Modulation-free Laser Stabilization Technique Using Integrated Cavity-Coupled Mach-Zehnder Interferometer

Laser frequency control loops are of interest as they enable stable and narrow linewidth lasers. Here, we propose and experimentally demonstrate a novel modulation-free laser stabilization technique using a cavity-coupled Mach-Zehnder interferometer as an optical frequency noise discriminator. The proposed laser stabilization architecture suppresses the frequency noise of a semiconductor laser by 4 orders of magnitude in the close-in frequency regime. The integral linewidth of the free-running laser is suppressed from 6.1 MHz to 695 KHz. The implemented photonic integrated circuit occupies an area of only 0.456 mm$^2$ and consumes no power consumption during the closed-loop operation. The photonic chip is integrated on AIM Photonics 180 nm silicon-on-insulator process.