High-Resolution Optical Sampling of 640-Gb/s Data Using Four-Wave Mixing in Dispersion-Engineered Highly Nonlinear As$_2$S $_3$ Planar Waveguides

We present the first demonstration of an optical sampling system, using the optical Kerr effect in a chip-scale device, enabling combined capability for femtosecond resolution and broadband signal wavelength tunability. A temporal resolution ${ ≪ }500$ fs is achieved using four-wave mixing in a 7-cm-short chalcogenide planar waveguide. The use of a short length, dispersion-shifted waveguide with ultrahigh nonlinearity ($10^4;{rm W}^{-1}{cdot}{rm{km}}^{-1}$) enables high-resolution optical sampling without the detrimental effect of chromatic dispersion on the temporal distortion of the signal and sampling pulses, as well as their phase mismatch. Using the device, we successfully monitor a 640-Gb/s optical time-division multiplexing (OTDM) datastream, showcasing its potential for integrated chip-based monitoring of signals at bitrates approaching and beyond Tb/s. We discuss fundamental limitations and potential improvements.      

Compensation for chromatic dispersion and nonlinear effect in highdispersive coherent optical repeater transmission system

A design for a chromatic dispersion equalizer that provides 4.4 times higher efficiency in the dispersion compensation characteristics, compared with a conventional equalizer, is proposed. In addition, the amplitude response slope in the frequency domain is less than half of the conventional characteristic. This extends the compensation limit for chromatic dispersion up to 82500 ps/nm for a 2.5-Gb/s heterodyne system, which corresponds to a 4900-km normal dispersion fiber transmission system. A compensation method for modulational instability is also proposed. The method was confirmed by a 2.5-Gb/s continuous-phase frequency-shift-keying (CPFSK) 764-km normal dispersion fiber transmission experiment, with the abovementioned chromatic dispersion equalizer. Employing computer simulations, an over-1000-km normal dispersion fiber optical repeater transmission system with 2.5-Gb/s CPFSK heterodyne detection was shown to be feasible     

Analysis of dynamic spectral width of dynamic-single-mode (DSM) lasers and related transmission bandwidth of single-mode fibers

A simple formula of the dynamic spectral width of a directly modulated dynamic-single-mode (DSM) laser, and the related maximum transmission bandwidth of a single-mode fiber limited by chromatic dispersion are theoretically given. The dynamic spectral width of a DSM laser is determined by the modulated optical shape and the linewidth enhancement factor α. The spectral width caused by the dynamic wavelength shift is shown to be larger by (1 + alpha^{2})^1/2than that caused by the sideband of the signal of the intensity modulation. Furthermore, the maximum transmission bandwidth of a conventional single-mode fiber with a DSM laser is expressed by using the parameter α and the chromatic dispersion of the fiber. The product of the maximum bit rate and the square root of the fiber length at the wavelength of 1.55 μm is estimated to be about 25 Gbit/s . km^1/2.     

Design of apodized linearly chirped fiber gratings for dispersioncompensation

We investigate and compare the equalization performance of various apodization functions in linearly chirped fiber gratings, with a view of determining an optimum profile for the design and fabrication of chromatic dispersion compensators. A discussion concerning the relation of these apodization functions with the group delay characteristic of the equalizer is presented yielding important results connected with the grating design. The analysis has been extended to consider nonideal effects such as nonconstant averaged index and a realistic optical source     

Tunable dispersion compensator based on a fiber Bragg grating written in a tapered fiber

We report a novel dispersion tunable device for first-order dispersion compensation. It is based on a fiber Bragg grating written in a tapered fiber with a specific profile. The taper profile allows tuning the dispersion of the grating by stretching the fiber while the linearity of the group delay is preserved. A device with 0.8 nm of useful bandwidth and dispersion value tunable over more than 400 ps/nm is reported.     

Optimal Equalization of Distortions due to Group Delay Ripples of Chirped Fiber Bragg Gratings (CFBG)

We present a closed solution for an optimal equalizer which compensates for signal distortions caused by group delay ripples in chirped fiber Bragg gratings (CFBG) employed for dispersion compensation in optical communication systems. The theory is verified with the help of group delay measurement results of a dispersion compensating CFBG and the improvements achieved by the equalizer are presented on the basis of simulation results.     

