Key technologies for terabit/second WDM systems with high spectralefficiency of over 1 bit/s/Hz

To fully utilize a limited gain bandwidth of about 35 nm (4.4 THz) in an erbium-doped fiber amplifier, an increase in signal spectral efficiency is required. In this paper, we investigate the key technologies to achieve terabit/second wavelength-division multiplexing (WDM) systems with over 1 bit/s/Hz spectral efficiency. Optical duobinary signals, which have narrower optical spectra than conventional intensity modulation signals, were applied to such dense WDM systems. The measured minimum channel spacing for 20-Gbit/s optical duobinary signals was 32 GHz and a spectral efficiency of over 0.6 bit/s/Hz was reached. By using polarization interleave multiplexing, spectral efficiency was expected to reach 1.2 bit/s/Hz in an ideal case with no polarization dependencies along the transmission lines. In such ultradense WDM systems with narrower channel spacing, stabilizing the wavelengths of laser diodes is an important issue for achieving stable operation over long periods. To do this, we developed a simple and flexible wavelength stabilization system which uses a multiwavelength meter. The wavelengths for 116 channels with 35-GHz spacing were stabilized within ±150 MHz. The stabilization system is applicable to ultradense WDM signals with a spectral efficiency of over 1 bit/s/Hz by employing wavelength interleave multiplexing and an optical selector switch. On the basis of these investigations, we demonstrated a 2.6-Tbit/s (20 Gbit/s×132 channels) WDM transmission by using optical duobinary signals. In addition, 1.28-Tbit/s (20 Gbit/s×64 channels) WDM transmission with a high spectral efficiency of 1 bit/s/Hz was achieved by using polarization interleave multiplexing     

Investigation on 2D photonic crystal-based eight-channel wavelength-division demultiplexer

In this paper, eight-channel wavelength-division demultiplexer (WDDM) is proposed and designed using two-dimensional photonic crystal (2DPC) ring resonator whose corresponding functional parameters such as transmission efficiency, resonant wavelength, Q factor are investigated. The proposed structure consists of bus waveguide, dropping waveguide and square ring resonators. Eight different channels are dropped by altering the cavity size and radius of the defect rods. The plane-wave expansion (PWE) and finite-difference time-domain (FDTD) methods are employed to analyse the photonic band gap (PBG) of periodic and non-periodic structure and to arrive normalized transmission spectra, respectively. The resonant wavelengths of eight-channel demultiplexers are 1496.9, 1502.3, 1506.9, 1512.3, 1515.0, 1520.4, 1525.3 and 1530.6 nm. The average transmission efficiency, Q factor and spectral width of proposed demultiplexer are 81%, 825 and 1.8 nm, respectively. The mean channel spacing is about 4.2 nm. The size of the demultiplexer is small; hence, it can be utilized for photonic integrated circuits (PIC).     

Digital Signal Processing of 400 Gbps CO-QPSK-WDM System Over Optical Wireless Channel for Carrier Phase Estimation

High bandwidth, low cost and small size has made Inter satellite optical wireless communication a promising and advance technology with an alternative to current microwave satellite systems. In this paper, advantages of coherent-detection quadrature phase shift keying (CO-QPSK) with DSP are investigated for the mitigation of non-linear effects. The technique of carrier phase estimation has been used to prolong the transmission range to several thousand kilometers. Further, 400 Gbps WDM-QPSK system has been analyzed for different distances with 30 dB transmitting power and 11 dB LO power. At last, system has been investigated at narrow channel spacing of 50 GHz and a brief comparison has been made with system having channel spacing of 100 GHz.     

On the effect of channel spacing,launch power,and regenerator placement on the design of mixed-line-rate optical networks

