IEEE/OSA Journal of Optical Communications and Networking

This paper presents a wavelength assignment algorithm suitable for optical networks mainly impaired by physical layer effects, named the Intelligent Wavelength Assignment algorithm (iWA). The main idea is to determine the wavelength activation order for a first-fit algorithm that balances the impact of the physical layer effects by using a training algorithm inspired by evolutionary concepts. The iWA presents some recently proposed concepts in intelligent optimization algorithms, such as an external archive to store the best solutions. Some different physical layer effects, such as four-wave mixing and residual dispersion, were considered in the tests of our proposal. We tested our proposal for transparent optical networks. However, we believe iWA can be used in other types of network, such as opaque networks and translucent networks. The proposed wavelength assignment algorithm was compared with five other wavelength assignment algorithms for two network topologies in three different scenarios. The iWA algorithm outperformed the other WA algorithms in most cases. The robustness of our proposed algorithm to the load distribution changes was also analyzed.

In transparent optical networks, signals propagate over all-optical lightpaths. The absence of regenerating devices that act in the electrical domain renders end-to-end monitoring difficult. Quality of transmission (QoT) metrics quantify the degradation in quality that a signal experiences as it traverses a lightpath. Hardware monitors that can directly measure QoT are expensive, which motivates the development of monitoring schemes that require fewer monitors but can still generate accurate QoT estimates. In this paper we describe a monitoring scheme that estimates the QoT of multiple lightpaths in a network. Our focus is on estimating bit-error-rates (BERs), but the methodology is also applicable for other metrics. One of the primary innovations in this monitoring framework is the establishment of “active lightpaths”-lightpaths that carry no useful data but are instead used as measurement probes. We describe a method for choosing where to establish the active lightpaths in order to maximize the information gain. We demonstrate with simulations the possibility to trade off the amount of costly hardware monitoring equipment with cheaper, temporary active lightpaths, while still achieving accurate monitoring.

This paper focuses on the connectivity issues of a non-line-of-sight (NLOS) optical wireless network operating in the ultraviolet UV-C spectral region. NLOS UV-C transmitters have a limited effective coverage and, hence, a dense node distribution is required in order to efficiently cover a large geographical area. Under this assumption, the concept of connectivity is more than important since it provides a strong indication of the network reliability and robustness. In the present study, we consider transmission with on-off keying and pulse position modulation schemes assuming both Gaussian and Poisson noise and adopt an effective experimental path loss model. Then, we evaluate the k-connectivity properties in terms of several network parameters. More precisely, we present and analyze the trade-off between node density and the degree of k-connectivity against other parameters (i.e., transmitted power, supported data rate, and error probability). The derived results are depicted using appropriate figures and tables and constitute the theoretical basis for the design and implementation of a reliable UV-C network in practice.

A regenerative all-optical grooming switch for interconnecting 130 Gbit/s on-off keying (OOK) metro/core ring and 43 Gbit/s-OOK metro/access ring networks with switching functionality in time, space, and wavelength domains is demonstrated. Key functionalities of the switch are traffic aggregation with time-slot interchanging functionality, optical time division multiplexing (OTDM) to wavelength division multiplexing (WDM) demultiplexing, and multi-wavelength 2R regeneration. Laboratory and field demonstrations show the excellent performance of the new concept with error-free signal transmission and Q-factors above 20 dB.

Free space laser communication is a potentially attractive technology that can offer intrinsically high data rates and resistance to jamming, and facilitates low probability of interception and low probability of detection (LPI/LPD). However, practical links established in the atmosphere are adversely affected by signal attenuation and dynamic turbulence, which can create spatial and temporal variations in the refractive index. The resulting distortions lead to reduced signal power and increased bit error rate (BER), even over short ranges. To overcome possible signal degradation under adverse conditions, laser communication systems must increase power and reduce the communication bit rate. Under dynamic link attenuation both of these parameters can be tuned to optimize performance. In this paper, we present and compare three methods for optimizing optical link efficiency. The work is based on experiments conducted with a commercially available system, and its scaled-down laboratory prototype. The proposed methods demonstrate different degrees of optimization capabilities under practical operating conditions, but, in general, they maintain the highest possible bit rate at the minimum power consumption, while obtaining an acceptable BER.

