Laser diode with vertical cavity emitting by surface
A laser diode with vertical cavity emitting by surface (or VCSEL for vertical-cavity English laser surface-emitting ) is a type of laser Diode with Semi-conducteur emitting a ray Laser perpendicular to surface, contrary to the conventional lasers with semiconductor emitting by the section.
The first VCSEL was presented in 1979 by Soda, Iga, Kitahara and Suematsu, but 1989 should have been waited until to see devices whose current of threshold was lower than 1 m has. In 2005, the VCSEL already replaced the lasers emitting by the section for the applications of communication by Fiberoptic to short range such as the protocols Gigabit Ethernet and Fiber Chanel.
The laser resonator consists of two mirrors of Bragg parallel at the surface of the wafer, and, between them, of an area activates made up of one or more quantum Puits S allowing the generation of the laser beam. The mirrors of Bragg are made layers alternating high and low indexes of refraction. The thickness of each layer is quarter wavelength of the laser in material, thus making it possible to obtain a factor of reflection higher than 99%. In the VCSEL, mirrors with high factor of reflection are necessary to compensate for the low length of the amplifying medium.
In the majority of the VCSEL, the mirrors higher and lower are doped materials respectively of type p and N , forming a Jonction P-N. In certain more complex VCSEL, the areas p and N can be buried between the mirrors of Bragg ; that implies a more complex process to carry out the electrical contact with the amplifying medium, but limit the electric losses in the mirrors of Bragg.
Research is undertaken on using systems VCSEL of new materials. In this case, the amplifying medium can be pumped by an external source of light of shorter Wavelength (in general, another Laser). That makes it possible to present the operation of a VCSEL without adding to it the problem of realization of electric good performances. However, these devices are not applicable to the majority of the current applications.
Between 650 Nm and 1300 Nm
VCSEL allowing to obtain beams wavelength ranging between 650 Nm and 1300 Nm are in general manufactured on Wafer S of Gallium arsenide (Ga As). The mirrors of Bragg are composed of an alternation of layers of GaAs and Arséniure of gallium-aluminum (Al x Ga (1-x) As). GaAs/AlGaAs alternation is interesting for the construction of VCSEL, because the Constante of network of material varies little when the composition changes, thus allowing the epitaxial growth multiple layers on GaAs substrate with agreement of Maille. On the other hand, the Index of refraction of AlGaAs strongly varies according to the voluminal fraction of aluminum : that makes it possible to minimize the number of necessary layers to obtain a mirror of effective Bragg (in comparison with other materials). Moreover, for strong aluminum concentrations, it is possible to form a Oxyde of AlGaAs, being able to be used to limit the current in a VCSEL, thus making it possible to use very weak currents of threshold.
Beyond 1300 Nm
Devices allowing to obtain beams between 1300 Nm and 2000 Nm exist, made up of Phosphure of indium at least for their amplifying medium.
The providing VCSEL of the beams wavelength even larger are not in 2005 qu ' at the experimental stage, and are in general pumped optically.
Particular structures VCSEL
VCSEL having several active areas (amplifying mediums).
- VCSEL with Junction tunnel : by using a junction tunnel ( N + p +), one can build a configuration N + p +- pine electrically advantageous, which can influence other elements bénéfiquement (for example in the form of junction tunnel buried). largely adjustable
- VCSEL thanks to electromechanical micromiroirs.
- VCSEL on wafers stuck or fondus : combination of semiconductor materials being able to be manufactured on Wafer S of different chemical nature. pumped
- VCSEL monolithic optiquement : structure made up of two VCSEL head-digs, one pumping the other optically.
- VCSEL with longitudinal diode of control intégrée : a Photodiode is integrated under the back mirror of the VCSEL.
- VCSEL with diode of transverse check intégrée : by an adapted engraving of the wafer including/understanding the VCSEL, it is possible to manufacture a resonant photodiode making it possible to measure the luminous intensity of a nearby VCSEL.
- VCSEL with external cavity, also called VECSEL for vertical-external-cavity laser surface-emitting , or laser with semiconductor disc. This configuration makes it possible to pump a greater zone of the device, and thus to extract more power (until 30 W). The use of an external cavity also authorizes techniques such as the doubling of frequency, the operations simple on frequencies and the impulses femtoseconde in blocked mode.
- BiVCSEL: who includes/understands 2 coupled cavities
- TriVCSEL: 3 cavities (see Natural January 2006)
As the VCSEL emit by surface, they can be tested directly on the Wafer, before being cut out in individual devices. That reduces their manufacturing costs, and also makes it possible to produce them in a matric way.
The large opening of exit of the VCSEL, by comparison with the majority of the lasers emitting by the section, produces an observation angle of the smaller beam. Thus, it is possible to connect a VCSEL to a Fiberoptic with a high effectiveness of coupling.
The strong coefficient of reflection of the mirrors of Bragg reduces the current of threshold of the VCSEL, which lowers their electricity consumption. On the other hand, the VCSEL emit with powers lower than the lasers emitting by the section. The weak current of threshold also makes it possible to obtain band-widths with strong intrinsic modulation.
The Wavelength of the VCSEL can be adjusted (inside the beach of profit of the amplifying medium) by modifying the thickness of the layers forming the mirrors of Bragg.
Lastly, whereas the first VCSEL emitted in multiple longitudinal modes or filament mode, it is current into 2005 to meet monomode VCSEL.
- Data transmission by Fiberoptic
- Transmission of signal analogical broad-band
- Spectroscopy of absorption (TDLAS)
- Printing laser
- optical Mouse
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