent are considered. A formula is obtained for the geometrical birefringence in a single-mode fiber due to bending, and is explicitly evaluated for a Gaussian field approximation, giving a simple analytic expression; it is also evaluated for more exact fields. Scalar theory is not sufficient to describe this birefringence, as reported previously, and vector or polarization corrections must be included in the theory. This birefringence is several orders of magnitude less than stress-induced bending birefringence     

Practical microbending loss formula for single-mode optical fibers

Microbending loss in a step-index single-mode fiber is formulated in an expression which provides an explicit dependence on wavelength λ and relative index difference Δ. For the permissible mean bending radiusRdaggercorresponding to a given loss,Delta^{3/2}Rdagger/lambdais the functionfof only a normalized frequency υ. This property resembles that for the uniform-bending loss. However,fin the microbending loss depends less critically on υ than in the uniform-bending loss.     

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.     

Fabrication of fluoride glass single-mode fibers

Single-mode optical fibers are obtained using ZrF4-based fluoride glasses. The fibers are drawn from a preform and jacketing tube. The preform with cladding/core ratio of 5.1 is made by using a built-in casting method. The cutoff wavelength of the fiber is experimentally determined to be 2.7 μm by bending loss measurement. Minimum transmission loss of the obtained fiber is 160 dB/km at a wavelength of 3.28 μm. TheV-value at this wavelength is estimated to be 2.03 from the core diameter and the refractive index difference.     

Dispersion statistics in concatenated single-mode fibers

Dispersion measurement data from two sets of fiber cable lengths were employed to determine the histograms of slope and wavelength of zero chromatic-dispersion in concatenated single-mode fibers. We use a Monte-Carlo technique under two concatenating scenarios, depending on whether those fibers being concatenated are or are not manufactured by the same process. Results show that the variances of slope and wavelength of zero dispersion are inversely proportional to the numberNof fiber cable lengths being concatenated. The average and standard deviation of zero-chromatic dispersion wavelength changes less than 0.005 percent or 1 percent, respectively, when the actual dispersion slopes of individual fiber lengths being concatenated are replaced by random quantities distributed with uniformity within 0.08-0.1 ps/km . nm².     

Two fibers or one? (a comparison of two-fiber and one-fiber stararchitectures for fiber-to-the-home applications)

Issues for consideration when deciding between the two-fiber (2-F) and one-fiber (1-F) architectures for fiber deployment in the distribution portion of the loop are presented. A link-loss assessment of both architectures is presented. 1-F star transmission concerns, namely, directivity and wavelength isolation, are discussed. System upgrade of both architectures is considered. Testing and maintenance are addressed. A cost analysis is presented. The 2-F star is conceptually a simple architecture offering maximum upgrade potential and few transmission and testing concerns. However, its distribution link and life cycle costs exceed that of the 1-F star. The 1-F star offer potential cost savings in fiber cable, splicing, and long-term maintenance. The 1-F star has transmission concerns, however, that could impose limitations on the type of transceivers and other loop components being deployed, and this could result in higher system costs     

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.     

Optical loss property of silica-based single-mode fibers

The optical loss property of silica fibers has been investigated theoretically and experimentally based on their Rayleigh scattering and absorption losses. The Rayleigh scattering loss for fibers has been estimated using Rayleigh scattering coefficients and power distribution in the fiber. The Rayleigh scattering coefficients are measured for preforms prepared for fiber fabrication and are discussed for GeO₂ -doped and F-doped glasses. The relationship between the optical loss and fiber parameters is clarified. Moreover, the loss increase due to residual stress which occurs during the drawing process is simulated. The optical loss limitations for GeO₂-doped and pure silica core fibers are shown     

Dispersion and bandwidth spectra in single-mode fibers

Bandwidth spectra of single-mode fibers are calculated from experimentally obtained chromatic-dispersion-versus-wavelength curves. Results include second-order effects on bandwidth which depend on the curvature of the dispersion curves. Examples illustrate how bandwidth spectra change as a function of source power spectra. They also show how small changes in fiber dimensions and refractive-index differences can cause significant bandwidth changes at 1.3 μm wavelength.     

Numerical aperture of single-mode photonic crystal fibers

We consider the problem of radiation into free space from the end-facet of a single-mode photonic crystal fiber (PCF). We calculate the numerical aperture NA = sin /spl theta/ from the half-divergence angle /spl theta/ /spl sim/ tan/sup -1/ (/spl lambda///spl pi//spl omega/) with /spl pi//spl omega//sup 2/ being the effective area of the mode in the PCF. For the fiber first presented by Knight et al. (1996), we find a NA /spl sim/ 0.07 which compares to standard fiber technology. We also study the effect of different hole sizes and demonstrate that the PCF technology provides a large freedom for NA engineering. Comparing to experiments we find good agreement.     

Eigenstates of polarization of elliptical single-mode fibers

The degree of polarization of radiation in an elliptical polarization-maintaining fiber and the polarization states of eigenpolarization modes of such fibers have been experimentally investigated in a wide spectral range. It has been shown that the elliptical fibers are uniform, homogeneously twisted fibers with elliptically polarized eigenpolarization modes. The ellipticity of the eigenpolarization mode is independent of fiber length and increases with wavelength, while the azimuth of the eigenpolarization mode is spectrally independent