Optical Fiberppt

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CAHAYA, light

• Aliran partikel yang dalam pemancarannya memenuhi

hukum optik reflection & refraction, snell law .

• Radiasi gelombang elektromagnetik (fresnel, maxwell)

dengan diffraction, interference dan pengubahan

polarisasi selain mengalami reflection & refraction.

• Pendekatan “ray” yang juga dapat mengalami diffraction,

interference dan pengubahan polarisasi selain mengalami

reflection & refraction.

• Arah rambat cahaya dari sumbernya dapat diasumsikan

gelombang spheric ataupun plane



Rambatan Cahaya

Gelombang merambatsecara spheric

If didekat sumber

Gelombang merambatsecara planar

If relatif jauh dari sumber



Rambatan GEM

/ 2

2

)].(exp[),(

k

xk t j Aet x A oi Polarisasi bisa linearataupun elliptical / circular

tergantung nilai medan E

dan H.



Axial Propagation Constant

axial propagation constant: In an optical fiber, the propagation constant

evaluated along the optical axis of the fiber in the direction of transmission. Note:

The real part of the axial propagation constant is the attenuation constant. The

imaginary part is the phase constant. [After 2196]

attenuation constant: 1. The real part of the propagation constant in any

electromagnetic propagation medium. Note 1: The attenuation constant is usually

expressed as a numerical value per unit length. Note 2: The attenuation constant

may be calculated or experimentally determined for each medium. 2. For a

particular propagation mode in an optical fiber, the real part of the axialpropagation constant.

phase constant: The imaginary part of the axial propagation constant for a

particular mode, usually expressed in radians per unit length.

http://www.its.bldrdoc.gov/fs-1037/dir-025/_3720.htm


































Polarisasi

Dengan asumsi bahwa cahaya merupakan gelombang EM, maka

ada phenomena “POLARISASI”

1. LINEAR (Vertical - Horizontal)

2. ELLIPTICAL (circular, RHCP, LHCP)



Polarisasi



Hukum Snellius

• Pemantulan cahaya terjadi apabila suatusinar mengenai batas antara dua médiumkemudian sinar dipantulkan pada médiumyang sama. Sinar yang mengenaipermukaan bidang pantul yang datar akanmenghasilkan sudut pantul yang samabesar dengan sudut datangnya.

• Sinar akan dibiaskan melalui bidang batasantara dua médium, apabila sinar mengenaimédium yang berbeda dan diteruskan kedalam medium yang berbeda tersebutdengan sudut yang proporsional terhadapbesarnya indeks bias medium yangdilaluinya.

• Jika medium yang dilalui sinar lebihrenggang maka sinar akan menjauhi garisnormal bidang batas.

• Tetapi jika sinar masuk pada medium yanglebih rapat terhadap medium semula, makasinar yang dibiaskan akan mendekati garisnormal bidang (Pedrotti, 1993).



TIR (Total Internal Reflection)

• Apabila sudut sinar bias

mencapai sudut 90 maka

sudut yang dibentuk sinar

datang terhadap normaldisebut sudut kritis



Karakteristik Serat Optik



Index contoh

Corning’s SMF-28 optical fiber

Region 1300 nm 1550 nm

Core 1.4535 1.4505

Cladding 1.4483 1.4447

CladdingCore

Coating



Numerical Aperture

• Sinar cahaya yang masuk ke dalam inti serat optik membentuksudut datang tertentu terhadap poros serat optik. Sudut yangmenuju ke arah permukaan serat optik (nudara = 1), tidak semuaakan diteruskan. Tetapi ada syarat tertentu agar sinar yang datangtersebut dapat diteruskan. Gambar berikut menunjukkan adanyasudut dimana sinar diterima oleh serat optik yang disebut sebagai

Numerical Aperture .



Propagasi Cahaya di Serat

Optik

http://localhost/var/www/apps/conversion/releases/20121024195125/tmp/My%20Documents/OAN_PL1_film/bending%20serat%20optik.WMV






Metode Drawing

• The fiber drawing step isessentially the same irrespectiveof the process used to make thepreform [91]. Figure 2.22 showsthe drawing apparatusschematically.

• The preform is fed into a furnacein a controlled manner where it isheated to a temperature of about2000◦C.

• The melted preform is drawn intoa fiber by using a precision-feed

mechanism.

• The fiber diameter is monitoredoptically by diffracting light emittedby a laser from the fiber.



Pengujian

• A change in the diameter changes thediffraction pattern, which in turn changes thephotodiode current.

• This current change acts as a signal for a

servocontrol mechanism that adjusts thewinding rate of the fiber.

• The fiber diameter can be kept constant towithin 0.1% by this technique. A polymer

coating is applied to the fiber during thedrawing step. It serves a dual purpose, as itprovides mechanical protection andpreserves the transmission properties of thefiber.

• The diameter of the coated fiber is typically250 μm, although it can be as large as 900μm when multiple coatings are used.

• The tensile strength of the fiber is monitored

during its winding on the drum.• The winding rate is typically 0.2 –0.5 m/s.

• Several hours are required to convert asingle preform into a fiber of about 5 kmlength.

Optical Fiberppt

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