Fiber Shuffles

Author: the photonics expert Dr. Rüdiger Paschotta

Fiber-optic shuffles (also called optical fiber shuffles), are specialized fiber-optic arrangements for routing signals in a large number of fibers. There are several or even many input and output fibers, which may be grouped, e.g. as ribbon fibers containing 8 fibers each, and possibly protected to form fiber cables.

The primary function of a fiber shuffle is to connect a set of input fibers to a set of output fibers. There may be a fixed routing of signals from input to output fibers, often according to a specification from a specific user, but there are also reconfigurable fiber shuffles.

Fiber-optic shuffles are widely used for efficient cable management, particularly in high-density network environments like telecom and data centers.

Basic Fiber-optic Shuffles

Basic fiber shuffles provide a fixed (non-reconfigurable) routing from input to output ports (with an equal number of inputs and outputs). The routing matrix is typically one with moderate complexity, and no electric power is required. Many different types routings are possible; some simple examples:

• Some shuffles are “perfect shuffles”, meaning that the inputs are divided into two equally large sets (e.g. 1-4 and 5-8 for an 8-port device), and these are interleaved (e.g. resulting in the output order 1-5-2-6-3-7-4-8).
• Another possibility is to always exchange two neighbored fibers, resulting in the output order 2-1-4-3-6-5-8-7.
• As another example, one may also connect each fiber of an input cable to a fiber of a different output cable, or collect one fiber input from each input fiber cable to one output cable.
• Completely irregular routing schemes, normally defined by a customer, can be custom-made.

The supported fiber types can be single-mode or multimode, and often some number of fibers are combined in a ribbon cable or some other type of multi-fiber cable. The input and output ports may be equipped with some type of fiber connectors, e.g. of LC, SC or MTP type, or simply have the fiber cables rigidly attached to them.

The insertion loss of a basic shuffle is typically quite small – often limited by the used fiber connectors rather than by the involved fibers. (A minimum bend radius of fibers is maintained to avoid significant bend losses.) Cross-talk between fibers is typically not significant at all. Signal delay times are sometimes balanced by optimizing fiber lengths; this is often important as symbol durations can be shorter than the transit time of a fiber shuffle.

The fibers are often attached to a flexible board so that they are essentially constrained to one plane, avoiding cable clutter. Multiple of such planar optical flex circuits can be installed next to each other without creating a risk of an entangled mess. There are also non-planar shuffles, e.g. with a compact cylindrical housing with multiple multi-fiber cables on each end.

In comparison to dealing with individual fibers, fiber-optic shuffles can substantially simplify the fabrication and installation of a complex fiber-optic system. At a later stage, maintenance and troubleshooting with tracing of fibers are facilitated. Technicians can readily access specific fibers (or multi-fiber cables) without having to disentangle a web of cables. This improved manageability translates to faster deployment, reduced maintenance costs, and minimized downtime during network upgrades or repairs.

These advantages of fiber-optic shuffles are particularly beneficial where space constraints are important, many fibers are needed, and cable paths can be intricate. Shuffles may be used at different locations, e.g. on an optoelectronic circuit board for internal routing purposes or for connecting multiple parallel cards on a board.

Reconfigurable Fiber-optic Shuffles

Reconfigurable fiber shuffles offer dynamic routing capabilities, i.e., the flexible reconfiguration of fiber optic connections between input and output ports. Unlike basic fiber shuffles, they can thus be adapted to changing network demands or component outages, e.g. in optical fiber communications, and optimize performance in real-time. This can be crucial in modern telecom and data centers.

Optical circuit switches are a core component of reconfigurable shuffles, enabling the rerouting of light signals without converting them to electrical signals. These switches can be controlled via software to adjust the network configuration dynamically and rapidly. Different switch technologies can be used. For large switching matrices, micro-optical-electrical mechanical systems (MOEMS) with movable micromirrors are a powerful solution. Robotic patch panels are another possibility, offering lower insertion loss and cross-talk but higher cost and lower switching speed.

Typically, the switch system is controlled with suitable drive electronics and ultimately via software. It requires a moderate amount of electric power.

Even reconfigurable fiber shuffles are optically transparent in the sense that optical signals get through without being somehow processed, e.g. with optical filters or even receivers and transmitters. That means that there is no dependency on particular modulation formats, for example. However, some performance limitations can arise from various effects:

• There is a limited wavelength range (optical bandwidth) in which the device can operate.
• The insertion loss can amount to several decibels, e.g. if MOEMS switches are used.
• There may also be stronger cross-talk between fibers – potentially higher than −20 dB.

It therefore must be carefully checked whether system performance might be compromised by non-ideal properties of a reconfigurable fiber shuffle.

While reconfigurable shuffles are substantially more expensive, they can enable cost savings through additional flexibility and the ease of reconfiguring a system rapidly, even automatically through software. For example, when some fiber is broken or a component is defect, or when some network demand changes, such a system can be reconfigured in milliseconds to be operational again. This also allows for a more efficient use of resources, e.g. achieving high reliability without excessive redundancies.

More to Learn

Encyclopedia articles:

• optical fiber communications
• fiber optics
• fiber connectors
• fiber patch panels