Enakshi K. Sharma

Propagation characteristics of single mode optical fibers with arbitrary index profiles: A simple numerical approach

We present here a rapidly converging numerical procedure for the direct evaluation of the propagation constant and its first and second derivatives in single mode optical fibers with arbitrary refractive index profiles. To illustrate the procedure we have also used it to evaluate the propagation constant and its derivatives in single mode optical fibers with power law profiles in the presence of a Gaussian axial index dip, and hence, studied the effect of a dip on the dispersion characteristics of the fibers.

Calculation of cutoff frequencies in optical fibers for arbitrary profiles using the matrix method

We here propose a simple numerical procedure to calculate the cutoff frequencies in optical fibers with any arbitrary refractive index profile including discrete numerical data from profile measurement. The cutoff problem is transformed into a matrix eigenvalue problem and the cutoff frequencies can be obtained by determining the eigenvalues of a matrix with elements given by simple expressions.

Exact ray paths in bent waveguides

We present here the Lagrangian formalism for studying the ray paths in cylindrically symmetric media. We have used the analysis to obtain the exact ray paths in bent slabs as well as in bent fibers with a separable profile.

Multilayer waveguide devices with absorbing layers: an exact analysis

We present here a simple exact procedure to obtain the complex propagation characteristics of multilayer waveguide devices with absorbing layers. We report the validity and illustrate the rapid convergence of our calculations on metal clad waveguide polarizers and detector loaded waveguides. The limited applicability of earlier proposed methods is also discussed

Matrix method for determining propagation characteristics of optical waveguides

We have transformed the scalar wave equation into a matrix eigenvalue equation, the diagonalization of which gives the guided modes and a discrete representation of the radiation modes. The method is simple and can be used for arbitrary refractive index profiles.

Variational analysis of directional couplers with graded index profile

A variational analysis of graded optical directional couplers is presented. Fabrication of such directional couplers by an electron-beam writing method has recently been reported. We have shown that our analysis gives better results than the WKB method which has been used previously to analyse such couplers. Further, our analysis involves much less algebraic and numerical work than the WKB method.

Long period grating refractive-index sensor: optimal design for single wavelength interrogation

We report the design criteria for the use of long period gratings (LPGs) as refractive-index sensors with output power at a single interrogating wavelength as the measurement parameter. The design gives maximum sensitivity in a given refractive-index range when the interrogating wavelength is fixed. Use of the design criteria is illustrated by the design of refractive-index sensors for specific application to refractive-index variation of a sugar solution with a concentration and detection of mole fraction of xylene in heptane (paraffin).

Field variational analysis for modal gain in erbium-doped fiber amplifiers

We define a complex refractive-index profile for the pumped erbium-doped fiber that depends on radial distance, pump and signal powers, and erbium-doping profile to obtain a modal gain and loss of the propagating signal and pump power by Rayleigh–Ritz variational analysis. This profile provides a novel way of looking at the gain characteristics of erbium-doped fiber amplifiers. The advantage of this approach is that it gives the actual modal gain and also eliminates the need to approximate the modal fields and can easily take into account any dopant and index profile.

Equivalent refractive index of MQW waveguides

In this paper, we have proposed some new numerical and semi-analytical methods for developing an equivalent three-layer model of an MQW waveguide. The waveguiding properties like effective index, field distribution, and fractional power within the core of the waveguide of these equivalent structures are compared with those of previously reported equivalent methods. These results are also compared with the results obtained from the exact multilayer analysis of the MQW waveguide. The waveguiding properties are accurately predicted by the semi-analytical method using variational analysis, and the computational effort is significantly reduced. The use of the three-layer equivalent is illustrated in obtaining an estimation of the waveguide losses and is used to study the effect of nonlinearity.

Analytical approximations for the propagation characteristics of dual-mode fibers

In this paper we present accurate analytical approximations for the modal fields of dual-mode optical fibers with power law profiles based on a scalar variational analysis. We propose single parameter and two parameter trial functions and use these to study the dispersion characteristics and estimate the value of the normalized frequency corresponding to zero intermodal dispersion, which defines the operating point for such fibers. Our results show that the relatively simple single parameter field for the LP11mode gives a good fit to the field inside the core and estimates the propagation constant fairly well, but is inadequate to calculate the dispersion characteristics. On the other hand, the two parameter field estimates all these characteristics with a high degree of accuracy and enables one to accurately compute the normalized frequency for zero intermodal dispersion as well as dispersion tolerance around this value.