Dual-polarization pump rejection filter in silicon nitride technology

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Nonlinear Optics

Background:

• On-chip pump rejection filters are crucial for nonlinear optical applications like Raman spectroscopy.
• Silicon-based filters achieve high rejection via non-coherent cascading of modal-engineered Bragg filters.
• Silicon nitride's lower index contrast limits polarization suppression in conventional filters.

Purpose of the Study:

• To overcome the polarization suppression limitations in silicon nitride waveguides.
• To propose and demonstrate a novel strategy for high-rejection on-chip filters.
• To enable advanced nonlinear optical functionalities in silicon nitride photonics.

Main Methods:

• Development of a novel cascading strategy combining modal- and polarization-engineered Bragg filters.
• Experimental demonstration of the proposed filter design in silicon nitride.
• Characterization of filter rejection levels and bandwidth for both polarizations.

Main Results:

• Experimental demonstration of a novel filter strategy in silicon nitride waveguides.
• Achieved optical rejection exceeding 60 dB for both transverse electric and transverse magnetic polarizations.
• Obtained a filter bandwidth of 4.4 nm for the demonstrated device.

Conclusions:

• The proposed modal- and polarization-engineered Bragg filter cascading strategy effectively overcomes limitations in silicon nitride.
• This work reports the highest rejection achieved for silicon nitride Bragg gratings supporting both polarizations.
• The demonstrated filters are key enablers for integrated nonlinear photonics utilizing silicon nitride.