טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYirmiyahu Yaniv
SubjectExcitation of a Single Hollow Waveguide Mode using
Inhomogeneous Anisotropic Subwavelength
Structures
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Erez Hasman
Full Thesis textFull thesis text - English Version


Abstract

Hollow waveguides present an alternative to solid core fibers at the infra-red (IR) regime where suitable optical materials are scarce. In addition, due to their air core, they can be used for broad-spectrum high power transmission as they suffer from small insertion losses. As a result, hollow waveguides are used in industrial and medical applications involving CO2 and Er:YAG lasers as well as for spectroscopic and radiometric measurements. The TE01 waveguide propagation mode possesses the least amount of loss in most hollow waveguides, including the recently realized hollow Bragg waveguide. Therefore, the ability for efficient excitation of a single waveguide mode, such as the TE01 mode, can improve power delivery. In addition, higher order modes can prove useful for blue detuned atom guiding and dispersion compensation.

In this work, we propose a general approach for coupling a free space beam to any of the hollow waveguide modes, thus enabling single mode operation. The required spatial polarization state manipulation is achieved by use of inhomogeneous anisotropic subwavelength structures. Demonstration is obtained by coupling a linearly polarized CO2 laser beam at a wavelength of 10.6µm to the TE01, TM01, HE11, EH11, EH21, and EH31 modes of a 300µm diameter dielectric-coated hollow metallic waveguide. Full polarization and intensity analysis of the beam at the waveguide's inlet and outlet ports indicates a high coupling efficiency to a single waveguide mode. Finally, shaping the waveguide mode, emerging from the waveguide outlet, to a nearly diffraction limited linearly polarized beam and to a radially polarized vectorial vortex is also demonstrated.