Fast trimming of electro-optic polymer waveguide Y-branches by post-photobleaching for tuning the power splitting ratio

We present a novel post-fabrication laser trimming technique to adjust the power splitting ratio of strip waveguide Y-branches made in thermally crosslinked electro-optic polymers. The trimming is based on the irreversible index change due to photobleaching. Our method uses simple equipment and the process takes only a few seconds. Waveguides made by both reactive ion etching and photobleaching are trimmable. An adjustable range of the splitting ratio as wide as +/-20% is achieved with less than 0.2 dB of excess loss. This in situ trimming technique is effective for both the TE and TM modes of the waveguide and is very suitable for automated device processing.