Optical Systems

Fiber optic, which started to be used in the 1920s, did not attract much attention due to the expensiveness of the material and the lack of usage area, and in the last 20 years, the potential in its technology was realized and it has found a very intensive use area. Fiber optic technology, which started to be used primarily in the field of medicine, is used in almost every field today.

Two techniques such as "fiber optic cables" and "optical systems" are used to transmit light today. With optical fiber, a large amount of information is transmitted at the speed of light along a single fiber cable. A large number of phone calls, television broadcasts and internet connections can be made at the same time from the finger-thick fibers in the fiber optic cable. In fiber optic systems, electromagnetic waves at different frequencies can be transmitted over long distances without any change.

The working principle of fiber cable is based on full reflection of light. Light travels through the fiber cable by reflecting in a balanced way, and this is called a "modeThe number of modes in the fiber depends on the diameter of the fiber cable, the wavelength of the light, and the magnitude called the numerical aperture.

There are two main types of fiber optic cables used today: single-mode and multimode fibers. It is not possible to distinguish them by their external appearance. However, both are used as communication media.

In fiber optic technology, any information, sound, data or image is first converted into electrical signals. In the light source, these electrical signals are converted into light. Fiber cable can carry both digital and analog signals. After the signals are converted to light, they move through the fiber until they reach the detector. In the detector, the light is converted back into an electrical signal. Finally, electrical signals are decoded and converted into information (sound, data or image).

Fiber cables used today consist of at least three parts. These are: Core, Clad, and Coating.

1. Core: It is the central region of the fiber cable and this is the region where the light moves.

2. Clad (Shell): Clad ensures that the light moves alone and does not leak into the external environment. In short, it protects or insulates the traveling light from environmental factors.

3. Coating: Coating, or in other words, buffer coating, is the outermost surface and is the layer that protects the cable from chemical and mechanical damages.

The main areas of use are;

•LAN & WAN applications

•Internet

•CATV (Common antenna system. System that distributes TV signals to more than one apartment with the help of a common switchboard)

•CCTV (Closed Circuit Television System - Security)

•SCADA Systems (Supervisory Control and Data Acquisition)

•Digital TV

•Videophone

•Video conferencing

•Multimedia applications

•Medicine

Fiber cables consisting of hundreds of optical fiber bristles are divided into two according to their center diameter, the material they are made from and the way the light is refracted.

1. Singlemode Fibers: The thin-centered cable, with a diameter of about 9 microns, transmits infrared laser light with a wavelength between 1300 and 1550 nanometers. This cable type is generally used where less data loss is desired.
2. Multiple Mode Fibers: The cable, which has a diameter of about 62.5 microns, transmits infrared laser light with a wavelength between 850 and 1300 nanometers. It is the most commonly used cable type because its production cost is more affordable.The amount of loss is higher than single mode cables.

Some fiber cables are made of plastic and have a center of up to 1mm. Visible red light with a wavelength of 650 nanometers is transmitted using these cables.

HOW DO FIBER OPTIC CABLES TRANSMIT LIGHT?

The light beam sent from the laser source initially follows a linear path. If the light signal is taken as a reference output from the lower and upper limits equidistant from the center of the cable, it continues on its way by reflecting from the points where the cable bends. During reflection, slowing down and back reflection occur to a certain extent. During this time, light losses occur. The use of fiber cable in a flat environment is very important for its efficiency.