Optical Communication in Free Space

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Forum Link http://www.knoxvillehackerspace.com/phpbb/viewtopic.php?f=6&t=13



  • Demonstrate point to point communications across a room with Class IIIa lasers and no receiver optics
  • Demonstrate point to point communications across a field with Class IIIa lasers and receiver optics present
  • Determine distance limitations of point to point communications using Class IIIa lasers
  • Procure Class IIIb lasers and necessary protective gear and attempt longer range communications?

Data Transfer

Half Duplex

  • Go/No Go with simple breadboard circuit
  • Modulate laser with Arduino pulse width modulation
  • Simple voice communication
  • High speed network communications

Full Duplex

  • Go/No Go with simple breadboard circuit
  • Simple voice communication
  • High speed network communications




The potential advantage of using a commercial laser pointer over over an optically enhanced LED is the lack of the additional optics assembly. Commercial beam divergences are such that over similar ranges to RONJA project the laser has a smaller spot diameter.

A 5 mW green laser pointer is available from http://www.optotronics.com/green-laser-pointers.php with very good beam properties Beam divergence: <1.2 mrad Beam diameter: <1.5 mm

  • Add equations for divergence and maybe wolfram alpha application for calculations


A CdS photoresistor seems like a good start but probably is not the best option for high data transfer rates. http://www.token.com.tw/pdf/resistor/cds-resistor-pgm.pdf Models are available with a spectral peaks at 540 nm or 560 nm. Our green laser pointer emits light at close by at 532 nm for a relative sensitivity between 80 and 90 percent, so the 540 nm models are recommended. It's a nice coincidence that our emission spectrum matches closely to the receiver spectral peak. Rise response times are typically 20 or 30 ms and decay response times are typically 30 or 40 ms.

Photodiode ... add section

Legal & Safety

Code of Federal Regulations Title 21 Section 1040 [1]

OSHA Technical Manual Section III Chapter 6 Laser Hazards [2]

ANSI Z136.1 (2007) - Safe Use of Lasers

ANSI Z136.6 (2005) - Safe Use Of Lasers Outdoors


External Links

RONJA (Reasonable Optical Near Joint Access) Project Homepage http://ronja.twibright.com/