Silicon ring resonators with a free spectral range robust to fabrication variations

Area of Science:

• Photonics
• Integrated Optics
• Materials Science

Background:

• Silicon ring resonators (RRs) are crucial components in photonic integrated circuits.
• Their performance, particularly the free spectral range (FSR), is highly sensitive to fabrication variations like waveguide width deviations.
• This sensitivity limits the accuracy and reliability of devices relying on precise FSR values, such as in microwave photonics.

Purpose of the Study:

• To propose and demonstrate a novel design method for silicon RRs that achieves FSR insensitivity to fabrication variations.
• To enable robust performance of RRs and improve the reliability of photonic integrated circuits.
• To provide a design strategy for applications requiring highly accurate and stable FSR values.

Main Methods:

• Utilizing two waveguide-core widths within the RR, engineered to have opposite signs for the group-index derivative with respect to width.
• Implementing a calibration step using the systematic deviation of realized width from the design width to refine the group index versus width relationship.
• Presenting and experimentally validating two robust design examples.

Main Results:

• The proposed dual-width design effectively cancels width-dependent FSR changes, leading to significantly reduced FSR variation under fabrication deviations.
• Experimental results show that for a ±10 nm core-width change, the FSR variation in robust designs is approximately 30% of that observed in single-width RRs.
• The calibration method allows for more accurate FSR prediction and robust device performance.

Conclusions:

• The proposed design method offers a viable solution for creating fabrication-tolerant silicon RRs with stable FSR.
• This approach enhances the performance and reliability of photonic integrated circuits, especially those employing multiple RRs.
• The robust design is particularly beneficial for applications demanding precise FSR, such as in microwave photonics, where tunability is limited.