Caltech Researchers Achieve Ultralow Optical Loss on Silicon Photonic Chips, Rivaling Fiber Optics
In a groundbreaking advance that promises to transform the landscape of photonic technology, scientists at the California Institute of Technology (Caltech) have developed a novel technique to guide light on silicon wafers with ultralow signal loss that approaches the benchmark set by optical fiber. This remarkable breakthrough heralds the advent of next-generation photonic integrated circuits (PICs) with unprecedented efficiency and coherence, unlocking profound possibilities across fields as diverse as precision measurement, quantum computing, and data communications.
Optical fibers have long been the backbone of global telecommunications, valued for their ability to transmit light signals over vast distances with minimal attenuation. This superior performance stems from their composition of highly pure glass and exquisitely engineered interfaces, which minimize absorption and scattering of photons. Replicating this level of performance within the confines of silicon-based photonic chips, however, has remained a significant scientific challenge. The new approach pioneered at Caltech seeks to emulate the ultralow-loss characteristics of fiber optics on compact silicon substrates used in conventional microelectronics manufacturing.
According to Kerry Vahala, a leading physicist and professor at Caltech with decades of expertise in photonics, the team’s innovation lies in combining fiber-grade glass materials with advanced lithographic fabrication. “We have developed a method to print optical circuits using germano-silicate — the very same glass that forms optical fiber — directly onto 8- and 12-inch silicon wafers,” Vahala explains. This fabrication technique preserves the hallmark ultralow-loss properties of fiber while leveraging the scalability and integration benefits of silicon chip technology, particularly at visible wavelengths.
Central to this advancement is the creation of waveguides — nanometer-scale pathways etched into the chip that confine and direct light with exceptional precision. By adapting germano-silicate to lithographic patterning, the researchers have engineered waveguides with atomically smooth surfaces through a ‘reflow’ process, reducing scattering losses to unprecedented levels. “Our devices demonstrate losses at visible wavelengths that are twenty times lower than the previous record holders made from silicon nitride, an industry-standard low-loss material,” notes Hao-Jing Chen, a postdoctoral scholar contributing to the work. This magnitude of improvement is significant, especially considering the critical role visible light holds in numerous optical applications.
The architecture of the waveguides involves spiraling the light path into compact, tightly wound geometries that magnify the effective optical path length within a minuscule footprint. This spiral design is reminiscent of winding fiber onto a spool but shrinks the entire assembly to a fraction of the size through cutting-edge nanofabrication. Such extended path lengths on chip not only reduce loss impacts but enhance performance parameters critical for resonant devices and lasers. The approach also integrates efficiently with conventional semiconductor lasers and fiber optic interconnects, optimizing energy costs in data-center infrastructure and other high-speed communication contexts.
Loss minimization in waveguides underpins the coherence and performance of integrated photonic devices. For example, lasers based on these new waveguides exhibit coherence times improved by orders of magnitude compared to their predecessors. Coherence is fundamental to applications ranging from atomic clocks and gyroscopes to emerging quantum information systems, wherein the duration over which light preserves its phase directly impacts precision and reliability. The researchers emphasize that every tenfold reduction in optical loss corresponds to a hundredfold boost in laser coherence, underscoring the far-reaching implications of their success.
Applications stretch beyond conventional telecommunications. The visible spectrum coverage afforded by the new platform enables scalable chip-based atomic sensors, ion traps, and optical clocks critical to next-generation navigation, timing, and sensing technologies. Kellan Colburn, a graduate student involved in the project, highlights that although chip dimensions are on the centimeter scale, the effective optical path lengths within ring resonators can mimic kilometers of fiber, vital for enhancing the functionality of fundamental optical elements used across research and industry.
This versatile ‘Swiss Army knife’ of photonics, as Vahala describes it, is already demonstrating its utility in multiple device classes fabricated in the lab. They include ring resonators with exceptional quality factors, various laser types exhibiting long coherence, and nonlinear optical devices capable of frequency generation extending across violet to near-infrared bands. These pioneering devices hint at the vast design freedom and performance improvements now accessible to photonics engineers addressing challenges in emerging quantum networks, AI data transfer, and precision metrology.
Despite the remarkable progress detailed in their recent Nature publication, the team asserts that this achievement is a stepping stone rather than a culmination. Significant engineering challenges remain as they aim to refine fabrication techniques, improve device uniformity, and broaden wavelength coverage further. However, the reported results mark a substantial leap forward, validating the potential of printing fiber-grade optical materials onto chip-scale platforms with record-low loss metrics.
The impact of this technology’s widespread adoption will be profound. Ultralow-loss integration on silicon chips bridges a long-standing gap between fiber optic communication quality and chip-compatible photonics, promising transformative enhancements in energy efficiency, signal integrity, and device miniaturization. As data generation and processing demands escalate in an increasingly interconnected world, the ability to manipulate light with minimal loss at the chip level provides a crucial foundation for the future of communication, sensing, and computation paradigms.
Supported by a collaborative effort involving researchers from Caltech, UC Santa Barbara, Leiden University, and the University of Southampton, this research is funded by agencies including DARPA and the Air Force Research Laboratory. The convergence of material science, quantum engineering, and nanofabrication demonstrably paves a new pathway to photonic circuit capabilities that could soon redefine the limits of integrated optics.
Subject of Research: Photonic integrated circuits, ultralow-loss waveguides, silicon photonics, optical coherence, visible wavelength photonics
Article Title: Towards fibre-like loss for photonic integration from violet to near-infrared
News Publication Date: January 7, 2026
Web References: https://www.nature.com/articles/s41586-025-09889-w
References: DOI 10.1038/s41586-025-09889-w
Image Credits: Vahala Lab / Caltech
Keywords: Photonics, Large scale integration, Quantum computing
