23-07-2012, 11:36 AM
Project on Laser communications systems
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INTRODUCTION
In 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-of-sight 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.
Laser communications have been a hot topic lately, as solutions for how to satisfy ever increasing bandwidth needs 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. With possible transmit speeds of up to a gigabit per second, this is an exciting area. Other applications for this technology include temporary connectivity needs (e.g. sporting events or space based communications.
WORKING OF LASER COMMUNICATION SYSTEM
This laser communication system transmits sound or music signals through a laser beam.Intensity of this beam changes with the amplitude of sound signal.The variations in intensity of the laser beam is converted into a variation in the voltage level by using a calculator voltage variation on the solar panel is amplified by a low voltage audio power amplifier.LM386 speaker,the maximum output of audio amplifier is 1 watt,while its gain is 20.The ckt consists of a transmitter & a receiver.Both of this are powered by 9 volt battery.Fig.shows the transmitter ckt.Here a diode(LD1)with maximum operating voltage & max.operating current of 45 mA is used the main audio signal.
In the place of laser diode,we can also use a laser pointer.Remove the battery from the laser wires from the terminals of LD1 & connect them to the battery terminals of laser pointers.The pointer is in the negative terminal.The output power of laser pointer is 5mW.Take care which as direct exposure to the laser beam can be hazardous to our eyes.Point a laser beam to the Potmeter VR1 is used to change the level of audio signal.The audio input to the preamplifier output of the music system(CD,DVD player etc.).Capacitor C2 & preamplifier vary the gain of the LM386. The inputs are ground referenced while the output automatically biases to one-half the supply voltage. The quiescent power drain is only 24 milliwatts when operating from a 6 volt supply, making the LM386 ideal for battery operation. Depending on construction, photovoltaic panels can produce electricity from a range of frequencies of light, but usually cannot cover the entire solar range (specifically, ultraviolet, infrared and low or diffused light). Hence much of the incident sunlight energy is wasted by solar panels, and they can give far higher efficiencies if illuminated with monochromatic light. Therefore, another design concept is to split the light into different wavelength ranges and direct the beams onto different cell.The audio signal transmitted by the laser diode is received by the solar panel & amplified by IC2.
Laser Diode :
A laser diode is formed by doping a very thin layer on the surface of a crystal wafer. The crystal is doped to produce an n-type region and a p-type region, one above the other, resulting in a p-n junction, or diode. Another method of powering some diode lasers is the use of optical pumping. Optically Pumped Semiconductor Lasers (OPSL) use a III-V semiconductor chip as the gain media, and another laser (often another diode laser) as the pump source. OPSL offer several advantages over ILDs, particularly in wavelength selection and lack of interference from internal electrode structures When an electron and emitting a photon with energy equal to the difference between the electron and hole states involved. (In a conventional semiconductor junction diode, the energy released from the recombination of electrons and holes is carried away as phonons, i.e., lattice vibrations, rather than as photons.) Spontaneous emission gives the laser diode below lasing threshold similar properties to an LED. Spontaneous emission is necessary to initiate laser oscillation, but it is one among several sources of inefficiency once the laser is oscillating.