Direct-access mode-division multiplexing switch for scalable on-chip multi-mode networks

By leveraging mode-division multiplexing (MDM), capacity of on-chip photonic interconnects can be scaled up to an unprecedented level. The demand for dynamic control of mode carriers has led to the development of mode-division multiplexing switches (MDMS), yet the conventional MDMS is incapable of directly accessing an individual lower-order mode that propagates in a multi-mode bus waveguide, which hinders its scalability and flexibility. In this paper, we propose and demonstrate the first direct-access MDMS as a novel platform for scalable on-chip multi-mode networks. At first, the highly efficient mode exchangers are developed for TE0–TE2 and TE1–TE2 mode swap, which are then employed to realize the direct-access mode add-drop multiplexers with high performances. The direct-access MDMS is then achieved based on the proposed mode add-drop multiplexers, which can be used for dynamically adding and dropping any selected mode carrier in a three-channel MDM. Moreover, the novel direct-access scheme is also adopted to simultaneously harness wavelength and mode carriers, leading to a wavelength/mode-hybrid multiplexing system with an enhanced link capacity of twelve channels. To further verify the utility of the MDMS, a multi-mode hubbed-ring network is constructed, where one hub and three nodes are organized within a ring-like multi-mode bus waveguide. The reconfigurable network traffic of 6 × 10 Gbps data streams are obtained by using three eigen modes as signal carriers. The measurement results show low bit-error rates (<10−9) with low power penalties (<3.1 dB).

Single Mode, Air-Cladded Optical Waveguides Supported by a Nano-Fin Fabricated with Direct Laser Writing

Single-mode, air-cladded optical waveguides have wavelength scale diameters, making them very fragile and difficult to handle and yet highly desirable for sensing and inter-chip photonic interconnects. These contradictory qualities are resolved in this work by supporting the optical waveguide with a nano-fin structure attached to a substrate, narrow enough and sufficiently tall to minimally impact the wave-guiding metrics of the solid core while providing structural mechanical integrity. The design considerations for the nano-fin-supported waveguide and its realization using a commercial direct laser writing system based on two-photon activation of a photopolymer is reported herein. The 3D printed waveguides are characterized and experimentally assessed, demonstrating low birefringence and an estimated propagation loss for LP01x and LP01y of 2.9 dB/mm and 3.4 dB/mm, respectively, attributed to surface roughness and the relatively high refractive index contrast with air.