Fast Switching And Generation Of Optical Vortex

Optical vortex is a special structured optical field with helical phase front.As a consequence of this helical phase,the phase front has a screw dislocations in the center of the beam.At the center of the beam,the phase is not defined,and accordingly,the wave amplitude is equal to zero.And the fact that the helical phase front of beam also gives the momentum flow leads to an orbital angular momentum(OAM)of photons in such beam.Because of these special classic and quantum property,optical vortex has a lot of applications in areas such as optical micromanipulation,optical testing,quantum state manipulation,optical communication and other diverse applications.Particularly promising is the use of optical vortex for optical communication,the OAM can provides a new degree of freedom for information transmissions,it has great potential to increase link capacity and spectral efficiency.Fast switching and detection of optical vortex are important for the applications of optical vortex.For example,when the optical vortex is used in optical communication,the information can be encoded as the OAM state of light,fast switching and detection of optical vortex are required to increase the communication capacity.However the present technology can't offer a high speed to switch and detect the optical vortex because of the principles,operations or equipment.The slow switching and detection of optical vortex are still factors limiting the application of optical vortices.To resolve these issues,we propose two new technologies to switch and detect optical vortex at a high speed,and these technologies can fill these gaps.The main research works are list as follow:1.A novel technology for fast generating optical vortices by beam coherent combining is proposed.An EOPM is used to modulate the phase of each sub-beam,and the optical vortices switching frequency will reach the level of that of EOPM according to the principle of beam combining.2.A novel technology for fast detection of optical vortices based on directdetection is proposed.According to the ring-shape intensity distributions of optical vortices,the optical vortices can be detected by the energy ratio of the two sub-beams.This technology can detect the optical vortices simply and efficiently without converting the optical vortices into Gaussian beams.3.An OAM-SK free space optical communication system with high speed modulation rate of OAM state based on coherent combining and direct detection is build.Compared with current OAM-SK technologies,the rate of OAM modulation can be significantly increased in this communication system.