Estimating intensity fluctuations in high repetition rate pulse trains generated using the temporal Talbot effect

We derive the upper limit of the peak intensity fluctuations for high repetition rate pulse trains generated using the fractional temporal Talbot effect for pulse repetition rate multiplication. Our analysis is general, can be applied to any input pulse shape, and can be used as a design tool to determine the input pulsewidth that will minimize the output amplitude fluctuations for a given multiplication rate.     

Generation of a 4 /spl times/ 100 GHz pulse-train from a single-wavelength 10-GHz mode-locked laser using superimposed fiber Bragg gratings and nonlinear conversion

In this paper, the design of a simple and practical repetition-rate multiplier based on superimposed-chirped fiber Bragg gratings (FBGs) is presented. A tenfold increase in the repetition rate of a mode-locked fiber source, by generating a 100-GHz optical pulse train from a 10-GHz train, is demonstrated experimentally. As compared with previous demonstrations, the superimposed FBG filter was specifically designed to decrease the duty cycle of the generated pulse train or, in other words, decrease the pulsewidth. In addition, a fiber nonlinear optical loop mirror (NOLM) is used to eliminate the pulse-to-pulse phase fluctuations in the output high-repetition-rate train and to achieve a wavelength-tunable transform-limited pulse sequence. Moreover, it is shown that nonlinear conversion using the NOLM can be used to simultaneously generate multiwavelength high-repetition-rate optical pulse trains (4 /spl times/ 100 GHz in the example shown here).     

Ring Resonator Arrays for Pulse Repetition Rate Multiplication and Shaping

Using numerical simulations, we demonstrate the use of ring resonator arrays (RRAs) for pulse repetition rate multiplication (PRRM) and arbitrary envelope shaping to generate a pair of output pulse trains with arbitrary binary code profiles simultaneously from a single input pulse train. We investigate three configurations of RRAs:$M times N$,$1times N$, and$M times 1$. All can perform PRRM and generate two pulse trains with the required binary code profiles simultaneously; however, the two-dimensional ($M times N$) configuration suffers less waveguide loss. We also show that a nonlinear optical loop mirror can be used to remove the pulse-to-pulse phase variations in the output pulse trains.     

Multiwavelength optical signal processing using multistage ringresonators

We show that all-pass filters based on multistage ring resonators can be used to perform optical signal processing. In particular, using numerical simulations, we demonstrate their use for performing real-time Fourier transformation and for pulse repetition rate multiplication (temporal Talbot effect) simultaneously over multiple wavelength signals     

Generating 4 20 GHz and 4 40 GHz Pulse Trains From a Single 10-GHz Mode-Locked Laser Using a Tunable Planar Lightwave Circuit

We demonstrate a tunable pulse repetition rate multiplier using a silica-based planar lightwave circuit (PLC). The PLC is a six-stage lattice-form Mach–Zehnder interferometer which can be tuned thermally to generate 20- and 40-GHz output pulse trains from a 10-GHz input. We use a nonlinear optical loop mirror as a wavelength converter to perform intensity-to-field conversion to eliminate pulse-to-pulse phase fluctuations in the higher-rate output pulse trains. Moreover, we use wavelength multicasting (simultaneous wavelength conversion) to generate multiple pulse trains (4$,times,$ 20 GHz and 4$,times,$ 40 GHz in the example shown here) from a single 10-GHz input.      

Generation of a 100-GHz optical pulse train by pulse repetition-rate multiplication using superimposed fiber Bragg gratings

We demonstrate the use of superimposed fiber Bragg gratings (FBGs) operating in reflection as amplitude and phase filtering stages for multiplying the repetition rate of a given optical pulse sequence. In particular, we use a 1-cm-long structure of two superimposed linearly chirped FBGs to generate a continuous optical pulse train with a repetition rate of 100 GHz (duty cycle /spl ap/50%) at a wavelength of 1.55 /spl mu/m from a 10-GHz mode-locked fiber laser.     

