Shedding Light on Optical Solutions

Learn about fiber and optical transmission

Converting Electricity to Light

Electrical data signals transmitted over copper are digital signals, so there is a ‘1’ or a ‘0’ that gets transmitted and then received at the other end to be processed into the video image. Optical transmission is nearly identical… the electrical ‘1’ or ‘0’ is read by a chip that then either tells the laser to output a higher signal for a ‘1’ or a lower signal for a ‘0’ and a photodetector and receiver chip on the other end reads these levels and sends the corresponding electrical ‘1’ or ‘0’ to the same processor that creates the video image.

Optical signals are especially beneficial because, unlike copper, multiple signals can be transmitted on the same fiber at the same time as long as they are using different wavelengths for the channels.

Unlike copper cables, where higher bandwidths cause problems with cross talk with neighboring signals, optical signals are actually guided in the core of a fiber and even laying a fiber right on top of another fiber will not cause any time of cross talk or electromagnetic interference issues. Goodbye EMI problems!!

Different Applications Have Different Types of Optical Transmitter/Receiver Systems

Systems/Extender Boxes

  • Extender boxes may use a standard Datacom SFP optical module to implement their optical link. The 10 Gbps Datacom modules are cheap and readily available, but if the optical link is limited to 10 Gbps, the system is limited to this and must be using compression. There are also 40 Gbps Datacom modules that would easily support the 18 Gbps needed for full rate 4K, 18 Gbps HDMI video, though these modules are still relatively expense and extender boxes that support them are limited.
  • Optics that are designed for video can support extender boxes that transmit the full 18 Gbps for 4K, uncompressed HDMI video. These types of boxes will not require any compression and can provide customers with an uncompromised video solution.

Optical Adapters

  • Optical adapters are a unique solution for point-to-point implementations. Optical adapters that support 4K and HDR at up to 18 Gbps are available. This allows the fiber to be installed between the end points and the adapters are just connected at the ends to provide a high-quality link up to 1000 m. Plus, it’s entirely upgradable – just swap out the ends when it is time to implement an 8K solution… the fiber doesn’t need to change.

Proprietary vs. Standard Cables

  • Proprietary hybrid optical cables include both copper and optical fiber to transmit the video data, generally keeping the control signals copper to provide a simple interface to the source and sink systems and improve interoperability. This limits the distance over which the solutions can be used and prevents field termination options as well.
  • Parallel optical cables transmit each channel over a different fiber, similar to a differential pair in an electrical cable. This approach is easy to implement because each channel can use the same transmitter laser since they are all on separate fibers. However, having 4 or more fibers in the link prevents field termination of the cables, so the delicate optical connector must be carefully pulled through the conduit during installation, and any damage renders the cable unusable.
  • Solutions that use standard optical cables, either pre-terminated or field terminated, have the benefit of being low cost and readily available. These cables are used in Datacom, telecom and videocom solutions worldwide and they can interface with a range of systems once installed. Additionally, if there is a cable break or connector damage during installation, they can simply be re-terminated.

There’s So Many Types of Fiber, What Do I Use?

The first decision when using fiber is whether you need single-mode or multimode. If the link is less than 1000m, multimode is the way to go. Why? Because a multimode fiber has a larger core for the light to transmit along so it is more forgiving for field termination. For distances above 1km, single-mode will be needed. The transmitter and receiver will have either single-mode or multimode optics, so make sure the equipment matches the fiber! Multimode hardware is generally less expensive than single-mode hardware, which is another reason to use multimode if the distances are less than 1000m.

There are four primary components to an optical fiber: the core, cladding, buffer and outer jacket. The core is the area where the light is actually transmitted. In single-mode fiber with 9μm diameter core, only a single mode, or light wave behavior, is supported. In multimode fiber, the core is a much larger at 50μm or 62.5μm, and multiple modes are supported. So how does the light stay in this core? The cladding layer provides a refractive index contrast that causes the light to reflect off the interface and propagate along the fiber. If the fiber is run as a single strand, it is referred to as a “simplex” fiber cable, whereas if there are two strands of fiber run side-by-side, it is referred to a “duplex” fiber cable. Applications that use special optics to perform multiplexing can simultaneously transmit and receive multiple high-speed signals on a single fiber, which makes the field termination even faster since it only needs to be performed once at each end.

The other terms that are used for multimode fiber are OM4, OM3, OM2 and OM1. OM1 has a 62.5μm core whereas OM2, OM3 and OM4 have 50μm cores. The higher OM number corresponds to higher modal bandwidth, so generally OM3 or OM4 should be installed in new installations for lengths longer than 100m, with OM4 preferred over OM3, especially for 200m+ installation links.

The type of connector needed for the fiber cable is dependent on the connector that is on the mating hardware. Generally, it will be SC, LC or maybe MTP/MTRJ. SC and LC connectors can both be readily terminated in the field with no-polish, no-epoxy termination kits from multiple vendors. SC connectors are slightly larger than LC connectors. MTP/MTRJ connectors have multiple fibers in them and cannot be terminated in the field because these fibers all must be carefully polished and aligned within the connector, which must be done in a factory with specialized equipment.

Is Fiber Really Rugged Enough to Pull in an Install?

Yes, it definitely can be pulled through conduit. Generally a fiber cable includes a strength member to help with the pull strength and it can be pulled just like a typical category cable. The cable jacket material also comes in various options for riser or plenum requirements as well as the new EU Construction Products Regulations for cables. These are standard options that are specified when ordering fiber cable, so the process is the same as any other category cable

Field Termination – Is This Really Feasible?

Field termination is actually pretty easy with field termination kits that are available from many different vendors and there are also training videos available for many of them. With minimal training, terminating a fiber can be just as fast and easy, if not faster, than terminating a Cat6 cable. Plus an additional benefit is that fiber cables don’t have the challenge of maintaining the critical shielding through the termination process as Cat6 cables have.

What if I just want to run a pre-terminated fiber because I’m just not comfortable with doing fiber terminations yet? No problem! Pre-terminated fiber cables in almost any length are available from many different vendors. Just make sure to put the dust cap on the fiber connector while pulling it and don’t exceed the pull strength of the connector end.

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