Wavelength Division Multiplexing Channels Research Articles

Optical network scaling: roles of spectral and spatial aggregation.

As the bit rates of routed data streams exceed the throughput of single wavelength-division multiplexing channels, spectral and spatial traffic aggregation become essential for optical network scaling. These aggregation techniques reduce network routing complexity by increasing spectral efficiency to decrease the number of fibers, and by increasing switching granularity to decrease the number of switching components. Spectral aggregation yields a modest decrease in the number of fibers but a substantial decrease in the number of switching components. Spatial aggregation yields a substantial decrease in both the number of fibers and the number of switching components. To quantify routing complexity reduction, we analyze the number of multi-cast and wavelength-selective switches required in a colorless, directionless and contentionless reconfigurable optical add-drop multiplexer architecture. Traffic aggregation has two potential drawbacks: reduced routing power and increased switching component size.

Fabrication and performance of 1.3-μm 10-Gb/s CWDM wafer-fused VCSELs grown by MOVPE

Recent progress in the fabrication and performance of 1.3-μm 10-Gb/s, low power consumption wafer-fused VCSELs grown by MOVPE under nitrogen atmosphere are presented and discussed. By optimization of the growth conditions and implementation of a cavity adjustment technique, the wavelength yield was increased to up to 70% for all four coarse wavelength division multiplexing (CWDM) channels implemented. It was demonstrated that single-mode devices can have threshold and operation currents below 1 and 7mA, respectively, in the full 0–80°C temperature range. The reproducibility of the fabrication process and prospects for enhancing performance and yield of such VCSELs are also discussed.

System-Level Modeling and Analysis of Thermal Effects in WDM-Based Optical Networks-on-Chip

Multiprocessor systems-on-chip show a trend toward integration of tens and hundreds of processor cores on a single chip. With the development of silicon photonics for short-haul optical communication, wavelength division multiplexing (WDM)-based optical networks-on-chip (ONoCs) are emerging on-chip communication architectures that can potentially offer high bandwidth and power efficiency. Thermal sensitivity of photonic devices is one of the main concerns about the on-chip optical interconnects. We systematically modeled thermal effects in optical links in WDM-based ONoCs. Based on the proposed thermal models, we developed OTemp, an optical thermal effect modeling platform for optical links in both WDM-based ONoCs and single-wavelength ONoCs. OTemp can be used to simulate the power consumption as well as optical power loss for optical links under temperature variations. We use case studies to quantitatively analyze the worst-case power consumption for one wavelength in an eight-wavelength WDM-based optical link under different configurations of low-temperature-dependence techniques. Results show that the worst-case power consumption increases dramatically with on-chip temperature variations. Thermal-based adjustment and optimal device settings can help reduce power consumption under temperature variations. Assume that off-chip vertical-cavity surface-emitting lasers are used as the laser source with WDM channel spacing of 1 nm, if we use thermal-based adjustment with guard rings for channel remapping, the worst-case total power consumption is 6.7 pJ/bit under the maximum temperature variation of 60 °C; larger channel spacing would result in a larger worst-case power consumption in this case. If we use thermal-based adjustment without channel remapping, the worst-case total power consumption is around 9.8 pJ/bit under the maximum temperature variation of 60 °C; in this case, the worst-case power consumption would benefit from a larger channel spacing.

WDM optical steganography based on amplified spontaneous emission noise.

We propose and experimentally demonstrate a wavelength-division multiplexed (WDM) optical stealth transmission system carried by amplified spontaneous emission (ASE) noise. The stealth signal is hidden in both time and frequency domains by using ASE noise as the signal carrier. Each WDM channel uses part of the ASE spectrum, which provides more flexibility to apply stealth transmission in a public network and adds another layer of security to the stealth channel. Multi-channel transmission also increases the overall channel capacity, which is the major limitation of the single stealth channel transmission based on ASE noise. The relations between spectral bandwidth and coherence length of ASE carrier have been theoretically analyzed and experimentally investigated.

WDM-to-OTDM Conversion Using Supercontinuum Generation in a Highly Nonlinear Fiber

We demonstrated an all-optical wavelength- division-multiplexing (WDM)-to-optical-time-division-multiplex- ing (OTDM) conversion using spectral broadening of super continuum (SC) generation in a highly nonlinear fiber. Four 10-Gb/s WDM channels were injected into time delay blocks for controlling the timing among them, and converted to OTDM channel by the SC-based multiplexing. The SC generation had advantages of eliminated the use of any pump in the WDM- to-OTDM conversion. All OTDM demultiplexed optical signals achieved error-free performance with <2-dB power penalty at BER = 10 �9 compared with the back-to-back signal.

A Cuckoo Search based WDM Channel Allocation Algorithm

More and more modern metaheuristics nature–inspired algorithms are emerging and they become increasingly popular. This paper formulates an algorithm for solving the channel–allocation problem in optical wavelength division multiplexing (WDM) systems to suppress four–wave mixing crosstalk (FWM) based on a novel nature–inspired algorithm, called Cuckoo Search algorithm by using the concept of Optimal Golomb ruler (OGR) sequences. Simulation results conclude the significance performance improvement, without the requirement of increased total optical channel bandwidth, unlike two existing classical channel–allocation algorithms i.e. Extended Quadratic Congruence (EQC) and Search Algorithm (SA) and one of the existing nature–inspired algorithm i.e. Genetic Algorithm (GA). General Terms Classical computing, Four–wave mixing, Metaheuristics, Optimization.

Widely tunable chaotic fiber laser for WDM-PON detection

A widely tunable high precision chaotic fiber laser is proposed and experimentally demonstrated. A tunable fiber Bragg grating (TFBG) filter is used as a tuning element to determine the turning range from 1533 nm to 1558 nm with a linewidth of 0.5 nm at any wavelength. The wide tuning range is capable of supporting 32 wavelength-division multiplexing (WDM) channels with 100 GHz channel spacing. All single wavelengths are found to be chaotic with 10 GHz bandwidth. The full width at half maximum (FWHM) of the chaotic correlation curve of the different wavelengths is on a picosecond time scale, thereby offering millimeter spatial resolution in WDM detection.

Heterodyne detection and transmission of 60-Gbaud PDM-QPSK signal with SE of 4b/s/Hz.

We experimentally demonstrate 8 × 240-Gb/s super-Nyquist wavelength-division-multiplexing (WDM) polarization-division-multiplexing quadrature-phase-shift-keying (PDM-QPSK) signal transmission on a 50-GHz grid with a net spectral efficiency (SE) of 4b/s/Hz adopting hardware-efficient simplified heterodyne detection. 9-ary quadrature-amplitude-modulation-like (9QAM-like) processing based on multi-modulus blind equalization (MMBE) is adopted to reduce analog-to-digital converter (ADC) bandwidth requirement and improve receiver sensitivity. The transmission distance at the soft-decision forward-error-correction (SD-FEC) threshold of 2 × 10(-2) is 2 × 420 km based on digital post filtering while largely extended to over 5 × 420 km based on 9QAM-like processing, which well illustrates 9QAM-like processing is more efficient for heterodyne coherent WDM system. Moreover, only two ADC channels are needed for simplified heterodyne detection of one 60-Gbaud PDM-QPSK WDM channel, and thus only one commercial oscilloscope (OSC) with two input ports can work well for each WDM channel.

Integrated frequency comb source of heralded single photons

We report an integrated photon pair source based on a CMOS-compatible microring resonator that generates multiple, simultaneous, and independent photon pairs at different wavelengths in a frequency comb compatible with fiber communication wavelength division multiplexing channels (200 GHz channel separation) and with a linewidth that is compatible with quantum memories (110 MHz). It operates in a self-locked pump configuration, avoiding the need for active stabilization, making it extremely robust even at very low power levels.

Joint Channel Estimation, Interference Mitigation, and Decoding for WDM Coherent Optical Communications

High spectral efficiency in wavelength-division multiplexing (WDM) coherent optical communications can be achieved by lowering the channel spacing to a value close to the baud rate. As a result, such communication systems are subject to a high level of two-dimensional (2D) interference, originating from both chromatic dispersion (CD) within WDM channels and cross talk between WDM channels. We propose to digitally restore the transmitted information at the receiver side by jointly processing the WDM channels, using 2D interference cancellation methods interacting with a forward error correction decoder. Such schemes have been investigated extensively for known channel parameters; however, little is known about the error performance in the absence of channel state information. This issue is important, since in practice uncertainties about the physical parameters of the optical fiber and noise levels are unavoidable. In this paper, we propose optical channel parameter estimation schemes with limited impact on the overall complexity. First, a decision-aided carrier phase recovery, taking the presence of 2D interference into account, is designed to compensate the laser beat linewidth. Then we provide a technique to estimate the linear channel impairments for each WDM channel, based on a limited number of training symbols. The validity of the proposed method is evaluated by numerical simulations taking into account linear and nonlinear fiber impairments. In particular, we show that for high-order modulations, joint processing of spectrally overlapping WDM channels becomes mandatory to obtain satisfactory performances.

Narrowband photon pair source for quantum networks

We demonstrate a compact photon pair source based on a periodically poled lithium niobate nonlinear crystal in a short cavity. This approach provides efficient, low-loss, mode selection that is compatible with standard telecommunication networks. Photons with a coherence time of 8.6 ns (116 MHz) are produced and their purity is demonstrated. A source brightness of 134 pairs (s. mW. MHz)(-1) is reported. The cavity parameters are chosen such that the photon pair modes emitted can be matched to telecom ultra dense wavelength division multiplexing (U-DWDM) channel spacings. The high level of purity and compatibility with standard telecom networks is of great importance for complex quantum communication networks.

Configuration of more than N DWDM channels with only one N × N cyclic-AWG-based wavelength routing device

A wavelength routing device based on only one N×N cyclic arrayed waveguide grating (AWG) having easy extended channels configuration is presented in this paper. It is easy to extend the dense wavelength division multiplexing (DWDM) channel configuration through this wavelength routing device. According to the cyclic wavelength of AWG, the wavelength routing devices are easy to configure more than N extended DWDM channels through cascading more proper tunable fiber Bragg gratings (FBGs). With only one 8×8 AWG, two different wavelength routing structures were built to evaluate static crosstalk and the bit-error-rate (BER). Three of the 16 inputted DWDM channels were demonstrated to verify that the proposed wavelength routing device, with only one 8×8 AWG, could configure extended DWDM channels without interfering with other channels. The results show that the wavelength routing device can produces a better performance and offers a cheaper way to extend the DWDM channel configuration for a dynamic network.

Multi-MetaRing fairness control in a WDM folded-bus architecture

The paper deals with fairness issues in a slotted, single-hop, WDM (Wavelength Division Multiplexing) optical architecture, based on a folded bus topology, previously proposed as a broadband access system or as a metro network. The peculiar fairness problem arising in this folded bus based architecture is addressed and an extension of the MetaRing protocol to the WDM scenario, named Multi-MetaRing, is proposed. Feasible Multi-MetaRing strategies are defined and analyzed. Both fair access and high aggregate network throughput can be achieved with a low complexity distributed access protocol by properly handling node access through all WDM channels.

Achievable Information Rate in Nonlinear WDM Fiber-Optic Systems With Arbitrary Modulation Formats and Dispersion Maps

The problem of analytical evaluation of the maximum rate at which information can be reliably transmitted on a nonlinear wavelength division multiplexing fiber-optic channel with a given modulation format and detection strategy is addressed. An approximate solution of the nonlinear Schrödinger equation is adopted to obtain an accurate analytical discrete-time channel model, valid for arbitrary link configurations and modulation formats. By exploiting the concept of mismatched decoding, considering a sub-optimum detection strategy that accounts for intra-channel nonlinearities, the proposed model is employed to derive closed-form expressions of the achievable information rate with various modulation formats. All the analytical results are verified through comparison with numerical simulations in different scenarios.

파장다중화 광신호의 3000km 전송을 위한 후치분산 보상 방법 비교

40 채널의 파장 다중화된 광신호를 3000 km 까지 전송하면서 후치분산 보상 방법의 차이에 따른 성능 변화를 조사하였다. 개별 광신호는 10 Gbps 대역폭의 RZ 신호포맷을 사용하였고 40 채널들의 파장은 1533.5 nm에서 1564.7 nm 사이에 100 GHz 의 주파수 간격을 가졌다. 후치분산 보상을 위해 40개의 개별채널 별로 후치분산을 최적화하는 경우, 전 40 채널들을 하나의 분산값으로 후치분산 보상하는 경우, 그리고 제안된 방법으로 8개씩 묶은 채널 그룹별로 최적화하는 경우의 세가지 경우가 비교되었다. 최저 성능 채널과 그 성능 값은 세가지 방식에서 차이가 없었다. 최고 성능값은 전 채널을 하나의 후치분산 값으로 사용하는 경우가 다른 두 가지 방식에 비해 성능에 떨어졌지만 그룹별 방식이나 개별 채널별 방식은 차이가 없었다. 따라서 채널 그룹별로 후치분산을 통해 신호 성능의 희생 없이 전송시스템을 단순화시킬 수 있음을 확인하였다. Post-dispersion compensation methods for the 3000 km long-haul transmission distance using 10 Gbps 40 wavelength division multiplexing channels were analyzed and compared. First, each channel was compensated by an individual dispersion value, next each group of eight channels by an individual value, and lastly all forty channels by a single value. Considering the lower and highest performance channels and their values, the post-dispersion compensation method by each channel group showed the possibility to simplify the transmission system without sacrifice of signal performance.

