Direct-current bias stable Ti:LiNbO(3) TE-TM mode converters produced by magnesium postdiffusion.

Area of Science:

• Materials Science
• Optical Engineering
• Solid State Physics

Background:

• Ti:LiNbO(3) (Titanium-doped Lithium Niobate) channel waveguides are crucial for integrated optics.
• Electrodes placed over waveguides can cause optical mode attenuation.
• Secondary diffusion of MgO is a technique to modify waveguide properties.

Purpose of the Study:

• To investigate the effect of MgO secondary diffusion on Ti:LiNbO(3) channel waveguides.
• To assess the optical isolation provided by the buffer layer formed by MgO diffusion.
• To evaluate the stability of mode-conversion devices under applied DC voltage and optical power.

Main Methods:

• Fabrication of Ti:LiNbO(3) channel waveguides with secondary MgO diffusion.
• Characterization of the buffer layer and its optical isolation properties.
• Testing device stability under various DC bias voltages (up to 60 V) and optical throughput powers (0.633 µm and 0.8 µm wavelengths).

Main Results:

• Secondary MgO diffusion forms a buffer layer, effectively isolating guided modes from electrode-induced attenuation.
• X-cut, z-propagating devices show high stability to optical drift with DC bias up to 60 V.
• Photoconductivity limits long-term stability, particularly at 0.633 µm with ≥100 µW throughput and 14 V bias.
• Stable operation at 0.633 µm is observed for 10 µW throughput over 8 hours.
• Stable operation at 0.8 µm is achieved even at 100 µW throughput with bias voltages up to 60 V.

Conclusions:

• The MgO buffer layer significantly enhances the performance and stability of Ti:LiNbO(3) mode-conversion devices.
• Device stability is wavelength-dependent, with 0.8 µm offering superior performance under high optical power.
• Photoconductivity remains a key factor limiting long-term operational stability, especially at shorter wavelengths and higher optical powers.