This article will show you the basic structure of fiber optic network, and introduce each element in the network.

Simply introduce fiber optic network in one words: the network linked each point with optic fiber. The bare fiber is thin like hair, very weak and easy to be broken. See Image 1 below is bare fiber. There are many kinds of fiber according to ITU. Different fiber different performance. For more information about each kind of fiber please go to https://www.anfkomftth.com/introduction-to-g651g652g653g654g655g656g657-fiber/

Obviously, the bare fiber can not be used to build network directly due to his weakness. In order to protect the weak bare fiber, fiber optic cable is designed. There are many kinds of fiber optic cable to meet the different application environments. Image 2 is fiber optic cable, which keep the bare fibers in the center. Outer Jacket, Yarn, reinforce will protect the bare fibers from being damaged .

Fiber optic network include Active Optical Network and Passive Optical Network. EPON and GPON are Passive Optical Network. If some active device is used in passive optical network, then it become active optical network. The maximum transmission distance is 2km for PON, while it can reach 100km for AON. The FTTX network can be PON or AON.

Passive Optical Network

The structure of PON

OLT   An optical line terminal (OLT) is a device that is located at the service provider’s central office and is the endpoint of a passive optical network (PON).

perform conversion between the electrical signals used by the service provider’s equipment and the fiber optic signals used by the passive optical network.

ONU  Optical network unit (ONU) is the user side equipment in the GEPON (Gigabit Ethernet Passive Optical Network) system designed for indoor residential installation.

Access network  the part between OLT and ONU, it is passive optic network. Also known as FTTX network.

FTTX network.

FTTA  Fiber to The Antenna, the endpoint of fiber optic network is Antenna of Base station. It reach the end users through wireless.

FTTB  Fiber to The Building

FTTC  Fiber to The Curb

FTTN  Fiber to The Node

FTTH  Fiber to The Home

From the endpoint of optic fiber to the end users, it is always cat5/cat6 cable.

Now you know the basic structure of PON. Then what products/equipment will be used to build such a network?

1. Fiber optic cable

Fiber optic cable is the channel to transmit information/data. It is the key part of fiber optic network.

A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable, but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.

It is typically divided into 2 categories according to application environment: outdoor fiber optic cable and indoor fiber optic cable.

1.1 Outdoor fiber optic cable

Outdoor is harsh environment. Raining, Sunning, animal biting, So much more protection must be done for the bare fiber. And the temperature varies a lot during day and night, so it is normally loose tube for outdoor fiber optic cable.

There are 3 features that outdoor fiber optic cable must pay more attention to:

1. Excellent mechnical performance
2. Waterproof
3. Good temperature performance,  working temperature range should be wide. Typically -40-80 degree

Material：

1.   loose tube is made of PBT, PP, PC
2.  Outer jacket is made of PE, LSZH. PVC

A brife information will be printed on the outer jacket when manufacturing, such as fiber type, fiber number, manufacturer, time, structure code.

1.2 Indoor fiber optic cable

Indoor fiber optic cable is used in the building. Its structure is more simply comparing to outdoor cable. Indoor environment is much mild. No raining, No sunning

Indoor fiber optic cable should meet 3 features below:

1.  Tight structure
2.  Soft and light
3.  Flame retardant

Indoor fiber cable is always tight buffer, not loose tube. Tight buffer cables are offered for a variety of applications, but the two most common are “Breakout” and “Distribution”

Breakout means fiber inside with 2.0 or 3.0mm jacket.

Distribution means fiber inside with 0.9mm jacket.

 

2.0mm 3.0mm indoor fiber optic cable, which is normally used to make fiber optic patch cord.

2. Fiber Optic Splice Closure

To splice two fiber optic cable, fiber optic splice closure must be used to protect the splice point. Splicing extends the length of fiber optic cable, help to enlarge the network.

Splicing is a little complicated, need well-trained people to do it. Why not produce a cable with the length equal to the length amount of the two splicing cables instead of splicing? Actually, it is a problem to storage and transport the cable which is too long since it is very heavy and large. Normally the cable length is less than 3km.

Splice closure capacity is from 12 fibers to more than 1000 fibers. 

It divides into 2 subcategories: Dome closure and Flat closure.

 

Flat closure is always Mechanical seal, while dome closure has one more way to seal–heat shrink.

Two cables are spliced by splice machine, the splice point is held in the closure. Fiber splicing should be done by a technical person. There are some special tool for splicing: splice machine, knife, protection sleeve. The professional people can do a better job, less loss will be caused.

