Highly-efficient thermally-tuned resonant optical filters.

Area of Science:

• Photonics and Microtechnology
• Silicon Photonics
• Integrated Optics

Background:

• Microphotonic filters are crucial for optical communication systems.
• Achieving efficient spectral tunability in these devices is essential for dynamic wavelength routing.
• Current thermal tuning methods often require significant power, limiting their practical application.

Purpose of the Study:

• To demonstrate enhanced spectral tunability for microphotonic add-drop filters.
• To improve the thermal tuning efficiency of ring resonators using CMOS-compatible fabrication.
• To establish a new performance criterion for evaluating thermal tuning efficiency.

Main Methods:

• Fabrication of microphotonic add-drop filters as ring resonators in a 130 nm Silicon-On-Insulator (SOI) CMOS technology.
• Integration of CMOS heaters for thermal tuning.
• Selective removal of the SOI handler substrate using bulk silicon micromachining to increase thermal impedance.
• Characterization of tuning efficiency and resonator quality factor (Q-factor).

Main Results:

• A ~20x increase in tuning efficiency was achieved for a 100 µm radius ring resonator compared to pre-micromachined devices.
• A tuning power of 3.9 mW shifted the filter resonant peak across one free spectral range.
• The Q-factor remained unchanged after the micromachining and co-integration process, confirming CMOS compatibility.
• A new performance criterion, power per 2π phase shift, was proposed for device comparison.

Conclusions:

• The demonstrated bulk silicon micromachining process significantly enhances thermal tuning efficiency for SOI CMOS-based microphotonic ring resonators.
• The co-integrated devices exhibit excellent tuning performance (2π shift with 3.9 mW power), among the best reported.
• The proposed performance criterion facilitates easier comparison of thermal tuning capabilities across different device designs.