All-Optical Sampling Using Nonlinear Polarization Rotation in a Single Semiconductor Optical Amplifier

We propose a novel all-optical sampling method using nonlinear polarization rotation in a semiconductor optical amplifier. A rate-equation model capable of describing the all-optical sampling mechanism is presented in this paper. Based on this model, we investigate the optimized operating parameters of the proposed system by simulating the output intensity of the probe light as functions of the input polarization angle, the phase induced by the polarization controller, and the ori- entation of the polarization beam splitter. The simulated results show that we can obtain a good linear slope and a large linear dynamic range,which is suitable for all-optical sampling. The operating power of the pump light can be less than lmW. The presented all-optical sampling method can potentially operate at a sampling rate up to hundreds GS/s and needs low optical power.

Towards 640 Gbit/s wavelength conversion based on nonlinear polarization rotation in a semiconductor optical amplifier

Taking into account ultra-fast carrier dynamics, this paper models 640 Gbit/s wavelength conversion scheme based on nonlinear polarization rotation （NPR） in a single semiconductor optical amplifier （SOA） and investigates the performance of this kind of wavelength conversion scheme in detail. In this model, two carrier temperature equations are introduced to substitute two energy density equations, which reduce the complexity of calculation in comparison with the previous model. The temporary gain and phase shift dynamics induced by ultra-short optical pulses are numerically simulated and the simulated results are qualitatively in good agreement with reported experimental results. Simulated results show that non-inverted and inverted 640 Gbit/s wavelength conversions based on NPR are achieved with clear open eye diagrams. To further investigate the performance of the non-inverted wavelength conversion scheme, the dependence of output extinction ratio （ER） on some key parameters used in simulation is illustrated. Furthermore, simulated analyses show that high performance non-inverted wavelength conversion based on NPR can be achieved by using a red-shifted filtering scheme.

Nonlinear Polarization Rotation Characteristic Phenomenon in a Bulk Semiconductor Optical Amplifier

The phenomena of polarization rotation induced by self-modulation in semiconductor optical amplifier (SOA) are analyzed theoretically. The relationship between polarization parameters and gain as well as phase is obtained by the correlation parameter of ellipse polarization and SOA nonlinearity polarization rotation theory. The experiment employs polarizer drive by walking electromotor and power meter, the light power of 360 degree is measured. The transformation law of output polarization power components is found for obvious polarization rotation in the selected coordinate axes based on connection of polarization state in difference axes. Using this law make the manipulation easily on getting ideal polarization state. It can offer a fine method to realize all-optical switch and other logic elements in experiment. This work is of great significance for the applications of SOA nonlinear polarization rotation at high-speed all-optical signal processing and all-optical logic gate.

Noise-like pulse generation from a thulium-doped fiber laser using nonlinear polarization rotation with different net anomalous dispersion

A mode-locked thulium-doped fiber laser(TDFL) based on nonlinear polarization rotation(NPR) with different net anomalous dispersion is demonstrated. When the cavity dispersion is-1.425 ps^2, the noise-like(NL) pulse with coherence spike width of 406 fs and pulse energy of 12.342 nJ is generated at a center wavelength of 2003.2 nm with 3 dB spectral bandwidth of 23.20 nm. In the experimental period of 400 min, the 3 dB spectral bandwidth variation, the output power fluctuation, and the central wavelength shift are less than 0.06 nm, 0.04 d B, and0.4 nm, respectively, indicating that the NPR-based TDFL operating in the NL regime holds good long-term stability.

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 pulses as optical sampling pulses. The system achieved high temporal resolution and high sensitivity using a 30 mm length PPLN with quasi phase match period of 19.3 μm and 151 fs sampling pulses which were generated by passive modelock fiber laser based on nonlinear polarization rotation （NPR）. Clear eye-diagram of 10 Gbit/s non-return-to-zeros （NRZ） pseudorandom binary sequence （PRBS） optical signal were successfully reconstructed by this system.

