Introduction of VCSEL: Working Principles And Characteristics

Semiconductor lasers such as FP, DFB, VCSEL and more are essential devices for regulating and improving the Internet and communication sector in the world. Laser’s outstanding properties such as high efficiency of the electrical energy into photons, excellent reliability, small footprint, modulation bandwidth, and low cost have made it a principle component in various communication applications.

VCSEL or Vertical Cavity Surface Emitting Laser is one such laser that is largely used in various industrial and military applications. This article discusses the basics of VCSEL, including its definition, working and characteristics.

What is VCSEL Laser?

Wikipedia defines VCSEL is the type of semiconductor laser diode with laser beam emission perpendicular from the top surface, as opposed to conventional edge-emitting semiconductor lasers which emit from surfaces.

In simple words, compared to conventional edge-emitting light diodes, VCSEL emits light or a vertical beam from its top surface.

Now let us comprehend how Vertical Cavity Surface Emitting Laser works. Note that, as it is challenging to cover the whole working process in detail, we have covered fundamental points only.

Working Principles of VCSEL

A typical Vertical-Cavity Surface-Emitting Laser is made of several layers. The top is a layer in electrical contact for current injection. The next layer, i.e. the second layer, is the high-reflectivity mirror with 99% reflectivity. The next– third layer is an oxide layer that develops a light-emitting window so that the light beam can be converted into a circular beam.

The next layer– the centre layer in the VCSEL is the laser cavity. It is the active gain region where lasing happens. Again there is an oxide layer below the center layer to confine the light. And the last layer is again a DBR– distributed Bragg reflector and the last– bottom layer is a reflective mirror with 99.9% reflectivity.

Note that the bottom mirror has more reflectivity than the top mirror so that lasing light can get out from the top mirror instead of the bottom mirror.

The quantum wells generate photos that travel between the top DBR mirror and the bottom DBR mirror. This lasing mechanism remains the same in every laser. The quantum well is made of three layers–a very thin gallium arsenide layer sandwiched between two thick aluminium gallium arsenide layers. This structure produces quantum confinement– an effect to increase lasing efficiency.

Now, let us learn about some of the significant characteristics of the VCSEL, which makes it a preferred option for a variety of medical, industrial and military applications.

The Major Characteristics of Vertical Cavity Surface Emitting Laser

• Since VCSELs emits a beam from the surface, i.e. top of the chip, it can be tested and analyzed on-wafer before it carves into any devices. This will reduce the fabrication cost.
• The mechanism and structure of Vertical-Cavity Surface-Emitting Laser make them able to use in two-dimensional arrays, unlike conventional edge-emitting lasers which can be used only in one dimensional.
• The light beam in a conventional edge-emitting laser has a high divergence angle and is difficult to couple into the optical fiber. Whereas VCSEL has a circular light beam, this is very easy for coupling into optical fibers, and it also has a lower divergence angle of the output beam.
• By regulating the thickness of the reflector layers, one can adjust the wavelength of the vertical cavity surface emitting laser.
• The surface-normal emission and almost identical geometry of the photodetector provide easy alignment and packaging.

In the next blog, we will cover VCSEL applications in detail. Keep following Inphenix.

Inphenix is a laser and light source manufacturing company headquartered in California, USA. The company develops a range of optic devices, lasers and light sources including distributed feedback lasers, superluminescent diodes, Fabry-Perot laser, swept source laser and VCSEL, among others.