4.Size, weight, and strength

A copper cable is bulky and heavy as compared to a fiber optic cable that is much lighter and thinner. It can be used very efficiently in underground pipes that are confined to the ground and are also much stronger, with eight times the pulling tension of a copper wire. It is also tough against environmental factors and atmospheric distortions and hard to damage or kink (**Figure 8**).

## 5.Cost

The initial cost of material and installation of an optical fiber is high as compared to a copper wire, but in the long run, the working cost is much less. Moreover, a fiber network has a low maintenance cost and requires very few networking hardware.

### 6.Durability

Fiber optic cable is highly resistant to many environmental factors that, otherwise, affect a copper cable network. No electric current can flow through the former as the core is made up of glass which is a perfect insulator. Fiber cables can be made to run next to any industrial equipment too. An optical fiber is also more resistant to temperature fluctuations as compared to copper and can also be submerged in water.

As discussed, optical fibers can communicate data through transmission of waves based on the phenomenon of total internal reflection. The theoretical bandwidth of optical fiber transmission is of the order of few terabits.

Bandwidth can be enhanced by employing two techniques. The first one is known as the time division multiplexing (TDM). Multiple channels are transmitted

**Figure 9.**

*Time division multiplexing (https://www.newport.com/t/fiber-optic-basics).*

**Figure 10.**

*Wavelength division multiplexing (https://www.newport.com/t/fiber-optic-basics).*

onto a single carrier by increasing the modulation rate, and each channel is allotted a time slot (**Figure 9**).

The second method is known as wavelength division multiplexing or WDM. Using this method, capacity can be increased by using more than one optical carrier (wavelength) in a single fiber. Therefore, adding a second transmitter and receiver to an optical fiber can double the bandwidth of that communications system (**Figure 10**).

As per the data on the Newport website, the ITU (International Telecommunication Union) had proposed a set of closely spaced wavelengths in the 1550 nm window. This method of WDM is known as Dense Wavelength Division Multiplexing or DWDM. These different wavelengths or channels, spaced 100 GHz apart or 0.8 nm approximately, form the ITU-T grid. The 1550 nm window has the smallest amount of attenuation and lies in the band in which erbium-doped optical amplifiers operate. DWDM systems have a fixed starting and a distinct ending point. Thus, these are, therefore, called point-to-point links. Research is being done to make these networks evolve into completely configurable networks that are not limited to fixed point-to-point links.

Transparency in the optical layer opens many possibilities for the future. Digital and analog transmission can occur on the same fiber. Different bit rates using different protocols will all travel together. Current research is being performed on reconfiguring an optical network in real time. Wavelength selective switching allows wavelengths to be routed through the network individually. Some of the applications of this are for network restoration and redundancy, which may reduce or entirely eliminate the need for an entire back up system to help the network recover from failures such as equipment malfunctions or fiber breaks. A reconfigurable network may offer bandwidth on demand to configure itself to optimize for traffic bottlenecks. The future may also include wavelength translation to convert traffic on one wavelength to another wavelength in the optical domain.

**35**

**Figure 12.**

**Figure 11.**

*Structured Light Fields in Optical Fibers DOI: http://dx.doi.org/10.5772/intechopen.85958*

All optical switching is still in the research phase; however, researchers are looking for ways to create reliable, low loss switches with fast switching speeds. Investigation into the possibility of optical packet switching and other novel technologies is currently underway. The all-optical network may be just around the corner. The future is fiber-optic technology, and the network is growing exponentially worldwide. Most major companies are already using fiber-optic systems in their

Today's optical-fiber communication systems use wavelength division multiplexing, as discussed in Section 2, to squeeze multiple channels of data through the

But there is another breakthrough research in squeezing photons into this light pipe! It is the "twisted light" or the photons with an orbital angular momentum (OAM) that can also be utilized to encode data channels. It is like another degree of freedom or another dimension on which data can be transferred. The angular momentum has an infinite number of states. Each wavelength can carry different values of this angular momentum. Thus, OAM appears to be one more parameter of

Researcher Miles Padgett and his coworkers in the University of Glasgow discovered in 2004 that OAM modes can be sent through air. They used a holographic

backbone applications. These systems offer higher reliability and speed.

same fiber simultaneously, offering much speedier data transfer rates.

light that was not explored till date for communications (**Figure 11**).

*Twisted light through an optical fiber (https://goo.gl/images/vAZD3C).*

*Light trails (https://www.creativity103.com/collections/Lightwaves/slides/twisted\_light\_loops.html).*

**4. Can structured beams propagate in optical fibers?**

**4.1 Yes... twisted light through the light pipe...**
