High-precision Fiber Delay

In comparison with electric delay line, Optical fiber delay lines(OFDL) have many advantages, such as, small size, low weight, broad bandwidth, no susceptibility to electro-magnetic interference, and squint-free array steering. OFDL are installed or to be installed on radar stations, satellites and communications field. The OFDL which has high precision, small size and high dynamic range is urgently needed in the field of application.The principle of OFDL is introduced and the developing situation which is at home and abroad is analyzed. In the design of topological structures, two structures are compared, because the structure of bypass cannot have small delay step and is hard to reach high precision, so we choose the difference structure. The error caused by an optical switch is analyzed, and we find that different topological structures have different influences in the precision of OFDL. The software MATLAB is used to get the best topological structure, by simulating, when the error caused by an optical switch is 1ps, the precision of optical fiber delay line can reach 2ps, and this method can be applied to any bit OFDL with arbitrary optical switches. In the choice of the key component, all of the optical switches are compared and we choose Magneto optical switch which has small size and high speed.In the research of method of measurement for high precision, many ways are analyzed including optical measurement and vector network analyzer. We choose the vector network analyzer to measure the length of the fiber, and the method is based on frequency domain method, that has high precision and is easy to measure for us. In the research of connection method for optical fiber, By using the work fixture and in the state of monitoring, we get good result in cutting the fiber and the precision can reach 1ps.The drive circuit and steering circuit which have high speed were finished, and the 5bit steering circuit is proved stable. By measuring, the switching time of the magneto optical switch is less than 20μs.At last, the optimal structure is used. The magneto optical switches and single mode fiber are used to build a 5bit OFDL. By measuring, when the step length is 100ps, the precision of the fiber delay line was better than 2.98ps, and the flatness of the loss is about 0.55dB.In the same state, the biggest difference of loss is 0.32dB at different temperatures.