Development Of Fiber Lasers And Their Applications In All-Optical Modulation Format Analyzer

With the rapid capacity enhancement of fiber optical transmission system,especially the upcoming commercial deployment of 5G communication technique,traditional optical signal monitoring schemes have been greatly constrained,due to the limited bandwidth of optoelctronic devices and the relaxation oscillation of electronic devices.Therefore,it is highly desired for novel solution of high-speed complex modulation format optical signal measurement and characterization.All-optical linear sampling technique is transparent to the bit-rate of optical signal,and capable to measure and obtain the full-field information of the optical signal,including amplitude,phase,and polarization,with high accuracy and low cost.Thus,it has attracted worldwide research interestes.As a key module of all-optical sampling system,optical sampling laser source plays a vital role in the wavelength measurement range of high-speed optical signals and characterization accuracy of complex modulation signals.Therefore,the research of sampling pulse laser source with low time jitter,high repetition rate,narrow pulsewidth and wide optical spectrum is the core technique for the development of high-speed all-optical modulation format analyzer.In this thesis,under the financial support from National Key Scientific Instrument and Equipment Development Project: The development of broadband high-speed optical signal analyzer,based on the theory of mode-locked fiber lasers,the implementation scheme of sampling pulsed laser source is comprehensively investigated in terms of scalar-vector soliton characteristics,tunable wavelength characteristics and the pulse stability.A femtosecond fiber laser suitable for all-optical modulation format analyzer is designed and developped.Based on such pulsed laser,an engineering prototype of all-optical modulation format analyzer is successfully developed.Finally,we carry out the function and reliability test by the independent and accredited organization,together with the on-site performance comparison of commercial high-speed optical signals.The overall research outcomes of the thesis are summarined as follows:(1)The scalar-vector soliton characteristics of fiber laser is investigated.In a traditional mode-locked fiber laser based on nonlinear polarization rotation(NPR)effect,weak vector soliton is stimulated within a polarization-constrained all-fiber resonator by minpulating the local birefringence intensity and using a length of high-birefringence erbium-doped fiber(EDF)with beat length of 5 cm.With the help of all-fiber polarization resolved module,we successfully verify the generation of vector solitons.Meanwhile,scalar and vector solitons are identified to transform between each other in the cavity.(2)A fiber laser with weak polarization constraints in the cavity is designed,and CNT is used to assist the mode-locking,in order to realize the switching between NPR and CNT mode-locked mechanisms.When the NPR effect dominates the mode-locking,the output is vector soliton.When CNT dominates the mode-locking,the output is scalar soliton.Switchanble output of the scalar and vector soliton can be obtain by the same fiber laser.(3)A dissipative soliton fiber laser is designed and developped with the help of semiconductor saturable absorber mirror(SESAM)together with the nonlinear birefringence filtering effect.We can simultaneously realize wavelength tunable and multi-wavelength pulse outputs.The wavelength of dissipative soliton can be continuously tunable over a range of 7 nm by adjusting the linear birefringence of the cavity without additional filter devices,and the corresponding optical spectral remains stable.Dual-wavelength and triple-wavelength dissipative soliton outputs with a wavelength spacing of 9 nm can also be obtained,and the intensity of individual wavelength channel is the same.(4)The stability and reliability of soliton fiber laser are investigated.A compact all polarization-maintaining fiber(PMF)femtosecond laser is designed and developped.The polarization evolution at specific postions of the fiber cavity by using several segments of PMF with specific splicing angles.Thus,the NPR effect is introduced to realize the dissipative soliton at the normal dispersion region.The bandwidth of optical specral is 20 nm,and the repetition rate of pulse is 24.5 MHz.The pulsewidth can be successfully reduced to 260 fs after the compression outside the laser cavity.The proposed fiber laser shows excellent environmental stability over a long period of time.(5)Based on the self-developed broadband femtosecond fiber laser,an engineering prototype of all-optical modulation signal analyzer is developed,and the waveform,bit-rate and eye diagram measurements of commercial 100 G signal can be realized.For 128 Gbps polarization division multiplexing quadrature phase shift keying(PDM-QPSK)signals with 50 wavelength channels over a range of 1550-1570 nm,a characterization comparison with Agilent commercial modulation signal analyzer(N4391A)verifies that the engineering prototype can obtain almost the same time-domain characterization results as the commercial equipment.The eye diagrams of the engineering prototype have sharp rising and falling edges because of the mitigation of electronic bottleneck.However,due to the under-sampling characteristic of all-optical sampling,constellation is not as dense as that of commercial equipment.