Zero-Birefringence Silicon Waveguides Based on Tilted Subwavelength Metamaterials

Abstract

Polarization independent silicon-on-insulator nanowires are highly sought after, due the inherent high birefringence of this material platform. State-of-the-art designs of non-birefringent waveguides include ridge waveguides and square nanowires, which either imply large dimensions, multiple etching steps, low fabrication tolerances or high wavelength dependence. In this work, we overcome all the aforementioned limitations through tilted subwavelength structures which provide anisotropy control of the resulting metamaterial. With a waveguide cross section of only 300 nm × 550 nm (height × width), the zerobirefringence point is obtained for an approximately 48 • -tilt of the subwavelength structure. Birefringence of the nominal design deteriorates by only 9.10 −3 even in the presence of size deviations of ±10 nm. Moreover, birefringence is maintained under 6.10 −3 in a 100-nm bandwidth around the central wavelength of 1550 nm. This innovative approach is readly adaptable to a wide range of waveguide sizes, while maintaining single-etch-step fabrication.

Silicon Photonic Platform for Passive Waveguide Devices: Materials, Fabrication, and Applications

“…[172] Several PBSs have been realized based on SWGs, [173][174][175] inverse design method, [176] and anisotropyengineered metamaterials. [177,178] The working bandwidth is limited for ADC-based PBSs, as the wavelength shift leads to variations in both the effective index and the coupling strength. A PBS was proposed and demonstrated through "effective Adv.…”

“…[ 172 ] Several PBSs have been realized based on SWGs, [ 173–175 ] inverse design method, [ 176 ] and anisotropy‐engineered metamaterials. [ 177,178 ] The working bandwidth is limited for ADC‐based PBSs, as the wavelength shift leads to variations in both the effective index and the coupling strength. A PBS was proposed and demonstrated through “effective medium anisotropy” to break the bandwidth bottleneck, instead of using “configuration asymmetry.” [ 177 ] The PBS exhibits a high ER of >20 dB and a large bandwidth of >200 nm.…”

Bricked Subwavelength Gratings: A Tailorable On‐Chip Metamaterial Topology

“…By periodically patterning waveguides at the subwavelength scale, a wide range of equivalent refractive indexes can be synthesized lithographically on a chip. [15][16][17][18] What is more, with the ability to engineer dispersion and anisotropy these metamaterials are enabling completely new design strategies yielding devices with unprecedented performance, including ultra-broadband nanophotonic components, [19,20] metalenses, [21][22][23] densely spaced waveguides, [24] polarization management devices, [25][26][27][28][29][30] low crosstalk bends, [31] or high sensitivity waveguide sensors. [32,33] However, to avoid Bragg resonances, subwavelength grating (SWG) metamaterials often require fabrication resolutions of 100 nm and below at telecom wavelengths.…”

Experimental demonstration of metamaterial anisotropy engineering for broadband on-chip polarization beam splitting

“…This principle was leveraged in the theoretical design of an MMI polarization beam splitter [26], resulting in a compact device under 100 µm long. Tilted SWGs were also applied to a polarization-independent monomode waveguide [27], achieving a birefringence under 6.10 −3 in a 100-nm bandwidth around a central wavelength of 1550 nm. However, both devices had, so far, only been proposed theoretically.…”