Understanding Fiber Optics

Learn everything about Fiber Optics. What is an optical fiber? What are characteristics of Optic Fiber? Why choose Fiber Optics? How to choose a fiber optic connector?

UNDERSTANDING FIBER OPTICS

WHAT IS AN OPTICAL FIBER ? Fiber structure and fiber types - An optical fiber is made of 3 concentric layers as described on the following sketch:

• core: This central section, made of silica, is the light transmitting region of the fiber. • cladding: It is the first layer around the core. It is also made of silica, but not with the same composition as the core. This creates an optical waveguide which confines the light in the core by total reflection at the core-cladding interface. • coating: It is the first non-optical layer around the cladding. The coating typically consists of one or more layers of a polymer that protect the silica structure against physical or environmental damage.

core cladding coating

• Multimode fiber

• Singlemode fiber

This type of fiber is called “multimode” because light rays travel through the fiber following different paths called “modes”.

In that case, the fiber is called “singlemode” because only one mode is propagated. It travels “straight” through the fiber. The core diameter is typically 9 µm.

Multimode fiber

Singlemode fiber 9 / 125

50 / 125 or 62,5 / 125

cladding diameter in microns ( µ m)

cladding diameter in microns ( µ m)

core diameter in microns ( µ m)

core diameter in microns ( µ m)

CHARACTERISTICS OF OPTICAL FIBER

Attenuation and wavelength Light is gradually attenuated when it is propagated along the fiber. The attenuation value is expressed in dB/km (decibel per kilometer). It is a function of the wavelength ( λ ), i.e. of the color (frequency) of the light. That means that the operating wavelength to transmit a signal in an optical fiber is not any wavelength.It corresponds to a minimum of attenuation. The following graph gives the linear attenuation as a function of the wavelength:

The operating wavelengths, which light sources have been developed for, are 850 nm (nanometers) and 1300 nm in multimode, and 1310 nm and 1550 nm in singlemode. Example: For a 850 nm operating wavelength, there is a 3 dB light attenuation after 1 km propagation (according to the graph). 3 dB mean that 50% of the light has been lost.

1 2 3 4 5

wavelength (nm)

850 nm

1300 nm

1550 nm

p2

UNDERSTANDING FIBER OPTICS

Bandwi d th Bandwidtihsameasuroefthedata-carryincgapacitoyfanopticalfibe.rItisexpresseadstheproducotffrequencaynddistanceF.or example, a fiber with a bandwidth of 500 MHz.km (Mega-hertz kilometer) can transmit data at a rate of 500 MHz along one kilometer. Bandwidth in singlemode fi bers is much higher than in multimode fi bers:

• multimode case

• singlemode case

A B C A B C

AABABCBCC AAABBBCCC

A B C A B C

A B C A B C

mode 1

mode 2

mode 3

Information (A, B or C) is propagated in fiber according to only one mode, therefore is not deformed. It is thus possible to closer the information, i.e. to obtain a much more important flow.

Information (A, B or C) is propagated in fiber according to N modes (paths), which deform it, as if it were “duplicated” N times (for example on the diagram above, the mode 3 path is longer than the mode 2 path, which is itself longer than the mode 1 path). If information is too close one to the other, there is a risk of mixing, and it will not be recoverable at the exit of fiber. That is why it is necessary to space it sufficiently, i.e. to limit the flow.

WHYTOCHOOSE FIBEROPTICS? The main benefits of fiber optics are:

•Lower loss: Optical fiber has lower attenuation than copper conductors, allowing longer cable runs and fewer repeaters. • Increased bandwidth: The high signal bandwidth of optical fiber provides a significantly greater information-carrying capacity. Typical bandwidths for multimode fibers are between 200 and 600 MHz.km, and > 10 GHz.km for singlemode fibers. Typical values for electrical conductors are 10 to 25 MHz.km. •Immunity to interference: Optical fibers are immune to electromagnetic and radio frequency interference and also emit no radiation themselves. •No detection: Standard fiber optic cables are dielectric, so they cannot be detected by any type of detector. •Electrical isolation: Fiberoptics enable stotransmint formatiobnetweetnwopointsattwo different electrical potentialsa,nd also next to high voltage equipments. •Decreased size and weight: Compared to copper conductors of equivalent signal-carrying capacity, fiber optic cables are easier to install, require less duct space, and weight about 10 to 15 times less.

