LASER COMMUNICATION 1 Light Amplification by Stimulated Emission

LASER COMMUNICATION 1

Light Amplification by Stimulated Emission Radiation of 2

LASER ØLASER stands for Light Amplification by Stimulated Emission of Radiation. ØA highly coherent, monochromatic and perfectly parallel beam of light. 3

Production of laser ØFirst successful laser was constructed by T. H. Maiman in 1960 using Ruby Laser. ØA few other lasers are helium-neon laser, carbon dioxide laser, dye laser, junction laser, etc. 4

RUBY LASER 5

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. 6

Free Space Laser Communication Transmitting information via a laser beam Video Data Sound Terrestrial / Space based systems 01000110 111011001111 001010000010 101110010001 111001011011 7

How Does it Work? Signal Laser Transmitter Receiver Signal laser 8

MCU UART Conditioning Laser Diode MCU PORT Conditioning A/D High Level design UART Conditioning Photo resistor 9

What is the Transmitter? Ø The transmitter involves: § Signal processing electronics (analog/digital) § Laser modulator § Laser (visible, near visible wavelengths) 10

Laser Diodes include Photodiodes for feedback to ensure consistent output. Obtained by polishing the two sides of a junction diode. 11

What is the Receiver? ØThe receiver involves: Antenna Signal Processor Detector PIN diodes Avalanche Photo Diodes (APD) Single or Multiple Detectors 12

Why Laser Communication? Current high speed communications technology: Radio Fiber Optics 13

Laser Link Geometry Critical Design Parameters Receive area = 200 cm 2 Receiver sensitivity Beam Divergence = 3 mrad Distance = 1 km Transmit Power Diameter = 3 m Beam area = 70686 cm 2 14

Why not Fiber Optics? Not always possible to lay fiber lines Physically / Economically not practical Emergencies ØLC being incorporated into fiber optic networks when fiber is not practical. 15

Why not RF? 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. 16

Current Applications 1. Defense and sensitive areas. 2. In surgery. 3. Mass communication 400 TV channels § 40, 000 phone conversations § 4. In industry. 5. In nuclear power production. 6. In weather forecasting. 7. NASA § Satellite - satellite § Earth – satellite Earth 17

Groundstation Description Control System (data and tracking) Telescope & LASER Mounts LASER & Transmission Optics Receiving Package (photodetector) Satellite Description §Utilize Science Team’s Telescope & Processing Capability for LASER Communication §Transmission & Receiving Package. 18

Uplink/Downlink Data Processing Sequence Bits Bit Encoder to Symbol LASER Error Correction Symbol Recovery Transfer Optics Channel (Atmos. ) Amplifier Receiving Optics Bits 19

Demerits Of Laser Communication Require direct line-of-sight. Operational distance is also a variable if there are intervening materials such as rain, smoke, fog, glass etc. Limited wavelength range. 20

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