Smart dust Active Laser Transmitter (SALT)

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Smart dust Active Laser Transmitter (SALT)

• Matthew Last, Kris Pister
• Berkeley Sensor and Actuator Center
• http//www.eecs.berkeley.edu/mattlast

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Smart dust Active Laser Transmitter (SALT)

• Free-space Communication
• Low-frequency Beam Steering (DC -gt 1kHz)

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Free-Space Communication using Agile Beamsteering

• What do we gain over RF?
• High Antenna Gain
• Excellent performance low power, long range,
  high bit rate
• 1mrad, 1mW beam 318 kW/steradian
• Isotropic 1mW radiator 80 ?W/steradian
• ? Antenna gain of 152 dB for typical laser
• No spectrum regulation issues
• SDMA (Space-Division, Multiple Access) with
  imaging receivers
• Only simple baseband modulation necessary (OOK)

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Free-Space Communication using Agile Beamsteering
(2)

• When to use?
• Need Line of Sight
• Need Clear Weather (no fog)
• At what cost?
• Tight alignment tolerances
• Only point-to-point networks (no broadcasting)
• Unidirectional links yield asymmetrical networks

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Long Range, Low Power Crosslinks
3 mW optical power

1. 5.2 km Berkeley Marina
2. 15.3 km Coit Tower
3. 21.4 km Twin Peaks

And plenty of power to go further
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Current Work
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Performance
Mechanical Angle of Deflection Unactuated (Probe Tip) Actuated (Thermal)
In-plane 45 degrees 11 degrees
Out-of-plane Untested 28 degrees
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Actuation Power - 1st Generation
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Actuation Power 2nd Generation
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2nd Generation Mirror Pictures
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Ongoing Projects

• Lenses and lens systems
• vary lens diameter
• lens quality evaluation?
• Laser diode mount
• Prototype laser transmitter system (laser diode
  -gt collimating lens -gt 2-DOF mirror)

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More Pictures
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Fun Numbers

• divergence 1.22 ?/d
• 1mm aperture _at_ 650nm ? .79 mrad divergence
• 1mrad divergence _at_ 650nm ? .79mm aperture
• 1mW 1mrad emitter puts out 40 times more
  power/steradian than a 100 W bulb