Characterization of ultrashort pulse formation in passivelymode-locked fiber lasers

Pulse formation in an all-solid-state passively mode-locked neodymium glass fiber laser is investigated by employing characterization techniques in the time, optical, and radio-frequency domains. The pulses are generated by a combination of passive amplitude modulation arising from nonlinear polarization evolution and passive frequency modulation due to quasi-soliton-like pulse shaping. Several distinct operation modes for ultrashort pulse generation are described and pulses as short as 38 fs are directly generated in the cavity     

Simulation of mode-locking by nonlinear polarization rotation in a semiconductor optical amplifier

We present a theoretical investigation of a mode locked laser that has a semiconductor optical amplifier (SOA) in its ring cavity. A mode-locked train of narrow pulses is obtained by combining nonlinear polarization rotation in the SOA and a polarization filter whose polarization axis is set such that the tail of optical pulses is removed in each cavity round-trip. The pulse narrowing process is demonstrated numerically and good qualitative agreement with experiments in our previous work is achieved. The pulse performance is largely determined by the ultrafast SOA gain dynamics and the cavity dispersion. Our simulation shows that the laser can produce a pulse train of subpicosecond pulsewidth at a repetition rate of 28 GHz for a moderate SOA current level. We observe that the laser can switch itself on or off depending on the initial pulse.     

利用非线性偏振旋转效应的可调谐多波长光纤激光器

提出了一种基于非线性偏振旋转(NPR)效应的可调谐多波长掺铒光纤(EDF)激光器,非线性偏振旋转诱导的强度相关非均匀损耗有效地抑制了均匀加宽增益介质掺铒光纤中的模式竞争,使光纤激光器在室温下产生稳定的多波长输出。其中利用保偏光纤和偏振相关隔离器组成的等效Lyot 双折射光纤滤波器作为波长选择器件,该滤波器可以通过选择合适的双折射光纤长度改变波长间隔,调节偏振控制器改变偏振态实现对波长的精密调谐。实验采用10 m长的保偏光纤(PMF),得到了波长间隔为0.35 nm、最多17个波长的稳定激光输出,并且实现了输出波长在4 nm范围内的连续可调谐。分别采用10:90、30:70和50:50的输出耦合器,激光信号分别从10%、30%和50%的端口输出,得到了最多17、14和13个波长的输出,其波长功率浮动分别为13 dB、10 dB和7 dB,另外,其最大输出功率分别为-7 dBm、-3 dBm和0 dBm。实验结果表明,输出耦合器输出端比例越大,输出波长就越少,各波长激光输出功率越平坦,且输出功率越高。     

非线性偏振旋转锁模光纤激光器数值模型

利用二能级Giles模型来计算掺铒光纤增益,并通过琼斯矩阵描述偏振控制器,提出了一种基于非线性薛定谔方程的非线性偏振旋转锁模光纤激光器的数值模型。该模型具有物理意义更加清晰、便于分析泵浦功率对锁模影响的优点。采用1.0 m长的掺铒光纤、5.8 m长的单模光纤和85:15的输出耦合器,当泵浦功率为25 mW时数值计算得到均方根宽度为0.30 ps的超短脉冲。研究了泵浦功率对锁模脉冲波形和光谱的影响,并讨论了泵浦功率与掺铒光纤中增益分布的关系。通过实验得到了锁模脉冲,其光谱形状与仿真得到的结果相似。测量了不同泵浦功率下脉冲的平均功率,变化趋势也与理论值吻合。     

非线性偏振旋转光纤激光器的原理与关键技术

非线性偏振旋转(NPR)锁模光纤激光器以其结构简单紧凑而备受关注,是光通信系统、光传感和光探测等的理想光源。介绍了非线性偏振旋转锁模激光器的研究进展,分析了其工作原理、锁模方法及关键技术,并按其腔内净色散的不同进行分类,分析其各自特点以及通过色散管理获得高能量超短脉冲的方法。     

Stable multiwavelength dispersion-tuned actively mode-locked erbium-doped fiber ring laser using nonlinear polarization rotation

We demonstrate a stable multiwavelength actively mode-locked erbium-doped fiber laser at 10 GHz based on a dispersion cavity and nonlinear polarization rotation (NPR) effect. The dispersion cavity allows simultaneous multiple wavelengths to satisfy the round-trip condition and smooth wavelength tuning, while the NPR ensures the stable operation and supermode noise suppression. A simple model is developed to explore the optimal setting of the cavity. Simultaneous dual- and five-wavelength operation is experimentally investigated.     

