Abstract

Connections between standard single-mode fibers and waveguides in photonic integrated circuits tend to have relatively high coupling losses due to a difference in mode size and mode profile between both light guiding media. Edge coupling strategies involving specialty fibers are frequently used to obtain the best performance in terms of coupling efficiency, bandwidth and polarization independence. We propose the fabrication of free-standing down-taper structures on top of cleaved fiber facets by two-photon direct laser writing and show their performance for silicon, silicon nitride and indium phosphide generic chip platforms. We present a comprehensive analysis of the design of such taper structures that show unprecedented flexibility. We demonstrate their fabrication and fully characterize them in terms of output modal fields and coupling efficiencies. Furthermore, we experimentally compare the fabricated down-tapers with commercially available lensed fibers and demonstrate equal or better coupling efficiency for four out of the five investigated photonic integrated circuit platforms, with a measured improvement in coupling efficiency up to 1.43 dB.

Highlights

  • T HE integration of many different optical components and functionalities into a compact device or chip has been actively investigated for many years

  • Photonic Integrated Circuits (PIC) platforms we found that the down-taper approach produces lower losses than the lensed counterpart, with an improvement in coupling loss of respectively 0.97 dB, 0.44 dB and 1.43 dB for the silicon oxynitride (SiON), silicon nitride (SiN), and indium phosphide (InP)-platforms

  • We have demonstrated the design and 2PP fabrication of linear and nonlinear down-taper structures on top of cleaved single-mode optical fiber tips with the aim of matching the mode profile of the fiber to that of on-chip waveguides in different generic photonic integrated circuit platforms

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Summary

INTRODUCTION

T HE integration of many different optical components and functionalities into a compact device or chip has been actively investigated for many years. We propose to use the 2PP additive manufacturing technique to print down-taper structures on the end-facet of SMFs. A taper structure with excellent modal match in terms of shape and size can be fabricated directly on top of the optical fiber, such that it can be butt-coupled with the photonic chip to minimize reflections. A taper structure with excellent modal match in terms of shape and size can be fabricated directly on top of the optical fiber, such that it can be butt-coupled with the photonic chip to minimize reflections This can be done without the need for physical changes to the PIC.

DESIGN AND ANALYSIS OF DOWN-TAPERED FIBER-TO-CHIP COUPLING STRUCTURES
Modal Field Matching and Transformation
Misalignment Tolerances
Impact of Adding a Cladding Material
TAPER FABRICATION AND CHARACTERIZATION
COUPLING EXPERIMENTS
Findings
CONCLUSION
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