Hans Blok

A normalized approach to the design of low-loss optical waveguide bends

A normalized approach for optimal design of abrupt junctions between straight and curved waveguides operating in the whispering gallery mode regime is presented. The optimization includes the widths of both the straight and the curved waveguides, the lateral offset between them, and the bending radius of the curved waveguide. With this approach, optimum bend design is possible from a simple set of formulas or normalized graphs. Predicted transmission losses for optimally designed junctions are well below 0.1 dB. >

Modal analysis of a planar waveguide with gain and losses

In this study, we analyze the waveguiding properties of a planar waveguide amplifier in which losses and gain can be present simultaneously. It is found that the subsequent modes comprise both loss and gain modes. Also, the dependence of the gain on the state of polarization turns out to be significant for realistic dielectric structures. For strong losses or gain, the standard transfer matrix approach may become numerically unstable, therefore, a scattering matrices formalism is employed. A semiconductor-like gain profile enables us to study the gain as a function of /spl omega/ for realistic laser amplifier structures. >

Creation and annihilation of phase singularities near a sub-wavelength slit

The anomalously-high transmission of light through subwavelength apertures is a phenomenon which has been observed in numerous experiments, but whose theoretical explanation is incomplete. In this article we present a numerical analysis of the power fl ow (characterized by the Poynting vector)of the electromagnetic fi eld near a sub-wavelength sized slit in a thin metal plate, and demonstrate that the enhanced transmission is accompanied by the annihilation of phase singularities in the power fl ow near the slit.

Domain-integral analysis of channel waveguides in anisotropic multilayered media

A domain-integral equation method is presented to determine both propagation constants and the electromagnetic field distributions of guided surface wave modes in integrated optical waveguides. Both the waveguide and its multilayered embedding are anisotropic. The permittivity tensor of the embedding is assumed to be piecewise homogeneous. The kernels of the domain-integral equations consist of Greens tensors. The integral equations form an eigenvalue problem where the electric field strength represents the eigenvector. This problem is solved numerically by applying the method of moments. Numerical results are presented for an anisotropic ridge waveguide, embedded in an anisotropic multilayered medium. >

Chirping of an MMI-PHASAR demultiplexer for application in multiwavelength lasers

We report the first chirped multimode interference-based phased-array (MMI-PHASAR) for application in multi-wavelength lasers (MWLs). To avoid wavelength ambiguity in MWLs, undesired orders are suppressed by chirping the array of arms in the demultiplexer. Simulations show that a suppression of adjacent orders of more than 2 dB can be achieved. A 1/spl times/5 MMI-PHASAR has been realized in which the effect of the chirping is clearly visible according to the simulations.

Crosstalk performance of integrated optical cross-connects

Crosstalk performance of monolithically integrated multiwavelength optical cross-connects (OXCs) depends strongly on their architecture. In this paper, a semiquantitative analysis of crosstalk in 11 different architectures is presented. Two architectures are analyzed numerically in more detail and the results of the analysis show good agreement with previously reported experimental results.

SEM approach to the transient scattering by an inhomogeneous, lossy dielectric slab; Part 1: The homogeneous case

Abstract In two companion papers, the singularity expansion method is applied to the computation of the transient scattering of a pulsed electromagnetic wave of finite duration by an isotropic, inhomogeneous, lossy dielectric slab. The time-domain electric field is expressed as a Laplace inversion integral over the Bromwich contour. Conditions for the validity of a representation in terms of natural-mode quantities only are derived, i.e. for a vanishing integral along the closing contour in the left halfplane, the latter being the contribution from the essential singularity at infinity. In the first of these two papers, this procedure was analyzed for the case of a homogeneous slab. Here, this analysis is generalized for the inhomogeneous case. For that case, an alternative method exists, where the nonvanishing contribution from the essential singularity at infinity is suppressed by taking into account at each instant only the part of the incident pulse that has emerged into the slab. This method also applies when the closing conditions are violated. The location of the poles and the corresponding natural-mode field distributions and coupling coefficients are determined numerically with the aid of a Runge-Kutta integration method and Mullers root-finding procedure. In the subsequent summation of the residual contributions, acceleration of the convergence is applied. Numerical results are presented and discussed.

The diffraction of light by narrow slits in plates of different materials

We analyse the diffraction of light incident on a sub-wavelength slit in a thin plate. It is found that plates with different material properties, such as conductivity and thickness, show a fundamentally different behaviour of the field near the slit. Depending on the material properties, the light transmission can either be enhanced or frustrated. A correspondence between the handedness of optical vortices and the transmission behaviour is demonstrated.

Propagation of polarized waves in semiconductor laser amplifiers

We study the wave propagation through a semiconductor optical amplifier. It is investigated how the anisotropy caused by the quantum wells and the waveguiding together determine the polarization sensitivity of the amplification. We also analyze how the tensile strain in the quantum well can be optimized such that the resulting amplifier operates independent of the state of polarization of the incident field. The promising properties of non-(001) grown quantum wells are discussed.

Polarization sensitivity of the amplification in semiconductor optical amplifiers

There are two main reasons which explain why in a semiconductor laser amplifier the amplification can depend on the state of polarization: (1) Waveguiding can give rise to an amplification that differs for TE polarization and for TM polarization. This can happen even if the confinement to the active layer is comparable for the two polarization states. (2) The interaction process between light and matter in a quantum well is, in general, anisotropic. This is because the electrons are confined in only one direction. So the response to an electromagnetic field will have a tensor character, rather than a scalar. We analyze these two causes and show how they can be balanced, so that the desired polarization amplification can be achieved.