All about Connectors in fiber optics. and manufacturers

1. Fiber Optic Connector
Falak Shah,
th
6 Semester, Electronics and Communications Department,
Institute of Technology, Nirma University.
Abstract
c) Buffer- A material applied over the coating
that may be used to protect an optical fiber
This paper reviews the fiber connectors available for
fromphysical damage, providing mechanical
connecting fibers in a link end to end and their isolation or protection, or both.
connection process. Beginning with the structure of d) Small form factor (SFF)-It refers to any of
the connector, followed by commonly used connector several physically compact connector
types and their applications, it journeys towards designs that have been developed for use in
special connectors for harsh military environments fiber optic systems. They are about half the
finally explaining the mechanism for end to end fiber size of conventional connectors.
e) Cladding- The dielectric material
connection.
surrounding the core of an optical fiber.
f) Cleave- The process of separating an optical
fiber by a controlled fracture of the glass for
thepurpose of obtaining a fiber end that is
1.Introduction flat, smooth, and perpendicular to the fiber
axis.
There are 110 design types of Fiber Optic connectors g) Coupling Loss- The optical power loss
[1]available as on today. Connectors are used for suffered when light is coupled from one
many different applications including optical device toanother.
h) Ferrule- A mechanical fixture, generally a
telecommunications, local area networks, and harsh
rigid tube, used to confine the stripped end
environments. When choosing a connector and of a fiberbundle or an optical fiber.
coupling for a particular application, fiber type, i) Fiber Optic Connector- A fiber optic
required optical performance, maintenance, and component normally assembled onto a cable
system cost are taken into consideration. If an and attachedto a piece of apparatus for the
existing system is being modified, compatibility with purpose of providing
existing components is must. Specifically, a contact interconnecting/disconnecting of fiber
opticcables.
scheme, a connector style, terminations, and j) Hackle- A surface irregularity characterized
materials need to be chosen. This paper introduces by a rippled or stepped break in the fiber,
the commonly used connectors followed by a usuallydue to improper cleaving.
discussion of military application connectors and k) Connector Insertion Loss- Total Optical
finally concludes explaining the mechanism for Power Loss caused by insertion of an optical
connecting fibers end to end. component such as a connector, splice, or
couple into a previously continuous path or
The loss in the power of a signal that results
2. Definitions[2] from inserting a passive component into a
previously continuous path. Examples
a) Adhesive-A polymeric compound, usually ofsuch passive devices are connectors, inline
an epoxy, used to secure the optical fiber in star couplers and splices
a spliceassembly or connector. l) Mode- In terms of ray optics, a possible path
b) Back reflection (Backscattering) - The followed by light raysdependent on index of
return of a portion of scattered light to the refraction, wavelength of light and
input end of afiber; the scattering of light in waveguide dimensions.
the direction opposite to its original
propagation.

2. m) Multi-mode Fiber- An optical fiber that will
allow two or more bound modes to
propagate in thecore at the wavelengths of
interest.
n) Pistoning- The axial movements of an
optical fiber within a connector or connector
ferrule.
o) Single-Mode Fiber- An optical fiber in
which only the lowest order bound mode
can propagateat the wavelength of interest.
p) Splice- An interconnection method for
joining the ends of two optical fibers in a
permanent orsemi permanent fashion.
q) Strength Member- That part of a fiber optic
Figure 2. Ferrule in connector
cable composed of Kevlar aramid yarn, steel
strands,or fiberglass filaments included for
increasing the tensile strength of the cable,
and in certain applications, to support the
weight of the cable. 4. Summary of commonly used
connectors
3. Fiber connector Structure 4.1. SC Connector
A fiber-optic connector joins fibers in a way that light SC stands for Subscriber Connector.
passes from one fiber to the other. The main goal is
minimizationof signal loss and reflections, while Manufactured By: NTT (Nippon Telegraph and
providing mechanical stability. Losses forvarious Telephone) of Japan.
connector types are in the range of 0.25 dB to
1.5dB[3].A fiber-optic connection consists of three Application: SC Connectors are frequently used for
components: twomale connector plugs, and a Network applications. SC connector is widely used in
coupling (or in-line adapter). Theconnector plug singlemode systems. SC connectors have low cost
consists of a ferrule, a strain relief boot, and housing and they are simple and durable.
or body. The coupling device allows twoconnectors
Ferrule Diameter:It has a 2.5mm diameter ferrule,
to mate through a panel. It hasreceptacles on each
made of ceramic or metal. A 124~127µm diameter
end and a precision sleeve toalign two mated
hole is drilled in the center of the ferrule. It is usually
connectors.
bonded by epoxy or adhesive. They provide accurate
alignment due to ceramic ferrules.
Standard: IEC 61754-4
Coupling Type: It hasa square shaped design, with
push-pull latching mechanism. Its molded
housingprovides optimum protection.
Losses & Other Details:The SC connector is also
available in a Duplex configuration. SC connectors
allowup to 1000 mating cycle. They have insertion
loss of 0.25 dB and return loss >55 dB.They are
available in single and multimode.
Figure 1. Fiber Connector Structure

