Abstract
All-optical tuning of the resonance of an optical cavity is used to realise optical signal-processing including modulation, switching, and signal-routing. The tuning of optical resonance is dictated by the two primary effects induced by optical absorption: charge-carrier-generation and heat-generation. Since these two effects shift the resonance in opposite directions in a pure silicon-on-insulator (SOI) micro-ring resonator as well as in a graphene-on-SOI system, the efficiency and the dynamic range of all-optical resonance-tuning is limited. In this work, in a graphene-oxide-silicon waveguide system, we demonstrate an exceptional resonance-tuning-efficiency of 300 p m/m W (0.055 π/m W), with a large dynamic range of 1.2 n m (0.22 π) from linear resonance to optical bistability. The dynamics of the resonance-tuning indicates that the superior resonance-tuning is due to large linear-absorption-induced thermo-optic effect. Competing free-carrier dispersion is suppressed as a result of the large separation between graphene and the silicon core. This work reveals new ways to improve the performance of graphene-on-waveguide systems in all-optical cavity-tuning, low-frequency all-optical modulation, and switching.
Highlights
All-optical control over optical cavities has been studied for optical transport as well as for applications in optical signal-processing and optical memory [1,2,3]
The dynamic range of the cavity-tuning before the onset of bistability is limited by two-photon absorption (TPA)
The resonator shows a tuning of 300 pm/mW (0.055 π/mW), dominated by the thermo-optic effect and an overall dynamic range of 1.2 nm (0.22 π) from linear resonance to bistability
Summary
All-optical control over optical cavities has been studied for optical transport as well as for applications in optical signal-processing and optical memory [1,2,3]. The bistability induced by the competition between TPA-generated thermo-optic effect and free-carriers in graphene has been experimentally observed in such geometries [19]. Time-domain spectral evolution is used for studying the carrier dynamics in silicon micro-ring resonators with and without graphene to investigate the reason behind the enhanced thermo-optic effect. We find that at low power levels, the resonator with graphene exhibits only thermo-optic effect due to cavity-enhanced linear absorption, while no such effect is observed without graphene [16]. In the resonator with graphene, both linear absorption and TPA make the thermo-optic effect stronger than the carrier-induced effects Such a system with dominant thermo-optic effect is useful for all-optical cavity-tuning with a large dynamic range
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