Fiber Optic

Fiber optic transmission medium is one that can deliver information to a large capacity with high reliability. Unlike other transmission media, then the optical fiber, the carrier waves instead of electromagnetic waves or electricity, but light / laser light.
In fiber optics, digital signal denagn data is transmitted using light waves so it is quite safe for data transmission because it could not be tap in the middle of the road so that the data can be stolen in the middle of the transmission. As with the cables as coaxial and twisted pair. Another advantage of fiber optic is in terms of speed (100 Mbps up to 200,000 Mbps based on testing that has been done in the laboratory).

Physical Description

Diameter optical fibers are very thin, between 2-125 um. Various glass and plastic materials can be used to make optical fibers, the best and has the smallest loss is to use ultra pure fused silica fibers. The material is very difficult to produce, because it is replaced by another material that has a greater loss but still tolerable, namely plastic and glass mixture.

Fibre optic cylindrical and consists of 3 sections, core, cladding and jacket. Core is the deepest and consists of one or more fibers. Each fiber is surrounded by a cladding and then covered by a coating. The outer portion is the duty jacket protects the optical fiber from moisture, abrasion and damage.

Application
            The difference between the use of optical fiber with twisted pair and coaxial cable include:

·         Large capacity

2 Gbps data transmission within tens of kilometers to do, compared to the coaxial cable that can only transmit data within a few Mbps up to 1 km or twisted pair only up to 100 Mbps in the tens of meters.

·         Small size and lighter

Optical fibers are smaller in diameter and lighter weight.

·         Attenuation lower

Attenuation is much lower than other cables.

·         Isolation electromagnetic
Fiber optic is not affected by electromagnetic fields from outside cable, o is also vulnerable to noise or crosstalk.

·          Repeater spacing greater
Larger distance between repeaters, AT & T has a 318 km long optical fiber without a repeater while the twisted pair or coaxial repeater installed every few feet.

Main Components

Optical transmission system has three main components, namely the transmission medium, the light source and detector. As a medium of transmission used a very fine glass fibers or fused silica. The light source can make use of Light Emitting Code or laser diode which emits light pulses both when given an electrical current. As used photodiode detector, which serves to generate electrical pulses when there is light shining. By combining Leser diode or LED to one end and optics, it can be obtained undirected data transmission system that receives an electrical signal, and transmits the changing pulse of light and convert it back into an electrical signal output at the receiving end.

Transmission Characteristics

            And optical systems operate in areas up to 1 million 100 000 Ghz. The working principle and optical transmission are as follows.
1. Light from a source into a glass or plastic cylindrical core.
2. Light beam is reflected and propagated along the fiber, while the part is absorbed by the surrounding material. Propagation in single mode provides better performance than multimode, as with multimode transmission, any file with a length of the path is different and this is resulting in a transfer in the fiber causes signal elements spread out in time, so it can happen that the data received is not accurate. Since there is only a single transmission path in the transmission mode, it will not happen distorted. In optical fiber transmission, there are 3 types, namely single mode, multi-mode and multi-mode graded index.

Two types of light sources used in fiber optic systems is LED (Light Emitting Diode) and ILD (Injection Laser Diode). Both are semi-conductor device that will emit light ketikadiberikan voltage. LED type is cheaper, can operate over a wide temperature range and has a longer operating time. ILD type that operates on the principle of laser, more efficient and can forward data rate greater. There is a link between the wavelength used, transmission type and data rate that can be sent.

Use
            Fiber optic transmission is very useful for varying distances. As an illustration, the distance that can be taken for data transmission on optical fibers are as follows.

·         Remote
For telephone network, is 900 miles, with a capacity of 20 000 to 60 000 voice channels.

·         Metropolitan
Located 7.8 miles and can menampun 100 000 channel sound.

·         Regional Rular
Is between 25 to 100 miles that connects various cities.

·         Loop Subscriper
Used to connect central with customers directly.

·         LAN
Use local network links between offices.

Type of Fiber Optics

            Based on the characteristic properties of optical fiber types in abundance can be divided into 2, namely:

1.      Multi Mode

In this type of optical fiber propagation of light from one end to the other going through some streaks of light, as it is called multi-mode. Diameter (core) in accordance with the recommendations of the CCITT G.651 at 50 mm and is covered by a jacket sheath (cloding) with a diameter of 125 mm. While based on the composition of the index is usually multi-mode optical fiber has two profiles are graded index and step index.

In graded index fiber, optical fiber has a refractive index of light is a function of the distance to the axis / spindle fiber. Thus chaya that runs through some tracks will eventually arrive at the other end pda the same time. Unlike the graded index, then at step index optical fibers (mempuyai same light refractive index) that runs on an axis beam will reach the other end first (dispersion).

This can occur because the path through the process is shorter than that experienced light reflection on the wall of the optical fiber. As a result of dilation pulse or otherwise reduce the width of the field frequency. Therefore, in practice only a graded index optical fiber alone is used as a transmission channel multi mode optical fiber.

2.      Single Mode

Single mode optical fiber has a diameter or mono mode (core) is very small 3-10 mm, so that only one beam of light that can be through. Because only one beam of light there is no influence of the refractive index for light travel or the effect of differences in the arrival time of the light from one end to the other Valentine (no disepersi). Thus the single mode optical fiber is often used in optical fiber transmission systems remotely or outside the city (long haul transmission system). While the graded index used for the local telecommunications network (local network).

Table 1.1 : Comparison between Single mode and Multi mode

Bit Rate (Mbps)	Repeater Spacing Multi Mode	Repeater Spacing Single Mode
140	30	50
280	20	35
420	15	33
565	10	31

Advantages and Disadvantages

This type of cable is not affected by noise and can not be intercepted. But the cable is very expensive, difficult installation and teknoologi is still under development. In addition to fiber optic transmission has advantages over other transmission media. Advantages include:

·         Damping small transmission

Fiber-optic telecommunications systems have attenuation per km transmission is relatively small compared with other transmissions, such as coaxial cable or PCM cable. This means that the fiber optic is suitable for use in long-distance telecommunications, because it only requires a smaller number of repeaters.

·         Sector wide frequency

In theory, optical fiber can digunakandengan high speeds, up to several gigabits / sec. Thus this system can be used to carry signaling information preformance large numbers with just a single optical fiber is smooth.

·         Small size and lightweight

Thus greatly facilitates installation pengangkuta the location. For example, can be fitted with a cable lam, without having to create a new hole.

·         There is no interference

This is due to optical fiber transmission system using light / laser light As with the carrier wave. The result will be free of competent cross (cross talk) is common in other words biasa.atau cable transmission or telecommunication quality produced better than with cable transmission. With no interference will allow fiber optic cables installed on a network of high voltage electric power (high voltage) without fear of interference caused by high voltage.