678
23 Electricity-to-Light Conversion
(a)
0.4
0.3
0.2
0.1
0
0.8
0.6
0.4
0.2
0
0
0.5
1.0
1.5
fiber
facet
(b)
Fig. 23.54 a Output power of an InGaAsP/InP cw single-mode DFB laser at 1427 nm with 2 mm cavity length from the
facet and coupled to a single-mode fiber versus driving current (T = 293 K). The dashed line represents the coupling
efficiency to the fiber (right scale). Adapted from [2004]. b Package with pigtail of fiber coupled 1550 nm DFB laser
with 40 mW output power in the fiber. From [2005]
23.4.12 Tunability
The tunability of the emission wavelength [2006] is important for several applications such as wavelength division multiplexing
21 and spectroscopy.
The simplest possibility to tune a laser is to vary its temperature and thus its band gap. This method
is particularly used for lead salt lasers in the mid-infrared region,
22 as shown in Fig. 23.55.
For monomode lasers, mode hopping, i.e. the discontinuous shift of lasing wavelength (or gain
maximum) from one mode to the next, poses a problem for continuous tuning, as shown in Fig. 23.56.
The continuous shift of emission wavelength is due to the temperature dependence of the index of
(a)
n-Pb Sn Te:Bi
In
n-Pb Sn Te:Bi
p-PbTe:Tl
MgF mask
2
Au
(b)
20
15
10
5
0
0
5 0
1 0 0
20
15
10
5
0
j (kA/cm )
2
PbTe/PbSnTe
Fig. 23.55 a Schematic drawing of PbTe lead salt laser. b Tuning characteristics of such laser: Emission wavelength
(left scale, filled circles: emission wavelength at cw threshold, empty circles: emission maximum under pulsed operation)
and cw threshold current density (right scale) as a function of the heat-sink temperature. Symbols are experimental data,
dashed lines are guides to the eye. Adapted from [2007]
21 In order to make better use of the high bandwidth of the optical fiber several information channels with closely lying
wavelengths are transmitted.
22 Note the anomalous positive coefficient dE g /dT as discussed in Sect. 6.7.
23 Electricity-to-Light Conversion
(a)
0.4
0.3
0.2
0.1
0
0.8
0.6
0.4
0.2
0
0
0.5
1.0
1.5
fiber
facet
(b)
Fig. 23.54 a Output power of an InGaAsP/InP cw single-mode DFB laser at 1427 nm with 2 mm cavity length from the
facet and coupled to a single-mode fiber versus driving current (T = 293 K). The dashed line represents the coupling
efficiency to the fiber (right scale). Adapted from [2004]. b Package with pigtail of fiber coupled 1550 nm DFB laser
with 40 mW output power in the fiber. From [2005]
23.4.12 Tunability
The tunability of the emission wavelength [2006] is important for several applications such as wavelength division multiplexing
21 and spectroscopy.
The simplest possibility to tune a laser is to vary its temperature and thus its band gap. This method
is particularly used for lead salt lasers in the mid-infrared region,
22 as shown in Fig. 23.55.
For monomode lasers, mode hopping, i.e. the discontinuous shift of lasing wavelength (or gain
maximum) from one mode to the next, poses a problem for continuous tuning, as shown in Fig. 23.56.
The continuous shift of emission wavelength is due to the temperature dependence of the index of
(a)
n-Pb Sn Te:Bi
In
n-Pb Sn Te:Bi
p-PbTe:Tl
MgF mask
2
Au
(b)
20
15
10
5
0
0
5 0
1 0 0
20
15
10
5
0
j (kA/cm )
2
PbTe/PbSnTe
Fig. 23.55 a Schematic drawing of PbTe lead salt laser. b Tuning characteristics of such laser: Emission wavelength
(left scale, filled circles: emission wavelength at cw threshold, empty circles: emission maximum under pulsed operation)
and cw threshold current density (right scale) as a function of the heat-sink temperature. Symbols are experimental data,
dashed lines are guides to the eye. Adapted from [2007]
21 In order to make better use of the high bandwidth of the optical fiber several information channels with closely lying
wavelengths are transmitted.
22 Note the anomalous positive coefficient dE g /dT as discussed in Sect. 6.7.