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.     

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     

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…     

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     

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     

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     

Analysis of polarization independent optical amplifiers and filtersbased on polarization rotation in periodically asymmetricwaveguides

Polarization rotation in periodically asymmetric passive and active waveguides is described theoretically. The analysis is based on the vector wave equation and analysis of the coupled mode equations. It is shown that these periodically asymmetric active waveguides can be employed as polarization-independent optical amplifiers, and that strictly polarization-independent amplifiers require a rotation of an integer multiplier of π radians. An illustrative example of such an amplifier with a buried waveguide structure suitable for monolithic integration is analyzed. Polarization-insensitive passive Bragg filters employing, in addition to the ordinary grating, a periodically asymmetric perturbation are also considered, and polarization rotation in a distributed feedback laser filter is discussed     

偏振模色散仿真器特性研究

光纤通信线路的偏振模色散已成为高速、长距离光纤通信系统发展的主要障碍之一 ,其特性、测量以及补偿方法的研究成为目前光纤通信研究热点之一。偏振模色散仿真器 ,用于仿真传输链路的偏振模色散特性 ,不仅可用于偏振模色散补偿器 ,也可用于高速长距离光纤通信系统的规划设计等。本文分析了光纤偏振模色散仿真器的研究现状 ,归纳总结了现有偏振模色散仿真器的设计原理和结构特征 ,并用蒙特卡罗法对常用的偏振模色散仿真器的特性进行了数值模拟     

Observation of polarization property in near-field optical imaging by a polarization-maintaining fiber probe

We fabricated an original near-field scanning optical microscopy (NSOM) fiber probe made of polarization-maintaining and attenuation-reducing (PANDA)-type polarization-maintaining optical fiber, and observed the polarization property of propagation light in a polymer optical waveguide. The distribution of the transmission coefficient in polarization angles through this NSOM probe showed that the linear polarization is maintained in the two crossing directions: the fast and slow axes. The polarization degree parallel to the slow axis decreases from 1000:1 to 2:1 by bending the fiber probe and the decrease is independent of the bending direction. Using this PANDA-type NSOM probe, we investigated the polarization property of periodic intensity modulation. It was found that the intensity modulation was observed clearly with the electric vector parallel to the radius direction of the waveguide, but was observed vaguely with the electric vector perpendicular to the radius direction.     

光纤激光器光场谐振中的附加相移

一、引言 光纤激光器作为一种新型激光器或有源光纤器件为国内外研究者所注目。自80年代以来,从光纤激光器的激活介质到工作形式都有较大的发展。但所研究的激光器一般分为两类:掺杂晶体光纤激光器和掺杂玻璃光纤激光器。谐振腔的形式既有在光纤端面镀反射膜的封闭腔式,也有将光纤置于通常谐振腔的外腔式。光纤激光器与普通激光器的不同点在于:光场在腔内不仅受到反射镜的限制,还受到光纤波导的约束。本文从光纤激光器光场谐振条件出发,提出了光纤激光器中存在光场谐振中的附加相移,并导出了谐振频率与光纤波导参数的关系。