p3

UNDERSTANDING FIBER OPTICS

The coated fiber, i.e. the two active layers (core and cladding) and the protective coating, has an external diameter of 250 microns. It is very fragile. It is thus necessary to build cables to reinforce this fiber and to make it easier to handle. There is a great number of different cable constructions (see below some examples). FIBER OPTIC CABLES

singleway cables:

multiway cables:

0,9 mm buffer

0,9 mm outer diameter

0,9 mm buffer

250 µm coated fiber

250 µm coated fiber

0,3 mm outer diameter

5,5 mm outer sheath

kevlar (strength members)

outer sheath

kevlar (strength members)

HOW TO LINK TWO OPTICAL FIBERS ? There are two ways of linking two optical fibers:

2 - Use of connectors In this case, it is important to terminate a connector at each end of the fibers to be connected. The two fibers can then be connected by connecting the two connectors together. Advantages: •This type of connection is robust. •The type of connector can be chosen according to the application field of the system. • Connection is removable. It is possible to connect and disconnect two fibers hundreds to thousands times without damaging the connectors. Drawbacks: • The implementation is longer than fusion, and requires an experiment as well as specific tools. • The light loss due to connection is higher than in the splicing solution.

1 - Fusion splice This operation consists in directly linking two fibers by welding with an electric arc, by aligning best possible both fiber cores. The specific device to make this fusion is called a fusion splicer.

Advantages:

•This linking method is fast and relatively simple to make. • The light loss generated by the welding, due to an imperfect alignment of the cores, remains very weak. Drawbacks: • This type of link is relatively fragile (in spite of a protection of fusion by a heat-shrinkable tube). • It is a permanent link. • It is necessary to invest in a fusion splicer.

p4

UNDERSTANDING FIBER OPTICS

CONNECTORS TYPES

Fiber termination in the ferrule Whatever the needed connector, the first step consists in inserting the fiber in a ferrule, to allow to simplify the fiber handling with less risk to damage it. This ferrule is generally made of ceramics and is manufactured with high precision machining process.

ceramic ferrule

fiber optic cable

glue

bare fiber (125 µm )

The different steps to terminate the fiber in the ferrule are: • fiber stripping to keep only the active layers (core and cladding). • fiber epoxy bonding in the ceramic ferrule. The fiber is introduced into the ceramic ferrule hole whose diameter is very precise, and adjusted to that of fiber. • fiber cleaving at the ceramic ferrule surface. • polishing of the end of the ceramic ferrule. Using lapping films of increasingly fine grains, the fiber surface is perfectly well polished, and all the awkward residual particles have been eliminated.

Butt joint technology Principle:

ceramic ferrule

The principle of the butt joint connectors consists in putting in physical contact the two ceramic ferrules. To realign perfectly fibers face to face, we use an alignment sleeve generally in ceramics. The light passes thus directly from one fiber to the other.

fiber

sleeve

Defects: The alignment of fibers is never perfect, some light is lost when going from one side to the other. This loss can be high according to the residual defects of alignment or polishing:

transverse shift

air gap (bad contact)

angular shift

bad polishing

p5

UNDERSTANDING FIBER OPTICS

Butt joint connectors characteristics: •The loss of light generated by connection (called Insertion Loss) is low (approximately 0,3 dB typical). • This type of connection is sensitive to pollution (dust, mud...). If a dirtiness stays between the two ceramic ferrules, a big part of the light can be lost.

Butt joint connectors examples:

ST (singleway)

RNJOP (4 channels)

Lens technology (expanded beam technology) Principle: The principle of the expanded beam connectors consists in placing a lens at the exit of each fiber, in order to widen the beam by collimating it - i.e. by creating light beams parallel to the optical axis. In this configuration, there is no more physical contact between the two optical fibers.

expanded beam

connector shell

ferrule

lenses

Defects: In this case it is the alignment of the two shells one to the other which will guarantee that the collimated beam going out from the first lens will be well refocused through the second lens. The precision of the mechanical interface parts of the connector is highly important. As for the butt joint connectors, transverse and angular shifts, and also bad polishing will generate losses. Lens connectors characteristics: •The light loss generated by connection (called Insertion Loss) is more important than in the previous case, due to the presence of the lenses and sometimes also of windows (approximately 1 to 1,5 typical dB). • This type of connection is much less sensitive to pollution because the beam is much larger than the one that goes out directly from a fiber. A dust at the interface of two butt joint connectors will create a much higher loss than located at the interface of two lens connectors.

