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Coupling between Light Sources and Fiber Optics
Transcript of Coupling between Light Sources and Fiber Optics
By: Mohamed A. Alshaer
1. For step-index fibers (where rs < a)
B at a given diode drive current is the optical power radiated into a unit solid angle per unit emitting surface area and is generally specified in terms of W/cm2.sr.
Optical power produced by optical sources can range from microwatts (mW) for LEDs to tens of milliwatts (mW) for semiconductor LDs.
However, it is not possible to effectively couple all the available optical power into the optical fiber for transmission.
Dependence of coupled power
1. The angles over which the light is emitted.
2. The size of the source's light-emitting area relative to the fiber core size.
3. The alignment of the source and fiber.
4. The coupling characteristics of the fiber (such as the NA and the refractive index profile)
Typically, semiconductor lasers emit light spread out over an angle of 10 to 15 degrees.
Semiconductor LEDs emit light spread out at even larger angles.
Coupling losses of several decibels can easily occur when coupling light from an optical source to a fiber, especially with LEDs.
Source-to-fiber coupling efficiency is a measure of the relevant optical power.
The coupling efficiency depends on the type of fiber that is attached to the optical source.
2. For step-index fibers (where rs > a)
3. For Graded Index Fiber