Invention:
This invention replaces traditional Fabry-Perot mirrors with Sagnac loop reflectors where the reflections from the loop have a phase response that depends on both the waveguide index and loop radius. These are both temperature-dependent properties, meaning that by choosing the right loop size and waveguide geometry, the phase drift from the mirrors can be designed to cancel the thermal drift of the cavity itself, resulting in an athermal Fabry–Perot cavity.
Background:
A central challenge in the silicon photonics market is maintaining stable optical performances in integrated devices as they are exposed to thermal fluctuations. Resonant structures like cavities and filters drift with temperature, leading to wavelength instability. This results in resonance wavelengths that are highly sensitive to temperature variations. Current solutions rely on active thermal tuning or external temperature control, which increases power consumption and limits scalability. Advancements like athermal on-chip cavities with Sagnac loop reflectors address these challenges by offering temperature-insensitive stability and reliable performance in a compact form.
Applications:
- Stable, narrowband filters
- On-chip color filters for imaging and spectroscopy
- Lasers with reduced wavelength drift
- Temperature-insensitive optical sensors
Advantages:
- Passive athermalization
- CMOS compatibility
- Compact
- Design flexibility
