- Behavior similar to electromagnetic waves.
- Visible Light 2.3x1014 cycles per second (hertz).
- Light frequency higher than others:
· AM=160-800 KHz.
· FM=1 MHz - 1 GHz.
OPTICAL FIBER
- FREQUENCY:
- 850 nm .............. 1st Window.
- 1,300 nm ............ 2nd Window.
- 1,550 nm ............ 3rd Window.
- 1,650 nm ............ 4th Window.
- VISIBLE LIGHT:
- 300 nm (blue) ........................ 670 nm (red)
CAUTION: DIRECT LIGHT!
- WAVELENGTH:
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1.2 PROPAGATION OF LIGHT
- SPEED:
- Determined from the refractive index "n"
- "n" represents the ratio between the speed of light in a vacuum (C 300,000 km/s) and the speed of light in the medium V.n =C/V
The speed of light in medium V is not constant; it depends on the nature of the material in which the light propagates.
The refractive index n represents the density of the optical medium.
| MATERIAL | SPEED (Kms/sec) V | REFRACTIVE INDEX n |
| Empty | 300.000 | 1,0000 |
| Air | 299.900 | 1,0003 |
| Water | 225.000 | 1,3333 |
| Quartz Crystal | 200.000 | 1,5 |
- REFRACTION
- Change in direction and speed of a light beam at the interface of two different media.
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- REFLECTION
- Part of the light is returned to its transmission medium while another part passes through the medium.
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- TOTAL REFLECTION
- Principle of optical transmission. At a certain angle of projection, the light emitted from inside the water would not pass through the medium, remaining totally reflected.
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1.3 TYPES OF OPTICAL FIBER
Optical fiber -> Silica crystal (beach sand).
- 2 Core regions (n1) ---> Different refractive index
coating (n2)
A ray with an incidence within the Numerical Aperture undergoes Total Internal Reflection
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- SIGNAL TRANSMISSION --> TOTAL REFLECTION (no refracted ray).
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- OPTICAL FIBER ---> Refractive index profiles.
MULTIMODE (MM): Propagation of more than one mode of light.
SINGLE-MODE (SM): Propagation of a single mode of light.
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- MULTIMODE
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- SINGLE MODE
