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Optical Transceiver / WDM Transceiver / Taking an In-depth Look at DWDM Transceivers

Taking an In-depth Look at DWDM Transceivers

Posted on By FS.COM


Taking an In-depth Look at DWDM Transceivers

It is no exaggeration to say that the advent of DWDM technology has almost changed the landscape of optical networks. It has been widely employed in many different areas in telecommunication networks, with DWDM transceiver being one of its most important applications.

What Is DWDM Transceiver and How Does It Work?

To put it simply, DWDM Transceiver is a kind of optical transceiver which combines the DWDM technology. DWDM transceiver uses different wavelengths to multiplex several optical signal onto a single fiber, without requiring any power to operate. While DWDM tunable transceivers are within the scope of DWDM transceivers, through which different DWDM wavelengths can be configured and output in the same optical module. The basic function and principle of DWDM transceiver is as same as other optical transceivers, to convert the electrical signal to optical signal and then to electrical signal. DWDM transceiver is designed for single-mode fiber and operates at a nominal DWDM wavelength from 1528.38 to 1563.86 nm (Channel 17 to Channel 61) as specified by the ITU-T. It is with the SFP 20-pin connector to allow hot-plug capability. Except from being adopted in long distance transmission, it can also be used in switch to switch interface, switched backplane applications and router/server interface etc. And the tunable transceivers are recent innovations in DWDM transport systems which are capable of operating on 40 or 80 channels. Through the following picture, it can be seen that the combination of transmitter and receiver for a particular wavelength is actually a transceiver.

the working principle of dwdm transceiver

Why Is There a Special Need for DWDM Tunable Transceivers?

In DWDM optical networks, either passive optical networks or wavelength routed optical networks, the multi-wavelength transmission or reception at each station is realized through either an array of fixed-wavelength transceivers or a tunable transceiver. The laser modules of traditional transceivers are based on a fixed wavelength. However, with the constant development and widespread application of optical communication, the disadvantages of fixed-wavelength DWDM lasers have gradually surfaced.

 Firstly, as the technology develops, hundreds of different wavelengths in DWDM 50GHz have been adopted, thus requiring a large quantity of backup DWDM optical modules. Because if a protection needs to be provided, the backup of each laser must be provided by the laser whose wavelength can be replaced, which leads to the increase in the number of backup DWDM optical modules and the rise of operating cost.  Secondly, since the wavelength of common DWDM optical module is fixed, therefore the stock quantity of DWDM optical module with fixed wavelength is increased and it is difficult to predict the number of stock in specific channels.  Thirdly, in order to support the dynamic wavelength assignment in optical network and improve network flexibility, there needs a large number of common DWDM optical modules with different wavelengths. But the fact is that the usage rate of each optical module is very low, thus resulting in a waste of resources.

To address these problems, tunable transceivers have sprung up with the unique advantage of flexibly selecting working wavelength.

The Current Status and Applications of DWDM Tunable Transceivers

Although it has been a long time since conventional or fixed wavelength DWDM transceivers are in market, we still feel that some of our customers are puzzled about how to choose between fixed and tunable optical transceivers. I will try to shed some light on this by expressing my opinion. When I first heard about the DWDM tunable transceiver, I thought it would definitely bring revolutionary change to future metro Ethernet and optical transport networks with its important practical value for flexibly selecting working wavelength. However, several years on, what is the reality of DWDM tunable transceivers in market? How many optical ports from total implemented are actually with tunable optical transceivers? We can see in this graph that from all optical ports shipped only about 0.5% are tunable.

tunable transceiver

So, what's the current application case of DWDM tunable transceivers and what's the time to employ tunable transceivers? I see the two following main applications:

 Spare use. When you are running big DWDM network with high number of nodes and let's say use up to 80 (50GHz spacing) different wavelengths, spare part management quickly could become nightmare. You need to have couple of transceivers of each wavelength and possibly in different locations. With DWDM tunable transceivers, the amount of spare optics you need to hold in stock was dramatically reduced.  Really big transport network with 400G or 1T applications on horizon. Yes, with already now available coherent optical technologies, it is possible to fit 100G transmission bandwidth within DWDM 50 GHz channel. But if 100G is too less for you one day, then future 400G and 1T transmission formats are expected to be bulky and not fit within 50GHz spacing. So, a more flexible channel plan/spacing is required to enable your OTN system adapt to new rates and re-arrange channel spacing to find place for new rates in it.


The Historical Evolvement and Future Trend of DWDM Transceivers

Speaking of the development of optical transceivers, we tend to think about the different package forms of them, which can actually show how these optical transceivers evolved during the past years .

Product Description
DWDM SFP DWDM SFP transceivers provide a high-speed serial link at signaling rates from 100 Mbps to 2.5 Gbps. The DWDM SFP modules meet the requirements of the IEEE802.3 Gigabit Ethernet standard and ANSI Fibre Channel specifications, and are suitable for interconnections in Gigabit Ethernet and Fibre Channel environments.
DWDM XENPAK DWDM XENPAK is an important step in the evolution. It is the first 10GbE transceiver ever to support DWDM. DWDM XENPAK supports 32 different channels for transmissions up to 200 km with the aid of optical amplifiers known as EDFAs.
DWDM X2 DWDM X2 transceiver is a high performance, serial optical transponder module for high-speed, 10G data transmission applications. The module is fully compliant to IEEE 802.3ae standard for Ethernet, making it ideally suited for 10GbE datacom applications.
DWDM XFP DWDM XFP transceiver complies with the current XFP MSA specification. It supports SONET/SDH, 10GbE and 10-Gigabit Fibre Channel applications. It is small in size and cheap in price.
DWDM SFP+ DWDM SFP+ is specifically designed for carriers and large enterprises that require a scalable, flexible, cost-effective network system. It is even smaller than the previous XFP and is the ideal choice for 10G highest-bandwidth application.

dwdm transceiver

As the core component in optical transmission system, optical transceivers are developing at a fast pace with an increased complexity. Seeing from the historical evolvement, here some predictions have been made on the future trend of DWDM transceivers.

 Smaller Size. It can be predicted that small-sized transceiver represents the development trend for the next high-speed Internet for its advantage of increasing the number of fiber port for network devices.  Higher Speed. It has been clearly proved in the past years that only higher speed Ethernet like 40G or 100G can keep up with the growing needs. Sales of 100G hardwares, like 100G transceiver, will increase largely.  Longer Distance. Currently, the optical network is rolling out with a longer and longer distance, which would require a long-distance transceiver model to support it.

Summary

No matter how fast the Internet technology grows and how advanced the technology will be in the future, optical transceivers will continue to be a indispensable part for optical transmission system. Where there is a need, there is a market. DWDM transceivers have been widely adopted during the past years, which will continue to get upgraded and developed in the following years. Although the market share for DWDM tunable transceiver is not big enough, we can still see huge potential from its application. To tune or not to tune, that’s a question depends on yourself.


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