Integrated photonics is growing rapidly, driven by the increasing needs of cloud computing, AI accelerators, new telecom technologies, and quantum advancements. As these devices become more complex, there is a rising demand in the industry for manufacturing tools that are dependable, scalable, and deliver precise corrections. One standout innovation among these solutions is Femtum’s laser trimming platform, considered a significant breakthrough in PIC manufacturing.
In this blog, we’ll explore what makes this trimming platform unique, how it operates, and its transformative impact on the advancement of photonics.
The Need for a Better Correction Method
Prior to engaging with the platform, it is essential to understand the specific manufacturing challenges it is designed to address. Photonic integrated circuits (PICs), which are fabricated using advanced lithography and etching processes, continue to be affected by nanometer-scale variations in waveguide geometry. These small discrepancies result in phase and spectral errors that can accumulate throughout large-scale circuits. Historically, fabs have relied on thermal phase shifters (TPS) to mitigate such issues. Although TPS can effectively adjust phase, they present significant limitations:
- Continuous power consumption
- Increased chip area and routing complexity
- Heating crosstalk when multiple TPS are present
- Inability to salvage dies that do not pass wafer-level testing
Despite TPS implementation, many dies still fail to meet specifications as circuit intricacy increases. This indicates a need for a more permanent, scalable solution.
How Femtum’s Laser Trimming Works
Femtum corrects the waveguide by using an indirect tuning approach. Instead of pointing ultrashort laser pulses straight at the silicon waveguide, which could cause amorphization and lead to signal loss, Femtum targets the glass cladding around the waveguide with the laser. This creates tiny, stable changes that form a local densification.
Utilizing the elasto-optic effect, this induced densification precisely adjusts the effective refractive index of the adjacent waveguide.
Key technical features include:
1. Predictable, Linear Phase Control
As illustrated in Figure 1, phase shift exhibits high linearity with respect to the number of applied laser pulses. This characteristic is essential for achieving consistent and repeatable corrections. Phase shift slope can be controlled by adjusting the laser parameters.
2. Ultra-Low Loss (<0.1 dB)
By modifying only the cladding rather than the silicon core, Femtum avoids the propagation losses typically associated with amorphous silicon. Most trimming adjustments are below the threshold of standard measurement uncertainty.
3. Sub-Micron Spatial Precision
Modifications can be implemented near sensitive structures without adversely affecting neighboring components. No new for extra footprint around the waveguides.
4. Permanent Corrections
Accelerated aging tests confirm that even corrections corresponding to a π-shift maintain their integrity after 900 hours at 125°C, with variations remaining under 0.01 radians and 0.02 dB. for restoring phase accuracy across an entire wafer.
Figure 1: Phase Correction in radians against the number of laser pulses near the optical waveguide. The high linearity of the process is at the core of the repeatability of the phase correction process.
The Trimming Platform: A Complete Wafer-Level Solution
Femtum’s technology is not just a laser: it is a complete industrial platform designed for high-volume PIC manufacturing. The complete system, shown in Figure 2, includes sub-micron positioning stages, adaptable die or chucks capable of handling industry-standard wafers up to 300 mm, the specialized laser source and the optical head which holds a high-precision 2D galvanometer scanner for rapid beam steering, and integrated controllers and software. The entire process is fully programmable and automated, allowing for wafer-level processing or die-level. The correction itself is fast, occurring on a millisecond timescale for each modification, enabling high-throughput processing.
Figure 2: A Complete Platform for Laser Trimming Processing, with sub-micron motion stages, a specialized laser and an optical head.
From Testing to Correction: A Seamless Workflow
Femtum’s system is designed to drop into existing PIC workflows with minimal disruption. After wafer-level testing (WLT):
- Dies that fail due to phase errors are identified.
- These dies are automatically routed to the laser trimming platform.
- The trimming algorithm applies localized corrections.
- Corrected dies return to the validated flow, now meeting performance specifications.
New Designs Flexibility with Lasting Phase Regulation
Beyond its immediate benefits in manufacturing yield, laser trimming changes the way PICs can be designed.
When static phase errors can be permanently corrected:
- TPS heaters can operate at lower power or be removed entirely.
- Power budgets are freed for computation or modulation.
- Device size and complexity decrease.
- Thermal management becomes simpler.
- FIT (Failure In Time) rates improve due to reduced heater stress.
Laser trimming becomes a foundational tool enabling denser, more energy-efficient architectures which are critical for AI photonics and quantum applications.
Expanding to New Materials and Photonic Architectures
Looking ahead, Femtum has a clear strategic roadmap to expand this platform’s capabilities:
- Beyond Silicon-on-Insulator (SOI), the technique is being applied to:
- Silicon Nitride (SiN): Crucial for low-loss passive circuits.
- Indium Phosphide (InP): The industry standard for monolithically integrated active components (e.g., lasers and modulators).
- The correction application will be extended from Mach-Zehnder Interferometers (MZIs) to other fundamental components, including:
- Micro-ring resonators
- Couplers
- Spot-size converters
Correcting the resonant wavelength of sensitive ring resonators is a major industry-wide challenge, and a reliable solution represents an enormous market opportunity. By building a versatile correction platform that can service the entire heterogeneous and hybrid PIC industry, Femtum is positioning itself as an indispensable partner in enabling the advancement of photonics.
The New Standard in Post-Fabrication Optimization
By providing permanent, ultra-low-loss phase corrections, Femtum’s technology removes the reliance on energy-intensive and inefficient tuning methods. This advancement significantly reduces power consumption, enhances manufacturing yield, and introduces new opportunities for integrated photonics design.
As integrated photonics becomes a foundational technology for AI, telecommunications, and quantum computing, laser trimming is quickly establishing itself as a new industry standard that will drive the innovation in the field.