Group Delay Characterization of Dispersive Devices Using a Pulse Temporal Intensity Measurement Setup

We propose and demonstrate a novel technique for group delay (GD) characterization of dispersive devices. The proposed technique involves the measurement of the temporal intensity profiles of a dispersed ultrashort optical pulse (i.e., after the device under test) and its first time derivative, which can be obtained by simple linear propagation through an all-fiber optical filter. The GD can be reconstructed using a direct and noniterative algorithm. We present experimental results for the measurement of the GD (including group-delay ripple) of high-dispersion and low-dispersion chirped fiber Bragg gratings.      

Variation in the performance of multispan 10-Gb/s systems due tothe group delay ripple of dispersion compensating fiber Bragg gratings

The variation in the performance of multispan lightwave systems that use dispersion-compensating fiber Bragg gratings (FBGs) is characterized in terms of the peak-to-peak group delay ripple over the -1dB bandwidth of the gratings. The irregular dependence of the group delay ripple on wavelength, and the variability in the properties of the group delay ripple for nominally identical gratings make it difficult to predict the overall reflection spectrum for a cascade of gratings. The uncertainty in the overall spectrum must be considered in the system design process. By considering 2401 distinct configurations for the gratings in a four-span 320-km system, simulation results are presented that specify the requirement for the group delay ripple in order for the system performance to remain within a specified penalty     

Group delay ripple reduction and reflectivity increase in a chirpedfiber Bragg grating by multiple-overwriting of a phase mask with anelectron-beam

The phase errors in electron-beam-written step-chirped masks can be reduced by using a method based on the continuous movement approach and overwriting a pattern at the same place on the substrate several times. The group delay ripple of chirped fiber Bragg gratings fabricated by a four-times-overwritten phase mask is comparable with that of gratings obtained using a holographically written chirped phase mask     

WDM系统中啁啾光纤光栅带外色散的影响

对啁啾光栅阻带外的色散特性进行了深入理论分析，在WDM系统中往往需要光栅级联来完成单个光栅不能实现的功能，级联光栅时，前面光栅的阻带外色散要对接续在其后面的光栅产生影响，增大了光栅的时延波动。对光栅级相互间的影响进行了理论分析与实验验证，提出了降低光栅间相互影响的方法是降低调制或光栅切趾，在光栅级联时采用高阶高斯切趾的效果最好。     

Study on Fabry–Perot cavity consisting of two chirped fiber Bragg gratings

Combined the effective mirror surface model with the transfer matrix method, a detailed theoretical and numerical study on Fabry–Perot cavity consisting of two chirped fiber Bragg gratings is investigated. Results demonstrate that transmission responses of the Fabry–Perot cavity can be adjusted by changing the cascading sequences of the two gratings. When the two gratings are connected in the direction of same chirping, approximately uniform resonance and group delay are exhibited. However, some distinctive non-uniformity of the neighboring resonance peaks intervals is shown if the two gratings are cascaded in the opposite chirping sequences. In addition, for the Fabry–Perot cavity constructed by chirped-fiber-Bragg-gratings with different amplitudes or bandwidths, efficient resonances are achieved only in the common reflection range.     

Figure-of-Merit of Dispersion Compensating Devices Based on Chirped Bragg Gratings

A promising technology for chromatic dispersion compensation in fiber communication networks are modules based on chirped Bragg gratings (DCM). Imperfections in the Bragg grating, however, give rise to a noise-like ripple in the phase characteristics of the DCM, which causes extra system penalty. In this paper, we derive an analytic formula that calculates an upper bound of the eye-opening penalty caused by a DCM in a transmission link with no optical amplifiers and with a chirp free NRZ optical signal. The primary use of this formula is as a quickly calculated quality measure (figure-of-merit) of the phase ripple characteristics of DCMs. It is shown that the difference in as given by the formula and obtained from simulation calculations is considerable smaller than given by other formulas found in the literature.     