Electrical Mitigation of Penalties Caused by Group Delay Ripples for Different Modulation Formats

Electrical equalizers are proposed to mitigate the distortions caused by group delay ripples (GDRs) of cascaded optical filters (e.g., fiber Bragg gratings for chromatic dispersion (CD) compensation). Different electrical equalizers including feedforward equalizer (FFE), decision-feedback equalizer (DFE), nonlinear FFE-DFE, and maximum-likelihood sequence estimator are investigated and compared comprehensively for four different modulation formats: ON-OFF keying, optical duobinary, optical single sideband, and differential phase-shift keying. Especially, we find that the relationship of electrical equalization performance on the modulation format is very similar for the mitigation of GDR and CD.     

Strain and Temperature Sensing Characteristics of Single-Mode–Multimode–Single-Mode Structures

We present a comprehensive study of the strain and temperature-sensing characteristics of single-mode–multimode–single-mode (SMS) structures based on the modal interference of guided modes of graded index multimode fiber (MMF) section spliced in between two single-mode fibers. A detailed theoretical study of the structures in terms of the refractive index distribution, effect of dopant and their concentrations, and the variation of core diameter has been carried out. Our study shows that for the SMS structure with a ${rm GeO}_{2}$-doped MMF there exists a critical wavelength on either side of which the spectrum shows opposite spectral shift with a change in temperature/strain, whereas for structures with a ${rm P}_{2}{rm O}_{5}$-doped MMF it shows monotonic red shift with increasing temperature/strain. It has been found that the critical wavelength shifts toward higher wavelengths with decreasing “ $q$” value/doping concentration. Using different MMFs, both the red and blue spectral shifts have been observed experimentally. It has also been found that the SMS structure has higher sensitivity toward this critical wavelength. The study should find application in designing strain-insensitive high-sensitive temperature sensors or vice versa.      

The Impact of Oxide Traps Induced by SOI Thickness on Reliability of Fully Silicide Metal-Gate Strained SOI MOSFET

In this letter, we investigate the effects of oxide traps induced by various silicon-on-insulator (SOI) thicknesses $({T}_{rm SOI})$ on the performance and reliability of a strained SOI MOSFET with SiN-capped contact etch stop layer (CESL). Compared to the thicker ${T}_{rm SOI}$ device, the thinner ${T}_{rm SOI}$ device with high-strain CESL possesses a higher interface trap $({N}_{rm it})$ density, leading to degradation in the device performance. On the other hand, however, the thicker ${T}_{rm SOI}$ device reveals inferior gate oxide reliability. From low-frequency noise analysis, we found that thicker ${T}_{rm SOI}$ has a higher bulk oxide trap $({N}_{rm BOT})$ density, which is induced by larger strain in the gate oxide film and is mainly responsible for the inferior TDDB reliability. Presumably, the gate oxide film is bended up and down for the p- and nMOSFETs, respectively, by the net stress in thicker ${T}_{rm SOI}$ devices in this strain technology.      

A Fully Integrated 0.13- $mu$m CMOS 40-Gb/s Serial Link Transceiver

A fully integrated 40-Gb/s transceiver fabricated in a 0.13-$mu$m CMOS technology is presented. The receiver operates at a 20-GHz clock performing half-rate clock and data recovery. Despite the low ${rm f}_{rm T}$ of 70 GHz, the input sampler achieves 10-mV sensitivity using pulsed latches and inductive-peaking techniques. In order to minimize the feedback latency in the bang-bang controlled CDR loop, the proportional control is directly applied to the VCO, bypassing the charge pump and the loop filter. In addition, the phase detection logic operates at 20 GHz, eliminating the need for the deserializers for the early/late timing signals. The four clock phases for the half-rate CDR are generated by a quadrature LC-VCO with microstrip resonators. A linear equalizer that tunes the resistive loading of an inductively-peaked CML buffer can improve the eye opening by 20% while operating at 39 Gb/s. The prototype transceiver occupies 3.4$, times ,$2.9 mm$^{2}$ with power dissipation of 3.6 W from a 1.45-V supply. With the equalizer on, the transmit jitter of the 39-Gb/s 2$^{15}-1$ PRBS data is 1.85 ${rm ps}_{rm rms}$ over a WB-PBGA package, an 8-mm PCB trace, an on-board 2.4-mm connector, and a 1 m-long 2.4-mm coaxial cable. The recovered divided-by-16 clock jitter is 1.77 ${rm ps}_{rm rms}$ and the measured BER of the transceiver is less than $10^{- 14}$ .      

