The Laser Communication System

This report is apprehensive with Optical communication in which the source of light is a laser and whose beam is modified for video, voice or data communication over the wide range of bandwidths, typically 1 GHZ or more. Since when the laser is invented, it has attracted the communication engineers because it is the revolutionary source of electromagnetic radiation. There are basically two principal reasons for this attraction. First, optical carrier frequencies are about ten thousand times higher than those available in the microwave part of the spectrum. If we can develop techniques for achieving even modest modulation percentage bandwidths, the information handling capacity can be increased at a great deal. The second reason relates to the narrow beam width that can be obtained from a laser. This means that power can be efficiently transmitted to distant points [1].

In this report I have prepared a Laser communication system in which we are transmitting our voice across the room with help of the Laser. We have described how the system is made i.e. complete description about the design of transmitter and complete description about the receiver. We also have tested the system and its working successfully. The components used for the project were very cheap and easily available (like transformer, led, solar cell, laser, microphone jacks, mic, amplifier, battery holder and batteries). This is in fact the best method to make a Cheapest Laser communication system.

Basics about Lasers and optical fibers are described as both were important to know. The advantages and disadvantages of both laser communication system and optical fibers are discussed in this report. To make an optical communication system we must require sources of light. The properties of the two mostly used sources of lights i.e. LASER (Light Amplification by the Stimulated Emission of Radiation) and LED (Light Emitting Diodes) is also been discussed in a tabular form. By using this table we can identify which source to use at what time.

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There are also some challenges faced by the laser communication system and optical fibers, these are discussed and solution to some of them is also given. It is also been told that what will be the business benefits, when we will find the solution of those problems. This report is all about the short range communication but also can be used for long communication systems.

Chapter 1: Literature review

1.1 Laser

LASER is a short form of Light Amplification by the Stimulated Emission of Radiation. The theory of laser is that an atom in excited state encounters a photon of same energy that is equal to the gap energy between the excited and ground states of the atom. When this type of photon is encountered, then another photon is emitted which is of the same energy.

The research in Lasers slowly continued and increased the scope area. There were different types of improvements in laser structure and design which enhanced the lifetime of the lasers, beam width was focused, improved continuity of output, regulated and short pulse duration, etc.

Henceforth Transportations became largest areas in which lasers were thought to have application. “Increasing telephone use, electronic transmission, relaying of television signals, and the need for communication in space all contributed to the emphasis placed on laser technology toward communications”[2]. The major attraction to lasers for communications purpose is the fact that the quantity of data or information that an EM wave can carry is proportional to its frequency. One more interesting thing about Optical light is its frequencies; the optical frequencies are 109 times greater than the radio waves and also105 times greater than microwaves. Communication technology was growing day by day and Lasers were emerging as the ideal solution for this complex problem. There were huge amount of technical complications in using lasers for the communications, and it took many years of hard work and invention of other technologies which made laser communication practical. The first invention was the discovery by Charles Kao and George Hockham in 1970 that glass fibers could transmit laser light [2].

The working principle of the Laser communication system is very similar to fiber optic links, but the difference is that the beam is transmitted through free space. While the transmitter and receiver must require line-of-sight conditions, this is the only so called constraint of the laser communication system. As any barrier between the transmitter and receiver can cause the data loss but they have the benefit of eliminating the need for buried cables and broadcasting rights. Laser communications systems can be easily deployed since they are cheap, small, low power and do not require any radio interference stuff to revision. The carrier used for the transmission signal is generated by a laser diode. Two parallel beams are required, one for transmission and one for reception. But the system which is to be implemented in this project is only one way.

Laser communications have been a very attractive topic lately, because it has given the solutions for how to satisfy ever increasing bandwidth needs which are in high demand. Some have suggested that bandwidth could be distributed in neighborhoods by putting laser communication systems on top of homes and pointing them towards a common transceiver with a fast link to the Internet [2]. With possible transmit speeds of up to a gigabit per second, this is an exciting area.

1.2 Optical fiber

Before starting with the laser communication system we must also be familiar with optical fiber communications i.e. the communications with the help of glass fibers because laser communications is a part of optical communications somewhere, as laser communication can be done with and without optical fiber and laser is also a source of light in optical communication with LED (Light emitting diode) [3,9].

This thinking of optical communications with the help of the glass fiber was generated at the time of Alexander Graham Bell [4]. Yet it took many years for its practical implementations as better quality of glass and low cost electronic equipment was invented quite a while after that.

