VLE 2 Optical Instruments I
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Total reflection
Normal
source: Demtröder, Experimentalphysik 2
Criticalangletotalreflectionreflectio
angle:
sin boundary n2
n1
Total reflection at optical thin media
Application: optical light guide
Flexible thin fused silica fibre with refractive index n1 coated by lower refractive index cladding n2<n1.
Cladding Core
Core
Cladding
source: Demtröder, Experimentalphysik 2
51
Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Structure of a optical fiber
Jacket
Cladding |
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Core |
Source: Demtröder, Experimentalphysik 2 |
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Wave guides of optical fibres are thin and flexible silica fibres (approx. 100 - 500 μm diameter) where the core (approx. 5 - 50 μm diameter) has a higher refraction index than the cladding.
Typical values of the refraction index are nCore = 1.48 and nCladding = 1.46.
52
Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Critical angle of an optical fiber
Jacket |
Total reflection |
sin crit n2
n1
crit 90 crit
Cladding Core
Source: Demtröder, Experimentalphysik 2
Numerical aperture of the fiber: |
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sin |
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n sin |
crit |
n cos |
crit |
n |
1 sin ² |
crit |
n |
n2 |
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n |
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53
Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Step index fiber
Refraction index of core and cladding are constant
Refraction index step at the boundary
Source: Demtröder, Experimentalphysik 2
54
Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Graded index fiber
Parabolic change of refraction index within the core
n1
Advantage:
Less dependency of propagation speed from angle of incident
Source: Demtröder, Experimentalphysik 2
55
Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Questions
1.How is the human eye constructed? What are the functions of its components?
2.Which kind of amentropia exist and can it be corrected?
3.How is angle magnification defined?
4.What is the difference between magnifying glass and telescope? What kinds of telescopes do you know?
5.How is the magnification of a telescope defined?
6.Explain and draw the optical path of a diascope.
7.How does a pin-hole camera work?
8.What is the principle setup of a zoom objective?
9.How do you compensate chromatic aberration?
10.What kind of optical light guides exist?
56
Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany