Reduced sidelobe integrated acousto-optic filter with birefringence apodization.

Area of Science:

• Photonics and Optical Engineering
• Materials Science

Background:

• Acousto-optic tunable filters (AOTFs) are crucial for wavelength selection.
• Reducing sidelobes in AOTFs is essential for improved spectral purity and signal detection.
• Existing AOTF designs often struggle with significant sidelobe levels, limiting their application.

Purpose of the Study:

• To design and fabricate a two-section integrated acousto-optic tunable filter with substantially reduced sidelobes.
• To investigate the effectiveness of birefringence apodization using variable-width Ti-stripe waveguides for sidelobe reduction.
• To experimentally validate the performance of the fabricated AOTF against theoretical predictions.

Main Methods:

• Fabrication of a two-section integrated acousto-optic tunable filter.
• Implementation of birefringence apodization via variable-width Ti-stripe waveguides.
• Integration of proton-exchanged TE and TM-pass polarizers.
• Experimental measurement of tuning curves and sidelobe levels.

Main Results:

• Successfully fabricated a two-section integrated acousto-optic tunable filter.
• Achieved significant sidelobe reduction, with the largest sidelobes 24 dB below peak transmission.
• Demonstrated a 5.3-dB improvement in sidelobe suppression compared to an ideal filter without apodization.
• Measured a Full Width at Half Maximum (FWHM) of 1.36 nm, a 16% increase over the predicted value for the given interaction length.

Conclusions:

• Birefringence apodization is an effective technique for reducing sidelobes in integrated acousto-optic tunable filters.
• The fabricated device shows excellent performance with significantly improved spectral characteristics.
• This advanced AOTF design holds promise for applications requiring high spectral resolution and purity.