Noise Limit on the Accuracy of Frequency Locking of Lasers for Ultra-acurate Fiber-optic Time Transfer

SummaryIn the paper we discuss the frequency error occurring when synchronizing two semiconductor lasers under the conditions when the optical power of the reference laser is relatively weak (usually below minus thirty some dBm). This synchronization approach is intended to be used in ultra-accurate long-distance fiber optic time transfer links, which require accurate and stable frequency offset between the lasers used to convey the timing information between the terminals of the transfer system. We identified that the problem is caused by the noise (and resulting insufficient signal to noise ratio) at the input of a high-frequency prescaler forming a part of the signal processing chain. To understand undergoing processes we developed a Simulink/Matlab simulation model, supported by a theoretical approach that can help designing the laser frequency synchronization circuits for the fiber optic time transfer systems.