An optical fiber cable, also known as a fiber optic cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light.
The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed. Different types of cable are used for different applications, for example long distance telecommunication, or providing a high-speed data connection between different parts of a building
What’s happening inside a fiber optic cable?
Light travels down a fiber-optic cable by bouncing repeatedly off the walls. Each tiny photon bounces down the pipe like a bobsleigh going down an ice run. Now you might expect a beam of light, traveling in a clear glass pipe, simply to leak out of the edges. But if light hits glass at a really shallow angle (less than 58 degrees), it reflects back in again as though the glass were really a mirror. This phenomenon is called total internal reflection. It’s one of the things that keeps light inside the pipe.
The other thing that keeps light in the pipe is the structure of the cable, which is made up of two separate parts. The main part of the cable in the middle is called the core and that’s where the light travels through it. Wrapped around the outside of the core is another layer of glass called the cladding.
The cladding’s job is to keep the light signals inside the core. It can do this because it is made of a different type of glass to the core.
Common Fiber Optic Cable Types
Generally, there are three types of fiber optic cables:
Single Mode Fiber Optic Cable
The mode in fiber optic cable refers to the path in which light travels.
Single mode fiber has a smaller core diameter 9 micron (8.3 microns to be exact) and only allows a single wavelength and pathway for light to travel, which greatly decreases light reflections and lowers attenuation.
Single mode fiber optic cable is slightly more expensive than its multi mode counterparts, which is often used in network connections over long length.
Multi Mode Optic Fiber
Multi mode optical fiber has a larger core diameter than that of single mode fiber optic cable, which allows multiple pathways and several wavelengths of light to be transmitted.
Multimode optical fiber is available in two sizes, 50 micron and 62.5 micron. It is commonly used for short distances, including patch cable applications such as fiber to the desktop or patch panel to equipment, data and audio/video applications in LANs.
Plastic Optical Fiber (POF)
POF is large core step-index optical fiber with a typical diameter of 1 mm. The large size enables it to easily couple lots of light from sources and connectors that do not need to be high precision.
So typical connector costs are 10-20% as much as for glass fibers and termination is simple. Being plastic, it is more durable and can be installed in minutes with minimal tools and training. Plastic optical cable price is more competitive, making it a viable option for desktop LAN connections and low speed short links.
FIBER OPTICS FOR CCTV
Over the past 10 to 15 years CCTV has become ubiquitous and while many applications are related to security almost as many are related to operational and safety matters. For example, road operators have been using CCTV for well over 30 years for monitoring traffic flows in many cities and large towns.
Until fairly recently, CCTV used technical standards derived from broadcast television and characterizing quality performance of systems likewise derived from the techniques and equipment typically used in the broadcast industry.
The advent of IP based CCTV and newer technologies related to High Definition (HD) TV have considerably widened the scope of surveillance systems.
Consequently, we now see a mix of both analog based and network-based technologies, the former using coaxial cable and the latter using Unshielded Twisted Pair (UTP) cable, typically so-called Cat-5 cable.
While coaxial cable is very easy and convenient to use, it does have limitations:
- Link distances are typically restricted hundreds of meters unless in-line amplifiers are used
- Susceptibility to interference from electrical machinery, lightning and other electronic equipment
- Ground loops can cause major problems
- Obviously, there are ways of reducing these issues but eventually coax runs out of puff.
Often it is inconvenient to install coax cable and if UTP is available then there is a great incentive to use it. However, similar issues arise when trying to use UTP cables to transmit analog video signals. Typically, passive or active, Balanced-to-Unbalanced converters (Baluns) are used and these can provide reasonable transmission over a few hundred meters (even more with active cable equalisation). The Ethernet systems typically deployed in local area networks are often used to transfer IP based video signals but as with coax and balun based analog systems, these also have severe distance limitations and are susceptible to EMC (Electromagnetic Compatibility) issues.
Which is where Fiber Optic technology comes into play: where distance or EMC are a problem fiber is a very straightforward technical fix for many situations. Fiber has some excellent technical features:
Optical fiber transmission links for analog CCTV
Signals from analog CCTV security cameras can be converted into optical form by MULTIMODE video converters.
Depending on the model, one optical fiber can carry signal(s) from 1, 4, 8 or 16 cameras. Thanks to the video converters and single-mode fibers, the camera points can be located at distances up to 20 km from the surveillance center. In many cases, the optical solutions are optimal also at much shorter distances, especially in places with high levels of electromagnetic interference or in locations exposed to lightning surges etc.
Optical fiber transmission links for IP CCTV
Video streams from IP cameras are converted into optical form using Ethernet media converters or switches with SFP (Small Form-factor Pluggable (optical transceiver module)) modules that can be selected according to the actual requirements.
IP CCTV systems based on fiber optic transmission medium can be very extensive, with central or distributed management, as well as smaller ones, used in places with high levels of Electromagnetic Interference or in locations exposed to lightning surges etc.
Advantages of using optical fiber cables
Long transmission distance
Dielectric protection and construction
Relatively easy installation (but skills are needed though)
Secure transmission (as opposed to wireless especially)
EMI and RFI immunity (you have no distortions for example in CCTV signal)
Fiber is a well-established technology that can offer enormous benefits to end users in enabling interference free transmission over almost any distance of high-quality video, whether it is in analog, IP or SDI (Serial Digital Interface) formats.
The fiber type used will often have been already decided due to factors outside the user’s control but if not, it is recommended that single mode be looked at very seriously.
Using APC style connectors for such SM infrastructure is also recommended. Factors such as the type of cable to be used will be determined by site conditions, e.g. typically loose tube types for the longer outdoor runs and tight buffer (aka distribution) within buildings. It is always recommended to use FOBOT’s (Fibre Optic Break Out Tray) to interface between the cabling and the equipment.
Various standards either recommend or mandate the use of the SC type connector for this building cabling but please note that the standards do not specify which connectors should be used on the transmission equipment: This is up to the manufacturer. Consequently, much use is made of patch cords with an SC on the FOBOT end and an ST or LC or whatever on the equipment end.
It is recommended that OTDR based testing of new installations other than the most simple be carried out and a record kept of these results. It is also suggested that an optical power meter be readily available for quick checks in case of any issues.