Due to the increasing heterogeneity and the growing volume of traffic, telecom backbone networks are going through significant innovations. Wavelength-division multiplexed (WDM) optical networks can now cost-effectively support the growing heterogeneity of traffic demands by having mixed line rates (MLR) over different wavelength channels.The coexistence of wavelength channels with different line rates, e.g., 10/40/100 Gbps, in the same fiber brings up various design issues: in this study, we focus on (1) choice of channel spacing; (2) choice of launch power; and (3) regenerator placement. Channel spacing affects the signal quality in terms of bit-error rate (BER), and hence affects the maximum reach of lightpaths, which is a function of line rates. Various approaches to set an opportunistic width of the channel spacing can be considered, viz., (i) uniform fixed channel spacing specified by the ITU-T grid (typically 50 GHz); (ii) different channel spacing for different line rates; or (iii) optimal value of channel spacing for all line rates that leads to minimum cost.The launch optical power of a signal is another important parameter that affects the network cost. Adjacent channels on different line rates, especially 10 Gbps and 100 Gbps, may exhibit serious degradation of signal quality and optical reach for both the channels due to cross-phase modulation (XPM) between them. Launch power plays a role in such a scenario as it governs the BER by affecting both the signal power and the noise power due to XPM. Moreover, intelligent choice of launch powers on different line rates can significantly reduce the number of regenerators required in the network. The tradeoff between placement of regenerators and choice of launch power is an important problem to address for MLR network design.In this work, we investigate the effects of channel spacing and launch optical power by evaluating the cost of a MLR network for different values of these parameters. We also study the interplay between regenerator placement and launch power. Our results show that (a) it is possible to identify optimal values of channel spacing for a minimum-cost MLR network design, and (b) controlling the power of 10 Gbps and 100 Gbps channels shows maximum sensitivity to the network cost.     

Joint relay assignment and rate–power allocation for multiple paths in cooperative networks

Multi-path transmission is an efficient way to balance the power consumption from a source to a destination. The previous works have studied rate–power allocation to prolong the network lifetime of multiple paths. As at least one relay node is required to participate into cooperative transmission, its assignment will greatly impact the power consumption of cooperative communication. Thus, this paper addresses the joint resource allocation problem which aims to prolong the lifetime of multi-path cooperative transmission. Given a path set from a source to a destination, we first define the lifetime-optimal relay assignment and rate–power allocation problem (LRRP) for multiple paths with cooperative communications. This paper then presents two heuristic algorithms, called BS-RRP and PS-RRP, to implement efficient resource allocation for multiple paths. The BS-RRP algorithm uses the binary search method to solve the LRRP problem on node-disjoint paths, and reaches the approximate performance 1 ? ?, where ? is an arbitrarily small positive constant. PS-RRP adopts the pattern search method for joint resource allocation on link-disjoint paths, and terminates after finite iterations. The simulation results show that the BS-RRP and PS-RRP algorithms can improve the network lifetimes about 26 and 30 % compared with the resource allocation methods under the non-cooperative communication scheme.     

A hybrid WDM ring–tree topology delivering efficient utilization of bandwidth over resilient infrastructure

This paper proposed a hybrid WDM ring–tree topology which employs spectrally efficient 60 Gbps non-return-to-zero/polarization shift keying optical orthogonal modulated signals. The reconfigurable optical add/drop multiplexers, optical cross-connects and semiconductor optical amplifiers are utilized to make hybrid ring–tree architecture. Each optical add/drop multiplexer node is connected to tree topology to further increase the number of users. The main contribution of the proposed spectrally efficient hybrid optical network is to support the maximum number of users within limited bandwidth for future communication networks. Also, the proposed resilient ring–tree architecture has advantages such as high optical node density and bandwidth/spectral efficiency as compared to conventional packet-switched optical access network.     

High Efficiency and Wideband 300 GHz Frequency Doubler Based on Six Schottky Diodes

A high efficiency and wideband 300 GHz frequency doubler based on six Schottky diodes is presented in this paper. This balanced doubler features a compact and robust circuit on a 5-μm-thick, 0.36-mm-wide, and 1-mm-long GaAs membrane, fabricated by LERMA-C2N Schottky process. The conversion efficiency is mainly better than 16% across the wide bandwidth of 266–336 GHz (3 dB fractional bandwidth of 24%) when pumping with 20–60 mW input power (P _in) at the room temperature. A peak output power of 14.75 mW at 332 GHz with a 61.18 mW P _in, an excellent peak efficiency of 30.5% at 314 GHz with 43.86 mW P _in and several frequency points with outstanding efficiency of higher than 25% are delivered. This doubler served as the second stage of the 600 GHz frequency multiplier chain is designed, fabricated, and measured. The performance of this 300 GHz doubler is highlighted comparing to the state-of-art terahertz frequency doublers.     

4 × 10 Gbps WDM repeaterless transmission system using asymmetrical dispersion compensation for rural area applications

We demonstrate experimentally 4?×?10 Gbps wavelength division multiplexing repeaterless transmission system using non-return-to-zero differential phase-shift keying modulation format over 300-km standard single-mode fiber. The channels used were 1546.9, 1547.7, 1548.51 and 1549.2 nm with 100 GHz spacing. In this system design, a dispersion compensation module is used; multi-channel-chirped fiber Bragg grating was deployed with asymmetrical configuration with different compositions of dispersion values at the transmitting and the receiving sides. The transmission system was pumped bidirectionally with 1445 and 1455 nm wavelength in a forward direction, and three pump wavelengths of 1430, 1440 and 1450 nm are deployed for the backward direction. The total on–off Raman gain is 47 dB from total pump power of 1.862 W. The result for dispersion pre-compensation of ??2006.0 and ??2338.3 ps/nm has minimal effect on nonlinearity showing the best performance for 300-km repeaterless transmission system.     

基于波分复用的红外图像光纤传输系统

针对目前红外搜索跟踪系统中,光纤千兆以太网带宽无法满足多传感器实时图像传输需求,设计了基于波分复用的红外图像光纤传输系统,此系统带宽达到4 Gbps,体积算法不变的情况下,可扩展到8 Gbps,满足红外搜索跟踪系统使用要求。     

Fiber nonlinearity compensation of WDM-PDM 16-QAM signaling using multiple optical phase conjugations over a distributed Raman-amplified link

In this paper, multiple optical phase conjugation (OPC) devices were used along the optical link to improve the performance of an \(8\times 256\) Gbps polarization-division multiplexing 16-state quadrature amplitude modulation signaling, producing total bit rate of 2.048 Tbps. A 50-GHz spaced, eight-channel wavelength division multiplexing (WDM) communication system was considered using 912 km dispersion-unmanaged standard single-mode fiber link with backward distributed Raman pumps. The performance of a dual-pump highly nonlinear fiber-based OPC was investigated analytically using a set of eight nonlinear Schrödinger equations taking into account the effect of polarization. Simulation results were compared with the case of mid-span optical phase conjugation (MS-OPC) compensation scheme showing better performance in terms of achievable Q-factor, optimal signal launched power, and the total length of the transmission link. In 256 Gbps, single-channel scenario, a Q-factor improvement of 1.35 dB was achieved and the nonlinear threshold was increased by \(\sim \) 4 dB compared to the case of MS-OPC. Moreover, using multiple OPC led to increase the length of the transmission link by 30.7% compared with the case of MS-OPC. In 2.048 Tbps WDM system, a maximum Q-factor of 9.27 dB over the same link was obtained showing an improvement of 0.62 dB over the MS-OPC case. The simulation results were compared with published analogous experimental data showing very good agreement.     

Design and analysis of all-optical up- and down-wavelength converter based on FWM of SOA-MZI for 60 Gbps RZ data signal

In this paper, the design and analysis of the all-optical up- and down-wavelength converter based on four-wave mixing (FWM) effect of semiconductor optical amplifier Mach–Zehnder interferometer (SOA-MZI) have been presented. The return-to-zero (RZ) modulated data signal at a bit rate of 60 Gbps has been evaluated for error-free operation to show the feasibility of proposed system at different pump wavelength. The converted signal power and quality factor are investigated as the function of variable signal power and pump power. The optimized operating input signal power of ?5 dBm with Q-factor of \(\sim \)28 dB for RZ modulated signal by using SOA-MZI structure with enhanced FWM effect. The important contribution of these investigations that it is possible to expand the optical network with limited available channel bandwidth by utilizing the wavelength converter and gives an approach to implement wavelength converter for future hybrid optical access networks.     

A high performance CNFET-based operational transconductance amplifier and its applications

High performance electronic systems face several challenges in driving innovative integrated circuits when the internal transistors are scaled down below 45 nm. Carbon nanotube field effect transistors (CNFETs) are considered as excellent candidates for building energy-efficient electronic systems in the near future, due to their unique characteristics such as ballistic transport, scalability, and better channel electrostatics. In this paper, a new high performance operational transconductance amplifier (OTA) based on 32 nm CNFET devices is presented. The proposed OTA maintains a highly linear wide continuous tuning range and a wide frequency response range, enabled by splitting the linear voltage-to-current conversion and tuning two different blocks. As an application, a universal second-order transconductance-capacitor (G _m  ? C) filter realized using the OTA is introduced. Simulation results show that the CNFET-based OTA offers very a low current consumption of 2.35 μA from a ± 0.9 V power supply, achieves a bandwidth of 9.5 MHz, and has an input dynamic range of ± 0.2 V.     

Capacity of Dual Branch MRC System Over Correlated Nakagami-<Emphasis Type="Italic">m</Emphasis> Fading Channels-A Review

Various papers on the channel capacity using different diversity combining techniques and/or adaptive transmission schemes are available to enhance channel capacity under fading environment without the necessity of increasing bandwidth and transmit powers. This paper provides the review on the channel capacity of MRC (Maximal ratio combining) over uncorrelated and correlated Nakagami-m fading channels with m = 1 (Rayleigh fading channel) under ORA (Optimum rate adaptation with constant transmit power), CIFR (Channel inversion with fixed rate) and OPRA (Optimum power and rate adaptation) schemes. We also highlight the effect of fade correlation on channel capacity and discuss the improvement of the system performance under the different adaptive techniques.     

