Tunable Optical Dispersion Compensator With Increased Bandwidth via Connection of a Mach–Zehnder Interferometer to an Arrayed-Waveguide Grating

We propose and demonstrate a novel colorless tunable optical dispersion compensator (TODC) consisting of a Mach-Zehnder interferometer (MZI) connected to an ar- rayed-waveguide grating with a thermooptic lens. The MZI approximately doubles the magnitude bandwidth at large dispersion settings. We demonstrate compensation of a 43-Gb/s nonreturn-to-zero signal dispersed over a range of -844 to + 1700 ps/nm. To our knowledge, +1700 ps/nm is the largest demonstrated dispersion compensation amount of a 40-Gb/s signal with a single TODC.     

Colorless tunable optical dispersion compensator based on a silica arrayed-waveguide grating and a polymer thermooptic lens

We present a colorless tunable optical dispersion compensator (TODC) comprised of a silica arrayed-waveguide grating (AWG) directly coupled to a polymer thermooptic lens. Using silica for the AWG allows it to be low loss and manufactured by a standard process, and using polymer for the thermooptic lens allows it to have a large tuning range and low electrical power consumption. This hybrid TODC is fully solid-state and scales to a large figure-of-merit (dispersion range times bandwidth squared). We demonstrate a version with 100-GHz free-spectral range and 1300-ps/nm tuning range with a 3-dB bandwidth >39 GHz and a lens power consumption <74 mW.     

Second- and third-order dispersion compensator using ahigh-resolution arrayed-waveguide grating

We have proposed a dispersion compensation scheme that uses a high-resolution arrayed-waveguide grating (AWG). When the diffraction order of the AWG is 59 and the number of waveguides in an arrayed-waveguide is 340, the calculated maximum second- and third-order dispersion compensation range is 18.0 ps/nm and ±6.0 ps/nm² , and 1100 ps/nm and ±937.5 ps/nm², for a 1 ps-pulse and a 12.5 ps-pulse, respectively. In experiments, second-order dispersion (-0.8 to +5.2 ps/nm) is effectively compensated for 1,1-ps pulses; and. Pulse compression by third-order dispersion compensation is successfully demonstrated     

Low chromatic-dispersion flat-top arrayed waveguide grating filter

A low chromatic dispersion (CD) flat-top arrayed waveguide grating (AWG) filter with a novel parabolic waveguide horn is proposed, and a 100 GHz-spacing 16-channel flat-top AWG that reduces the CD from -20.9 to -3.2 ps/nm has been successfully fabricated.     

Validity of the Additive White Gaussian Noise Model for Quasi-Linear Long-Haul Return-to-Zero Optical Fiber Communications Systems

In this paper, we study the validity and limitations of the additive white Gaussian noise (AWGN) model in quasi-linear, long-haul, return-to-zero, direct-detection optical fiber communications systems. Our approach is to compare bit-error ratios (BERs) computed using the additive white Gaussian noise method to those obtained using standard and multicanonical Monte Carlo (MMC) simulations and to a noise-linearization method, referred to as the noise covariance matrix (NCM) method. We show that the AWGN method provides a very good approximation to the actual system BER for power levels and dispersion profiles that are used in typical modern-day quasi-linear systems. For example, the BER obtained using the AWGN method is within a factor of 4 of the actual system BER computed using MMC simulations for a realistic 10 Gb/s, 6000 km system based on dispersion-shifted fiber in which the peak signal power at the transmitter is 1 mW and the absolute residual dispersion at the receiver is less than 200 ps/nm. However, when the peak power is increased to about 4 mW, or the average map dispersion is zero and the absolute residual dispersion exceeds 200 ps/nm, the AWGN and NCM methods may simultaneously breakdown due to a combination of nonlinear signal–noise and noise–noise interactions during transmission. In addition, for a 5000 km system based on low-nonlinearity $D_+$ and $D_-$ fiber with an average map dispersion that is 4% of the dispersion variation within the map, and that operates at a peak power of 5 mW, we find that the BERs obtained using the AWGN and NCM methods are about 500 times smaller than the actual system BER computed using MMC simulations.      

