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DIAMOND Polarization Maitaining products
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Index

• Introduction and theory
• Diamond PM Technology
• Passive/Active axis orientation tools
• Available products Specifications
• Application
• Glossary

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Introduction Theory
More and more telecommunication and fiber optic
measuring systems refer to devices that analyse
the interference of two optical waves. The
information given by the interferences can not be
used unless the combined amplitude is stable in
time, which means, if the waves are in the same
state of polarisation. In those cases it is
necessary to use fibers that transmit a stable
state of polarisation. As light passes through a
point in space, the direction and amplitude of
the vibrating electric field traces out a path in
time. Polarised light can be classified as
linearly, elliptically or circularly polarised,
in them the linearly polarised is the simplest.
In this case, the electric field vector just
vibrates up and down in a specific direction,
instead of drawing an elliptical or circular
trace.
Different states of polarisation
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Introduction Theory
Polarisation maintaining fiber-optic systems
requires specialised fiber and connectors and
careful assembly as well as alignment to achieve
optical performances, which are affected by the
polarisation of the light travelling through the
fiber. To solve the problem of polarisation-depend
ent losses, several manufacturers have developed
polarisation-maintaining fibers (PM fibers).
These fibers work by inducing a birefringence
within the fiber core. Birefringence is created
within a PM fiber either by forming a
non-circular fiber core (shape induced
birefringence), or by inducing constant stresses
within the fiber with stress applying parts (SAP)
(stress induced birefringence). This
birefringence breaks the circular symmetry in an
optical fiber, creating two principal
transmission axes within the fiber, known
respectively as the fast and slow axes of the
fiber.
At present the most popular fiber type in the
industry is the circular SAP type (stress induced
birefringence), or PANDA fiber. One advantage of
PANDA fiber over most other fiber types is that
the fiber core size and numerical aperture is
compatible with regular single mode fiber,
ensuring minimum losses in devices using both
types of fibers.
Polarisation maintaining fiber
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Introduction Theory
Provided the input light into a PM fiber is
linearly polarised and orientated along one of
these two axis, then the output light from the
fiber will remain linearly polarised and aligned
with the principal axis, even when subjected to
external stresses. While in theory one can
produce perfectly linearly polarised light, in
practice this is not the case. Instead there is
always some residual polarisation, random or
elliptical, present in the output light. To
measure the quality of the polarised beam, one
must measure its polarisation extinction ratio
(ER).
Naturally, how well a fiber maintains
polarisation depends on the input launch
conditions into the fiber. Perhaps the most
important factor is the angular alignment between
the polarisation axis of the light with the slow
axis of the fiber. Assume that we have a
perfectly polarised input beam into an ideal
fiber, misaligned by an angle ? with respect to
the slow axis of the fiber. Because of this
misalignment, a small amount of light will be
transmitted along the fast axis of the fiber.
This will degrade the ER of the output beam. The
maximum possible value of the output extinction
ratio is thus limited by EXTINCTION RATIO (ER)
? 10 log (tan2?) Thus to achieve output
extinction ratios greater than 20dB, the angular
misalignment must be less than 6 degrees. For
30dB extinction ratios, the angular misalignment
must be less than 1.8 degrees.
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DIAMOND PM Technology

• PM fiber products show a highly delicate nature
  due to the sensitivity of PM fiber to stress.
• Stress in the fiber modify the birefringence and
  reduce the ER value, which is the parameter that
  describes the efficiency of polarization
  maintaining.
• Connectors usually stress the tip of the fiber
  and reduce its ER.
• Diamond specific production technology

Same first crimping process as for Diamond 0.1dB
standard products

• Use of 0.1dB ferrule having max 0.75µm of
  eccentricity.
• Avoids damaging stress on PM fiber during the
  manufacturing process
• Leaves the required birefringence properties of
  the PM fiber by performing active core alignment.

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DIAMOND PM Technology

• The second crimping process is made using Diamond
  standard tools but only along the slow and fast
  axis, in order to preserve the birefringence of
  the PM fiber as good as possible.

• Diamond PM connectors shows a suitable
  mechanical stability during the mate-demate
  cycling in connection with all DIAMOND as well as
  competitors products

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Axis orientation
Passive PM fiber axes alignment The connector
key is visually orientated with the geometrical
fiber axis with the fast axis of the fiber using
a microscope. The Stress Applying Parts (SAP)
are aligned horizontally to the connector key,
therefore the geometrical fiber axis stands
perpendicular and the connector key may now
be aligned accordingly. The fast or the slow axis
may be aligned depending on customers
specifications. Advantages - Simplicity and
speed Limitations - Alignment of geometrical
axis instead of optical axis. The accuracy
is ? 2. - Optical axis not always oriented
perfectly on stress members Passive fiber axes
alignment is done when a light source at the
entry is not possible, e.g. a confection with a
module on one side.

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Axis orientation
Active PM fiber axes alignment Orient the
connector key optically with one of the optical
fiber axis (fast or slow), by rotating the 2
polarisators until the maximum extinction is
achieved.
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Active Axes Alignment Tools
Thanks to a computerassisted optical
workbench both polarisation axes (fast or slow)
can be perfectly aligned with the connector key,
resulting in a higher ER.

