PXT999 Research Project: Fiber Optic Communication System

Introduction 

Fiber optic communication system are based on the fiber optic cable which provides for extremely high data rates which allow the very large masses of data to be transmitted at the speed of light. The fiber optic cable, FOC, transmits data over very long distance. One very common example is the sea or ocean underground cable that connect continents on the planet earth. According to the basic model, the bandwidth of the fiber optic communication system determines the maximum data rate [1]. A FOC link denotes the signal pathway between two points using the cable. The pathway is the mode or channel that enables transmission of the data from the sender to the receiver points. The links are often described in terms of their ability to send and receive signals as part of the communication system. There are two modes of communication generally referred to as the simplex and duplex. This is a classification based on the direction or flow of data or information. For the simplex mode of communication, data flows in one direction only, for instance, home radio communication or broadcasting. The duplex mode refers to the communication where the sender and receiver can communicate to each other. The half-duplex allows one speaker at a time while the full-duplex allows for information to flow both ways at the same time [2].

The fiber optic link is a typical communication link that uses the optical fiber instead of the copper or aluminum wire [3]. The fiber communication system comprises of the transmitter, receiver, optical fiber, and the connectors. During transmission, the engineers focus on converting the information into a form compatible with the communications medium. The conversion is done using an analog-to-digital converter. It is crucial to note that information transmitted directly from a computer network is already in digital form [4]. The digital pulses are used to flash a powerful light source in binary form. Two kinds of light sources are used depending on the type of fiber cable. For a multi-mode fiber which transmits over short distance, the light emitting diode is used whereas the solid-state laser is used in the single-mode fiber which transmits a single information signal over very long distances, up to several hundred kilometers [5]. Alternatively, one can use a semiconductor device that generates an extremely intense single frequency light beam. The light beams are fed into the FOC at an angle,

On the receiver end there is another light sensitive device that is known as the photocell or the light detector that detects the light pulses. The photo detector converts the light pulses into an electrical signal. The electrical pulses are amplified and reshaped back into digital form. The light sources at the sender and receiver points must be capable of operating at the same data rate. The circuitry that drives the light source and the circuitry that amplifies and processes the detected light must both have suitable high-frequency response [6]. The fiber is required to carry the information signals without distortions at the set data rate. For the single mode transmission FOC, repeater units are used to restore the signal strength that may attenuate while propagating. Special relay stations are used to pick up light beams, convert them back to electrical pulses that are amplified and then they are retransmitted on another beam. There are several stages of repeaters that may be needed over very long distances. The attenuation problem occurs as a universal problem for all the transmission cables, for instance, the electrical copper cables.

Some merits that are obtained from using FOC over other wire systems are the elimination of conventional problems such as ringing, cross talk, electromagnetic interference, and other induced errors. Some of the advantages that FOC offers are:

• High bandwidth; more information can be carried by each fiber as compared to its equivalent copper cable.
• Noise immunity; fiber can withstand environmental conditions such as salt, pollution and radiation with no resulting corrosion and minimal nuclear radiation effects, so it is more reliable.
• Inherent radiation hardness
• Reduced weight
• Low bit error rate size and it is more secure and private.
• Weight and volume reduction as compared to the bulky copper cable.

There are many uses of fiber; can be used as sensors to measure the strain, temperature, pressure, and other quantities by modifying a fiber so that the quantity to be measured modulates the intensity based on the losses, phase, polarization, wavelength, or transit time.

Figure 1 Fiber optics communication system-wavelength division multiplexing 

Aims & Objectives 

1. To identify all the physical quantities that can be measured using fiber optics technology
2. To classify the optical fiber-based sensors based on their technical operating principles.
3. To explain in detail the principles of operation of the fiber optics-based sensors used to measure such quantities.
4. To discuss the performance, advantages and disadvantages of using the fiber optics-based sensors in comparison to the traditional sensing techniques.
5. To multiplex and de-multiplex the different light wavelengths for commercial infrared-based communications systems, specialized components; minimizing the losses.

Research Findings & Observations 

Table 1 Part 1: Digital/TTL -01

Table 2 Part 2: Digital/TTL-02

Table 3 Part 3: Testing for crosstalk

Implementation

Comparing the results obtained in part 3 with the WDM- wave division multiplex

Power budget implementation

To obtain the loss,

These refer to the insertion losses, fiber losses, connector loss, and the non-linear loss.

To obtain the gain,

The fiber-based sensors in the technical operating principles

These sensors measure the properties of their surroundings. They can measure anything which changes the way light travels through the fiber or alters the properties of light. There are a number of physical quantities that can be measured using the fiber optics technology such as temperature, pressure, strain, displacement, acceleration, flow rate, vibration, chemical concentrations, electrical and magnetic fields, and rotation rate. The sensors can be used in explosive environments, corrosive environments, hot environments, and remote sensing [7]. Some of the commonly used sensors are:

• Amplitude-and intensity-based sensors
• Frequency- and wavelength- varying sensors
• Polarization and phase-modulating fiber-optic sensing

Principles of operation of the fiber optics-based sensors used to measure such quantities are such as the micro bending, interferometric effects, refractive index change, polarization change, fiber length change, fiber diffraction grating effects, and the Signac effect [8].

Conclusion

In a nutshell, the report covers all the objectives and aims set out in the coursework. The fiber communication system is efficient and effective in the delivery of information especially over very long distances as well as in hostile environment where human intervention is least required. The communication system allows for multiplexing and demultiplexing, such that the data rates and communication method performance is largely improved.

Recommendations

• Improvement of the micro bending sensor detection to ensure that less light signals are lost as a result of the FOC bending beyond the set or standard maximum angle of bending.

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