Design And Implement Of The Fast Programmable Fiber-Optic Delay Line

Optical fiber plays an important role in long distance signal transmission system. In the area of microwave photonics, the application of optical fiber will bring lots of advantages, such as high bandwidth, low loss, and good immunization ability on electromagnetic interference. Fiber delay line (FDL) is one of the typical examples of such applications, which has small size, low weight, simple structure complexity, and high product of bandwidth & distance.The basic principle of fiber delay line is that the different delay time is obtained by choosing corresponding different pathway. This paper proposed a novel structure of fiber delay line, which is based on the using of Semiconductor Optical Amplifier (SOA) and 1×3 optical couplers. By numerical analysis of the relationship between the number of SOAs used and the total delay amount obtained, a parallel-series connected structure of FDL was found with good expanding ability. The switching time is fast enough due to the use of SOAs, and the polarization performance of the system was also improved by the application of Faraday Rotator Mirrors (FRM) and the optical circulators in the structure.SOA, as a fast switching element and tunable optical gain controller, plays an important role in Chapter Three. The characteristics of SOA have been firstly introduced briefly. The details of driving circuit have been given further. The last of this part are test results of SOA, e.g. the inner resistance, the power gain characteristics, the saturation output power and signal noise ratio (SNR).The precision of delay time is another issue of the system. High precision is the key of the fiber-optic delay lines. In chapter four, a new micro-drawing platform on the heated fiber was implemented by the using of the precision reflectometer (HP8504A) to monitor the length of delay lines. It shows that the precision of the optical fiber delay is less than 0.1ps.We implemented a 3×3 FDL structure and test its characteristics. The switching time had a rise time of 40ns and a fall time of 20ns. The output optical power differs below 0.2dB under different input optical polarization conditions. Experiment results verified our structure design and some problems were discussed then.