chapter6 optical source and amplifiers.ppt

Chapter 6
Optical Source and Amplifiers
Light-Emitting Diodes
p
n
LED
i
V
+ -
p
n
Energy Level Diagram for V = 0 (zero bias)
Wg
Conduction Band
Valence Band
- - - - - - -
+ + + + + +
Hole Energy
Electron Energy
P
N
Energy Level Diagram for V > 0 (forward bias)
Wg
Conduction Band
Valence Band
- - - - - - - - - - - - -
- - - - - - - - - -
+ + + + + +
+ + + + + +
Hole Energy
hf = Wg
Electron Energy
Wg = bandgap energy
Its value depends on the semiconductor used.
The released energy takes the form of a photon.
()
Wg is in joules and l is in meters
Suppose Wg is given in eV. Compute the output wavelength.
()
with Wg in eV and l in mm.
Material (m) Wg (eV)
GaAs
AlGaAs - -
InGaAs - -
InGaAsP - -
GaInP - -
Common Characteristics of LED
LED Operating Characteristics
0
5
Output Power
(mW)
Input Current (mA)
Linear Region
Nonlinear Region
100
()
()
where Wg is in eV and P is in Watts
where Wg is in joules and P is in Watts
decreases at high currents, creating the nonlinear
saturation region.
+
-
Lost Photons
LED