Ramanand Tewari

Dispersion-shifted dual-shape core fibers. Optimization based on spot size definitions

Design features, for very low bend and splice losses, in dispersion-shifted dual-shape core (DSC) single-mode fibers are obtained in terms of characteristic mode spot sizes W responsible for splice loss, and W/sub infinity / responsible for bend loss. Dual-shape core fiber designs are given with W/sub infinity //W lying between 1.16 and 1.33 while maintaining the mode spot size between 4 and 5 mu m at the operating wavelength of 1550 nm. With this design goal it is shown that bending loss would be lower in a step-index than in a graded-index DSC fiber. Further, conventional single clad step-index or triangular-index dispersion-shifted fibers are seen to have higher bending loss than well-designed DSC fibers. >

Analysis of tunable single-mode fiber directional couplers using simple and accurate relations

We present simple and accurate relations for the study of parallel and curved tunable single-mode fiber directional couplers employing step-index or graded-index fibers. Analytical results for the various coupler parameters such as coupling coefficient, effective interaction length, tunability, and channel wavelength separation in directional coupler wavelength filters are presented. These results must prove very useful for an easy, quick, and accurate prediction or design of tunable single-mode fiber directional couplers.

Accurate analysis of single-mode graded-index fiber directional couplers

We present an accurate coupled-mode analysis to evaluate the coupling characteristics of identical single-mode graded-index fiber directional couplers. We also give an empirical relation for calculating the coupling length of a fiber coupler formed by fibers having profile parameter<tex>q</tex>, normalized frequency<tex>V</tex>, and normalized separation<tex>d/a</tex>;<tex>d</tex>is the distance between the fiber centers and<tex>a</tex>, the radius of the fiber core.

Scalar variational analysis of single mode fibers with Gaussian and smoothed-out profiles

Abstract A scalar variational analysis is presented to study the propagation characteristics of weakly guiding single mode fibers with gaussian and smoothed-out form of refractive index profiles. It is shown that the two parameter gaussian-exponential approximation for the fundamental mode describes the propagation characteristics with much higher accuracy as compared to the single parameter gaussian approximation.

Estimation of the modal field profile of single mode graded-index fibers from the far-field pattern

Abstract We give a method to estimate the transverse modal field profile of weakly guiding single mode graded-index fibers from the far-field radiation pattern. We also show that if the parameter k o a is known, then the q and V values of the fiber can also be determined; here k o is the free space wave number, a the radius of the fiber core, q the profile parameter, and V the normalised frequency.

On microbending loss calculations in single mode fibers with arbitrary index profiles

Abstract We present an analytical method to evaluate the auxiliary function and spot sizes determining microbending loss in single mode fibers with arbitrary refractive index profiles. Comparison with the exact numerical results shows that the present method gives very accurate results for spot sizes. The method is simple and requires relatively less computational effort.

Modified in-line dispersion prism

We present a simplified design for a modified in-line dispersion prism that disperses light for zero deviation following the principle of total internal reflection. This design eliminates the need for a high-reflection coating on the faces of the prism. Correction in the lateral displacement of the beam is achieved using Murtys technique. Some possible applications are given.

Analysis of nonlinear TE waves in silver-sodium ion exchanged waveguides in glass

The paper presents the formulation of nonlinear TE waves guided by waveguides having second order polynomial in the film with nonlinear cover medium. These waveguides are usually obtained in glass by silver-sodium ion exchange technique. It is shown in this paper that the formation leads to an exact dispersion relation and an exact expression for power flow.

A TECHNIQUE TO CHARACTERIZE POLISHED FIBER BLOCKS AT NEAR-INFRARED WAVELENGTHS

Abstract A technique to estimate the characteristics of polished fiber blocks at near-infrared wavelengths from measurements made with a HeNe laser in the visible region is proposed. It exploits the liquid-drop overlay index method to characterize polished fiber blocks in the region where the overlay index is larger than the effective index of the fiber mode. The study reveals a good agreement between the estimated and experimental results.

An accurate analysis of directional couplers typical of electron beam writing techniques

Abstract An accurate analysis of graded index optical directional couplers of a kind which could be fabricated by electron beam writing techniques, is presented. Modelling the refractive index profile of the channel waveguides, forming the coupler by a secant hyperbolic function, we have obtained exact expressions describing various characteristics of the directional coupler, including the variation of coupling length with waveguide spacing.