Phase-conjugate pump dithering for high-quality idler generation in a fiber optical parametric amplifier

We experimentally demonstrate a simple technique to cancel the idler broadening in a fiber optical parametric amplifier (OPA) by using two pumps phase-modulated 180/spl deg/ out of phase, one of them being obtained by four-wave mixing in an auxiliary fiber. The resulting OPA idler quality is comparable to that of the output signal.     

Record performance of parametric amplifier constructed with highly nonlinear fibre

Record performance from a two-pump parametric amplifier constructed with highly nonlinear fibre is reported. Equalised continuous-wave parametric gain of 40 dB was achieved over 33.8 nm without any gain-flattening elements. Maximal difference between signal and idler powers was measured to be 1 dB within the equalised gain band.     

Broad-band 88% efficient two-pump fiber optical parametric amplifier

We demonstrate, for the first time to the best of our knowledge, a highly efficient continuous-wave two-pump fiber optical parametric amplifier. We used a total pump power of /spl sim/280mW in a 14-km-long fiber and obtained 88% power transfer from pumps to signal and idler over 25-nm bandwidth centered at 1568 nm.     

10-GHz 0.5-ps Pulse Generation in 1000-nm Band in PCF for High-Speed Optical Communication

We achieved the first 10-GHz subpicosecond pulses in the 1000-nm band by employing the higher order soliton effect in a 190-m photonic crystal fiber (PCF). We obtained 0.5-ps pulses at 1063 nm by compressing 11-ps pulses from a harmonically mode-locked Yb fiber laser with a 10-GHz repetition rate, which was stabilized with phase-locked-loop technology. This light source is attractive in terms of realizing a hundreds-of-gigabits-per-second optical-time-division-multiplexing transmission over a low-loss PCF in the 1000-nm band     

A Design Theory for Wide-Band Parametric Amplifiers

A new exact design theory for a nondegenerate parametric amplifier with double-tuned signal circuit and single-tuned idler circuit is described. If the resistance of the signal circuit, which is neglected in previous papers, is considered, there exists a frequency band in which the amplifier gain is positive. In this paper the band characteristics of the gain are related to this frequency band. Slope parameters of the idler and signal circuits are normalized by the slope parameters which are associated with the diode itself. These normalized slope parameters are used to relate the actual circuit and gain-bandwidth characteristics. The slope parameter of the external signal resonator is related to the negative slope parameter of the diode, and bounds on this ratio are given over which stable amplification is possible. A design table which gives the coupling ratio and slope parameter of the external signal resonator is derived by computer calculation. Experiments were made at 19 GHz. Positive-gain bandwidth was around 4.0 GHz, and flat bandwidth at 10-dB gain was 2.4 GHz. The ratio of these bandwidths coincided with the theory.     

Investigation on gain characteristics in non-degenerate cascaded phase sensitive parametric amplifiers

We theoretically and experimentally show the impact of the ratio between the signal and idler generated from the PIA part on the gain characteristics in the continuous wave (CW) pump non-degenerate cascaded phase-sensitive fiber optical parametric amplifier (PS-FOPA). The results show that the length of highly nonlinear fiber (HNLF) used for generating the idler can cause the variation of power ratio between the idler and signal, which significantly affects the gain characteristics of the PS-FOPA under the small signal gain condition. To obtain high gain, it is better to choose long HNLF to generate idler. In our experiment, 5.5 dB gain and 18 nm bandwidth (on/off gain>10 dBm) in PS-FOPA can be achieved when 300 m-long HNLF instead of 200 m-long HNLF is used in PIA.     

Application of a Prechirp Technique to 10-Gb/s Transmission at 1064 nm Through 24 km of Photonic Crystal Fiber

The prechirp effect on 10-Gb/s transmission in the 1000-nm band over photonic crystal fiber (PCF) was investigated both experimentally and theoretically. We performed transmission experiments using a 24-km-long PCF whose optical loss and chromatic dispersion were 0.94 dB/km and$-$20 ps/nm/km at 1064 nm, respectively. We confirmed an improvement in the bit-error-rate performance after the transmission, namely a “negative power penalty” of about$-$0.5 dB. Our experimental result and theoretical estimation revealed that the signal degradation induced by the chromatic dispersion can be effectively suppressed by employing the prechirp technique with a conventional$Z$-cut lithium niobate modulator.     