Statistical Analysis of Optical Signal-to-Noise Ratio Monitoring Using Delay-Tap Sampling

We derive analytical expressions for the optical signal-to-noise ratio (OSNR) monitoring using delay-tap sampling for intensity-modulated direct-detection (IM/DD) systems. We demonstrate through our theoretical analysis and experimental results that modeling of noise correlation due to low-pass filtering between delay-tap samples enables accurate monitoring of OSNR, without recalibration for each system setup. Effects of chromatic dispersion (CD) and polarization-mode dispersion on the proposed technique are investigated through numerical simulations. The monitoring error remains within $pm$ 1 dB for CD up to 400 ps/nm and differential group delay up to 45 ps.      

Dispersion Compensation Configuration Applying a Combination of EDC and Tunable-ODC for Extended $L$-Band WDM Transmission

We propose effective polarization-mode dispersion (PMD) and chromatic dispersion (CD) compensation configuration for practical use in the field, taking into consideration the system cost and the field condition such as the CD changes due to fiber temperature dependence or transmission route change, and rapidly fluctuate state of polarization of the signal lightwave. Our configuration combines electric dispersion compensators (EDCs) with fixed taps in each channel with a multichannel tunable optical dispersion compensator (T-ODC) that can simultaneously compensate all channels' accumulated CD. We demonstrate widely extended $L$-band 43-Gb/s-based wavelength-division-multiplexing transmission over 450 km using our dispersion compensation configuration, and obtain effectiveness that the PMD penalty is suppressed by 2 dB at a differential group delay of 33 ps by using the EDC and that the CD penalty is improved by about 2 dB at the accumulated CD change of $+{/}-$ 30 ps/nm by using T-ODC and EDC.      

Soft Glass Equiangular Spiral Photonic Crystal Fiber for Supercontinuum Generation

An equiangular spiral photonic crystal fiber (ES-PCF) design in soft glass is presented that has high nonlinearity ( $gamma>5250 hbox{W}^{-1}cdothbox{km}^{-1}$ at 1064 nm and $gamma>2150 hbox{W}^{-1}cdothbox{km}^{-1}$ at 1550 nm) with a low and flat dispersion (${D}sim {hbox {0.8}} hbox{ps/km}cdothbox{nm}$ and dispersion slope $sim-0.7 hbox{ps/km}cdothbox{nm}^{2}$ at 1060 nm). The design inspired by nature is characterized by a full-vectorial finite element method. The ES-PCF presented improves over the mode confinement of triangular core designs and dispersion control of conventional hexagonal PCF, combining the advantages of both designs; it can be an excellent candidate for generating supercontinuum pumped at 1.06 $mu{hbox {m}}$.      

Performance Analysis of Steepest Descent-Based Feedback Control of Tunable-Dispersion Compensator for Adaptive Dispersion Compensation in All-Optical Dynamic-Routing Networks

In this paper, we report the performance-analysis results of our proposed high-speed and low-cost feedback-control method of a tunable-dispersion compensator (TDC) for adaptive dispersion compensation in all-optical dynamic-routing networks. In this method, we monitor the received waveform in the time domain and control a TDC repeatedly to reshape the waveform by means of the steepest descent method. Transmission experiments and simulations show that the proposed method can compensate for the dispersion quickly over a wide dispersion range. The compensation range is from $-$6000 to 6000 ps/nm in 10-Gb/s transmission. The compensation time is 1–2 s for dispersions within 1000 ps/nm. This method is applicable to the adaptive dispersion compensation in all-optical dynamic-routing networks.      

Experimental Investigation of Delay-Tap Sampling Technique for Online Monitoring of RZ-DQPSK Signals

We experimentally demonstrate optical performance monitoring of 20-Gb/s return-to-zero differential quadrature phase-shift keying signals using an asynchronous delay-tap sampling technique. This method allows online monitoring of accumulated chromatic dispersion in the range from $-$600 to $+$600 ps/nm. We also show evaluation of optical signal-to-noise ratio at a level of 6.7 dB and monitor operation at input power of $-$ 16 dBm.      

