On-chip transformation optics for multimode waveguide bends

Abstract

Current optical communication systems rely almost exclusively on multimode fibres for short-and medium-haul transmissions, and are now expanding into the long-haul arena. Ultra-high bandwidth applications are the main drive for this expansion, based on the ability to spatially multiplex data channels in multimode systems. Integrated photonics, on the other hand, although largely responsible for today's telecommunications, continues to operate almost strictly in the single-mode regime. This is because multimode waveguides cannot be compactly routed on-chip without significant inter-mode coupling, which impairs their data rate and prevents the use of modal multiplexing. Here we propose a platform for on-chip multimode devices with minimal inter-mode coupling, opening up the possibilities for integrated multimode optics. Our work combines a novel theoretical approach-large-scale inverse design of transformation optics to maximize performance within fabrication constraints-with unique grayscale-lithography fabrication of an exemplary device: a low-crosstalk multimode waveguide bend.

Silicon-based on-chip multiplexing technologies and devices for Peta-bit optical interconnects

“…On the other hand, when using the multimode SDM technology, the waveguide design should be avoid any undesired mode coupling/conversion to low the channel crosstalk. For example, a multimode waveguide cannot be bent sharply and one has to introduce a large bending radius [161]. Besides, it is not easy to handle too many modes (e.g., > 10) in a planar waveguides due to the mode coupling and crosstalk.…”

“…In order to achieve a small bending radius as well as low mode crosstalk, one can reduce the mode mismatching by modifying the refractive index profile with the assistance of transformation optics theory [161]. Another simple way is introducing a bending section with a gradually-varying curvature, which has been applied to bent singlemode SOI nanowires successfully [166].…”

Silicon Multimode Photonic Integrated Devices for on-Chip Mode-Division-Multiplexed Optical Interconnects

“…In Ref. [25], an SiO 2 -on-Si asymmetric mode coupler is utilized to convert the LP 01 to the LP 11 mode and the waveguides are connected to the few-mode fiber by butt coupling method. In Ref.…”

“…In order to reduce the complexity, fewmode fibers have been developed and the few-mode (de)multiplexing is realized with some complicated free-space optical setups [16][17][18][19][20][21][22][23][24][25], which, however, is very difficult to extend to include additional modes. For photonic networks-on-chip, the situation becomes much better because multi-mode planar optical waveguides can be precisely fabricated to manage the propagation of multi-modes and some specific PICs can be designed to realize the conversion between the eigen-modes conveniently [14].…”

Mode-selective wavelength conversion based on four-wave mixing in a multimode silicon waveguide

“…This technology is also promising in order to increase the capacity of silicon databusses for on-chip optical interconnections [2][3][4][5][6][7] . MDM may be used to enhance the throughput of the interconnections while limiting the number of required optical sources 2 , whose integration onto the silicon platform is still the object of investigations. In wavelength division multiplexing (WDM) networks, wavelength-conversion is an essential functionality.…”