Optical loss analysis and parameter optimization for fan-shaped single-polarization grating coupler at wavelength of 1.3 µm band

Abstract

Fan-shaped grating couplers (F-GCs) can be smaller than straight ones but are less efficient in general in coupling to single-mode fibers. To find a small F-GC with sufficiently high fiber-coupling characteristics, we numerically compared the dependencies of coupling efficiencies on wavelengths, the starting width of gratings, and misalignment distances among 25, 45, and 60° tapered angles of fan shape by using the three-dimensional finite-difference time domain method. A F-GC with a tapered angle of 25° exhibited the highest performances for all dependencies. The optical loss origins of F-GCs were discussed in terms of the electric field structures in them and scattering at the joint between the fan-shaped slab and channel waveguide. We fabricated an optimized 25° F-GC by using ArF photolithography, which almost exactly reproduced the optical coupling efficiency and radiation angle characteristics that were numerically expected.

Systematic identification of crosstalk and bandwidth upper limit in highly cascaded Mach–Zehnder lattice optical filters

“…We laid out the DCs with R = 10 μm, G = 200 nm, and L DC = 0, 1, 2, 3, 5, 10, 12, 15 and 20 μm at every position on the SOI wafer shown in . The input and output ports of each DC were connected with single polarization grating couplers (GCs) 31) in order to measure the transmission spectrum by using the waferlevel auto-probing system. A pair of GCs was also measured for calibration of the transmission signal detected in DC measurements.…”

Design and investigation of a dual-layer grating coupler for efficient vertical fiber-chip coupling

“…Considering one-dimensional (1D) gratings with high wavelength and polarization sensitivities, several kinds of 1D-GCs are demonstrated at the specific wavelength and polarization state. [14][15][16][17][18] To achieve polarization diversity, two-dimensional (2D) gratings are a promising solution, studied in both theory and experiments. [19][20][21][22] However, 2D gratings couple orthogonal polarization states of a single mode fiber to the same waveguide mode; moreover, the optimization and fabrication of 2D gratings are also a complex work.…”