Study On Key Issues Of Optical Fiber True-Time Delay For Optical Controlled Phased Array Antenna

Optical fiber true time delay lines play an extremely important role inoptical buffer, optical time division multiplexing and optical informationprocessing, especially in microwave photonics application to opticalcontrolled phased array antennas (PAA). The fiber delay line (FDL)technology can provide ultra-wideband and low loss phase shift for PAAunits. It can also be used for synchronic phase controlling between diffierentsub antenna arrays.The FDL technology includes the design, implementation andmeasurement of the delay structure. This dissertation studies in detail thetechniques to prepare various FDLs, the method to precisely measure theFDL length with optical low coherence interferometer (OLCI) and thescheme to extend the rangeability of OLCI. Using these technologies, weconstructed a programmable microwave phase shifter with high precision anddesigned multi-wavelength optical beamforming network. Their microwavetransmission performance are measured and analyzed.The main contents of the dissertation are summarized as follows:1. The manufacturing method of high-precision FDLs, which is based onthe fiber fixture platform with a precise micrometer and microscopicobservation system, is proposed. Using simple microscopic observation andpitch controlling, we can achieve the precision cutting of the fiber up to0.1~0.2mm resolution.2. The method to improve measurement precision of short fiber lengthor fiber length change with OLCI is proposed and experimentallydemonstrated. It is realized by inserting a fiber-loop structure composed by acoupler and a circulator into the test arm of OLCI or optical low coherence reflectometer (OLCR), to artificially multiply the length of the fiber undertest. By measuring the multiplied fiber length under test, the measurementprecision is enhanced, which is at the cost of shortened measurement range.We analyze the performance of this method and give some suggestions tooptimize the power splitting ratio of coupler in the fiber loop. The precisionenhancement of10times is successfully achieved.3. A simple method is demonstrated to effectively extend the rangabilityof OLCR. This method is based on a cascaded structure of multi-stage fiberdelay lines laid in one arm of the OLCI. By choosing the number of stagesused in the cascaded fiber delay lines, the length of fiber under test can becontinuously measured within a large measurement range. As one typicalexample, one7-stage fiber delay line with measurement range of0.81km andthe spatial resolution of60μm are successfully realized.4. A programmable FDL structure composed of3×3couplers andsemiconductor optical amplifiers (SOAs) is put forward. Different microwaveshift can be obtained by tuning FDL with different true time delay. SOAs actas optical switching and optical gain component. The SNR (signal to thenoise ratio) of the microwave is analyzed and measured. It is helpful to studythe noise result due to the introduction of SOAs5. Optical beamforming network based on FDLs and dense wavelengthdivision multiplexing (DWDM) technology for PAA is proposed. We haveachieved3-stage FDLs with DWDM and2×2MEMS switches, and thebasic delay between the channels is about40ps. We measure and demonstratethe microwave shift performance with8status of the programmable fiber truetime delay.At the last, the dissertation summarizes the work and refines theinnovations. Technology foresight for the field of the microwave signal andoptical processing is given and suggestions of further work on FDLs arepresented.