Red/Blue Filters in DWDM Systems

Abstract

With the fast and crazy growth in communications, we need to install more cables to satisfy the increasing demands of transmission speed and bandwidth. In fact, as the technology increasing and the intense competition of the market, the cost of fiber cables has been unprecedented low nowadays. In addition, the installation methods of fiber cables are more efficient, like mass fusion splicing etc. Thus, installing more cables seems to be the preferred method in many cases, especially in metropolitan areas. However, it's not the only one way to better expand the network infrastructure. If conduit space is not available or major construction is necessary, this may not be the most cost effective. In contrast, WDM (Wave Division Multiplexing) has proven more cost effective in many instances, especially the DWDM (Dense Wave Division Multiplexing) when using in MAN (Metropolitan Area Network).

DWDM (Dense Wave Division Multiplexing) is the clear winner in the backbone. What delivers additional value in the metropolitan market is DWDM’s fast and flexible provisioning of protocol- and bit rate-transparent, data-centric, protected services, along with the ability to offer new and higher-speed services at less cost. While Red/Blue filter, as an additional passive component added to the optical networks, is often used to increase bandwidth, and reduce link insertion loss, in high-channel count DWDM systems.

This tutorial is explaining the Red/Blue Filters in DWDM systems.

Terminologies related to Red/Blue Filter

Before explaining the Red/Blue Filter, we firstly understand some related Terminologies.

Red Band & Blue Band

The ITU (International Telecommunication Union) approved DWDM band extends from 1528.77 nm to 1563.86 nm, and divides into the red band and the blue band.

Since only the Red Band is amplified by the EDFA, Blue Bands may require traditional optical-electrical-optical conversion amplifiers along the way. So if a system only requires a limited number of DWDM wavelengths, make sure to use the higher, Red Band frequencies. Using the red band wavelength yields the lowest overall system cost.

DWDM Band Wavelength Range

As fiber optic networks have developed for longer distances, higher speeds and wavelength-division multiplexing (WDM), fibers have been used in new wavelength ranges, now called "bands," where fiber and transmission equipment can operate more efficiently. Detailed DWDM band wavelength range is shown in the following table.

Thin Film Filter (TFF) technology

Thin film technology is based mainly on vacuum processes (sputtering, CVD, evaporation) and for thicker conductive metal layers (Cu, Au, Ni) on electro-deposition. The structure is etched (subtractive process) or plated (additive process) using photolithography. The main advantage of thin film filters is its ability to achieve high accuracy in processing in small device sizes when compared it to competing technologies. For example, FWDM (Filter Wave Division Multiplexer) is a device based on environmentally stable Thin Film Filter technology that is extensively used in EDFA, Raman amplifiers, WDM networks and fiber optics instrumentation.

What's Red/Blue Filter?

Like DWDM filters, the Red/Blue filter is a thin-film filter device. In other words, red/blue filter is a kind of FWDM. In general, it is a three-port device. One port is called the "Common" and the other two ports provide the conduit for the two wavelength "bands". The two bands are the Blue (l<1543 nm) and the Red (l>1547 nm). One band goes through the Reflected port, and the other band goes through the Pass port. (Note: the Reflected band and the Pass band must be designated either Red or Blue. The band, which requires the highest isolation, goes on the Pass port.)

The C Band Red/Blue Filter Wavelength Division Multiplexer is a micro-optics device based on environmentally stable Thin Film Filters technology. It is used to separate or combine Red band wavelength signals and Blue band wavelength signals in C band range in DWDM systems. The components are characterised with wide passband, low insertion loss, high return loss, excellent environmental stability and high power handling capability.

How Is Red/Blue Filter Used?

Red/Blue Filter may be used in several ways. The device can be used as a band combiner or a band splitter. As a combiner, the bands are combined in the filter and sent to the Common port. Or, as a splitter, the both bands are fed from the Common prot, and split to the corresponding ports. Typically, however, the device is used as a two-way (i.e. bidirectional) WDM. One band is sent to the Common port, while the other band is delivered from the Common port.

In a DWDM module, which uses a Red/Blue filter, a Mux may be combined with a Demux. For example, the Mux combines DWDM channels in the Red band, while the Demux separates DWDM channels in the Blue Band. Using a Red/Blue filter, one can combine the Red Transmit channels and the Blue Receive channels onto a single fiber.

Fiber-Mart DWDM Red/Blue C Band Filter Solution

Fiber-Mart 1x2 DWDM Red/Blue C Band Filter is a good choice for your DWDM system applications. To meet your special control and application, Fiber-Mart supplies custom channel and custom band filters, all units are available as steel tubes, modules, rack mounts or custom mount designs with a more competitive price.

DWDM Red/Blue C Band Filter Solutions

Note: Fiber Diameter, connector type, fiber length, Channels, reflect band and pass band are optional.

Customizing Your DWDM Red/Blue C Band Filter (Example: FSBR-C45000211)

Featured Products

FTTX Filter WDM Supply Customize FWDM Module to fit your specific requirements

SDH Optical Amplifiers Booster Amplifier, in-line Amplifier, Pre-Amplifier for SDH networks

WDM Transponder (OEO) SFP to SFP, SFP+ to SFP+, XFP to XFP, SFP to XFP, QSFP to QSFP OEO Transponder.