Tunable slow and fast light with large bandwidth in the band-edge of gain spectrum of the wide band fiber optical parametric amplifier

We propose a novel method theoretically to generate the slow and fast light with large bandwidth and low gains, which is based on the parametric process in fiber. In our scheme, the wide band fiber optical parametric amplifier is employed and the whole signal bandwidth should be located at a certain frequency range of the band-edge of gain spectrum, and then signal waves will be delayed or advanced with low signal gains because of the peculiar feature of signal gain and phase shift. By changing the pump power, the delay time is continuously-tunable optically. The ultimate delay bandwidth and the delay bandwidth product are constrained by the shape of time delay spectrum. Our simulation verifies that 22.4 ps delay or advanced time for the bandwidth of 10 GHz with little distortion can be obtained at certain wavelengths in the optical communication waveband, and their gains are nearly zero. The tunable range is from 0 ps to 22.4 ps for the signal bandwidth of 10 GHz, and it is from 0 ps to 15.6 ps for the bandwidth of 15 GHz. This type of slow and fast light in wide band FOPA has the potential capability to produce the tunable slow and fast light for large bandwidth with low signal gains in future.     

Near-noiseless amplification of light by a phase-sensitive fibre amplifier

We report near-noiseless (noise figure of 0.4 dB, which is an improvement over the theoretical limit of 1.2 dB for a conventional laser amplifier with the same gain of 1.7 dB) optical amplification of laser light in a phase-sensitive fibre amplifier.     

Two-pump fiber optical parametric amplifiers with three-section fibers allocation

Based on the theory model of two-pump fiber optical parametric amplifier with single-section fiber allocation (FOPA-SF), a new two-pump fiber optical parametric amplifier with three-section fibers arrangement (FOPA-TFs) is put forward, which can provide gain bandwidth of more than 405 nm with optimum fiber parameters calculated by genetic algorithm. The numerical simulation is performed to investigate the influence of pump wavelength allocation on the gain spectrum of FOPA, and it is found that the smaller wavelength separation between the two pumps (Δλ) can provide more uniform gain over a relatively wide bandwidth. Moreover, the gain ripple owing to random fluctuations of zero-dispersion wavelength (ZDW) can be improved to a large extent by reducing pump separation Δλ.     

Theoretical study of gain distortions in dual-pump fiber optical parametric amplifiers

We study analytically and numerically the small signal gain in dual-pump fiber optical parametric amplifiers by including the phase modulation of the pump waves needed for practically increasing the stimulated Brillouin scattering threshold. As for the single-pump case, we show that large signal gain distortions are generated under co-phase modulation, which depend on the rise/fall time of the phase modulation and on the fiber dispersion slope. However, it is clearly confirmed that the counter-phase modulation scheme allows to efficiently suppress these gain distortions over the whole flat gain region. In addition, we demonstrate through realistic numerical simulations that this useful technique overcomes the additional impact of pump-phase modulation to amplitude modulation conversion and zero-dispersion wavelength variations.     

Multi-channel 80-GHz RZ pulse train generation based on parametric process in highly-nonlinear fiber

It is experimentally shown that six-channel C + L-band 80-GHz short pulse trains are generated based on parametric process in highly-nonlinear fiber (HNLF). By launching a pulsed pump and three-channel continuous wave (CW) lights into 1-km HNLF, three-channel signals are amplified and three-channel idlers are generated. The waveforms of the generated 80-GHz short pulses are measured by an auto-correlator. The bit-error-rate (BER) of each channel is analyzed numerically. In the back-to-back case, the power penalties of the generated channels are less than 1.5-dB.     

Thermal noise for SBS suppression in fiber optical parametric amplifiers

We demonstrate a new and simple solution to suppress stimulated Brillouin scattering in fiber optical parametric amplifiers. Cumbersome PRBS or sinusoidal generators used to broaden the pump spectrum are replaced by a filtered microwave noise source. Stimulated Brillouin scattering threshold can be increased up to large values still keeping an excellent quality of amplification of nonreturn to zero signals. The simplicity and the performances of this setup open the way for a wide variety of applications for FOPAs.     

