Abstract
Broadband Silicon-On-Insulator (SOI) directional couplers are designed based on a combination of curved and straight coupled waveguide sections. A design methodology based on the transfer matrix method (TMM) is used to determine the required coupler section lengths, radii, and waveguide cross-sections. A 50/50 power splitter with a measured bandwidth of 88 nm is designed and fabricated, with a device footprint of 20 μm × 3 μm. In addition, a balanced Mach-Zehnder interferometer is fabricated showing an extinction ratio of >16 dB over 100 nm of bandwidth.
Highlights
The use of directional couplers as 2 × 2 power splitters / combiners is ubiquitous in photonic integrated circuits
Numerical studies indicate that SOI curved directional couplers have the advantages of being low loss, comparable in size with conventional straight directional couplers, and being fabrication and temperature tolerant[21]
We study in detail the design of curved asymmetric directional couplers, where the asymmetry arises due to different bending radii between the two constituent waveguides of the coupler
Summary
The use of directional couplers as 2 × 2 power splitters / combiners is ubiquitous in photonic integrated circuits. We used the TMM to determine the coupler section lengths and curved coupler radii that give the desired wavelength insensitive operation.
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