• Alignment workstation containing
• Incoherent Lightsource
• Powermeter
• Polariser
• PC with custom made software
• Alignment workbench with control system

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Active Axes Alignment Tools

• Procedure
• The specially developed axes alignment workbench
  is a key to the success
• of polarisation maintaining systems.
• Furthermore aligning the fiber-axes is an
  essential step when working with
• polarisation. The exact alignment will permit
  you better cross talk values
• independent of wavelengths, positions of cable
  (i.e. qty of turns), orientation and diameter,
  torsion etc.

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Surface polishing

• Convex PC or APC polishing of the fiber surface
  guarantees fiber contact and reduction of the
  reflection
• Repeatable polishing thanks to the well known
  reduced hardness of the DIAMONDs ferrule
• Minimal fiber undercut
• High performance connector mating

PM 0 (PC) connector front-face
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Available products

• Diamond provides high performance PM
  terminations directly to both passive and active
  optical devices as well as for pigtails and
  patchcords assemblies. Standard assemblies are
  made with Panda PM fiber for operation at 1310nm
  or 1550nm wavelengths and are available in both
  PC and APC finishes in various connector styles
  (E-2000, SC, FC, DMI, DIN, AVIM).

• All standard assemblies are 100 tested for IL,
  RL and Extintion Ratio.
• Note Other fiber types such as Bow Tie, Oval
  inner clad, Oval Core, D-Fiber, connector styles,
  and wavelengths requirements can be accommodated
  to meet your specific application needs.

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Specifications
SM 0 PC SM 8 APC Units Test
conditions Insertion Loss (IL)
typ 0.2 max 0.5 dB IEC 61300-3-4
1300/1550nm Return Loss (RL) typ. 40 min 30
typ. 70 min 55 dB IEC 61300-3-6
1300/1550nm Repeatability of IL
/- 0.1 dB Over service life Extintion Ratio
typ. 20 min. 23 dB
May be further limited by cable specifications.
Notes - Optical performance values based on use
of Panda PM fiber, use of other types
or wavelengths may impact performance values. -
Diamond performs extinction ratio (ER)
measurements using the crossed-polarizer method
(similar to IEC 61300-3-40). - ER nominal value
and accuracy 20 dB 1.5 dB 25 dB 2.5 dB 30 dB
3.5 dB
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Why a PM fiber optic connector?

• The following questions must be answered
• What advantage does a PM fiber optic system
  grant?
• What are future market requirements?
• What are important parameters of a PM optical
  connector?
• The answers are as follows
• Polarisation maintaining fiber optic systems show
  a stable state of polarisation, allowing easy
  analysis of interference of two optical waves
• Many modern optical components, particularly
  those used in coherent optical communications
  already rely on a fixed state of polarisation,
  tendency is increasing (Modulator-Technology)
• Extremely precise axes alignment and core
  centring, which allow
• Consistent, repeatable low insertion loss /
  stressless fiber / High extinction ratio / High
  return loss

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Applications
For use in WDMs including optical
modulators, sensors, interferometers.
Practical examples Sensor measuring
instruments - ABB Power, EMS Interfero
meters - Hewlet Packard, Agilent Modulators
- In various Telecommunication- systems
around the world - Chiaro, Alcatel and many
more.
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Glossary
Active Alignment Optical alignment of one of the
optical axes (fast or slow) with the connector
key. Beat length The beat length is the length
of fiber after which the wave in the slow axis is
delayed by exactly one optical wavelength. The
Beat length of modern single-mode fibers is
usually several meters if the fiber is straight.
Actual beat lengthof PM fibers are on the order
of 1 to 3 mm. Birefringence In all
single-mode fibers there are 2 perpendicular
orientations of the (transverse) electric field
which leadto a maximum difference in phase
velocity the fiber exhibits linear
birefringence. BOW-TIE fiber Birefringence is
created within a BOW-TIE PM fiber by forming a
non-circular fiber core (shape induced
birefringence). (ER) Extinction ratio To
measure the quality of the polarised beam, one
must measure its polarisation extinction ratio
(ER)or so called cross talk. PANDA fiber At
present the most popular fiber type in the
industry is the circular SAP type (stress induced
birefringence), or PANDA fiber. One advantage of
PANDA fiber over most other fiber types is that
the fiber core size and numerical aperture is
compatible with regular single mode fiber. This
ensures minimum losses in devices using both
types of fibers. Passive Alignment Visual
alignment of one of the geometrical axes (fast or
slow) with the connector key. (PM) Polarisation
maintaining fiber PM fibers are based on the
concept of a large difference in velocity, i.e.
large birefringence. The desired index
difference can be introduced by lateral pressure
on the fiber. Several types of fiber have been
invented to produce this type of stress, the most
popular types being the PANDA fiber and the
BOW-TIE fiber. (SAP) Stress applying parts
(Stress induced birefringence) is created within
a PM fiber by inducing constant stresses
withinthe fiber with stress applying parts (SAP).