Optical Transponder—an Important Component in WDM System

Introduction to Optical Transponder

Optical transponder is also referred to as WDM transponder, wavelength-converting transponder or OEO (Optical-Electrical-Optical) 3R (re-timing, re-shaping, and re-amplifying) converter, and the word “transponder” is named according to the combination between transmitter and responder. It is an important unit in WDM system which main function is to convert the wavelength and the pattern of the optical signals and amplify the optical signals for long-haul transmission. At present, the optical transponder unit is commonly used in 10G connections including SFP+ to XFP, SFP+ to SFP+ and XFP to XFP fiber connections, and 40G QSFP+ to QSFP+ connections.

Working Principle of Optical Transponder

The optical transponder is designed to automatically receive a signal, amplify it and then retransmit the signal with another wavelength, without changing the content of the signal, which enables the different system to be connected. For instance, a 10G DWDM system can be deployed on the basis of a normal 10G system if using the optical transponder to convert a 850nm signal into a 1550nm one. What’s the working principle of the optical transponder? In general, when an optical input signal passes through the optical transponder, it will be firstly converted into an electrical one. Then a logical copy of the input signal is generated that features a new amplitude and shape and is used for driving the transmitter. Finally, an optical output signal with a new wavelength would be generated, as shown in the following figure.

Wavelength Conversion Case Analysis

As mentioned above, the optical transponder unit plays an important role in WDM system, which is very welcomed when deploying a CWDM or DWDM system on the basis of a normal system. It is well known that 850nm, 1310nm or 1550nm are used in a normal system for optical signal transmission, while CWDM or DWDM wavelengths are applied in a CWDM or DWDM system. Hence, if we want to transmit the normal signals to a CWDM or DWDM system, the optical transponder should be required that enables the normal wavelengths to be converted into CWDM or DWDM ones without changing the signal data. Here shows a wavelength conversion case by using the optical transponder.

We can learn from the case that a 10G-LR 1310nm SFP+ module is connected to a 10G switch on site A, while a 10G CWDM SFP+ module working on 1610nm is used with the CWDM Mux Demux on site B. As the 10G 1310nm signal from site A is required to be transmitted to the existing CWDM system on site B, a two SFP+ ports optical transponder should be used for converting the 10G 1310nm signal into a 10G 1610nm CWDM signal. To achieve this, another 10G-LR 1310nm SFP+ module and 10G CWDM 1610nm SFP+ module should be inserted into the 10G SFP+ to SFP+ optical transponder, separately. Furthermore, fiber patch cables are required to link the two 10G-LR 1310nm SFP+ modules and two 10G CWDM 1610nm SFP+ modules together, so that a complete link for wavelength conversion can be done.

Conclusion

The optical transponder is an important component in WDM system that makes the wavelength conversion easy, so that the signal data can be transmitted from a normal system to a WDM system. For instance, with the use of the optical transponder unit, a 1310 signal from a 10G fiber optical network can be converted into a 1610 CWDM signal and transmitted to the 10G CWDM network. If you are facing the problem about wavelength conversion for connection between a normal network with a WDM network as noted above, the optical transponder is quite recommendable for you.

Why Not Using DWDM Technology to Build Your Network?

Currently, more and more users choose to deploy DWDM networks on the basis of their existing networks, as the normal network can’t afford enough capacity for their daily use. Considering that there may be some confusion for designing the DWDM networks, this paper will mainly introduce the basic knowledge of DWDM technology and analyze the difference between SDH and DWDM technology. To better understand the DWDM technology, this paper will also guide users to deploy two common kinds of DWDM network. Hope the DWDM information in the paper would be useful for deploying a smooth DWDM network with higher transmission rate and capacity.

Introduction to DWDM Technology

DWDM technology is an ideal solution to address the capacity-hungry issue, which can multiplex several wavelengths for transmission different kinds of signals through one single fiber. In principle, the network utilizing DWDM technology enables carry up to 140 channels for transmitting signals, finally achieving high bandwidth transmission. As for the DWDM components, it basically includes DWDM multi-channel Mux/Demux, dispersion compensation module, fiber optic amplifier, optical transponder, and so on.

SDH vs DWDM Technology

As we know, SDH is the technology combining more than one lower-speed electrical or optical signals into a single higher bit rate signal with a single wavelength for transmission over a single fiber or wire. In the network utilizing SDH technology, Time division multiplexing (TDM) or statistical TDM is used, which means the signals in SDH network will be received by distributed across time slots. As for the DWDM technology, it uses wavelength multiplexing method, so that the signals can arrive at the receiver simultaneously. In the DWDM network, the DWDM multi-channel Mux/Demux mentioned above is the key components that can give different wavelengths to the different optical signals and multiplex them, so that the integrate signal with different wavelengths can be transmitted over a single fiber.

In short, SDH uses time division multiplexing, while DWDM works with wavelength division multiplexing. Compared to the SDH technology, DWDM can give different wavelengths to the optical signals, which allows the signals to be transmitted with their own speed and protocol and arrive at the same time. Besides, the SDH network can transmit both electrical or optical signals, while DWDM network only supports optical signal transmission.

Common DWDM Network Designs

Generally speaking, there are many kinds of DWDM networks with topological configurations, each of them has different requirements and can be used for different applications. They are basically DWDM point-to-point network, fully connected mesh network, star network, ring network and hybrid DWDM network consisting of stars and/or rings that are interconnected with point-to-point links. The following will mainly introduce the two most common DWDM networks, point-to-point network and ring network for your reference.

DWDM Point-to-Point Network: this kind of DWDM network is always deployed for long distance transmission with fast transmission speed, high bandwidth, great reliability and path restoration capability. The numbers of fiber optic amplifier used in this DWDM network is often less than 10, while the transmission distance can be up to several hundred kilometers. If optical add-drop multiplexer (OADM) is used, channels can be dropped or added along the path of the DWDM link. To better know the DWDM point-to-point network, here offers a figure that shows a DWDM point-to-point network design with the use of DWDM multi-channel Mux/Demux, OADM and fiber optic amplifier.

DWDM Ring Network: In general, this kind of DWDM network is often applied in local or metropolitan areas that can support the DWDM network at lengths up to dozens of kilometers. A basic DWDM ring network is shown in the following figure that has many nodes fully interconnected by the fiber, and sometime there are two fiber rings in a DWDM ring network which are deployed for protecting the network. Besides, the DWDM components like DWDM multi-channel Mux/Demux, OADM and optical amplifier are also required in the DWDM ring network.

Conclusion

DWDM technology is an economical solution for transmitting multiple signals through one fiber, which can solve the problem of insufficient capacity in your network. In contrast with SDH technology, DWDM technology enables the optical signals to be transmitted fast and arrive at the receivers simultaneous, while offering much higher capacity and transmission rate. If you are interested in DWDM technology, you can visit FS.COM where the wholesale DWDM Mux Demux, OADM and optical amplifier are available. It is recommended because of the good DWDM Mux Demux, OADM and optical amplifier price and quality.