Test equipment for the “All Optical Network”

Test equipment for the “All Optical Network”: Optical test equipment has been used exclusively for qualifying the transmission path after installation of the fiber optic cables in current systems. The overall loss of the fiber is checked using power level generators and receivers, and an OTDR is used to check the quality of individual splices. The SDH/SONET analyzer has been the main tool used for the next stage, commissioning the line equipment.

The use of an optical spectrum analyzer has become mandatory as a result of using DWDM for transmission and optical add-drop multiplexers and optical cross-connects for switching.
It is also necessary to qualify the signal quality as quickly as possible. In critical situations, even the fiber properties may need to be tested, requiring the use of PMD test equipment.

Test equipment for Optical Network

Test equipment for the “All Optical Network”

All Optical Network test details

In fact the Q-factor measurement will not replace an end to end measurement with an SDH/SONET analyzer, since this is used to demonstrate and record the quality of service of a transmission path for the customers of network providers. The Q-factor measurement determines the signal quality at a particular point in the transmission range.

the Q-factor measurement promises a significant contribution towards reducing the measurement time required. This is particularly so during the installation of DWDM systems with large numbers of channels operating at 2.5 Gbps and 10 Gbps, where a conventional BER measurement is of only limited use.

The Q-factor measurement method is the only way that all the setup parameters of a DWDM system using 80 wavelengths can be checked within an acceptable time.

On the other hand high channel count DWDM systems require multiport capability in the SDH/SONET analyzers used for the quality of service measurement that forms the final measurement made during installation.

Superimposed switching of individual channels of a DWDM system is only possible up to a certain number of channels, after which various transmission properties start to degrade the overall picture.In addition, applications such as Packet over SONET (PoS) must be supported for end-to-end measurements.

Future-oriented test technology must respond to these challenges.Depending on use, it can

be fitted with a Q-factor meter, an optical spectrum analyzer and/or up to four SDH/SONET analyzers for up to 10 Gbps. This modular concept means that future test modules for new applications are possible, thus protecting your investment.

Installation teams need new test equipment

The number of channels in DWDM systems will increase rapidly. Even if most of the systems installed now a days use 4, 8 or 16 colors (that is, channels or wavelengths) as a rule, the first transmission systems with 40, 80 or more wavelengths are already commercially available. Up till now, systems have used the so-called C band wavelengths, from 1525 nm to 1565 nm.

No fiber amplifiers are needed in MAN systems, as the distances involved are short. The second optical window with the center wavelength of 1310 nm is therefore used. The disadvantage of higher fiber losses in this range is acceptable over such short distances. The advantage lies in the wider wavelength range, meaning that the channel spacing can be more generous. This has a direct effect on the cost of the terminal equipment, allowing services to be provided to the user at a more economical price.

All this has an effect on the test equipment. Optical spectrum analyzers, among the most important test devices for work on DWDM systems.

The OSNR is an important indication of the quality of service of each transmission channel. The properties of the optical fiber amplifiers in the transmission path make adjustment of each channel necessarily delicate.The fiber amplifiers generate additional noise, which depends on the number of occupied channels and the wavelengths selected in the third

optical window.

The fiber dispersion can no longer be ignored in systems operating at 10 Gbps or even higher bit rates. The chromatic dispersion (CD) is a wavelength-dependent property of the fiber that causes a broadening in the signal pulses.a measurement time of at least seven minutes is required in order to determine a bit error ratio (BER) of < 10 power 11 in a 10 Gbps system.