Broadband Component Characterization
To help you select the right combination of source and power meter, we have put together the table below, which illustrates at a glance the most appropriate combination of products for each application.
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IQS test modules are housed in the
IQS-500 Intelligent Test System, which offers fully
integrated and complete test solutions to component
manufacturers. The IQS-500 is a scalable, modular,
rackmount platform that houses a controller, expansion
units and a comprehensive range of plug-in test modules.
It offers up to 10 slots that can support any
combination of our protocol and optical test modules.
Systems can be expanded to support up to 100 test
modules and are ideal for manufacturing, lab and R&D
environments.
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Typical Passive-Component Testing: IL, ORL and PDL
Measuring Insertion Loss (IL)
The insertion loss (IL) of a component is the difference between the power entering and leaving it; i.e., IL (dB) = 10log10((Pin Pout)/Pin). It quantifies the power loss in the device at a particular wavelength or over a given spectral region. Obviously, insertion loss should be as low as possible.
To accurately measure the insertion loss of a fiber-optic component, use a stable light source and a power meter.
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Perform an offset nulling of the detector(s), if needed.
- Connect the source to the power meter using two appropriate test jumpers and a bulkhead connector (as shown below). This setup will be used to record a reference value.
- Connect the source to the power meter using two appropriate test jumpers and a bulkhead connector (as shown below). This setup will be used to record a reference value.
A specific standard as to how insertion loss should be defined in the presence of PDL has not yet been established. Nonetheless, one very reasonable definition has been proposed by standards committees. First, insertion loss must be measured with a depolarized source according to the formula above; the PDL will be the (max-to-min) variation of this value. Alternatively, insertion loss may be defined as the best-case loss, as the input state of polarization into the device under test (DUT) of a fully polarized source (e.g., laser) is adjusted. The worst-case loss would then be the sum of the IL and PDL.
Measuring Return Loss
Reflected optical power contributes to overall power loss, degrades laser performance and causes interference with communication and video signal processing. Therefore, to maintain system and component integrity, optical backreflection measurements must be performed. Two terms are used to quantify backreflection: reflectance and optical return loss.
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Reflectance typically describes a reflection at a single interface or reflection site; for example, a connector or splice. It is the individual component`s reflectance.
- Optical return loss (ORL or return loss) describes the combined reflections of a fiber-optic system or subsystem as measured from a specific point. It includes the reflectance of each system component, along with reflections generated along the fiber itself.
The setup illustrated below can be used to test both ORL and reflectance:
Even though ORL and reflectance have a different meaning, depending on the specific application, they both represent a ratio between the incident and reflected power. As it is common to refer to ORL and reflectance in dB, conversion from one to the other is simply a matter of changing the sign.
Measuring Polarization-Dependent Loss (PDL)
Polarization-dependent loss (PDL) consists of the difference in dB between the maximum and the minimum values of loss (attenuation) due to the variation of the polarization states of light propagating through a device.
Accumulation of component PDL can produce wide variations in a systems optical power. These variations are caused by changes in the environmental conditions under which the optical system works. In addition, the cumulative system attenuation is not equivalent to the sum of component polarization-dependent loss values. Changes in the state of polarization may create polarization-dependent loss (PDL) or polarization-dependent gain (PDG) for certain components of the optical system
PDL may be caused by optical components such as attenuators, isolators or couplers, whereas PDG may be caused by a burnt polarization hole in optical amplifiers. PDL and PDG cause a polarized signal to be attenuated or amplified differently from non-polarized noise. This difference changes the signal-to-noise ratio (SNR) at the system output and results in performance degradation. Furthermore, since the state of polarization of the transmitted light is changed randomly, PDL and PDG may cause system performance to fluctuate over time.
A polarization scrambler is a device that transforms the input state of polarization (SOP) of a light beam into a different output SOP. A polarization scrambler is commonly used combined with a fast power meter, to measure the difference between minimum and maximum loss of a component over time (= PDL), as the SOP is changed at the output of the polarization scrambler. It is important to ensure to statistically cover most of the possible SOP in a (short) period of time and to ensure adequate and consistent acquisition of the loss values on the power meter not to under-estimate the components PDL.