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FAQs

We have listed below many of the popular questions we are asked. 

Turnkey has many year experience in fibre optic networking as well as all types of copper ethernet networking. 

If you have a question that is not covered below please go to our Ask the Expert page to send your question to us.

What is fibre optics?

Fibre Optics if a cabling more advanced that standard copper cabling. It sends information in the form of light which is guided through thin fibres of glass or plastic. The signals transmitted can be either digital or analogue in forms of voice, video or data information. Fibre can transmit data over much greater length and in a shorter time than copper cable.

How is fibre measured?

Fibre is measured in the form of microns: 1/1,000,000th of a metre. 50 microns equal 0.002 inch.

What does the fibre core mean?

The fibre core is the centre of the fibre that the light is transmitted down. The core varies in size from 9 microns to 62.5microns.

What is the cladding?

The cladding is the outer layer of the fibre. Its purpose is to keep the light trapped inside the core as it travels down the length of the fibre.

What is the buffer coating?

The buffer coating is the layer surrounding the core and the cladding. Its purpose is protection against physical damage and moisture ingress.

What does Mode mean?

There are four different mode types, each mode is distinguished by its core size and capabilities. They are known as Multimode and Singlemode fibres.

Multimode fibres consist of OM1 (62.5/125), OM2 (50/125) and OM3 (50/125 enhanced). These multimode fibres have a larger core size than singlemode fibres. The 62.5/125 and the 50/125 modes are used with LED sources at wavelengths of 850 and 1300 nm for short distances. These modes are used for lower speed networks such as LAN.

Multimode OM3 fibre is a more advanced form of 50/125 and is used with Gigabit transmission equipment.

Singlemode fibre (OS1) has a smaller core size (9 microns) and is used in CATV and telecommunications applications with laser sources at 1300 and 1500 nm. Singlemode is used where information is required to be transmitted over very long distances at high speeds.

What is a patchcord cable?

Patchcords are used for patching between a fibre optic cabling systems and fibre optic transmission equipment such as media convertors, switches, video transmitters etc. They provide moveable links between sections of a permanently installed cable at patch panels or distribution frames.

What is Ethernet?

Ethernet is the most widely installed local area network (LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox, and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless LAN’s. The most commonly installed Ethernet systems are called 10BaseT and provide transmission speeds up to 10 Mbps.

Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second). 10-Gigabit Ethernet provides up to 10 billion bits per second.

What is Bandwidth?

Bandwidth refers to the amount of data that can be carried from one point to another. Fibre bandwidth is given in MHz-km. A product of frequency and distance, bandwidth scales with distance: if you half the distance, you double the frequency. If you double the distance, you half the frequency. What does this mean in premises cabling? For a 100 metre run (as allowed for twisted pair cable), the bandwidth for 62.5/125 micron fibre is 1600 MHz at 850 nm and 5000 MHz at 1300 nm. For the 2-km spans allowed for most fibre networks, bandwidth is 80 MHz at 850 nm and 250 MHz at 1300 nm. With Singlemode fibres, the bandwidth for a 100 metre run is about 888 GHz.

What is the Numerical Aperture (NA)?

Numerical aperture (NA) of the fibre defines which light will be propagated and which will not. NA defines the light-gathering ability of the fibre. Imagine a cone coming from the core. Light entering the core from within this cone will be propagated by total internal reflection. Light entering from outside the cone will not be propagated.

A high NA gathers more light, but lowers the bandwidth. A lower NA increases bandwidth.

NA has an important consequence. A large NA makes it easier to inject more light into a fibre, while a small NA tends to give the fibre a higher bandwidth. A large NA allows greater modal dispersion by allowing more modes in which light can travel. A smaller NA reduces dispersion by limiting the number of modes.

What is Attenuation?

Attenuation is loss of power. During transit, light pulses lose some of their energy. Attenuation for a fibre is specified in decibels per kilometer (dB/km). For commercially available fibers, attenuation ranges from approximately 0.5 dB/km for Singlemode fibre to 1000 dB/km for larger core plastic fibres.

