All-optical, silicon based, fiber optic modulator using a near cutoff region

Abstract

We demonstrate, using molecular beam epitaxy and chemical vapour deposition grown silicon thin films, an all-optical modulator for single-mode guided light at 1.32 pm. A control beam of above band-gap light is used to generate electron-hole pairs via inter-band absorption and the resultant lowering of the effective refractive index brings the waveguide to cutoff thus limiting throughput. Near 100% modulation is obtained with less than 150 pJ energies with subnanosecond initiation and recovery times. The operation is stable and is polarization and wavelength independent in a three port geometry suitable for use as a logic gate. To reduce the total energy required to bring the waveguide to cutoff, the effects of using a small, already near cutoff and leaky region at the interaction region is investigated here. Preliminary measurements on a graded index, leaky mode, chemical vapour deposition sample resulted in a reduction by a factor of five or better in drive energy. By keeping the leaky region short, the losses can be kept to negligible values. Results in time resolved imaging of the guided mode are also presented along with the necessary design considerations for performance compatible with presently available communication solid state laser sources.Nous decrivons un modulateur entibrement optique pour la lumibre guidCe ? i un seul mode i 1,32 pm utilisant des couches minces de silice obtenues par Cpitaxie de faisceau molCculaire et deposition chimique de vapeurs. Un faisceau lumineux de contrble, d'Cnergie supCrieure a la largeur de la bande interdite, est utilisC pour gCnCrer des paires Clectron-trou par absorption inter-bandes; la diminution de I'indice de rifraction effectif qui en rCsulte provoque la coupure de la transmission dans le guide d'onde. On a obtenu une modulation de prbs de 100% avec des energies inferieures i 150 pJ et des temps de montCe ou de descente sous la nanoseconde. Le fonctionnement est stable, indkpendant de la polarisation et de la longueur d'onde, dans une gComCtrie ti trois entrees convenant ii I'utilisation du dispositif comme porte logique. Dans le but de rCduire l'energie totale requise pour provoquer la coupure dans le guide d'onde, nous Ctudions les effets de l'utilisation, i la rCgion d'interaction, d'une faible rCgion deji prks de la coupure et avec pertes. Des mesures prkliminaires sur un Cchantillon, fabriquC par dCpbt chimique de vapeur, ti indice gradue, en mode avec perte, ont montrk une reduction de I'Cnergie requise par un facteur Cgal ou supCrieur i cinq. En gardant courte la region en question, les pertes peuvent Ctre maintenues ? i des valeurs nigligeables.On prksente aussi des resultats sur la representation du mode guide avec resolution temporelle, en mCme temps que les considCrations de design nCcessaires pour assurer une performance compatible avec les sources laser i Ctat solide disponibles pour les communications.[Traduit par la revue]Can.

All-optical switching on a silicon chip

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