3. Figure 4. ST connector
Figure 3. SC connector
4.3. FC Connector
4.2. ST connector
FC stands for Ferrule connector or fiber channel.
Stands for straight tip connectors.
Application: It is designed for telecommunication
Manufactured By: AT&T
applications.It is being used in long haul and local
Application: ST connectorsare used in network connections. They are also useful in high-
telecommunications fieldfor both long haul and local vibration environments.[4]
network applications. They are the most commonly
Ferrule Diameter: FC connector also has a 2.5mm
used connectors for multimode applications.
ferrule made of ceramic (zirconia) or stainless alloy)
Ferrule Diameter:It has a 2.5mm keyed long
Standard: IEC 61 754-143
cylindrical ferrule for the durability and repeatability
requirements in telecommunication links. Coupling Type:It is designed with a threaded
coupling. Due to such coupling, connections are
Standard: IEC 61 754-2 standard[9]
durable. It makes use of screw on mechanism in
Coupling Type: Ithas a twist-lock bayonet couplers.
coupling.Couplers are keyed and spring-loaded. They
Losses &Other Details:It is available in simplex
come in push-in and twist types. Because they are
mode only. It is rated for 500 mating cycles. The
spring-loaded, they must be seated properly. It must
Insertion Loss for FC connectors is 0.25 dB. It is
be removed and reconnected if high insertion loss is
available in single mode and multimode. It is now
observed. It can be inserted and removed easily due
gradually being replaced by SC and LC connectors.
to its design. It can have metal or plastic housing.
Losses & Other Details: They are available in
simplex version only. Itallows 500 mating cycles.The
Insertion Loss for correctly matched ST connectors is
0.25 dB.It is available in single mode as well as
multimode fibers.

4. 4.5. MU Connector
MU stands for miniature unit connector.
Manufactured By:It was developed by NTT.
Application: It is a popular connector type in Japan.
Applications include high-speed data
communications, voice networks and
telecommunications. They even support dense
wavelength division multiplexing (DWDM). They
can also be used for multiple optical connections.
Figure 5. FC connector
Ferrule Diameter: 1.25 mm
Standard: IEC 61754-6
4.4. LC connector
Coupling Type:It has push/pull mechanism, but
LC stands for Lucent Connector. benefit is that 2 channels can fit in the footprint of a
single SC. It is with square shaped.
Manufactured By:Lucent
Losses & Other Details:It comes in simplex as well
Application: The LC has good performance and is as duplex form. It is a small form factor SC
highly favored for single mode. Due to its small size, connector. They have insertion loss of 0.25 dB and
it is used forhigh-density connections. return loss >55 dB.
Ferrule Diameter:LC connectors use a 1.25mm
ceramic ferrule –half the size of the 2.5mm ferrule
used in above mentioned connectors.
Standard: IEC 61754-20
Coupling Type: simplex and duplex – push and latch
Losses & Other Details: Externally LC connectors
resemble a standard RJ45 telephone jack. Internally
they resemble a miniature version of the SC
connector. Insertion loss is <0.2 dB and return loss
>50 dB. The LC is a small form-factor (SFF) Fiber
optic connector. Figure 7. MU connector
4.6. SMA Connector
SMA stands for Subminiature version A.
Manufactured By:Amphenol Fiber Optic Products
Application: Industrial lasers, military; telecom
multimode. The SMA connector has exceptional
mechanical durability.
Figure 6. LC Ferrule Diameter: The SMA connector holds a
connector single fiber. The Ferrule is traditionally made of

