A novel technique for secure transmission of two channels using a single optical pulse position modulated signal for free space optical communication

We propose a novel all-optical technique for the transmission of multiple channels over a single optical carrier by employing pulse position modulation (PPM). The proposed technique partly solves the issue of low spectral efficiency associated with the PPM transmission scheme. Furthermore, our proposed technique also improves the security of the FSO link against eavesdroppers, especially if they are located close to the receiver and are able to detect some part of the wide beamwidth optical signal. We have employed the Gamma-Gamma channel model to observe the performance of the FSO link for different lengths.