LASER COMMUNICATION SYSTEM
Naveen, Shreyas A S, Ravi Ghael, Najashree
Department of electronics and communication, IEEE
Abstract— Laser communications systems are wireless connections through the atmosphere. They work similarly to fiber optic links, except the beam is transmitted through free space. While the transmitter and receiver must require line-ofsight conditions, they have the benefit of eliminating the need for broadcast rights and buried cables. Laser communications systems can be easily deployed since they are inexpensive, small, low power and do not require any radio interference studies. The carrier used for the transmission signal is typically generated by a laser diode. Two parallel beams are needed, one for transmission and one for reception. Due to budget restrictions, the system implemented in this project is only one way.

event, disaster scenes, communications). conventions

or

space

band

I. INTRODUCTION (HEADING 1)
Laser communication is one of the emerging area of wireless communication system. Due to its low noise ratio makes its one of the well suited communication medium for exchanging of information. Currently laser communication is adopted in satellite communication for space research activities and due to its efficiency on low noise ratio, inexpensive, low power, flexibility and its resistance to the radio interference makes laser communication as one of the research area in wireless communication. In this process, this paper comprises one such application of laser communication for information exchange between any two devices.

Laser communication can be used to transmit sound and data signal through the laser beam of system. The intensity of the carrier beam changes with change in amplitude of sound signal. The variation intensity of laser beam is converted into a variation in the voltage level by using solar panel. In this mode of communication the transmitter and receiver requires to satisfy the line-of-sight conditions. The carrier requires for transmission of signals in laser communication system is generated by laser diodes.
II. EASE OF USE
A. Design:

In laser communication the transmitter and receiver must require a line-of-sight condition and laser communication system have the benefit of eliminating the need for broadcast rights and buried cables. The carrier used for transmission signal is typically generated by a laser diode. Two parallel beams are needed, one for transmission and other for reception.
The optical communication system consists of transmitter uses a laser beam of wavelength 650nm as a carrier in free space.
Laser communication plays a key role, as solutions for satisfy ever increasing high demand of bandwidth. In laser communication system bandwidth could be distributed in neighborhoods by putting system on top of homes and pointing them towards a common transceivers with a fast link to the internet. It supports possible transmit speeds of up to a gigabit per second, other application of laser communication system technology include temporary connectivity needs (e.g. sporting

B. HARDWARE COMPONENT REQUIRED
C. Transmitter circuit:
D. IC1 LM386, 9V battery source, C1=100uF 25V, LD-1,
C2=C3=10u 25V, VR3=220, C4=0.047 uF, R1=100,
R2=R3=560.
E. Receiver circuit:
F. IC2 LM386, C5=C6=C7=10uF 25V, C8=0.047 uF, R4=100, calculator solar panel, VR4=10K POT, 9V battery source,
LD2=laser diode, loud speaker 8ohms 0.5W
G. EQUIPMENTS REQUIRED:
H. Potmeter VR1 (10K ohms), multimeter.

III. METHODOLOGY

the music from the CD player connected at the input (Vin) of
IC1.

PROJECT DISCRIPTION:
A. CONSTRUCTION:
The voltage variation on the solar panel is amplified by a low-voltage audio power amplifier LM386 and reproduced by a speaker. The maximum output of audio amplifier LM386 is 1 watt, while its voltage gain is 20 to 200.
The circuit consists of a transmitter and a receiver. Both the transmitter and the receiver are built around IC LM386, powered by a 9V battery.
Fig. 3 shows the transmitter circuit here a laser diode (LD1) with maximum operating voltage of around
2.6V DC and maximum operating current of 45 mA is used to transmit the audio signal. The voltage divider network formed by R2, R3 and VR3 keeps the voltage as well as the current for the laser diode in the safe region. In place of the laser diode, you can also use a laser pointer. The spring inside the laser pointer is the negative terminal. The output power of the laser pointer is 5 mW. Take care while working with laser, as direct exposure to the laser beam can be hazardous to your eyes. Point the laser beam to the solar panel. Pot meter VR1
(10-kilo-ohm) is used to change the level of the input audio signal. The audio input (Vin) is taken from the preamplifier output of the music system (CD player, DVD player, etc.).
Capacitor C2 and preset VR2 are used to vary the gain of the
LM386.

