Foundry-based waveguide-enhanced Raman spectroscopy in the visible.

Area of Science:

• Analytical Chemistry
• Materials Science
• Spectroscopy

Background:

• Waveguide-enhanced Raman spectroscopy (WERS) is crucial for chemical and biological sensing.
• Visible wavelength operation offers signal enhancement due to the inverse fourth power dependence on excitation wavelength.
• Previous visible WERS platforms suffered from high losses and low yields due to custom fabrication.

Purpose of the Study:

• To demonstrate a silicon nitride (SiN) visible WERS platform fabricated using standard CMOS foundry processes.
• To characterize the performance of SiN WERS spirals at visible wavelengths (532 nm and 633 nm).
• To compare visible WERS performance with near-infrared (NIR) WERS and identify optimal configurations.

Main Methods:

• Fabrication of SiN WERS spirals in a 300 mm CMOS foundry.
• Measurement of propagation loss, coupling loss, WERS signal, and background noise.
• Theoretical validation of WERS configurations for visible and NIR wavelengths.
• Comparison of WERS performance at 532 nm, 633 nm, and 785 nm.

Main Results:

• Demonstration of a functional SiN visible WERS platform using CMOS fabrication.
• Quantification of losses and signal characteristics for 532 nm and 633 nm WERS spirals.
• Comparison with a state-of-the-art NIR WERS platform at 785 nm.
• Identification of optimal WERS configurations for visible wavelength operation.

Conclusions:

• A CMOS-compatible SiN platform enables efficient visible WERS.
• Optimal WERS configuration for signal-to-background ratio in the fingerprint region is at 785 nm.
• Pumping at 633 nm maximizes Stokes signal up to 3000 cm^-1, offering advantages for specific applications.