Photonic Chip Crosstalk Model Improves Interferometer Stability and Accuracy

Photonic integrated circuits experience operational inaccuracies due to crosstalk between components. Research identifies ‘induced phase shifters’ arising from crosstalk on waveguide sections, providing a comprehensive analysis and mitigation framework. Experimental validation on a 12-mode Clements interferometer demonstrates accurate crosstalk recovery and effective cancellation of these induced phase shifts.

The reliable manipulation of light within integrated photonic circuits is crucial for advances in quantum technologies and high-performance computing, yet imperfections in fabrication and operation introduce unwanted interference known as crosstalk. This limits the precision of these circuits and hinders their practical application.

Researchers at Quandela, alongside colleagues at the Centre for Nanosciences and Nanotechnologies, have developed a comprehensive model to characterise and mitigate this crosstalk, extending beyond previous approaches that focused solely on interactions between actively controlled components. Their work, detailed in the article “Resource-efficient crosstalk mitigation for the high-fidelity operation of photonic integrated circuits with induced phase shifters”, by Andreas Fyrillas, Nicolas Heurtel, Simone Piacentini, Nicolas Maring, Jean Senellart, and Nadia Belabas, introduces the concept of ‘induced phase shifters’ – unintended effects arising from crosstalk on passive waveguide sections – and proposes a framework for their systematic analysis and cancellation, validated experimentally on a 12-mode Clements interferometer.

Characterising and Mitigating Crosstalk in Photonic Integrated Circuits

Photonic integrated circuits (PICs) offer a pathway to compact and stable light manipulation, but practical application is limited by imperfections arising during fabrication and operation. A significant challenge is accurately characterising and mitigating crosstalk – unwanted interference – between reconfigurable phase shifters within these circuits, which degrades performance and reliability. Recent research addresses this limitation by identifying ‘induced phase shifters’ – crosstalk originating from bare waveguide sections, as predicted by simulations – and presents a comprehensive framework for analysis and mitigation, offering a route to improved device performance.

The study establishes a method for characterising these induced phase shifters in physical devices, utilising a technique to accurately determine their properties and impact on signal integrity. Crucially, the research proposes a criterion for assessing ‘crosstalk robustness’ within an interferometer, moving beyond traditional analyses focused solely on direct connections between phase shifters. This robustness hinges on the topology of a simplified representation of the circuit – a ‘pruned graph’ – where the absence of cycles indicates minimal susceptibility to interference, providing a quantifiable metric for design optimisation.

Researchers demonstrate that an interferometer achieves crosstalk robustness when its pruned graph is acyclic, preventing signals from propagating in closed loops and minimising unwanted interference. A greedy algorithm efficiently identifies the minimal set of phase shifters needed to eliminate cycles within the pruned graph, ensuring optimal control and minimising system complexity.

Experimental validation on a 12-mode Clements interferometer confirms the efficacy of the extended crosstalk model in accurately recovering physical crosstalk properties, demonstrating its practical relevance. The proposed mitigation framework successfully cancels induced phase shifters, offering a pathway to enhance the performance and reliability of photonic integrated circuits.

The research begins by acknowledging the limitations of current crosstalk analysis methods, which often overlook the contribution of induced phase shifts arising from bare waveguide sections. These induced phase shifts, though often subtle, can accumulate and significantly degrade the performance of interferometers, particularly in complex designs. To address this, the researchers developed an extended crosstalk model that incorporates these induced phase shifts, providing a more accurate representation of the physical system and enabling more effective mitigation strategies.

The study establishes a robust methodology for characterising induced phase shifters in physical devices, utilising a combination of experimental measurements and computational modelling. Researchers carefully measure the crosstalk between different optical paths within the interferometer, identifying the contribution of induced phase shifts and their impact on signal integrity.

The research highlights the importance of considering the full complexity of photonic integrated circuits, including the often-overlooked contribution of induced phase shifts. By developing a comprehensive model that incorporates these effects, researchers have provided a valuable tool for designers and engineers seeking to optimise the performance of their devices. The proposed criterion for assessing crosstalk robustness, based on the topology of a pruned graph, offers a clear and intuitive guideline for minimising interference and improving the stability of optical systems.

Furthermore, the successful demonstration of a mitigation framework that cancels induced phase shifters opens up new possibilities for the development of more robust and reliable photonic integrated circuits. This framework can be implemented in a variety of applications, including optical communications, sensing, and imaging.

In conclusion, this research provides a comprehensive framework for characterising and mitigating crosstalk in photonic integrated circuits, addressing a critical challenge in the development of advanced optical technologies. By incorporating the effects of induced phase shifts, developing a criterion for assessing crosstalk robustness, and demonstrating a successful mitigation framework, researchers have made a significant contribution to the field. The findings have the potential to enable the creation of more robust, reliable, and versatile optical systems, paving the way for a wide range of applications in communications, sensing, and imaging.