Demonstration of an Integrated LiNbO $_3$ Synchronized Double Phase Modulator and Its Application to Dual-Pump Fiber Optical Parametric Amplifiers and Wavelength Converters

We report the fabrication of an integrated LiNbO₃ Y-junction synchronized double phase modulator fully packaged for RF-application up to 40 GHz. This optical modulator allows for delivering simultaneously counter-phase high-speed modulation and coupling for two input channels. It was designed for application to fiber-optical parametric amplifier and wavelength converters for suppressing idler spectral broadening and signal gain distortion caused by phase modulation itself. With this component, Idler spectral broadening suppression is experimentally demonstrated over all the parametric gain band of a two-pump parametric amplifier operating in the 1.55-mum region. In addition, we present a useful technique for straightforward and full coupling of the pumps and the signal.     

基于光子晶体光纤的宽带色散补偿光纤的设计

采用矢量光束传输法(VBPM)对小纤芯光子晶体光纤(PCF)的色散特性进行了数值分析,研究发现通过调节光子晶体光纤的结构参数可以灵活的对其色散补偿值进行调整,能够实现C L波段(1 530～1 565 nm)的宽带色散补偿功能,并且对标准单模光纤的色散斜率有很好的补偿.在∧=1.0μm,d/∧=0.7时,1 550 nm处的色散值可以达到-339.1 ps/(km×nm),相关色散斜率(RDS)可以达到0.003 2 nm-1,能够有效的对标准单模光纤进行色散斜率补偿.     

基于光学参量振荡器的高分辨率CARS光谱研究

提出了一种基于三硼酸锂（LBO）晶体的飞秒绿色泵浦光学参量振荡器（OPO）,其采用飞秒525 nm绿光光纤激光器作为泵浦源。OPO产生的信号光其可调谐的光谱范围由780～940 nm,光功率可达到250 mW以上;闲频光可调谐范围从1630～1190 nm,光功率可达到300 mW以上。利用本系统可在波数为1330 cm－1和6650 cm－1之间进行相干反斯托克斯拉曼散射（CARS）光谱测量。由于脉冲啁啾,光谱分辨率达到100 cm－1,与时间带宽限制脉冲激励源相比,分辨率达到后者的2.5倍。     

Mode selection in doubly-resonant optical parametric oscillators

By using a computer model to calculate the threshold for each signal and idler mode-pair in doubly resonant optical parametric oscillators, we investigate the effects of the three principal tuning parameters (temperature, cavity length, and pump wavelength) on the mode selection. Through consideration of type I and type II noncritical phase-matched geometries for lithium triborate optical parametric oscillators, we illustrate that the tuning behavior depends on the difference between the refractive indexes experienced by the signal and idler fields     

轨道角动量纠缠光子对联合探测概率的研究

研究了自发参量下转换过程产生的轨道角动量纠缠光子对的联合探测概率,在忽略光子的偏振和晶体为薄晶体的情况下推导出轨道角动量纠缠光子对的联合探测概率的表达式。研究表明：自发参量下转换过程中抽运光、信号光以及空闲光的参数（束腰、轨道角动量和径向指数）的大小决定着纠缠光子的联合探测概率。     

Characterization and modeling of a noncollinearly phase-matchedfemtosecond optical parametric oscillator based on KTA and operating tobeyond 4 μm

We describe the design and operation of a critically phase-matched femtosecond optical parametric oscillator based on KTA. By employing a small pump-signal noncollinear angle, tuning of the idler to beyond 4 μm is achieved using a Ti:sapphire pump laser. A Gaussian-beam model is described which can be used to identify the optimal noncollinear phase-matching geometry. Idler and signal pulses are characterized fully both temporally and spectrally and interferometric autocorrelation data at 3.5 μm showing idler pulses of only eight optical cycles duration are presented     

中红外高能量输出复合腔抽运光参量振荡器

报道了采用复合腔技术研究Nd:YAG激光抽运LiNbO₃晶体光参量振荡器(OPO)的实验研究结果。得到OPO输出单脉冲平均能量56.4mJ,闲频光(3097nm)脉冲平均能量22.8mJ,脉宽8ns,抽运光转换成参量光输出效率46%(重频1Hz～10Hz)。测得角度调谐的波长范围是:信频光1479nm～1621nm,闲频光3097nm～3793nm。     

CW periodically poled LiNbO3 optical parametricoscillator model with strong idler absorption

An analytical model is described for predicting the gain and performance of CW singly resonant optical parametric oscillators with strong idler absorption, strong pump depletion, and thermally induced dephasing. Pump and signal beam focusing effects are included by using the Guha et al. h_sm parameters. It is shown that significant parametric gain can be generated with an idler absorption-length product exceeding 10, and in some cases idler absorption is seen to enhance the pump depletion by impeding back conversion. The model accurately predicts current experimental results with weak idler absorption. Validation with strong idler absorption awaits experimental measurements to be completed     

