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Abstract
We report three experimental setups for communication of sound signal trough laser. Laser beam is just a transporter of information. When laser light falls off a sound source (vibrating body producing sound), variation in intensity of laser embedded the information on laser beam by vibrations. Using photodiode and receiver this information can be converted into a sound signal again .The laser communication allows us very fast communication service between two or more devices held very far apart even at earth moon distance, than other modes of communications. The laser communication has lot of application in astronomy, global communication system and a data relay satellite now days.
Apparatus
Mice, diode laser, transmitter receiver power supply connecting wires 3 speakers strip mounts, pre amplifier, and amplifier
Laser communication methods
We used the following three methods for laser communication. 1 Strip method 2 Reflection method 3 Laser Diode Method The experimental setup for all these three methods was already pre-arranged. We just explore the advantages and drawbacks. Lets start description
1. Strip method
Experimental arrangement is shown in fig.1 we set amplifier at low gain so that sound of strip speaker is not hearable. Initially distortion is heard at receiver due to invirmental noise amplification and weak connections which is removed by setting
proper gain of receiver and checking connection with AVO meter. it is important that the strip should be light weight so that the speaker can respond to the high frequency without any distortion in the signal. Speaker must be of good quality so that it can respond linearly to the input sound signal over a good frequency range.
Figure 1; set up for communication by strip method
We performed the work as.
A small light strip was mounted normally to the speaker cone. When a voice signal is given to speaker through amplifier to which will produces vibration in strip. A laser beam subjected in path perpendicularly in such a way that vibrating strip modulated it by intensity variation. In this final step the modulated laser light is received by receiver setup, amplified by an amplifier and finally output is obtained through a speaker.
2. Reflection method
He- Ne AS
AMPLIFIE AMPLIFIER
Voice signal is directly given to diode laser through an amplifier. Due to variation in voice signal, voltage given to laser will also vary the intensity of beam. This variation will be detected at the receiver side. And can be heard after amplification
.
Figure 3: Setup for communication using diode laser
The applied electronic modulating signal given to the laser diode should operate the laser in the linear region. An operation in the non-linear region will destroy the input signal and distortions will appear in the output signal.
Comparison of each method
We are going to compare results of these three schemes.
. Strip method
This method of modulation has the following advantage
๏ This method can be used for communication through long distances, provided that a high power laser is used.
DIODE LASER
AMPLIFIER (AMP.3)
AMPLIFIER (AMP.2)
Mice
Speaker
This process has some draw backs:
๏ Strip alignment is very sensitive for modulating a laser signal; the quality of received signal depends upon the fine alignment of the laser beam and strip. ๏ Strip should be light weighted for proper modulation. ๏ External noise can introduce in this method.
Reflection method
This method has also some advantages.
๏ This method can be used for communication through long distances if a powerful laser and a collimated laser beam is used. Its drawbacks are. ๏ Since in this case a laser beam falls on a mirror it requires a collimated beam other wise at long distances it will lost appreciable amount of intensity and information. ๏ Alignment of the mirror is difficult. ๏ The mirror used on the speaker for reflection of laser beam should be light weighted.
Diode Laser Method
This has the following advantages
๏ It is free of any external noise to be occurring during modulation due to the fact that the signal is directly given to the diode laser. ๏ Sound quality is best due to freedom of external noise. ๏ Circuit to be construct is short and easy ๏ There are no difficulties in its alignment. ๏ Once this arrangement is implemented then it cannot easily distortable.
But this method has a great draw back.
๏ We cannot use it for communication through long distances due to small intensity of diode laser
Precautions;
๏ AVO meter should check required parts. ๏ Battery connection arranged at last.
