According to a study published in the journal Nature , researchers from the Chinese Academy of Sciences, Colorado School of Mines and EPFL developed an electro-optical comb frequency generator with more than 2,000 comb lines, achieving a spectral range of 450nm.
In modern optics, frequency combs are essential tools for applications in telecommunications, environmental monitoring, and astrophysics. Despite their usefulness, designing compact and efficient frequency combs remains a challenge.
Electro-optical frequency combs, introduced in 1993, generate optical combs through cascaded phase modulation. However, high power requirements and limited bandwidth have hindered further development, leading to femtosecond lasers and Kerr solitons dominating the field. Although effective, these alternatives require advanced tuning and significant power, limiting their practical implementation.
Recent advances in thin-film electro-optic integrated photonics have sparked renewed interest in materials such as lithium niobate. However, achieving higher bandwidth while reducing power consumption remains challenging, and lithium niobate’s inherent birefringence further limits its performance.
The researchers addressed these limitations by integrating microwave and optical circuit designs onto a lithium tantalate platform. Lithium tantalate has 17 times lower birefringence than lithium niobate, improving bandwidth and reducing microwave power consumption, reducing power requirements by almost 20 times compared to previous designs.
The research team introduced a “triple-resonance integration” design in which two optical and microwave fields resonate simultaneously. This is achieved by a co-designed system that combines monolithic microwave circuits with photonic components. Distributed coplanar waveguide resonators are integrated into the lithium tantalate photonic circuit to improve microwave confinement and energy efficiency.
The small area of the device, just 1×1 cm², minimizes interference between light waves, allowing for smooth and consistent frequency comb generation.The system operates using simple, freely running distributed feedback laser diodes, eliminating the need for complex tuning procedures required for Kerr soliton-based combs.
The comb generator provides ultra-wideband coverage of 450 nm and operates stably over more than 90% of the free spectral range. Its stability and simplicity make it suitable for field-deployable applications.
The robust design and compact size of this device have potential applications in areas such as high-precision gas sensing for environmental monitoring and laser distance measurement in robotics. A co-design approach combining photonic and microwave technologies highlights the potential for creating next-generation photonic devices.
All samples were fabricated at EPFL’s Center for Micro-Nanotechnology (CMi) and Institute of Physics Clean Room (IPHYS). Lithium Tantalate-on-Insulator (LTOI) wafers are supplied by Shanghai New Silicon Integration Technology (NSIT) and SIMIT-CAS.
Journal References:
Zhang, J., et al . (2025) Ultrawideband integrated electro-optical frequency comb in lithium tantalate. Nature . doi.org/10.1038/s41586-024-08354-4
sauce:
Swiss Federal Institute of Technology Lausanne
