Photonic integrated circuits (PICs) are enabling breakthroughs in several areas, including quantum computing, neuromorphic processors, wearable devices, and more. Nevertheless, existing PIC measurement methods lack the spectral precision, speed, and sensitivity required for refining current applications and exploring new frontiers such as point-of-care or wearable biosensors. Here, the “sweeping optical frequency mixing method (SOHO)” is presented, surpassing traditional PIC measurement methods with real-time operation, 30 dB higher sensitivity, and over 100 times better spectral resolution. Leveraging the frequency mixing process with a sweeping laser, SOHO excels in simplicity, eliminating the need for advanced optical components and additional calibration procedures. Its superior performance is demonstrated on ultrahigh-quality factor (Q) fiber-loop resonators (Q = 46 × 10⁶), as well as microresonators, realized on a new optical waveguide platform. An experimental spectral resolution of 19.1 femtometers is demonstrated using an 85-meter-long unbalanced fiber Mach Zehnder Interferometer, constrained by noise resulting from the extended fiber length, while the theoretical resolution is calculated to be 6.2 femtometers, limited by the linewidth of the reference laser. With its excellent performance metrics, SOHO has the potential to become a vital measurement tool in photonics, excelling in high-speed and high-resolution measurements of weak optical signals.

In most optical waveguides employed within photonic integrated circuits, light confinement is achieved by etching the high-index layer. However, these waveguides often lack versatility in optimizing optical properties, such as mode size, shape, dispersion, and polarization. Moreover, they frequently suffer from high coupling losses and their propagation losses are significantly influenced by the quality of the etching process, especially for materials with high mechanical rigidity. Here, we present a hybrid optical waveguide concept that effectively addresses these limitations by combining a strip of easily processible low-index material (SU8) with a high-index hard-to-etch guiding layer (amorphous silicon carbide, SiC). Our approach not only eliminates the need for SiC etching but also offers flexibility in waveguide design to accommodate advanced functionalities. One of the key advancements of this hybrid configuration is its ability to suppress the transverse magnetic mode by 62 dB at 1550 nm, effectively functioning as a transverse electric pass waveguide. This simplifies the measurements by eliminating the need for polarization controllers and polarizers. Furthermore, through tailored waveguides, we achieve 2.5 times higher coupling efficiency compared to untapered hybrid SiC waveguides. We also demonstrate that thermal baking of the polymer layer reduces the scattering losses from 1.57 to 1.3 dB/cm. In essence, our hybrid approach offers a versatile way of realizing low-loss SiC-based integrated optical components with advanced features, such as excellent polarization suppression, flexible mode shapes, and dispersion control, compared to etched counterparts.