In 1960s the development of the optical communication was started with the invention of the new devices and fibers and which is going on till now. The most interesting thing happened in 1980s. During these 10 years the public communication networks were developed for the optical communications and it became the most dominant technology.

There were 3 major milestones in all the developments and they were following: [4]

In late 1950s LASER was invented

In 1970s low loss optical fiber was developed.

In 1980s amplifier for the optical fiber was invented.

The use of the optical communication technology blowout like a fire. And the coaxial copper wire, which were used in early times, were replaced by the optical fibers and a new era of technology emerged called as optical communications technology.

The two technologies electronics communications and optical communications are very much closely related to each other but the principle of operation in both the technologies is different.

There is a misconception in the people about optical communication that the light travels in the optical fiber as the current or electricity travels in wires. This is not true, because in optical communication systems light is an electromagnetic wave and optical fiber is a waveguide.

Also the connection between the wires i.e. in the electronic communications is very easy as compared to the optical fibers. In optical communications we require connectors to join two optical fibers [3,4].

1.3 Advantages and Disadvantages of optical fiber

Now we should discuss some advantages and disadvantages of optical fibers over copper wire:

1.3.1 Advantages of optical fibers

Data secrecy i.e. security of the data

Data Truthfulness i.e. very low loss of data

Long distance communications is possible without involving repeaters, amplifiers and boosters.

Large amount of data can be communicated.

Optical fibers are insusceptible to EM interference, but not immune to the alpha and the beta energies.

These optical fibers are not unsafe to use them near the high voltage devices and an area where the earth’s potential is different because they have High electrical resistance.

The power necessities of the optical fibers are low as compared to the wires.

The optical fibers are very light in weight, so they are easy to carry.

The speed of the transmitting is very high

1.3.2 Disadvantages of optical fibers

The initial cost and the preservation cost of the optical fiber is quite high as compared to the wires

To connect two optical fibers we need connectors and splices which are costly and more difficult to operate than wires.

Optical fibers don’t have ability to transmit electrical power for the operation of terminal devices

Extra care is to be taken while handling the optical fibers, as they are very sensitive to physical shocks.

1.4 Sources of light in Optical communication system

There are two main sources of the light in Optical communication systems and they are namely [3]

LED – Light Emitting Diode

LASER- Light Amplification by the Stimulated Emission of Radiation

It totally depends upon the certain factors like application, cost, performance, stability, power and cost, to use which type of source for the system. LED is generally used when them system power requirements is low. As LED make system small in size, reduces its cost, reduces the complexity of the system and also stable with temperature.

LASER is used where the power requirement of the signal is high because if we use LED in high power requirements then the cost of the system will go high. Also in LASER the transmission rate is high, can do long distance communication and more reliable.

The table on the next page compares properties of LED and LASER [3].

S. No.

Features

LASER

LED

1.

Power

100 mW

40 mW (max)

2.

Light source

Coherent

Incoherent

3.

Temperature Dependence

High

Low

4.

Interference

Self-interference

No self-interference

5.

Lifetime

Long but lees than LED

Long

6.

Modulation speed

Can be 1 GHz and faster

100 Hz – 30 MHz (max)

7.

Beam divergence

Narrow

Wide

8.

Bandwidth req.

Less than 1 nanometer

40 – 100 nanometers

9.

Noise at receiver

Low

High

10.

System cost

Low for high power & vice versa

Low for low power & high for high power

11.

Reliability

High

Low

12

Accuracy

High

Low

13

Efficiency

High

Low

14.

Use

Long & short distance communications

Short-distance Communication

15.

Signal damage

Low

High

Table 1

According to this above table we can choose our source of light.

In this technical report, we develop a basic Laser communication model which is used for long or short distance communications. Sometimes for the long n short Laser communication systems we use optical fibers and some times we do not use, totally depends upon the system [5].

Actions can be taken to increase the capability of the system i.e. to boost the data rate with low noise. This all is discussed in this report.

Chapter 2: Review from the key paper

The key paper I took for this topic is not actually a paper but a page on the internet called Light and Optics made by Simon Quellen Field [6]. It is equivalent to my key paper because the work done on this paper is very much similar to my project area.

2.1 Summary of the key paper

2.1.1 Project Objective

The objective of this project is to make an optical communication system in which the source of light is a laser and which can transmit the signal from one point to another without using any cables wires etc. I am interested in this laser communication system because in this system the loss of data and the probability of erroneous are very low and It can also transmit the data at the great speed. This project only deals with the short distance communication [3].