5. steel, although ceramic versions are available. SMA
905 and SMA 906 multimode connectors are
available with stainless alloy or stainless steel
ferrules. The stainless alloy ferrule may be drilled
from 125um to 1550um to accept various fiber sizes.
Coupling Type:SMA connectors use a threaded plug
and socket. SMA connectors have a threaded
Coupling nut.
Figure 8. MT-RJ connector
Losses & Other Details:Simplex only.
Multimodeonly.SMAconnectors come in two
varieties: the SMA-905 has a straight ferrule,
whereas the SMA-906 has a stepped ferrule design
SMA 906 ferrule has a step, which requires a half 5. Connectors for harsh military
sleeve to be installed when mating a SMA 906 environment
connector with SMA 905 mating sleeves.
AT&T has developed a new type of connector that
uses expanded-beam optics to maintain accurate
alignment, even under severe shock and vibration.
4.7. MT-RJ Connector The reliable optical card-edge connector (ROC) uses
expanded beam optics to achieve optical alignment.
MT-RJ stands for Mechanical Transfer Registered Each terminus consists of a cleaved fiber aligned on-
axis with a sapphire ball lens. The gap between the
Jack or Media Termination - recommended jack. fiber end and the ball lens is filled with an index-
matching gel. The LRM assembly was subjected to
Manufactured By:Tyco Inc. high frequency (sine sweep) vibration, random
vibration, and mechanical shock test but negligible
Application:MT-RJ connectors are used in building increase in optical loss was observed[6].The self-
communication systems for duplex multimode sealing feature of the connector provides adequate
connections. protection for handling in military environments.An
additional feature of the ROC connectoris its ability
Ferrule Diameter: It has a miniature 2.45×4.4 mm to self-seal or shield the optical fiber ends
two-fiber ferrule with two guide pins parallel to the whenunmated, protecting the fibers and internal
fibers on the outside. It is easier to terminate and mechanisms fromenvironmental contamination and
install than ST or SC connectors. [5] abusive handling. [7]
Standard: IEC 61754-18
Coupling type: It is derived from MT ferrule design.
The guide pins align ferrules precisely when mating
two MT-RJ connectors. MT-RJ connectors are Figure 9. ROC connector expanded beam method
designed with male-female polarity which means
male MT-RJ connector has two guide pins and
female MT-RJ connector has two holes instead. MT-
RJ uses a form factor and latch similar to the RJ45 6. Connection mechanism
connectors. Two separate fibers are included in one
The steps for Fiber optic Connection are as follows
unified connector. The small size allows double the
density than ST or SC connectors. 6.1.Setup and Tools

6. The tools that are needed for fiber optic Connection The steps involved in the stripping process
include are
a) Jacket preparation is the first step wherein a
a) Safety Glasses for protection and safety. tight knot is to be tied at one end of the
b) Cable to be assembled. jacket to prevent the internal parts from
c) Jacket Stripper for stripping outer jacket. sliding out. The boot of the connector is
d) Buffer Scissors for cutting Buffer member inserted into the cable, small side first. This
e) Kevlar Scissors to cut through strength is followed by the crimp sleeve.
member. b) The strip Dimension/marking of the Jacket
f) Alcohol pads for wiping the fiber clean stripping tool is set as per the jacket
before insertion to connectors. diameter. The jacket is bitten firmly without
g) Syringe and epoxy for injecting epoxy and twisting or pulling the stripping tool. Then
adhesion. after the removal of tool, the jacket is
h) Hand Crimp Tool for crimping sleeve onto twisted slowly and it comes off quite easily.
the jacket holding assembly together. c) The Kevlar and inside it the PVC coated
i) Polishing disk for polishing the end face of glass fiber are then exposed. The Kevlar is
the fiber cut using the Kevlar scissors leaving about
j) The required connector. 3/8 inches of strength member.
k) Scribing tool to scribe the glass from the d) The buffer stripping tool is used to strip
connector itself away the protective buffer coating from the
l) Three types of lapping film for deburring, wire thus leaving the glass uncovered. For
rough and fine polishing. this, the fiber has to be kept slightly taut to
m) Glass plate for smooth surface when fix the fiber tightly in the jacket and prevent
polishing slipping. Then the buffer is cut out bit by bit
n) Small trash bin in straight motion such that the fiber doesn’t
bend while stripping. Taking large bites or
6.2. Fiber Stripping bending can crack the glass as the buffer
Knowledge about internal Fiber structure needs to be tube is strongly attached to it.
known for this section. It consists of e) After clearing all debris left over from the
stripping process in the trash bin, the fiber
a) Outer jacket is cleaned of any minute surface debris
b) Strength member-Usually aramid Yarn or using good quality alcohol (91% to 99%
Kevlar alcohol). Wiping it with alcohol pads in
c) Buffer member-PVC coating straight motion removes all the leftover
d) Fiber-core and cladding debris thus ending the stripping process.
6.3. Adhesive preparation
It is made up of two steps
a) Mixing the epoxy-It has 2 portions that need
to be mixed properly (dark and light). They
must be properly mixed together to ensure
hardening after some time. Setting time is
around 30 minutes so only to be mixed when
all tools ready to use.
Figure10. Fiber coating layers

