Chiral spiral waveguides based on MMI crossings: Theory and experiments

Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review


We introduce a novel type of chiral spiral waveguide where the usual waveguide crossings are replaced by 100:0 Multimode Interferometers (MMIs), i.e. 2x2 splitters that couple all the input light in the cross output port. Despite the topological equivalence with the standard configuration, we show how resorting to long MMIs has non-trivial advantages in terms of footprint and propagation length. An accurate analytic model is also introduced to show the impact of nonidealities on the spiral performances, including propagation loss and cross-talk. We have designed and fabricated three chiral spirals on our platform, based on 3 μm thick silicon strip waveguides with 0.13 dB/cm propagation loss, and 1.58 mm long MMIs. The fabricated spirals have 7, 13 and 49 loops respectively, corresponding to the effective lengths 6.6 cm, 12.5 cm and 47.9 cm. The proposed model is successfully applied to the experimental results, highlighting MMI extinction ratio of about 16.5 dB and MMI loss of about 0.08 dB, that are much worse compared to the simulated 50 dB extinction and 0.01 dB loss. This imposes an upper limit to the number of rounds, because light takes shortcuts through the bar MMI ports. Nevertheless, the novel chiral spiral waveguides outperform what is achievable in mainstream silicon photonics platforms based on submicron waveguides in terms of length and propagation losses, and they are promising candidates for the realization of integrated gyroscopes. They can be significantly further improved by replacing the MMIs with adiabatic 100:0 splitters, ensuring lower cross-talk and broader bandwidth.
Original languageEnglish
Title of host publicationSilicon Photonics XI
EditorsGraham T. Reed, Andrew P. Knights
PublisherInternational Society for Optics and Photonics SPIE
ISBN (Print)978-1-6284-1987-0
Publication statusPublished - 1 Jan 2016
MoE publication typeA4 Article in a conference publication
EventSilicon Photonics XI - San Francisco, United States
Duration: 15 Feb 201617 Feb 2016

Publication series

SeriesProceedings of SPIE


ConferenceSilicon Photonics XI
Country/TerritoryUnited States
CitySan Francisco


  • Integrated Optics
  • Multimode interference splitters
  • Photonic Integrated Circuits
  • Silicon Photonics


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