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arXiv:1208.1124 · Journal of the Optical Society of America B

Analysis of bistable memory in silica toroid microcavity

Wataru Yoshiki, Takasumi Tanabe

Published Nov 16, 2012• 15 citations
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Abstract

We model the nonlinear response of a silica toroid microcavity using coupled mode theory and a finite element method, and successfully obtain Kerr bistable operation that does not suffer from thermo-optic effect by optimizing the fiber-cavity coupling. Our analysis shows it is possible to demonstrate a Kerr bistable memory with a memory holding time of 500 ns at an extremely low energy consumption.

DOI
10.1364/josab.29.003335

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We model the nonlinear response of a silica toroid microcavity using coupled mode theory and a finite element method, and successfully obtain Kerr bistable operation that does not suffer from thermo-optic effect by optimizing the fiber-cavity coupling. Our analysis shows it is possible to demonstrate a Kerr bistable memory with a memory holding time of 500 ns at an extremely low energy consumption.
We quantitatively analyze the performance of optical memories based on Kerr bistability in microcavites. We model a silicon nitride microring and a silica toroid microcavity, and examine the performances of these cavities in an actual situation where there is a thermo-optic effect. Numerical simulations based on coupled mode theory and the thermal diffusion equation reveal that an input power of 1.8 W is necessary to achieve a Kerr bistable memory in a silicon nitride microring, while that of only 1.7 mW is necessary in a silica toroid microcavity. This result shows that the use of silica toroid microcavity is advantageous when we want to demonstrate a Kerr bistable memory operation with a reasonably low input power. In addition, we quantitatively investigate the trade-off between the required input power and the response speed of the device.
Abstract All-optical tunable buffering was recently achieved on a chip by using dynamically tuned coupled mode induced transparency, which is an optical analogue of electromagnetically induced transparency. However, the small Q s of about 105 used in those systems were limiting the maximum buffering time to a few hundred ps. Although employing an ultra-high Q whispering gallery mode (WGM) microcavity can significantly improve the maximum buffering time, the dynamic tuning of the WGM has remained challenging because thermo-optic and pressure tunings, which are widely used for WGM microcavities, have a very slow response. Here we demonstrate all-optical tunable buffering utilizing coupled ultra-high Q WGM cavities and the Kerr effect. The Kerr effect can change the refractive index instantaneously, and this allowed us to tune the WGM cavity very quickly. In addition, from among the various WGM cavities we employed a silica toroid microcavity for our experiments because it has an ultra-high Q factor (>2 × 107) and a small mode volume, and can be fabricated on a chip. Use of the Kerr effect and the silica toroid microcavity enabled us to observe an on-chip all-optical tunable buffering operation and achieve a maximum buffering time of 20 ns.
Optical bistable responses in AlGaAs-based photonic crystal cavities with Al fractions of 0.16 and 0.27 under a stationary condition are studied. An analysis of the experimental results with a one-dimensional etalon model indicates that the bistable response is primarily driven by optical nonlinearities that stem from a heat generation in two-photon absorption and in free-carrier absorption. A free-carrier plasma effect is not influential, which is a major difference from the case of Si photonic crystal cavities. The accumulation of heat enables the phase or index to significantly change. An estimate indicates that a highQQQ-factor is advantageous for driving bistability exclusively by the Kerr effect.