Vertical-cavity surface-emitting laser
The surface emitting or VCSEL [ v'ɪxl ] (from English vertical- cavity surface - emitting laser ), a semiconductor laser in which the light is emitted perpendicular to the semiconductor chip level, in contrast to conventional edge emitter, wherein the light of one or two edges of the chip exits.
Features
Crucial features in surface emitters, even compared to edge emitters are, firstly, the low manufacturing cost and low power consumption. On the other hand, the beam profile is better at the same time lower output compared to edge emitters. The VCSEL is characterized by the fact that he single-mode available and the wavelength is tunable. In addition, the coupling efficiency in optical fibers is high.
Applications
Surface emitters are used as an optical transmitter for fiber-optic data transmission and they are suitable for analog broadband signal transmission. For the scope of absorption spectroscopy ( Tunable Diode Laser Absorption Spectroscopy, TDLAS ) are also used surface emitter. Another area of VCSEL laser printer.
Structure
The laser resonator is formed by two parallel to the wafer plane are arranged Bragg mirrors, between which an active zone ( commonly referred to as two-dimensional quantum wells, quantum well film ) is embedded to generate the laser light. Such planar Bragg mirrors are composed of alternating layers of high and low refractive index each have an optical path length L of a quarter of the laser wavelength in the material, L = λ / (4n ) where n = refractive index of the medium. Characterized the required in the emitter surface reflectance of 99 percent is achieved. Due to the small dimensions of the actual laser of only a few microns in each direction have smaller surface emitter output power compared to edge emitters.
A distinction is optically pumped surface emitter, wherein the active zone is excited by the outside light with a shorter wavelength to the beam, and electrically pumped surface emitter, representing a PIN diode.
Surface emitter for wavelengths between 650 nm and 1300 nm based virtually exclusively on GaAs wafers, while at wavelengths between 1300 nm and 2000 nm ( long-wave emitter surface ), at least the active region is based on InP or GaInAsN. Surface emitter with even greater wavelength are currently pumped experimentally and mostly visually.
Special shapes
Sonderformern of surface emitters are listed here:
- Surface emitter tunnel junction. Here (n p ) is the tunnel junction, an n- n p generated electrically beneficial -pin configuration that can affect a variety of other structural details is positive, for example, the buried tunnel junction ( BTJ ).
- Widely tunable surface emitter with a micro-mechanically movable mirror, and Vertical External Cavity Surface Emitting Laser ( VECSEL ) called.
- Bonded wafer or wafer- fused surface emitter: a combination of the semiconductor material which can be produced on different types of wafer substrates
- Monolithic optically pumped surface emitter: Two successive set surface emitter, in which one of the other optically pumped
- Surface emitter with longitudinally - integrated monitor diode: Under the rear mirror a photodiode is integrated
- Surface emitter transverse integrated monitor diode: By appropriately etching can be manufactured from the wafer surface of the emitter and a photodiode for resonant light of a surface adjacent the emitter.
Historical
The first surface emitter in 1979 soda, Iga, Kitahara and Suematsu presented, other than elements were presented with a threshold current below 1 mA until 1989. Today emitter surface have replaced edge emitter for optical short-range connectivity such as Gigabit Ethernet or Fibre Channel.