Modal Tuning by Optical Film Stacks

Is your sensor only seeing half the light?

While donut-shaped modes are common in VCSELs due to oxidation-based processes, Gaussian beams can actually outperform them in certain sensing applications.
At iReach, we’ve redesigned VCSEL emission profiles using stacked optical films—giving us precise control over beam shape, central brightness, and SNR for smarter, more adaptable sensing.

Modal Tuning in Action

Many high-precision sensing devices—like laser mice, LiDAR, and facial recognition modules—depend on VCSELs operating in Gaussian mode for their narrow, focused beams.

Compared to LEDs, VCSELs offer:
✔ Higher directionality
✔ Faster modulation
✔ Easier packaging than EELs
→ Making them a high-performance, cost-effective solution.
But oxidation-based VCSELs often emit donut-shaped modes—with light stronger at the edges and weaker at the center.

Here's the twist:

Compared to the donut mode, the Gaussian modes significantly increase energy density per unit area—enhancing SNR and improving accuracy across a wide range of sensing applications.

So what did we do? (Figure A: TCO VCSEL Structure)

At iReach, we developed a tunable optical mode structure using:
✔ Transparent conductive oxide (TCO)
✔ Dielectric film stacks
✔ Aperture-level reflectance tuning
✔ Central current guiding (gain guiding)
✔ Suppression of higher-order modes


As shown in the far-field emission patterns below, this design significantly reduces edge intensity while increasing central brightness.
Adjusting the TCO aperture size enables precise tuning of the emission profile.
In Figure B, the aperture is larger than in Figure C—resulting in the emergence of higher-order modes and a gradual shift from a Gaussian to a donut-shaped pattern.

Real-World Applications

At iReach, we don’t believe in one-size-fits-all.
We co-create with customers across:
✔ Epitaxial growth
✔ VCSEL chip development
✔ Optical packaging & integration
✔ Simulation, IP, and circuit-level support

Let’s shape the future of sensing—One beam, one breakthrough at a time.