The team focused on germano-silicate resonators, employing an inductively coupled plasma chemical vapor deposition (ICP-PECVD) technique to deposit the upper silica cladding at a relatively low temperature of 250 °C. This process used a deuterated silane precursor combined with oxygen plasma, which allowed precise control over film thickness and composition. Notably, the researchers implemented a rapid thermal annealing step at 1,000 °C for 20 minutes following every 500 nm of cladding deposited. This annealing served a dual purpose: it mitigated stress-induced optical losses and repaired damage caused by direct plasma exposure during deposition.

The effectiveness of this approach was confirmed by depositing a 6-micron thick upper cladding, which fully encapsulated the resonator’s coupling gap, thereby significantly shielding the device from environmental contaminants. This protective encapsulation contributed to maintaining ultrahigh Q values—up to 160 million over several months. Although this represented some reduction from the pristine, unclad Q of approximately 250 million, the results affirmed that partial recovery and long-term stability were attainable through the annealing treatment. The observed trade-offs align well with previous findings in ultralow-loss (ULL) silicon nitride, suggesting that further refinement in deposition methods or precursor materials might eliminate this Q degradation entirely.

To analyze the Brillouin gain spectrum, the researchers utilized a highly sensitive dual-intensity-modulation pump-probe technique. The test devices had upper claddings made of 1.5 mol% P₂O₅-doped silica deposited via plasma-enhanced chemical vapor deposition (PECVD). This slightly phosphorus-doped glass demonstrated excellent ability to produce thick, stress-free films critical for confining both optical and acoustic modes effectively. Post-fabrication characterization revealed waveguide propagation losses below 0.5 dB/m and facet coupling losses around 1.4 dB, underscoring the exceptional optical quality achieved.

In their experimental setup, counterpropagating pump and probe lasers operating near 1560 nm were used. The pump laser was intensity-modulated at 10 MHz, while the probe was modulated slightly off-frequency at 10.075 MHz. A lock-in amplifier measured the probe transmission signal referencing a 75 kHz beatnote originating from the modulation difference. Scanning the probe over a 20 GHz detuning range from red to blue relative to the fixed pump frequency allowed precise acquisition of the stimulated Brillouin scattering (SBS) gain spectrum.

Complementing experimental work, numerical simulations based on finite element methods were employed to calculate the optical and acoustic fields. Material parameters derived from prior studies formed the basis of their models, including indices of refraction, material densities, Poisson ratios, Young’s moduli, Brillouin linewidths, and photoelastic coefficients for the core, upper cladding, and bottom cladding layers. This multi-parameter simulation framework facilitated a holistic understanding of the interaction between optical and acoustic waves within the device structure.

To investigate thermorefractive noise (TRN), the study also employed sophisticated COMSOL Multiphysics simulations using a fluctuation-dissipation theorem-based model. Simulations compared Ge-silica waveguides with both thin and thick silicon nitride (SiN) structures, each modeled as 3 mm diameter microresonators with specific rectangular waveguide cross sections. These simulations incorporated detailed material thermal properties such as thermo-optic coefficients, thermal conductivities, specific heat capacities, and densities, all calibrated to an ambient temperature of 300 K. The Ge-silica waveguides featured air cladding, while the SiN devices were silica-clad, reflecting realistic fabrication conditions.

The combination of meticulous material engineering, thermal processing, and rigorous experimental verification offers a promising route toward integrated photonic devices with loss figures rivalling those of bulk optical fibers. Such advancements are critical in enabling the next generation of on-chip lasers, modulators, and frequency combs, which rely heavily on ultralow-loss resonators to achieve unprecedented performance in communications, sensing, and quantum technologies.

However, challenges remain. The slight but persistent reduction in Q factor upon cladding deposition indicates that further innovation in deposition chemistry or approaches may be necessary. Alternatives such as low-pressure chemical vapor deposition or novel precursors like tetraethoxysilane PECVD may hold the key to minimizing plasma-induced damage and residual stress. The researchers highlight these potential pathways, underscoring that the current work lays a solid foundation for ongoing optimization.

