Optical transmission network and optoelectronics industry

    Abstract: This article explains the concept and development of Optical Transport Network (OTN), and discusses the driving force of the booming OTN on the optoelectronics industry.

    Keywords: Internet optical transport network dense wavelength division multiplexing

Internet and its supporting network

Since the end of the last century, the rapid expansion of the Internet has promoted the great development of information and communications, and the development of the latter has provided favorable conditions for further growth of the former. In this way, the benign influence between the two has accelerated the penetration of the Internet into every corner of the world. At the same time, the popularity of personal computers and mobile phones has created and continues to create a very favorable environment for the development of various online electronic activities (such as e-commerce, e-logistics, distance education, e-government, telemedicine, etc. )become possible. Moreover, it can truly be done in all directions, all day long, and can be carried out no matter when and where.

From the perspective of information transmission capabilities, the International Telecommunications Union's ITU-TG.803 specification recommends that telecommunications networks be regarded as a transmission network, which generally refers to resources with the "network" function of transmitting user information between different geographical locations, constituting telecommunications The various functions of the network can be divided into two categories: transmission function group (transmitting any telecommunications information from one point to other points); control function group (implementing various auxiliary services and operation and maintenance functions). Since the transport network is a large and complex network, it has many components. In order to simplify the description and facilitate design and maintenance, G.803 recommends using the concepts of layering and partitioning to model the transport network. . Therefore, from a vertical perspective, the transmission network is broadly divided into three layers: customer (circuit) layer, channel layer, and transmission (media) layer. In these three layers, there is a client/server relationship between adjacent layers. The former is the client of the latter, and the latter provides services (bears the load) to the former. See Figure 1.

We know that the Internet deals directly with "online" users, so it belongs to the customer layer, which itself should be supported by the channel layer and the transport layer. To this end, building a flexible, scalable information and communication infrastructure with multiple potentials will be a very important basic condition.

Optical transport network and its development

As can be seen from Figure 1, the transmission (media) layer network is the foundation, which carries all channel layer and customer layer networks. The channel layer functions are electrical domain technologies such as PDH, SDH/SONET and ATM, all of which have been developed for more than ten years. The research and development and construction of transmission (media) layer networks formed by optical network technology have become particularly active since the end of the 20th century. Objectively speaking, the development of optical fiber communication technology and the dramatic increase in information communication services have promoted The rapid development of optical network technology research. In the mid-1990s, optical fiber transmission quickly developed from "one fiber, one wave" to "one fiber, multiple waves." The characteristics of optical fiber transmission, wavelength division multiplexing (WDM) technology and the networking potential based on them make optical networks based on dense wavelength division multiplexing (DWDM) undoubtedly the best foundation for the transport layer. For this reason, the research and construction of optical network technology has become a hot spot worldwide.

However, how and what kind of optical network to develop is still very particular. The key lies in the network's transparent procedure for optical signals. From the perspective of the transparency of the network to optical signals, it is certainly good to be fully transparent. This can fully and clearly utilize the potential of light and optical fibers. The bandwidth of the network is almost unlimited. Relatively speaking, translucency can only make limited use of the potential of light and optical fibers, and the performance of the network will be limited by light-to-electricity-to-light conversion and electronic circuits. But on the other hand, they can make use of mature technologies and resources in the electrical domain, such as SDH technology and SDH equipment that have been laid out in large quantities. From a technical point of view, there are still many difficulties in realizing a fully transparent network. In order to avoid technical and operational difficulties, ITU-T recommends studying optical network technology and formulating corresponding standards based on the concept of optical transport network (OTN). OTN is named according to the functions and main characteristics of the network. It does not limit the transparency of the network. Its ultimate goal is a fully transparent all-optical network. However, you can start with translucency.

The concept of OTN is based on reality and reflects the reality of optical network technology. It also predicts the stages of OTN development based on the development trend of optical network technology. Figure 2 indicates the three stages and characteristics of the development of optical transmission networks from the development of optical transmission technology, optical networking methods, optical path connection characteristics, and network efficiency. From the perspective of network construction, most of them are still in the initial stage of development of relatively low-efficiency optical networks, and point-to-point WDM systems are mainly used to expand transmission capacity. A few cities that are developing rapidly are only in the process of developing from point-to-point WDM to OADM/OXC. Some key technologies of optical networking, such as wavelength conversion technology, are only in the laboratory stage, and long-term optical packet technology based on fast optical switching is only in the exploratory stage.

The basic composition of the point-to-point DWDM optical fiber transmission system is shown in Figure 3. In the figure, OA is usually an erbium-doped fiber amplifier (EDFA), and OMUX/ODMUX is a wavelength division multiplexer/demultiplexer. They are all passive devices that can multiplex branch signals of different wavelengths into an optical signal containing multiple wavelengths or perform the opposite work. Under the same branch signal rate, its transmission capacity can be increased by N times compared with a system with a single operating wavelength. Moreover, the increase or decrease in capacity only increases or decreases the number of branch accesses of OMUX/ODMUX. The introduction of optical add-drop multiplexers (OADM) and optical cross-connect equipment (OXC) will provide a more effective means for optical networking. OADM can dynamically select add-and-drop wavelengths for flexible networking. OXC can provide cost-effective recovery and routing functions for optical networks, form large-capacity or ultra-large-capacity network nodes, and can realize core optical networks (ON) managed directly in the optical domain.

The influence of optical transmission network on the optoelectronics industry

The main optical devices that make up the DWDM system and the entire optical transmission network usually fall into the following five categories:

*Optical transmitters/receivers, including lasers and modulators;

*Optical multiplexer/demultiplexer;

*Optical amplifier;

*Optical add-drop multiplexer/optical cross-connect equipment;

*Others (attenuators, optical switches, couplers, splitters, filters, optical fibers, etc.).

Some market surveys on fiber photonics technology point out that the DWDM system market has a cumulative annual growth rate of 73% in the four years from 1997 to 2000, reaching US$1.7 billion in 1997, US$4.2 billion in 1999, and soaring to US$8.9 billion in 2000. During this one-year period, the number of DWDM suppliers increased from 15 to more than 30 (although there were many mergers and acquisitions in the industry during this period). The number of network operators using DWDM systems increased from 75 to 175. The development of optical transmission will continue to promote the expansion of DWDM equipment from long-distance core networks to metropolitan area networks, access networks and enterprise networks closer to users. Therefore, the demand and variety of optical networking equipment and its components will increase further. Prediction in 2000: By 2003, the long-distance network will be 4 times, the metropolitan area network will be 10 times, and the optical switching will be 30 times. The market growth of optical network will be very considerable.

in conclusion

In view of the huge and continuous driving force of the explosive growth of Internet services on network belts, the optical transmission network based on DWDM technology has huge bandwidth potential and can economically, flexibly and effectively utilize existing optical fiber transmission equipment, as well as network Advantages such as upgrade capabilities have enabled the optical transmission network and the corresponding optoelectronics industry to continue to grow rapidly in recent years.

Optical fibers contain almost unlimited bandwidth potential, and the continuously developing photonic technology provides us with the means to explore and utilize these bandwidth resources. The development of OTN is not only a necessity in the information society and network era, but it will also promote the rapid development of the photonics industry, and then promote the entire optoelectronics industry related to it.