Assemble the transmitter and receiver circuits on separate
PCBs and enclose in suitable cabinets. In the transmitter cabinet, fix two terminals for connecting the audio signal. Fix switch S1 on the front panel and the laser diode (LD1 or laser pointer) to the rear side of the cabinet. Keep the 9V battery inside the cabinet. In the receiver cabinet, fix the calculator’s.
Solar panel to the rear side such that the transmitted beam directly falls on it. Fix switch S2 on the front panel and the speaker to the rear side. Keep the 9V battery inside the cabinet. B. Software:
The software is designed to be completely interrupt driven. Timing is based around the ability to control an output pin, allowing us to accurately control the motor for scanning purposes. The interrupt service routine is called once every
5usec. Upon each interrupt, program updates its timing counters, reads the output of the analog-to-digital convertor when necessary, and performs state updates for receiver tracking purposes.

Fig 1
Fig. 2 shows the receiver circuit. The audio signal transmitted by the laser diode (LD1) is received by the calculator’s solar panel and amplified by IC2. The gain of the amplifier is fixed by capacitor C7. Preset VR4 is used to change the signal level from the solar panel. This signal is fed to input pin 3 of IC2 through coupling capacitor C5 so that the
DC value from the solar panel can be eliminated. The amplified output from IC2 is fed to the speaker, which plays

The above diagram shows the block diagram of Laser
Communication System, which mainly comprise of 2 sections such as transmitter section and receiver section.
Transmitter section is used to transmit the data and sound signals, which comprised by microphone, Conditioning circuit, analog to digital converter and laser diode to generate medium for transmission of signals. The receiver section is used to receive the laser beam using the photo transmitter, which incorporated with the data or sound signals from the transmitter comprised of Conditioning, MCR and Digital to
Analog convertor to extract the data from the received laser

beam and given as input to the speaker. The detector means preferably includes means for recognizing the confirmation signal. WORKING
When we give the input like sound or data, microphone receives the data or sound signal. This signal coming off the microphone was far too low to be read by the analog to digital converter. So, for increase the strength of the signal we pass the signal through the microphone amplifier. Before the signal is put through the microphone amplifier, first put the signal through a capacitor to removed, and then through a voltage divider to appropriately bias the signal. The gain is adjusted by the resistors and for the microphone the gain is around 50100. After, pass the amplified signal into analog to digital converter to convert physical signal to digital signal. This digital signal is given to, after the A/D converter translates the microphone signal into 8bits,the MCU generates the appropriate bits to send and applies them to the laser driver circuit a 5V and provides the proper current according to the diode. Later this signal is passing to UART. Hear signal speed will increase and this signal is given to conditioning. Data contain signal is thrown into the atmosphere through the laser device. A photo diode detects the laser pulses in a different location. This signal is put through a comparator in order to generate solid 5V and 0V values which are applied to the receive pin on the microcontroller. This digital signal is speed up by the UART. Then signal is received by MCU. That provides the capability for 3 or more terminals or gateways to participate in a multi-point conference. It generates the appropriate bits to send and applies them to port. Port is in ordered to get the parallel port support. It’s a 8bit at a time transmission. Its help to transmit the more data signal and it increases the speed of system. Once this signal is put through the DAC, it converts the digital signal to analog, and also it is boosted and low pass filtered. The result is then fed directly to an audio jack, where the signal can be heard using any compatible device. The analog signal is sent via analog transmission instead of decoding it to a digital signal. Optical

transmission is usually done using digital signals requiring hardware for decoding at the receiver end.

