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Whenever a connector is installed
on the end of fiber, loss is incurred. Some of this light loss is
reflected directly back down the fiber towards the light source that
generated it. These back reflections, or Optical Return Loss (ORL),
will damage the Laser Light Sources and also disrupt the transmitted
signal. To reduce back reflections, we can polish connector ferrules
to different finishes. A typical hand polished connector will
measure at –30dB. This polish is referred to as a PC or Physical
Contact polish, which for some systems is considered too high of an ORL
measurement. To reduce the back reflection of a connector, we can
machine polish it to SPC (Super Physical Contact) polish or UPC (Ultra
Physical Contact) polish. Industry standard is a minimum of –40dB for
SPC Back reflection measurement and –50dB for UPC back reflection
measurement. If even less back reflection is required, an APC, or
Angled Physical Contact polish, might be necessary. An APC
connector has an 8º angle cut into the ferrule. These connectors are
identifiable by their green color. An APC polished connector has an
Industry Standard Minimum f –60dB ORL measurement. Abroad most CATV and
telephone companies require the use of these low back reflection connectors. |
Connector Ferrule Polishes: Performance and
Compatibility
Alain Poirier, http://www.exfo.com/en/support/WaveReview/January2003/WRarticle3.asp
FC, SC, ST, D4, DIN, and E2000 are currently
some of the most widespread fiber-optic connectors.
Although sizes, shapes and interlocking mechanisms can vary, one element is
shared by all connectors: the ferrule. Since connector performance and
compatibility depends on which ferrule polish is used, it is important to
understand the differences between types of polish.
Four Types of Ferrule Polish
The ferrule (made of metal or ceramic) is the central part of the male
connector. It is designed to both align and protect the fiber core during
connection. The ferrule tip is polished to ensure a smooth finish on the fiber
end. Polish can also minimize connector loss or backreflection, depending on
the angle used.
There are four types of polish: PC, super PC (SPC), ultra PC (UPC) and angled
PC (APC). Each one is illustrated below.
PC Polish
Designed to eliminate connector loss caused by gaps between two fiber ends,
physical contact polish (PC) was the first type available (see Figures 1 and 2).
Originally flat, PC ferrules were later slightly curved--a principle then
applied to FC, SC, ST and D4 connectors--to optimize connection. The result:
typical insertion loss values of 0.2 dB for singlemode fibers and maximum
return loss values of 35 dB. The high return loss values motivated connector
manufacturers to continue seeking better solutions.
APC and SPC Polishes
APC was the next polish developed (see Figure 3). For this connector, the
ferrule end was cut to an 8° angle, eliminating almost all reflections at the
connector end and giving a final return loss specification of 60 dB.
Early APC connectors did not deliver the repeatable performance of today's
devices. Research on angled connectors therefore continued while other
polishing methods were developed. SPC polish appeared next and was applied to
FC and ST connectors, which provided return loss values of 40 dB while
maintaining 0.2 dB insertion loss.
UPC Polish
Further work introduced UPC connectors, bringing return loss down to an
impressive 55 dB in singlemode fibers. This performance was obtained by
perfecting the polishing technique and adjusting the curvature at the ferrule
end. Nowadays, UPC polish is available for almost all singlemode
connectors--namely FC, SC, ST, DIN and E2000--but, unlike its predecessors, is
not available for multimode fibers.
Compatibility
Due to their special angled design, APC connectors are not compatible with PC,
SPC or UPC types. Joining an APC connector to a different connector type should
be avoided, since this will cause more insertion and return loss than either
connector would normally produce on its own.
PC, SPC and UPC connectors are all compatible and any cross between them will
typically generate an insertion loss of 0.2 dB. Return loss is more difficult
to predict when different polishes are cross-connected, but it generally falls
somewhere between the individual return loss specifications for each polish.
For example, an FC/SPC to FC/UPC connection might give an insertion loss of 0.2
dB and a return loss of approximately 58 dB.
Test instruments equipped with UPC connectors would therefore be capable of
measuring PC, SPC and UPC systems without affecting their normal performance.
On the other hand, test instruments equipped with PC connectors are not capable
of measuring SPC and UPC systems, because the instrument connector's return
loss could be greater than the return loss of the system itself.
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What is the difference between a
PC, APC and UPC finish on a fiber optic connector and why would someone
want to use one verses the other? |
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Whenever
a connector is installed on the end of fiber, loss is incurred. Some of
this light loss is reflected directly back down the fiber towards the light
source that generated it. These back reflections, or Optical Return
Loss (ORL), will damage the Laser Light Sources and also disrupt the
transmitted signal. To reduce back reflections, we can polish connector
ferrules to different finishes. A typical hand polished
connector will measure at –30dB. This polish is referred to as a PC or
Physical Contact polish, which for some systems is considered too high of an
ORL measurement. To reduce the back reflection of a connector, we can
machine polish it to SPC (Super Physical Contact) polish or UPC (Ultra
Physical Contact) polish. Industry standard is a minimum of –40dB for
SPC Back reflection measurement and –50dB for UPC back reflection
measurement. If even less back reflection is required, an APC, or
Angled Physical Contact polish, might be necessary. An APC
connector has an 8º angle cut into the ferrule. These connectors are
identifiable by their green color. An APC polished connector has an
Industry Standard Minimum f –60dB ORL measurement. Abroad most CATV and
telephone companies require the use of these low back reflection connectors.
PDR has the state of the art technology and equipments to produce higher
standard Super, Ultra and Angled patchcords. PDR assemblies are prepared by
highly skilled technicians and each assembly is checked to guarantee highest
performance. |
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What is the
difference between Singlemode and Multimode Patchcord and why would someone
want to use one verses the other? |
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All
fiber consist of a light carrying core in the center covered by an optical
coating called cladding that traps light within the core. The difference
between multimode and singlemode is the diameter of the fiber core. The core
diameter is either 50 or 62.5 micron for multimode and 9 micron for
Singlemode. Multimode patchcords are primarily used with LED sources for LAN
and security systems. Its large core makes it easy to couple lots of light
from inexpensive LED’s and it has adequate bandwidth for most premises
applications. |
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What is the difference between a SC/PC and SC/APC Adapter? |
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The
most visible difference between the two adapters is color. Most singlemode
SC/PC adapters are blue and SC/APC adapters are green. This allows for quick
identification, especially when used in distribution panels so the end-user
inserts the correct connector type. Often users cannot see the connector
plugged in on the backside of the panels, therefore the color indicates the
SC connector that’s required. SC connectors correspond with the adapter; most
singlemode SC/APC connectors have green outer shells while singlemode SC/PC
connectors have blue outer shells. SC/APC adapters use premium zirconia split
sleeves to achieve the tightest tolerance possible providing critical
alignment of the two angle polished ferrules. Whether it is a singlemode
SC/PC or SC/APC connector be sure to choose a zirconia (ceramic) sleeve
material rather than a phosphor bronze or polymer. The zirconia alignment
sleeves have a tighter tolerance and better elasticity, maintaining tight
tolerances after several matings. |
Type-1 and type-2 14-pin
laser pinout definition
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(From http://www.thorlabs.com/NewGroupPage9_PF.cfm?Guide=10&Category_ID=97&ObjectGroup_ID=1558 ) Pin Assignment of the 14-pin Sockets
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