DWDM transport systems

Dense wavelength division multiplexing (DWDM) refers originally to optical signals multiplexed within the 1550 nm band in order to leverage the capabilities of erbium doped fiber amplifiers (EDFAs), which are effective for wavelengths between approximately 1525-C1565 nm, or 1570-C1610 nm. EDFAs were originally designed to replace SONET/SDH optical-electrical-optical (OEO) regenerators, that they can make practically obsolete. EDFAs can amplify any optical signal in their operating range, no matter the modulated bit rate. In terms of multi-wavelength signals, as long as the EDFA has enough pump energy accessible to it, it can amplify as much optical signals as can be multiplexed into its amplification band. Inside the DWDM fiber area, EDFAs therefore allow a single-channel optical connect to be upgraded in bit rate by replacing only equipment on the ends of the link, while retaining the present EDFA or number of EDFAs via a long run route. Furthermore, single-wavelength links using EDFAs can similarly be upgraded to WDM links at reasonable price. The EDFAs price is thus leveraged across as many channels as possible multiplexed in to the 1550 nm band.
A basic DWDM system contains several primary ingredients.

1.A DWDM terminal multiplexer or DWDM multiplexer. The terminal multiplexer actually contains one wavelength converting transponder for each wavelength signal it will carry. The wavelength converting transponders obtain the input optical signal, convert that signal to the electrical domain, and retransmit the signal employing a 1550 nm band laser. The terminal mux also includes an optical multiplexer, that takes the different 1550 nm band signals and places them onto just one fiber. The terminal multiplexer might or might not also support an area EDFA for power amplification from the multi-wavelength optical signal.

2.Medium difficulty line repeater is put approx every 80-C100 km for compensating losing in optical power, as the signal travels across the fiber. The signal is amplified by an EDFA, which often consists of several amplifier stages.

3.An intermediate optical terminal, or optical add-drop multiplexer. It is a remote amplification site that amplifies the multi-wavelength signal that could have traversed up to 140 km or maybe more before reaching the remote site. Optical diagnostics and telemetry tend to be extracted or inserted at this kind of site, to enable localization of any fiber breaks or signal impairments. In additional sophisticated systems, several signals from the multiwavelength signal may be removed and dropped locally.

4.A DWDM terminal demultiplexer. The terminal demultiplexer breaks the multi-wavelength signal into individual signals and outputs them on separate fibers for client-layer systems to detect. Originally, this demultiplexing was performed entirely passively, except for some telemetry, since many SONET systems can receive 1550-nm signals.

5.Optical Supervisory Channel (OSC). It becomes an additional wavelength usually outside the EDFA amplification band. The OSC carries details about the multi-wavelength optical signal along with remote conditions in the optical terminal or EDFA site. It is also normally used for remote software upgrades and user Network Management information.

DWDM systems need to maintain more stable wavelength or frequency than those needed for CWDM as a result of closer spacing from the wavelengths. Precision temperature control of laser transmitter is necessary in DWDM systems to prevent get to sleep a very narrow frequency window of the order of a few GHz. In addition, since DWDM provides greater maximum capacity it is often used in a higher level in the communications hierarchy than CWDM, for instance on the web backbone and is also therefore related to higher modulation rates, thus creating a smaller market for DWDM devices with high performance levels. These factors of smaller volume and better performance bring about DWDM systems typically being more costly than CWDM.

Recent innovations in DWDM transport systems include pluggable and software-tunable transceiver modules able to operate on 40 or 80 channels. This dramatically cuts down on the requirement for discrete spare pluggable modules, when a number of pluggable devices can handle the entire range of wavelengths. For further fiber optic products information, please arrived at FiberStore.