光学差分参量放大布里渊时域分析优化研究

为了优化设计基于光学差分参量放大的布里渊光时域分析抽运的脉冲编码形式以及斯托克斯光与反斯托克斯光脉宽差,采用微扰法和小信号近似法,获得了探测光与斯托克斯光脉冲、反斯托克斯光脉冲在较小作用区域内的脉冲响应,对其性能进行了理论分析与数值验证。结果表明,相位斯托克斯光脉冲可有效压缩布里渊增益谱宽,提高布里渊信号信噪比;当斯托克斯光与反斯托克斯光传感脉冲脉宽差为8ns时,探测光布里渊增益最大。这一结果对进一步分析基于光学差分参量放大的布里渊光时域分析系统性能以及开展相关实验研究是有帮助的。     

Raman amplification of Stokes pulse in ultra-small silicon-on-insulator optical waveguide

The stimulated Raman amplification of picosecond Stokes pulse is numerically investigated in ultra-small silicon-oninsulator optical waveguide. Numerical results show that we obtain the gain of up to 30-dB for weak Stokes pulse in the copropagation configuration for 10 mm Jength waveguide using high intensity pump oPtical pulse. The peak gain, purse width, rise time, and fall time of Stokes pulse will experience the variation course of decaying then increasing with increasing waveguide length. The time delay of output Stokes pulse is controlled by adjusting the initial time delay of both pump and Stokes pulses.     

Theory of the synchronously pumped fiber Raman laser

Analyses of the synchronously pumped fiber Raman laser are presented under the parabolic approximation for gain shaping in both frequency and time domains. A master equation for the Stokes pulse consists of the group velocity dispersion of the fiber, the gain dispersion of the stimulated Raman scattering, a gain-shaping term due to the pump curvature, small depletion, and a walk-off effect. The pump power dependences of the Stokes power and the pulse width and the threshold condition are revealed. The frequency tunability of the present laser is also discussed. It is shown that the oscillation wavelength (carrier frequency of the Stokes pulse) will change linearly with Stokes power because of walk off during depletion.     

Wavelength-tunable multicolor Raman soliton generation using an ellipse polarized pump pulse and highly birefringent optical fibers

Wavelength-tunable multicolor optical pulse generation based on the self-frequency shift of a Raman soliton was demonstrated. An ellipse polarized pump source, a highly birefringent (HB) optical fiber, and a highly nonlinear dispersion-shifted fiber were used to generate Raman soliton pulses. The wavelength was tuned by controlling the polarization of the pump source. Raman soliton pulses with six different colors and low wavelength crosstalk under 20 dB have been successfully generated.     

色散位移光纤中参量放大和拉曼散射增益谱特性

根据高双折射色散位移光纤中参量放大和拉曼散射共同作用下的耦合波方程,通过引入拉曼增益的洛伦兹模型,研究了增益谱随相关参量的变化关系。结果表明,增益谱只与三阶色散项的大小及四阶色散项有关;在正常色散区sgn(β4)=1的较大输入功率区域,T频率斯托克斯波增益谱呈现单一峰值。所以,利用色散位移光纤,可提取单一T频率脉冲。     

G652光纤中背向自发拉曼散射的增益特性

讨论了背向自发Raman散射脉冲在自生分布式G652光纤Raman放大器中传输的增益特性。实验发现，反Stokes Raman（ASR）和Stokes Raman（SR）自生分布式脉冲光纤Raman放大器的阈值抽运峰值功率是25．4W和18．0W。在入射功率为52W时，ASR和SR的增益分别为5．0dB和8．6dB。放大的反Stokes和Stokes背向自发Raman散射光时域反射（OTDR）曲线上放大的阈值时间位置随激发功率的增高前移并具有规律性。放大的ASR背向自发散射强度受光纤温度调制，具有温度效应，已应用于远程分布光纤Raman温度传感器系统。     

Noise characteristics and statistics of picosecond Stokes pulsesgenerated in optical fibers through stimulated Raman scattering

The growth of the Stokes pulse from spontaneous noise during stimulated Raman scattering of picosecond pump pulses in optical fibers, is investigated by using a Langevin-noise term in the coupled nonlinear Schrodinger equations, which include pump depletion, group-velocity mismatch, fiber dispersion, and self- and cross-phase modulation. The model makes use of the actual Raman-gain spectrum of optical fibers. Numerical simulations are used to examine the average behavior of the Stokes pulse, and shot-to-shot fluctuations that are likely to occur in practice. It is shown that the Raman-induced energy transfer is significantly affected by group-velocity dispersion for pump-pulse widths shorter than 5 ps. Examination of the average temporal width shows that the Stokes pulse is initially as wide as the pump pulse, undergoes a gain induced compression and then rebroadens for distances longer than a walk-off length. The effect of varying pump and fiber parameters is to change the minimum value of the Stokes-pulse width, and the distance at which the minimum occurs. The shot-to-shot energy and pulse-width fluctuations initially increase before being reduced at fiber lengths longer than the walk-off length. The primary effect of dispersive and nonlinear effects is to change the distance beyond which fluctuations decrease     

