CoaXPress-over-Fiber

CoaXPress-over-Fiber (CoF) is a light but significant extension of the existing CoaXPress specification to support transport over fiber optics.

CoaXPress (CXP) is the de-facto standard for high-bandwidth computer vision applications. CoaXPress 2.0, the latest version of the specification, specifies the CXP-12 speed, a 12.5 Gbps (Gigabit per second) link over a coaxial copper cable. As link aggregation is common with CoaXPress, bandwidths of 50 Gbps (12.5 x 4) are easily achievable with four CXP-12 links. The CoaXPress specification is hosted by the JIIA (Japan Industrial Imaging Association).

CoaXPress-over-Fiber has been designed as an add-on to the CoaXPress 2.0 specification. It provides a way to run the CoaXPress protocol, as it is, unmodified, over a standard Ethernet connection, including fiber optics. As such, CoaXPress-over-Fiber uses standard electronics, connectors and cables designed for Ethernet, but the protocol is CoaXPress, not Ethernet, not GigE Vision.

What are the pros and cons of using fiber optics?

Pros

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First and foremost, cable length is not an issue anymore as fiber connectivity is basically not limited in length.

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Fiber optics provide more bandwidth, as connectivity at 10 and 25 Gbps per fiber is standard today and widely used in data centers.

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Fiber optics are immune to electrical noise, which will be a significant advantage on the production floor in and some medical applications.

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Fiber optics are lighter and smaller in size than the equivalent copper cabling, making it appropriate for applications where this characteristic is essential, like in aircrafts or vehicles.

Cons

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There is no "power over fiber". As signals in fiber optics are transmitted using light, there is no way to transfer power over fiber optics and devices such as cameras must be powered separately.

What are the cable options for CoaXPress-over-Fiber?

One of the most important benefits of CoaXPress-over-Fiber is the wide variety of connectivity options already available from multiple companies.

The initial connectivity options for CoaXPress-over-Fiber and the 3625 Coaxlink QSFP+ at 10 Gbps are SFP+ and QSFP+ (Quad, or four times SFP+) modules. The advantage of using modules compared to fixed interfaces is that ports can be equipped with any suitable type of transceiver as required by the application. A variety of transmitter and receiver types is available, allowing users to select the appropriate transceiver to provide the required optical reach over multi-mode fiber (MMF) or single-mode fiber (SMF).

3625 Coaxlink QSFP+ fitted with an AOC (Active Optical Cable) transceiver

The first option is using a 40GBASE-SR4 QSFP+ Optical Transceiver Module for multi-mode fibers. It uses an MTP/MPO fiber connector with a maximum 150-meter fiber optic cable. This solution is suitable for machine vision applications.

40GBASE-SR4 QSFP+ 850nm 150m MTP/MPO Optical Transceiver Module for MMF
MTP/MPO fiber connector, with maximum 150 m fiber optic cable

The second option is using a 40GBASE-ER4 QSFP+ LC DOM Optical Transceiver Module for single-mode fibers. It uses an LC-Duplex fiber connector with a maximum 40-km fiber optic cable. This solution is suitable, for example, for video transmission applications.

40GBASE-ER4 QSFP+ 1310nm 40km LC DOM Optical Transceiver Module for SMF
LC-Duplex fiber connector, with maximum 40 km fiber optic cable

 

What are the jitter and latency of CoaXPress-over-Fiber? How do they compare to "traditional" CoaXPress?

CoaXPress-over-Fiber is based on the CoaXPress protocol and it exhibits the same high performance as CoaXPress in terms of jitter and latency. In addition, as CoaXPress-over-Fiber supports higher transmission speed compared to CoaXPress, the jitter and latency will be further improved in these versions.