Study On Key Technologies And Applications Of 40 GHz Mode-locked Picosecond Laser Signal Source

The high repetition-frequency picosecond pulse generated from the mode-locked fiber laser is an ideal signal source for the optical fiber communication system with ultra-high speed,large-capacity,and long-distance.Besides,it has the potential to be applied in quantum communication.In this thesis,we mainly study the key technologies of the mode-locked picosecond laser signal source,including the passive mode-locked ring fiber laser and its special output pulse,40 GHz high-order active mode-locked fiber laser as well as the control and stabilization of polarization states in fiber laser systems.Furthermore,the new applications of mode-locked picosecond laser in all-optical-clockrecovery and preparation of the quantum light sources are explored and studied.The main innovative results can be summarized as follows:(1)A mode-locked fiber ring laser with dual gain medium is proposed and developed based on the nonlinear polarization rotation of semiconductor optical amplifier.A passive mode-locked pulse,Q-switched pulse,and square-wave pulse is generated,respectively.Compared with the dissipative soliton resonance in the passive mode-locked laser,it has no peak power clamp effect.The width of the square-wave pulse can be varied continuously from 500 ps to 165 ns.(2)An open-loop controlled high-speed polarization stabilizer based on the Muller matrix is proposed and developed and experimentally verified.The average stability error for any objective polarization is about 0.035 rad,and the time cost is less than 300?s from any polarization to the objective,which is tens of milliseconds faster than the closed-loop controlled polarization stabilizer.We experimentally demonstrate the ability of the polarization stabilizer to recovery after a sudden and huge force and improve the quality of the received signal under environmental disturbing.(3)An incavity EDFA-enhanced mode-locked fiber ring laser based on the NPR effect of SOA is proposed and developed and experimental verified.A mode-locked pulse train with 1.36 ps pulse width and a high repetition rate of GHz is generated.By adjusting the system parameters,the rational harmonic mode-locked pulses of order 2,4,5,6,7,8,10 are obtained.Besides,by using high-order active mode-locking,the 40 GHz picosecond pulse train is achieved,and the signal-to-noise ratio in its RF spectrum is over 40 d B.The high-repetition picosecond pulse source can be directly applied to the ultra-high speed optical communication system(such as optical time division multiplexing system).(4)A novel all-optical clock recovery scheme based on high-order active modelocked fiber ring laser is proposed.The all-optical clock extraction of non-return to zero optical signals modulated by Pseudo-random binary sequences codes with clock frequencies of 6 GHz and 12 GHz is demonstrated.The optical clock signals of 6 GHz and 12 GHz are obtained.Compared with other clock extraction schemes of non-return to zero signal,the preprocess non-return to zero signal outside the cavity is nolonger needed in this scheme,which greatly reduces the system complexity.(5)Based on the active mode-locked fiber laser and the pulse attenuation method,a single photon source with an ideal Poisson distribution with a rate of about 10 k/s has been successfully fabricated,which can be directly used for quantum cryptography communication.Furthermore,the doubled frequency at 776 nm is obtained using 1552 nm mode-locked laser based on type I BBO crystal.And then using parameter down conversion of type II BBO crystal,the entangled quantum light source with a wavelength of 1552 nm in C-band is obtained,which can be used as the entanglement state light source for quantum communication.The high repetition-frequency active mode-locked picosecond laser signal source fabricated in this paper has the advantages of short pulse(?1 ps),high repetitionfrequency(40 GHz and above),adjustable repetition-frequency,good stability,etc.It is an ideal signal source for future ultra-high-speed optical communication.Meantime,a single photon source with adjustable frequency can be obtained directly by using this signal source,which can meet the requirements of high-speed quantum key distribution.Entanglement can also be prepared using nonlinear process and can be applied in quantum teleportation.