Optical comb filter based on spectral talbot effect in uniform fibre bragg gratings

A comb optical filter based on the spectral Talbot effect in uniform low reflecting fibre Bragg gratings is numerically and experimentally demonstrated, relaxing the need for any chirp or equivalent phase shifts between the gratings. It can be understood by the analogy between the compression and rate multiplication of phase modulated pulse trains and sampled fibre Bragg grating spectrum formation     

Realization of true-time-delay using cascaded long-period fiber gratings: theory and applications to the optical pulse multiplication and temporal encoder/decoder

This paper proposes and demonstrates a technique for repetition-rate multiplication of an optical pulse train having an arbitrary period or pattern and the optical temporal encoding/decoding for the optical-code-division multiple-access (O-CDMA) system. The technique exploits the difference in the propagation speeds between the core and copropagating cladding modes of a fiber to obtain true-time-delay between the modes traveling in the core mode and the cladding mode, which can be used to achieve pulse multiplication. For the coupling to the cladding mode, long-period fiber gratings (LPGs) were used. A series of cascaded LPGs imprinted in a fiber with a specific separation has been employed to obtain a specific rate of pulse multiplication with a single input pulse. Second, by controlling the separations among the gratings, the temporal encoder/decoder for O-CDMA could be implemented. The principle and the applications of the proposed device are investigated in detail. The effect of the birefringence of fiber and fiber gratings on the system performance in the time and spectral domains is presented. The sensitivity of the cladding modes in a conventional fiber to the perturbations at the cladding has been overcome by replacing the conventional fiber with inner-cladding fiber. The properties and the benefits of using the inner-cladding mode are investigated.     

基于半导体光放大器环形腔的全光频率倍增/恢复

提出了一种利用具有干涉作用的半导体光放大器(SOA)环形腔实现全光频率倍增/恢复的新方法,该方法同相关实验比较具有显著优势.数值结果表明:2.5 GHz的光脉冲序列注入SOA环形腔,可输出重复频率为5～25 GHz振幅均衡、与入射光偏振无关的光脉冲序列;SOA的偏置电流对SOA环形腔输出脉冲振幅的均衡度影响显著,对于基频为2.5 GHz和10 GHz输入脉冲序列分别存在一最佳的SOA偏置电流值;从传输速率为2.5 Gbit/s的27-1伪随机信号中可提取出重复频率为分别2.5 GHz和5 GHz的幅度均衡的时钟信号.     

Pulse repetition frequency multiplication with spectral selection in Fabry-Perot filters

We present methods for obtaining high-repetition-rate full duty-cycle RZ optical pulse trains from lower rate laser sources. These methods exploit the memory properties of the Fabry-Perot filter for rate multiplication, while amplitude equalization in the output pulse train is achieved with a semiconductor optical amplifier or with a second transit through the Fabry-Perot filter. We apply these concepts to experimentally demonstrate rate quadruplication from 10 to 40 GHz and discuss the possibility of taking advantage of the proposed methods to achieve repetition rates up to 160 GHz.     

基于高SBS阈值的HNLF产生高重复频率超短光脉冲

基于光纤中的四波混频(FWM)产生高重复频率超短光脉冲的原理,并为抑制光纤中的受激Brillouin散射(SBS),采用非均匀掺杂高SBS阈值非线性光纤,通过FWM对双拍频信号进行整形压缩,实验上获得了100GHz的高重复率超短光脉冲序列,进而分析了入纤功率对输出光脉冲的影响。     

Polarization-independent all-optical clock division using asemiconductor optical amplifier/grating filter switch

We propose and experimentally demonstrate, for the first time to our knowledge, polarization-independent all-optical clock division (CD) of an optical pulse train at 2.88 GHz. This is achieved using a semiconductor optical amplifier (SOA)/grating filter switch, where the SOA acts as a spectral shifter by a self phase modulation and the grating filter acts as a spectral shutter. The proposed scheme is very insensitive to the polarization of input pulses and requires very low switching energy (~102 fJ). After the all-optical CD operation, we have obtained the output pulse train at 1.44 GHz, which is half the input repetition rate, with high extinction ratio (>20 dB)     

Spectral analysis of the temporal self-imaging phenomenon in fiber dispersive lines

A spectral analysis of the temporal Talbot or self-imaging effect based on the exact computation of the radio frequency spectrum of the intensity of pulse trains after propagation in media with arbitrary first-order (/spl beta//sub 2/) and second-order (/spl beta//sub 3/) dispersion is presented. This allows the investigation of the performance of fiber dispersive lines as Talbot devices, where second-order dispersion is considered as a degradation factor. Conditions for repetition-rate multiplication and pulse compression over trains composed of linearly chirped Gaussian pulses, describing the effect as a filter in the intensity domain, are analyzed. The Talbot filter acts as a multiple bandpass filter that selects intensity harmonics. The filter's rejection capability depends on the train's spectral width normalized by the repetition-rate frequency of the output. The intensity fluctuations and pulse distortions of the output train are described from the spectral point of view. The tolerances of the filter under length and timing variations are also considered, and conditions for optimal filter stability are derived.     

