Minimum-mode-size low-loss Ti: LiNbO3channel waveguides for efficient modulator operation at 1.3 µm

Efficient operation of Ti-diffused LiNbO
3
modulators and switches requires small, tightly guiding channel waveguide modes which effectively overlap the applied modulating field. This in turn requires Ti:LiNbO
3
channel waveguides with minimum mode size. The small-mode-size waveguides are obtained in
z
-cut crystals by optimizing the fabrication parameters to achieve maximum index change in the wave-guiding region and the optimum diffusion depth and width. For 6 h diffusion at 1025°C, and Ti strip thickness of 800 Å and strip width of 4 μm, the TM mode has a
1/e
intensity full width of 3.9 μm and full depth of 2.8 μm. This is by far the smallest mode size at
\lambda = 1.32 \mu
m presented to date for Ti:LiNbO
3
waveguides. Since these waveguides have small mode size, large
\Delta n
, and low propagation loss (0.2 dB/cm) at
\lambda = 1.32 \mu
m, it should be possible to fabricate modulators and switches with small voltage-length products and optical circuits that incorporate small bending radii curves, thus decreasing the total device length.