A new diffractive device for light coupling between a planar optical waveguide and free space is proposed. The device utilizes a second-order waveguide grating to diffract the fundamental waveguide mode into two free propagating beams and a subwavelength grating (SWG) mirror to combine the two free propagating beams into a single beam. The finite-difference time-domain (FDTD) simulations show that the SWG mirror improves the coupling efficiency of the waveguide fundamental mode into the single out-coupled beam from about 30% to 92%. A high efficiency (>90%) is predicted for a broad wavelength range of 1520-1580 nm. The proposed device is compact (∼80 μm in length) and it eliminates the need for blazing the waveguide grating.

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Keywords Finite-difference time-domain, Silicon-on-insulator (SOI) waveguides, Subwavelength grating, Waveguide grating coupler
Persistent URL dx.doi.org/10.1109/LPT.2005.860037
Journal IEEE Photonics Technology Letters
Cheben, P. (Pavel), Janz, S. (Siegfried), Xu, D.-X. (Dan-Xia), Lamontagne, B. (Boris), Delâge, A. (André), & Tanev, S. (2006). A broad-band waveguide grating coupler with a subwavelength grating mirror. IEEE Photonics Technology Letters, 18(1), 13–15. doi:10.1109/LPT.2005.860037