Temporal contrast enhancement by nonlinear elliptical polarization rotation in a multi-pass cell

We demonstrate the simultaneous temporal contrast improvement and pulse compression of a Yb-doped femtosecond laser via nonlinear elliptical polarization rotation in a solid state multi-pass cell.The temporal contrast is improved to 109,while the pulse is shortened from 181 to 36 fs,corresponding to a compression factor of 5.The output beam features excellent beam quality with M^(2) values of 1.18×1.16.The total efficiency of the contrast enhancement system exceeds 50%.This technique will have wide applications in high temporal contrast ultra-intense femtosecond lasers.

Investigation of ellipticity and pump power in a passively mode-locked fiber laser using the nonlinear polarization rotation technique

An elliptical initial polarization state is essential for generating mode-locked pulses using the nonlinear polarization rotation technique. In this work, the relationship between the ellipticity ranges capable of maintaining mode-locked operation against different pump power levels is investigated. An increasing pump power, in conjunction with minor adjustments to the polarization controller＇s quarter waveplate, results in a wider ellipticity range that can accommodate mode-locked operation. Other parameters such as noise, pulsewidth, and average output power are also observed to vary as the ellipticity changes.

基于半导体光放大器的明暗激光脉冲研究

为了解决激光明脉冲在光通信和光纤传感等领域的应用瓶颈,设计了一种基于半导体光放大器(SOA)的锁模光纤环形激光器,该激光器由SOA、偏振控制器、滤波器和起偏器等构成。分析了横电/横磁(TE/TM)模式光场经历SOA时的增益比值和相位差的变化机理,研究了环腔内总色散管理与SOA动态增益的关系,获得了稳定输出的明脉冲和暗脉冲,以及2种类型脉冲的动态演变过程。实验结果表明:当SOA的工作电流为242 mA时,成功获得脉冲重复频率均为14.83 MHz、脉宽为1.1ns的明脉冲和脉宽为0.95ns的暗脉冲,并验证了在相同工作电流时,暗脉冲的强度显著大于明脉冲的强度。

环形铥光纤激光器中台阶形脉冲的产生

研究了基于非线性偏振旋转(NPR)锁模的铥光纤激光器中台阶形脉冲的产生。通过在NPR锁模器件前后各引入一段长度分别为100 m和350 m长的SMF-28光纤以增强腔内非线性和积累负色散,得到底座宽度为50 ns,重复频率为615.6 kHz,信噪比为55 dB的双波长(波长分别为2025 nm和2034 nm)台阶形脉冲。发现仔细调节偏振控制器和改变泵浦功率可以精细调节台阶形脉冲的形态。通过研究发现台阶形脉冲是由两个矩形脉冲组合而成,且前后泵浦对两个矩形脉冲的影响不同,通过改变偏振态能实现能量在前后两个矩形脉冲之间的转化。本实验为研究被动锁模光纤激光器脉冲动力学和脉冲整形提供了良好的实验平台。

重频可调谐U波段被动谐波锁模光纤激光器

U波段(1 625~1 675 nm)高重频锁模光纤激光器在甲烷气体检测、扩展通信波段、光子显微镜、眼部手术等领域有广泛的应用前景。基于被动谐波锁模(Harmonic Mode-Locking, HML)的孤子自频移(Soliton Self-Frequency Shift, SSFS)技术是一种实现高重频U波段激光输出的有效方式。首先搭建了基于非线性偏振旋转(Nonlinear Polarization Rotation, NPR)的被动HML光纤激光器,并以此为种子源,通过级联的放大系统将输出功率最高放大至1.7 W。而后将放大的脉冲输入到一段反常色散的色散位移光纤(Dispersion-Shifted Fiber, DSF)中,利用SSFS效应将其中心波长频移至U波段。研究了其中三个重复频率(722.0、941.7、1 224.2 MHz)状态,系统地探究了脉冲重复频率对SSFS的影响。首次使用NPR被动HML光纤激光器作为SSFS效应种子源,实现了波长可覆盖整个U波段范围的GHz脉冲输出。

非线性偏振旋转光纤滤波器模拟

多波长光纤激光器在密集波分复用、非线性频率转换、光纤传感等领域中具有重要应用价值。目前有多种实现多波长光纤激光输出的方式,其中,非线性偏振旋转(NPR)是一种比较常见的方式。理论模拟了NPR光纤滤波器在1550 nm附近的光谱滤波特性,主要包括:在不同的出射角度、光纤双折射和单模光纤长度的条件下,光谱滤波效应的变化情况;自由光谱范围与激光中心波长、正交偏振方向光程差之间的关系。通过对NPR光纤滤波器的光谱滤波效应进行系统地模拟,确立不同参数对滤波效应的作用规律,为相关的多波长光纤激光器的实验研究提供有效指导。

