(mat 2) serat optic
TRANSCRIPT
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Basic Optical Laws
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Pembiasan & Pemantulan
Incident ray
1
2
1
2
1
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Lanjut
• Indek bias dalam material:
n=c/n = indek bias
c = kecepatan cahaya dlm ruang hampa
= kecepatan cahaya dlm media• Berdasarkan hukum Snell’s (dari gb. diatas)
n1sin 1=n2 sin 2 atau
n1 cos 1=n2 cos 2
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Proses Pembiasan
Exit ray
Incident ray
Partial internal reflection
Low index
High index
n2<n1
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Sin = n2/n1 atau
Cos = n2/n1
Critical angel :
Cahaya pada Sudut kritis
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Total internal reflection
Total Internal Reflection (pemantulan Sempurna)
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Mode Pada Serat Optik dan
Konfigurasi
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• Core (inti) • Silinder sebagai saluran inti dari serat optik dengan
indeks bias n1.
• Cladding (selubung) • Lapisan dielektrik padat dengan indeks bias n2, dimana
n2<n1• Lapisan ini berfungsi meredam rugi-rugi hamburan
sebagai akibat adanya diskontinyuitas pada permukaan inti.
• Buffer Coating• Merupakan lapisan yang terbuat dari plastik (umumnya),
dengan fungsi menambah kekuatan mekanis dari serat optik
Bagian-Bagian Serat Optik
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Konfigurasi Serat Optik
core Cladding Buffer coatting
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Tipe Serat Optik
• Step Index Fiber• Single Mode• Multi Mode
• Graded Index Fiber• Single Mode• Multi Mode
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Perbandingan Struktur Serat Optik
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Step dan Graded Indeks
n1
n2
21
3
nO
n1
21
3
n
n2
OO' O''
n2
(a) Multimode stepindex fiber. Ray pathsare different so thatrays arrive at differenttimes.
(b) Graded index fiber.Ray paths are differentbut so are the velocitiesalong the paths so thatall the rays arrive at thesame time.
23
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
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Lanjut
n decreases step by step from one layerto next upper layer; very thin layers.
Continuous decrease in n gives a raypath changing continuously.
TIR TIR
(a) A ray in thinly stratifed medium becomes refracted as it passes from onelayer to the next upper layer with lower n and eventually its angle satisfies TIR.(b) In a medium where n decreases continuously the path of the ray bendscontinuously.
(a) (b)
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
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Struktur Serat Step-Index• Selubung memiliki indeks bias n2
dimana:n2 = n1 (1-Δ)
• Parameter Δ disebut core cladding indeks difference atau mudahnya perbedaan indeks bias.
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Perambatan Berkas Cahaya• Ada 2 tipe dari berkas cahaya yang
dapat merambat melelui serat optik, yaitu
• Skew Rays• Meridional Rays
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Perbedaan keduanya
Fiber axis
12
34
5
Skew ray1
3
2
4
5
Fiber axis
1
2
3Meridional ray
1, 3
2
(a) A meridionalray alwayscrosses the fiberaxis.
(b) A skew raydoes not haveto cross thefiber axis. Itzigzags aroundthe fiber axis.
Illustration of the difference between a meridional ray and a skew ray.Numbers represent reflections of the ray.
Along the fiber
Ray path projectedon to a plane normalto fiber axis
Ray path along the fiber
© 1999 S.O. Kasap, Optoelectronics (Prentice Hall)
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Metode Perambatan Skew rays
• Berkas sinar optik yang digambarkan dengan skew-rays bergerak dengan metode step-indeks mode
Skew rays berjalan melingkar disekitar inti dan meningkatkan dispersi
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Metode Perambatan Meridional ray
• Meridional ray optic menunjukkan mekanisme propagasi dalam kondisi ideal pada penghantar gelombang step-index.
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Snell’s laws
• Dari aturan Snell, sudut minimum Фmin yang mempengaruhi total internal reflection,
1...per .......... sin 1
2
minn
n
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Lanjut
1 dimana
Δ2n)n-(nθsin n NA
:(NA) aperture numerical sebagaikan didefinisi 2Per
kritissudut θ
2er .........p )n-(n θsin nθ sinn
:maka ,θ
masuksudut dengan erat berkaitan 1per Kondisi
1212
221max0
C
2122
21C1max0
max0
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Lanjut-1
Diamter inti
(m)
Diameter Clad
(m)
NA
50 125 0.19 - 0,25
62,5 125 0,27 – 0,31
85 125 0,25 – 0,30
100 140 0,25 – 0,30
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Light propagation