Propeller head question about LED vs VCSEL.

[Unabomber]

Does anyone know what the difference is between an LED and a VCSEL (vertical cavity surface emitting laser)? I have done a little looking on the internet and some of the VCSELs look like LEDs, and some look like the flat type LEDs. Am I right in saying that VCSEL is just another name for LED? When I was going through fiber optic repair school they said they were the same thing.

 

[**DONOTDELETE**]

Some LEDs are laser diodes; all laser diodes are LEDs.
Some laser diodes are VCSELs; all VCSELs are laser diodes.

So VCSEL is a laser LED, and, as a consequence, an LED. But an LED is not necessarily a laser LED, and a laser LED is not necessarily a VCSEL.

Laser LEDs are LEDs that have feedback cavity. VCSELs are laser LEDs whose feedback cavity contains layers of internal mirrors (or something like that).

 

[The_LED_Museum]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by mad_scientist:
Laser LEDs are LEDs that have feedback cavity. VCSELs are laser LEDs whose feedback cavity contains layers of internal mirrors (or something like that).<HR></BLOCKQUOTE>

Close enough for government work.

I have a couple of VCSELs; they appear to only be made in NIR and IR wavelengths (780.5nm is the shortest wavelength I've found).

All laser diodes have a cavity or resonator structure of some kind, flanked by very tiny mirrors - one is close to 100% reflective (HR) and the other is somewhat less reflective (OC). The laser beam comes from the end that has the less reflective of the two mirrors.

(HR) stands for "high reflector" and (OC) stands for "output coupler".

In a VCSEL, the parts are arranged vertically, rather than horizontally like in the more common "edge emitter" like you find in your CD-ROM drive and in common laser pointers. Because the VCSEL is built layer by layer on the substrate, and certain parts of the laser cavity can be selectively masked on-chip, it is capable of generating a round beam with more of a gaussian profile than your typical edge emitting diode, which always creates a highly ellipitcal beam.

Those so-called "round beam" or "circulaser" diodes get their relatively round beams probably from a combination of selective vignetting and corrective optics. These are *not* VCSELs.