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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]

Abstract Asymmetric light transmission components, such as optical diodes, have attracted great interest for the capability of unidirectional light propagation. Highly desirable key performances of above devices are high unidirectionality, wide operational bandwidth and small scale. In this paper, we present an efficient design for asymmetric light transmission components in two-dimensional air-hole photonic crystals based on silicon. Through introducing tapered structure on the heterostructure interface, the forward transmittance of the optimized photonic crystal structure has increased greatly than that of the original structure almost within the entire frequency range (0.18–0.261 c/a). Meanwhile, the peak transmittance for the optimized structure increases by about 68.3%, varying from 28.4% to 47.8%. Moreover, the designed optical devices can effectively function as unidirectional equal-beam splitters, and multiple functions can be achieved synchronously in only one structure, which are important in the complex optical integrated circuits. Highlights • Asymmetric light transmission components based on PC heterointerface optimization are realized in broad bandwidths. • The optimized PC structure can effectively function as unidirectional equal-beam splitters. • Multiple functions can be achieved synchronously in only one PC structure. [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]

Ultra-slow light can enhance light–matter interactions and effectively realize all-optical buffering and modulation. In this paper, we present an efficient design for a two-dimensional square-lattice photonic crystal coupled-cavity waveguide, which can realize multi-frequency band slow-light transmission in the near-infrared band (1500–1640 nm).Through adjusting intercavity spacing N and structural parameters of elliptical air holes, high group index n g (202.46) within the bandwidth of 5.04 nm and improved normalized delay–bandwidth​ product of 0.6583 can be obtained at the wavelength of 1550.05 nm. Moreover, the designed devices can effectively function as a slow light sensor with the wavelength sensitivity of 585 nm/RIU. Multiple functions can be achieved synchronously in only one structure, which is essential in complex optical integrated circuits. • Multi-frequency band slow-light transmission is achieved in the near-infrared band (1500–1640 nm). • Both high group index (ultra-slow light) and high NDBP values can be obtained at the wavelength of 1550.05 nm. • The designed devices can effectively function as a slow light sensor with the wavelength sensitivity of 585 nm/RIU. [ABSTRACT FROM AUTHOR]