Navy

Laser-induced plasma filaments for communications

Use of a plasma tunnel for free-space optical transmission

Communications Photonics

In Figure 1, the first laser sends its plasma inducing signal through a combiner, (26) and both beams are sent through a focusing lens (28) and a collimating lens (30). The laser-induced plasma filament (40) allows for the clear path of the communication signal (25) produced by the second laser. The free space (50) can be upwards of several kilometers.

A laser beam propagating through the atmosphere is affected by absorption and scattering of radiation from fog, clouds, rain, snow, smoke, and dust.

Atmospheric attenuation is typically dominated by fog and clouds and is, therefore, the primary focus of interest for communications research.

In the particular case of free-space optical links, the amount of light transmitted through fog and clouds will affect the link, first degrading the bit error rate and eventually, at a higher attenuation level the laser communication system will cease to operate.

A new communication system developed by the Navy could be used under those adverse conditions where attenuation is high due to scattering, absorption, scintillation, dispersion, and turbulence.

The novel two-laser set up utilizes the first laser to generate a plasma filament using high-power femtosecond pulses. Laser-induced plasma filaments have been known to exhibit balanced Kerr-effect self-focusing and plasma-effect defocusing resulting in a defraction-free channel or filament. Within this clear channel, the second laser generates a communication signal. In this way, the laser-induced filament acts as a conduit for the communication beam.

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