基于NPR效应的多波长SOA光纤激光器

为了实现稳定的多波长输出,设计了一种基于半导体光放大器(SOA)的非线性偏振旋转(NPR)效应的多波长光纤激光器。该激光器利用SOA的NPR效应,将SOA与其它偏振器件组合引起强度相关损耗(IDL),抑制SOA均匀加宽线宽内的模式竞争,在室温下实现了波长间隔为0.63 nm的35个稳定的多波长输出。此外,通过偏振调节实现了12 nm的波长调谐。最后,实验验证了增加保偏光纤(PMF)长度能够实现更小波长间隔的稳定多波长输出。

All-optical 2R regeneration based on self-induced polarization rotation in a single semiconductor optical amplifier

An all-optical 2R regeneration based on self-induced polarization rotation in a single semiconductor optical amplifier is presented.A theoretical model is built up to simulate the system performance.Experiment evidence is also provided.An extinction ratio improvement of 8.3 dB is obtained at a bitrate of 10 Gbit/s.In the BER measurements,6 dB improvement of the power penalty is achieved,clearly demonstrating the feasibility of the proposed scheme.Our approach has a simple structure,and allows photonic integration.

基于对称双模耦合器的波长可切换柱矢量光纤激光器

为了实现高纯度脉冲柱矢量光的输出,提出并搭建基于对称双模耦合器的波长可切换的被动锁模柱矢量全光纤激光器。根据光纤传输原理得到基模向高阶模转换的折射率匹配直径,运用模式耦合模理论及光束传播法模拟分析了对称双模耦合器的结构参数对模式选择及耦合特性的影响,采用熔融拉锥法并免去传统的模式选择耦合器制作上的预拉锥工艺制作了对称双模耦合器,通过搭建一套被动锁模柱矢量全光纤激光器实现了中心波长1039 nm和1068 nm可切换、脉冲时间间隔为113.8 ns、重频为8.78 MHz、脉宽660 ps/656 ps、最大输出平均功率为5.25 mW/5.2 mW、模式纯度大于97%的柱矢量光输出。实验验证了对称双模耦合器的可行性,为后续高纯度柱矢量光的获得提供一种可行的方案。

基于K-means算法的自动锁模光纤激光器

研究了一种基于K-means算法和非线性偏振旋转谐振技术的自动锁模传统孤子光纤激光器。实验中通过K-means算法对电动偏振控制器进行调节,利用示波器实时采集数据,并基于脉冲判决算法将脉冲分为基频锁模态和其他状态。当泵浦驱动电流为230 mA时,实现了1531 nm、脉宽为456 fs的基频传统孤子输出。然后,通过调节电动偏振控制器遍历激光器输出状态,并进行脉冲判决分类。最后,通过K-means算法将处于基频锁模态时电动偏振控制器旋转桨的角度按空间坐标系聚类分析。当光纤激光器处于非基频锁模态时,通过K-means算法调节电动偏振控制器,恢复到基频锁模状态。经过100次测试,从失锁或其他状态调节到基频锁模态点所需平均时间为0.25 s。该工作为实现高效、便捷的光纤激光器自动锁模提供了新的方案。

基于非线性偏振旋转锁模技术的光纤飞秒激光振荡器

基于非线性偏振旋转(nonlinear polarization rotation,NPR)锁模机制的光纤激光器因其结构紧凑、可靠性高而备受关注。基于这一锁模原理设计并搭建了掺镱光纤飞秒激光器。当双向泵浦功率为380 mW,在1030 nm波段获得了基频重复率为22.8 MHz的锁模脉冲。脉冲宽度为224 fs,平均功率180 mW,单脉冲能量8 nJ,10 dB带宽约为40 nm,信噪比大于50 dB。该激光器采用环形腔结构产生稳定的锁模飞秒脉冲输出,可实现自启动锁模。泵浦功率增加到1.6 W可观察到最高三阶被动谐波锁模,三次谐波对应68.5 MHz重复频率。该激光器由于在线宽、脉宽、脉冲能量上的优势,在光谱测量、拉曼成像等领域具有应用意义。

