Compact passive silicon photonic devices with high performance are always desired for future large-scale photonic integration. Inverse design provides a promising approach to realize new-generation photonic devices, while it is still very challenging to realize complex photonic devices for most inverse designs reported previously due to the limits of computational resources. Here, we present the realization of several representative advanced passive silicon photonic devices with complex optimization, including a six-channel mode (de)multiplexer, a broadband 90 deg hybrid, and a flat-top wavelength demultiplexer. These devices are designed inversely by optimizing a subwavelength grating (SWG) region and the multimode excitation and the multimode interference are manipulated. Particularly, such SWG structures are more fabrication-friendly than those random nanostructures introduced in previous inverse designs. The realized photonic devices have decent performances in a broad bandwidth with a low excess loss of <1 dB, which is much lower than that of previous inverse-designed devices. The present inverse design strategy shows great effectiveness for designing advanced photonic devices with complex requirements (which is beyond the capability of previous inverse designs) by using affordable computational resources.
Multimode silicon photonics have drawn tremendous attention because the introduction of higher-order modes greatly enhances the capacity of mode-division-multiplexing (MDM) data transmission systems as well as improves the flexibility of on-chip photonic device designs. As the cornerstone of multimode silicon photonics, plentiful multimodemanipulation photonic devices have been developed successfully. On the other hand, more and more emerging applications have been stimulated by higher-order modes introduced in multimode silicon photonics. This paper gives a review for our recent processes in the development of multimode silicon photonic devices. Keywords: mode, multiplexer, conversion, bend, filter, silicon, waveguide.
A graphene photodetector based on ultra-thin silicon waveguide at 1.55μm is proposed. By reducing the silicon core thickness, the fundamental TE waveguide mode is less confined and light-graphene interaction is enhanced. Benefiting from the ultrathin silicon waveguide and reflector structure, the graphene absorption coefficient reaches 0.36 dB/μm. A 10nm-thick CVD-grown hexagonal boron nitride is covered on the graphene to improve the device performance. With the help of metal-graphene-metal structure, the contact resistance is reduced dramatically. The devices have shown a responsivity of 1.4 mA/W at 0 V bias and 23.1 mA/W at 0.3 V bias with 0.24 mW input optical power. The measured 3-dB bandwidth is 17GHz under 0V bias voltage at 1550 nm.
SU-8 optical waveguides and devices are developed for the 2 μm wavelength range for the potential applications in the future high-capacity optical communications operating at 2 μm. The mode properties of the SU-8 optical waveguides are analyzed numerically. The SU-8 optical waveguides and devices are fabricated with the spin-coating process. The measured propagation losses for the fabricated SU-8 optical waveguides is about 10dB/cm. The demonstrated microring resonator (MRR) has a Q-value of 5000.
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