2.1.2 Project Description

Fig. 1 Laser Communication System

Figure 1 – Laser communication system

The system shown in the figure can send data at very high rate. The system illustrated above is set up to send voice data. The microphone input is fed to the transmitter, where the signal is modulated and then transmitted in free space with the help of a laser. The Laser output is according to the format of the result produced by the transmitter section i.e. varying intensities of light.

On the receiver side, the signal is read by a photo transistor which converts the light signal to the electrical signal and then it is applied to a speaker.

the basic principle is Amplitude modulation an in this case amplitude is intensity of light.

This is the basic principle of the Laser communication system.

2.2 Experimental approach of the research [6]:

Now we are going to discuss about the technique by which a laser communication system can be made. This method is the simplest method to make a laser communication system. Also this is the cheapest one.

For the transmitter we will need

A laser pen pointer.

A battery holder which can contain equal number of batteries as the laser pointer is having. The size of the batteries may vary, but they should be of the same voltage as the laser batteries. Generally we have a battery holder which contains two batteries, but in this project we need at least three cells. So we can use one battery holder which holds two batteries n one battery holder which holds one battery, and a wire to connect them in series.

A transformer as an audio output transformer having an 8 ohm coil and a 1000 ohm coil.

A microphone and an amplifier or speaker.

Some clip leads normally connecting wires with crocodile clips to connect every component. One clip lead must be the type with a long point, to get connected to the inner part of the laser pointer. The soldering procedure and simple wires can be used for this but the leads are fast, reliable and simple.

At last we require a 2 lead bi-color light emitting diode (LED), to protect the damage done to the laser from high voltage spikes.

For the receiver we will need:

A small solar cell or a light sensitive diode i.e. photodiode having clips to attach simply or if clips are not possible then use soldering procedure.

A microphone jack which fits into the audio amplifier or speaker by which we will get our audio output

2.2.1 Transmitter

The clip lead is connected to the inner part of the laser where battery is touched. Now we have two clips to attach, to the laser and we do it in a normal way. Usually one of the clip is attached to the small spring which is in the laser’s battery area and the second clip lead is usually attached to the case of the laser. Since there are various different types of laser pointers, we may have to do different type of settings with the placement of the clip lead for the proper working of the laser with the new external battery pack. There may arise some situations when we have to hold the laser’s push button switch with help of a rubber band or any wire around it. The connection is tested before a transformer is attached to it. It done to make sure that the laser is working with the new battery pack or not. During the testing if the laser doesn’t light, then the problem may be with the direction of the battery, the battery is reversed and tested again. This reversal of the battery will not damage the laser.

As said before the transformer has two sides. One is 1000ohm and second is 8 ohm. The laser and battery is connected to the 1000ohm side. There are three wires which are coming out of the 1000ohm side of the transformer. We only use the outer two wires to connect the laser and the battery and the middle wire is not used in this circuit and is called a center tap wire.

One end of the laser (clip lead used) is connected to the first wire of the 1000ohm side of transformer and the other end is connected to the battery’s positive end. The negative end of the battery is connected to the second third wire of the 1000ohm side of transformer and the second one is left open. The bicolor light emitting diode (LED) is also connected to the two outer wires i.e. wire one and wire three of the transformer on the 1000ohm side. This part or LED is used as a protector of the laser which protects the laser from the high voltage spikes. As high voltages go to the LED and low voltages required for the laser go to laser.

The laser is tested by attaching the battery. The laser must operate at this time. Now the connection to the 8 ohm side of transformer is made. The earphone jack is connected to that side of transformer.

The schematic diagram of the transmitter looks like this:

Figure 2 – Transmitter for Laser communication system

This is how it works. The work of the transformer here is to modulate the power which going to the laser. The signal which comes from the mike is added to and subtracted from the battery power accordingly to the situation, and the intensity of the laser is brightened or it is dimmed correspondingly with the amplitude of the voice in the signal.

2.2.2 Receiver

The simplest part of laser communication system is its receiver. We just have to make the connection between the microphone jack and the solar cell. The two ends of the microphone jack are attached to the terminals of the solar cell. It hardly matters in which way the connection is made to it.

The schematic of the receiver:

Figure 3 – Receiver for Laser communication system

2.2.3 Setup and testing

We need to take care of two things at first. The mic should be off and laser should be on. Then we need to plug the jack of the transmitter into the opening of the mic.

