Optically-controlled extinction ratio and Q-factor tunable silicon microring resonators based on optical forces

Abstract

Tunability is a desirable property of microring resonators to facilitate superior performance. Using light to control light, we present an alternative simple approach to tuning the extinction ratio (ER) and Q-factor of silicon microring resonators based on optical forces. We design an opto-mechanical tunable silicon microring resonator consisting of an add-drop microring resonator and a control-light-carrying waveguide (''controlling'' waveguide). One of the two bus waveguides of the microring resonator is a deformable nanostring put in parallel with the ''controlling'' waveguide. The tuning mechanism relies on the optical force induced deflection of suspended nanostring, leading to the change of coupling coefficient of microring and resultant tuning of ER and Q-factor. Two possible geometries, i.e. double-clamped nanostring and cantilever nanostring, are studied in detail for comparison. The obtained results imply a favorable structure with the microring positioned at the end of the cantilever nanostring. It features a wide tuning range of ER from 5.6 to 39.9 dB and Q-factor from 309 to 639 as changing the control power from 0 to 1.4 mW. Silicon photonics has become one of the most promising photonic integration platforms in the recent years owing to its small footprint, reduced power consumption, and availability of complementary metal-oxidesemiconductor (CMOS) fabrication technology [1][2][3][4][5][6] . The attractive small footprint feature of silicon waveguide structures is because of the high refractive index contrast between silicon and its oxide or air, which enables tight light confinement and benefits small bending radius of waveguide. Because of its unprecedented small size for potential high-density photonic interaction, silicon microring resonator, i.e. compact bended silicon waveguide in a small loop configuration, is of great importance to accelerate the success of silicon photonics 7 . Silicon microring resonators have been employed to facilitate miscellaneous applications, such as sensors 8 , modulators Generally speaking, all the optical properties of a passive silicon microring resonator, e.g. resonance wavelength, free spectral range, extinction ratio (ER), quality factor (Q-factor), are predetermined by the structure design and thus fixed once fabricated. In particular, it is always common to see the offset between the actually achieved properties and preliminarily designed ones due to the unavoidable fabrication errors. Hence, tunability of microring resonators is highly desirable in practical applications to facilitate superior performance. Previous tuning operations were mostly achieved by changing the refractive index of the materials of microring resonators. The already presented tuning mechanisms included the use of free-carrier dispersion effect 9 and thermo-optic effect 13 . The free carriers and the thermal nonlinear optical effect required for tuning can be generated either electrically or optically, enabling different applications including electro-optic modulators, optical switch...

Bandwidth and Wavelength Tunable All-Optical Filter Based on Cascaded Opto-Mechanical Microring Resonators

“…As the tuning results of the optical filter are mainly determined by the characteristics of the silicon opto-mechanical MRRs, the performances could be significantly improved by optimizing the device structures and parameters. Firstly, the nonlinear effects in the opto-mechanical MRRs could be enhanced by optimizing the separation gap between the oxide substrate and the free-hanging arc [37], [38]. In this case, the required pump powers could be reduced and the tuning efficiencies would be accordingly increased.…”

Optically-controlled extinction ratio and Q-factor tunable silicon microring resonators based on optical forces

“…In this scenario, a laudable goal would be to flexibly tune the optical properties of silicon microring resonators (e.g. ER, Q-factor) using optical forces 24 .…”