Free-Air Laser Light Communications

  
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Because light is at such a high frequency in the electromagnetic spectrum, it`s an even better medium for communications than radio waves. Lasers are perfect instruments for communications links because they emit a powerful, slender beam that`s least affected by interference and is nearly impossible to intercept. This section explains the basics o
Free-Air Laser Light Communications - schematic

f laser light communications using both helium- neon and semiconductor lasers. You`ll discover the different ways light can be modulated and cajoled into carrying an analog signal from a microphone or FM radio. The following section details advanced projects in laser light communications. Higher frequencies in the radio spectrum provide greater bandwidth. The bandwidth is the space between the upper and lower frequencies that define an information channel. Bandwidth is small for low-frequency applications such as AM radio broadcasts, which span a range 540 kHz to 1600 kHz. That`s little more than 1 MHz of bandwidth, so if there are 20 stations on the dial, that`s only 50 kHz per deejay. Television broadcasts, including both VHF and UHF channels, span a range from 54 MHz to 890 MHz, with each channel taking up 6 MHz. Note that the 6 MHz bandwidth of the TV channel provides more than 100 times more room for information than the AM radio band. That way, television can pack more data into the transmission. Microwave links, which operate in the gigahertz (billions of cycles per second) region, are used by communications and telephone companies to beam thousands of phone calls in one transmission. Many calls are compacted into the single microwave channel because the bandwidth required for one phone conversation is small compared to the overall bandwidth provided by the microwave link. Visible light and near-infrared radiation...



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