高功率光纤激光器

1、引言。所谓高功率光纤激光器是相对于光纤通讯中作为载波的低功率光纤激光器而言(功率为mW级)，是定位于机械加工、激光医疗、汽车制造和军事等领域的高强度光源。高功率光纤激光器巧妙地将光纤技术与激光原理有机地融为一体，铸造了21世纪最选进和最犀利的激光器。即使是在激光技术发达的国家，光纤激光器也是尖端、神秘和充满诱惑的代名词、2002年6月，光纤激光器空降中国，震撼了中国激光学术界和产业界，并引起了至尊院士的关注。     

基于SOA非线性偏振旋转效应谐波锁模光纤激光器的数值研究

基于半导体光放大器(SOA)的锁模光纤环行激光器因其能得到高质量、高重复率的光脉冲而受到人们的广泛关注.在考虑SOA非线性偏振旋转效应下,建立了基于SOA的谐波锁模光纤激光器理论模型,利用该模型,着重研究了在不同SOA注入电流情况下,SOA非线性偏振旋转效应对谐波锁模光纤激光器输出脉冲波形、峰值功率及脉冲宽度的影响.研究结果表明:当SOA注入电流分别为102 mA和106 mA时,可以获得峰值功率为0.16 mW和0.56 mW、脉冲宽度为6 ps和19.8 ps的稳定锁模脉冲.     

Optical sampling system using periodically-poled lithium niobate waveguide and nonlinear polarization rotation mode-locked fiber laser

A novel design of optical sampling system has been developed by using sum-frequency generation (SFG) in a periodically-poled lithium niobate (PPLN) waveguide and using passive mode-locked fiber laser p...     

Polarization rotation in nonlinear bimodal optical fibers

The effect of nonlinear interactions on second-order modes in circular cross-section optical fibers is considered. In the linear case, analysis using the proper modes reveals that the fiber is a natural polarization rotator. An initial linearly polarized (LP) mode is actually a mixture of proper modes and recurs only periodically as the field propagates; at half-periods the input polarization and field pattern are rotated by 90°. Complete analytical expressions and numerical examples describing the modification of this phenomenon by nonlinearity are presented. For lower powers, the phenomenon persists with period increasing toward infinity at a transition point, beyond which complete polarization rotation is suppressed. At very high powers, the Kerr effect dominates: polarization is fixed in one direction and an LP mode does become a real mode of the system     

A broad-band single polarization optical fiber

The authors report on a single-mode optical fiber that transmits one and only one polarization state of the fundamental mode over a broad wavelength band (13%). The good broadband performance is attributed to the fiber's refractive-index profile, which mathematically allows only one polarization state to cutoff. The authors discuss general design principles and show that the mode field diameter is a qualitative indicator of the fiber's performance. The fiber's guided polarization state is similar to the fundamental mode of a step-index fiber in its low attenuation, 5.5 dB/km, and small mode diameter, 5.8 μm (both measurements at 840 nm). Most important, the fiber shows a broad single polarization band, 13%, a feature well described by the change in mode field diameter with wavelength of an ideal, circularly symmetry, W -profile fiber     

基于非线性偏振旋转锁模孤子光脉冲的产生及模拟

非线性偏振旋转(NPR)技术是被动锁模光纤激光器中实现超短脉冲的一种有效方式,因其结构紧凑,可靠性高而备受关注。本文利用基于NPR锁模的掺铒光纤激光器,在1557.7 nm波段,获得了脉冲宽度为1.35 ps,基频重复率为9.49 MHz的脉冲序列输出。利用耦合的金兹堡-朗道方程,数值模拟了激光器中锁模孤子光脉冲的产生,并对锁模建立过程中孤子时域和频域演化进行了分析,模拟分析和实验观察相吻合。该结果有助于加深人们对NPR锁模光纤激光器中孤子锁模动力学特性的理解。     

Self-coupled phenomena of semiconductor lasers caused by an optical fiber

Output intensity noise spectra of semiconductor lasers coupled to optical fibers with end-butt joints are measured to show periodic peaks with a fundamental frequency decided only by the fiber length. The frequency is found to coincide with the reciprocal of the roundtrip time of the light beam in the optical fibers.     

