Optical Communication in Free Space: Difference between revisions
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*Demonstrate point to point communications across a field with Class IIIa lasers and receiver optics present | *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 | *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 | *Procure Class IIIb lasers and necessary protective gear and attempt longer range communications? | ||
==Data Transfer== | ==Data Transfer== | ||
===Half Duplex=== | ===Half Duplex=== | ||
*Go/No Go with simple breadboard circuit | *Go/No Go with simple breadboard circuit | ||
*Simple voice communication | *Modulate laser with Arduino pulse width modulation | ||
*Simple voice communication | |||
*High speed network communications | *High speed network communications | ||
===Full Duplex=== | ===Full Duplex=== | ||
*Go/No Go with simple breadboard circuit | *Go/No Go with simple breadboard circuit | ||
*Simple voice communication | *Simple voice communication | ||
*High speed network communications | *High speed network communications | ||
=Optics= | =Optics= | ||
==Transmitter== | ==Transmitter== | ||
=== Lasers === | === Lasers === | ||
The potential advantage of using a commercial laser pointer over over an optically enhanced LED is the lack of the additional optics assembly. | 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. | ||
'' | |||
*Calculate intensity difference at distance between RONJA project and a commercial laser pointer with Gaussian beam equation http://en.wikipedia.org/wiki/Gaussian_beam | |||
A 5 mW green laser pointer is available from http://www.optotronics.com/green-laser-pointers.php with very good beam properties | A 5 mW green laser pointer is available from http://www.optotronics.com/green-laser-pointers.php with very good beam properties | ||
| Line 32: | Line 32: | ||
'' | '' | ||
*Add equations for divergence and maybe wolfram alpha application for calculations'' | *Add equations for divergence and maybe wolfram alpha application for calculations'' | ||
==Receiver== | ==Receiver== | ||
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= | =Legal & Safety= | ||
Latest revision as of 03:35, 17 April 2011
Overview
Forum Link http://www.knoxvillehackerspace.com/phpbb/viewtopic.php?f=6&t=13
Milestones
Range
- 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
Optics
Transmitter
Lasers
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.
- Calculate intensity difference at distance between RONJA project and a commercial laser pointer with Gaussian beam equation http://en.wikipedia.org/wiki/Gaussian_beam
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
Receiver
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
http://en.wikipedia.org/wiki/Laser_safety
External Links
RONJA (Reasonable Optical Near Joint Access) Project Homepage http://ronja.twibright.com/
http://en.wikipedia.org/wiki/RONJA
http://members.misty.com/don/laserfaq.htm
http://www.repairfaq.org/sam/laserdps.htm
http://captain.haddock.8m.com/laser/laser1.html
http://en.wikipedia.org/wiki/Free-space_optical_communication