Hosung Chang

All-Optical Logic Functions in a Bent Nonlinear Y-Junction Waveguide

We propose and study all-optical logic gates, performing two input AND, OR and exclusive-OR (XOR) functions in a bent nonlinear Y-junction waveguide. The operation of the proposed device is based on the evolution of a nonlinear guided wave along a bent nonlinear waveguide. Since the characteristics of beam propagation depend on the nonlinearity, input power and bending angle of the waveguide, we could implement several all-optical logic functions (AND, OR and XOR) in the waveguide end and nonlinear medium, varying the above parameters.

A multimode-interferenced electrooptic TE/TM mode splitter

TE/TM mode splitting is an important integrated-optic function for fiber communication system and fiber sensors, where orthogonal polarization states of the signals are particularly emphasized. Guided-wave TE/TM mode splitting has been demonstrated in LiNbO/sub 3/, III-V compound semiconductors and polymers. They used an asymmetric Y-junction with different preferences of polarizations, a double mode waveguide with different coupling lengths for TE and TM modes, and the photo-bleaching induced birefringence, respectively. We present a novel TE/TM mode splitter utilizing the multimode interference and the linear electrooptic (LEG) effect, It employs a new operating principle, and shows several important characteristics: high extinction ratio, low excess loss, easy fabrication and large fabrication tolerance, and integratibility with other photonic devices.

A modified coupled‐mode analysis for asymmetric coupled waveguides

We present a modified coupled-mode formulation for an asymmetric two-waveguide coupler in which the trial field is expressed as a linear combination of the fundamental modes of the individual waveguides, with an additional phase-variation term determined from the orthogonality of the normal modes. The method provides more accurate solutions than the conventional theory, and the results satisfy power conservation.

Design of Tapered Transmission Lines with Arbitrary Reflection Characteristics

The Fourier transform method for the design of tapered transmission lines with arbitrary reflection characteristics is extended by employing an iterative scheme. We derive an approximate spectral function which consists of an amplitude function and a phase function from a nonlinear Riccati equation and the spectral function improves numerically by iteration. We also resolve the problem of discontinuity that may occur at both ends of the taper section. This method enhances the degrees of freedom in designing tapered lines and numerical examples of microwave filters and impedance matching circuits are given to illustrate the validity of the present method.

A coupled‐mode formulation based on the second‐order coupled‐mode equations

We present a trial solution for second-order coupled-mode equations and derive power-conservation law from the coupled-mode equations. We investigte the validity of using the second-order equations and the slowly varying envelope approximation, and the numerical results show that the usual assumption, which is that the total field may be expressed as a linear combination of individual guided modes, must be modified when the structure is strongly coupled.