A research team from Nanyang Technological University (NTU) in Singapore used nano-scale photonic crystals to create the first all-optical switch operating in the near-infrared range, which is expected to be used in communications and consumer electronics. Find many applications.

    In the past, optical switches were mostly fabricated with microelectromechanical systems (MEMS), but they were limited by the upper limit of the speed at which mechanical components can move. In contrast, optically operated switches will likely have high switching in the picosecond (ps) range rate. NTU's Ai-QunLiu et al. recently successfully fabricated the first-ever fully optical switch by using the unique light absorption effect of photonic crystals, which is expected to be applied in the future global information and communication technology industry.

    Liu et al. first etched a square lattice of photonic crystals with a period of 100-200 nm on a silicon layer with a refractive index of 3.4. Each cylinder was 13 μm in height and 100-230 nm in diameter, and then removed two vertical rows in the center of the photonic crystal. The intersecting cylinders form a cross-shaped waveguide. Theory predicts that such a design would allow light to enter along one of the waveguides, and then pass through a pump laser (pumplaser) to illuminate a silicon pillar in the center of the cavity, guiding the light to flow out from any of the other three waveguides, forming a light switch.

    Earlier scientists in Canada have demonstrated that free carriers can be used to control the properties of photonic crystals. Therefore, Liu et al. hit a pulsed laser on the central silicon pillar of the structure, and used high-energy photons to excite free electrons and holes, thereby changing the local refractive index and light transmission characteristics. By precisely controlling the intensity of the pulsed laser, the researchers can control which waveguide the light flows from, achieving the effect of an optical switch.

    Liu pointed out that the biggest challenge is to fabricate photonic crystal structures with different radii and high aspect ratios, which usually requires specialized fabrication techniques and is currently a major obstacle to the development of photonic crystal components. The NTU team uses deep ultraviolet lithography and reactive ion etching (deep-reactive ion etching) to fabricate the above components.

    The most obvious application of all-optical modulators, or high-speed switches, is in communications, where picosecond-level switching rates are expected to dramatically increase transmission speeds that are currently limited to microelectronic components. The NTU group is trying to design new applications with nanophotonic crystal circuits and looks forward to working with industry to develop commercial applications of this technology