With the continuing growth in the amount of backbone traffic, improving the cost-effectiveness and ensuring survivability of the underlying optical networks are very important problems facing network service providers today. In this paper, we propose a bandwidth squeezed restoration (BSR) scheme in our recently proposed spectrum-sliced elastic optical path network (SLICE). The proposed BSR takes advantage of elastic bandwidth variation in the optical paths of SLICE. It enables spectrally efficient and highly survivable network recovery for best-effort traffic as well as bandwidth guaranteed traffic, while satisfying the service level specifications required from the client layer networks. We discuss the necessary interworking architectures between the optical path layer and client layer in the BSR in SLICE. We also present a control framework that achieves flexible bandwidth assignment as well as BSR of optical paths in SLICE. Finally, we describe an implementation example of a control plane using generalized multi-protocol label switching (GMPLS).

In this paper, a power and bandwidth efficient pulsed modulation technique for optical wireless (OW) communication is proposed. The scheme is called optical spatial modulation (OSM). In OSM, multiple transmit units exist where only one transmitter is active at any given time instance. The spatially separated transmit units are considered as spatial constellation points. Each unique sequence of incoming data bits is mapped to one of the spatial constellation points, i.e., activating one of the transmit units. This is the fundamental concept of the spatial modulation (SM) technique. In OW communication systems, the active transmitter radiates a certain intensity level at a particular time instance. At the receiver side, the optimal SM detector is used to estimate the active transmitter index. An overall increase in the data rate by the base 2 logarithm of the number of transmit units is achieved. The optical MIMO (multiple-input multiple-output) channel and the channel impulse response are obtained via Monte Carlo simulations by applying ray tracing techniques. It will be shown in this paper that the optical MIMO channel is highly correlated if transmitter and receiver locations are not optimized, which results in a significant power penalty. The power efficiency can be improved by increasing the number of receive units to enhance receive diversity and/or by using soft and hard channel coding techniques. Conversely, it is shown that aligning transmit and receive units creates nearly uncorrelated channel paths and results in substantial enhancements in system performance even as compared to the diversity or coding gain. The resultant aligned scheme is shown to be very efficient in terms of power and bandwidth as compared to on-off keying, pulse position modulation, and pulse amplitude modulation. In this paper also, the upper bound bit error ratios of coded and uncoded OSM are analyzed. The analytical results are validated via Monte Carlo simulations and the results de- - monstrate a close match.

The Ethernet passive optical network (EPON) has been considered as one of the most suitable next-generation optical access solutions. As a time-division multiplexing PON (TDM-PON) technology, the transmission media of EPON is shared among multiple users. Therefore, medium access control (MAC) protocol plays an important role in enabling a dynamic bandwidth assignment (DBA) mechanism that provides efficient and fair utilization of the PON resources. However, the DBA mechanism implemented in products is open for vendor customization. In this paper, we propose a novel local-traffic-prediction-based dynamic bandwidth assignment (LT-DBA) mechanism applicable in a remote-repeater-based EPON system with active forwarding. The LT-DBA aims to improve the bandwidth utilization and average packet delay performance of EPON in upstream transmission in comparison to conventional bandwidth assignment techniques such as static bandwidth assignment (SBA) and the interleaved polling algorithm (IPACT), leading to a more efficient PON system.

We have proposed and experimentally demonstrated a new radio-over-fiber system technique generating optical millimeter-waves with central carriers suppressed by simply tuning the modulation index of an optical phase modulator without requiring any complicated bias control circuits or narrowband optical filters. Error-free transmission of the generated 40-GHz optical mm-wave with 2.5-Gb/s data over 10-km single mode fiber (SMF-28) and 3-m air distance was achieved. The experimental results were analyzed and compared with the traditional method that requires a specific carrier suppression optical filter. The power penalty caused by the crosstalk between wavelength division multiplexed (WDM) channels was experimentally measured and studied and was about 4 dB at a bit error rate (BER) of 10-9. The filter bandwidth requirement, achievable carrier suppression ratio, and harmonics fluctuation due to fiber dispersion were also theoretically analyzed.