Vortex Phase Modulation And Its Application In Optical Trapping And Free-space Optical Communication

Vortex beam is a kind of beam where there is an azimuth phase exp(il)Φ,with Φis the azimuth angle,and l is the topological charge.And the singularity of the spiral phase makes the intensity look like the donut.By modulating the vortex phase,a variety of designed vortex beams can be generated.The development of artificial intelligence has led to a great development in the information industry,which made a significant progress in the manufacturie of related materials and devices.Therefore,the technology and equipment of the light manipulation is improved,and the freedoms such as the frequency,amplitude,phase,polarization,and coherence can be flexibly manipulated.Then it becomes realistic to seperately or jointly modulate any dimensional resources of beams.The modulated structure brings various novel behaivors and unique properties to the vortex beams,and it has been widely applied in the fields of quantum storage,microscopic imaging,optical trapping,and optical communication.Optical tweezer is an important application of optical vortices.As the advantages of non-contact and non-invasive characteristics is quite suitable for the life science,it has been deeply studied in recent years.Optical sorting is one kind of the optical tweezers,which is used to select the particles mixed in a background environment.Recently,it has become the important tool in the fields of life science,colloid physics and so on.Now,the primary task is improving the sorting efficiency.Therefore,finding the effective methods to enhance the sorting efficiency for the application requirements is one of the key tasks in the thesis.Free-space optical communication has the advantages of low cost and flexible installation.The development of light manipulation technology drives the structured light field perform better in optical communication.The communication quality can be improved,and the error rate can be decreased.The requirements of optical communication systems are high-speed,high-security and high-capacity.The optical beams with different wavelength,frequency,polarization,and other spatial dimensions have been applied in high-capacity optical communications to alleviate the spectrum restriction and improve the spectrum utilization.In addition,many factors in the transmission medium will reduce the communication quality,such as the atmospheric turbulence caused by temperature,humidity,and other factors.As well as the opaque obstacles and obstructions encountered in the transmission process would interupt the signal.Therefore,it is urgent for the sustainable development of free-space optical communication to study the physical mechanism of the interaction of turbulence,obstacles,and obstructions with signal beams.Based on the the background,the thesis is carried out by the following parts.Firstly,the phase modulation of vortex beam is studied.The physical model of partially coherent perfect vortex beams has been established,and its propagation characteristics and the determination of the topological charges have also been discussed by theoretical analysis and experimental verification.In this research,a simple and effective method has been illustrated to keep the radius of the beam keep independent of the topological charge.Meanwhile,the special ring structure can keep for a longer distance in the propagation.It can be applied in the optical trapping and optical communications.Further,the modulated vortex beam applied in the field of optical trapping has been studied.The vortex phase function is specifically modulated to generate a linear vortex beam and the boudary of the beam can be increased.Compared to other methods,the beam can greatly improve the sorting efficiency which can be demonstrated by the fractal theory.This sorting platform has great advantages in parallel sorting of massive particles in the fields such as biomedical science and colloidal physics.Finally,the modulated vortex beam applied in free-space optical communication has been studied.The evolution properties of beams propagating in the atmospheric turbulence has been studied.And it is found that the partially coherent beams propagated in turbulence has universal self-similarity properties.Then,the detection of objects in the atmospheric turbulence is also studied.And it is found that the accurate parameters of objects can be obtained quantitatively by using the inverse analysis of the interaction between the incident beam and the object,which can be regarded as a reference for the detection of a bistatic laser radar system.Besides,the demultiplexing method of optical vortex beams obstructed by large opaque obstacles(i.e.,topological charge detection)is discussed.And it is demonstrated that the determination of topological charge can be effectively realized by the self-reconstructed phase after propagation.Besides,a free-space encoding and decoding communication system based on optical polygonal vortex beams is established.The feasibility of the communication strategy is demonstrated by experiments,and a variety of routing functions are also realized.This communication system can greatly improve the communication capacity.