Wide Bandwidth Silicon Nitride Strip-Loaded Grating Coupler on Lithium Niobate Thin Film

In this research, a vertical silicon nitride strip-loaded grating coupler on lithium niobate thin film was proposed, designed, and simulated. In order to improve the coupling efficiency and bandwidth, the parameters such as the SiO2 cladding layer thickness, grating period, duty cycle, fiber position, and fiber angle were optimized and analyzed. The alignment tolerances of the grating coupler parameters were also calculated. The maximum coupling efficiency and the −3 dB bandwidth were optimized to 33.5% and 113 nm, respectively. In addition, the grating coupler exhibited a high alignment tolerance.

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Grating Coupler Design for Vertical Light Coupling in Silicon Thin Films on Lithium Niobate

Crystals ◽

10.3390/cryst10090850 ◽

2020 ◽

Vol 10 (9) ◽

pp. 850

Author(s):

Huangpu Han ◽

Bingxi Xiang

Keyword(s):

Lithium Niobate ◽

High Efficiency ◽

Grating Period ◽

Grating Coupler ◽

Silicon Thin Film ◽

Cladding Layer ◽

Silicon Thin Films ◽

Light Coupling ◽

Mismatch Loss ◽

Fiber Position

In this paper we provide a design for a vertical grating coupler for a silicon thin film on lithium niobate. The parameters-such as the cladding layer thickness of lithium niobate, fiber position, fiber angle, grating period, and duty cycle are analyzed and optimized to reduce the mode mismatch loss and the internal reflections. The alignment tolerances, for the grating coupler parameters, are also simulated and evaluated. We determine that our simulated grating coupler exhibits high efficiency, enhanced light coupling, and high alignment tolerance.

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Comparison of Fiber-to-Waveguide Couplers in Point Diffraction Interferometer Based on Waveguide Reference Wavefront Source

Applied Sciences ◽

10.3390/app10249115 ◽

2020 ◽

Vol 10 (24) ◽

pp. 9115

Author(s):

Yuankai Chen ◽

Jian Bai ◽

Chen Wang ◽

Yingze Xue ◽

Yongying Yang

Keyword(s):

Silicon Nitride ◽

Coupling Efficiency ◽

Maximum Efficiency ◽

Grating Coupler ◽

Polarization Dependent Loss ◽

Te Mode ◽

Fabrication Tolerance

To improve the power of reference wavefront generated by reference wavefront source (RWS) based on silicon nitride (SiN) waveguide in point diffraction interferometer (PDI), we design the Y-branch coupler and grating coupler, and then compare the maximum coupling efficiency, 3 dB fabrication tolerance, 3 dB alignment tolerance and polarization dependent loss of two couplers. Our results show that grating coupler has higher coupling efficiency, lower etching difficulty and alignment difficulty, while Y-branch coupler has lower coating difficulty. To get the maximum efficiency, mode in the fiber must be TE mode no matter for grating coupler or Y-branch coupler. This paper improves the power of the wavefront by selecting appropriate fiber-to-waveguide couplers for waveguide RWS. PDI based on the power improved waveguide RWS is expected to be used in many measurement fields.

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