Bridging Ultra-High-Q Devices and Photonic Circuits
The paper "Bridging ultra-high-Q devices and photonic circuits" addresses a critical challenge in the field of optical microcavities: integrating ultra-high-Q devices with photonic circuits. Optical microcavities, known for their numerous functions such as frequency microcombs, Brillouin lasers, and bio- and nanoparticle sensors, increasingly rely on high cavity-Q factors to enhance performance metrics like reduced power consumption and decreased phase noise. Historically, ultra-high-Q resonators have been limited to discrete crystalline or silica-based devices. This work successfully demonstrates an integrated monolithic microcavity with a record-high Q factor, surpassing 200 million, opening new possibilities for photonic integration.
The authors present an integrated ridge resonator with a remarkable Q factor exceeding 200 million, enabling a suite of device functionalities that have traditionally been confined to discrete systems. This work prominently features two device demonstrations: soliton sources with electronic repetition rates and high-coherence Brillouin lasers, both integrated on a single cavity platform. The integration leverages PECVD silicon nitride waveguides to achieve full integration of these ultra-high-Q resonators with other photonic devices. This approach provides the design flexibility necessary for realizing various device functions previously exclusive to non-integrated devices.
In demonstrating the potential of this new platform, the authors achieve soliton generation with a repetition rate of 15 GHz at a low pumping power level. This result is significant as it marks the first instance of integrated soliton generation at an electronics-rate competitive with larger-scale frequency comb systems. Moreover, they achieve high-coherence Brillouin laser action within the integrated system, highlighting the platform's capability to produce narrow-linewidth signals vital for applications such as microwave synthesizers and photonic gyroscopes.
The implications of this work are multifaceted. Practically, the integration of ultra-high-Q resonators with photonic circuits can transform the design and functionality of nanophotonic systems, enabling compact and efficient systems-on-a-chip. Theoretically, this advancement in microcavity integration could pave the way for further research into novel photonic architectures and applications, leveraging the advantageous scaling of performance metrics with the Q factor. Future research directions may explore the optimization of integration techniques and the synthesis of even more complex photonic circuits with varied functionalities tailored for specific applications in optical communications and sensing.
The demonstrated integration of high-Q devices opens possibilities for the development of robust, scalable fabrication methods that maintain the high-performance metrics essential for advanced photonic systems. This work provides a critical advance in photonic circuit integration, offering a new pathway toward scalable optical technologies with enhanced capabilities.