Vol 6, No 4 (2015) > Electrical, Electronics and Computer Engineering >

Noise Suppression in the Signal Spectral Induced by Atmospheric Turbulence on the FSO (Free-Space Optical) Communications

Ucuk Darusalam, Purnomo Sidi Priambodo, Eko Tjipto Rahardjo

 

Abstract:

Beam
wander and spatial noise that are modulated on optical propagation produce
noise modulation in the signal spectral before being received by a
Photodetector (PD). In order to suppress noise modulation in the signal
spectral, we present an Optical Spatial Filter (OSF) method that is composed of
the cone reflector and a pinhole as a detection method. A cone reflector is
designed to suppress beam wander in order to minimize temporal noise that
fluctuates randomly and governs reflection of the deflected focus spot into the
narrow region of pinhole.  The pinhole
governs the Fresnel diffraction in order to suppress spatial noise in the
center of focus spot that undergoes fluctuation and random frequencies as well.
Through simultaneous suppression in temporal noise caused by beam wander and
spatial noise using the OSF method, noise modulation in the signal spectral can
be minimized optimally. We compared the OSF with the Direct-Detection (DD)
method by experimentation. The results of the experiment show significant
improvements for noise suppression in the signal spectral. The average values of the
Signal-to-Noise Ratio (SNR) increase, namely, 37.5 dB, 38.5 dB, 38.7 dB and
39.2 dB for pinhole diameters of 50 µm, 40 µm, 30 µm, and 20 µm,
respectively.

Keywords: Beam wander; Cone reflector; FSO; Pinhole; Optical Spatial Filter; Spatial noise

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