Tailoring Dispersion and Confinement Losses of Photonic Crystal Fibers Using Hybrid Cladding

We present a hybrid cladding photonic crystal fiber (PCF) for shaping nearly zero ultraflattened dispersion and low confinement losses in a wide range of wavelengths. The finite difference method with anisotropic perfectly matched boundary layer is used to investigate the guiding properties. It has been shown theoretically that it is possible to obtain nearly zero ultraflattened dispersion of ${hbox{0 }} pm {hbox{0.25}} ~{hbox{ps}}/{hbox{nm}}/{hbox{km}}$ in a wavelength range of 1.44 to 2.0 $ mu{hbox{m}}$ with low confinement losses less than 0.005 dB/km within the entire band of interest from a five-ring hybrid cladding PCF.      

Compensation for Second-Order Temperature Dependence in Athermal Arrayed-Waveguide Grating Realizing Wide Temperature Range Operation

We propose a new compensation technique for the second-order temperature dependence in a silica-based arrayed-waveguide grating (AWG) multi/demultiplexer with a resin-filled groove that realizes a wide operating temperature range. We newly employ an additional interferometer in the input port and control the optical field perturbation by using a first-mode lightwave at the entrance to the first slab waveguide. We employ the design to fabricate a 32-channel 100-GHz-spacing athermal AWG that is as compact as a conventional AWG, and demonstrate a reduction in the passband wavelength variation from 70 to 22 pm over an extended $-$ 40 $^{circ}hbox{C}$ to 80 $^{circ}hbox{C}$ temperature range.      

10 GHz再生锁模光纤激光器获得光纤超连续谱的研究

报道了利用10GHz再生锁模光纤环形激光器（RML-FRL）获得波长在1528～1563nm连续可调、脉宽为4．6～5．8ps的短脉冲输出作为高稳定的光纤超连续（SC）谱泵浦源。对RML-FRL输出的脉冲直接放大泵浦4．5km色散位移光纤（DSF）,得到20dB带宽46．08nm的SC谱输出,经阵列波导光栅（AWG）谱切片后,得到间隔100GHz、中心波长符合ITUT标准的30信道输出,脉宽在6．5～7．8ps,示波器显示任意信道的抖动均值小于1．4ps。     

$N times N$ Cyclic-Frequency Router With Improved Performance Based on Arrayed-Waveguide Grating

We have developed an $N times N$ cyclic-frequency router with improved performance by employing two types of modified configuration; a uniform-loss and cyclic-frequency (ULCF) arrayed-waveguide grating (AWG) and an interconnected multiple AWG. We have demonstrated a compact 50-GHz-spacing 64 $,times,$64 ULCF-AWG router with low and uniform insertion losses of 5.4–6.8 dB and frequency deviations from the grid of less than $pm {8}~{rm GHz}$. We have also demonstrated a 100-GHz-spacing 8$,times,$8 interconnected multiple-AWG router with a practical configuration, very low and uniform insertion losses of 2.3–3.4 dB, and frequency deviations from the grid of less than $pm {6}~{rm GHz}$. We discuss the suitable or realizable scale $N$ of the two types of routers by comparison with a conventional AWG router in terms of optical and dimensional performance and productivity.      

Adjustable dispersion-compensation devices with wavelength tunability based on enhanced thermal chirping of fiber Bragg gratings

We demonstrate a dispersion compensation device based on thermal chirping of a glued fiber Bragg grating. The device can change the group velocity dispersion (GVD) while maintaining a center wavelength or change the center wavelength while preserving a GVD value. The GVD can be tuned from -122.5 to -57 ps/nm with a center wavelength at 1552.9 nm. On the other hand, the center wavelength can be shifted by 2.2 nm with a GVD value around -105 ps/nm.     

