Dielectric overlayer for polarization discrimination in KTP channel waveguides

Area of Science:

• Optics and Photonics
• Materials Science
• Nonlinear Optics

Background:

• Dielectric films and KTP (potassium titanyl phosphate) substrates are crucial in integrated optics.
• Channel waveguides are fabricated using ion exchange for light manipulation.
• Controlling light polarization (TM and TE modes) is vital for laser applications.

Purpose of the Study:

• To investigate a composite waveguide structure for controlling laser oscillation modes.
• To enable efficient frequency doubling of diode-laser radiation using periodically poled KTP waveguides.

Main Methods:

• Deposition of a 2-microm-thick dielectric film with a refractive index of 1.81 onto a KTP substrate.
• Fabrication of channel waveguides in the KTP substrate via ion exchange.
• Analysis of TM and TE mode guidance in the composite structure.
• Integration of the waveguide into an extended-cavity GaAlAs laser system.

Main Results:

• The composite structure guided TM modes in the KTP channel and TE modes in the dielectric film.
• Spatial separation and weak lateral confinement of TE modes led to higher round-trip loss for TE-polarized light.
• This loss mechanism successfully forced the extended-cavity laser to oscillate in the desired TM mode.

Conclusions:

• The engineered composite waveguide effectively controls laser oscillation modes.
• This method provides a pathway for efficient frequency doubling in diode-laser-pumped KTP systems.
• The findings are significant for advancing nonlinear optical device performance.