Broadband frequency conversion via adiabatically tapered $\chi^{(2)}$ waveguide in photonic integrated circuits

TL;DR

This paper introduces an adiabatically tapered aluminum nitride waveguide design for broadband, high-efficiency optical frequency conversion on photonic chips, enabling scalable on-chip information processing.

Contribution

It demonstrates a novel adiabatic taper design that broadens bandwidth and enhances efficiency in integrated $ ext{chi}^{(2)}$ frequency conversion, outperforming traditional uniform waveguides.

Findings

Broader bandwidth with constant efficiency in tapered waveguides

Conservation of the product of bandwidth and efficiency ('area law')

Higher saturation thresholds compared to uniform waveguides

Abstract

We propose to use the integrated aluminum nitride waveguide with engineered width variation to achieve optical frequency conversion based on $\chi^{(2)}$ nonlinear effect on a photonic chip. We show that in an adiabatically tapered waveguide, the frequency conversion has a much broader bandwidth and the efficiency within the bandwidth is almost constant, which is favorable for short pulses. We demonstrate both analytically and numerically an "area law" for the frequency conversion, i.e. the product of bandwidth and efficiency is conserved as long as peak conversion efficiency does not saturate. The adiabatic structure shows higher saturation thresholds in pump power or interaction length, outperforming the conventional uniform waveguide design. With our approach, high-efficiency and wavefront-keeping conversion for short pulses is possible on a photonic chip, which will surely find applications for scalable on-chip information processing.