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Silicon-based electro-optic modulators are the key devices in integrated optoelectronics. Integration of the graphene layer and the photonic crystal (PC) cavity is a promising way of achieving compact modulators with high efficiency. In this paper, a high-quality (Q) acceptor-type PC nanocavity is employed to integrate with a single-layer graphene for realizing strong modulation. Through tuning the chemical potential of graphene, a large wavelength shift of 2.62 nm and a Q factor modulation of larger than 5 are achieved. A modulation depth (12.8 dB) of the reflection spectrum is also obtained. Moreover, the optimized PC nanocavity has a large free spectral range of 131.59 nm, which can effectively enhance the flexibility of the modulator. It shows that the proposed graphene-based PC nanocavity is a potential candidate for compact, high-contrast, and low-power absorptive modulators in integrated silicon chips. [ABSTRACT FROM AUTHOR]

We present tunable double and multistep heterostructure air-slot nanocavities in two-dimensional silicon photonic crystals by introducing structural changes. Through changing the air-slot width, air hole radius and air hole position in the cavity region, the continuous tunability in resonant frequency and Q value can be realized synchronously in a wide frequency bandwidth. Finite-difference time-domain methods are used to study the optical properties of the nanocavities and the attainable Q exceeds 10 6 in a wide frequency range of 0.0152 a / λ . The results show that our designs may be promising for constructing flexible photonic devices with broadband and controllable frequency tuning. [ABSTRACT FROM AUTHOR]

The splitting properties are investigated in two dimensional silicon photonic crystals by adjusting the interface of the structure. Introducing elliptical air holes with optimized parameters on the heterointerface, the forward transmittance is significantly improved in a wide frequency range. Correspondingly, the unidirectional two-beam splitter is realized and the relative light intensities of each beam can be continuously adjusted by modulating the area ratio (AR) of elliptical air holes. Furthermore, the output beams can be changed into three and five beams by alternately introducing elliptical air holes on the monolayer output interface. Not only the forward light intensities of each beam can be continuously adjusted, but also the reverse can be tuned simultaneously by modulating the shape of elliptical air holes. Particularly, the light transmission behaviors along two opposite directions are significantly different. Moreover, the elliptical-shaped air holes have more structural freedoms and increase the design flexibility of the devices. The performance of the splitter is found to be very encouraging in the complex photonic integrated circuits. [ABSTRACT FROM AUTHOR]