Multicarrier Light Source With Flattened Spectrum Using Phase Modulators and Dispersion Medium

This paper describes a phase-locked multicarrier light source that employs a continuous wave (CW) light source, two phase modulators, and a dispersion medium. A sinusoidal phase modulation (PM) with a modulation index of $pi/4$ and a group velocity dispersion of ${pm}1/(4pi f_{m}^{2})$, where $f_{m}$ is the modulation frequency, are applied to a CW light followed by a large sinusoidal PM. This configuration provides a multicarrier light with a flattened optical power spectrum for any modulation index of the second PM. By adopting a chirped fiber Bragg grating (FBG) as a dispersion medium instead of a long normal dispersion fiber, we can increase the stability of the optical output spectrum and reduce the size of the multicarrier light generator. We have built a prototype with this configuration that generates a 61-carrier light with a 25 GHz interval and a power deviation of less than 8 dB.      

A 40 Gb/s CMOS Serial-Link Receiver With Adaptive Equalization and Clock/Data Recovery

This paper presents a 40 Gb/s serial-link receiver including an adaptive equalizer and a CDR circuit. A parallel-path equalizing filter is used to compensate the high-frequency loss in copper cables. The adaptation is performed by only varying the gain in the high-pass path, which allows a single loop for proper control and completely removes the RC filters used for separately extracting the high- and low-frequency contents of the signal. A full-rate bang-bang phase detector with only five latches is proposed in the following CDR circuit. Minimizing the number of latches saves the power consumption and the area occupied by inductors. The performance is also improved by avoiding complicated routing of high-frequency signals. The receiver is able to recover 40 Gb/s data passing through a 4 m cable with 10 dB loss at 20 GHz. For an input PRBS of 2 $^{7}-$1, the recovered clock jitter is 0.3 ps$_{rm rms}$ and 4.3 ps$_{rm pp}$. The retimed data exhibits 500 mV $_{rm pp}$ output swing and 9.6 ps$_{rm pp}$ jitter with ${hbox{BER}}≪ 10^{-12}$ . Fabricated in 90 nm CMOS technology, the receiver consumes 115 mW , of which 58 mW is dissipated in the equalizer and 57 mW in the CDR.      

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     

Optical equalization of fiber chromatic dispersion in a 5-Gb/stransmission system

A 5-Gb/s lightwave transmission experiment demonstrates the effectiveness of an all-pass-type fiber Fabry-Perot optical equalizer for eliminating an error floor caused by laser chirp and chromatic dispersion     

Investigation into the temperature dependence of chromaticdispersion in optical fiber

The change in the chromatic dispersion of optical fiber with temperature is an important design parameter for 40-Gb/s systems. We derive an equation for the change in dispersion with a temperature that is more general than what has previously been published. We present experimental results for the change in fiber dispersion with temperature for six commercially available fiber types of interest for 40-Gb/s communication systems. In addition, we demonstrate that the empirical model developed by Ghosh et al in 1994 for the temperature-dependent index of refraction of SiO₂ can be used to accurately model the temperature dependence of the chromatic dispersion of a wide variety of optical fibers     

Pressure Sensing Based on Nonconventional Air-Guiding Transmission Windows in Hollow-Core Photonic Crystal Fibers

