Dipakbin Q. Chowdhury

Dispersive optical bistability in a dielectric sphere

Dispersive optical bistability in a dielectric sphere is modeled. The analysis is applicable to cases in which the incident frequency is near a morphology-dependent resonance of the sphere. The refractive index of the sphere is assumed to vary as m(r) = m0 + m2I(r), where I(r) is the internal intensity at position r. In general I(r) contains all the modes of the sphere. However, we first obtain a simplified analytical expression for bistability in which we assume that I(r) consists of a single near-resonant mode. We also analyze the bistability problem; in the analysis we include all the modes of the sphere in computing I(r). The agreement between the all-mode and the single-mode results is good when the incident frequency is within a few linewidths of ahigh-Q (>104) mode. We compare bistability in a dielectric sphere with that in a Fabry–Perot cavity. We use a quasi-steady-state approximation to calculate the time-dependent backscattering from a CS2 sphere near a resonance. The computed backscattered intensity has bistable characteristics.

Perturbation model for computing optical fiber birefringence from a two-dimensional refractive-index profile

A vector perturbation model for computing optical fiber birefringence for an arbitrary two-dimensional index profile is developed. The vector wave equation is solved to yield the unperturbed vector f ields for an azimuthally symmetric refractive index. These f ields are used as the basis for the degenerate perturbation analysis. Unlike with the scalar perturbation theory, only f irst-order perturbation analysis suff ices for the computation of birefringence. Computed birefringence for various perturbations are reported.

Absorptive bistability in a dielectric sphere

Theoretical results on absorptive optical bistability of micron-sized droplets doped with a saturable absorber are presented. Bistability is observed only when the incident light frequency is near or on a morphology dependent resonance of the sphere. Results on Q-switching are also presented.

Polarization dependent loss induced gain ripple statistics in erbium-doped fiber amplifiers

A Monte-Carlo model is used to simulate the wavelength-dependent polarization dependent loss (PDL) statistics and PDL induced gain-ripple statistics for a chain of concatenated optical elements in an erbium-doped fiber amplifier (EDFA). Simulations indicate that unlike polarization-mode dispersion (PMD), the quadrature sum of PDL overestimates the mean of the PDL distribution. We show that EDFA total PDL variance scales linearly with the individual component PDL variance. Moreover, the relative impact of PDL on the gain ripple is reduced in the presence of the PDL independent gain ripple in the EDFA.

Analytic estimation of penalty due to filter transfer function variation on WDM systems

Analytic estimates of pulse broadening and system penalty caused by wavelength-division-multiplexing (WDM) filter amplitude variation is derived. We show that root mean square pulsewidth is not a reliable measure of system penalty and noise equivalent bandwidth plays a key role in determining system penalty.

Ultrafast optical fiber polarization-mode dispersion measurement using wavelength scanning technique

Summary form only given. Jones matrix eigenanalysis provides the most direct and reliable polarization-mode dispersion (PMD) vs. wavelength measurement. However, wavelength scanning (WS) technique has also been commercially available for optical fiber PMD measurement. Here we use the WS technique for an ultrafast realtime measurement of arrival-time statistics and, hence, PMD.

Polarization mode dispersion in optical communication systems

Summary form only given. Polarisation mode dispersion (PMD) is a major impairment for high-bit-rate optical systems. The objective of this course is threefold: (1) understand the physical phenomena of PMD, (2) review the current status of understanding of the impact of PMD on optical systems, and (3) PMD mitigation approaches. In this course we will introduce the concept of PMD and its various mathematical description briefly with emphasis on visualizing and comparing different ways of describing PMD. Then, very briefly, we will concentrate on some measurement aspects of PMD in systems. Current understanding of PMD impact on systems will be summarized next. System impact of PMD will be reviewed in three stages. (1) Impact of fiber PMD, 1st and higher order, in high-bit-rate systems in presence of chromatic dispersion. (2) Impact of fiber and discrete component PMD on optical systems. (3) Impact of fiber and component PMD on optical systems in presence of polarization dependent loss. Finally, PMD mitigation approaches will be discussed.

Perturbation Model for Computing Optical-Fiber Birefringence from a 2-D Refractive Index Profile

In a cylindrically symmetric optical fiber the vector modes are twofold degenerate. Two orthogonally polarized modes have the same propagation constant. Any deviation from perfect azimuthal symmetry would remove the polarization degeneracy, introducing birefringence. For a weakly- guiding fiber scalar perturbation theory have been used successfully to investigate birefringence caused by an elliptic deformation [1-4]. A vector correction to the scalar modes, i.e., a second order perturbation theory, is necessary to compute the birefringence. For an arbitrary 2-D profile these computations are complicated. However, if we start with the vector modes of a radially varying but azimuthally symmetric fiber and then treat the azimuthal variation as a perturbation to the vector modes, only first order perturbation suffice. Here we present a perturbation model based on the above idea. We closely follow the derivation of Ref. [4]. The formulation is applicable to planar waveguides once the vector modes are known.