Microwave phase shifter with 25-GHz dense wavelength division multiplexing channel spacing tuning using multimode interferometer-coupled microring resonator

The microwave phase shifter using 25-GHz dense wavelength division multiplexing (DWDM) channel spacing tuning on the silicon-on-insulator microring resonator (MRR), which was utilizing the multimode interference as the coupling function to achieve wavelength independence, is proposed and demonstrated. With a quality factor of 1199 for the MRR, there was 25-deg phase tuning for every 25-GHz DWDM channel spacing at 5-GHz microwave frequency. The total tunability from the microwave phase shifter could achieve 350 deg using 22 DWDM channels with 25-GHz spacing.

RDPS가 랜덤하게 분포하는 분산 제어 광전송 링크에서 전체 전송 거리에 따른 유효 전체 잉여 분산

분산 제어 (DM; dispersion management)와 광 위상 공액 (optical phase conjugation)이 적용된 파장 다중 (WDM; wavelength division multiplexing) 시스템의 유연한 구성을 위하여 중계 구간 당 잉여 분산 (RDPS; residual dispersion per span)이 랜덤하게 분포하는 전송 링크에서 전체 전송 거리에 따른 설계 기준을 도출하였다. 설계기준 분석에 사용된 DM 파라미터는 유효 전체 잉여 분산 (NRD; net residual dispersion)과 유효 입사 전력이다. 단일 모드 광섬유 (SMF; single mode fiber) 기준 전체 전송 거리가 1,000 km 이하인 링크에 랜덤 분포의 RDPS가 적용되는 경우 일정 분포에 비해 시스템 성능이 크게 차이나지 않아 유연한 네트워크 구성이 가능하고, 넓은 범위에 걸쳐 있는 WDM 채널에 대해 하나의 값이 아닌 폭넓은 NRD를 링크에 적용할 수 있다는 것을 확인하였다. The design rule depending on total transmission length is induced in the optical links with residual dispersion per span (RDPS) of the random distribution, which is adopted for implementing the flexible systems of wavelength division multiplexing (WDM) transmission with dispersion management (DM) and optical phase conjugation. DM parameters used for the analysis of the design rule are the effective net residual dispersion (NRD) and the effective launch power. It is confirmed that the flexible optical network configuration with the total transmission length lower than 1,000 km is possible, because the system performance difference between the randomly distribution and the uniform distribution of RDPS is small. And, in the optical links with the randomly distributed RDPS, the wide NRD can be applied for transmitting WDM channels of the relatively wide launch power.

No guard-band wavelength translation of Nyquist OTDM-WDM signal for spectral defragmentation in an elastic add–drop node

We demonstrate a seamless spectral defragmentation in an elastic all-optical add-drop node based on wavelength division multiplexing (WDM) channels of Nyquist optical time division multiplexing (OTDM) signal. A 172 Gbaud Nyquist OTDM signal occupying a 215 GHz range is elastically shifted adjacent to its neighboring channel, completely filling a variable spectral gap caused by the dropped channel. The frequency shift is done in a dual-stage polarization-diversity four wave mixing-based converter using polarization-maintaining highly nonlinear fiber. The spectrally defragmented signals are successfully transmitted over a 80 km fiber link with BER<10(-9).

Semiconductor optical amplifier based multi-wavelength lasers in 0.4 nm channel spacing

We propose a multi-wavelength fiber laser employing a double-pass Mach–Zehnder interferometer filter, a piece of polarization maintaining fiber, a semiconductor optical amplifier and an optical isolator. The proposed fiber laser has the advantages of stable multi-wavelength lasing with 33 channels in standard wavelength division multiplexing channel spacing of 0.4 nm using 15 m polarization maintaining fiber. Power ripple among channels could be reduced by increasing the bias current of the semiconductor optical amplifier.

Fabrication-Tolerant Four-Channel Wavelength-Division-Multiplexing Filter Based on Collectively Tuned Si Microrings

We demonstrate a robust, compact and low-loss four-channel wavelength-division multiplexing (WDM) filter based on cascaded double-ring resonators (2RR) in silicon. The flat-top channel response obtained by the second-order filter design is exploited to compensate for the detrimental effects of local fabrication variations and their associated phase errors on the ring-based filter response. Full wafer-scale characterization of a cascaded, four-channel 2RR filter with channel spacing of 300 GHz shows an average worst-case insertion loss below 1.5 dB and an average worst-case crosstalk below -18 dB across the wafer, representing a substantial improvement over a first-order based ring (1RR) design. The robust 2RR filter design enables the use of a simple collective thermal tuning mechanism to compensate for global fabrication variations as well as for global temperature fluctuations of the WDM filter, the WDM laser source, or both. Highly uniform collective heating is demonstrated using integrated doped silicon heaters. The compact filter footprint of less than 50×50 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> per channel enables straightforward scaling of the WDM channel count to 8 channels and beyond. Such low-loss collectively tuned ring-based WDM filters can prove beneficial in scaling the bandwidth density of chip-level silicon optical interconnects.