A nano-silicon-photonic switch driven by an optical gradient force

Abstract

Using light to dynamically and stably redirect the flow of another beam of light is a long-term goal for photonic-integrated circuits. However, it is challenging to realize a practically all-optical switching device in silicon owing to its weak optical nonlinearity. Major published work on all-optical switches were using single-photon absorption and two-photon absorption, which requires ultrahigh switching energy. This paper presents a nano-silicon-photonic all-optical switch driven by an optical gradient force, in which a fast switching speed with low power consumption is obtained. Each switching element is composed of a waveguide crossing connection and a micro-ring resonator. The ring resonator is side-coupled to a double-etched waveguide crossing, while the micro-ring resonator is partially released from the substrate and becomes free-standing. When the “drop” port is in “OFF” state, the wavelength of the signal light from the “input” port does not satisfy the resonant condition in the micro-ring. Therefore, light is mainly transmitted to the "thru" port without control light. When a control light is loaded to the “add” port, of which the wavelength satisfies the resonance condition in the micro-ring, a strong optical gradient force is generated by the induced evanescent optical field. The freestanding arc of the ring is then bent down to the substrate, leading to a cavity resonance wavelength shift. As a result, the signal light is diverted to the “drop” port and the corresponding transmission state is switched to the “ON” state. The optical switch is fabricated by nano-photonic fabrication processes using standard silicon-on-insulator (SOI) wafer. The waveguide structures have a width of 450 nm and a height of 220 nm for a single mode transmission; the outer radius of the ring in the switching element is 15 μm; the coupling gap between the ring and the nano-waveguide is 200 nm; the system is fabricated through two-step lithography and plasma dry etching processes while the free-standing arc is released by undercutting the buried oxide layer. #br#A switching time of 180 ns(rise) and 170 ns (fall) is experimentally demonstrated, which is much faster than that of conventional optical switches. The present optical switch can reach a high extinction ratio (10.67 dB) and a low crosstalk (-11.01 dB). In addition, the proposed switch has the advantages of compact size and low power consumption. Potential applications of this optical switch include photonic integrated circuits, signal processing, and high speed optical communication networks.