Characteristic And Application Study On Physical Dimentions Of Optical Fields

Optics has undergone several stages of development,arranging from geometric optics,wave optics,quantum optics,and modern optic.With deeply understood for light beams,the technological advances brought by optical development are rapidly changing people's production and life.In particular,since the birth of the laser in the second half of the last century,optics and optoelectronics have rapidly flourished and gradually been applied to many realms,such as optical communication,optical metrology,optical imaging,laser processing,and etc.As is well known,basic research always determines application research.All these optical technologies can be well exploited on condition that the basic physical properties and laws of light have been deeply studied and mastered.These optical physical quantities cover energy,momentum,and angular momentum of light.As for the electromagnetic-field manifestation of light,it involves four degrees of freedom,including amplitude,polarization,frequency(wavelength),and phase.As for the spatial dimensions of the optical fields,their amplitude,polarization and phase may vary with different positions in the transverse space.This kind of optical fields is known as structured optical fields,for example,the vectorially polarized field that manifests polarization orientation variation periodically with spatial positions,the vortex beam characterized by phase variation in the same form,and the more general evanescent field locallly bound at the interface of dielectric mediums.Being different from the conventional plane-phase field,the structured fields exhibit many characteristics,giving rise to multi-dimensional spatial distribution of their basic physical quantities,especially for the momentum and angular momentum,with both transverse and longitudinal directivities.In addition,optical fields must be manipulated arbitrarily to fully exploit them,provided that the basic physical laws of light-matter interaction can be well studied and mastered.Because of the abundant degrees of freedom of optical fields,as well as its spatial multi-dimensions of basic physical quantities,when interacted with matters,they may exhibit many new optical phenomena and effects,such as the rotational Doppler effect of the vortex field,and the spin Hall effect of the evanescent field,and so on.In this graduation thesis,firstly,the basic physical quantities related to electromagnetic fields,as well as optical forces on a dipole are deduced and arranged in the second chapter.The superposition of vector optical fields is studied to reveal the origination and physical mechanism of optical spin and orbital angular momentum.Based on this,the multi-demensional angular momentum with arbitrary mean angular quantum numbers can be obtained and the mechanism of spin-orbit coupling is well shown.Finally,the transverse spin anguar momentum of eigenmodes in nanofibers is studied systematically,as well as the extreme conditions of getting the maximum surface transverse spin.Convenrional photon spin Hall effect or chiral coupling behavior based on the spin-orbit interaction of light in micro-nano waveguides has very low efficiency because of large amount of light scattering to non-guided modes.To solve this problem,based on the principle of mode conversion and interference in inverted-trapped silicon-based waveguides,the silicon-based chiral coupler with ultra-high directionality and coupling efficiency is successfully designed and fabricated,which is shown in the third chapter.Especially,the gotten directionality enables to approach ?1,and the coupling effect reaches up to over 70%.Structured fields can produce the rotational Doppler effect.In the fourth chapter,the rotational Doppler effect of the vortex beam is well studied from different perspectives,such as phase variation,energy conversion and momentum conservation,and its inherent relationship with the conventional linear Doppler effect is revealed.Based on this,the structured light interferometry is exploited to application on simultaneous measurement of multidimensional motion information of the moving objects.Eigenmodes in fibers as the structured fields have many special properties.In the fifth chapter,the waveguiding properties and coupling characteristics of the structured fileds in fibers are systematically studied.Firstly,the expansion using Jones matrix is adopt to reveal the close relationship between the eigenmodes and the circularly polarized vortex modes supported in fibers.Based on the coupled-mode theory,the polarization-dependent and-isolated characteristics of the vectorial mode coupling in fibers are uncovered and analyzed.Based on these,the transformation mechanism of helical fiber gratings is presented to convert mode's orbital angular momentum in fibers.Further-more,an all-fiber polarization beam splittor and rotator is designed based on vector-mode-assisted coupling.