This study heralds a significant milestone for photonic integration, demonstrating that fibre-like loss performance across a broad spectral range is achievable, connecting violet to near-infrared wavelengths seamlessly. Such capability opens new horizons for compact, high-performance photonic chips, integrating functionalities once thought to require bulky and fragile fiber setups.

In summary, by innovating on cladding deposition methods and leveraging advanced characterization and modeling, the researchers have resolved longstanding challenges in photonic device losses. Their results promise transformative impacts across telecommunications, precision metrology, and quantum information science, where low-loss photonics are essential cornerstones. Future efforts will doubtless extend and refine these techniques, pushing photonic integration toward new frontiers in performance and scalability.

Subject of Research: Photonic integrated circuits, ultralow-loss waveguide resonators, and deposition techniques for high-quality silica cladding.

Article Title: Towards fibre-like loss for photonic integration from violet to near-infrared.

Article References:
Chen, HJ., Colburn, K., Liu, P. et al. Towards fibre-like loss for photonic integration from violet to near-infrared. Nature 649, 338–344 (2026). https://doi.org/10.1038/s41586-025-09889-w

DOI: 08 January 2026

Keywords: ultralow-loss resonators, photonic integration, silica cladding, ICP-PECVD, thermal annealing, Brillouin scattering, thermorefractive noise, waveguide propagation loss, phosphorus-doped silica, COMSOL Multiphysics simulations

Recent breakthroughs, however, have resulted in a sophisticated simulation method bolstered by enhanced stability and computational efficiency. This method focuses on inductively coupled plasmas and is embodied in a novel particle-in-cell code that adeptly balances speed with physical fidelity. Developed through a collaborative initiative between the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) and Applied Materials Inc., a leader in chip manufacturing technology, this cutting-edge tool incorporates the expertise of researchers from the University of Alberta, PPPL, and Los Alamos National Laboratory. The collaboration exemplifies how governmental research institutions and industry partners can jointly accelerate innovation by harnessing advanced simulation techniques.

The crux of the challenge lies in the kinetic nature of the plasma, which necessitates tracking individual particle interactions to generate detailed distribution functions. Unlike fluid models that average particle effects, kinetic simulations must resolve how particles move and interact under electromagnetic forces, providing unparalleled insights into plasma dynamics. Such insights include how particle densities fluctuate within confined spaces and how electric and magnetic fields evolve during plasma generation and sustainment. By simulating these phenomena with increasing precision, researchers aim to tailor plasma processes to etch microscale patterns on silicon wafers with enhanced precision, thereby pushing the boundaries of speed and information storage in microelectronics.

A significant advancement in the new simulation approach comes from a fundamental reformulation of the underlying equations governing the plasma’s behavior. The initial incarnation of the code was plagued by instability, often crashing or producing unreliable results. This setback was overcome by carefully redesigning the mathematical framework, enabling the simulation to consistently deliver stable and repeatable outcomes. According to Dmytro Sydorenko, a research associate at the University of Alberta and primary author of the study, these extensive modifications have transformed the program into a reliable instrument for analyzing two-dimensional plasma structures. This breakthrough effectively opens the door to more complex and realistic simulations that were previously unattainable.

Central to the enhanced simulation’s success is its refined calculation of the solenoidal electric field—a critical component of inductively coupled plasma generation. This solenoidal field arises when an alternating current flowing through a coil produces a time-varying magnetic field, which in turn induces electric fields that energize the plasma. Precise modeling of this process is essential because it dictates how energy is coupled into the plasma, directly influencing plasma temperature, density, and overall stability. By improving the fidelity of the electric field calculations, the researchers have substantially increased the model’s predictive power.

