Silicon photonics has become one of the enabling technologies behind today’s fastest-growing industries. AI accelerators, hyperscale data centers, LiDAR systems, quantum computing, and future 6G networks all rely on photonic integrated circuits to move more data while consuming less power.
But as these devices become more sophisticated, manufacturing them becomes increasingly difficult.
One of the biggest and least visible challenges is contamination.
The Hidden Yield Killer
Building a photonic integrated circuit is a long journey. From wafer fabrication and dicing to assembly, packaging, and testing, a device passes through dozens of manufacturing steps before it reaches its final application. Every one of those steps introduces opportunities for contamination.
Dust particles, polishing debris, epoxy overflow, solvent residue, and airborne contaminants can settle on optical components throughout the manufacturing flow. While these particles are often microscopic, their impact is anything but.
On most chips, this is manageable. On silicon photonic devices, it can be devastating.
The most sensitive spots are the optical couplers, the structures that guide light into and out of the chip. Even a particle invisible to the naked eye sitting on one of these features can increase optical losses, corrupt signal transmission, and tank manufacturing yield. The physics doesn’t forgive small contamination when you’re routing light through structures measured in microns.
So how do you clean something that fragile?
The Catch: Conventional Cleaning Doesn’t Work Here
The obvious approaches don’t hold up under scrutiny.
Mechanical cleaning such as swabs, brushes, contact methods, is simply too risky. Edge couplers are built from suspended silicon waveguides so delicate that a light touch can destroy them entirely. You can’t scrub something you can barely touch.
Wet chemical cleaning has its own problems. It can leave residues behind, introduce reliability concerns, and isn’t always compatible with the materials involved.
As silicon photonics pushes toward high-volume manufacturing, the industry needs something different: a cleaning method that is precise, completely non-contact, and safe for the most sensitive components on the chip.
A Different Approach: Clean the Particle, Not the Chip
In silicon photonics, it is all about optical performance, high-volume manufacturing and At Femtum, we’ve developed a fundamentally different approach based on mid-infrared laser cleaning.
Instead of treating the entire surface, the process takes advantage of wavelength selectivity.
Our laser operates at 2.78 µm, a wavelength where common contaminants absorb laser energy very efficiently, while silicon remains largely transparent.
The result is remarkably simple.
The laser heats the contaminant, not the silicon beneath it.
During a laser pulse lasting just 60 nanoseconds, the particle rapidly expands. Depending on its size and composition, it either lifts cleanly off the surface or breaks apart into microscopic fragments. A flow of clean, dry air immediately removes the debris, leaving the optical surface clean.
Throughout the process, the silicon substrate experiences virtually no heating.
Figure 1 – Mid-IR laser cleaning mechanism illustrating selective absorption and particle removal.
Can It Clean the Most Delicate Photonic Structures?
The real question isn’t whether laser cleaning works.
It’s whether it works on the structures manufacturers worry about damaging the most.
To answer that, we evaluated the process on two of the most critical optical interfaces found in photonic integrated circuits: edge couplers and grating couplers.
Edge Couplers
Edge couplers are among the most delicate structures on a photonic chip. Their suspended silicon waveguides are extremely vulnerable to mechanical stress, making conventional cleaning particularly risky.
After Mid-IR laser cleaning, microscopy confirmed complete removal of debris with no measurable structural damage to the suspended waveguides.
Figure 2 – Edge couplers before and after laser cleaning.
Grating Couplers
Grating couplers face a different type of contamination. Airborne particles, solvent residue, and oils can accumulate on the finely patterned surface, reducing optical coupling efficiency.
Using a pulse energy of only 4.4 µJ which is less than 8.5% of the laser’s available power, the contaminated grating couplers were completely cleaned without any visible modification to the underlying structures.
Figure 3 – Grating couplers before and after laser cleaning.r Epoxies (left) and different transparent substrates materials (right)
A Clean Surface Means Little Without Optical Performance
Removing visible contamination is only half the challenge.
The real objective is restoring optical performance without introducing new damage.
To evaluate this, silicon debris was intentionally deposited onto photonic loopback circuits consisting of two grating couplers connected by a 1.3 mm silicon waveguide.
The contamination reduced optical transmission by nearly 5 dB at 1310 nm.
After Mid-IR laser cleaning, transmission recovered to within measurement uncertainty of the original baseline.
The result demonstrates that the process doesn’t simply remove contaminants, it restores device performance.
Figure 4 – Optical transmission before contamination, after contamination, and after laser cleaning.
Reliable Enough for Manufacturing
Industrial processes must be repeatable.
To verify long-term robustness, grating couplers were subjected to 100 consecutive laser cleaning cycles using the same cleaning parameters.
Even after repeated exposure, high-resolution microscopy revealed no detectable surface damage. Optical measurements performed across 24 loopback circuits showed no statistically significant difference between laser-cleaned devices and untreated control samples.
In other words, the cleaning process remained both effective and non-destructive after repeated use.
Figure 5 – Comparison of an untreated grating coupler (a) and a device after 100 laser cleaning cycles (b).
Looking Ahead
The rapid growth of AI infrastructure, co-packaged optics, advanced sensing, and next-generation communications is placing unprecedented demands on silicon photonics manufacturing.
As devices become more complex and production scales toward millions of units, contamination control will become a critical part of achieving high yield and consistent performance.
Mid-IR laser cleaning offers manufacturers a new tool designed specifically for this challenge. The process is:
- Non-contact, eliminating the risk of mechanical damage.
- Dry and chemical-free, simplifying integration into manufacturing lines.
- Selective, removing contaminants while leaving silicon untouched.
- Compatible with fragile photonic structures, including edge couplers, grating couplers, and fiber-array units on glass.
- Proven to preserve optical performance, even after repeated cleaning cycles.
Laser cleaning may never be visible to the end user.
But as silicon photonics becomes the foundation of tomorrow’s computing and communications infrastructure, it could become one of the most important steps in manufacturing every chip.
If you require more information on Femtum’s laser cleaning solution, please contact us to discuss your challenges.