High-Speed Networking Is Driving the Shift to Optical Connectivity

Aaron Frank

Curtiss-Wright

High-Speed Networking Is Driving the Shift to Optical Connectivity

Modern defense platforms are producing and processing more data than ever before. Higher-resolution radar, electro-optical/infrared (EO/IR), software-defined RF, and other advanced sensors are generating massive data streams, while sensor fusion and increasingly powerful embedded processors are creating demand for faster movement of that data throughout the system.

At the same time, the U.S. military’s Modular Open Systems Approach (MOSA) mandate is driving greater use of networked, interoperable system architectures via open architecture initiatives such as the Sensor Open Systems Architecture, or SOSA®, Technical Standard and CMOSS (C5ISR/EW) Modular Open Suite of Standards). The result is a steady progression from Gigabit Ethernet to 10, 25, 40, 50, and now 100 Gigabit Ethernet (100GbE).

But increasing network speed solves only part of the problem. System designers also need a physical interconnect capable of moving that data reliably through and between rugged embedded systems.

Where copper becomes challenging

Copper remains an important part of embedded system architectures, particularly for short connections within a chassis. As data rates and connection distances increase, however, maintaining signal integrity over copper becomes increasingly difficult.

Higher-frequency electrical signals experience greater attenuation and are more susceptible to crosstalk and electromagnetic interference (EMI). Maintaining reliable high-speed copper connections can require additional signal conditioning, shielding, and careful cable design.

Those challenges become especially significant when data must travel outside the chassis to sensors, other processing systems, or equipment located elsewhere on the platform.

Optical fiber provides another option.

Fiber can transport high-speed data over much greater distances without the same signal degradation experienced by copper. Because fiber does not carry electrical signals, it is also immune to EMI and radio-frequency interference (RFI). Its smaller size and lower weight can provide additional advantages in size, weight, and, power- (SWaP)-constrained airborne, ground, and naval platforms.

Using fiber creates a different design challenge

Moving to optics isn't simply a matter of replacing a copper cable with fiber.

Somewhere in the data path, electrical Ethernet signals must be converted to optical signals. System architects must determine where that conversion should occur, how fiber should enter and leave the chassis, and which approach best preserves the connectivity needed within the system.

In a space-constrained 3U VPX architecture, those decisions become particularly important. Backplane connector space is limited, and using some of that space for optical interfaces can reduce the copper connections available between other modules.

Performing electrical-to-optical conversion externally can preserve backplane connectivity, but may add custom hardware circuitry, cabling, power consumption, and integration complexity.

Front-panel optical connectivity offers another approach by enabling fiber to connect directly to the front of a module while preserving all copper backplane connections. But deployed defense applications introduce additional challenges, including connector ruggedness, shock and vibration operational reliability, environmental exposure, maintainability, and fiber bend radius considerations.

There is no single optical implementation that is right for every system.

Think about the entire optical data path

As defense architectures move toward 100GbE, optics increasingly needs to be considered at the system level rather than as an individual interface.

A high-bandwidth data path may begin at an external sensor, enter a chassis over fiber, pass through an Ethernet switch, move to FPGA-based processing, and ultimately reach general-purpose or accelerated compute resources.

Where should fiber enter the system? Where should optical-to-electrical conversion occur? Which connections should remain copper? And how can designers introduce optics without compromising backplane connectivity, ruggedness, SWaP, or future scalability?

These are becoming important architectural decisions as network speeds continue to increase.

The white paper Overcoming the Optical Connectivity Challenge in SOSA Systems examines these tradeoffs and explores approaches for building rugged, high-speed optical data paths from sensor ingest through switching and processing.