Laboratory-simulation experiment for optical communication through low-visibility atmosphere using a diode laser

A laboratory-simulation experiment has been performed to determine the feasibility of exploiting the scattered (in addition to the unscattered) radiation to improve optical communication through low-visibility atmosphere. A multiple field-of-views (FOV) (
0.043-0.945\deg
full angle) optical receiver was designed which utilizes a narrow-band interference filter (
\Delta\lambda \sim 15
Å) for background-light suppression. The laser transmitter was a CW GaAlAs laser diode (
\lambda = 0.8486 \mu
m) capable of emitting ∼ 7 mW power output of 15° divergent beam. Both polydisperse (particle diameters,
d
in the range of
\sim0.2-5.17 \mu
m) and monodisperse (
d \sim 0.2 \mu
m and
d = 3.01 \mu
m) latex spheres in water were used for simulating haze, fog, etc. Results include signal-to-noise ratio (SNR) and scattered-to-unscattered signal ratio as a function of field-of-view of reception for various optical thickness of the medium. Also, SNR is plotted as a function of optical thickness for various FOV's. The unique feature of this simulation is that it can simulate worst case solar background where the sun enters the FOV of receiver. Finally a new technique of estimating forward-scattering efficiency and root-mean-square forward scatter angle has also been presented with examples.