Wavelength and repetition rate tunable optical pulse source using a chirped fiber Bragg grating and a nonlinear optical loop mirror

We experimentally demonstrate a simple and novel scheme for tunable real-repetition-rate multiplication, based on the combined use of fractional Talbot effect in a linearly tunable chirped fiber Bragg grating (FBG) and cross-phase modulation (XPM) effect in a nonlinear optical loop mirror (NOLM). By tuning the group-velocity dispersion of the chirped FBG fabricated with the S-bending method using a uniform FBG, we obtain high quality pulses at pseudorepetition rates of 20/spl sim/50 GHz from an original 8.5-ps 10-GHz soliton pulse train. We subsequently convert this pseudorate multiplication into a real-rate multiplication using XPM effect in an NOLM. A wavelength tuning is also achieved over a /spl sim/15-nm range.     

Additive noise and jitter performance analysis of passive optical interferometers operated at ultrahigh rates

In this paper, we theoretically associate the additive noise, the amplitude jitter and the timing jitter at the input and output of passive optical interferometers. We make use of the theoretical results to assess the noise and jitter performance of interferometer based applications such as pulse repetition frequency multiplication and clock recovery. We show that, for both applications, interferometers may successfully reduce the noise and the jitter existing in the input signals, and thus yield very high quality output signals. Furthermore, we focus on the practical aspects of deploying Fabry-Pe/spl acute/rot interferometers in rate multipliers and clock recoveries, and provide rules for selecting the characteristics of the Fabry-Pe/spl acute/rot interferometer to meet specific quality requirements for the output signal.     

Influence of Input Pulse Durations on Properties of Er^3＋/Yb^3＋ Co-doped DCFA

Based on propagation-rate equations, the influence of different input pulse durations on the properties of Er^3＋/Yb^3＋ co-doped double-clad fiber amplifier at dynamic equilibrium was analyzed. The change characteristic of output power sag with pulse duration and repetition rate was shown. Whether single or multichannel input pulses are amplified, the shorter the input pulse duration is, the smaller the power sags of output pulse will be. At low repetition rate, upper gain values（Gupper） of gain swing are almost the same for different input pulse durations, which tend to the small signal gain, but lower gain value（Glower） of short input pulse is larger than that of long input pulse. At highrepetition rate, lower gain value（Glower） approaches to upper gain value（Glower）.     

Q-switched mode-locked diode-pumped Nd:YVO4 laser with a saturable Bragg reflector

We demonstrated a diode-pumped passively Q-switched mode-locked Nd:YVO4 laser by using a relaxed saturable Bragg reflector (SBR). Stable mode-locked pulse train with the repetition rate of ～230 MHz was achieved and the pulse train was modulated by the Q-switched envelope with the repetition rate of ～150kHz. The maximum output of 4 W was obtained under the pump power of 13.5 W. The optical-to-optical efficiency was 30%. We also discussed the transition of each process having emerged.     

Single and Multiwavelength All-Optical Clock Recovery in Single-Mode Fiber Using the Temporal Talbot Effect

We introduce and demonstrate an all-optical clock recovery scheme for return-to-zero transmission systems based on the buffering property of the temporal Talbot effect. This linear, dispersive, and, in principle, lossless phenomenon allows us to generate a regular pulse train from a pseudorandom (aperiodic) input train. Proof-of-principle operation at one and two simultaneous wavelengths is demonstrated using the single-mode fiber as the dispersive medium to implement the temporal Talbot effect. We examine both the limitations and the tolerance of our approach. [All rights reserved Elsevier].     

Efficient frequency multiplication by odd factors without idlers

Antiparallel connection of two varactors in a multiplier as a means of efficient idlerless frequency multiplication by odd factors is discussed. For a tripler, the dependence of efficiency, output and dissipated power on input frequency is shown. A practical multiplier and its properties are described.     

Simultaneous Optical Pulse Multiplication and Shaping Based on the Amplitude-Assisted Phase-Only Filter Utilizing a Fiber Bragg Grating

A novel all-optical simultaneous pulse multiplication and shaping approach is proposed, which is based on the simultaneous utilization of two amplitude-assisted phase-only spectral filters realizable by using a short fiber Bragg grating. This proposed method enables to create a high-repetition-rate rectangular pulse train with both an ideal rectangular envelop and a high energy efficiency. As a particular example, a repetition rate of 90 GHz rectangular pulse train is numerically demonstrated from an initial 10 GHz Gaussian pulse train.