3. Fiber Optic Splitter

Fiber optic splitter, also named fiber optic coupler. Which is a device that splits the fiber optic light into several parts by a certain ratio. For example, when a beam of fiber optic light transmitted from a 1X4 equal ratio splitter, it will be divided into 4-fiber optic light by equal ratio that is each beam is 1/4 or 25% of the original source one.

Normally 1:2, 1:4, 1:8, 1:16, 1:32, 1:64.

It has three types: Mini, Box, Cassette

Fiber optic splitter is installed in distribution box or termination box.

4. Distribution Box/termination box

Most of these boxes are plastic. The direct application of termination box is to terminate fiber optic cables and connect the core of the cable and pigtail. the access fiber cables can be multi-core. For example, a 6-fibers fiber optic cable (namely fiber optic cables with 6 cores), then, after this fiber optic cable accessing to the termination box, it can be splice into 6 pigtails, for 6 fiber patch cords. Also some termination box can hold fiber optic splitter.

5. Fiber Optic Fast Connector

Fast Field connectors provide a quick, simple and clean solution for field terminating SC, LC and ST connectors with polishing (APC, UPC). It plays an import role in FTTH solutions. When fiber in the building go to homes. It usually fast field connector, only take 1 minute to assemble the connector on the cable, even without splicing.

Fast field connector: Hot Melting or mechanical.  Hot Melting connector is more complicated to assemble, splicing machine is required.  Mechanical fast connector are more popular in the market. It is easy to assemble just take 1 minute for 1 connector to finish the work.

6. Fiber Optic Patch cord

Normal fiber optic patch cord.

Fiber optic patch cord, also named Fiber optic patch lead, is a cable with connector(s) at either end. SC LC ST FC are the most popular connectors used in patch cord. Normal fiber optic patch cords are made of 2.0mm,3.0mm indoor cables, to link two fiber optic device/equipment/patch panel, used for indoor applications. If used for outdoor application, must use special waterproof connector. PDLC, ODVA, FULLAXS, OPTICAP/SENKO IP are widely used in harsh environment.These waterproof connector are always assembled on tactical cables

Waterproof Fiber Optic Patch cord

MPO patch cord

MPO is Multi-fiber Push On. MPO patch cord is a cable with one or more MPO connectors.  MPO can hold 12/24 fibers in one connector. It is high density and save much installing space.

7. Fiber Optic Adapter

Also named fiber optic coupler.  Two connector are mated through fiber optic adapter when making two patch cord linked. They come in versions to connect single fibers together (simplex), two fibers together (duplex), or sometimes four fibers together (quad)，or six fibers together, or 8 fibers together.

The fiber optic adapter color is different for different type, normally Blue means single mode while Grey means multimode,. and Green is for APC. Sometimes 12 colors are used to distinct different links.

Normall it is made of plastic, sometims is made of metal.  Plastic is more popular than metal since the cost is much lower.

The key part of fiber optic adapter is sleeve, it is in the central.  Fber optic onnectors are mated in the sleeve, the insert loss mainly depend on the sleeve quality.

Fiber optic adapters are typically connecting cables with similiar connectors (SC to SC, LC to LC, etc.). Some adapters, called “hybrid”, accept different types of connectors (ST to SC, LC to SC, etc.). When the connectors have differing ferrule sizes (1.25mm to 2.5mm), as found in LC to SC adapters, the adapters are significantly more expensive because of a more complicated design/manufacturing process.

Please note PC can not link to APC.

Two MPO connector are mated through MPO adapter

8. Fiber Optic Attenuator

Fiber optic optic attenuator is used to reduce the light power. The higher light power go into the device(SFP) may break the device. It has two types: Fixed and Variable.

Fixed means the attenuation is fixed at a number 3db, or 5db, or 7d, or any other number.

Variable means the attenuation can be adjust according to the requirement, typically  0~30db.

Attenuation fiber is the key element for Attenuator, Only few companies provide attenuation fiber. Not a big requirement in the market for fiber optic attenuator. 

LC fiber optic attenuator is most popular in the market.

9. WDM

Wavelength-division multiplexing is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser。

Below is a standard wdm product, does it looks like a box splitter?

AON

If Active devices are added in the PON, then it said Active optical network. Active device is the optical unit which cannot work without power. For example, Media converter, Optical router, Optical Transceiver.

For more information about AON, please wait for next article.