Research On Negative Coefficient Microwave Photonic Filter Based On A Novel Multi-wavelength Fiber Laser

Microwave photonics is a new interdisciplinary approach to enable the realization of microwave millimeter wave signal processing and transmission by using optical system's advantages of large bandwidth and low-loss.It is a hot research topic to microwave photonic filter among them because of the advantages of its anti-electromagnetic interference,low-loss,unrestricted electronic bottleneck,good design flexibility,etc.At present,the microwave photonic filter is widely achieved by incoherent method.So that the tap coefficient of the filter is positive and it can only realize low-pass filter,which limits the application range of the filter.Consequently,the design of microwave photonic filter with negative coefficient is particularly significant.Microwave photonic filter require a suitable tap optical source,which is generally used to spectral cutting broadband optical source,independent laser array or multi-wavelength fiber laser as tap optical source.Among them,the spectral cutting broadband optical source will introduce excessive system noise and reduce the performance of the filter,the independent laser array is very costly,the output spectrum of the multi-wavelength fiber laser is not ideal and is not easy to control,which leads to the low main sidelobe suppression ratio(MSSR)of the microwave photonic filter.In this thesis,the tunable negative coefficient microwave photonic filter is proposed using tunable multi-wavelength fiber laser based on high erbium-doped fiber as a tap optical source,which greatly improves the tunable,reconfigurable and MSSR of microwave photonic filter,the negative coefficient of microwave photonic filter is realized by a mixture of phase modulator and cascaded dispersion devices which is cascaded by single-mode fiber and F-P fiber ring.The main contents are as follows:1.Starting from the lasing mechanism of a multi-wavelength fiber laser with four-wave mixing effect,studied the influence of erbium ion doping concentration,the length of the gain medium and the power of pumping optical source on the lasing characteristics is in depth research.2.The mechanism and characteristics of phase modulation to intensity modulation conversion are discussed in detail.The conversion from phase modulation to intensity modulation is accomplished by using phase modulator and dispersion device.Thereby,the negative coefficient of microwave photonic filter is realized.3.Based on the above theory,we designed a tunable,narrow bandwidth,negative coefficient of microwave photonic filter.It uses the tunable multi-wavelength fiber laser as the tap optical source,and uses the Sagnac interferometer to shape the output signal of the tap optical source,which effectively improves the MSSR of the microwave photonic filter and realizes the reconfiguration of the filter.The free spectrum range of the microwave photonic filter can be tuned by changing the wavelength interval of the tap optical source and the length of the single mode fiber in the delay unit.4.The experimental platform is established for multi-wavelength fiber laser,and the main performance parameters of the laser are optimized.As many as 37 stable laser signals with 0.34nm wavelength interval are obtained by the experiment.5.Based on the experimental results of multi-wavelength fiber laser,the effects of coupling coefficient of Coupler in the F-P fiber ring,different length TODL,and different length SMF in the delay unit etc.on the microwave photonic filter performance are simulation studied.