Precise Bias Control of Mach–Zehnder Modulators Without Second‐Order Pilot Tones

We propose a novel and robust bias control method for Mach–Zehnder modulators that enables precise stabilization using low‐amplitude pilot tones without requiring the detection of second‐ or higher‐order harmonics. The technique relies on the ratio of the partial derivative of the direct current component to that of the first‐order pilot tone with respect to the bias voltage, serving as a high‐sensitivity feedback signal. Simulation and experimental results verify that the method significantly lowers the required pilot tone power, mitigates intermodulation distortion, and improves system linearity. Furthermore, it ensures stable and accurate bias control even under optical power fluctuations, making it particularly well‐suited for microwave photonic links that demand high signal‐to‐noise ratios.