High speed visible light communication using blue GaN laser diodes
2016
GaN-based laser diodes have been developed over the last 20 years making them desirable for many security and defence
applications, in particular, free space laser communications. Unlike their LED counterparts, laser diodes are not limited
by their carrier lifetime which makes them attractive for high speed communication, whether in free space, through fiber
or underwater. Gigabit data transmission can be achieved in free space by modulating the visible light from the laser with
a pseudo-random bit sequence (PRBS), with recent results approaching 5 Gbit/s error free data transmission. By
exploiting the low-loss in the blue part of the spectrum through water, data transmission experiments have also been
conducted to show rates of 2.5 Gbit/s underwater. Different water types have been tested to monitor the effect of
scattering and to see how this affects the overall transmission rate and distance. This is of great interest for
communication with unmanned underwater vehicles (UUV) as the current method using acoustics is much slower and
vulnerable to interception. These types of laser diodes can typically reach 50-100 mW of power which increases the
length at which the data can be transmitted. This distance could be further improved by making use of high power laser
arrays. Highly uniform GaN substrates with low defectivity allow individually addressable laser bars to be fabricated.
This could ultimately increase optical power levels to 4 W for a 20-emitter array. Overall, the development of GaN laser
diodes will play an important part in free space optical communications and will be vital in the advancement of security
and defence applications.
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