164
4 Light Sources for Fiber Links
[1, 9]
E g = 1.424 + 1.266x + 0.266x
2
(4.4)
Given the value of E g in electron volts, the peak emission wavelength in
micrometers is found from Eq. (4.3).
Example 4.3 A particular Ga 1−x Al x As laser is constructed with a material ratio x
= 0.07. Find (a) the bandgap of this material; (b) the peak emission wavelength.
Solution (a) From Eq. (4.4), E g = 1.424 + 1.266(0.07) + 0.266(0.07)
2
= 1.51 eV.
(b) Using this value of the bandgap energy in Eq. (4.3) yields.
λ(μm) = 1.240/1.51 = 0.82 μm = 820 nm
The bandgap energy and lattice-constant range for the quaternary alloy InGaAsP
are much larger. In this case, the compositional parameters x and y follow the relationship y = 2.20x with 0 ≤ x ≤ 0.47. For In 1−x Ga x As y P 1−y compositions that are
lattice-matched to InP, the bandgap in eV varies as
E g = 1.35 − 0.72y + 0.12y
2
(4.5)
Bandgap wavelengths from 0.92 to 1.65 μm are covered by this material system
[8, 10].
Example 4.4 Consider the material alloy In 0.74 Ga 0.26 As 0.57 P 0.43 , that is, x = 0.26
and y = 0.57 in the general formula In 1−x Ga x As y P 1−y . Find (a) the bandgap of this
material; (b) the peak emission wavelength.
Solution (a) From Eq. (4.5), E g = 1.35 − 0.72(0.57) + 0.12(0.57)
2
= 0.97 eV (b)
Using this value of the bandgap energy in Eq. (4.3) yields (in micrometers)
λ(μm) = 1.240/0.97 = 1.27 μm = 1270 nm
Whereas the FWHM power spectral widths of LEDs in the 800-nm region are
around 35 nm, this increases in longer-wavelength materials. For devices operating
in the 1300-to-1600-nm region, the spectral widths vary from around 70 to 180 nm.
Figure 4.13 shows examples for devices emitting at 1300 nm. In addition, as Fig. 4.13
shows, the output spectral widths of surface-emitting LEDs tend to be broader than
those of edge-emitting LEDs because of different internal absorption effects of the
emitted light in the two device structures.
Table 4.2 lists typical characteristics of surface-emitting LEDs (SLED) and edgeemitting LEDS (ELED). The materials used in these examples are GaAlAs for operation at 850 nm and InGaAsP for 1310-nm devices. The fiber-coupled power listing
is the amount of light that can be accepted by a 50-μm core diameter multimode
fiber.
4 Light Sources for Fiber Links
[1, 9]
E g = 1.424 + 1.266x + 0.266x
2
(4.4)
Given the value of E g in electron volts, the peak emission wavelength in
micrometers is found from Eq. (4.3).
Example 4.3 A particular Ga 1−x Al x As laser is constructed with a material ratio x
= 0.07. Find (a) the bandgap of this material; (b) the peak emission wavelength.
Solution (a) From Eq. (4.4), E g = 1.424 + 1.266(0.07) + 0.266(0.07)
2
= 1.51 eV.
(b) Using this value of the bandgap energy in Eq. (4.3) yields.
λ(μm) = 1.240/1.51 = 0.82 μm = 820 nm
The bandgap energy and lattice-constant range for the quaternary alloy InGaAsP
are much larger. In this case, the compositional parameters x and y follow the relationship y = 2.20x with 0 ≤ x ≤ 0.47. For In 1−x Ga x As y P 1−y compositions that are
lattice-matched to InP, the bandgap in eV varies as
E g = 1.35 − 0.72y + 0.12y
2
(4.5)
Bandgap wavelengths from 0.92 to 1.65 μm are covered by this material system
[8, 10].
Example 4.4 Consider the material alloy In 0.74 Ga 0.26 As 0.57 P 0.43 , that is, x = 0.26
and y = 0.57 in the general formula In 1−x Ga x As y P 1−y . Find (a) the bandgap of this
material; (b) the peak emission wavelength.
Solution (a) From Eq. (4.5), E g = 1.35 − 0.72(0.57) + 0.12(0.57)
2
= 0.97 eV (b)
Using this value of the bandgap energy in Eq. (4.3) yields (in micrometers)
λ(μm) = 1.240/0.97 = 1.27 μm = 1270 nm
Whereas the FWHM power spectral widths of LEDs in the 800-nm region are
around 35 nm, this increases in longer-wavelength materials. For devices operating
in the 1300-to-1600-nm region, the spectral widths vary from around 70 to 180 nm.
Figure 4.13 shows examples for devices emitting at 1300 nm. In addition, as Fig. 4.13
shows, the output spectral widths of surface-emitting LEDs tend to be broader than
those of edge-emitting LEDs because of different internal absorption effects of the
emitted light in the two device structures.
Table 4.2 lists typical characteristics of surface-emitting LEDs (SLED) and edgeemitting LEDS (ELED). The materials used in these examples are GaAlAs for operation at 850 nm and InGaAsP for 1310-nm devices. The fiber-coupled power listing
is the amount of light that can be accepted by a 50-μm core diameter multimode
fiber.