Integrated photonics cascaded attenuation circuit towards single-photon detector calibration.

Area of Science:

• Integrated photonics
• Optical metrology
• Nanophotonics

Background:

• Scalable photonics technologies rely on integrated platforms.
• Characterizing on-chip photodetectors requires low-power, single-photon level calibration sources.
• Current methods use external setups for laser attenuation, limiting scalability.

Purpose of the Study:

• To demonstrate an on-chip integrated attenuation solution for photonic circuits.
• To enable precise calibration of on-chip photodetectors for ultra-sensitive applications.
• To reduce reliance on bulky off-chip attenuation systems.

Main Methods:

• Coupling a mW-level laser beam into a silicon nitride photonics circuit.
• Utilizing cascaded directional couplers (DCs) for progressive light attenuation.
• Employing an integrated silicon photodetector for measuring attenuation levels.
• Implementing scattering mitigation techniques within the photonic circuit.

Main Results:

• Achieved an attenuation of up to 16.61 dB per DC stage at 685 nm wavelength with 0.24 dB expanded uncertainty.
• Inferred a total achievable attenuation of 149.5 dB (0.5 dB expanded uncertainty) using 9 cascaded DC stages.
• Demonstrated the capability to generate single-photon power levels directly on-chip.

Conclusions:

• The developed on-chip cascaded directional coupler system provides a scalable solution for precise light attenuation.
• This integrated approach facilitates on-chip calibration of photodetectors for quantum sensing and photonic computing.
• Eliminates the need for complex off-chip setups, paving the way for more compact and efficient photonic systems.