Laser communication uses lasers to transmit information through free space instead of fiber optic cables. It works similarly to fiber optics but transmits the beam through the atmosphere instead of cables. The transmitter converts signals into laser light and the receiver includes a telescope to capture the beam and detectors to convert it back into signals. Laser communication has advantages over radio frequency and fiber optics for applications where laying cable is not possible or practical such as for satellites, remote areas, and emergencies due to its high bandwidth, directivity, security, and smaller antenna size.

1. Laser Communication

2. What Is Laser Communication? Laser communications systems are wireless connections through the atmosphere. They work similarly to fiber optic links, except the fact that, in lasers, beam is transmitted through free space.

3. L ight A mplification by S timulated E mission of R adiation

4. Free Space Laser Communication Transmitting information via a laser beam Video Data Sound Terrestrial / Space based systems 010001100110111011001111001010000010101110010001111001011011

5. How Does it Work? Signal Transmitter Receiver Signal Laser laser

6. Photo resistor High Level design Conditioning MCU MCU Conditioning Conditioning UART UART A/D PORT Laser Diode

7. What is the Transmitter? The transmitter involves: Signal processing electronics (analog/digital) Laser modulator Laser (visible, near visible wavelengths)

8. RUBY LASER

9. Laser Diode Laser Diodes include Photodiodes for feedback to insure consistent output.

10. Modulation AM Easy with gas lasers, hard with diodes PWM (Pulse Width Modulation) PFM (Pulsed FM) Potentially the highest bandwidth (>100kHz)

11. What is the Receiver? The receiver involves: Telescope (referred to as ‘antenna’) Signal processor Detector Often both ends will be equipped with a receiver and transmitter - PIN diodes -Avalanche Photo Diodes (APD) -Single or multiple detectors

12. Avalanche photodiode-2 Stabilisation of working point of APD: . Gain =75 Temperature stabilisation. Thermoelectrically cooler stabilisation system is inside of APD module AVALANCHE PHOTO DIODE

13. System Comparison (OC3 1km products) OpticalAccess ICS LightPointer Transmit Power (mW) 10 (10 dBm) 100 (20 dBm) 4 (6 dBm) Beam Diverg (mrad) 2.5 11 3 Receive Area (cm^2) 52 232 200 Min Recv Power (nW) 100 (-40 dBm) 32 (-45 dBm) 50 (-43 dBm) Price $19.5k $25k $24k

14. Why Laser Communication? Current high speed communications technology: Radio Fiber Optics

15. Laser Link Geometry Critical Design Parameters Beam Divergence = 3 mrad Diameter = 3 m Beam area = 70686 cm 2 Distance = 1km Receive area = 200 cm 2 Transmit Power Receiver sensitivity

16. Not always possible to lay fiber lines Satellites Combat zones Physically / Economically not practical Emergencies LC being incorporated into fiber optic networks when fiber is not practical. Why not Fiber Optics?

17. Bandwidth for Laser Communication (LC) is 100 times greater than for RF. Power in LC is directed at target, so much less transmission power required. Also the power loss is less. Size / Weight LC antenna is much smaller than RF. Security Due to low divergence of laser beam, LC is more secure than RF. Why not RF?

18. Current Applications Defense and sensitive areas. At airports for communication across the runways. Mass communication 400 TV channels 40,000 phone conversations NASA Satellite - satellite Earth - satellite Earth

19. Groundstation Description Control System (data and tracking) Telescope & LASER Mounts LASER & Transmission Optics Receiving Package (photodetector) Utilize Science Team’s Telescope & Processing Capability for LASER Communication Transmission & Receiving Package. Satellite Description

20. Uplink/Downlink Data Processing Sequence Bits Bit Encoder to Symbol LASER Transfer Optics Channel (Atmos.) Receiving Optics Amplifier Symbol Recovery Error Correction Bits

22. Opportunities For Student Involvement LASER Research LASER Modulation Circuitry Encoding/Decoding Circuitry

23. Contact Information Matthew Johnson (mjohnson@u.arizona.edu) Freddy Valenzuela (acv@bigdog.engr.arizona.edu) Http://www.physics.arizona.edu/ssp/sti For more information regarding laser communication: