Long-haul Communication Research Articles

Low Dark Current 1.55 Micrometer InAs Quantum Dash Waveguide Photodiodes

Photodiodes and integrated optical receivers operating at 1.55 micrometer (μm) wavelength are crucial for long-haul communication and data transfer systems. In this paper, we report C-band InAs quantum dash (Qdash) waveguide photodiodes (PDs) with a record-low dark current of 5 pA, a responsivity of 0.26 A/W at 1.55 μm, and open eye diagrams up to 10 Gb/s. These Qdash-based PDs leverage the same epitaxial layers and processing steps as Qdash lasers and can thus be integrated with laser sources for power monitors or amplifiers for preamplified receivers, manifesting themselves as a promising alternative to their InGaAs and Ge counterparts in low-power optical communication links.

Critical link analysis of a national internet backbone via dynamic perturbation

Long-haul backbone communication networks provide internet services across a region or a country. The access to internet at smaller areas and the functioning of other critical infrastructures rely on the long-haul backbone high speed services and resilience. Hence, such networks are key for the decision-making of internet service managers and providers, as well as for the management and control of other critical infrastructures. This paper proposes a critical link analysis of the physical infrastructure of the UK internet backbone network from a dynamic, complex network approach. To this end, perturbation network analyses provide a natural framework to measure the network tolerance facing structural or topological modifcations. Furthermore, there have been taken into account variations on data-traffic for the internet backbone that usually happen in a typical day. The novelty of the proposal is, then, twofold: proposing a weighted (traffic informed) Laplacian matrix to compute a perturbation centrality measure, and enhancing it by a time-dependent perturbation analysis to detect changes in link criticality within the network, coming from data traffic variation in a day. The results show which are the most critical links at every time of the day, being of main importance for protection, maintenance and mitigation plans for the UK internet backbone.

Performance analysis of physical-layer security in ISK quantum-noise randomized cipher based on wiretap channel

Based on the conventional analytical method on wiretap channel model, the physical-layer security of intensity shift keying (ISK) quantum-noise randomized cipher (QNRC) systems is analyzed quantitatively. The wiretap channel models for the key and the data in ISK-QNRC systems are established respectively. The secrecy rates are employed to evaluate the physical-layer security level of both the key and data. Further, the maximal achievable secrecy rate of ISK-QNRC system is proposed, which guarantees the secrecy of the key and data. In order to further optimize the security of ISK-QNRC systems, the impacts of various system parameters and cases on secrecy rates are assessed and compared in detail. The simulation results indicate ISK-QNRC system combined with proper channel codes can realized high-speed and long-haul anti-interception communications. The maximal achievable secrecy rate of ISK-QNRC system is constrained mainly by the security of the running key in general cases. It is helpful to choose the proper power of mesoscopic quantum state, gain of optical amplifier at the transmitter and number of bases for improving the security performance of ISK-QNRC system.

A 640-Gbps, 15.2344-b/s/Hz full-duplex optical fiber/wireless single-channel coherent communication system using IQM-based DP-256-QAM and DSP techniques

A full-duplex optical fiber/wireless single-channel coherent communication system is presented for high-speed data center interconnections. In-phase and quadrature modulator (IQM)-based dual polarization 256 quadrature amplitude modulation (DP-256-QAM) is implemented to achieve a maximum data rate of 640 Gbps with 40 Gbaud symbol rate for both the single-mode fiber (SMF) and free-space optics (FSO) links. Advanced digital signal processing (DSP) algorithms have been implemented at the receiver to compensate for signal impairments during propagation. The system with optical IQM and DSP algorithms can be fabricated in the form of cost-efficient integrated circuits and possess a potential spectral efficiency of 15.2344 b/s/Hz. A maximum transmission distance of 160 km and 4 km is achieved in simulation platform for the SMF and FSO links, respectively. The system performance is evaluated regarding laser linewidth requirements, optical signal-to-noise ratio tolerance, receiver sensitivity and launched optical power. This transceiver system shall be useful in high-speed long-haul communications, and the FSO system provides the same data rate to the remote areas, and last mile connections where laying of an optical fiber is not possible or cost is a major concern.

Bending and twisting effects on multicore fiber differential group delay.

In this paper we provide the theoretical and experimental evaluation of fiber bending and twisting effects on the group delay performance of a homogeneous 7-core fiber. We have experimentally evaluated the differential group delay between the central and outer cores for different curvature radii and twisting conditions, demonstrating that fiber twisting counteracts the degradation introduced by the curvature itself. These findings are generally applicable to time-sensitive application areas such as radio-over-fiber distribution and microwave photonics signal processing in fiber-wireless access networks, as well as high-capacity long-haul digital communications where digital multiple-input multiple-output processing may be required.

High Speed OTDM-DWDM Bit Compressed Network for Long-Haul Communication

This paper represents an optical communication network design that incorporates both OTDM and DWDM techniques which provides up to 240 Gbit/s data transfer rate, long-haul communication distance of 2700 km with a maximum number of 384 channels in this designed architecture. Each channel has a bitrate of 625 Mbit/s that follows optical signal hierarchy OC-12, STS-12 (SONET ANSI), and STM-4 (SDH CCITT), and the design maintains standard parameters for commercially available channel grids at 100 GHz spacing. The communication is done by Single Mode Fiber (SMF) of 50 km and Dispersion Compensating Fiber (DCF) of 10 km followed by one optical amplifier gain in each span. Bit error rate (BER) remains significantly low while transmission distance for only OTDM is 18000 km at a BER < 10-12, and for the hybrid OTDM-DWDM it is 2700 km at a BER < 10-16. Both values are measured under 128 bits sequence length. Three compression stages are used for 8 channels each in order to minimize the gap between bits, and to utilize the space for more channels within a specific time window.

Quantum teleportation-based state transfer of photon polarization into a carbon spin in diamond

Quantum teleportation is a key principle for quantum information technology. It permits the transfer of quantum information into an otherwise inaccessible space, while also permitting the transfer of photon information into a quantum memory without revealing or destroying the stored quantum information. Here, we show reliable quantum state transfer of photon polarization into a carbon isotope nuclear spin coupled to a nitrogen-vacancy center in diamond based on photon-electron Bell state measurement by photon absorption. The carbon spin is first entangled with the electron spin, which is then permitted to absorb a photon into a spin-orbit correlated eigenstate. Detection of the electron after relaxation into the spin ground state allows post-selected transfer of arbitrary photon polarization into the carbon memory. The quantum state transfer scheme allows individual addressing of integrated quantum memories to realize scalable quantum repeaters for long-haul quantum communications, and distributed quantum computers for large-scale quantum computation and metrology.

Plasmonic IQ modulators with attojoule per bit electrical energy consumption

Coherent optical communications provides the largest data transmission capacity with the highest spectral efficiency and therefore has a remarkable potential to satisfy today’s ever-growing bandwidth demands. It relies on so-called in-phase/quadrature (IQ) electro-optic modulators that encode information on both the amplitude and the phase of light. Ideally, such IQ modulators should offer energy-efficient operation and a most compact footprint, which would allow high-density integration and high spatial parallelism. Here, we present compact IQ modulators with an active section occupying a footprint of 4 × 25 µm × 3 µm, fabricated on the silicon platform and operated with sub-1-V driving electronics. The devices exhibit low electrical energy consumptions of only 0.07 fJ bit−1 at 50 Gbit s−1, 0.3 fJ bit−1 at 200 Gbit s−1, and 2 fJ bit−1 at 400 Gbit s−1. Such IQ modulators may pave the way for application of IQ modulators in long-haul and short-haul communications alike.

Energy-Efficient High-Throughput VLSI Architectures for Product-Like Codes

Implementing forward error correction (FEC) for modern long-haul fiber-optic communication systems is a challenge, since these high-throughput systems require FEC circuits that can combine high coding gains and energy-efficient operation. We present very large scale integration (VLSI) decoder architectures for product-like codes for systems with strict throughput and power dissipation requirements. To reduce energy dissipation, our architectures are designed to minimize data transfers in and out of memory blocks, and to use parallel noniterative component decoders. Using a mature 28-nm VLSI process technology node, we showcase different product and staircase decoder implementations that have the capacity to exceed 1-Tb/s information throughputs with energy efficiencies of around 2 pJ/b.

ASIC Implementation of Time-Domain Digital Back Propagation for Coherent Receivers

Digital back propagation (DBP) is often proposed and implemented offline for the mitigation of nonlinear impairments in long-haul fiber communications. However, complexity in terms of chip area and power consumption in a realistic application-specific integrated circuit implementation is yet to be determined. Here, we implement time-domain DBP (TD-DBP) in a 28-nm fully-depleted silicon-on-insulator process technology, considering digital implementation aspects such as limited-resolution arithmetic and finite-length filters. We choose as example a coherent optical transmission system, viz. a single-channel, single-polarization, and 20-GBd 16-QAM system, for which the DBP is known to perform well. For the considered system, we find that the TD-DBP can enable a reach increase from 3400 to 5300 km, at a power dissipation of $10^{-2}$ .

What could and should be done differently: failure-oriented-accelerated-testing (FOAT) and its role in making an aerospace electronics device into a product

High operational reliability of an electronic material or a device intended for aerospace applications is critical, and, in the author’s opinion, cannot be assured, if the underlying physics of failure is not well understood and the never-zero probability of failure is not predicted and made adequate for the particular material, device and application. The situation is the same in some other areas of electronics materials engineering, such as military, medical, or long-haul communications, where high level of reliability is required. The situation is different in today’s commercial electronics, where cost and time-to-market are typically more important than high reliability. Failure-oriented-accelerated-testing (FOAT) of aerospace electronics materials and products and its role in making a viable device into a reliable product is addressed and discussed vs. very popular today highly-accelerated-life-testing (HALT). The differences of the two accelerated test procedures and objectives is briefly discussed. FOAT is an essential part of the recently suggested probabilistic design for reliability (PDfR) approach in electronics engineering. It is argued that high (adequate) reliability level of aerospace electronics materials and devices cannot be achieved and assured, if their never-zero probability-of-failure is not quantified for the given (anticipated) combination of the loading conditions (stresses, stimuli) and time in operation. It is the application of the FOAT, the heart of the highly effective and highly flexible PDfR concept, that should be employed and mastered, when high reliability of a material or a device is imperative. The general concepts are illustrated by numerical examples. They are based on an analytical modeling approach, as the FOAT models are.

Long-haul coherent communications using microresonator-based frequency combs.

Microresonator-based frequency combs are strong contenders as light sources for wavelength-division multiplexing (WDM). Recent experiments have shown the potential of microresonator combs for replacing a multitude of WDM lasers with a single laser-pumped device. Previous demonstrations have however focused on short-distance few-span links reaching an impressive throughput at the expense of transmission distance. Here we report the first long-haul coherent communication demonstration using a microresonator-based comb source. We modulated polarization multiplexed (PM) quadrature phase-shift keying-data onto the comb lines allowing transmission over more than 6300 km in a single-mode fiber. In a second experiment, we reached beyond 700 km with the PM 16 quadrature amplitude modulation format. To the best of our knowledge, these results represent the longest fiber transmission ever achieved using an integrated comb source.

Loss Analysis in Optical Fiber Transmission

Most of telecommunication traffic (voice and data) around the globe is carried over the optical fiber cable. Theinternational traffic through various countries is carried over optical fiber cables laid under the sea. Similarly the long-haul traffic within the country is through optical fiber laid underground. Stress, strain, humidity, temperature, bending at acute angles affects the propagation of light energy in the optical fiber cable. All such factors increase the optical loss and attenuate the signal. The attenuation, especially in the long-haul communication increases the bit error rate and degrades the quality of service. In this paper, different optical losses are analyzed by setting up several experiments at a single mode optical fiber spool of 4 km. The optical fiber segment was subjected to various stress, temperatures and acute bending conditions. The resulting losses and degradation of the signal was measured using OTDR and Power meter.

Chromatic dispersion mitigation in long-haul fiber-optic communication networks by sub-band partitioning.

We propose and experimentally demonstrate a novel sub-band multiplexed data architecture for chromatic dispersion (CD) mitigation. We have demonstrated 32 GBaud multi-sub-band (MSB) dual-polarization (DP) 16QAM transmission over 2400 km. Using this approach, the transmitted signal bandwidth is divided into multiple narrow-bandwidth sub-bands, each operating at a lower baud rate. Within each sub-band bandwidth, the CD frequency response can be approximated as a linear-phase band-pass filter, which can be considered as an analog delay that does not require compensation. Therefore, the resulting receiver digital signal processing (DSP) is simplified due to the removal of the CD compensation equalizer. In addition, this leads to efficient parallelization of DSP tasks by deploying multiple independent sub-band processors running at a lower clock rate. The proposed system reduces receiver computational complexity and offers 1 dB higher Kerr-nonlinearity tolerance and 2% extended transmission reach in comparison to the conventional single carrier systems.

On-chip WDM mode-division multiplexing interconnection with optional demodulation function.

We propose and fabricate a wavelength-division-multiplexing (WDM) compatible and multi-functional mode-division-multiplexing (MDM) integrated circuit, which can perform the mode conversion and multiplexing for the incoming multipath WDM signals, avoiding the wavelength conflict. An phase-to-intensity demodulation function can be optionally applied within the circuit while performing the mode multiplexing. For demonstration, 4 × 10 Gb/s non-return-to-zero differential phase shift keying (NRZ-DPSK) signals are successfully processed, with open and clear eye diagrams. Measured bit error ratio (BER) results show less than 1 dB receive sensitivity variation for three modes and four wavelengths with demodulation. In the case without demodulation, the average power penalties at 4 wavelengths are -1.5, -3 and -3.5 dB for TE₀-TE₀, TE₀-TE₁ and TE₀-TE₂ mode conversions, respectively. The proposed flexible scheme can be used at the interface of long-haul and on-chip communication systems.

Investigation of Four Wave Mixing Effect at Different Transmission Power Levels and Channel Spacing

There is an incredible focus on broadband fiber optical transmission system as it offers many advantages over other communication systems such as large bandwidth and significantly low losses [1]. This high bandwidth in optical communication networks is further increased by using Wavelength Division Multiplexing. In WDM based fiber optical communication systems nonlinearities in fiber are a limiting factor which degrade the system performance and limit the data rate and bandwidth of the system [3]. As we increase the transmission power levels so as to transmit data for long-haul communications systems these non linear effects tend to accumulate. Due to these non linear effects, all input signals may interact with each other in a complicated way which degrades overall performance of optical communication system. In WDM systems, the interaction of input signals with each other adversely affects the performance of the system. Hence it is of great importance to understand fiber non linear effects and its effect on optical fiber communication system. The main objective of this paper is to study non linear effects in fiber optic communication system mainly Four Wave Mixing (FWM) and to analyze to effect of increasing optical transmission powers and channels spacing in a wave division multiplexing system. The results show that as the transmission power is increased, the efficiency of four wave mixing effect increases. Also if the channel spacing in a WDM system is kept uneven, the power levels of mix frequencies produced as a result of FWM effects is reduced to a considerable amount. General Terms Investigation, Four Wave Mixing, Wave Division Multiplexing

Energy-Efficient Wavelength Multiplexers Based on Hydrogenated Amorphous Silicon Resonators

