660
23 Electricity-to-Light Conversion
(a)
p-t ype active
layer
laser
radiation
n-type
cleaved
facet
(b)
n-type
DBR
p-type
DBR
insulator
n-type
substrate
Fig. 23.29 a Schematic drawing of edge-emitting semiconductor laser. b Schematic drawings of vertical-cavity surfaceemitting lasers with top emission (left) and emission through the substrate (right). Black areas are metal contacts
Fig. 23.30 Revenue in
worldwide diode laser
market. Based on numbers
from [1978], data for 2020
estimated
on one facet, semiconductor lasers can be set up with an external cavity.
15 If both facets are antireflection
coated, feedback is missing and the chip can be used as an optical amplifier (cf. Sect. 23.5).
Most lasers are pn-diodes and are then called laser diodes. They rely on the gain of interband
transitions and the emission wavelength is determined and (more or less) given by the band gap of the
semiconductor. The cascade laser [149] (Sect. 23.4.16) is a unipolar structure with a superlattice as
active layer. Here, the intersubband transitions (mostly in the conduction band but also in the valence
band) carry the gain. The emission wavelength depends on the subband separation and lies typically in
the far- and mid-infrared. Extensions to the THz regime and also to shorter wavelengths are possible.
A third type of laser is the ‘hot-hole’ laser (Sect. 23.4.17), typically fabricated with p-doped Ge, which
can be viewed as unipolar and functions only in a magnetic field; its emission is in the THz regime.
23.4.2 Applications
In Fig. 23.30, the revenue in the worldwide diode laser market is shown. The drop after 2000 is due to
the burst of the ‘internet bubble’. Nondiode laser (gas, ruby, excimer, …) revenue is currently stable
at around 2 billion US$, thus semiconductor lasers account for the largest share of all laser types sold.
The following applications rely on semiconductor lasers:
• optical communication, mostly optical fiber based (senders), typically at 10 GBit/s, in special situations also 40 GBit/s data rate.
15 Such external cavities can be used for manipulation of the laser properties such as wavelength tuning.
23 Electricity-to-Light Conversion
(a)
p-t ype active
layer
laser
radiation
n-type
cleaved
facet
(b)
n-type
DBR
p-type
DBR
insulator
n-type
substrate
Fig. 23.29 a Schematic drawing of edge-emitting semiconductor laser. b Schematic drawings of vertical-cavity surfaceemitting lasers with top emission (left) and emission through the substrate (right). Black areas are metal contacts
Fig. 23.30 Revenue in
worldwide diode laser
market. Based on numbers
from [1978], data for 2020
estimated
on one facet, semiconductor lasers can be set up with an external cavity.
15 If both facets are antireflection
coated, feedback is missing and the chip can be used as an optical amplifier (cf. Sect. 23.5).
Most lasers are pn-diodes and are then called laser diodes. They rely on the gain of interband
transitions and the emission wavelength is determined and (more or less) given by the band gap of the
semiconductor. The cascade laser [149] (Sect. 23.4.16) is a unipolar structure with a superlattice as
active layer. Here, the intersubband transitions (mostly in the conduction band but also in the valence
band) carry the gain. The emission wavelength depends on the subband separation and lies typically in
the far- and mid-infrared. Extensions to the THz regime and also to shorter wavelengths are possible.
A third type of laser is the ‘hot-hole’ laser (Sect. 23.4.17), typically fabricated with p-doped Ge, which
can be viewed as unipolar and functions only in a magnetic field; its emission is in the THz regime.
23.4.2 Applications
In Fig. 23.30, the revenue in the worldwide diode laser market is shown. The drop after 2000 is due to
the burst of the ‘internet bubble’. Nondiode laser (gas, ruby, excimer, …) revenue is currently stable
at around 2 billion US$, thus semiconductor lasers account for the largest share of all laser types sold.
The following applications rely on semiconductor lasers:
• optical communication, mostly optical fiber based (senders), typically at 10 GBit/s, in special situations also 40 GBit/s data rate.
15 Such external cavities can be used for manipulation of the laser properties such as wavelength tuning.