Laser Communication

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.

Light

Amplification by

Stimulated

Emission of

Radiation

Free Space Laser Communication

►Transmitting information via a laser beam

Video

Data

Sound

►Terrestrial / Space based systems

010001100110

111011001111

001010000010

101110010001

111001011011

How Does it Work?

Signal Transmitter

Receiver Signal

Laser

laser

Photo resistor

High Level design

Conditioning MCU MCU

Conditioning Conditioning

UART UART A/D

PO

RT

Laser Diode

What is the Transmitter?

►The transmitter involves:

Signal processing electronics (analog/digital)

Laser modulator

Laser (visible, near visible wavelengths)

RUBY LASER

Laser Diode

Laser Diodes include

Photodiodes for

feedback to insure

consistent output.

Modulation

►AM

Easy with gas lasers, hard with diodes

►PWM (Pulse Width Modulation)

►PFM (Pulsed FM)

Potentially the highest bandwidth (>100kHz)

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

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

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

Why Laser Communication?

►Current high speed communications technology:

Radio

Fiber Optics

Laser Link Geometry Critical Design Parameters

Beam Divergence = 3 mrad

Diameter = 3 m

Beam area = 70686 cm2

Distance = 1km

Receive area = 200 cm2

Transmit Power

Receiver sensitivity

►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?

►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?

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

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

Uplink/Downlink Data Processing Sequence

Bits Bit Encoder

to Symbol LASER Transfer

Optics

Channel

(Atmos.)

Receiving

Optics Amplifier Symbol

Recovery

Error

Correction

Bits

Opportunities For Student Involvement

•LASER Research

•LASER Modulation Circuitry

•Encoding/Decoding Circuitry

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: