Laser communication system and methods

A method of operating a laser communication system for data transmission for data transmission in excess of 1.5 Mbps between buildings at distance of 1-20 km and with unobstructed line of sight, comprising the steps of:

• providing a laser transmitter, thermoelectric cooler means, transmitter electronics and receiver electronics;
• generating laser light with said laser transmitter at a power level to transmit laser light in excess of 1 km and 1.5 Mbps;
• actively cooling said laser transmitter with said thermoelectric cooler means;
• modulating transmitted laser light with said transmitter electronics in accordance with data to be transmitted;
• detecting said transmitted modulated laser light and generating an electrical signal corresponding thereto;
• demodulating said corresponding electrical signal with said receiver electronics;
• correcting burst errors arising from atmospheric scintillation with forward error correction block codes and deep interleaving both prior and subsequent to the demodulating step.

A dichroic wavelength-multiplexed laser communication system for full duplex wideband data transmission in excess of 1.5 Mbps between buildings at distance of 1-20 km and with unobstructed line of sight, comprising:

• first terminal means having a first laser source for transmitting laser light at a first wavelength;
• a first laser receiver means for receiving laser light at a second wavelength;
• and a first optical system through which both said laser light at said first wavelength and said laser light at said second wavelength travel, said first optical system including first optical means for multiplexing said transmitted laser light at said to first wavelength and said received laser light at said second wavelength;
• and
• second terminal means having a second laser source for transmitting said laser light at said second wavelength;
• a second laser receiver means and receiving said laser light at said first wavelength;
• and a second optical system through which both said laser light at said first wavelength and said laser light at said second wavelength travel, said second optical system including second optical means for multiplexing said transmitted laser light at said second wavelength and said received laser light at said first wavelength, wherein
• each of said first and second laser sources includes a housing;
• a laser transmission source in said housing for transmitting modulated laser light;
• a window element in said housing through which said transmitted modulated laser light travels, said window element having a transparent resistive coating;
• means for controlling a temperature of said window element by applying electrical current to said transparent resistive coating;
• laser diode means for generating laser light and formed so as to generate at a power level so as to transmit laser light in excess of 1 km and 1.5 Mbps;
• thermoelectric cooler means for actively cooling said laser diode means;
• an autoranging device including a collimating lens in the optical axis of said laser light and electronic translation means for moving said collimating lens longitudinally in said optical axis to adjust beam divergence so as to adjust beam divergence and thereby achieve a desired range;
• a sighting scope for aiding in positioning said first terminal means;
• and
• a closed-loop tracking system for tracking incoming laser energy, including a position-sensing detector associated with said sighting scope for generating a time-varying error signal, steering means for deviating the direction of said transmitted modulated laser light with said steering means, and control electronics for controlling said steering means in accordance with the time-varying position-sensing detector error signal so as to maintain said first terminal means and said second terminal means in a communication link with each other in the presence of unstable mounting or platform motion.

A method of operating a laser communication system for data transmission for data transmission in excess of 1.5 Mbps between buildings at distance of 1-20 km and with unobstructed line of sight, comprising the steps of:

• providing a laser transmitter, thermoelectric cooler means, transmitter electronics, receiver electronics, a window element with a transparent resistive coating, a collimating lens in the optical axis of said laser light, a sighting scope, a position-sensing detector associated with said sighting scope, and steering means;
• generating laser light with said laser transmitter at a power sufficient to travel in excess of 1 km and 1.5 Mbps;
• actively cooling said laser transmitter with said thermoelectric cooler means;
• modulating transmitted laser light with said transmitter electronics in accordance with data to be transmitted;
• detecting said transmitted modulated laser light and generating an electrical signal corresponding thereto;
• applying electrical current to said transparent resistive coating through which said modulated laser light travels so as to control the temperature of said window element;
• moving said collimating lens longitudinally in said optical axis so as to adjust beam divergence and thereby achieve a desired range;
• positioning said laser transmitter with said sighting scope;
• generating a time-varying error signal with said a position-sensing detector;
• deviating the direction of said modulated laser light with said steering means;
• controlling said steering means with the control electronics in accordance with the time-varying position-sensing detector error signal so as to operate said laser transmitter in the presence of unstable mounting or platform motion;
• demodulating said corresponding electrical signal with said receiver electronics;
• correcting burst errors arising from atmospheric scintillation with forward error correction block codes and deep interleaving prior and subsequent to the modulating step.