Influence of Raman effect on the noise characteristics in a dual pump FOPA

Influence induced by Raman effect on the noise characteristics of a depleted and lossy dual pump fiber optical parametric amplifier (FOPA) is investigated. Taking the Raman effect into account, the modified coupled amplitude equations are firstly built, then the influences of Raman effect on the stokes and anti-stokes wavelengths with different initial signal powers are further analyzed. Besides, the effect on the FOPA gain is also shown with the same initial signal power and constant noise figure (NF).     

200-nm-bandwidth fiber optical amplifier combining parametric andRaman gain

Theory shows that the gain bandwidth of a one-pump fiber optical parametric amplifier (OPA) using highly nonlinear fiber (HNLF) could be more than 200 nm. Under these circumstances, the OPA gain would overlap the pump-induced Raman gain. We have studied the combined effects of OPA and Raman gain theoretically and experimentally. The experimental results demonstrate a 200-nm bandwidth from a single fiber-optical amplifier and also verify that the influence of the Raman effect is relatively small, as predicted by the theory     

声光调Q内腔式Nd:YAG/RTP级联拉曼激光特性

报道了基于磷酸钛氧铷（RTP）晶体的内腔式级联拉曼激光输出特性。采用半导体激光端面抽运声光调Q Nd:YAG晶体产生的1 064 nm激光作为基频光,尺寸为4420 mm3、沿x轴切割的RTP晶体作为拉曼增益介质。分别对X（ZZ）X和X（YY）X几何配置的RTP拉曼激光系统进行实验研究。X（YY）X几何配置的拉曼增益相对较低,导致腔内不同非线性频率变换过程的竞争,只测量到对应光参量振荡激光的输出。在X（ZZ）X几何配置下成功获得了271 cm-1和687 cm-1两个拉曼频移共同参与级联拉曼激光输出。高阶Stokes光随着抽运功率的增加而依次出现。在10 W入射抽运功率和15 kHz脉冲重复频率下,获得了总平均输出功率480 mW,转化效率4.8%的多波长激光输出。波长涵盖了1 000~1 200 nm之间各阶Stokes光。     

Influence of pump parameters on two-pump optical parametric amplification

An analysis of two-pump optical parametric amplifiers is proposed in order to evidence strategies to project and develop flat two-pump fiber parametric amplifiers (2P-OPAs). Amplifier gain profile is evaluated through a model that takes into account the four-wave mixing process with pump depletion. Disturbing influence of degenerate three-wave mixing processes is separately addressed. Through the analysis, important 2P-OPA project guidelines are obtained. Theoretical forecasts are confirmed by experimental measurements on different 2P-OPAs, realized by changing power and spectral allocations of the two pumps, obtained by Raman amplification.     

Theory of stimulated Raman scattering in optical fibers in thepulse walkoff regime

It is shown that the process of forward stimulated Raman scattering in a single-mode fiber, which involves the pump pulse and the first Stokes wave, is an exactly soluble problem, provided that the temporal duration of these waves is sufficiently long. The analysis takes into account the effects of pulse walkoff arising from the dispersion of the fiber as well as self- and cross-phase modulation. The procedure is applied to two examples: the first is that of stimulated Raman scattering as it builds up from spontaneous Raman emission; the second is that of launching pump and Stokes pulses     

The performance limit of coherent OTDR enhanced with optical fiberamplifiers due to optical nonlinear phenomena

This paper theoretically and experimentally clarifies the limit of incident optical pulse power in coherent optical time-domain reflectometry (C-OTDR) enhanced with optical fiber amplifiers. The critical pulse power, at which the performance of C-OTDR is degraded by the effect of optical nonlinear phenomena in a single-mode optical fiber, depends on the amplified optical pulse waveform and the pulse width. For a pulse width of 1 μs or longer, the incident pulse power is limited by the effect of self-phase modulation (SPM). When an optical pulse having a power gradient within the pulse width is incident to a single-mode optical fiber, the optical frequency of the backscattered signal is shifted by SPM, and the center frequency of the signal moves outside the receiver band, so the sensitivity of C-OTDR is degraded. For a pulse width of 100 ns, the incident optical pulse power is limited by four-wave mixing (FWM) which transfers the energy from the incident optical pulse to Stokes and anti-Stokes light as a result of the interaction between the incident optical pulse and amplified spontaneous emission. This paper also demonstrates the high performance of C-OTDR enhanced with EDF A's with 48, 44, 39, and 29 dB single-way dynamic ranges for pulse widths of 10 μs, 4 μs, 1 μs, and 100 ns, respectively, limited by the effect of SPM or FWM. These results are believed to be the best performance of C-OTDR with EDFA's     