Transmission of 160-Gb/s Modified Manchester modulation over WDM system

The paper examines the performance of Modified Manchester (MM) modulation scheme over wavelength division multiplexing (WDM) in high-speed optical communication links. The MM as a new modulation technique has a narrow spectral width compared to conventional Manchester coding, which allows its implementation in WDM systems beneficial. In this study, the performance characteristics of MM and conventional Manchester modulation formats are assessed in WDM system at 10 Gb/s bitrate for each channel, for the least allowable channel spacing as well as tolerance to chromatic dispersion (CD). It is revealed from the results of simulation that MM performs meaningfully well in comparison with conventional Manchester in terms of tolerance against narrow optical filtering, spectral efficiency, which is improved by 32% and CD tolerance, which is improved by +100 ps/nm. Sixteen wavelength channels (16 × 10 Gb/s) are modulated to provide 160 Gb/s data capacity, which was transmitted successfully over 224 km standard single mode fibre (SSMF) using MM while the conventional Manchester only covered about 157 km.     

Adaptive bandwidth mechanism using dual rate OLT for energy efficient WDM–TDM passive optical network

This paper reviews various energy efficient approaches in existence and proposes a Hybrid WDM–TDM PON architecture that allows the adaptive bandwidth allocation mechanism to reduce central office power consumption with acceptable performance. Our proposed architecture allows sending two signals, one broadband and other narrowband to each optical networking unit so an appropriate signal can be utilized according to the traffic demand. In case of very low traffic, only narrowband signal is used and a significant amount of energy consumption and OPEX is reduced. By using \(2\times \hbox {N}\) power splitter and interleaver, proposed architecture provides broadcasting at both broadband and narrowband signal depending on the required link rate. This further reduces energy consumption and OPEX by avoiding the transmission of same signal from multiple sources. Offered data rates to the optical distribution networks (ODNs) may also be varied by doubling the wavelength spacing of remote node AWG so that two contiguous wavelengths can be transmitted at each port or ODN. This provides the geographical dynamic bandwidth allocation. Proposed architecture also support simultaneous transmission of both broadband and narrowband signals to the ODN to provide bandwidth scalability and network extensibility for supporting future access network in terms of new users and data rates. As two signals are reaching to any ODN, resiliency against OLT TRx and line card failure is also achieved. The performance of the proposed design is verified by simulation results in terms of bit error rate and receiver sensitivity to demonstrate its feasibility for the next-generation optical access network.     

Terahertz MMICs and Antenna-in-Package Technology at 300 GHz for KIOSK Download System

Toward the realization of ultra-fast wireless communications systems, the inherent broad bandwidth of the terahertz (THz) band is attracting attention, especially for short-range instant download applications. In this paper, we present our recent progress on InP-based THz MMICs and packaging techniques based on low-temperature co-fibered ceramic (LTCC) technology. The transmitter MMICs are based on 80-nm InP-based high electron mobility transistors (HEMTs). Using the transmitter packaged in an E-plane split-block waveguide and compact lens receiver packaged in LTCC multilayered substrates, we tested wireless data transmission up to 27 Gbps with the simple amplitude key shifting (ASK) modulation scheme. We also present several THz antenna-in-packaging solutions based on substrate integrated waveguide (SIW) technology. A vertical hollow (VH) SIW was applied to a compact medium-gain SIW antenna and low-loss interconnection integrated in LTCC multi-layer substrates. The size of the LTCC antennas with 15-dBi gain is less than 0.1 cm³. For feeding the antenna, we investigated an LTCC-integrated transition and polyimide transition to LTCC VH SIWs. These transitions exhibit around 1-dB estimated loss at 300 GHz and more than 35 GHz bandwidth with 10-dB return loss. The proposed package solutions make antennas and interconnections easy to integrate in a compact LTCC package with an MMIC chip for practical applications.     

