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Simulating the effects of refractive index difference on the coupling efficiency of periodically segmented waveguide mode converter

Zheng Yu, He Hao, Jiang Lianqiong, Duan Ji'an

Optica Applicata

2021

Vol. 51, nr 4

565--577

Efficient coupling of micro/nano-optical waveguides with single-mode fibers is the premise for the efficient operation of the integrated photonic chip, which directly determines its optical performance. In this paper, the design principles of periodically segmented waveguide (PSW) structure used for high-efficiency fiber-chip coupling are proposed, and the effects of refractive index difference Δ on coupling efficiency and structural parameters are studied by simulation. It is found that as the Δ of the PSW increases, the period of the PSW tends to be smaller, and the coupling efficiency decreases continuously, reduced by around 0.673 dB in the range of Δ = 3% to Δ = 7%. Through the analysis of PSW optical mechanisms, it demonstrates that the main reason for the decrease of coupling efficiency is that the transmission loss of the tapered section increases sharply with the increase of Δ. High-Δ PSW is difficult to apply to highly integrated silica optical chips due to the unignorably insertion loss.

Increasing semiconductor laser-optical fiber coupling efficiency by introducing microlens

Ozyazici M.S.

Optica Applicata

2004

Vol. 34, nr 2

185-202

The efficiency of coupling between semiconductor lasers and single-mode optical fibers can be greatly increased by a microlens of an appropriate focal length being fabricated at the end of the fiber. The reason for this is that the lens can effectively improve the mode matching of the laser and fiber fields. Theoretical work has been carried out to predict this improvement of coupling efficiency as a function of the focal length and spot size associated with the laser and fiber. A simple method was then used to fabricate the microlenses whose focal lengths required a radius of curvature ranging from about 10 mm to 15 mm for maximum coupling. The method comprised in tapering of the fiber to the required radius using a grinder and then with an electric arc and heating the end which next forms into a hemisphere due to surface tension forces. Another way is to dip the tapered end into molten optical glass picking up a droplet of glass.