A. Koster

Polarization-independent single-mode rib waveguides on silicon-on-insulator for telecommunication wavelengths

A theoretical analysis of the influence of geometrical parameters on the polarization sensitivity properties is reported for single-mode silicon-on-insulator rib waveguides. The SOI rib-waveguide dimensions (height, width and etching depth) leading simultaneously to single mode propagation and polarization independence have been calculated for waveguide heights ranging from 0.75 to 2 μm and for telecommunication wavelengths from 1.53 to 1.61 μm. The minimum etching depth is obtained for a nearly constant value of the ratio of the rib width over the waveguide height, within the considered height range, and is close to the rib width.

Experimental demonstration of a low-loss optical H-tree distributionusing silicon-on-insulator microwaveguides

The experimental demonstration of an optical H-tree distribution from one input to sixteen outputs compatible with the size of a microelectronic chip is reported. It is based on low-loss silicon-on-insulator rib submicron waveguides. Each branch is 1cm long and includes four ultracompact T splitters and two mirrors allowing 90° direction changes. The mean value of the global losses has been measured and is found equal to 26dB, which corresponds to a power of 2.6μW at each output, for a 3mW laser diode power at the input. This demonstration is an important step for on-chip optical clock distribution in complementary metal–oxide–Semiconductor integrated circuits.The experimental demonstration of an optical H-tree distribution from one input to sixteen outputs compatible with the size of a microelectronic chip is reported. It is based on low-loss silicon-on-insulator rib submicron waveguides. Each branch is 1cm long and includes four ultracompact T splitters and two mirrors allowing 90° direction changes. The mean value of the global losses has been measured and is found equal to 26dB, which corresponds to a power of 2.6μW at each output, for a 3mW laser diode power at the input. This demonstration is an important step for on-chip optical clock distribution in complementary metal–oxide–Semiconductor integrated circuits.

On-chip optical interconnects with compact and low-loss light distribution in silicon-on-insulator rib waveguides

The possibility of on-chip optical interconnects using rib waveguides on silicon-on-insulator substrates (SOI) is demonstrated. It is shown that ultrasmall (<0.4 /spl mu/m/sup 2/) rib waveguides intrinsically combine the advantages of low measured propagation losses (<0.5 dB/cm), negligible crosstalk between waveguides and no crosstalk at right angle crossings. A set of devices have been studied using finite difference time domain analysis to realize 90/spl deg/ change of direction and beam splitting, including fully etched mirrors and 1/spl times/2 star couplers of 14 /spl times/8-/spl mu/m area. Considering the compactness and efficiency of all studied devices, it is shown that a compact and low-loss light distribution can be achieved in an integrated circuit toward at least 64 photodetectors with SOI rib waveguides that fully meets requirements of minimal power to be delivered to receiver circuitry.

Low-loss optical waveguide on standard SOI/SIMOX substrate

Propagation loss measurements are reported for silicon waveguides formed by the thin silicon film of standard SIMOX substrate. Values very close to the theoretical limit associated with leakage towards the substrate are obtained when a high quality interface between the silicon film and the passivation layer is achieved.

Room temperature photocurrent spectroscopy of SiGe/Si p-i-n photodiodes grown by selective epitaxy

We present the photocurrent spectroscopy of Si/sub 1-x/Ge/sub x//Si double heterostructure p-i-n diodes selectively grown by low pressure chemical vapor deposition. The growth onto patterned wafers permits to obtain dislocation-free, fully strained Si/sub 1-x/Ge/sub x/ layers, much above the critical thickness. The band gap energy of Si/sub 1-x/Ge/sub x/ was determined at room temperature using the photocurrent spectra for Ge concentration in the range x=0.12-0.20 and compared to similar data obtained by electroluminescence.

Modelling of two-dimensional grating couplers on silicon-on-insulator waveguides using beam propagation method

We show how the parameters of a 3-D laser beam can be taken into account in the calculation of the coupling efficiency into a waveguide via a diffraction grating. Two well known formalisms are used: (i) differential analysis of the stratified guiding structure supporting the grating, and (ii) beam propagation method used to model the propagation in the waveguide. Both are linked by the Helmholtz equation in which a source term has been added corresponding to the field diffracted by the grating. Some results are given.

