Microring resonators for vortex beam emission and their all-optical wavelength tuning

Abstract

A vortex beam possesses a helical phase front and carries a phase singularity along the propagation axis. The salient properties of vortex beams, including the theoretically unbounded orbital angular momentum (OAM) and spatially variant states of polarization (SOPs), have been utilized for a range of applications, including optical sensing, communications, manipulation and imaging. This thesis reports integrated vortex beam emitters and all-optical wavelength tuning based on microring resonators. The work may be further explored for potential applications such as light detection and ranging (LiDAR) and communication systems. An integrated Terahertz (THz) vortex beam emitter is presented for the first time based on simulation to generate tunable OAM states. The design can convert infrared waveguide modes into a freely propagating THz beam via difference-frequency generation. The output OAM state carries a topological charge that is tunable with input wavelengths. Three devices are evaluated in a test frequency range from 9 THz to 13.5 THz, and the topological charge can change from -2 to 4. A frequency shift accompanies the change in the topological charge, and its magnitude depends on the planar dimensions of the emitter. An on-chip vector vortex beam emitter is demonstrated for the first time via numerical simulation to generate all points on a first-order Poincaré sphere (FOPS). It consists of a wave guide coupled, nanostructured Si microring resonator. The fundamental transverse electric and transverse magnetic input modes produce radial and azimuthal polarization, respectively. These two linear polarization states can form a pair of eigenstates for the FOPS. Consequently, tuning the phase contrast and the intensity ratio of these two coherent inputs can control the SOPs of generated vortex beams. Flexible wavelength modulation of the generated vortex beams is desired to enhance sensing and communication performance. An all-optical wavelength tuning device is experimentally demonstrated based on two coupled microrings, which may combine with the proposed emitters. Pumping the symmetric and antisymmetric resonances of the device can induce attractive and repulsive optical gradient forces, respectively. The optical gradient forces can reconfigure the device and tune its resonant wavelengths. Besides, the wavelength difference between the symmetric and antisymmetric resonances can be significantly increased and decreased by the device's positive and negative pull-back instabilities, respectively.

More information

Identifiers

ORCID for Jize Yan: orcid.org/0000-0002-2886-2847

Catalogue record

Export record