Attenuation varies with the wavelength of light. There are three low-loss "windows" of interest: 850 nm, 1300 nm, and 1550 nm. The 850 nm window is perhaps the most widely used because 850 nm devices are inexpensive. The 1300 nm window offers lower loss, but at a modest increase in cost for LED’s. The 1550 nm window today is mainly of interest to long-haul telecommunications applications.

What is SFP?

Small form-factor pluggable (SFP) is a specification for a new generation of optical modular tranceivers. The devices are designed for use with small form factor (SFF) connectors, and offer high speed and physical compactness.

Several companies have formed a consortium supporting the use of SFP transceivers to meet their common objectives of broad bandwidth, small physical size and mass, and ease of removal and replacement. What is SFF?

Small form factor (SFF) refers to any of several physically compact connector designs that have been developed for use in fibre optic systems. They are about half the size of conventional connectors. Currently there are at least three designs: the LC by Lucent, the VF-45 by 3M, and the MT-RJ by Tyco.

The main motivator for the development of SFF connectors is an ongoing demand for smaller components in network systems. Using SFF connectors, it is possible to get many more interfaces on a single card. In addition, the use of connectors, rather than direct soldering, increases the flexibility and versatility of network systems, and makes it easier and less expensive to maintain them.

The fact that there are several SFF connector configurations allows the use of products from multiple sources. An argument has been made for standardisation, but individual connector makers have so far resisted this idea, preferring instead to develop and promote their own connector designs.

What is Fibre Channel?

Fibre Channel is a technology for transmitting data between computer devices at data rates of up to 4 Gbps (and 10 Gbps in the near future). Fibre Channel is especially suited for connecting computer servers to shared storage devices and for interconnecting storage controllers and drives. Since Fibre Channel is three times as fast, it has begun to replace the Small Computer System Interface (SCSI) as the transmission interface between servers and clustered storage devices. Fibre channel is more flexible; devices can be as far as ten kilometers (about six miles) apart if optical fibre is used as the physical medium. Optical fiber is not required for shorter distances, however, because Fibre Channel also works using coaxial cable and ordinary telephone twisted pair.

Fibre Channel offers point-to-point, switched, and loop interfaces. It is designed to interoperate with SCSI, the Internet Protocol (IP) and other protocols, but has been criticized for its lack of compatibility - primarily because (like in the early days of SCSI technology) manufacturers sometimes interpret specifications differently and vary their implementations.

Standards for Fibre Channel are specified by the Fibre Channel Physical and Signalling standard, and the ANSI X3.230-1994, which is also ISO 14165-1.

What’s the difference between a Simplex and Duplex patchcord?

A Simplex patchcord is a cable with only one fibre running through it terminated with a connector at each end a Duplex patchcord is basically two simplex cable joined together so there are two fibres and two connections at each end.

What is the difference between a PC an APC and a UPC finish on a fiber optic connector?
Whenever a connector is installed on the end of fibre, loss is incurred. Some of this light loss is reflected directly back down the fibre towards the light source that generated it. These back reflections, or Optical Return Loss (ORL), will damage the Laser Light Sources and also disrupt the transmitted signal. To reduce back reflections, we can polish connector ferrules to different finishes. A typical hand polished connector will measure at –30dB. This polish is referred to as a PC or Physical Contact polish, which for some systems is considered too high of an ORL measurement. To reduce the back reflection of a connector, we can machine polish it to SPC (Super Physical Contact) polish or UPC (Ultra Physical Contact) polish. Industry standard is a minimum of –40dB for SPC Back reflection measurement and –50dB for UPC back reflection measurement. If even less back reflection is required, an APC, or Angled Physical Contact polish, might be necessary. An APC connector has an 8º angle cut into the ferrule. These connectors are identifiable by their green color. An APC polished connector has an Industry Standard Minimum of –60dB ORL measurement. Most CATV and telephone companies require the use of these low back reflection connectors.

 

 

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Turnkey Fibre Solutions Ltd
6 Sunbeam Road
Woburn Road Industrial Estate

Kempston
Bedfordshire
MK42 7BY

Tel: 01234 743039 / 07967 017446

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