Source-linked AI summary
Arbitrarily routed mode-division multiplexed photonic circuits for dense integration
Yingjie Liu, Ke Xu, Shuai Wang, Weihong Shen, Hucheng Xie, Yujie Wang, Shumin Xiao, Yong Yao, Jiangbing Du, Zuyuan He, Qinghai Song
TL;DR
Compact multimode routing must avoid mode leakage and inter-mode coupling in tiny structures. This paper uses digitized meta-structures and demonstrates arbitrarily routed MDM circuits with compact bends and crossings.
Problem
Compact multimode routing must avoid mode leakage and inter-mode coupling in tiny structures.
Method
The circuits use digitized meta-structures designed through index engineering and direct binary-search optimization of binary-material pixels.
Results
The first demonstrated MDM circuit supports arbitrary routing using extremely compact bending and crossing structures.
Takeaways & Limitations
The demonstration establishes compact, arbitrarily routed MDM circuitry based on engineered meta-structures.
Abstract
from arXiv · showhide
Mode-division multiplexing (MDM) is becoming an enabling technique for large-capacity data communications via encoding the information on orthogonal guiding modes. However, the on-chip routing of a multimode waveguide occupies too large chip area due to the constraints on inter-mode cross talk and mode leakage. Very recently, many efforts have been made to shrink the footprint of individual element like bending and crossing, but the devices still occupy >10x10 um2 footprint for three-mode multiplexed signals and the high-speed signal transmission has not been demonstrated yet. In this work, we demonstrate the first MDM circuits based on digitized meta-structures which have extremely compact footprints. The radius for a three-mode bending is only 3.9 μm and the footprint of a crossing is only 8x8um2. The 3x100 Gbit/s mode-multiplexed signals are arbitrarily routed through the circuits consists of many sharp bends and compact crossing with a bit error rate under forward error correction limit. This work is a significant step towards the large-scale and dense integration of MDM photonic integrated circuits.
Discussion
The work demonstrates an arbitrarily routed MDM circuit using extremely compact bends and crossings enabled by deep-subwavelength index engineering. An optimized index profile supports mode matching that avoids mode leakage and inter-mode coupling.
- Discussion: The study demonstrates an MDM circuit that can be arbitrarily routed using extremely compact bending and crossing.The authors describe this as the first such demonstration.
- Discussion: Deep-subwavelength index engineering enables optical-wave manipulation in the compact structures.The passage identifies index engineering at a deep-subwavelength scale as the basis for manipulating the optical wave.
- Discussion: An optimized index profile provides mode matching that helps avoid mode leakage and inter-mode coupling.The passage presents the optimized profile as key to suppressing both effects.
- Discussion: Δn=2.48 is the index contrast of the nanoholes with air cladding.The passage reports this contrast before discussing the usual deposition of thick oxide cladding on silicon.
Methods
The devices were optimized using a direct binary search over pixelated silicon-or-air meta-structures, then characterized with a 1550nm tunable-laser and fiber-chip coupling setup.
- Optimization method: Direct binary search provides fast convergence and straightforward implementation for optimizing digital meta-structures with binary material states.The method is suited to binary material optimization.
- Optimization method: The design area is discretized into circular or square pixels, with minimum feature size set by fabrication capability.Each pixel represents a localized design variable.
- Optimization method: Each pixel uses a binary material state of silicon or air.The binary material property defines the digital meta-structure.
- Device characterization: 1550nm tunable-laser characterization uses single-mode fibers, TE-polarization control, TE grating couplers, and a benchtop power meter.The setup includes a fiber-chip coupling stage, and the grating coupler is designed with 10-degree tilt relative to the chip.