Tag: Single mode fibers

Exploring the Anatomy of A Fiber Optic Cable

What’s really inside a fiber optic cable? That’s a question that most customers of fiber optic cable suppliers want to know. Fiber optic is the communications medium that works by sending optical signals down hair-thin strands of extremely pure glass or plastic fiber. Fiber optic cables are capable of carrying high volume of data over long distances. This article is written to take a peek inside fiber optic cables. Starting at the center and working our way outside.

A standard fiber optic cable is comprised of four specific parts:
Core: A fiber optic’s center is made of glass, and this tube carries the cable’s light signals. Depending on the type of fiber optic cable (single more of multimode), the core varies in size. Single mode fibers consist of a tiny glass core that typically has a diameter between 8.3 and 10 microns. This type of cable is used for telephone and CATV with laser sources at 1300 and 1550nm because it has a lower loss and virtually infinite bandwidth. For multi mode fibers, the core is larger. Their core size ranges from 5 to 7 times larger than a single mode core. With a diameter ranging between 50 to 62.5 microns,it supports the transmission of multiple mode (rays) of light and perfect for high data applications. Multimode is generally used with LED source at wavelengths of 850 and 1300nm for slower local area networks (LANs) and lasers at 850 (VCSELs) and 1310nm (Fabry-Perot lasers) for networks running at gigabyte per seconds or more. Multi mode cables are typically used over shorter distances than single mode fiber optic cables.
Cladding layer: The core is surrounded by an optical material called the “cladding” that traps the light in the core using an optical technique called “total internal reflection.” When transmitting data (especially over long distances), light rays can reflect off each other and travel in different directions. The cladding keeps those signals straight.Buffer: Buffer is made to protect fiber from moisture and physical damage. The buffer is what one strips off the fiber for termination or splicing. More often than not, the buffer is made of
Plastic.

Jacket: The fiber optic’s cable exterior is typically made of tough, durable polyurethane. Its job is to protect the overall integrity of the fiber optic cable. The jacket is the first line of defense in a fiber optic cable. Routing cables can put stresses on a fiber optic cable and a jacket sometimes contains an extra layer to avoid these potential hazards.

Water Barrier: Common water barriers for ordinary cable include: an axially laid aluminum foil/polyethylene laminated film immediately inside the polyurethane of polyethylene plastic sheaths;
and/or the use of moisture resistant compounds around the fibers.
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How to Calculate Fiber Optic Loss Budget

Fiber optic loss budget calculation is conduct to analysis a fiber optic system’s operation characteristics. It included the items such as routing, electronics, wavelengths, fiber type, and circuit length, attenuation and bandwidth of which are the key parameters for budget loss analysis.

Design of a fiber optic system is a balancing act. As with any system, you need to set criteria for performance and then determine how to meet those criteria. It’s important to remember that we are talking about a system that is the sum of its parts.

Calculation of a system’s capability to perform is based upon a long list of elements. Following is a list of basic items used to determine general transmission system performance:

Fiber Loss Factor – Fiber loss generally has the greatest impact on overall system performance. The fibre optic cable manufacturers provide a loss factor in terms of dB per kilometer. A total fiber loss calculation is made based on the distance x the loss factor. Distance in this case the total length of the fiber cable, not just the map distance.

Type of fiber – Most single mode fibers have a loss factor of between 0.25 (1550nm) and 0.35 (1310nm) dB/km. Multimode fibers have a loss factor of about 2.5 (850nm) and 0.8 (1300nm) dB/km. The type of fiber used is very important. Multimode fibers are used with L.E.D. transmitters which generally don’t have enough power to travel more than 1km. Single mode fibers are used with LASER transmitters that come in various power outputs for “long reach” or “short reach” criteria

Transmitter – There are two basic type of transmitters used in a fiber optic systems. LASER which come in three varieties: high, medium, and low (long reach, medium reach and short reach). Overall system design will determine which type is used. L.E.D. transmitters are used with multimode fibers, however, there is a “high power” L.E.D. which can be used with Single mode fiber. Transmitters are rated in terms of light output at the connector, such as -5dB. A transmitter is typically referred to as an “emitter”.

Receiver Sensitivity – The ability of a fiber optic receiver to see a light source. A receiving device needs a certain minimum amount of received light to function within specification. Receivers are rated in terms of required minimum level of received light such as -28dB. A receiver is also referred to as a “detector”.

Number and type of splices – There are two types of splices. Mechanical, which use a set of connectors on the ends of the fibers, and fusion, which is a physical direct mating of the fiber ends. Mechanical splice loss is generally calculated in a range of 0.7 to 1.5 dB per connector. Fusion splices are calculated at between 0.1 and 0.5 dB per splice. Because of their limited loss factor, fusion splices are preferred.

Margin – This is an important factor. A system can’t be designed based on simply reaching a receiver with the minimum amount of required light. The light power budget margin accounts for aging of the fiber, aging of the transmitter and receiver components, addition of devices along the cable path, incidental twisting and bending of the fiber cable, additional splices to repair cable breaks, etc. Most system designers will add a loss budget margin of 3 to 10 dB

Let’s take a look at a typical scenario where a fiber optic transmission system would be used.

Two operation centers are located about 8 miles apart based on map distance. Assume that the primary communication devices at each center is a wide area network capable router with fiberoptic communication link modules, and that the centers are connected by a fiber optic cable. The actual measured distance based on walking the route , is a total measured length (including slack coils) of 9 miles. There are no additional devices installed along the cable path. Future planning provides for the inclusion of a freeway management system communication link within 5 years.

(Assume that this system will have at least 4 mid-span fusion splices. )

Fiber Loss: 14.5 km × 35dB = -5.075

Fusion splice Loss : 4 × .2dB = -.8

Terminating Connectors : 2 × 1.0dB = -2.0

Margin: -5.0

Total Fiber Loss : -12.875

Because a loss margin of 5.0dB was included in the fiber loss calculation, the short reach option will provide sufficient capability for this system. In fact, the total margin is 8.0db because the difference between the loss budget and receiver sensitivity is 3.0db.

Remember FiberStore provides all the components in the complete fiber optic cable plant, including all the passive and active components of the circuit. As a main fiber optic cable supplier, you can find different designs of cable such as tight buffer, loose tube or even fiber optic ribbon cable, which are manufactured compliant high industry standard and will save your cable plant loss budget largely.