7. b) After removing the needle plunger, the lightly for about 20 seconds.As the stub of
epoxy is poured into the syringe and at three glass is rubbed off, the sound gets quieter;
quarters filled condition, plunger is fitted an indication to stop brushing.
back and needle pushed removing any air c) The 3 micron yellow colored lapping film is
bubbles present. used for the pre-polishing stage. Here, the
connector is first fixed into the polishing
disk and placed on the double layer of
6.4.Connectorization process yellow lapping film placed on glass. It is
rubbed slowly in figure of eight motion till
a) This epoxy is then injected into the smoothening is felt and the piece of glass is
connector till a small dark spot is visible at completely gone.
the connector face. After removing the d) There is also a 0.3 microns white lapping
needle halfway through the body. More film for final smoothing polish. Two layers
epoxy is filled in till a similar spot is visible of this film are placed on the smooth and
at the back end of the connector. cleaned glass plate for cushioning effect so
b) The fiber is then inserted through the back that the round curve at fiber end is obtained.
end of the connector while rotating the The gentle motion of figure eight is
connector back and forth to allow fiber find repeated in this film too for three times.
the hole in the ferrule. The connector is This concludes the polishing process unless
brought down till some portion of it covers an stub is visible in which case, above three
the Kevlar it just meets the jacket. steps need to be repeated.
c) The crimp sleeve previously loaded into the
fiber is brought forward to the junction of 6.6. Visual inspection
jacket and connector. The large part of the
crimp sleeve is crimped hard down onto the a) The fiber connector is finally observed for
connector and smaller on the jacket using a any scratches on its face by using a
hand crimp tool. microscope and if any scratches found,
d) The boot also previously loaded is now motion on white lapping film is repeated
brought up and attached over the back end once or twice till its completely clean.
of the cable. A protective sleeve is attached
over the ferrule to protect the fiber and
connector while it is allowed to settle and fix 7. Acknowledgement
for 18 hours. The other end of the cable too
I acknowledge the motivation provider for writing of
has to be left as it is to prevent slipping of
this term paper, Dr. DhavalPujara, for his constant
the fiber during this settling process.
guidance and words of motivation. I also
6.5. Polishing acknowledge Professor Dhaval Shah for guiding me
regarding technical paper writing rules and
a) After settling, the protective sleeve is regulations.
removed. Three cuts are made on the glass
protruding from the connector end with a 8. References
scribing tool having a wedged of 60° and
then this glass protrusion is twisted and [1]Fleck Research, Global Connector Research
Group, Inc.
pulled away. A tiny portion still remains [2] NASA-NASA-STD 8739.5 with Change 2
that has to be deburred. Approved: 1998-02-09 Revalidation Date: 2008-07-
b) The 12 micron pink colored lapping film is 25
used to debur the tiny stub of glass that is [3]Practical LEOS Applications -M. Leonard Riaziat
protruding [8]. The connector is first [4]Keiser, Gerd (August 2003). Optical
brushed on this film while it is held in hand Communications Essentials. McGraw-Hill
Networking Professional.

8. [5] Shimoji, Naoko; Yamakawa, Jun; Shiino,
Masato. "Development of MT-RJ Connector"
[6] THE RELIABLE OPTICAL CARD-EDGE
CONNECTOR (ROC) Stephen L. Benning Wright
Laboratory - Avionics Directorate Wright-Patterson
AFB OH 45433-7301
[7] A New Type of Fiber Optic Connector Designed
for Military Optical Backplanes R.J. Pimpinella,
AT&T Bell Laboratories
[8] www.thefoa.org (Fiber optic association)
[9] International Standard IEC(International
electrotechnical Commission)-61754 Fibre optic
connector interfaces