Fiber Optic CWDM DWDM MUX

The choice comes down to three numbers: channels needed today, distance to cover,

and wavelengths expected over the life of the route. Everything else follows from channel spacing.

Six decisions define the part number. Each one changes the bill of materials, so all six belong in the enquiry.

CWDM Mux Demux — Thin Film Filter

DWDM Mux Demux — Thin Film Filter

Two of these numbers do most of the engineering work. Insertion loss is consumed twice on a point-to-point link — once at the multiplexer, once at the demultiplexer — so a 40 channel dense pair can take more than 13 dB out of the span before a kilometre of fiber is counted. Adjacent isolation determines how much neighbouring-channel energy reaches the receiver as crosstalk, which appears as a noise floor no amount of launch power will fix. Reading a budget therefore means reading insertion loss and return loss together with receiver sensitivity and fiber attenuation; where a channel arrives too hot, the correction is a fixed optical attenuator, not a different module.

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What Are CWDM and DWDM Mux Demux Modules?

A wavelength division multiplexing mux demux combines several optical signals, each on its own wavelength, onto a single fiber pair — or onto one fiber — and separates them again at the far end. The modules are entirely passive: no electronics, no power, transparent to protocol and bit rate. An existing route can be multiplied in capacity without trenching new cable and without changing the equipment at either end beyond the transceivers.

CWDM spaces channels 20 nm apart across 1270–1610 nm under ITU-T G.694.2. That wide spacing is the entire economic argument: the passband is loose enough that lasers need no cooling or wavelength locking, which is why CWDM SFP transceivers and coarse multiplexers cost a fraction of their dense equivalents per channel. Reach is typically 70–80 km unamplified, and beyond about 40 km deployments are usually limited to the eight channels above 1470 nm, because the shorter wavelengths sit near the water peak of standard G.652 single-mode fiber. Cable television networks were an early adopter, separating downstream and upstream onto widely spaced wavelengths; the same principle underlies 10GBASE-LX4, where four wavelengths near 1310 nm each carry 3.125 Gbit/s. In SDH transport, coarse multiplexing is a standard way of stacking STM circuits onto one fiber pair.

DWDM places channels on the ITU-T G.694.1 frequency grid at 200, 100 or 50 GHz — roughly 1.6, 0.8 and 0.4 nm — inside the C-band and L-band. Packing channels this tightly requires temperature-stabilised, wavelength-locked lasers and sharper filters, which raises cost per channel. What it buys is capacity and distance: 40, 48, 80 and 96 channel systems are routine, and because every channel falls inside the erbium gain window the line can be boosted by an EDFA and carried hundreds of kilometres. Over long spans the limiting factor shifts from loss to chromatic dispersion, corrected with a dispersion compensation module at the amplifier site.

CWDM Module Coarse Wavelength Division Multiplexing

Originally, the term coarse wavelength division multiplexing (CWDM) was fairly generic and described a number of different channel configurations. In general, the choice of channel spacings and frequency in these configurations precluded the use of erbium doped fiber amplifiers (EDFAs). Prior to the relatively recent ITU standardization of the term, one common definition for CWDM was two or more signals multiplexed onto a single fiber, with one signal in the 1550 nm band and the other in the 1310 nm band.

CWDM Applications

CWDM is being used in cable television networks, where different wavelengths are used for the downstream and upstream signals. In these systems, the wavelengths used are often widely separated. For example, the downstream signal might be at 1310 nm while the upstream signal is at 1550 nm.
Some GBIC and small form factor pluggable (SFP) transceivers utilize standardized CWDM wavelengths. As a classic synchronous digital transmission solution in optical fiber communications, SDH is often paired with CWDM technology to achieve efficient networking. GBIC and SFP CWDM optics allow a legacy switch system to be “converted” to enable wavelength multiplexed transport over a fiber by selecting compatible transceiver wavelengths for use with an inexpensive passive optical multiplexing device.
The 10GBASE-LX4 10 Gbit/s physical layer standard is an example of a CWDM system in which four wavelengths near 1310 nm, each carrying a 3.125 gigabit-per-second (Gbit/s) data stream, are used to carry 10 Gbit/s of aggregate data.
Passive CWDM is an implementation of CWDM that uses no electrical power. It separates the wavelengths using passive optical components such as bandpass filters and prisms. Many manufacturers are promoting
passive CWDM to deploy fiber to the home.

What Is DWDM Dense Wavelength Division Multiplexing?

Unlike CWDM, DWDM (Dense Wavelength Division Multiplexing) connections can be amplified and can, therefore, be used for transmitting data much longer distances.

As the demand for Dark Fibre and capacity has increased, Dense Wavelength Division Multiplexing (DWDM) has been an important component. This involves multiplexing of multiple virtual fibres – that is, the splitting out the colours of the infrared spectrum using laser transmitters tuned to each colour wavelength – meaning more data can be sent via a single fibre at the same time thus increasing bandwidth.

CWDM supports up to 18 wavelength channels transmitted through a fiber at the same time. To achieve this, the different wavelengths of each channel are 20nm apart. DWDM, supports up to 80 simultaneous wavelength channels, with each of the channels only 0.8nm apart. CWDM technology offers a convenient and cost-efficient solution for shorter distances of up to 70 kilometers. For distances between 40 and 70 kilometers, CWDM tends to be limited to supporting eight channels.

Focc Technology is one of the leading China manufacturers and suppliers providing you with fiber optic CWDM DWDM MUX. Our factory has applied the most advanced equipment and technology to better serve you. Please be free to buy our fiber optic CWDM DWDM MUX products with competitive price. The customized service and the quotation consultation are available.