Mode coupling in nonuniform fibers: comparison between coupled-mode theory and finite-difference beam-propagation method simulations

Finite difference beam propagation method is an accurate numerical procedure, used here to explore the switching dynamics of a nonlinear coherent directional coupler. The coupling lengths derived from this simulation are compared with coupled mode theories. BPM results for the critical power follow the trend of the coupled mode theories, but it lies in between two coupled mode theories. Coupled mode theory is sensitive to numerical approximations whereas BPM results practically do not depend on grid size and longitudinal step size. Effect of coupling-region-width and core-width variations on critical power and coupling length is studied using BPM to look at the aspects of optical power-switch design.

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Theory analysis of mode coupling in tilted long period fiber grating based on the full vector complex coupled mode theory

Optics & Laser Technology ◽

10.1016/j.optlastec.2012.10.002 ◽

2013 ◽

Vol 48 ◽

pp. 60-66 ◽

Cited By ~ 22

Author(s):

Guolu Yin ◽

Shuqin Lou ◽

Qi Li ◽

Hui Zou

Keyword(s):

Mode Coupling ◽

Coupled Mode Theory ◽

Fiber Grating ◽

Theory Analysis ◽

Mode Theory ◽

Coupled Mode ◽

Long Period Fiber Grating ◽

Long Period ◽

Period Fiber Grating ◽

Full Vector

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Chiral Optical Tamm States: Temporal Coupled-Mode Theory

10.20944/preprints201702.0108.v1 ◽

2017 ◽

Author(s):

Ivan V. Timofeev ◽

Pavel S. Pankin ◽

Stepan Ya. Vetrov ◽

Vasily G. Arkhipkin ◽

Wei Lee ◽

...

Keyword(s):

Mode Coupling ◽

Cholesteric Liquid Crystal ◽

Stop Band ◽

Polarized Light ◽

Coupled Mode Theory ◽

Circularly Polarized Light ◽

Circularly Polarized ◽

Mode Theory ◽

Coupled Mode ◽

Localized State

The chiral optical Tamm state (COTS) is a special localized state at the interface of a handedness-preserving mirror and a structurally chiral medium such as a cholesteric liquid crystal or a chiral sculptured thin film. The spectral behavior of COTS, observed as reflection resonances, is described by the temporal coupled-mode theory. Mode coupling is different for two circular light polarizations because COTS has a helix structure replicating that of the cholesteric. The mode coupling for co-handed circularly polarized light exponentially attenuates with the cholesteric layer thickness since the COTS frequency falls into the stop band. Cross-handed circularly polarized light freely goes through the cholesteric layer and can excite COTS when reflected from the handedness-preserving mirror. The coupling in this case is proportional to anisotropy of the cholesteric and theoretically it is only anisotropy of magnetic permittivity that can ultimately cancel this coupling. These two couplings being equal results in a polarization crossover (the Kopp--Genack effect) for which a linear polarization is optimal to excite COTS. The corresponding cholesteric thickness and scattering matrix for COTS are generally described by simple expressions.

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