Non-conventional core-guided transmission windows within the visible spectral range are identified in commercial hollow-core photonic crystal fibers designed to operate at 1550 nm. These windows are likely to be related to higher-order cladding photonic bandgaps and are found to be highly dependent on the cladding microstructure, thus being affected by pressure-induced stress/deformation. 20-cm-long fiber samples are then used to demonstrate simple and temperature-independent hydrostatic pressure sensing with two different setups. While in the first setup pressure is externally applied to the fiber and results in operation in the hundreds of ${rm kgf}/{hbox {cm}} ^{2}$ (or tens of MPa) range, the second setup applies pressure directly to fiber internal microstructure and is sensitive to pressures down to a fraction of ${rm kgf}/{hbox {cm}} ^{2}$ (hundredths of MPa). The fact that pressure is directly transduced into transmitted power greatly simplifies the required sensor interrogation setup.      

弱非周期性相位取样啁啾光栅的优化方法

取样光栅可以同时对多个信道进行滤波或色散补偿，所以在波分复用(WDM)系统中有广泛的应用，其中周期相位取样光栅是一种很有前途的设计方法，但周期取样的方法会使取样光栅的所有信道具有相同的色散补偿能力。提出设计弱非周期性相位取样啁啾光栅的优化方法，通过引入一组与信道色散补偿量有关的啁啾控制参数，可使不同信道的色散补偿量存在差异。运用该方法设计出弱非周期的取样光栅后，可用传输矩阵法来模拟该光栅的复反射谱，结果显示通过调整啁啾控制参数，可方便地控制不同信道的色散补偿能力，从而能实现对光纤链路色散与色散斜率的同时补偿，而且取样函数的幅度值的起伏则被完全消除。     

Tunable dispersion device based on a tapered fiber Bragg grating and nonuniform magnetic fields

We present a new variable dispersion device based on tuning the chirp of a tapered fiber Bragg grating by means of a magnetic transducer. By using a nonuniform magnetic field, we demonstrate a 188-472-ps/nm dispersion tuning range, suitable for tunable radio-frequency filters and dispersion compensation, among others.     

A Novel 3-D Microcavity Based on Bragg Fiber Dual-Tapers

In this paper, a novel 3-D microcavity based on Bragg fiber dual-tapers is proposed. The principle and characteristics of the Bragg fiber dual-taper are analyzed firstly, showing that the dual-taper can function as a fiber mirror. Its reflection and transmission can be adjusted by the design of taper structure parameters. Then, the structure of a 3-D microcavity composed by two Bragg fiber dual-tapers is investigated by the finite-difference time domain method. The relation between the cavity-mode wavelengths and the cavity lengths shows that it can be looked as a Fabry–PÉrot cavity, using the Bragg fiber dual-tapers as the mirrors. By proper design, a cavity-mode Q factor up to $4.0093times 10^{6}$ can be realized in this cavity. Its characteristics as narrowband filters are investigated, showing that its transmission spectrum has the shape of Lorenz curve and a finesse up to $10^{5}$ can be realized if cavity mode with a high Q factor is used. The analysis shows that high-quality 3-D light confinement can be realized in the proposed Bragg fiber dual-taper microcavity, which has great potential in high-efficiency light-emitting devices and small fiber components.      

Design of High-Channel-Count Multichannel Fiber Bragg Gratings Based on a Largely Chirped Structure

We propose a novel technique to design a high-channel-count, multichannel fiber Bragg grating (FBG) based on a largely chirped structure. The minimization of refractive-index modulation has been widely discussed in the previously demonstrated multichannel grating designs. The complexity of the grating structure, however, is also important from the point of view of practical fabrication. In this paper, the degree of grating complexity (DGC) is defined. We show that the DGC of a multichannel grating can be significantly reduced by designing a grating with a largely chirped structure. A detailed grating design process based on this technique is discussed, by which four multichannel gratings are designed and numerically studied, for applications such as periodic and nonperiodic spectral filtering, chromatic dispersion compensation and dispersion slope compensation. The proposed theory and examples show that different gratings with high-channel-count and multichannel responses can be designed and fabricated using a single commercially available phase mask, and all the gratings can be realized by a conventional FBG fabrication facility since the gratings have a low DGC with low index modulation.