Optical Connector Loss
Connector loss is
the signal loss through the connector (insertion loss), often
expressed in decibels (dB), caused by impedance mismatching, impurities or
structural changes that cause reflections and/or absorption to a signal
that is passing through the connector.
Core size mismatch
is the signal insertion loss that occurs in a fiber optic connector that
is due to the difference between the size of the fiber core in one
connector compared to the size of the fiber core in the mating connector.
This figure shows
how the core size of fiber strands can vary. This example shows that the
light from the larger core size will not be transferred fiber with the
smaller core size.
Core
Size Mismatch Optical Connector Loss Diagram
Coaxiality
(Misalignment)
Coaxiality is the
axial (core centerline) alignment of fiber cores. Coaxiality insertion
loss occurs when the positioning of the fiber cores is offset
(misalignment). Coaxiality is also called radial offset or radial
misalignment.
This figure shows
how the coaxiality (axial misalignment) of fiber cores result in insertion
loss. This example shows that the some of the light from the fiber cores
size will be absorbed by the cladding and not be transferred between the
fibers.
Coaxiality
Misalignment Optical Connector Loss Diagram
Contamination
Contamination loss
is the optical signal loss that occurs due to the inability for optical
signals to pass through contamination particles (e.g. dirt) in an optical
connector. A key potential source of contamination for the fiber
connection is oil that is transferred from fingers to the surface of the
connector.
This figure shows
how dirt particles (contamination) in an optical connector can cause
insertion loss. This diagram shows that some of the signals are absorbed
or reflected by the contamination particles as the optical signal attempts
to pass from one fiber to the other fiber.
Optical
Connector Loss due to Contamination Diagram
Axial
Alignment (Angular Mismatch)
Axial alignment
loss is the signal loss that occurs when the optical cables are connected
at an angle relative to the axis (centerline) of each other. When the
optical fibers are at an angle relative to each other, some or all of the
light is transmitted from one fiber to the other outside the NA, which
does not allow the optical signal to be coupled into the other fiber.
Axial Alignment is also called angular mismatch or angular misalignment.
This figure shows
how incorrect axial alignment on fiber optic connectors can cause
insertion loss. This diagram shows two optical fibers that are not exactly
aligned along their axis (centerline). As a result, some of the optical
signal from the fiber ends cannot enter the fiber on the mating connector
and this results in some of the signal energy being lost.
Optical
Connector Losses Diagram
End
Gap (Lateral Separation)
End gap loss is the
signal attenuation that results from an excessive amount of space that is
between optical fibers in an optical connector. Because the optical fiber
gap is large, some of the rays that travel from the end of one fiber
extend beyond the numerical aperture acceptance angle of the other fiber.
End gap is also called lateral separation or lateral misalignment.
This figure shows
how an excessive gap between fibers in an optical connector can result in
connector insertion loss. This diagram shows two fibers that have an
excessive gap between them. Because of the excessive gap, some of the
light rays from one fiber fall outside the numerical aperture (NA)
acceptance angle of the other fiber resulting in some loss of optical
signal level.
End
Gap Optical Connector Loss Diagram
End
Angle
End angle loss is
the signal attenuation that results from an angle cut in the end of the
fiber cable. When an optical fiber is cut on an angle, this changes the
direction of light rays as they exit the fiber. Some of the redirected
rays that travel from the end of one fiber do not fall into the acceptance
angle of the other fiber resulting in some signal loss level.
This figure shows
how a fiber cut on an end angle can result in connector insertion loss.
This diagram shows a connection of two fibers where one fiber is cut at an
angle. Because some of the light rays that exit the fiber with the cut
angle are redirected, some of the light rays from the angled fiber cannot
be coupled into the other fiber resulting in some loss of optical signal
level.
End
Angle Optical Connector Loss Diagram
Cocentricity
Cocentricity is the
sharing of a common center point of circular items (such as a fiber core
and fiber cladding or a center conductor in a coaxial cable). When a fiber
core is not positioned in the center of the fiber (not concentric), this
can cause losses as the end of one fiber may not exactly align with the
core of the other fiber.
To overcome some of
the loss due to cocentricity offset, some optical connectors allow for the
rotation of the connector to help align the fiber cores so their cocentric
offsets are aligned as much as possible.
This figure shows
how cocentric offset can cause optical connector insertion loss. This
diagram shows how the fiber core of one fiber has a concentric offset
(core not in the center). When the end of one fiber is connected to the
end of the other fiber, the fiber cores do not align. This results in some
of the light signals from each fiber core not being transferred to the
other fiber (blocked by the cladding).
Concentricity
Optical Connector Loss Diagram
Numeric
Aperture Mismatch (NA Mismatch)
Numeric aperture
(NA) mismatch loss is the signal attenuation that results from differences
in NA between optical fibers. Because the optical pattern of one optical
fiber gap is larger than the NA of the receiving fiber, some of the rays
that travel from the end of one fiber extend beyond the numerical aperture
acceptance angle of the other fiber.
Undercutting
(Over Polishing)
An undercut is the
distance below the desired surface of a fiber connector or optical device
and the actual surface of the fiber strand. Undercutting may result from
excessive fiber polishing.
Over polishing is
the undercutting of the surface of a fiber connector or optical device due
to excessive polishing. Over polishing can result from repeated cleaning
maintenance of an optical connector.
Optical Communication Terms
Optical Add Drop Multiplexer - OADM
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