Modulation-free laser stabilization with aided acquisition for extended locking range

Stable lasers are essential in precision optical systems, where noise suppression and extended locking range are critical for long-term stability. However, conventional stabilization techniques often involve trade-offs between achievable phase noise, complexity, scalability, and locking range. Here, we propose and experimentally demonstrate a modulation-free laser stabilization system that integrates a cavity-coupled Mach-Zehnder interferometer (CCMZI) with an aided acquisition (AAQ) system (CCMZI-AAQ). The implemented CCMZI-AAQ, fabricated on a commercially available low-loss silicon nitride (SiN) photonic integrated chip, achieves more than 36 dB of laser frequency noise suppression at 1 kHz offset frequency and extends the locking range to the full free spectral range (FSR) of the on-chip micro-ring resonator (MRR), 3.95 GHz-representing an order-of-magnitude improvement over the stand-alone CCMZI. This compact and scalable photonic chip, occupying just 5.43 mm², demonstrates significant potential for integrated low-noise lasers in applications such as fiber sensing and optical communication.