VI. APPLICATIONS:
[1] In the Laser communications systems 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, other applications for Laser communications systems technology include temporary connectivity needs (e.g. sporting events, disaster scenes, or conventions), or space based communications. [3] With the powerful laser, it would even be possible to communicate using satellites to reflect the signals.
[4] It can be used to reproduce sound in large public meetings on open grounds or for communication between tall buildings.
Direct communication between high-rise buildings in a crowded city would become easy.

VII. ADVANTAGES:
[1] The advantages of laser communication is that it allows very fast communication service between two or more devices than other modes of communications.
[2] It can provide speed more than 1GBps.So it overtakes the
LAN or wireless LAN comprehensively.
[3] Laser communications systems have the benefit of eliminating the need for broadcast rights and buried cables.
[4] Laser communications systems can be easily deployed since they are inexpensive, small, low power and do not require any radio interference studies. The carrier used for the transmission signal is typically generated by a laser diode.
Two parallel beams are needed, one for transmission and one for reception.
[5] The transmitting and receiving station are smaller and lighter for given range. Less overall power is required for the given distance and data rate. Higher data rate may be achieved for given distance and power output.
[6] A tiny light detector may allow for superfast broadband communication over interplanetary distances. This technology advance offers the space laser communication system designer

the flexibility to design very lightweight, high bandwidth, low-cost communication payloads for satellites whose launch costs are a very strong function of launch weigh.
[7] Signals can be reproduced without distortion, even long distances. So the system could be used for communication and cable television transmission.

likely transmit data and sound much faster than the other system (like 1 GB/s). Because of this laser communication system became more popular than other system. The paper firstly analyzed the component of maritime laser communication system, the paper maid some explanations on the components and functions of the servo system.

REFRENCES:
[8] Optical fibers can carry more information as opposed to conventional cables. Optical fibers are not affected by radio frequency interference Information carried in an optical fiber
[9] “A one way laser communications system is capable of the transmission of both text and sound.”
[10] Even by a minute fraction of a degree, the laser will miss by thousands of miles. Instead of better and faster pictures, there could be no pictures.

DISADVANTAGES
[1] The noise in photodiodes: The main sources of noise are dark current noise, shot noise and thermal noise in a photodiode. There is one more source of noise due to random nature of the avalanche in an APD. The dark current noise arises due to dark current which flows in the circuit when the photodiode is in unilluminated environment under bias condition. It is equal the reverse saturation current is strongly dependent on the operating temperature, the bias voltage and the type of detector. In an optical receiver, dark current sets a noise floor for the detectable signal power level. Therefore, it should be minimized by careful device design and fabrication.
Dark current in optical telecommunication grade Si PINphotodiode is typically 100pA, while in Si APDs it is typically
10pA. In GaAs based PIN-photodiodes and APDs, the dark current is of the order of 100nA and it could pose a serious problem unless the device is cooled at appropriate temperature. [2]Atmospheric Attenuation: In general, attenuation is the relation between transmitted signal power and received signal power as follow
Attenuation=10logP transmitted (dB)
P received
[3] Optical receiver noise: The receiver noise is created by itself such as thermal noise and dark current noise.

Conclusion:
This is new wireless technology to transmit the data or sound signal from one section to other section through the laser beam of the system. This system is safe and without radiation, so it is harmless to living beings. The system can

[1] EFY.com, E&C Projects.
[2] MIT Lincoln Laboratory is working on a similar, but much more complex, concept for long-range laser communication.
[3] TECH IN EC.com
[4] Solar cell & Laser (from Wikipedia & encyclopedia)
[5] Laser communication.com
[6] ESA’s Space satellite link experiment (SILEX)
[7] The Japanese’s Laser Communication Experiment (LCE)
[8] http://www.semiprojects.com
[9] The datasheets for all of the parts used are included in the parts section.
[10] M. Young, the technical Writers Handbook. Mill Valley,
CA: University Science.
[11] The “well written” Mega 32 datasheet.STK500 datasheet,
ECE 476 website.