Introduction to Optical Fiber and Fiber Optics

Optical fibers are widely used in telecommunication, imaging and Laser industry. Optical fiber is basically transparent flexible cylindrical rods made of drawn silica glass or plastic. As you may know our hair has typically a diameter of around 70 micrometers. An optical fiber has slightly more diameter compared to our hair.

An optical fiber can be used as a waveguide, or light pipe. This means light can be sent through an optical fiber from one end to another end just like we pass water through a pipe. Sending light through an optical fiber needs precise engineering and design. The field of applied science and engineering that deals with the design and application of optical fiber is known as fiber optics.

Even if you are not associated with fiber optics, you might have noticed the installation crew deploying small diameter cables of different colors mostly black in your city or countryside. Optical fiber cables come in different colors as per the requirements telecom operators. Optical fibers are widely used in fiber-optic communications. Optical fibers permit transmission of high bandwidth over longer distance in comparison with the legacy cables. Optical fibers are used instead of copper wires. Optical fibers use light, while copper cables use electricity. Optical signals travel along the length of optical fibers with low loss (attenuation). Light signals are immune to electromagnetic interference to a great extent.

You might be familiar with illuminated Christmas trees. Optical fibers are also used for illumination. In imaging industry optical fibers are wrapped in bundles to carry images from one end to other end. This allows us to view confined spaces such as inside our body or physical infrastructures. Sensor and Laser applications require specially designed optical fibers.

As we saw above, an optical fiber is a transparent medium. An optical fiber will have transparent core that is surrounded by a transparent cladding. Cladding will have lower refractive index than core so that the light is confined almost in the core by a phenomenon called total internal reflection. Total Internal Reflection, which is shortly written as TIR allows the optical fiber to act as waveguide. Some optical fibers support many (more than one) propagation light paths or transverse modes. They are called multimode fibers (MMF). Some optical fibers support only one transverse mode. They are called Single mode fibers (SMF).

Multimode fibers have larger core diameter compared to that of singlemode. Multimode fibers are suitable for short distance communication links. Multimode fibers find their best applications where high power transmission is required. Singlemode fibers are used for most communication links that are longer than one kilometer.

With the introduction of high precision technology products, jointing two optical fibers usually called splicing is easy now. Two types of connections that are permanent and temporary are used in jointing two optical fibers. Temporary connection method utilizes mechanical connectorization techniques while permanent connection method makes use of fusion splicing technique. In fusion spicing, glass portions (core and cladding) of two precisely cleaved optical fibers are fused together by using thermal energy through electrodes.

Author: Nimura

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