Picosecond stimulated Raman generation, pump pulse fragmentation, and fragment compression in single-mode optical fibers

Pump pulse depletion has been examined for high peak power (∼ 100 kW) 90 ps pulses from aQ-switched and mode-locked Nd:YAG laser in 4 m of single-mode optical fiber. Fragmentation of the fundamental and low Stokes Raman orders has been observed for this cascading process. Pulse compression using an interferometric technique has been carried out, obtaining compression ratios of up to times five, on these fragments which exhibited a negative frequency chirp.     

Limitations imposed by stimulated Raman scattering of 1550 nmhigh-energy pulse transmission

The limitations imposed by stimulated Raman scattering on 1550 nm high-energy pulse transmission in single-mode optical fiber are investigated. The generation of a Stokes pulse from an input pulse with peak power up to 60 W and duration on the order of 10 ns is experimentally studied and numerically simulated. This is the first demonstration of Stokes pulse generation in optical fiber from pump pulses within the 1550 nm telecommunications window. Experiment and theory show that there is an optimum input power for a given pulse duration and distance that maximizes the energy transmitted over long fibers     

YVO4激光抽运的G652光纤受激拉曼散射超宽连续谱的实验研究

用脉宽15ns、重复频率20kHz、中心波长为1064nm的全固态Nd：YVO4激光抽运2km的G652单模石英光纤产生受激拉曼散射(SRS)。得到分离的前三级斯托克斯谱和四级以上自1300nm至1700nm（光谱仪的截止频率)的超宽连续谱，并在光纤的零色散波长1310nm附近(四至六级斯托克斯频段上)观察到明显四波混频现象。     

低频移拉曼模式多阶级联的1.7 μm激光器

基于固体介质的拉曼频率变换是产生新波段激光的有效技术方案。利用1572 nm KTP光参量振荡器腔内泵浦KGW晶体,实现了1616 nm （2阶）、1638 nm （3阶）、1662 nm （4阶）、1686 nm （5阶）、1711 nm （6阶）拉曼激光输出,其中1711 nm占据主导地位。激光器最大总平均输出功率为1.13 W,最小脉冲宽度为20 ns。该多阶级联拉曼变频对应的单阶平均拉曼频移为86 cm?1,与文献报道的KGW晶体低频拉曼模式相吻合。采用1572 nm KTP光参量振荡器作为拉曼激光器的腔内泵浦源有两个优势,一方面可以有效拓展拉曼变频的输出波长,另一方面可以基于光参量振荡器的脉冲窄化特性为后续多阶拉曼转换提供高强度的泵浦光。通过引入多阶级联拉曼变频的方案,为有效利用固体介质非常规低频移拉曼模式提供了新思路。     

光纤参量放大器技术及其最新进展

介绍和论述了一种非常有实用前景的基于光纤非线性效应的光参量放大器(OPA)及其最新技术进展．最新发展揭示了它的很多技术特性优于传统的掺铒光纤放大器(EDFA)、半导体光放大器(SOA)和近年来很热门的光纤拉曼放大器(FRA)，如对信号的调制形式、比特率的完全透明性、相位共轭、超宽的增益带宽、很低的噪声指数和具备优异的全光波长转换功能．     

Raman amplifier model in single-mode optical fiber

Equations to describe the process of Raman amplification in single-mode optical fiber and Stokes and anti-Stokes spontaneous emission generation with conservation of photon number are derived from first principles. The numerical simulation of Stokes and anti-Stokes spontaneous emission is in good agreement with experimental results. The importance of the sometimes-omitted anti-Stokes spontaneous emission terms in wavelength-division-multiplexed situations for optical signal-to-noise ratio is demonstrated by the simulation of light propagation through transmission fiber with and without Raman amplification.     

拉曼增益对回音壁模式光学微腔的全光调制

基于光通信系统对于全光调制和全光开关等的需求,从理论上和实验上研究了拉曼增益对回音壁模式光学微腔系统共振模式的全光调制。理论分析表明,拉曼增益能够补偿回音壁模式光学微腔系统的损耗,进而改变微腔系统的耦合机制,在不对微腔系统做任何机械性移动的前提下实现对系统共振透射率的连续调制。实验中采用光纤锥耦合的二氧化硅微芯圆环腔,利用560W的低功率泵浦光引发的拉曼散射,波长为1 545.7 nm的信号光实现了13.5 dB的调制度,使得系统的耦合机制由欠耦合转化为临界耦合。