One of physical quantities of light, orbital angular momentum (OAM) has attracted great
attention in various fields. Contrary to spin angular momentum (SAM), which is another
angular momentum of light related to the polarization, OAM is associated with spatial
distribution of electric field and has azimuthal angular dependence. The most distinguishing
characteristic of OAM is its unbounded quantum number. Compare to SAM, which can
have only two values: +ħ and -ħ per photon, OAM can have infinite values: lħ per photon,
where l is a topological charge number which can be any integer.
Since OAM carrying modes of different topological charge number are orthogonal to each
other, communication system that using OAM modes has great potential to increase a
transmission capacity like as mode division multiplexing technique. Also, a recently
discovered state of matter, photonic topological insulator, which has OAM dependent edge
states is another remarkable feature of OAM.
However, due to the difficulty of OAM mode generation, propagation, and modulation,
most of OAM related researches are limited to fiber, bulk, and free space optics. Since
integration and miniaturization are inevitable requirement for commercial and compatible
application, the investigation of OAM-based integrated photonic devices is highly required.
In this thesis, several OAM-based photonic devices for integrated photonic circuit are
proposed: a waveguide structure for guiding higher-order OAM mode, a OAM modulator
which can switch between +l OAM mode and -l OAM mode, a OAM directional coupler,
and a one-way propagation tunable photonic chip based on topological insulator. All of
these devices are designed based on mode analysis and simulated through finite-difference
time-domain (FDTD) method or finite element method (FEM). Also, the topological charge
number of OAM modes is numerically calculated to measure the purity of OAM mode.