A 20 Gbps inductorless CMOS optical receiver for short-distance VCSEL-based 850 nm optical links

This paper presents a circuit design and experimental results for a 20 Gbps CMOS inductorless optical receiver, a transimpedance amplifier (TIA) and a limiting amplifier, for a vertical-cavity surface emitting laser based 850 nm optical link. The proposed optical receiver apply a power supply noise canceling technique, an additional path from the power supply to the TIA output to generate a reversed phase signal that reduces the power supply noise, and bandwidth enhancement circuit design that dose not require internal inductors. The simulation results shows a power supply rejection ratio of ?96.6 dB at 10 MHz, a total gain of $82.8\,\hbox{dB}\Upomega$ and a ?3 dB bandwidth of 15.5 GHz. A test chip fabricated in 90 nm CMOS technology and demonstrated with a PIN photo-diode, a bandwidth of 17 GHz and a responsibility of 0.53 A/W. The measurement results show a 25 % eye opening and an input sensitivity of ?7.1 dBm at a bit error rate of 10^?12 with a 2⁹ ? 1 pseudo-random test pattern at 20 Gbps. The core circuit of the optical receiver occupies only an area of 0.02 mm².     

Efficient routing and wavelength assignment for multicast in WDMnetworks

The next generation multimedia applications such as video conferencing and HDTV have raised tremendous challenges on the network design, both in bandwidth and service. As wavelength-division-multiplexing (WDM) networks have emerged as a promising candidate for future networks with large bandwidth, supporting efficient multicast in WDM networks becomes eminent. Different from the IP layer, the cost of multicast at the WDM layer involves not only bandwidth (wavelength) cost, but also wavelength conversion cost and light splitting cost. It is well known that the optimal multicast problem in WDM networks is NP-hard. In this paper, we develop an efficient approximation algorithm consisting of two separate but integrated steps: multicast routing and wavelength assignment. We prove that the problem of optimal wavelength assignment on a multicast tree is not NP-hard; in fact, an optimal wavelength assignment algorithm with complexity of O(NW) is presented. Simulation results have revealed that the optimal wavelength assignment beats greedy algorithms by a large margin in networks using many wavelengths on each link such as dense wavelength-division-multiplexing (DWDM) networks. Our proposed heuristic multicast routing algorithm takes into account both the cost of using wavelength on links and the cost of wavelength conversion. The resulting multicast tree is derived from the optimal lightpaths used for unicast     

Energy Efficient Scalable Sub-band based Ultra-Wideband System

In this paper, a scalable sub-band ultra-wideband (S-SUWB) system is proposed. The technique provides scope for using the ultra-wideband bandwidth efficiently by exploiting the available link margin for short range communications with medium data rates. The bandwidth of 500 MHz or more is divided into a fixed number of sub-bands. The data transmission scheme over multiple sub-bands can be designed to achieve higher data rate or higher reliability while providing multiuser support in both uplink and downlink communications. The proposed system provides enhanced scalability by the efficient utilization of the code-frequency dimensions. Sub-banding in conjunction with orthogonal spreading code facilitates transmission of plurality of data streams within a sub-band and along sub-bands for each user. Very importantly, the proposed system incorporates methods at the receiver facilitating low power receiver designs. Primarily, S-SUWB enables reduced sampling rate receiver designs significantly reducing the power consumption. Also, the spreading code based sub-band selection method obviates the need for individual down-conversion and filtering of the sub-bands thus reducing the complexity. Moreover, an interference rejection filtering (IRF) method incorporated into the despreading process is proposed to improve the performance without significantly increasing the receiver complexity. The simulation results in terms of the bit error rate performance of the scalable multiuser S-SUWB transceiver for the IEEE 802.15.4a channel models are presented demonstrating the usefulness of the proposed scheme. Performance improvements with the use of the IRF and also multi-user results are presented. The results indicate the desirable performance is obtained using the energy efficient techniques for low and medium delay spread channels even without the use of any equalization method.     

Design of a high gain and highly linear common-gate UWB mixer in K-band

In this paper, in order to design a K-band common-gate Gilbert-cell mixer via a 0.18 μm CMOS technology, the π-Network and post-distortion cancellation (PDC) techniques are implemented simultaneously, resulting in the improvement of gain, bandwidth, noise figure and linearity. Also, a new method for implementing the π-Network, using the parasitic capacitances between RF and LO stage nodes, is proposed which improves the mixer performance and makes the mixer design possible at high frequencies. It is shown that the π-Network enhances the gain and bandwidth by generating complex poles in system frequency response without the need for extra power consumption. The suitable location of these poles, which gives rise to high gain and high bandwidth, is discussed and determined by MATLAB simulation. Results of simulation illustrate 3.36 dB improvement in power conversion gain and 2 dB reduction in noise figure at the same power consumption with LO power of ?1 dBm in comparison with the case when PDC technique is used only. Compared to conventional mixer, it improves the IIP3 by 6 dB. Also, the power consumption of the mixer together with the designed bias circuit is 9.68 mW at 1.8 V.