A Fabry-Perot Cavity Filtering Scheme for Authentication of Free-Space Laser Communication

In free space optical communication one of the major obstacles is the effect of different atmospheric conditions resulting in loss or complete absorption or scattering of the optical signal. In recent years, the discovery of Orbital angular momentum (OAM) of light beams has led to advancement of free space optical communication systems. The OAM beam is proved to be very stable against adverse atmospheric conditions. The difficulty with OAM is the lack of proper method of filtering OAM beam from normal light. In our proposed method, we have designed a Fabry-Perot cavity which will filter OAM light. This method is based on the principle of resonance. The filter design can be easily modified to work for any frequency by altering the length of the Fabry-Perot Resonant cavity. We have simulated the Fabry-Perot cavity using a mixture of normal light and Laguerre-Gaussian mode as input. It has been verified that this filter can filter out desired mode from other modes of light.