광도파로형 광미분기 설계

Abstract

In this thesis, we have proposed a novel first-order and second-order optical differentiators based on symmetric directional coupler and asymmetric directional coupler. asymmetric directional couplers with dissimilar waveguides are designed for ultrafast optical differentiation within the femtosecond regime (corresponding to processing bandwidths > 10 THz). Theoretically proposed asymmetric directional coupler can be produced by wavelength matching of the propagation constants of two different waveguides in the coupler can be designed to achieve either a first-order differentiator or a second-order differentiator by properly fixing the product of coupling coefficient and coupling length of the coupler. We have demonstrated the first-order differentiation and the second-order differentiation of the design optical differentiator in simulations. We evaluated the differentiation errors and energetic efficiency of the design optical differentiator through numerical simulations. The proposed design has a strong potential to provide a feasible solution as an integrated differentiation unit device for ultrafast optical signal processing circuits. The symmetric directional coupler play a role of ultrafast optical differentiator operated at single-wavelength region and multi-wavelength regions due to the fact that its transfer function is sinusoidally varying in frequency domain. Single-wavelength optical differentiator at 1550 nm and dual-wavelength optical differentiator at both 1310 nm and 1550 nm were designed with a symmetric directional coupler in specific condition. The proposed device has a potential for ultrafast optical differentiator which provides unparalleled performances in terms of wide bandwidth, easy fabrication, and multi-wavelength operation.