Photonic meshes previously required a growing number of programmable components as systems scaled; universal transformations on N modes demanded O(N squared) phase shifters, limiting speed, size, and energy efficiency. A new circuit architecture now achieves signal routing between inputs and outputs using only O(N) programmable phase shifters. Researchers built and tested a three-by-three router in lithium niobate at an equipment-limited speed of ten megahertz with extinction ratios exceeding eleven decibels.

The design simplifies how signals are routed by requiring far fewer programmable components than current technology. This architecture uses a unique approach to connect inputs and outputs needing only a linear increase in the number of control elements, a sharp improvement over existing systems which demand an amount growing at a much faster rate. The need for greater computing power is driving innovation in distributed architectures, from artificial intelligence clusters to modular quantum processors; however, communication between nodes faces challenges regarding bandwidth, capacity, and energy consumption.

Reconfigurable optical switches offer a solution by dynamically allocating paths within networks without converting light into electrical signals. A key limitation of current technology lies in the number of programmable components needed: existing systems require an amount that grows dramatically as complexity increases, imagine needing a cable running from every house on a street to every other house. Researchers at Massachusetts Institute of Technology and Technical University of Denmark have now unveiled this new circuit design which simplifies signal routing using only a linear increase in control elements.

Linear Scalability Enables Simultaneous High Performance Photonic Routing

Signal routing now achieves connectivity between inputs and outputs utilising only O(N) phase shifters, a significant reduction from the previously required O(N squared) programmable components. This advancement has achieved a fundamental shift in scalability for photonic circuits. It overcomes limitations that prevented simultaneous low voltage operation, gigahertz speeds, zero static power consumption, lossless modulation, and compact designs; these features were unattainable together until now.

The researchers and Technical University of Denmark demonstrated this new architecture using a $3× $3 router fabricated on lithium niobate achieving sequential routing at an equipment-limited speed of ten megahertz with extinction ratios exceeding eleven decibels. The devices exhibit 1.92 GHz/V resonance tuning efficiency via the Pockels effect, allowing for an tiny footprint of just 100,μm^2 per programmable component alongside operation at voltages below five volts.

An impressive 6.2GHz electro-optic bandwidth is achieved by these phase shifters, enabling rapid switching speeds. Detailed characterisation confirmed that all output channels during routing tests exceeded eleven decibels in extinction ratio and demonstrated sequential data transfer at ten megahertz, a rate limited by testing equipment rather than circuit performance.

While achieving gigahertz-level continuous throughput remains challenging due to limitations in driving the Pockels effect rapidly enough for sustained high frequency modulation, this architecture’s reliance on a single passive multimode interferometer coupled with only N reflective phase shifters represents a strong reduction in complexity compared to existing designs needing O(N squared) components.

Pockels Effect Based Multimode Interferometer Signal Routing Architecture

To tackle scaling challenges within photonic circuits, the team developed an architecture centred around signal routing instead of universal transformations; this approach dramatically reduced component numbers. Their design employs a passive multimode interferometer which splits light into multiple channels that travel together without interfering and couples it with just one row of programmable reflective phase shifters. These devices use the Pockels effect to manipulate properties like refractive index (similar to squeezing clear gel and changing its shape).

They built a three-by-three router using x-cut thin-film lithium niobate utilising only one row of these phase shifters alongside a multimode interferometer connecting inputs to outputs in three steps. Achieving 1.92GHz/V resonance tuning efficiency, the devices reach an electro-optic bandwidth of 6.2GHz while operating at sub-5 Volt drive voltages within a footprint of 100 square micrometres; routing states demonstrated extinction ratios exceeding 11 dB with sequential speeds up to 10MHz.

Simplified Architecture Faces Speed Limits From Material Properties

While this new photonic circuit architecture dramatically reduces component numbers needed for signal routing, moving from quadratic to linear scaling with system size, achieving gigahertz speeds remains elusive. Demonstrations are currently limited by testing equipment to ten megahertz; however, material properties themselves could fundamentally constrain pushing performance much higher. The reliance on the Pockels effect presents challenges regarding radio frequency efficiency and capacitance that must be overcome before realising truly high-speed interconnects.

Despite current limitations and acknowledged constraints preventing immediate gigahertz operation, a strong step forward has been made. This simplification promises more energy efficient interconnects vital for applications like high performance computing clusters or modular quantum processors where bandwidth capacity is critical. A new era of compact, efficient interconnects for both classical and quantum computing may begin with this breakthrough.

This research demonstrated a photonic circuit architecture capable of connecting multiple input-output pairs in just N steps using only O(N) programmable phase shifters, a significant reduction from previous designs requiring O(N²). The team built and tested a 3×3 router utilizing x-cut thin-film lithium niobate and single-sided photonic-crystal nanobeam cavities, achieving resonance tuning efficiency of 1.92GHz/V within an area of 100 μm².

While current sequential routing speeds are limited to 10MHz by testing equipment, the authors note that material properties present fundamental constraints on reaching gigahertz operation; however, this approach offers potential for more energy efficient interconnects in computing systems.

👉 More information
🗞 Multiport photonic routing with a single cavity-based electro-optic phase shifter per port
✍️ Alessandro Buzzi, Bjarke A. Frederiksen, Dashiell L. P. Vitullo and Dirk R. Englund (Massachusetts Institute of Technology); Mikkel Heuck (Technical University of Denmark)
🧠 ArXiv: https://arxiv.org/abs/2610.31757

More like this