Fibre Optic Cable, Optical Fibre, Fibre To The Home, Fibre Optic Test Equipment, Ftth Products

Fibre Optics Resources

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Brief Overview of Fibre Optic Cable

Fibre Optic Overview:

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

Advantages over Copper:

Fibre cable has many advantages that cannot be matched via copper or wireless transmission. First- optical fibre can transport more information to much longer distances in less transmission time. This is because fibre 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. Fibre cable is also relatively secure since the optical transmission cannot be tapped as easily as electrical transmission.

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

Bandwidth: Large carrying capacity.

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

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

Maintenance: Fibre optic cables costs much less to maintain.

Higher carrying capacity: Because optical fibres are thinner than copper wires, more fibres can be bundled into a given-diameter cable than copper wires.

Non-flammable: Because no electricity is passed through fibre cable there is no fire hazard.

Singlemode: Singlemode fibre optic cable has a typical core diameter of 8.3 to 10um, through which only one mode will propagate typically at 1310 or 1550nm. Carries higher bandwidth than multimode fibre, but requires a light source with a narrow spectral width.

Singlemode fibre has a much smaller core than multimode. The small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fibre cable type. Single path through the fibre.

Multimode:

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 than 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 and beyond. Multiple paths through the fibre.

MSS Fibre Systems offers both types of fibre cable and other optical fibre products including fibre to the home products (ftth products), fibre enclosures and fusion splicers.

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Fibre Optic Cable Specifications:

Industry Standard Colour Codes

Fibre optic cables are terminated using an industry standard colour code.

For fibre cables that consist of more than 12 strands of fibre the colours are repeated with some variation eg. the 1st group of 12 strands are solid colours and the 2nd group are solid colours with a stripe or some other identifying mark.

MSS Fibre Systems products including multi and single mode fibre cable, fibre to the home products (ftth products), fibre enclosures and fusion splicers are all manufactured to suit the Australian market.

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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 fibre optic 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. MSS Fibre offer technical advice and training to help our customers understand the importance of maintaining clean fibre optic connector ends.

Illustrations

• Shows a clean single mode ceramic fibre optic connector end face at 200x magnification

  

• Shows a fibre optic connector with scratches through the cladding.
  These scratches are not detrimental to the end face as the scratches are not across the core.

  

• Shows a fibre optic connector with liquid contamination that needs cleaning.

  

• Shows a fibre optic connector with damage to the cladding. Cleaning cannot remove damaged cladding.
  A small amount of epoxy around the cladding is allowable, but this shows excessive epoxy around the cladding that does not clean off.
  This connector must be replaced or repolished.

  

• Shows a fibre optic connector with dust particles spread across the surface of the end face that needs cleaning.

  

• Shows a fibre optic connector with alcohol residue that needs cleaning.

  

Measuring Optical Loss for Fibre Optic Cable

Link Loss (Attenuation)

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) is 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 fibre uniformity, splice characteristics, and total link distance.

ORL (Optical Return Loss)

ORL is a measure of the total fraction of 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.

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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, ellipticity, 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

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 at least 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 therefore O.K. If the total loss is 14dB, the margin or “head room” is 6dB.

For more information on fibre optic cable, ftth products, fibre optic test equipment, fusion splicers and fibre enclosures call MSS Fibre Systems on (03) 9729 0244 or submit an online contact form.

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