About VCSEL

VCSEL: Vertical Cavity Surface Emitting Laser.

VCSEL's laser resonator consists of two distributed Bragg reflector (DBR) mirrors with high reflectance >99%. This high reflectance is required to compensate for the short axial length of the gain region.

Advantages (compared to edge-emitters, of course):
1. Laser cavity is short (1~1.5 λ), so only one longitudinal mode can oscillate. (The longitudinal mode spacing is λ/2).
2. The high reflective resonator mirrors results in low threshold current so VCSEL has lower power consumption. (However lower output optical power.)
3. λ vs. T (<0.1 nm/K) is ~5 times smaller than edge emitters (0.2~0.3 nm/K).
4. Easier thermal dissipation and high T operation.
5. Circular output beam. This brings easier beam shaping, easier fiber-coupling, etc.
6. High reliability. VCSEL is not subject to catastrophic optical damage (COD).
7. When put in external-cavity, EC-VCSEL has no mode-hops during tuning or modulation because of the large mode-spacing.

Disadvantages:
Need to do more search on this.
The brightness of the high-power VCSEL is still lower than edge-emitters (why?)

References:
[1] Princeton Optronix website.
[2] http://en.wikipedia.org/wiki/VCSEL