Building upon mathematical procedures initially developed by Salomon Janhunen at Los Alamos National Laboratory, and further optimized by PPPL scientist Jin Chen, the simulation marries physics, mathematics, and computer science in unique ways to solve this complex problem. Chen highlights that integrating these diverse fields was key to achieving the significant improvements over earlier models. The seamless fusion of theoretical and numerical techniques results in a code that not only predicts plasma behavior with remarkable accuracy but also remains computationally tractable on modern supercomputing platforms, thus facilitating its adoption for industrial process design.

The particle-in-cell methodology underpinning the simulation is particularly suited to low-pressure plasma environments common in many industrial applications. Unlike fluid models, which treat plasma as a continuous medium, particle-in-cell approaches follow discrete particle trajectories through a spatial grid, capturing kinetic effects and resolving non-equilibrium phenomena that fluid models cannot. This granularity allows for nuanced observations of particle distribution functions—the probability landscapes describing where, and at what velocities, particles exist. Such detail is crucial for revealing microscopic plasma characteristics that influence macro-scale outcomes, such as chamber uniformity, etching precision, and defect reduction in semiconductor manufacturing.

Ensuring physical accuracy extends beyond tracking particles; one of the major achievements of this new model is its rigorous enforcement of the conservation of energy. In any realistic physical system, energy neither magically appears nor vanishes. Yet, in some numerical simulations, small errors trickle into computational steps, potentially corrupting results after many iterations. The improved kinetic model meticulously maintains energy balance, thereby safeguarding against the accumulation of numerical artifacts that could lead to deceptive or useless predictions. Igor Kaganovich, a principal researcher at PPPL, emphasizes that this fidelity to physical laws imbues the simulation outputs with trustworthiness, thereby supporting confident decision-making in industrial contexts.

The enhanced simulation not only accelerates computational speed but also scales effectively to larger plasma setups, promising industrial users the ability to explore and optimize plasma processes that were previously too complex to model practically. This breakthrough is anticipated to congregate widespread attention in sectors reliant on plasma technology, especially semiconductor fabrication, where even marginal improvements in plasma control and uniformity can translate to significant economic and performance benefits.

All developments leading to this simulation were backed by the Cooperative Research and Development Agreement between Applied Materials Inc. and PPPL, which underscores the crucial role of public-private partnerships in advancing applied science. This collaborative framework brought together cutting-edge hardware expertise from industry and state-of-the-art plasma physics knowledge from academia and government laboratories, melding them into a cohesive development pipeline. The contract under which this work was conducted, DE-AC02-09CH11466, represents a strategic investment by the U.S. Department of Energy to drive technological advancements with real-world applications.

Ultimately, this progress exemplifies how detailed computational modeling can elevate the understanding of plasma behavior and propel industrial process innovation. The ability to simulate inductively coupled plasmas in two spatial dimensions while faithfully representing kinetic physics and conserving energy marks a monumental stride in plasma physics and its application to practical technologies. The ripple effects of this research may unlock new frontiers in semiconductor device fabrication, paving the way for smaller, faster, and more energy-efficient microchips critical to the information technologies of tomorrow.

As PPPL continues to harness plasma science, their advancements stretch beyond industrial applications to include fusion energy research, nanoscale fabrication, and emerging quantum technologies. Their multidisciplinary expertise ensures that plasma continues to serve as a versatile medium not only for understanding nature at the fundamental level but also for engineering transformative technological breakthroughs. The progress reported here could very well become a cornerstone of future plasma simulation efforts globally, inspiring further inquiry and innovation.

Subject of Research: Not applicable

Article Title: Simulation of an inductively coupled plasma with a two-dimensional Darwin particle-in-cell code

News Publication Date: April 9, 2025

Web References:

• https://www.pppl.gov
• https://doi.org/10.1063/5.0241152

References:
Kaganovich, I., Sydorenko, D., Chen, J., Ethier, S., et al. "Simulation of an inductively coupled plasma with a two-dimensional Darwin particle-in-cell code." Physics of Plasmas, 2025.

Image Credits:
Credit: Dmytro Sydorenko / University of Alberta

Keywords

Electronics, Fusion energy, Physics, Plasma physics, Electronic circuits, Microprocessors, Plasma