Long spiral waveguides with small footprint and low-loss were fabricated on a micron-thick SOI platform. In particular an interferometer delayed by a 9.5 mm long spiral was measured to effectively demodulate 7.1 Gbps DPSK signals.
Cherchi, M., Harjanne, M., Ylinen, S., Vyrsokinos, K., Kapulainen, M., Vehmas, T., & Aalto, T. (2014). Compact low-loss delay lines on a micron-scale SOI platform. In IEEE International Conference on Group IV Photonics GFP (pp. 81–82). IEEE Computer Society. https://doi.org/10.1109/Group4.2014.6962031