As HPC clusters scale to unprecedented sizes, traditional packet-based fabrics alone can no longer deliver the latency, resiliency, and flexibility researchers demand—this is where Optical Cross-Connects enter the picture.

HPC applications are communication-intensive. Whether the workload is MPI-based CFD, large-scale molecular dynamics, weather prediction, or distributed AI training, the fabric must deliver:

>> Deterministic latency and low jitter for tightly synchronized collectives.
>> Losslessness (or near-losslessness) for RDMA flows that dislike retransmissions.
>> High bisection bandwidth to support all-to-all and many-to-many patterns.
>> Rapid reconfiguration as queues and job mixes change throughout the day.
>> Fault isolation and serviceability without draining the entire cluster.

The most common deployments rely on high-performance Ethernet (RoCE) or InfiniBand, organized in Clos/fat-tree, dragonfly, or torus-like topologies. Switch silicon has advanced rapidly, but several structural issues remain:

1. Over-subscription and congestion: Even with deep buffers and congestion control, elephant flows from checkpoints, data staging, or distributed training can induce head-of-line blocking and microbursts—degrading tail latency for other jobs.

2. Operational rigidity: Packet fabrics are designed as fixed topologies. Re-cabling or re-architecting for experiments or seasonal demand is disruptive and labor-intensive.

3. Maintenance risk: Replacing leaves/spines or performing fiber work typically requires maintenance windows. Bypass capabilities are often limited.

4. Multi-tenancy pressures: Shared centers need hard isolation between research groups or sensitive projects—preferably at Layer-1, not just with VLANs or VRFs.

5. Power and complexity: A large fabric requires many active packet stages to connect distant racks. Sometimes all you need is a transparent, fixed lightpath between two endpoints—without intermediate packet processing.

These gaps create an opening for Layer-1 optical switching—specifically, Optical Cross-Connects (OXC)—to complement, not replace, the packet fabric.

An Optical Cross-Connect is a non-blocking, transparent fiber-level matrix that connects any input fiber to any output fiber under software control. Unlike packet switches, an OXC does no packet parsing, queuing, or buffering. It simply establishes a deterministic optical circuit—often called optical circuit switching (OCS)—between endpoints.

Practical Benefits for HPC

1. Near-zero added latency and jitter: Because an OXC is transparent, it introduces only the physical path delay of fiber plus insertion loss—no packet processing. For latency-sensitive collectives, this is valuable.

2. Protocol and rate agnostic: OXCs pass light, not bits. They are compatible with 10G/25G/100G/200G/400G/800G optical modules, InfiniBand or Ethernet PHYs, PAM4 or NRZ, and both CWDM and DWDM wavelengths when used with appropriate optics.

3. Dynamic topology control: Operators can rewire at software speed. Need to carve a dedicated ring for a large MPI job? Build it. Need to isolate two research groups at L1 for a week? Stitch it. Need to A/B test different topologies? Reconfigure in minutes, not days.

4. Resiliency and maintenance: An OXC can instantly re-route around a failed fiber, transceiver, or switch, or create maintenance bypasses while keeping links up—reducing or eliminating downtime.

5. Resource consolidation: Where packet-only fabrics would require additional active hops to interconnect distant racks, OCS can provide direct lightpaths, reducing hop count and power.

6. Security and multi-tenancy: L1 circuits offer physical isolation between tenants or experiments; there is no L2/L3 bleed-through to worry about.

In short, an OXC gives HPC teams a programmable physical layer, enabling deterministic paths for the heaviest, most latency-sensitive workflows while freeing the packet fabric from transient hot spots.

While OXCs differ by vendor and technology, high-quality systems share a common set of optical, electro-mechanical, and control components.

1. Switching Core Technologies

1) MEMS Micromirror Arrays (2D/3D)

Tiny mirrors steer collimated beams from any input port to any output port. Advantages include large port counts (e.g., 64×64, 128×128, 256×256 and beyond), low insertion loss for the scale, and latching (no hold power when idle).

2) Mechanical/Latching Relay-Type Optical Switches

Used inside smaller OXCs or as building blocks for protection switching. They offer very low loss and excellent stability, commonly in 1×2/2×2 to small matrix forms.

3) Motor-Driven and Magneto-Optical Switches

Found in specialized modules where environmental robustness, high power handling, or specific latching behavior is needed.

Note: Wavelength Selective Switches (WSS)—often based on LCoS—are used in wavelength-layer ROADMs. In HPC data centers, OXCs are primarily space-switching (fiber-to-fiber). However, in campus/metro HPC interconnects using DWDM, WSS can complement OXCs for wavelength grooming and ROADM-like flexibility.

2. Optical Paths and Passive Optics

1) Fiber Arrays (FA) & Collimator Arrays

Precisely aligned arrays couple fibers to free-space optics. Quality alignment reduces loss and maintains stability over temperature.

2) Micro-Lens Arrays / Beam Expanders

Shape and stabilize beams across the free-space path to the MEMS mirrors.

3) Connectors & Adapters

LC/UPC, LC/APC, MPO/MTP, or SC variants. OXCs aimed at HPC often provide high-density LC on the front and MPO trunking options on the rear for rapid roll-out.

4) MUX/DEMUX (CWDM/DWDM)

Optional inside or adjacent to the OXC to aggregate multiple wavelengths when long-distance

3. Monitoring and Control

1) Optical Power Monitoring

Small taps with photodiodes monitor path power levels to detect fiber degradation or transceiver drift.

2) Control Plane & Management

Dual-controller designs with SNMP/NETCONF/REST, CLI, and APIs for orchestration tools. Look for 1+1 controller redundancy, dual hot-swap PSUs, and field-replaceable fan trays.

3) State Persistence

Latching or non-volatile switch elements ensure connections survive controller reboot or power events, improving resilience.

4. Complementary Modules around the OXC

1) Fiber Bypass Modules

Automatically route around inline devices (instrumentation, security taps, or test appliances). In HPC, they provide fail-safe paths for critical inter-rack links.

2) Optical Protection Switches (1+1, 1:1, 1:N)

Provide rapid switchover between working and protection fibers.

3) Polarization-Maintaining (PM) Optical Switches

For labs and photonics research needing polarization control.

4) EDFAs (rare inside data centers, common for campus/metro)

If HPC nodes span buildings or cities via DWDM, Erbium-Doped Fiber Amplifiers may be used to close the power budget.

GLSUN provides Matrix Optical Switch / OXC Systems designed for deterministic, scalable L1 connectivity in demanding environments.
Large non-blocking matrices (e.g., 32×32 to 256×256+), based on MEMS or high-reliability latching elements, delivering low insertion loss, excellent repeatability, and millisecond switching. High-density front panels (LC) with MPO trunking options simplify integration across rows and pods.

HPC has entered an era where the interconnect is strategy. As node counts explode and communication patterns intensify, the network must offer both performance determinism and operational flexibility. Optical Cross-Connects (OXC) provide exactly that: programmable, protocol-agnostic lightpaths that remove queuing from the equation, accelerate bulky flows, simplify maintenance, and enforce hard isolation when needed.

By introducing OXC into the fabric—initially for protection and express paths, then expanding to topology orchestration—HPC operators can improve job completion times, raise utilization, and reduce risk. With mature OXC platforms, robust management, and integration-ready APIs, GLSUN is ready to help you design and deploy light-speed interconnects that keep pace with modern science and engineering.