Bringing telecom networks up to speed [planar lightwave circuits]

Planar lightwave circuits (PLCs) provide various important devices for WDM systems, TDM systems, and subscriber networks. This article reviews the recent progress and future prospects of PLC technologies including arrayed-waveguide grating (AWG) wavelength filters, optical add/drop multiplexers (ADMs), programmable dispersion equalizers, and hybrid optoelectronics integration technologies. Continuous improvements in waveguide fabrication, circuit design, and device packaging will further bring these technologies to a higher level of integration of optics and electronics, aiming at the next generation of telecommunication systems     

OA&M framework for multiwavelength photonic transport networks

Photonic networks based on wavelength division multiplexing (WDM) and optical path technologies are expected to realize flexible, transparent, and cost-effective transport networks with a large transmission capacity. This paper explores the design framework of photonic transport networks taking into consideration the operation administration and maintenance (OA&M) functions required for the successful introduction of WDM systems based on the optical path concept. From the view point of network maintenance, clear distinction is made between the optical path layer and the optical section layer to facilitate accurate and smooth failure localization. The digital multiplexing span between physical multiplexing interfaces at the end-to-end digital nodes should have the same maintenance span as the corresponding optical path. We argue that cooperative maintenance by OA&M functions at both the digital and optical layers can be a practical way of network supervision. A supervisory (SV) signal transfer method and a configuration that is suitable for the terrestrial trunk network are also indicated. As an example, a practical SV system design methodology and an actual procedure developed for a single channel optical transmission system based on optical in-line amplifiers are introduced. Furthermore, application of the developed SV system and network restoration schemes is discussed for future WDM-based photonic networks. The OA&M aspects introduced will be valuable for creating future photonic network systems     

Photonic crystal add–drop filter: a review on principles and applications

Add–drop filter (ADF) is a key component in optical integrated circuits that can be used in all-optical communication networks and wavelength division multiplexing (WDM) systems. The quality factor, coupling efficiency, transmission efficiency and coupling length are important parameters in add–drop filters. Photonic crystal (PC) optical devices have become popular among researchers because their structure is suitable to embed into optical circuits. This paper covers a comprehensive review of the principle structure of ADF, coupled mode theory (CMT), types and recent applications in WDMs, accelerometer and bio/chemical sensors. Although there are some different categories of photonic crystal ring resonator-based ADF in general, all of them can be divided into photonic to two class of non-circular and circular. This article is reported a comprehensive study about ADF and improvement of these ADF.

     

AWG-based metro WDM networking

A plethora of metropolitan area wavelength-division multiplexing networks have been proposed and examined in recent years with the aim to alleviate the bandwidth bottleneck between increasingly higher-speed local/access networks and high-speed backbone networks. Many of the considered metropolitan area networks use the arrayed waveguide grating as an optical building block. As we review in this article, in ring, interconnected ring, and meshed metro WDM networks, the AWG is typically used to realize wavelength multiplexers, demultiplexers, or optical add-drop multiplexers without capitalizing on spatial wavelength reuse. By using the AWG as a wavelength router, highly efficient star metro WDM networks can be realized due to extensive spatial wavelength reuse. We give an overview of star metro WDM networks that are able to meet modular upgradability, transparency, flexibility, efficiency, reliability, and protection requirements of future metro networks. AWG-based star networks also enable an evolution path of ring networks toward highly efficient and fault-tolerant hybrid star-ring metro network solutions.     

Photonic gateway: multiplexing format conversions of OCDM-to-WDM and WDM-to-OCDM at 40 Gb/s (4/spl times/10 Gb/s)

Photonic gateway, which performs the bilateral conversion and reconversion of multiplexing format, is proposed. 40-Gb/s (4/spl times/10 Gb/s) optical code-division multiplexing (OCDM)-to-wavelength-division multiplexing (WDM) conversion and WDM-to-OCDM reconversion are experimentally demonstrated for the first time. The experimental scheme is based upon ultrafast photonic processing both in the time domain and frequency domain, namely, optical encoding/decoding along with optical time-gating in the time domain and supercontinuum generation followed by spectrum slicing in the frequency domain. Thus, the possibility of ultra-high-speed operation features this photonic conversion scheme in the future photonic networks.     

Statistical Analysis of WDM Photonic Microwave Filters With Random Errors

Several photonic microwave filters based on a set of optical carriers of different wavelength and a dispersive medium have been proposed to benefit from their flexibility and a variety of commercial wavelength division multiplexing (WDM) devices. However, practical implementations of such filters suffer random errors in the optical power and the wavelength of the optical sources. In this paper, the statistical analysis of the performance of photonic microwave filters based on multiple optical carriers (i.e., WDM) and a dispersive medium with random errors in amplitude and wavelength spacing between optical carriers is presented, showing that these errors translate in a residual sidelobe level dependent on the statistics of the random errors. An expression of the residual sidelobe level is derived. Finally, experimental results showing a good agreement with theory are provided.     

用于波分复用的光子晶体滤波器

本文从光子晶体的光子频率禁带特性出发，提出了用2个或以上的均匀周期结构光子晶体叠加在一起，形成叠层结构光子晶体，以获得窄带滤波特性的设想；利用光学传输矩阵法对这种结构进行了数值计算，结果证实了构思的正确性；设计了信道间隔为8nm的8信道波分复用（WDM）和信道间隔0.8nm的8信道密集波分复用（DWDM）光子晶体滤波器。     

Scalable WDM access network architecture based on photonic slotrouting

This paper introduces an approach to solving the fundamental scalability problem of all-optical packet switching wavelength-division multiplexing (WDM) access networks. Current optical networks cannot be scaled by simply adding nodes to existing systems due to the accumulation of insertion losses and/or the limited number of wavelengths. Scalability through bridging requires, on the other hand, the capability to switch packets among adjacent subnetworks on a wavelength basis. Such a solution is, however, not possible due to the unavailability of fast-switching wavelength sensitive devices. In this paper, we propose a scalable WDM access network architecture based on a recently proposed optical switching approach, termed photonic slot routing. According to this approach, entire slots, each carrying multiple packets (one on each wavelength) are “transparently” routed through the network as single units so that wavelength sensitive data flows can be handled using fast-switching wavelength nonsensitive devices based on proven technologies. The paper shows that the photonic slot routing technique can be successfully used to achieve statistical multiplexing of the optical bandwidth in the access network, thus providing a cost-effective solution to today's increasing bandwidth demand for data transmissions     

A large-scale AWG-based single-hop WDM network using couplers with collision avoidance

Single-hop wavelength division multiplexing (WDM) networks based on a central arrayed waveguide grating (AWG) have attracted a great deal of attention as a solution for metropolitan area network applications because they can achieve high throughput with reduced cost due to the periodic wavelength-routing property of the AWG. Unfortunately, scalability is a significant problem in an AWG-based single-hop WDM network because the number of transceivers required at each node is equal to the total number of nodes. This problem can be solved by providing optical couplers between the AWG and the nodes and by aggregating multiple nodes before connecting to the AWG. In this case, however, packet collisions at the couplers will seriously increase the packet network delay. Therefore, we propose a novel AWG-based single-hop WDM network in which an autonomic collision avoidance mechanism is introduced in the couplers. We derive the optimum number of couplers for this architecture. Through numerical study, we clarify that the proposed network architecture can reduce the total network cost dramatically.     

Architectural considerations for photonic IP router based uponoptical code correlation

A photonic label switching router (PLSR) of which the photonic label processing is based upon optical code correlation, is investigated. To resolve the electronic router's bottleneck in current Internet protocol (IP) over wavelength division multiplexing (WDM) networks, we will envision IP over photonic networks in which the PLSRs totally replace the electronic routers. The architectures of PLSR including the photonic label processing, the photonic label swapping, and the optical switching and their optical implementations are studied. Results of proof-of-concept experiments for the photonic label processing and photonic label swapping will confirm the feasibility to attain the target performance: the throughput of 100 Tb/s at least, the processing speed around 10 Gpacket/s, and the number of label entries up to 10 k     

Key building blocks for high-capacity WDM photonic transportnetworks

The objective of this paper is to give an overview of the different studies we have performed at the research level regarding the design and implementation of a photonic wavelength division multiplexing (WDM) layer providing transparent transport services to client layers (SONET/SDH, ATM, etc.). Such a network requires a number of enabling factors to be assessed in order to become a reality. Among these factors are the availability of high-capacity WDM transmission systems and efficient optical routing nodes based on mature technology, the design of robust networks optimizing the utilization of resources, and the development of a management system in accordance with presently applied standards for transport networks. We review our achievements in these different fields     

Photonic transport network architecture and OA&M technologiesto create large-scale robust networks

In order to realize a large-scale and robust photonic transport network, a network protection strategy and operation, administration, and management (OA&M) realization scheme in wavelength division multiplexing optical path (WDM OP) transport networks has been developed. This paper discusses the networking (restoration/protection) concepts in each optical layer and proposes the most suitable networking strategy. To develop the OA&M technique, the characteristic information format of each optical layer must be discerned. A network node interface (NNI) structure for the WDM OP transport network is proposed. The proposed NNI is defined as the optical transport module (OTM). An OP signal format is defined as the optical transport unit (OTU). Overhead information and schemes to transmit it are also discussed     

硅锗基区异质结双极晶体管的研究进展

叙述了硅锗基区异质结双极晶体管的研究发展现状，分析了该晶体管的结构机理、特点及制造技术，并且阐述了该器件的发展前景。     

WDM光网络中的业务量疏导

波分复用（WDM）技术在主干传送网中巳广泛应用，WDM光网络的研究进展也非常迅速，光网络中的业务量疏导定义为复用、解复用和交换低速率业务流到大容量的光路中的行为。介绍了WDM光网络的业务量疏导的重要性，研究方法及其最新研究进展情况。     

