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Applications

Optical Component Test Applications

Coarse Wavelength Division Multiplexing

Improvements in the bandwidth of access network, including

commercialization of FTTx, are expected to increase the push for

expanded metro area network (MAN) development. Coarse wavelength

division multiplexing (CWDM) is often the technology of choice for the

MAN, allowing use of the complete single-mode fiber wavelength range

over unamplified spans while keeping down the costs of the transmitters

and wavelength multiplexers.

The CWDM concept of spacing the wavelength channels 20 nm apart

is also adopted for the LX-4 method of multiplexing 4 wavelengths in the

O-band over multimode fiber to provide 10 Gb/s parallel transmission

over spans too long for 10Gb/s serial transmission.

Avoiding crosstalk between the CWDM signals requires the wavelength

filters to have high isolation. Measuring this isolation with a tunable laser

source (TLS) can be hindered if the spontaneous emission, SSE, is not

sufficiently suppressed. The wide pass band of CWDM filters can transmit

too much SSE. Using tunable lasers, configured to the desired wavelength

range and optimized for low SSE and high power stability for spectral

characterization provides high dynamic range of >75dB and allows

simultaneous measurement of multiple output channels, including

polarization dependence with fast swept-wavelength measurements.

Ease of customization for automated manufacturing test is supported

with Agilent’s software library such as Plug&Play drivers to allow

minimum investment cost for maximum operational efficiency.

WDM Test

Figure 3. CWDM solution

WDM Networking at 10Gb/s and Beyond

WDM networks are deployed to enhance bandwidth and connectivity,

including to countries still in need of a modern communications infrastructure.

Optimization of optical components and fibers in these high-performance

networks is required to provide cost-effective networks and assure

reliability. The amount of traffic carried by the fiber is increased by adding

channels (with closer spacing) and raising the data rates.

The high channel count and close spacing of DWDM systems require

tight control of multiplexer isolation, demanding high-dynamic testing with

low-SSE tunable lasers to measure the channels in parallel for speed and

low cost. Operation over long spans and multiple amplifiers also requires

assurance of low PDL in components for signal stability. This can be

provided by swept-wavelength measurements using the Mueller Matrix

method with the setup above, including polarization control.

Assuring that the fiber and components serve not only the need of today

but also the next five to ten years, expandable to 10Gb/s and beyond,

also requires control of dispersion, both chromatic dispersion and

polarization mode dispersion. These are primarily properties of the fiber,

but also in components like filters to a sufficient degree to impede signals

at 40Gb/s and sometimes already at 10Gb/s.

Agilent’s 86038B Polarization Dispersion and Loss Analyzer (PDLA) gives

the performance needed in testing all parameters of IL, PDL, GD, DGD,

CD and PMD, and can be configured for any wavelength from 1260 to

1640nm, as shown in Figure 4.

Polarization Dispersion and Loss Test

Figure 4. Component and Network Test for 10Gb/s and beyond

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