Evaluation of Output Phase Stability in a Fiber-Optic Two-Way Frequency Distribution System

摘要

The assembly of a real-time actively controlled fiber-optic frequency transfer link based on additions to an existing static solution is proposed and evaluated. The dynamic variations of transmission delays, caused mainly by temperature dependence of the fiber, is continuously measured and used to adjust a delay at the transmitter for net cancellation of the effect. The resulting link shows no visible temperature dependence; however, the feedback induces added noise at short integration times. Frequency distribution from one master oscillator to different users within a local area can be easily implemented using commercial, often optical multimode, equipment. The distribution channel can be either wireless or wired, and the latter could be electrical cable or optical fiber. An electrical cable system will heavily suffer from surrounding interference and attenuation, while a fiber system will be more resilient to interference and attenuation for local area ranges. However, both cable and fiber will suffer from temperature-dependent delays which can be significant at transmission distances on the order of hundreds of meters, which is a reasonable distance in local area frequency distribution. These variations are slow and their influence on the output frequency stability is small. When the output phase stability is an important factor, the variations will nevertheless be significant, and several solutions address this issue through two-way solutions with datalogging and recalculation of phase data in retrospect.