Electron–Hole Plasma-Induced Spectral Blueshift of Optical-Data Injection Mode-Locked Semiconductor Optical Amplifier Fiber Laser

Under an optical nonreturn-to-zero (NRZ) data injection at 10 Gbit/s, the 10-GHz mode-locking and pulsed return-to-zero (RZ) clock extraction from a semiconductor optical amplifier (SOA) based fiber ring is investigated in this paper. The diagnoses on gain and intracavity-power-controlled anomalous blueshifted spectrum and subpicosecond timing jitter are demonstrated. By increasing the injecting power of the optical NRZ data from ${-}3$ to 8 dBm into the SOA bias at different currents, the mode locking is completed with a dc level greatly decreasing from 480 to 50 $mu$ W (only 1.5% of the mode-locked pulse power at 3 mW), corresponding to a pulse/dc amplitude contrast ratio up to 18 dB. Increasing the SOA bias current up to 350 mA significantly suppresses the timing jitter from 1.8 ps to 345 fs, and the extracted RZ clock pulse is shortened from 55 to 27 ps. The pulsewidth of the amplified SOAFL is compressed from 11 ps to 836 fs after dispersion compensation. At constant data injection level, the increasing SOA bias or gain oppositely redshifts the mode-locked SOA fiber ring laser (SOAFL) spectrum by 5 nm. The amplifier spontaneous emission of SOA at short wavelength region (${sim} {hbox {1520}}$ nm) is eliminated with increasing NRZ data power, whereas the mode-locking gain peak arises and blueshifts from 1558 to 1552 nm due to the band-filling effect. Such a blueshift in mode-locking spectrum becomes more significant in SOA at lower bias (or gain) condition. A theoretical model interprets the correlation between the nonlinear gain suppression-induced variation of electron–hole plasma in SOA and the blueshifted mode-locking SOAFL spectrum, which is occurred when the gain saturation condition for the SOA becomes more pronounced.      

基于SOA啁啾管理的连续可调谐色度色散补偿的研究

提出了一种新型的可小范围连续调谐的色度色散(CD)补偿方案.该CD补偿方案包括一个半导体光放大器(SOA)和一段固定长度的色散补偿光纤(DCF).利用SOA的交叉相位调制(XPM)效应,通过调节SOA的偏置电流和控制脉冲光的强度,可以对进入SOA的光信号引入不同大小的附加啁啾量,从而可以利用固定长度的DCF得到补偿后的无啁啾光信号.实验中,实现了10 Gb/s可调谐CD补偿器,在无需替换DCF的情况下,实现了补偿范围为-40 ps/nm到60 ps/nm的连续可调谐CD补偿.     

50-GHz-Spacing Athermal Mach–Zehnder Interferometer-Synchronized Arrayed-Waveguide Grating With Improved Temperature Insensitivity

We describe a technique designed to compensate for the residual temperature sensitivity of an athermal silica-based arrayed-waveguide grating (AWG) and its application to a 50-GHz-spacing multi/demultiplexer with a low loss and a wide passband. The device has a Mach–Zehnder interferometer (MZI)-synchronized configuration, in which the AWG and the MZI are athermalized with resin-filled grooves. The point is that we employ a temperature-dependent phase-generating coupler (TD-PGC) in the MZI to compensate for the second-order temperature dependence of the AWG passband wavelength. The fabricated device exhibits practical characteristics including a low loss of less than 3.5 dB and a wide 0.5-dB bandwidth of 24.1 GHz as well as a reduced wavelength variation of less than 10 pm in a ${-}$ 5 $^{circ}hbox{C}$ to 65 $^{circ}hbox{C}$ temperature range.      

Tunable dispersion equalizer with a divided thin-film heater for40-Gb/s RZ transmissions

We have developed tunable dispersion equalizers with a chirped fiber grating on the divided thin-film heater. The divided thin-film heater took an important role in the control of dispersion and dispersion slope. We successfully demonstrated the dispersion control from -304 to -196 ps/nm, the dispersion slope control from +100 to -300 ps/nm², and good performance in 40-Gb/s return-to-zero transmission by using this tunable dispersion equalizer     

宽带色散补偿模块的开发

文章从理论出发设计了一种色散补偿光纤波导结构,并制备出一种高性能的色散补偿光纤.测试结果表明:该色散补偿光纤在1 525～1 625 nm波长范围内具有较大负色散,1 545 nm波长的色散系数为-141 ps/(nm·km).采用该色散补偿光纤成功制备出宽带色散补偿模块.G.652光纤传输链路经过该色散补偿模块的补偿后,C波段的残余色散小于5.0 ps/nm,C波段色散斜率也实现了100%的补偿.