[Paper Review] Silicon photonic MEMS switches based on split waveguide crossings

Yinpeng Hu, Yi Sun+5 more|arXiv (Cornell University)|May 27, 2023

Photonic and Optical Devices4 citations

TL;DR

This paper proposes a silicon photonic MEMS switch using split waveguide crossings (SWX) to achieve low-loss, low-crosstalk, and ultrawideband switching by mechanically reconfiguring the waveguide halves. The 2×2 switch and a 64×64 Benes-topology array demonstrate excellent performance with excess loss below 1.5 dB and crosstalk below -30 dB across a broad bandwidth, enabling applications in photonic interconnects, LiDAR, and photonic computing.

ABSTRACT

The continuous push for high-performance photonic switches is one of the most crucial premises for the sustainable scaling of programmable and reconfigurable photonic circuits for a wide spectrum of applications. Conventional optical switches rely on the perturbative mechanisms of mode coupling or mode interference, resulting in inherent bottlenecks in their switching performance concerning size, power consumption and bandwidth. Here we propose and realize a silicon photonic 2x2 elementary switch based on a split waveguide crossing (SWX) consisting of two halves. The propagation direction of the incident light is manipulated to implement the OFF/ON states by splitting/combining the two halves of the SWX, showing excellent performance with low excess loss and low crosstalk over an ultrawide bandwidth. Both elementary switch and a 64x64 switch array based on Benes topology are fabricated and characterized, demonstrating great potential for practical scenarios such as photonic interconnect/routing, Lidar and spectroscopy, photonic computing, as well as microwave photonics.

Motivation & Objective

• To overcome performance limitations in conventional optical switches based on mode coupling or interference.
• To address bottlenecks in size, power consumption, and bandwidth of existing photonic switches.
• To develop a mechanically reconfigurable switch using split waveguide crossings for high-performance, scalable photonic circuits.
• To demonstrate practical feasibility through fabrication and characterization of a 2×2 switch and a 64×64 switch array.

Proposed method

• The switch is based on a split waveguide crossing (SWX) structure composed of two independent waveguide halves that can be physically moved relative to each other.
• Mechanical actuation separates or recombines the two halves to route light between input and output ports, enabling ON and OFF states.
• The design leverages MEMS actuation to control the relative position of the waveguide segments, minimizing optical mode perturbation.
• The SWX structure enables low excess loss and low crosstalk by maintaining mode overlap and symmetry during switching.
• A Benes network topology is used to scale the 2×2 switch into a 64×64 reconfigurable switch array.
• Fabrication is performed using standard silicon photonics processes, with post-processing for MEMS actuation integration.

Experimental results

Research questions

• RQ1 Can a mechanically reconfigurable waveguide crossing achieve low excess loss and low crosstalk across a wide optical bandwidth?
• RQ2 How does the split waveguide crossing design compare to conventional mode-coupling-based switches in terms of power efficiency and bandwidth?
• RQ3 What is the performance scalability of the SWX-based switch when integrated into a large-scale Benes network?
• RQ4 Can the SWX-based switch maintain low crosstalk and high extinction ratio in a 64×64 switch array configuration?
• RQ5 What are the practical limits of mechanical stability and switching speed in this MEMS-actuated silicon photonic switch?

Key findings

• The fabricated 2×2 SWX-based MEMS switch achieves an excess loss of less than 1.5 dB across a broad optical bandwidth.
• Crosstalk is suppressed below -30 dB across the entire operating bandwidth, indicating high signal isolation.
• The 64×64 switch array based on the Benes topology successfully demonstrates reconfigurable routing with low crosstalk and low loss.
• The switch operates over an ultrawide bandwidth, suitable for applications requiring multi-wavelength operation.
• The mechanical design enables stable switching with minimal optical mode distortion due to precise waveguide alignment control.
• The integration of MEMS actuation with silicon photonics enables scalable, low-power, and high-performance photonic switching.