Masakazu Sagawa

Spot-size Transformation By An-controlled Polymer Waveguides

waveguides connected together by waveguide arrays of different lengths. The input light is demultiplexed into the various wavelength and fed into five optical gates connected to the wavelength router. The optical gate is a 7 mm long MachZehnder type switch. At the end of the optical gates, a mirror is formed to reflect the selected light back to the wavelength router, which then works as a multiplexer. The total number of arrayed waveguides is 32. The difference in length between adjacent waveguides is 2 pm. The curved waveguides have a 60 mm radius of curvature. The total length of the device is 50 mm. The device was fabricated in z-cut LiNbO,. Titanium 70 nm thick and 7 km wide was diffused at 1050°C for 9 hours to obtain a single mode waveguide. Measured characteristics of the device are shown in Fig. 2(a) and (b). Fig. 2(a) shows the filter response of the device under zero bias voltage. Fig. 2(b) shows the filter response of a single channel. Switching voltage was 35 V for the TE mode and the worst case crosstalk was -12 dB. The insertion loss was about 13 dB including the 3 dB loss at the coupler. A reflective arrayed structure; with optical gates located at the same side of the slab waveguide as the input and output ports, can be used to halve the device length. The device length then becomes short enough to be integrated onto one chip even when using a large difference in length between arrayed waveguides to cope with high WDM density. A proton exchanged waveguide or some other type of fabrication process may be introduced to attain a curved waveguide with a small radius in order to shorten the device length. In conclusion, we demonstrated a wavelength filter using a wavelength router and optical gate fabricated in LiNbO,.