Subwavelength grating (SWG) structures are an essential tool in silicon photonics, enabling the synthesis of practical metamaterials with controllable refractive index. Here we propose, for the first time, tilting the grating elements to gain control over the anisotropy of the metamaterial. Rigorous FDTD simulations demonstrate that a 45°tilt results in an effective index variation on the fundamental TE mode of 0.23 refractive index units, whereas the change in the TM mode is 20 times smaller. Our simulation predictions are corroborated by experimental results. We furthemore propose an accurate theoretical model for designing tilted SWG structures based on rotated uniaxial crystals, which is functional over a wide wavelength range and for both the fundamental and higher order modes. The proposed structures open up promising venues in polarization management of silicon photonic devices.

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We present two techniques for mitigating the effects of temperature drifts in waveguide spatial heterodyne Fourier--transform on--chip spectrometers. In high--resolution devices, large optical path length differences result in an increased sensitivity to temperature variations and impose stringent requirement on the thermal stabilization system. In order to overcome this limitation, here we experimentally demonstrate two new temperature mitigation techniques based on a temperature--sensitive calibration and phase errors correction. The spectrometer chip under analysis comprises an array of 32 Mach--Zehnder interferometers fabricated on a silicon--on--insulator platform. The optical path delays are implemented as microphotonic spirals of linearly increasing length up to 3.779 cm, yielding a spectral resolution of 17 pm. We demonstrate that the degradation in retrieved spectra caused by temperature drift is effectively eliminated by temperature--sensitive calibration and phase errors correction. [5, 6], and cascaded micro--ring resonators [7, 8] can achieve sub--nanometer spectral resolution and compact chip sizes. However, the optical throughput (étendue) of these devices is fundamentally limited by the need for a single--mode input waveguide. On the contrary, spatial heterodyne Fourier--transform (SHFT) spectrometers can provide a substantially larger étendue due to the possibility of multiple input waveguide apertures [9]. In an SHFT system, multiple interferometric measurements are performed in parallel using an array of interferometers each with a different optical path length difference (OPD) [10]. The input spectrum is calculated by the Fourier transform (FT) of the stationary spatial interferogram, which can be captured by a detector array in a single shot.SHFT spectrometers have been successfully implemented on silicon--on--insulator (SOI) platform [9]. The high refractive index contrast of SOI provides a high modal confinement with a correspondingly reduced bend radius which ultimately allows to achieve a larger spectral resolution on a smaller chip footprint, The SHFT spectrometer can be implemented on an SOI platform as an array of N waveguide Mach--Zehnder interferometers (MZIs) [9]. In such configuration, the spectral resolution (δλ) is determined by the OPD of the most unbalanced interferometer while the free spectral range (FSR) is set by the numbers of interferometers (N) [9, 11]:(2) where λ0 is the device central wavelength, ΔLmax is the maximum MZI geometrical path difference and ng is the waveguide group index. For an arbitrary input signal, all the interferometer outputs (each corresponding to a different optical path difference) are

Polarization management is of paramount importance in integrated optics, particularly for highly birefringent photonic platforms such as silicon-on-insulator. In this paper, we present a polarization beam splitter based on a multimode interference coupler incorporating tilted subwavelength gratings. The tilt provides accurate control of the structural anisotropy and enables independent selection of the beat length for two orthogonal polarization states. As a result, device length is reduced to less than 100 μm while simultaneously achieving broadband operation through subwavelength grating dispersion engineering. Insertion losses below 1 dB and an extinction ratio higher than 20 dB are demonstrated through three-dimensional FDTD simulation in a 131-nm bandwidth.