Universal loss and gain characterization inside photonic integrated circuits

TL;DR

This paper introduces a universal, nondestructive method to measure loss and gain inside photonic integrated circuits using nonlinear optical devices, significantly improving characterization precision and aiding complex circuit optimization.

Contribution

The authors present a novel technique leveraging nonlinear optical devices to nondestructively characterize loss and gain at the component level within PICs, with high precision and broad applicability.

Findings

Achieved measurement precision better than 0.1 dB.

Successfully characterized loss of fiber-chip coupling and unknown devices.

Demonstrated measurement of quantum efficiency in a quantum PIC.

Abstract

Integrated photonics has undergone tremendous development in the past few decades, transforming many fields of study in science and technology. Loss and gain are two fundamental elements in photonic circuits and have direct impacts on nearly all key performance metrics. Surprisingly, the tools to characterize the optical loss and gain inside photonic integrated circuits (PICs) are very limited. This is because, unlike free-space or fiber optics, integrated circuits cannot be nondestructively disassembled. Here, we report a universal method to see inside the photonic integrated circuits and measure loss and gain on the component level nondestructively. The method leverages nonlinear optical devices as optical power discriminators to retrieve the loss and gain information inside the PICs. Our method has a precision better than 0.1 dB, and can characterize the loss of individual fiber-chip coupling facet and general unknown devices under test. As a demonstration of applications, we measured the true on-chip quantum efficiency of a quantum PIC consisting of heterogeneously integrated balanced photodiodes, a critical building block for integrated quantum technology. Our method can be implemented on different photonic platforms, and can be used to understand gain and loss in complex photonic circuits, which is essential to optimize circuit design and to create large-scale systems with predictable, reproducible performance.