Brief Overview of Fibre Optic Cable

An optical fibre is a glass or plastic fibre that carries light along its length. Fibre optic cables are widely used in communication which permits transmission over longer distances and at higher data rates than other forms of communications. It is used instead of metal wires as signals travel along them faster with less loss.

Advantage Over Copper
Fibre cable has many advantages that connot be matched via copper or wireless transmission. Firstly, it can transport more information to much longer distances in less transmission time. This is because this type of cable has less attenuation (loss) and more bandwidth (capacity). Aside from distance and speed, optical transmission cannot be affected by electromagnetic interferences, making it handy to use in environments where this is a problem. It is also relatively secure since the optical transmission cannot be tapped as easily as electrical transmission.

Fibre optic cable networks operate at high speeds - up into the gigabits.

Large carrying capacity.

Signals can be transmitted further without needing to be "refreshed" or strengthened.

Greater resistance to electromagnetic interferences such as radios, motors or other nearby cables.

It costs much less to maintain.

Higher Carrying Capacity
They are thinner than copper wires and more fibres can be bundled into a given-diameter cable than copper wires.

Because no electricity is passed through this type of cable there is no fire hazard.

Multimode fibre cable has a larger core size, with common diameters of 50, 62.5um and (1mm POF). Light waves are dispersed into numerous paths, or modes, as they travel through the cable's core typically at 850 or 1300nm.

However, in long fibre optic cable runs (greater then 3000 feet [914.4 meters]), multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission so designers now call for single mode fibre in new applications using Gigabit amd beyond.

We offer both types of cable and other optical related products including fibre enclosures and fusion splicers.

Core Diameter 9 50 62.5 85 100
Cladding Diameter (um) 12 125 125 125 140
Numerical Apeture (um) 0.11 0.2 0.29 0.26 0.30
Attenuation (db/km) 850nm - 3 3.5 5 6
Attenuation (db/km) 1300nm - 1 1.5 4 5
Attenuation (db/km) 1310nm 0.5 1 - - -
Attenuation (db/km) 1550nm 0.25 - - - -
Bandwidth (MHz/km) 850nm N/A 600 200 200 100
Attenuation (dB/km) 1300nm N/A 750 500 300 300
Primary Coating Layer (um) 250 250/900 250/900 250/900 250/900

Fibre Optic Cable Core Inspection
Any contamination in the optical fibre connection can cause failure of the component or failure of the entire network. Even microscopic dust particles can cause a variety of problems for optical connections. A particle that partially or completely blocks the core generates strong back reflections, which can cause instability in the laser system. Dust particles trapped between two fibre faces of the optical connector can scratch the glass surfaces. Even if a particle is only situated on the cladding or the edge of the end face, it can cause an air gap or misalignment between the fibre cores which significantly degrades the optical signal. We offer technical advice and training to help our customers understand the importance of maintaining clean fibre optic connector ends.


Measuring Optical Loss for Fibre Optic Cable

Link Loss
Fibre optic test equipment for link loss, or attenuation, verifies whether fibre spans meet loss budget requirements.

Attenuation includes intrinsic fibre loss, losses associated with connectors and splices, and bending losses due to cabling and installation. An OTDR (Optical Time Domain Reflector) used when a comprehensive accounting of these losses is required. The OTDR sends a laser pulse through each fibre; both directions of the fibre are tested at 1310 nm and 1550 nm wavelengths for singlemode or 850nm and 1300nm for multimode. OTDRs also provide information about uniformity, splice characteristics, and total link distance.

ORL (Optical Return Loss)
ORL is a measure of the total fraction of the light reflected by the system. Splices, reflections created at optical connectors, and components can adversely affect the behaviour of laser transmitters, and they all must be kept to a minimum of 24 dB or less. You can use either an OTDR or an LTS equipped with an ORL meter for ORL measurements. However, an ORL meter yields more accurate results.

Chromatic Dispersion
Chromatic dispersion testing is performed to verify that measurements meet your dispersion budget.

Chromatic dispersion is the most common form of dispersion found in singlemode fibre cable. Temporal in nature, chromatic dispersion is related only to the wavelength of the optical signal. For a given fibre type and wavelength, the spectral line width of the transmitter and its bit rate determine the chromatic dispersion tolerance of a system.

Portable chromatic dispersion measurement instruments are essential for testing the chromatic dispersion characteristics of installed fibre.

PMD (Polarisation Mode Dispersion)
PMD has essentially the same effect on the system performance as chromatic dispersion, which causes errors due to the "smearing" of the optical signal. However, PMD has a different origin from chromatic dispersion. PMD occurs when different polarization states propagate through the fibre at slightly different velocities.

The causes are fibre core eccentricity, ellipitcity, and stresses introduced during the manufacturing process. PMD is a problem for higher bit rates (10 GE and above) and can become a limiting factor when designing optical links.

Fibre Optic Cable and Fibre Optic Connector Performance
Cable dB/km MHz/km dB/km MHz/km
Multimode 850nm 300nm
OM1 (62.5/125um) 3.5 200 1.0 500
OM2 (50/125um) 3.5 500 1.0 500
OM3 (50/125um) 3.5 1500 1.0 500

Singlemode 1310nm 1500
OS1 Maximum 3.5 - 1.0 -

Connectors Typical (dB) Insertion Loss Typical (dB) Insertion Loss
ST, SC, FC, LC, MTRJ 0.3 > 20
SMA 1.5 > 20 Splicing (fusion) Splice loss (dB)
ESCON 1.5 > 20 Multimode 0.3
FDDI 1.5 > 20 Singlemode < 0.2
ST, SC, FC, LC, MTRJ 0.25 -50
SCI/APC (angled) 0.25 -60
FC/APC (angled) 0.25 -60
FDDI 0.30 -40

Calculating Optical Loss
To calculate the total optical loss (in dB) in an optical fibre system, add the cable loss, fusion splicer loss, and fibre optic connector loss. Compare the loss figure obtained with the allowable optical loss budget of the receiver. Be certain to add a safety margin factor of atleast 3dB to the entire system. If the peak transmitter power is -10dBm and the receiver sensitivity is -30dBm, the available power budget is 20dB. If the total loss is less than 20dB, the loss does not exceed the available budget and therfore O.K. If the total loss is 14dB, the margin or "head room" is 6dB.