Generation and amplification of dual-color femtosecond pulses by a noncollinear optical parametric up-conversion process

Noncollinear optical parametric up-conversion generation and amplification are realized in a thick β-barium borate (BBO) crystal, and a couple of visible femtosecond up-conversion laser pulses can be achieved by a femtosecond pulse at 800 nm as the pump sources. The theoretical and experimental results indicate that there exist phase-matching conditions for dual-color noncollinear parametric up-conversion generation and amplification, and their wavelengths can be tuned by rotating the BBO crystal. This parametric up-conversion generation and amplification can be attributed to three and five-wave mixing in a thick BBO crystal, and it shows the potential application on optical parametric chirped pulse amplification (OPCPA) to generate multi-color ultraviolet or visible femtosecond laser pulses pumped directly by femtosecond fundamental laser pulses without frequency-doubling or tripling.     

Optimized design of two-pump fiber optical parametric amplifier and its noise characteristics

In the paper, based on the pump depleted model of two-pump fiber optical parametric amplifier (FOPA), the simulations are done to indicate the effect of amplifier parameters on gain characteristics, such as the input signal power, the wavelength separation between the two pumps, the fiber length, the nonlinear coefficient and the fourth-order dispersion of fiber. By optimizing the amplifier parameters, when FOPA attains low gain-saturation, the FOPA has a higher gain, a broader flat gain bandwidth and a lower noise figure. However, with the enhancement of gain-saturation the parametric gain decreases, the flat gain bandwidth becomes narrow and the noise figure also increases.     

Bit-rate adaptive optical performance monitoring method for fiber communication systems

A novel bit-rate adaptive method, by varying the optical sampling rates alternatively, is proposed in this paper for optical performance monitoring. Firstly, the theoretical model and the differential software-synchronized algorithm are developed. Then, the results verify that different channel bit-rate can be estimated with high precision irrespective of the modulation formats and signal distortion caused by chromatic dispersion and nonlinearity along the fiber link. Employing the proposed bit-rate adaptive method, the eye diagrams and Q values of 10 Gbit/s, 40 Gbit/s and even higher bit-rate signal can be monitored by a single optical performance monitoring system without any prior knowledge about bit-rate or signal period. The method we propose in this paper has the advantage that different channel bit-rates can be adaptively estimated and the differential software-synchronized algorithm is much simpler.     

信号光的调制对基于光纤光参量放大光脉冲源的改善

在理论上从四波混频的强度耦合方程出发,给出了基于光纤光参量放大(FOPA)光脉冲的光场表达式,并进一步分析了信号光被相位调制或强度调制后,光脉冲的频率啁啾和强度演化.结论指出：若信号光被强度调制,对所生成脉冲宽度无明显的影响,但可以提高消光比;若信号光被相位调制,所生成的脉冲具有更大的线性正啁啾,可以在相同的抽运功率条件下得到比无相位调制时更窄的脉冲.实验上给出了10 GHz工作速率下的结果,其结果与理论分析符合得很好.通过信号光的相位调制,在05 W平均抽运功率条件下得到了消光比22 dB,脉宽为5 关键词： 光纤参量放大 四波混频 光脉冲源 频率啁啾     

Modulation of spatial spectrum in tunable two crystal optical parametric generator

We report on theoretical and experimental investigations of two crystal traveling-wave optical parametric generator (OPG). It is shown that the efficiency and angular structure of traveling-wave tunable OPG output depends on the distance between the two crystals. Air dispersion driven efficiency modulation at different OPG output wavelengths is observed experimentally and confirmed by theoretical calculations.     

Broadly tunable parametric line emission from β-barium borate on pumping with picosecond pulses

Tunable line emission (LE) over a large wavelength region (340–980 nm) is obtained by pumping thick crystals of β-barium borate (BBO) with picosecond pulses at 532 nm. Phenomena of group velocity dispersion, diffraction and phase matching take place simultaneously such that the radiation shows specific features that are characteristic of (i) strongly coupled fundamental and harmonic fields, (ii) amplified phase matched superfluorescence, (iii) conical emission and (iv) four wave mixing.     

Gain characteristics and optimization of dual-pump fiber optical parametric amplifier using two-section highly nonlinear fibers

In this paper the gain characteristics of two-pump fiber optical parametric amplifiers (FOPA) with two-section highly nonlinear fibers are analyzed numerically and the parameters of the fibers are optimized to reach broad and flat gain spectra using genetic algorithm. Different from the previous methods, here the space between two pump wavelengths and the parameter β₄ of the fibers are included as a pivotal factor in the optimization. The numerical simulation shows that using two-section practical high nonlinear fibers, the amplifier may reach 110 nm bandwidth covering 1495–1605 nm with 10.5 dB average gain and gain ripple of 0.17 dB, when the total pump power is 1 W.     