Limitations of phase-shift method in measuring dense group delayripple of fiber Bragg gratings

The phase-shift method is an established technique for measuring the group delay of fiber-optic components. In devices, such as chirped fiber Bragg gratings, the group delay exhibits ripple as a function of wavelength. We have analyzed the dependence of the measured ripple amplitude on the modulation frequency and present a physical model, which gives an analytical formula for estimating the measurement error     

Dispersion oscillations in ultrafast phase-correction devices

Dispersion compensation is one of the most important tools for the generation of ultrashort optical pulses. Chirped mirrors have significantly increased the possibilities of compensation for arbitrarily shaped high-order dispersion. However, all design methods and manufacturing attempts reported so far have shown a spectral ripple on the phase characteristics of the mirror. We investigate the origin of this dispersion ripple and its consequences on pulse shaping. Recently, similar effects have also been reported in telecommunication applications of short pulses in devices such as fiber Bragg gratings and arrayed waveguide gratings. This calls for a systematic analysis of the phase ripple artifacts, which will be addressed both by numerical simulations and approximate analytical expressions. The results allow for an estimation of the severity of phase distortions in mode-locked lasers, external compression schemes, and telecommunication applications.     

The design of dispersion equalizers using chirped fiber Bragggratings

Dispersion equalizers designed to compensate for the arbitrary dispersion characteristics of optical fibers can be synthesized by cascading chirped fiber Bragg gratings and optical circulators. We have derived a synthesis rule for the equalizers and applied it to the fabrication of a third-order dispersion equalizer operating at the zero dispersion wavelength     

42.8-Gb/s RZ-DQPSK Transmission With FBG-Based In-Line Dispersion Compensation

Phase ripple impairments induced through cascaded fiber Bragg gratings (FBGs) are discussed for 42.8-Gb/s transmission. We show the feasibility of transmission over 1140 km (12 times 95 km) using return-to-zero differential quadrature phase-shift keying modulation and FBG-only dispersion compensation. We further compare FBGs with dispersion-compensating fiber for dispersion compensation and analyze the influence of wavelength detuning.     

三包层级联长周期光栅的传输谱特性

运用传输矩阵法对三包层级联长周期光纤光栅(LPFG)的传输谱特性进行分析,讨论了级联处光纤的长度、位置以及薄膜参数等对级联光栅传输谱的影响,并对级联长周期光栅和相移长周期光栅的传输谱进行了比较.结果表明两者传输谱在级联光纤长度较小或级联位置靠近光栅两端时具有较强的一致性;而在级联处光纤较长并且级联位置在中间时,两者表现出截然不同的特性,这一点和两包层级联光栅一致.另外,薄膜参数可以更灵活地调节传输谱衰减峰位置和峰值损耗的大小.     

Wavelength division multiplexing all-fiber hybrid devices based onFabry-Perot's and gratings

In this paper, we propose and experimentally demonstrate a series of new all-fiber, tunable, and highly selective filters based on fiber gratings and Fabry-Perot's. The structures combine high fiber Fabry-Perot (FFP) selectivity and fiber Bragg grating (FBG) bandpass nature and presents high flexibility in the response by using nonuniform gratings. An ultraselective filter (a few MHz in range) is also addressed by cascading two FFP     

Record bandwidth, spectrally flat coupling with microbend gratings in dispersion-tailored fibers

We demonstrate resonant grating couplers with the broadest bandwidth (565 nm) reported to date, using microbend gratings in dispersion-optimized few-mode fibers. Control of modal dispersion enables the demonstration of spectrally flat (< 0.25-dB ripple) coupling. This enables a compact (1 cm), broad-band (110 nm) variable optical attenuator, which is highly cost-effective, since device assembly simply involves pressing an as-drawn fiber between two corrugated blocks.     