Lens connectors examples:

CTOS (2/4 channels)

CTOL (8 channels)

p6

UNDERSTANDING FIBER OPTICS

CHARACTERISTICS OF FIBER OPTIC LINKS A fiber optic interconnection system can generally be described by the following sketch:

Emission

Reception

Connection

Optical patchcord

It is made of the following elements : • emission system It contains a light source. To obtain a well functioning system, it is important to know : • the type of light source (LED or laser). • the operating wavelength (1300 nm for example). • the light source power. • the interface connector type at the light source output. • one or more optical patchcords The pachcords are defined by: • the fiber optic cable described by its length, the number of channels, the fiber type (singlemode, multimode 50/125 or 62,5/125). • the connectors terminated at both ends of the cable. • the whole patchcord is characterized by a loss named Insertion Loss, expressed in dB. This loss gives the quantity of lost light when introducing this patchcord in the transmission line. It includes the linear attenuation of the cable and the loss due to the connectors. • for singlemode patchcords, another important parameter, called Return Loss, represents the quantity of light which is reflected by the line and which returns in the direction of the source. The laser sources used in singlemode applications can be very sensitive to this phenomenon.

P in

P out

optical link

P back

The Insertion Loss of the link is: The Return Loss of the link is:

PI = 10 log (Pout / Pin) RL = 10 log (Pback / Pin)

• reception system It contains a receiver which has a photosensitive surface, and which converts the light into electric signal. It is important to know: • its sensitivity, i.e. the minimal quantity of detectable light. • the interface connector type at the receiver input.

Amphenol is the fiber optic expert you need to solve your problem !

p7

UNDERSTANDING FIBER OPTICS

AMPHENOL JAPAN MIL/AERO INDUSTRIAL 689-1, Iseochi, Ritto-shi Shiga 520-3044 - Japan Telephone: 81-77-553-8501 Fax: 81-77-551-2200 AMPHENOL DAESHIN 558 Sosa, SongNea Bucheon-city, Kyunggi-Do - Korea 420-130 Telephone : 82-32-610-3800 Fax: 82-32-673-2507/665-6219 REST OF THE WORLD AMPHENOL MEXICO Prolongacion Reforma 61-6 B2 Col. Paseo de las Lomas - C.P. 013130 Mexico Telephone : 52-55-5258-9984 Fax: 52-55-5081-6890 AMPHENOL SOUTH AFRICA 30 Impala Road 2196 Chislehurston-Sandton - South Africa Telephone: 27-11-783-9517 Fax : 27-11-783-9519 BAR TEC LTD 4 Hagavish St, PO Box 279 - Kfar Saba 44102 - Israel Telephone: 972-9-767-4097 - Fax: 972-9-767-4324 GESTAS 34630, Besyol Londra Asfalti Florya is Merkezi Kat.2 - Sefakoy / Istanbul - Turkey Telephone: 90-212-624-52-29 Fax: 90-212-599-30-68 AMPHENOL ARGENTINA “Av. Callao 930 2do piso Oficina B “Plaza” C1023” Fax: 54-11-4814-5779 TFC SOUTH AMERICA BUENOS AIRES, ARGENTINA Local Sales Office - Tucuman 540 - Suite 28 “C” C1049AAL- Buenos Aires - Argentina Telephone: 54-11-4325-3471 Fax: 54-11-4327-1339 AMPHENOL AUSTRALIA PTY LIMITED 2 Fiveways Blvd., Keysborough Melbourne, Victoria 3173 - Australia Telephone: 61-3-8796-8888 Fax: 61-3-8796-8801 AMPHENOL DO BRAZIL Rua Diogo Moreira, 132, 20 andar, rooms 2001-2-3 CEP: 05423-010 Sao Paulo SP - Brazil Telephone: 55-11-3815-1003 Fax: 55-11-3815-1629 - AAP Buenos Aires - Argentina Telephone: 54-11-4815-6886

NORTH AMERICA AMPHENOL PCD, Inc. 2 technology Drive Peabody, MA 01960 Telephone: 1-978-532-8800 Fax: 1-978-532-6800

