Tag Archives: DWDM Wiki

Wavelength Multiplexing: CWDM and DWDM

CWDM: An optical industry interim standard uses up to eight wavelengths, this scheme is referred to as coarese wavelengtb division multiplexing(CWDM), in accordance with ITU-T(any channel spacing between 8 and 50 nm). ITU-T Recommendation approved in june 2014, extends this down to 1270 nm(18 wavelengths), anticipating the ready commercial availability of fiber with no “water peak” of loss between the 1310-nm and 1550-nm transmission windows, as discussed in Chapter. Such an extended-wavelength planis, of course, applicable only to nonamplified systems until such time as optical amplifiers with similarly extended bandwidths are developed.

DWDM: The International Telecommunications Union(ITU) has defined a usage plan that can scale to as many as 45 wavelengths in the third window and whose spacings have been further split in some systems to yield twice that number. The defined channel designations are for channels spaced 100 GHz apart (about 0.8 nm). Regardless of whether 200-GHz, 100-GHz, or 50-GHz spacings are used, the usage plan is referred to as dense wavelengtb division multiplexing(DWDM). (More about DWDM: DWDM WIKI)

A fwe properties are common to all the plans, each with obvious parallels in RF technology.

♦ The closer the wavelengths are spaced, the harder(and more expensive) it is to separate them in the demultiplexers and simultaneously achieve adequate adjacent channel isolation, minimal in-channel flatness variation, and low insertion loss.

♦ The closer the wavelengths are spaced,the more frequency stabillity is required of the transmitters.

♦ The closer the wavelengths are spaced, the better the signal transmission velocities will match. Four-wave mixing and cross-phase modelation are both maxmum when the signals travel at nearly the same velocity. The degree of matching is, of course, also dependent on fiber dispersionm with standard fiber having high dispersion at 1550 nm but low dispersion at 1310 nm. By contrast, close wavelength spacing leads to reduced crosstalk from stimulated Raman scattering. These mechanisms are discussed later.

♦ The more wavelengths that share a fiber, the lower must be the power per wavelength for a given amount of mutual interaction due to nonlinear glass properties.

As shown in figure shows the relationship of bands, CWDM channels, and DWDM channels. Gable systems using linear DWDM technology generally use 200-GHz-spaced channels from among the set of 20 listed in Table 1, though a few vendors offer 100GHz spacing. For network designs that use fewer than 20 of the listed wavelengths, various vendors have chosen to offer different subsets.


             Relationship of wavelength bands.


           Wavelength Division Multiplexing

Most offer C21 through C35 as the first eight, but noe vendor offers C39 through C53 as the second eight, another offers C45 through C59, and a third has chosen to offer C37 through C51. This is obviously inconvenient for operators who wish to have multiple sources for optical transmitters and DWDM Multiplexer.

Optical fiber connector application and terminal considering analyses

With the A/V industry the BNC connectors, widely used in optical fiber connector as the development of optical fiber technology matures gradually.Copper wire connector on the AV system signal loss does not generally is very big, the influence of the fiber optic connection is different, its transmission system of each interface plays a very big impact.Let’s take a look at the fiber produced some of the problems in the physical connection, optical fiber transmission device can be connected instruction itself, but in some cases, almost all or most of the optical fiber transmission connection option are personally.Fiber optic cables that had been lost in the process of signal transmission is mainly composed by the amount of signals which is determined by the quality and type of fiber optic cable, will produce certain signal loss every end connection.According to user’s choice of different types of optical fiber connector end connection signal loss add up the total amount of likely over fiber optic cable to the signal loss from itself.
Maintain system normal operation
In the optical system design, system to normal operation, achieved very good results, in system design, we need to consider the system may appear some unexpected problems, and to make the system normal operation.In system design, we should consider the system may occur in the worst case, and make corresponding plan, looking forward to better operation result.Optical fiber connector design, be sure to put this idea in mind.In system design, security, stability, the optical fiber end is smooth, founder system requirements.End to end connection between must be precise, accurate and even to reach microns, one over one million meters.Commonly used of multimode fiber from 50 to 62.5 microns in diameter, and single-mode fiber is only 8-9 microns in diameter.The diameter size and the diameter of a human hair (17-180 microns), compared to visible any little mistake can bring in a catastrophic loss.
Optical fiber connection precision requirements of the equipment is very strict, so the connector must be very clean.Optical fiber connectors and accessories are usually installed in a condom, a finger print or external dust may seriously affect the connector performance, even cause the failure of transmission, therefore, when the connector is not connected, it should be stored in a clean case.
In the connection, we should also optical fiber connector chocking, all optical fiber connector design in current was conducted through the “ring”, guarantee the accuracy of the connector when collocation and correct.Optical terminal is through viscose or tight pressure inside the ring, become a permanent element.Insert the built-in optical fiber, then grinding ring side is smooth, smooth interface for fiber connector connection.Ring is usually made of more hard materials such as ceramic, of course, also can be stainless steel, plastic, or tungsten carbide materials, SC, ST, and FC general ring is 2.5 mm in diameter, LC general ring diameter is 1.25 mm.Due to the features of ring can undertake production in accordance with the requirements for precision, also became a primary important to determine the characteristics of optical fiber connector.In numerous connecting ring, spring loaded container connecting ring ensures the coaxial alignment between optical fiber and LED or laser source.
With the expansion of the development and application of technology, optical fiber connector also rapid development.Now in the market the use of optical fiber connector is about 12 more even, each of which is to meet the specific needs and arises at the historic moment, of course, there are certain technical limitations.Now the market is mainly in the price is moderate, compact connector mode of development, to support the new transmission distribution system requires greater transmission density.As users expect, the continuous development of the telecommunications industry has pushed the widespread application of the fiber, is largely due to the various types of communications and entertainment services for fiber optic connection caused by rapid growth in demand.
Terminal to consider
Traditionally, optical fiber terminal tend to be slow, the price is higher also, requirements for equipment and technical requirements are very high.In considering of optical fiber terminal single-mode cable, these factors should be considered.In some cases, we can choose a few already set up the terminal depending on the type of all kinds of optical fiber cables.
Type tailored to install applications, we can only choose a particular terminal, however, after the use of the lap joint tools, can reduce the length of the extended single-mode fiber field terminal, reduce the amount of the demand for equipment and technology to use.For multimode optical fiber cable, the new way of spliced using a simple optical fiber cutting method, cable assembly into the connector/cable design in advance.This method is very simple, but fiber to fiber butt joint, joint are usually adopt a kind of special optical gel, optical fiber terminal setting up.