Abstract

We have designed slow light photonic crystal waveguides operating in a low loss and constant dispersion window of Dl = 2 nm around l = 1565 nm with a group index of ng = 60. We experimentally demonstrate a relatively low propagation loss, of 130 dB/cm, for waveguides up to 800 mm in length. This result is particularly remarkable given that the waveguides were written on an electronbeam lithography tool with a writefield of 100 mm that exhibits stitching errors of typically 10–50 nm. We reduced the impact of these stitching errors by introducing ‘‘slow–fast–slow’’ mode conversion interfaces and show that these interfaces reduce the loss from 320 dB/cm to 130 dB/cm at ng = 60. This significant improvement highlights the importance of the slow–fast–slow method and shows that high performance slow light waveguides can be realised with lengths much longer than the writing field of a given ebeam lithography tool.