Analysis of integrated optical waveguide mirrors

A new method is presented to analyze reflection losses of integrated mirrors, taking into account the exact guided mode profile and assuming that this profile remains unchanged up to the reflecting plane. The fraction of the reflected light coupled to one of the guided modes of the output waveguide is calculated, taking into account the mirror reflection coefficient. The influence of both translation and tilt of the reflecting plane is investigated. The method applies for every guided mode and any reflection angles. Numerical calculations are derived for a 90/spl deg/ optical corner mirror.

Numerical simulation of a silicon-on-insulator waveguide structure for phase modulation at 1.3 /spl mu/m

This paper presents an analysis of a silicon-on-insulator (SOI) waveguide structure to be used for phase modulation at 1.3 /spl mu/m. The device consists of a two-dimensional (2-D) strip waveguide and a p/sup +//N/sup -//N/sup +/ lateral diode to realize the effective index modulation by free-carrier injection. We have calculated that an effective index modulation between 5/spl middot/10/sup -4/ and 10/sup -3/ could be obtained with current densities in the range from 500 to 1600 A/cm/sup 2/. A detailed numerical simulation of the device transient response is also reported. We demonstrate that an effective index modulation of 5/spl middot/10/sup -4/ could be obtained with a cutoff frequency of about 100 MHz. The phase modulator has a predicted figure-of-merit (FoM) of 160/spl deg//V/mm and a chirp factor of 25. Due to its full compatibility with complementary metal-oxide-semiconductor (CMOS)-SOI technology, the device is interesting for low-cost silicon-based optoelectronic systems.

Numerical simulation of a silicon-on-insulator waveguide Fabry-Perot interferometer for intensity light modulators at 1.3 /spl mu/m

We present a new silicon-on-insulator (SOI) integrated optics structure to be used as an intensity light modulator at 1.3 /spl mu/m. The device consists of a waveguide Fabry-Perot interferometer. In association with a grating coupler this device could function as a spatial light modulator or a reflective-mode modulator. The Fabry-Perot reflectivity is tuned by free-carrier injection from a forward-biased lateral P/sup +//N/sup -//N/sup +/ diode. Consequently, the reflected back guided-mode has an intensity that is a function of the effective index modulation in the central waveguide of the Fabry-Perot. Our numerical simulation reveals that such a structure could function for current densities not exceeding 500 A/cm/sup 2/ with a cutoff frequency of 100 MHz. This new type of device is compatible with the mature silicon technology and could replace in applications the standard liquid-crystal spatial light modulators or for fiber-to-the-home intensity modulators.

A new type of spatial light modulator at 1.3 µm on silicon-on-insulator substrate

The excellent thickness uniformity of the silicon film of standard silicon-on-insulator Simox substrates and the maturity of microelectronics processes allow to design optical modulator arrays using original waveguide ring resonators combined with two grating couplers. A first grating couples light from a monomode optical fiber into the resonator, part of the stored light is outcoupled by a second grating towards the output fiber. The output power is modulated by free-carrier injection in the waveguide core. Optical and electrical simulations show that for the modulator with a size compatible with fiber bundles, 10 ns switching times are achievable. Optimizations of the integrated optical elements and electrical control simulations are presented. A brief description of the fabrication process of the devices is also given.RésuméL’excellente uniformité d’epaisseur du film de silicium sur isolant Simox standard et la maturité des procédes de la microélectronique permettent de concevoir des matrices de modulateurs optiques é résonateur en anneau a structure en guide d’onde incorporant deux coupleurs à reseau. Un premier réseau permet d’injecter dans le résonateur la lumière issue d’une fibre optique monomode et une partie de la lumiére emmagasinèe est dècouplèe par un second rèseau vers la fibre de sortie. La puissance de sortie est modulèe par injection de porteurs dans le cceur du guide. Les simulations optiques et èlectriques montrent que pour un modulateur de taille compatible avec les faisceaux de fibres optiques, des temps de commutation de I’ordre de 10 ns sont accessibles. L’optimisation des èlèments d’optique intègrèe et les simulations de la commande èlectrique sont prèsentès. Le procèdè de fabrication de ces composants est brièvement dècrit.