T. Wongcharoen

Accurate analysis of MMI devices with two-dimensional confinement

The accurate analysis of multimode interference (MMI) devices with two-dimensional (2-D) confinement has been demonstrated by using the least squares boundary residual (LSBR) method. Accurate modal propagation constants and spatial field profiles in the MMI section are obtained by using the vector H-field based finite element method. The accurate calculation of the excited modal coefficients is achieved by using the LSBR, which satisfies the continuity of the transverse field components more rigorously than using simple overlap integrals.

Electro-optic directional coupler switch characterization

Results are presented on a study of the important parameters of synchronous and nonsynchronous, weakly and strongly coupled optical directional couplers using the finite element method. Accurate propagation constants and field profiles have been obtained for the modes of the isolated guides and the supermodes of the coupled system. The power transfer efficiency between nonidentical coupled optical waveguides has been calculated using the coupled mode, the least squares boundary residual and the finite element-based propagation methods. To show the advantages of the finite element-based approaches, the power transfer efficiency between coupled waveguides with two-dimensional confinement is presented.

Accurate characterization of optical filters with two-dimensional confinement

A rigorous numerical procedure is presented for the accurate characterization of optical filters incorporating two nonidentical coupled waveguides. Numerically simulated results are shown for InGaAsP/InP-based design indicating narrow bandwidth is achievable, by using waveguides with two-dimensional confinement. The numerical solution presented here also suggests that by using the multiple quantum well (MQW) region for a waveguide core the polarization dependent properties of the device can be compensated.

Improved laser-fiber coupling by using spot-size transformer

Improved coupling between a laser and a fiber is demonstrated using a synchronous directional coupler section with nonidentical waveguides to enlarge the spot-size for improved butt-coupling.

Rigorous beam propagation analysis of tapered spot-size converters in deep-etched semiconductor waveguides

A rigorous study of a tapered spot-size converter in a deep-etched GaAs/AlGaAs optical modulator is reported through the use of full vectorial approaches. Mode beating in the tapered section, the expansion of the spot-size, and the consequent enhancement of the coupling to an optical fiber are also reported.

Accurate analysis of multimode interference devices

The accurate analysis of multimode interference devices is demonstrated by using the least-squares boundary residual (LSBR) method. Accurate modal propagation constants and spatial field profiles in the multimode interference (MMI) section can be obtained by using the finite-element method. The accurate calculation of the excited modal coefficients is achieved by using the LSBR, which satisfies the continuity of the transverse field components more rigorously than the simple overlap integrals.

Characterization of directional coupler-based optical guided-wave devices

The accurate characterization of directional coupler-based photonic devices is presented using the coupled mode and the least squares boundary residual approaches along with the finite element method. Results are obtained showing the power transfer ratio between such coupled waveguides, and compare favourably with those of published data.

POWER COUPLING EFFICIENCY FOR ELECTRO·OPTIC DIRECTIONAL COUPLER SWITCH

The investigation of coupling between optical waveguides is important for many directional coupler-based devices. Optical directional couplers, made from electro-optic materials, are the basis of several guided-wave devices including switches and modulators. The refractive index of the waveguide material changes due to the applied modulating field, which in turn affects the propagation constants of the two individual guides, the phase matching between them and the coupling length. When the change of refractive indices in the two guides are not identical due to unequal change of refractive indices in two coupled guides, then the power transfer efficiency deteriorates due to lack of phase matching between the guides. All these effects, combined together, change the total power transfer from one guide to another as a function of the applied potential, for switches and modulators.

Spot-size conversion and near-circular far-field profile for efficient laser-fiber coupling

When a photonic integrated circuit (PIC), incorporating active devices, producing a small and noncircular spot-size is directly butt-coupled to single mode fiber (SMF) with a larger and circular spot-size, use of this arrangement can cause typically a 10 dB (or 90% power) loss. In this presentation, an approach of using two non-identical but phased matched uniform coupled waveguides is considered, to achieve the necessary spot-size conversion where such a system can be easily fabricated by using standard techniques.

Polarization maintaining semiconductor waveguides

A novel optical waveguide with a layered core, which supports only a single polarization state, is optimized by adjusting the layer compositions and its expected performance is reported by using rigorous numerical methods.