光纤中无波分裂脉冲的平坦超连续谱产生

基于无波分裂脉冲产生的平坦超连续谱被报道。笔者采用非线性偏振旋转(NPR)作为锁模方法来实现耗散孤子脉冲和无波分裂脉冲的切换输出。在0.3 W的泵浦功率下,获得了耗散孤子脉冲。脉冲宽度为5.8 ps,脉冲间隔为54 ns,与11.05 m的腔长一致,信噪比为55 dB,压缩后的脉冲宽度为0.61 ps。值功率可以被提升到1.18 kW。通过适当调整腔偏振态和增加泵浦功率,耗散孤子可以演化为无波分裂脉冲。随着泵浦功率的提高,脉冲宽度从11.7 ps增加到20.2 ps,几乎增加了两倍。经过计算,时间带宽积从23.9增加到53.43。较大的啁啾可以抵抗非线性相移的影响,从而避免脉冲分裂。无波分裂脉冲的脉冲能量可以提高到3.89 nJ,是耗散孤子脉冲能量的五倍。随后,使用耗散孤子和无波分裂脉冲作为种子源去获得超连续谱。结果表明,在锥形高非线性光纤中,无波分裂脉冲产生的超连续谱范围和平坦度均优于耗散孤子脉冲。基于耗散孤子脉冲和无波分裂脉冲产生的超连续谱范围为1400~2000 nm,覆盖了S波段、C波段、L波段三个主要通信波段,20 dB带宽分别为310.3 nm和426.4 nm。这项工作将有助于高能量脉冲光纤激光器的发展,并提高其在超连续谱产生和光通信领域的潜在应用。

基于多模光纤的时空锁模激光器的研究进展

介绍了时空锁模的基本原理和时空锁模的理论模型——吸引子解剖。从空间结构和全光纤结构两方面介绍了近年来国内外在时空锁模光纤激光器方面的研究进展,包括激光腔型的改进、输出性能的提升和实时动力学的观测等。最后分析了目前时空锁模激光器的优势和不足,并对其发展方向进行了展望:时空锁模激光器在产生高功率超短脉冲方面有着巨大的优势,但输出光斑质量差在一定程度上限制了它的实际应用;利用时空自相似演化、波前整形等技术提升光束质量将是未来时空锁模激光器的发展方向。

非线性偏振旋转被动锁模光纤激光器自动锁模电路

针对基于非线性偏振旋转(NPR)原理的被动锁模光纤激光器稳定性差和不能自行进入锁模状态的问题,本文设计了自动锁模电路,用于对激光器进行实时调控以获得稳定的锁模输出。该项设计利用高速光电探测器(PD)将NPR被动锁模光纤激光器输出的光信号转化为电脉冲信号,经过线性放大、整形处理后输出至单片机进行计数;单片机根据快速锁模判定算法判断该激光器的输出状态,并自动反馈调节加装在光纤激光器上的电控偏振控制器(PC),从而实现激光器的锁模稳定状态输出。实验结果表明,对于重复频率为6.238MHz的NPR被动锁模激光器,自动锁模电路能够在6ms内检测到失锁状态,在最长10.24s内自动搜索达到稳定锁模工作状态。对于重复频率在16MHz以下的NPR被动锁模激光器,自动锁模电路都能够快速地实现自行启动或将启动后因故失锁的状态调节回锁模状态,达到预先的设计要求,具有结构简单、成本低、功耗低及性能稳定等优点。

基于非线性偏振旋转效应的多波长掺铥锁模光纤激光器

运用非线性偏振旋转效应实现了一种掺铥锁模多波长光纤激光器.采用环形腔结构,以1 565nm半导体光源为泵浦源,3m长掺铥光纤为增益介质.利用非线性偏振旋转效应进行滤波.当泵浦功率在800mW时,通过调节光纤偏振控制器,激光器出现了被动锁模状态的脉冲输出,脉冲重复频率为3.178MHz,脉冲宽度为617ps.进一步增加泵浦功率,激光器进入多波长输出的工作状态.调节偏振控制器在室温下得到1~5个稳定的波长激光输出,边摸抑制比为40~60dB.