Crosstalk reduction in N×N WDM multi/demultiplexers bycascading small arrayed waveguide gratings (AWG's)

This paper shows a new scheme which improves the crosstalk performance of large optical multi/demultiplexers, a key component in wavelength division multiplexing (WDM) systems. This scheme uses arrayed waveguide gratings (AWG's) of various sizes and requires no additional equipment. It is well known that a large multi/demultiplexer can be constructed by cascading small multi/demultiplexers. We have studied the impact of the number and size of AWG stages on crosstalk performance. This paper proves that to obtain a multistage multi/demultiplexer with minimum crosstalk, the total channel number of each AWG stage must be minimized. For example, cascading 10-channel AWG's and 11-channel AWG's improves the crosstalk performance of a 110-channel multi/demultiplexer by about 7.5 dB. Furthermore, the crosstalk performance degradation due to fabrication error is theoretically investigated taking channel bandwidth into account. Optimum design parameters of multistage AWG's are introduced: When the AWG suppression ratio is 30 dB and the ratio of channel bandwidth to channel spacing is about 0.24, the degradation in crosstalk performance due to fabrication error is minimized. The tradeoff between the crosstalk performance and the efficiency in terms of hardware and wavelength are also discussed. It is discovered that this simple scheme can yield a crosstalk-free WDM router. Crosstalk reduction obtained by this scheme allows the realization of flexible multiwavelength networks based on wavelength routing     

Analysis and design for optical video transport distribution systemwith video on demand service

A cost-effective methods of multiplexing, transmitting, and selecting optical video signals is proposed and demonstrated by using appropriate combinations of bidirectional optical trunk-amplifier, medium-density wavelength division multiplexing (WDM) and optical space switching techniques for rapid cost-effective construction. The major factors affecting optical video transport/distribution system design are described. In particular, a tapping-type optical loop-shaped trunk section network is proposed from the viewpoint of system reliability, probability of call-loss, and B-ISDN with analog overlay. The experimental results and design philosophy for an optical selector composed of WDM filters and space switches connected by silica-based waveguide on a chip are also discussed     

DWDM在通信网中的应用

首先介绍通信设施使用多路利用技术的发展进程,然后叙述了波分复用在光纤传输线路中的应用,最后解释了波分复用在光核心网的应用。     

Hybrid WDM and optical CDMA implemented over waveguide-grating-based fiber-to-the-home networks

This paper presents a hybrid wavelength-division multiplexing (WDM) and optical code-division multiple-access (OCDMA) scheme over fiber-to-the-home (FTTH) networks. Exploiting the periodic free-spectral-range (FSR) properties of arrayed-waveguide grating (AWG) routers, the total ONU (optical network unit) capacity in the network is partitioned into different groups based on the subscriber's geographical locations. Maximal-length sequence (M-sequence) codes are taken as signature addresses to take advantage of the cyclic properties of AWG routers. The proposed scheme is suitable for networks in which the distance between the OLT (optical line terminal) and the individual ONUs varies. The influence of the degree of polarization (DOP) on the signal to phase-induced intensity-noise ratio is evaluated. By introducing a depolarizer in front of the balanced photo-detector, the maximum permissible number of simultaneous active ONUs can be improved by approximately 20% for a 10⁻⁹ error probability. By exploiting the inherent cyclic FSR characteristics of AWG routers, the OLT enables a significant reduction in the number of AGW-based network codecs compared to the previous coded WDM (i.e., OCDMA in spectral domain) scheme. Furthermore, while the number of AWGs in the proposed scheme is comparable to that of conventional WDM-EPON schemes, the current scheme is more flexible, confidential, and scalable.     

Large-scale WDM star-based photonic ATM switches

This paper describes the large-scale photonic asynchronous transfer mode (ATM) switching systems being developed in NTT Laboratories. It uses wavelength division multiplexing (WDM) techniques to attack 1 TB/s throughput. The architecture is a simple star with modular structure and effectively combines optical WDM techniques and electrical control circuits. Recent achievements in important key technologies leading to the realization of large-scale photonic ATM switches based on the architecture are described. We show that we can obtain a 320 Gb/s system that can tolerate the polarization and wavelength dependencies of optical devices. Our experiments using rack-mounted prototypes demonstrate the feasibility of our architecture. The experiments showed stable system operation and high-speed WDM switching capability up to the total optical bandwidth of 12.8 nm, as well as successful 10 Gb/s 4×4 broadcast-and-select and 2.5 Gb/s 16×16 wavelength-routing switch operations     

密集波分多路在组建通信网中的应用

首先说明通信设施使用多路技术的发展进程，从过去的频分多路（FDM）至数字的时分多路＊TDM）到最近的波分多路（WDM），接着，叙述WDM在光纤传输线路中的应用，对加大传输容量非常有效，最后，解释WDM在光核心网中的应用，以期扩大通信网容量，适应快速增长的通信业务量的需要。