级联型长周期光纤光栅传输谱的研究

采用级联多个长周期光纤光栅的方法有效拓宽了长周期光纤光栅反射谱带宽.分析了LPFG透射谱的谐振峰的定位问题,并通过级联多段周期相同但长度和微扰不同的LPFG来形成一个级联型的长周期光纤光栅,然后通过使用传输矩阵的方法,对级联光栅的传输谱进行了数值分析.经过分析发现,如果适当地调整级联型长周期光纤光栅的各个参数如级联的段数以及各段的长度和微扰等值,则所得到的这个级联型长周期光栅的透射谱的有效带宽将显著地增大,其透射谱的形状也会发生显著改变.

Abstract：

An improved method of cascaded long-period fiber gratings (LPFGs) is proposed, which can effectively broaden the resonant spectrum bandwidth of LPFGs. The positioning of the resonance peak of transmission spectra in LPFGs was analyzed. A cascaded LPFG was obtained by cascading various LPFGs with the same period but different length and index perturbation. Transfer matrix method was used to numerically calculate its transmission spectrum, and it is found that the effective bandwidth will become wider and the shapes will correspondingly change if the related parameters in cascaded LPFG, such as the number of segments and length and index perturbations of each segment, are adjusted correctly.     

Analysis of deep waveguide gratings: an efficient cascading and doubling algorithm in the method of lines framework

In this work, a computationally fast, numerically stable, and memory-efficient cascading and doubling algorithm is proposed within the method of lines framework to model long planar waveguide gratings having thousands of periods in the propagation direction. This algorithm can model 2/sup n/ grating periods in n calculational steps and needs N/sup 2/ matrices for N sample points in the problem space. It can model periodic, quasi-periodic, symmetric, and asymmetric gratings efficiently. Different deep waveguide gratings are modeled using this scheme and results for the fundamental TE mode spectral reflectivity are compared with published results showing excellent agreement.     

Optimization of refractive index sampling for multichannel fiber Bragg gratings

A comprehensive analysis of multichannel grating optimization strategies is presented. The central idea is in dephasing of partial gratings with respect to each other. This dephasing allows the utilization of ultraviolet-induced refractive index changes with maximum efficiency. The dependence of group delay ripple on optimization strategy, number of channels, and other grating characteristics is also briefly discussed. Finally, we discuss further generalization of the dephasing approach to the case of multichannel gratings with nonidentical spectral characteristics.     

啁啾光纤光栅补偿光纤色散的研究

啁啾光纤光栅被认为是目前最有实用价值的色散补偿方案之一。分析了啁啾光纤光栅补偿色散的基本原理,从简单模型出发分析了啁啾光纤光栅的色散补偿能力,用数值法研究了啁啾光纤光栅的时延及色散特性,并比较了变迹型与非变迹型啁啾光纤光栅。结果表明要获得较大的色散,要求光纤光栅有较长的长度和较小的啁啾。同时为了消除色散曲线的振荡还必须采取适当的变迹方法。     

Low-loss 10-GHz-spaced tandem multi/demultiplexer with more than1000 channels using a 1×5 interference multi/demultiplexer as aprimary filter

A very large channel-count low-loss optical multi/demultiplexer with more than 1000 channels is described. It was achieved by cascading a 1×5 flat-top interference multi/demultiplexer as a primary filter and five 10 GHz-spaced 1×288 arrayed-waveguide gratings as secondary filters in a tandem configuration     

Tunable passive all-optical pulse repetition rate multiplier using fiber Bragg gratings

We demonstrate a tunable passive all-optical pulse repetition rate multiplier based on the fractional temporal Talbot effect. The multiplier comprises a series of identical linearly chirped fiber Bragg gratings (LCFBGs) interconnected via two multiport (N/spl times/N) switches. Discrete multiplication factors are obtained by simply using the switch to set the optical path of the input pulse train to be reflected by the required number of gratings, and hence, corresponding dispersion, to satisfy the Talbot condition. In our demonstration, we reflect an 8.62-GHz input pulse train from a cascade of one to four LCFBGs, resulting in discrete repetition rate multiplication factors of 12, 6, 4, and 3, respectively. We obtain output repetition rates exceeding 100 GHz; the multiplied train exhibits excellent signal stability with low amplitude ripple and timing jitter, and the output pulses are of similar duration to those at the input.