New Horizons in Micro-Optical Assembly Fabrication
The rapid evolution of optical technologies in telecommunications, quantum computing, medical devices, and semiconductor manufacturing is fundamentally changing the requirements for micro-optical assemblies and their fabrication. Selective Laser-Induced Etching (SLE) can provide a solution, as a two-step process (Figure 1) that enables the fabrication of complex 3D microstructures in transparent materials such as fused silica, borosilicate glass, and to some degree even sapphire.
Step 1: Laser modification
A focused femtosecond laser beam is scanned within the bulk of the substrate, locally modifying the material’s structure at precise 3D coordinates. The laser parameters (pulse energy, repetition rate, scanning speed) are carefully controlled to induce changes in the material’s etch rate without causing cracks or significant thermal damage. The modified zones can be as small as a few micrometers in diameter, and the process can be repeated at multiple depths to create intricate internal geometries.
Step 2: Chemical etching
The laser-modified substrate is then immersed in a suitable chemical etchant (for example, KOH or HF solution). The modified regions dissolve much faster than the unmodified material, allowing selective removal of the desired structures. The result is a monolithic component with complex 3D features, such as microchannels, glue pockets, alignment structures or even flexures, all integrated within a single piece of material.
SLE combined with CO2 laser polishing
While SLE provides excellent control over geometry and feature size, the resulting surface roughness is typically in the range of 100-500 nm Ra. This is sufficient for most microfluidic and mechanical applications, depending on process parameters and etchant chemistry. Achieving surface roughness around 10 nm Ra is not feasible with SLE alone, but possible with CO2 laser polishing, which is also done in-house. In this process, the laser energy melts the surface allowing surface tension to smooth out micro-scale irregularities before re-solidification.
Overcoming industry limitations
The combination of SLE with optical assembly and CO₂ laser polishing introduces new technical capabilities in the fields of photonics, semiconductor/electronics fabrication, and medical technology. Below, several use cases that reflect the capabilities of this technique are detailed.
- Medical endoscopes
Modern endoscopes (Figure 2) require optics with diameters below 1.5 mm, often superimposing optical beam paths for illumination, imaging and metrology, together with additional working channels in a single probe. The ability to create smooth, continuous channels is particularly valuable to ensure easy passage of instruments, prevent damage to the scope and minimize the risk of infection.
- Quantum photonic circuits
Quantum computing relies on precise control of light at the single-photon level, requiring micro-optical assemblies with micron-level alignment and minimal optical losses. SLE can fabricate resonators and features for passive alignment (Figure 3) directly in fused silica, enabling integration of multiple optical functions in a single substrate.
- Semiconductor/electronics inspection equipment
In semiconductor/electronics fabrication, numerous applications of micro-optics for inspection purposes can be found. For example, telecentric optical objectives, made from single-piece fused silica, can be integrated into automated optical inspection systems for semiconductor wafer and printed circuit board inspection. Or take confocal chromatic Z-sensors, designed as integrated fused-silica micro-optical benches consolidating fibre channels, micro-prisms and objectives; they can be deployed, for example, in solder-paste inspection machines on surface-mount assembly lines to verify paste volume and height.
Scaling-up of ultra-precise assemblies
At LouwersHanique, SLE-fabricated components are integrated into complete assemblies using state-of-the-art pick & place automation in ISO 7 cleanrooms. The modular pick & place system with submicron repeatability handles delicate micro-optical parts, positioning them with six degrees of freedom and with far greater accuracy and consistency than manual methods can achieve. Submicron positioning of droplets with volumes down to 2 nanolitre combined with active alignment techniques and force-controlled placement of components, ensures optimal adhesion without compromising the optical path. Due to the modularity of the system, it is highly customisable to specific product needs.
Hybrid integration, combining SLE-fabricated glass parts with metallic housings, semiconductor chips, or polymer elements, is also possible, enabling the creation of multifunctional photonic modules. The result is a scalable, reliable process suitable for both prototyping and series production, supporting the stringent requirements of telecom, quantum, semiconductor/electronics and medical markets.
Author: Martin Hermans
Martin Hermans is a Senior Engineer in the R&D department at LouwersHanique. He focuses on optimizing existing laser technologies and exploring new laser technologies and applications to expand the company’s capabilities in high-end machining of technical glass and ceramic materials.