Optical multiplexers are key components of modern data transmission systems that have evolved from long-haul fiber communication applications down to the photonic interconnect level on-chip, which demand high bandwidths and low-power photonic links with small footprint. We present compact, energy-efficient, and high-bandwidth optical add/drop multiplexers that are based on complementary metal-oxide-semiconductor (CMOS) backend-compatible hydrogenated amorphous silicon microring resonators. We study the manufacturing nonuniformity of the as-fabricated devices and analyze the static power consumption that is required to actively align the multiplexers to a 100-GHz grid by using state-of-the-art microheaters. The microring filter banks are in excellent agreement with the design and satisfy a good tradeoff between concurrent properties of high-data-rate capability, low filter loss, high channel isolation, and manufacturing uniformity, which facilitates the operation with low static power consumption. In addition, we demonstrate that it is possible to permanently correct the unavoidable fabrication imperfections and to arrange the individual wavelength channels by a postfabrication trimming method so that the static power is reduced by more than an order of magnitude and allows minimization of these parts of the overall power requirements of such photonic integrated circuits down to record low metrics of a few femtojoules per bit.

Terabit-Per-Second Optical Super-Channel Receiver Models for Partial Demultiplexing of an OFDM Spectrum

Terabit-per-second (Tb/s) transmission capacity for the next generation of long-haul communication networks can be achieved using multicarrier optical super-channel technology. In an elastic orthogonal frequency division multiplexing (OFDM) super-channel transmission system, demultiplexing a portion of an entire spectrum in the form of a subband with minimum power is critically required. A major obstacle to achieving this goal is the analog-to-digital converter (ADC), which is power-hungry and extremely expensive. Without a proper ADC that can work with low power, it is unrealistic to design a 100G coherent receiver suitable for a commercially deployable optical network. Discrete Fourier transform (DFT) is often seen as a primary technique for understanding partial demultiplexing, which can be attained either optically or electronically. If fairly comparable performance can be achieved with an all-optical DFT circuit, then a solution independent of data rate and modulation format can be obtained. In this paper, we investigate two distinct OFDM super-channel receiver models, based on electronic and all-optical DFT-technologies, for partial carrier demultiplexing in a multi-Tb/s transmission system. The performance comparison of the receivers is discussed in terms of bit-error-rate (BER) performance.

Silicon-chip source of bright photon pairs

Integrated quantum photonics relies critically on the purity, scalability, integrability, and flexibility of a photon source to support diverse quantum functionalities on a single chip. Here we report a chip-scale photon-pair source on the silicon-on-insulator platform that utilizes dramatic cavity-enhanced four-wave mixing in a high-Q silicon microdisk resonator. The device is able to produce high-quality photon pairs at different wavelengths with a high spectral brightness of 6.24×10(7) pairs/s/mW(2)/GHz and photon-pair correlation with a coincidence-to-accidental ratio of 1386 ± 278 while pumped with a continuous-wave laser. The superior performance, together with the structural compactness and CMOS compatibility, opens up a great avenue towards quantum silicon photonics with capability of multi-channel parallel information processing for both integrated quantum computing and long-haul quantum communication.

Measurement of the radiation patterns of navy shipboard High Frequency (HF) antennas on a large warship

Warships use strategic and tactical communications to be connected with national command headquarters and other units around the world. Therefore vessels need a communication system to be able to provide line-of-sight and long-haul communications. High Frequency (HF) communications can meet this requirement. Thus the ship needs to know the behavior of HF communications systems, for example, if they have any null in the radiation pattern. This article describes the measurements of the radiation patterns of HF whips in different places and with different polarizations (2–30MHz) on a large vessel. Theoretically, HF shipboard antennas are close to be omnidirectional, so that the transmission and reception do not depend on where the ship is heading. We need to know the patterns at different frequencies first, to evaluate if the place where the antennas have been placed is adequate and second, to detect the possible nulls in the radiation pattern.