Measurement of Measurement of Attenuation of the Attenuation of the

Optical FiberOptical Fiber

Group members:

Hamizah binti MokhtorNorhidayah binti AhmadSiti Nor Dayana binti AziziWan Nur Hidayu binti Wan Juslee

Lecture name : Prof. Dr. Hjh. Norsheila Binti Fisal

Problem StatementProblem Statement• We have been assigned to

determine the characteristic of the new fiber that has just arrived which have been produced by the fabrication optical fiber company.

• We need to run several tests on those brand new fibers using the available tools provide by our company.

Objectives Objectives • To investigate main characteristic

of optical fiber.• To measure losses between

different length.• To measure losses between fiber

gap (0mm-4mm).• To measure losses at different fiber

bending (10mm-40mm).

Introduction Introduction • Structure of fiber:

Core: carries the light of signals.

Cladding: to prevent the light from going out from the core.

Coating: act as insulator to give protection for the core.

How an Optical Fiber How an Optical Fiber WorksWorks• An Optical Fiber works on the

principle of Total Internal Reflection• Light rays are reflected and guided

down the length of an optical fiber.• The acceptance angle of the fiber

determines which light rays will be guided down the fiber.

Core CharacteristicCore Characteristic1. The diameter of the light carrying

region of the fiber is the "core diameter."

2. The larger the core, the more rays of light that travel in the core.

3. The larger the core, the more optical power that can be transmitted.

4. The core has a higher index of refraction than the cladding.

5. The difference in the refractive index of the core and the cladding is known as delta.

Type of Optical FiberType of Optical Fiber

Diagram Diagram

Step index optical fiber Graded index optical fiber

Comparison of simplex and duplex optical fiber

Simplex optical fiber• receiver receives the

signal from the device that is transmitting.

• there is only one fiber which allows the cable to send information one way.

• fiber can be single mode, multimode, or polarization maintaining mode.

Duplex optical fiber• allows a transmission

to go both ways at the same time.

• has two fibers in it and this cable is used when a transmission needs to go in two directions, to the receiver and back.

• can be single mode or multimode.

Advantage of Optical Advantage of Optical FiberFiber

• Low transmission loss• Optical fiber networks operate at high speeds• Wider bandwidth – large carrying capacity• Signals can be transmitted further without

needing to be refreshed or strengthened.• Greater resistance to electromagnetic noise

such as radios, motors or other nearby cables.

• Optical fiber cables costs much less to maintain.

• Can be handled economically, uses, less space in cable duct.

• Non inductive – does not radiate energy, communication security enhance.

Optical Fiber attenuationOptical Fiber attenuation• Attenuation is the loss of optical power as light travels

along the fiber. • Signal attenuation is defined as the ratio of optical

input power (Pi) to the optical output power (Po).

• Input power, Pi = input power is the power injected into the fiber from an optical source.

• Output power, Po = the power received at the fiber end or optical detector.

• Length (L) is expressed in kilometers. Therefore, the unit of attenuation is decibels/kilometer (dB/km).

• attenuation is caused by absorption, scattering, and bending losses.

Factors of attenuationFactors of attenuation

Absorption Absorption • Absorption is defined as the portion of

attenuation resulting from the conversion of optical power into another energy form, such as heat.

– Intrinsic absorption: correspond to absorption by fused silica (material used to make fibers)

– Extrinsic absorption: related to losses caused by impurities within silica.

Scattering Scattering • caused by the interaction of light with density

fluctuations within a fiber. – Rayleigh scattering:

• occurs when the size of the density fluctuation (fiber defect) is less than one-tenth of the operating wavelength of light.

• The loss is proportional to the fourth power of the wavelength ( λ4).

• As the wavelength increases, the loss caused by Rayleigh scattering decreases.

– Mie scattering:• Occurs when the size of the defect is

greater than one-tenth of the wavelength of light.

Bending lossesBending losses• classified according to the bend radius of curvature:

– Microbend: • caused by small discontinuities or imperfections

in the fiber.• Uneven coating applications, improper cabling

and external forces procedures increase microbend loss.

• Microbend loss increases attenuation because low-order modes become coupled with high-order modes that are naturally lossy.

– Macrobend:• bends having a large radius of curvature relative

to the fiber diameter.

• The smaller diameter bending of the fiber, the greater the power loss was determined.

• When the fiber bend is less than some critical radius, the mode phase velocity must increase to a speed greater than the speed of light. However, it is impossible to exceed the speed of light. This condition causes some of the light within the fiber to be converted to high-order modes. These high-order modes are then lost or radiated out of the fiber.

EQUIPMENTEQUIPMENT

Module KL-95001

Fiber optic - Fiber optic - 1m,3m,5m(duplex)and 1m,3m,5m(duplex)and

10m(duplex)10m(duplex)

Power meterPower meter

METHODOLOGYMETHODOLOGY

• Module KL-95001 is placed on the worktable.

• The cinch nut of TX1 was loosened. One end of 1meter fiber is inserted into the TX1 until the tip of the fiber makes contact with the interior back wall of the photo detector. tightened the cinch.

• The other end of fibre was inserted into power meter. The fibre optic must in straight condition

• The power receiver for 1meter was taken as reference.

• The power receiver was recorded in dBm

• By using 3meter fibre, end of fibre optic that inserted into TX1 module KL-95001 was gap with 1mm, 2mm, 3mm and 4mm.

• repeated by using 5meter (duplex) and 10meter (duplex) fibre optic.

• The experiment was repeated with bend experiment, with 3meter fibre optic was inserted into TX1 of module KL-95001 until the fibre makes contact with the interior back wall and centre of the fibre optic was bending in radius 10mm, 20mm and 30mm.

• This experiment was repeated with 5meter (duplex) and 10meter (duplex) fibre optic.

• The attenuation was calculated

ATTENUATION ATTENUATION CALCULATIONCALCULATION

Result For Different Result For Different Length AttenuationLength Attenuation

Result For Different Fiber Result For Different Fiber Gap AttenuationGap Attenuation

Result For Different Fiber Result For Different Fiber Bending AttenuationBending Attenuation

DISCUSSIONDISCUSSION

• Factors of attenuation:Length of fiber optic

Fiber gapFiber bending

LENGTH OF FIBER OPTICLENGTH OF FIBER OPTIC The length of fiber optic , the attenuation

• During the transmission, there is power loss in fiber optic.

• So, if the length of fiber optic increase, the greater power loss in fiber optic.

FIBER GAPFIBER GAP Fiber gap between fiber optic

and wall of interior back photo detector ,the attenuation

• As the gap increases, larger amount of the transmitted power miss the receiving core, because of the beam divergence

• Rays traveling from a lower-index (air) to a higher-index medium (the fiber core)

Refractive ray

FIBER BENDINGFIBER BENDINGRadius for bending of fiber , the attenuation

• Cause some of the light to leave the fiber’s core area

• If a bend is imposed on optical fiber, strain is placed on the fiber along the region that is bent

• The bending strain affects the refractive index and critical angle of the light ray – light traveling in the core can refract out, and loss occur

• Fiber bending - greater than 25mm with negligible loss

CONCLUSIONCONCLUSION• The shorter of length, less

attenuation in optical fiber• The greater fiber gap between fiber

optic and the wall of interior back photo detector , the greater power loss.

• For a large radius bend, the loss can be negligible.

THANK YOU