Now the solar cell is connected to the audio amplifier or speaker and the volume is increased till we are able to listen distortion and mocking noise when ever laser light falls on it. When we are able to listen that, then we decrease the volume till the noise is negligible.

Now the next step is to aim the laser to fall on the solar cell. The laser is aimed to it and we can listen some noise in form of pop or click. Now if we move the laser beam over the solar cell from one end to another to it, then we will be able to listen these clicks till the laser falls on the solar panel and disappears when laser is not hitting the solar panel. If this all is happening, then everything is right till now [6].

Now the mic is switched on very watchfully and gradually the volume of mic is adjusted and something is said in the mic. The volume of mic is adjusted so that we can listen our voice coming out of the amplifier or speaker which is in the other corner of the room.

If we are not able to listen our voice coming out of the amplifier, then we must check the laser, that the laser is hitting on the solar panel or not. If it is not hitting then we must adjust it to hit the panel, only then we can listen our voice. Now after doing all this adjustment, just increase the volume of amplifier or speaker instead of increasing the volume of mic, to listen your voice across the room. But precautions must be taken during the increase of the volume as if increased then a limit, will damage the laser.

Now it is time to do some testing, just break the connection between the laser and the solar panel i.e. to put some obstruction in between, we will notice that the when the obstruction is inserted the amplifier does not produce any sound. Now move this obstruction back and forth or up and down such that connection is made and then broken at regular intervals, we will notice that our voice is chopped by the obstruction as it moves back and forth [6].

The basic principle behind the Laser communication system is Amplitude modulation. The amplitude of the carrier signal is modulated. In simple words, in this case the intensity of the light is varied along the time.

Now what happens in transmitter is that when the sound is transferred through mic it travels through transformer which modulates the signal. Then the modulated signal is added and subtracted from the battery power. Then the signal produced goes to the laser and produces a laser beam of the varying intensities i.e. electric signal is converted to the light signal. This varying intensity beam hits the solar panel across the room, whose work is to convert this light signal to the electric signal and which goes to the audio amplifier to produce sound. Now it is interesting that how this speaker produces sound. This is very simple; speaker is just a paper cone which is attached to the coil of wire, which is in magnetic field due to a powerful permanent magnet. Now when electric current flows through the coil, it makes coil an electromagnet which moves away and towards the permanent magnet, which disturbs the air in paper cone, if it is moving away then it will compress the air at back and expand the air at front. These waves produced from compression and expansion is heard by our ears. This is how a Laser communication system is made [6].

On critically evaluating the key paper against the objectives which the author had set, the out come is that he is completely able to satisfy the aim of the project. By doing the procedures told in the project we can transmit signal from one end to another with the help of LASER. This project is cheap and very much informative too.

Chapter 3: Evaluation and Outcomes

If whole assessment of the data or information present in this research is done, then the conclusion is that researcher’s finding are justified. As by following the methodology or procedures of the researcher we are successfully transmitting data from one end to another with the help of the Laser by using cheap and simple components. In this experiment we can transmit data in form of voice from one end to another by the use of Laser wirelessly.

The conclusions and the predictions made by the researcher are totally justified and also the methods used are completely working. This is an experimental procedure which tells that it is possible to transfer data from one point to another point with the help of the Laser.

The outcome of the detailed research is positive. And following are the points which will tell us about the advantages of Laser communication systems [7].

3.1 Enormous Bandwidths

If we have used optical fibers in the system, then the data holding capability of the system is increased at a great rate. As this data holding capacity is directly proportional to the frequency of signal.

3.2 Low transmission loss

As the signal is directly transmitted to the other end, and if no obstruction is in between the light, then the transmission loss is very low.

3.3 Invulnerable to noise

The laser communication system using optical fibers are immune to noise and cross talks. And the systems which does not use the optical fibers are also immune to noise up to a limit, as there is very less transmission

3.4 High data rate

The data rate in the Laser communication system is very high

3.5 Electrical Isolation

Laser and optical fibers both are not affected by the electrical shocks. So both of them can operate near high voltage devices

3.6 Small size and weight

The size and weight of both Laser and optical fibers is very small. So they are easy to handle. They occupy very less space as compared to the electrical equipments. Due to these rewards it makes it possible to use in aircrafts and satellites more successfully.

3.7 Signal security

This point has two different point of views, if in system we are using optical fiber. Then our system is 100 percent secure as optical fibers do not radiate any power. Whereas if we are not using optical fibers then our information is not secured

3.8 Cheap and good availability

Since Lasers and optical fibers both are available easily. And they are cheap also, which makes a efficient and cheap communication system.