高光束质量闲频光谐振中红外MgO:PPLN光参量振荡器

报道了采用纳秒脉冲激光器泵浦基于掺杂氧化镁周期极化铌酸锂(MgO:PPLN)晶体的高光束质量、闲频光谐振中红外光参量振荡器。通过选取曲率半径为200 mm的凹面输入镜和平面输出镜来建立平凹腔,实现了高光束质量的近-中红外激光输出。当输入的最大泵浦能量为21 mJ时,输出信号光和闲频光的最大能量分别为3.2 mJ和1.12 mJ,对应信号光和闲频光的斜效率分别为24%和9%。通过在25～200℃范围内改变MgO:PPLN晶体温度,实现信号光波长1.505～1.566μm和闲频光波长3.318～3.628μm的激光调谐输出。由于闲频光单谐振的光参量振荡器具有较大的衍射损耗和光束发散角,可以提高输出闲频光的光束质量。采用刀口法测量得到中红外激光在两个正交方向的光束质量因子分别为M_x²≈1.2和M_y²≈1.2。     

Hot spots in parametric fluorescence with a pump beam of finitecross section

The parametric fluorescence from a nonlinear crystal driven by a pump beam of finite cross section displays a hot spot in the angular and spectral distribution of the signal radiation. The hot spot in the signal radiation occurs where the pump and idler Poynting vectors are collinear. Similarly, a hot spot in the idler radiation is predicted when the pump and signal Poynting vectors are collinear. Signal photons entering the signal hotspot are generally not correlated in direction or frequency with idler photons entering the idler hot spot. We report experimental observation of the signal hot spot in a AgGaS₂ crystal pumped by a Nd:YAG laser and describe a theory developed to understand the phenomenon. Qualitative and quantitative comparisons of the theory and data show good agreement     

Stabilization of the Gain versus Frequency Characteristics of Parametric Amplifiers at High Input Signal Levels

Decreasing the negative bias voltage of varactor diodes in a parametric amplifier causes the gain versus frequency characteristic of the amplifier to shift to the higher-frequency side, resulting in a so-called "positive slope" at the signal center frequency. The same happens when the pump power is increased or when the signal power is increased, but in the latter case only when the idler circuit load resistance is below a certain value. The slope of the gain characteristic can be partially or completely compensated by detuning the signal-circuit characteristic relative to the gain versus freqnency characteristic in such a way that the latter is located on a certain point of the left or right slope of the signal-circuit chara-teristic, or by resistive loading of the idler circuit. Complete cancellation was achieved in the range from -30 to -20 dBm signal input power by using both methods simultaneously on a practical model of a parametric amplifier operating at a signal center frequency of 3.95 GHz and a pump frequency of 11.76 GHz. The loading of the idler circuit was done by drawing a little rectified diode current. The necessary increase in pump power, in order to maintain the same gain as with both signal and idler circuits tuned to resonance, was less than 3 dB, the increase in noise figure a few tenths of 1 dB from a typical value of approximately 3 dB.     

正弦型相柑位调制对闲频光展宽抑制的研究

理论分析了双抽运光纤光参量放大POPA系统中抽运光相位调制对闲频光光谱展宽的影响,提出可以采用多个耦合的低频正弦信号对两路抽运光进行反相相位调制,在提高受激布里渊散射(SBS)阈值的同时抑制闲频光光谱的展宽。通过采用300MHz与900MHz的耦合信号作为调制信号,实验演示了该方案的可行性,得到无展宽的闲频光。比较了传统PRBS信号作为调制信号的方案,发现采用正弦调制信号对系统器件的性能有更好的容忍度。     

Influence of the Stimulated Raman Scattering on the Four-Wave Mixing Process in Birefringent Fibers

The influence of the stimulated Raman scattering in the four-wave mixing process in high birefringent fibers is theoretically analyzed. We consider the dual pump configuration in both co-polarized and orthogonal polarization schemes and treat simultaneously the stimulated Raman scattering and the four-wave mixing processes. The obtained results are valid even when the shift between the pumps and signal lies inside the Raman band. Results show that when the phase-matching condition is achieved the generation of the idler wave is mostly dependent on the real part of the fiber nonlinear response function, whereas the amplification of the signal wave is mostly dependent on the imaginary part. Results also show that when the phase-matching condition is satisfied the optical power evolution of the signal and idler waves for small frequency detunings are mostly described by the anisotropic Raman response of the fiber, whereas for high frequency detunings the isotropic response dominates. Our analysis also shows that the stimulated Raman scattering can increase the efficiency of the four-wave mixing process, for certain frequency detunings.