High coupling efficiency, passive alignment setup for visible-range fiber-to-waveguide edge coupling

Nathan C Lin,Sakib Hassan,Xuan Zhao,Ashok Veeraraghavan,Jacob T Robinson

doi:10.1117/1.jnp.14.046018

Abstract

We present a method to passively edge couple multiple optical fibers with silicon nitride waveguides in the visible wavelengths. We efficiently convert the fiber mode to the waveguide mode using an inverse taper mode size converter and support passive alignment using a U-groove that centers the optical fiber to the inverse taper. In our prototypes, we measure a coupling efficiency of −4.2 dB per facet. To reduce light leakage to the silicon substrate, we use a 6-μm oxide layer, which also eliminates the additional processes of undercutting the silicon substrate underneath the waveguide. Furthermore, the U-groove structure has a polished edge surface for coupling, reducing the steps of edge polishing the die. Fabrication of this visible-range edge coupler is complementary metal–oxide–semiconductor-compatible, making it a highly scalable method for passively packaging multiple visible-range integrated photonics devices.

Highlights

There is growing interest in silicon photonics devices due to their scalability and compatibility with the complementary metal–oxide–semiconductor (CMOS) processes
To determine the optimal inverse taper length of the mode size converter, we used the Lumerical Eigenmode expansion (EME) solver to sweep through a range of inverse taper tip widths and taper lengths
We demonstrated a passively aligned edge coupler in the visible range with a low insertion loss

Summary

Introduction

There is growing interest in silicon photonics devices due to their scalability and compatibility with the complementary metal–oxide–semiconductor (CMOS) processes. Mohanty et al edge coupled a fiber onto a silicon nitride waveguide without the use of a mode size converter, and the device has an insertion loss of 16 dB.[3] Wu et al.[23] and Shin et al.[24] use U-groove for passive edge coupler alignment in conjunction with micrometer-dimension low refractive index waveguide to mode-match with the fiber. Their measured coupling losses are more than 10 dB. This work integrates the spot size converter design with U-groove passive alignment setup to facilitate the fiber-to-waveguide coupling process

Simulations

Fabrication

Measurement and Discussion

Conclusion