3.9 Reliability

There is less attenuation of the signal, so the integrity of the signal is saved. Therefore it makes the system more reliable.

Some more advantages are [8]

No difficulty in deployment

High Data rate

Bit error rate is very low

Process can be fully duplex

Protocol simplicity

Fresnel zone is not important

The Laser communication system using optical fiber is more preferred because using this method laser can be traveled to very far distances and also without any losses. The optical fibers can be connected using the connectors and splices. By using these, light can be made to move across the curvature of earth. Eventually we can’t move light in circular path or can’t be bent along the corners. But with the use of these connectors the light made to move like that without losses [10].

Chapter 4: Personal Recommendation for Further Investigation

The recommendations for the further investigation will conclude some challenges faced by the Laser communication systems for the long distance. These challenges must be encountered to have a very good communication system [3, 4].

4.1 Challenges in laser communication system

Some of the major challenges are:

Physical barriers

This is one of the major challenges faced by Laser communication system. As whenever any obstructions comes in between the laser then the connection is broken immediately and we lose our data.

Beam scattering

During the long distance communications in Laser communication systems we face a problem called beam dispersion. That means after traveling a long distance the laser beam starts dispersing, which reduces the reliability of the systems. But if we use optical fibers then this dispersion can be ruled out.

Fog, Snow, Rain and Smog or Pollution

These are some of the elements which reduce the efficiency of the laser communication systems. They do not provide great deal of attenuation to the signal but still it hampers the signal.

Circumstantial light and Shadowing

The effectiveness of the system is also reduced when there is a background light source to the laser as the light from that source is also received by the receiver which create errors in the signal

Atmospheric captivation

Some part of the light signal is absorbed by the atmosphere. Due to which the signal is not completely attainted by the receiver.

Scintillation

All the laser communication systems are affected by the scintillation at the great deal in clear sunny days. But there are also some methods by which it can be controlled like tuned receivers, tuned filters, equally spaced transmitters and all.

Pointing stability

This is also an important factor in the Laser communication systems. To avoid this we may widen the beam divergence so that receiver still remains in contact.

Security

Security is the most important challenge to be faced by the Laser communication system. We have got the models for laser communication systems but the information is not secured. It can be theft by anyone easily. That is a different case if we are using optical fibers but in system in which we do not use these fibers are very much in secure and this is an important issue.

4.2 Challenges in optical fibers

The optical fibers are very costly.

Optical fibers are delicate and can be easily broken.

Optical fibers are affected by the chemicals.

There opaqueness is also a problem.

To operate and work on the optical fiber we need a specialist and skilled person.

All of the above points fall in the area of further investigation. Some of them are done and some are still there to be investigated. These areas are very important and we need to investigate in these areas because today the communication industry is a backbone of every industry without communication industry no industry can survive.

4.3 Business benefits

On taking the business perspective of the improvements in these area will lead to the better communications at low cost, low loss of the signals, better performance, negligible time delay, better security, less complex systems, will increase the reliability of the communications, more and more application areas (such as medical, lighting and many more)

Chapter 5: Personal Development Plan

5.1 Personal Description

I am Gibbran Jamil. Currently I am pursuing my Masters of Science (MSc.) in Mobile and Satellite Communications from London Metropolitan University, London. I have done my Bachelors of Science in Computer Enigineering in Pakistan.

From starting of my technical career I had a great interest in all this communication systems. I always was curious to know about communication systems, how they work, how they are made, how they transfer data, how link is made, how can two persons talk or share stuff on wires or how we can talk to each other without having any physical connection and all that. So I decided to go for my MSc. in Mobile and Satellite communications. I am doing this MSc. course because at present I am not that good in the technical stuff, so I want to improve my knowledge and grow technically and personally in this field. I want to work in the area, where I can improve the efficiency of the communication system. I either can work for a company or can work alone, but the basic idea is to reduce all the limitations in the communication system. There are many things in any communication system to be improved; like noise can be further reduced, received power from satellite can be increased, accuracy of the data can be increased, security of communication system can be increased, cost can be more reduced and many more things like that. Definitely first, I will go for one particular task and then move forward.

I hope I am on the right path and I also hope after completing my Masters I will be having good technical and practical knowledge because right now I am concentrating on my all the modules and trying to grasp as many things as possible and my tutors are helping at a great deal in that. Still there is never an end for learning, i