AMPHENOL AIR LB GmbH Am Kleinbahnhof 4 - 66740 Saarlouis Germany Telephone: 49-6831-981-00

Fax: 49-6831-981-030 AMPHENOL ITALIA

Via Barbaiana n. 5, 20020 Lainate - Milano - Italy Telephone: 39-293-55-03-71 - Fax: 39-348-361-7249 AMPHENOL IBERICA C/Calderon de la barca, 3 4A, 28 100 Alcobendas, Madrid - Spain Telephone: 34-91-654-83-52 - Fax: 34-91-640-73-07 AMPHENOL SCANDINAVIA Snosvangen 14 13466 Ingaro - Sweden Telephone: 46-8-571-423-90 Fax: 46-8-571-423-89 AMPHENOL BENELUX Zadelmaker 121 NL-2401 PD Alphen aan den Rijn The Netherlands Telephone: 31-172-444-903 - Fax: 31-172-240-254 AMPHENOL CENTRAL EUROPE Topolowa 13, 41 600 Swietochlowice - Poland Telephone: 48-32-3484-201 Fax: 48-32-3484-202 AMPHENOL EUROPEAN SALES OPERATIONS Hoofdveste 19 - 3992 DH Houten - The Netherlands Telephone: 31-30-635-8000 Fax: 31-30-637-7034 ASIA CHINA (FOP) 3rd Floor, The 4th Ind. District of Ind. Headquarters Dong Keng Road, Gong Ming Town Shenzen 518132, Guangdong Province - PR China Telephone: 86-755-717-7945 Fax: 86-755-717-7622 AMPHENOL TAIWAN CORPORATION No. 116, Lane 956, Zhong Shan Road Taoyuan City, R. O. C., 330 - Taiwan Telephone: 886-3-379-5677 Fax: 886-3-360-7259 Sales/CS/Eng./QA/MIS AMPHENOL EAST ASIA LIMITED 2201 Railway Plaza, 39 Chatham Road South Tsmishatsui, Kowloon - Hong Kong Telephone: 852-2699-2663 Fax : 852-2691-1774 AMPHENOL INTERCONNECT INDIA PRIVATE LIMITED 105 Bhosari Industrial Area - Pune 411 026 - India Telephone: 91-20-712-0363/0463/0155 Fax: 91-20-712-0581

AMPHENOL AEROSPACE OPERATIONS AMPHENOL INDUSTRIAL OPERATIONS 40-60 Delaware Street Sidney, New York 13838-1395 - USA Telephone: 1-607-563-5011 Fax: 1-607-563-5157 AMPHENOL BACKPLANE SYSTEMS 18 Celina Avenue Nashua, New Hampshire 03063 - USA Telephone: 1-603-883-5100 - Fax: 1-603-883-0171 AMPHENOL CANADA CORPORATION 20 Melford Drive - Scarborough, Ontario M1B 2X6 Canada Telephone: 1-416-291-4401 Fax: 1-416-292-0647 1870 boul. des Sources, Suite 204 Pointe Claire, Quebec H9R 5N4 - Canada Telephone: 1-514-630-7242 ext. 225 Fax: 1-514-630-7697 AMPHENOL FIBER OPTIC PRODUCTS- RICHARDSON OPERATION 1778 North Plano Road, Suite 212 Fax: 1-972-744-9022 AMPHENOL FSI 1300 Central Expwy N, Suite 100 Allen, TX 75013 U.S.A. Toll-Fere: 800-472-4225 - Fax: 214-547-9344 info@fibersystems.com EUROPE Richardson, Texas 75081 Telephone: 1-972-744-9801

AMPHENOSLOCAPEX 948Promenade l’Arve- 74311ThyezCedex- France Telephone3:3-4-5089-2800 Fax:33-4-5096-1941

AMPHENOLLIMITEDWHITSTABLE ThaneWt ay,Whitstab-leKent,CT53JF UnitedKingdom Telephone4:4-1227-773-200 Fax:44-1227-276-571 AMPHENOLLIMITEDNOTTHINGHAM UnitD1CrossgatDeriveQ, ueenDs riveIndustrial Estate- NG21LW- Notthingha-mUnitedKingdom Telephone4:4-1159-866-200 Fax:44-1159-866-212

Amphenol reserves the right to change the content of this document without prior notice

Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8

Made with FlippingBook Publishing Software