Einstein——Podolsky——Rosen entanglement in time-dependent periodic pumping non-degenerate optical parametric amplifier

The solution of the time-dependent periodic pumping non-degenerate optical parametric amplifier (NOPA) is derived when the pump depletion is considered both above and below thresholds. Based on this solution, the quantum fluctuation calculated shows that a high entanglement and a good squeezing degree of the parametric light beams are achieved near and above thresholds. We adopt two kinds of pump fields: (i) a continuously modulated pump with a sinusoidal envelope; (ii) a sequence of laser pulses with Gaussian envelopes. We analyse the time evolution of continuous variable entanglement by analytical and numerical calculations, and show that the periodic driven pumping also improves the degree of entanglement. The squeezing and Einstein-Podolsky-Rosen (EPR) entanglement by using the two pumping driven functions are investigated from below to above the threshold regions, the tendencies are nearly the same, and the Gaussian driven function is superior to that of the sine driven function, when the maximum squeezing and the minimum variance of quantum fluctuation are considered. In the meantime, the generalization of frequency degenerate OPA to frequency non-degenerated OPA problem is investigated.     

A novel actively and passively mode-locked semiconductor optical amplifier fiber ring laser

A novel actively and passively mode-locked semiconductor optical amplifier fiber ring laser was presented, where semiconductor optical amplifier provided cavity gain and introduced nonlinear polarization rotation, whereas, intensity modulator not only acted as modulator but also polarizer. The pulses with duration below 3 ps (FWHM) and peak power about 16 mW at a repetition rate of 10 GHz can be obtained in our system and the system stability may be enhanced. To investigate system parameters effects on mode-locked pulses, a theoretical model was developed.     

Controllable ultraslow light propagation in highly-doped erbium fiber

We report on slow light propagation induced by the coherent population oscillation in an erbium-doped optical fiber (EDOF). The slowdown of group velocity of light is demonstrated in a solid-state material at room temperature. We observe a maximum fractional delay of 0.129 and a maximum delay of 8.75 ms corresponding to a group velocity as low as 228.57 m/s in a sinusoid-like modulated waveform. We study in details the influences of the erbium ion density and the length of fiber on the fractional delay and the slow light propagation. The data show that the fractional delay can be increased using the fiber with high erbium ions density or long interaction length.     

Numerical study on SBS slow light systems using a super-Gaussian filtered incoherent pump

We numerically investigate the performance improvement and its limitations using super-Gaussian filtered incoherent pumping in Stimulated Brillouin Scattering (SBS) slow light systems, especially for 2.5-Gb/s return-to-zero (RZ) OOK data streams. As compared to regular Gaussian filtering schemes, super-Gaussian filters can reduce the signal broadening without sacrificing the generated delay. On the other hand, although the figure-of-merits (FOM) in terms of the normalized delay and signal Q-factor products can be improved as well, additional sub-pulses may appear and subsequently the curve of FOM versus slow-light bandwidth exhibits a fluctuated behavior.     

利用周期性极化KTiOPO4晶体参量缩小过程产生明亮振幅压缩光

利用周期性极化KTiOPO₄晶体构成的连续准相位匹配简并光学参量缩小谐振腔， 获得了注入红外的明亮正交振幅压缩光.参量振荡阈值为35mW.当抽运光功率为20mW时，测得压缩度为223dB，特别是当抽运光功率为8mW时，测得压缩度为217dB. 关键词： 准相位匹配 简并光学参量放大器 明亮振幅压缩光     

Alternating approach of implementing frequency encoded all-optical logic gates and flip-flop using semiconductor optical amplifier

In conduction of parallel logic, arithmetic and algebraic operations, optics has already proved its successful role. Since last few decades a number of established methods on optical data processing were proposed and to implement such processors different data encoding/decoding techniques have also been reported. Currently frequency encoding technique is found be a promising as well as a faithful mechanism for the conversion of all-optical processing as the frequency of light remains unaltered after refection, refraction, absorption, etc. during the transmission of light. There are already proposed some frequency encoded optical logic gates. In this communication the authors propose a new and different concept of frequency encoded optical logic gates and optical flip-flop using the non-linear function of semiconductor optical amplifier.