- Laser Photonics Rev. 7, No. 6, L67-L70 (2013)/00110.1002/lpor.201300063 Subwavelength grating Fourier-transform interferometer array in silicon-on-insulator Przemek J. Bock 1 ·•·••, Pavel Cheben 1 ·*, Aitor V. Velasco 2 , Jens H. Schmid 1 , André Delage 1 , Mirostaw Florjañczyk 1 , Jean Lapointe1, Dan-Xia Xu1, Martin Vachon1, Siegfried Janz1, and María L. Calvo 2 The difficulties arising from the limited étendue (commonly referred to as light throughput) in conventional dispersive spectrometers are traditionally solved by using Fourier- transform (FT) Michelson intcrferomctcrs, which benefit from an intrinsically large étendue - the property also re- ferred to as Jacquinot's advantage [ l ]. However, bulk optics Ff spcctromcters require significant mechanical complex- ity since moving optical components (mirrors) are required. In bulk optics instruments, this need for moving elements is circumvented by a spatially heterodyne configuration which employs diffraction gratings as a stationary alter- native to mirrors [2]. Furthermore, in many applications, pl anar waveguide configurations offer distinct advantages by markedly reducing size, weight and cost of the spectrom- eter. However, dispersive planar waveguide spectrometers, such as array waveguide gratings (AWGs) [3], have a sin- gle input waveguide, limiting light throughput. In planar waveguide Ff spectrometers, étendue is increased by using multiple input waveguides feeding into an array of interfer- ometric elements with a suitable periodic spectral response. Such interferometer arrays require no moving parts to pro- duce an interferogram, and were originally developed for water vapor detection from micro-satellites [4, 5] and im- plemcnted in silicon waveguidcs [5 ]. Glass waveguidc FT spectrometers have also recently been developed [6, 7]. To achieve a high spectral resolution, a large optical path length 1 National Research Council Ganada, Ottawa, Ontario K1 A OR6, Ganada imbalance is requircd between the two arms of the MZls. This is usually achieved with different waveguide lengths, requiring waveguide bends [5] or crossings [7]. Even in a high-refractive index contrast material platform, which fa- cilitates small waveguide bend radii, such devices can be quite large on the arder of centimeters (6 cm x 4 cm for [5]). The device size can be reduced using silicon nano meter scale strip waveguides, but the comparatively large waveg- uide propagation losses limit the interferometric contrast (large Ioss difference between the two MZr arms of differ- ent lengths) [8]: In this letter, we presenta solution to maximize inter- ferometric modulation contrast by utilizing subwavelength gratings waveguides to produce the required MZI optical path imbalance without using waveguide bends. This ap- proach also allows for a compact layout of densely arrayed MZis in a small device footprint. Subwavelength gratings are particularly attractive because they allow for the engi- neering of the waveguide refractive index without adding new materials to the fabrication process [9, 10]. A custom effective refractive index can be obtained by design, sim- ply by changing the size, duty cycle, or periodicity of the subwavelength structure. Silicon subwavelength gratings have been used as mirrors [11 ], waveguides (12], waveg- uide claddings [13], crossings [14], fiber-chip edge couplers [15], surface grating couplers [16], polarization converters 2 Departamento de Óptica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid 28040 Madrid, Spain "Przemek J. Bock is currently with CMC Microsystems, Kingston, Ontario, K7L N6, Ganada ·corresponding author: e-mail: przemek.bock@sympatico.ca @WILEY lírj ONLINE LIBRARY () 2013 by WILEY·VCH Verlag GmbH & Co. KGaA, Welnheim