Cable Assembly, Connector and Splitter Testing - Technology Overview
Importance of Backreflection and Insertion Loss Measurements
As communication
systems evolve toward higher bit rates and relatively high power, measuring
optical return loss (ORL) or discreet reflectance is a growing concern.
To ensure proper transmission stability, quality and performance of high-speed
digital and analog systems, all of their constituents such as connectors,
splitters and other components must be qualified and tested for insertion loss
(IL) and optical return loss (ORL).
Figure 1: Testing simplex, duplex, multifiber, and fanout cables with or without hybrid connectors
Figure 2: Example of test setup for FTTx splitters
When light is launched into a fiber-optic component (e.g., connector, fiber, coupler, etc.) some of the energy is transmitted, some is absorbed and some is reflected. When measuring IL, the combined effect of absorption and reflection is measured. When measuring ORL or reflectance, only the losses resulting from reflected light are measured. In fiber-optic systems, reflected light is due to Rayleigh scattering and Fresnel reflections. Fresnel reflections occur at discrete components (connectors, adapters, etc.) and are a result of air gaps, misalignments, and non-matching refractive indexes.
Reflected power is undesirable for three reasons:
- It contributes to overall power loss.
- High-performance laser transmitters are very
sensitive to reflected light. Laser stability and
system signal-to-noise ratio (SNR) can be
significantly degraded. Under extreme
conditions, the laser transmitter can be damaged.
- Reflected light can be re-reflected in the
forward direction. These forward-propagating
reflections lag behind the original signal and cause
problems with communication and video signal
processing.
ORL vs. Reflectance
ORL and reflectance are two terms often used when
quantifying reflected power, and they are often
confused.
ORL (also known as return loss) is generally used to describe the combined
reflections of a fiber-optic system (or subsystem), as measured from a specific
location.
As shown in the equation above, ORL (in dB) will always be a positive
value (incident power will always be higher than reflected power).
A higher return loss value means less reflected power and thus better
performance. For example, if at a system interface there is 1.0 mW
incident power and 1.0 μW reflected power, the return loss is 30 dB, as
illustrated in the following equation.
Reflectance, on the other hand, is typically used to describe a
reflection at a single interface or reflection site, for example a
connector.
As shown in the equation above, reflectance (in dB) will always be
a negative value (reflected power will always be lower than incident
power).
A higher negative value means less reflected power and thus better performance.
For example, if there is 1.0 mW incident power and 1.0 μW reflected power at a
connector, the reflectance is −30 dB.
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.
Table 1. Accepted ORL values according to
the type of connector
Multimode Insertion Loss Measurements and Launch Conditions
An important aspect when measuring insertion loss of multimode
components such as fiber cable or connectors is the launch
conditions of the light source used. The same light source
with different launch conditions will give different insertion loss
measurement for the same component.
To read more on this topic, download the following application note:
Understanding Launch Conditions for Multimode Connectors and Cable Assembly
Testing
Manufacturing Environment: Integration and Automation
In a manufacturing environment, the production throughput is critical in
order to control the cost of the finished goods. Often times,
final-product testing can be a source of inefficiency as it remains a
very manual process. The typical steps that need to be carried out by
the operator are shown in Table 2:
Table 2. Typical manufacturing environment integration and
automation process
Simplifying or even automating these steps would
save considerable time and money ─ turnkey systems, such as the
IQS-12001B Cable Assembly Test System, do just that. For example,
the IQS-12001B will:
- Manage the various cable-assembly types and the
specific test procedure associated with them
- Guide the operator step by step through the
entire test sequence
- Command the optical switch (internal or
external) to automatically test each individual
fiber when testing multichannel systems
- Manage the results by associating serial numbers
and detailed information for each cable assembly
tested
- Link the results to a central database from
which statistics and reports can be generated or
analyzed
- Print labels after all measurements
Other time-saving possibilities include:
- Integrating test cells into overall
manufacturing management system. For example,
the IQS-12001B (MSDE) allows you to link test data
to the main production database.
- Controlling test equipment via an external
computer for specific tests. The IQS-12001B
comes with DLL interfaces that enable you to create
your own applications and remotely control your
system. These system-level commands ensure smooth,
efficient application creation without compromising
the system’s measurement accuracy and speed. EXFO
provides simple demos to help you get started with
your own application.
Fig 3: Example of a customizable test system
programmed for different manufacturing applications