光纤激光器在空军中的应用

美国空军研究实验室的定向能管理组目前正在开发激光集成技术项目 (LITE) ,并已在Kirt land空军基地取得了稳步进展。光纤激光器虽已在照明器、指示器和传感器领域得到应用 ,但只有当其功率达到较高水平时 ,才能达到军事目的的应用。而实现这一目的的方法之一就是要使单元光纤激光器的功率达到最高可能的水平 (如千瓦级 )。为了达到用于定向能武器的目的 ,组合多个光纤激光器为同相位的阵列结构 ,可以大幅提高在靶上的功率。美国空军实验室已采用各种方法并投入大量资金 ,现已初见成效 ,但距 1 0 0kW或更高的目标仍相去甚远。目前 ,该实…     

Raman fiber lasers for optical communication application

We review the principle and characteristics of cascaded Raman fiber lasers in their telecommunication applications. The fundamentals of Raman fiber lasers are described, such as pumping scheme, fiber type and reflectors. We explain simple equations forcw laser operation as well as a possible way to calculate spectral width. We investigate the common issues in the use of Raman fiber lasers: theoretical optimization, control of the linewidth, suppression level of the other Stokes orders and relative intensity noise. Finally the more complex multiple-wavelength Raman fiber lasers are reviewed.     

Semiconductor lasers for coherent optical fiber communications

The current status of semiconductor lasers used in coherent optical fiber communications is reviewed for nonexperts in the field. The issues of spectral purity, tuning, modulation, and advanced fabrication methods for photonic integration are discussed, with examples drawn from current experimental devices     

光纤耦合光双稳半导体激光器的研究

介绍一种紧凑的、能以较低输入光功率工作的光学双稳器件,由光电检测器、光纤定向耦合器和半导体激光二极管组合而成的。描述了工作原理,解释所观测到的一些效应,例如滞后回线、微分增益以及记忆功能。     

光纤非线性偏振不稳定性的研究

光纤中的交叉相位调制将导致非线性双折射,从而引起偏振不稳定性。研究了光纤中线偏振光的入射角度与非线性双折射拍长的关系, 得出了入射偏振光接近快轴时,非线性使双折射增强,拍长变短的结论。这一结果与文献［２］ 的理论相反     

基于非线性极化旋转技术的640G全光解复用

考虑超快载流子动态特性,文章通过仿真详细分析了基于半导体光放大器的非线性极化旋转效应实现640Gb/s到80Gb/s的解复用方案.结果表明:开关窗口的上升沿随时钟脉冲能量的变化不是很明显,而FWHM和下降沿则随时钟脉冲能量的增加而增加.此外,在相同条件下,当输入的时钟信号为TE模式时,输出的解复用信号具有最高的信道压制比.     

Anisotropic polarization maintaining optical fiber ring resonators

Suppression of the polarization drift of optical fiber ring resonators is investigated both theoretically and experimentally by employing anisotropy in a polarization maintaining fiber ring. A general analytic expression for the transmission of the device is derived allowing the fiber modes to exhibit any combination of polarization crosstalk, differential loss or differential coupling. The analysis shows that a moderate level of ring anisotropy, such as that of 10 dB in line polarizer or polarization selective coupler, is sufficient to greatly suppress the drift of the eigenstates of polarization (ESOPs), finesse and resonant point, restoring the device's suitability for most practical applications. An inevitable consequence of introducing ring anisotropy is the loss of orthogonality of the ESOPs. This effect limits the anticipated benefit in high sensitivity applications. A practical anisotropic PMRR is demonstrated by inserting a thin film of nematic liquid crystal between the two halves of the polished coupler of the ring. This resonator demonstrates a polarization response immune to environmental perturbations