Silicon Membrane Waveguides Research Articles

Genetic optimization of Brillouin scattering gain in subwavelength-structured silicon membrane waveguides

On-chip Brillouin optomechanics has great potential for applications in communications, sensing, and quantum technologies. Tight confinement of near-infrared photons and gigahertz phonons in integrated waveguides remains a key challenge to achieving strong on-chip Brillouin gain. Here, we propose a new strategy to harness Brillouin gain in silicon waveguides, based on the combination of genetic algorithm optimization and periodic subwavelength structuration to engineer photonic and phononic modes simultaneously. The proposed geometry is composed of a waveguide core and a lattice of anchoring arms with a subwavelength period requiring a single etch step. The waveguide geometry is optimized to maximize the Brillouin gain using a multi-physics genetic algorithm. Our simulation results predict a remarkable Brillouin gain exceeding 3300 W−1m−1, for a mechanical frequency near 15 GHz.

Design and simulation of widely tunable picosecond synchronously pumped terahertz parametric oscillator based on silicon waveguide platform

AbstractA picosecond synchronously pumped terahertz optical parametric oscillator based on silicon membrane waveguide (Si‐based WTPO) is proposed and numerically simulated. Through designing the structure parameters of the silicon membrane waveguide, a broadband terahertz frequency range is obtained by satisfying the phase matching condition. The parametric oscillation process and output characteristics of Si‐based WTPO are numerically analyzed by solving the four‐wave mixing coupled‐wave equations, and the result has indicated that the parametric oscillation within the resonant cavity can apparently enhance the output terahertz wave power. Meanwhile, high bandwidth and efficiency output terahertz wave can be obtained, and too high pump power will lead to a reaction of reverse conversion. Finally, the threshold pump power is calculated. The Si‐based WTPO system we proposed is expected to make some contributions to the study of compact and efficient terahertz wave sources.

Subwavelength engineering for Brillouin gain optimization in silicon optomechanical waveguides.

Brillouin optomechanics has recently emerged as a promising tool to implement new functionalities in silicon photonics, including high-performance opto-RF processing and nonreciprocal light propagation. One key challenge in this field is to maximize the photon-phonon interaction and the phonon lifetime, simultaneously. Here, we propose a new, to the best of our knowledge, strategy that exploits subwavelength engineering of the photonic and phononic modes in silicon membrane waveguides to maximize the Brillouin gain. By properly designing the dimensions of the subwavelength periodic structuration, we tightly confine near-infrared photons and GHz phonons, minimizing leakage losses and maximizing the Brillouin coupling. Our theoretical analysis predicts a high mechanical quality factor of up to 700 and a remarkable Brillouin gain yielding 3500(W⋅m)-1 for minimum feature size of 50 nm, compatible with electron-beam lithography. We believe that the proposed waveguide with subwavelength nanostructure holds great potential for the engineering of Brillouin optomechanical interactions in silicon.

THz-wave generation via difference frequency mixing in strained silicon based waveguide utilizing its second order susceptibility χ((2)).

Terahertz (THz) wave generation via difference frequency mixing (DFM) process in strain silicon membrane waveguides by introducing the straining layer is theoretically investigated. The Si(3)N(4) straining layer induces anisotropic compressive strain in the silicon core and results in the appearance of the bulk second order nonlinear susceptibility χ((2)) by breaking the crystal symmetry. We have proposed waveguide structures for THz wave generation under the DFM process by .using the modal birefringence in the waveguide core. Our simulations show that an output power of up to 0.95 mW can be achieved at 9.09 THz. The strained silicon optical device may open a widow in the field of the silicon-based active THz photonic device applications.

Efficient terahertz-wave generation via four-wave mixing in silicon membrane waveguides

Terahertz (THz) wave generation via four-wave mixing (FWM) in silicon membrane waveguides is theoretically investigated with mid-infrared laser pulses. Compared with the conventional parametric amplification or wavelength conversion based on FWM in silicon waveguides, which needs a pump wavelength located in the anomalous group-velocity dispersion (GVD) regime to realize broad phase matching, the pump wavelength located in the normal GVD regime is required to realize collinear phase matching for the THz-wave generation via FWM. The pump wavelength and rib height of the silicon membrane waveguide can be tuned to obtain a broadband phase matching. Moreover, the conversion efficiency of the THz-wave generation is studied with different pump wavelengths and rib heights of the silicon membrane waveguides, and broadband THz-wave can be obtained with high efficiency exceeding 1%.

On the Modeling of Losses in Short Length Photonic Crystal Waveguides

The 3-D finite difference time domain (FDTD) cut-back method is used to study losses in non-disordered photonic crystal silicon membrane waveguides. Losses above the light-line have been shown to be in good agreement with other methods. Below the light-line, however, FDTD is predicting a rapid increase in losses. This paper studies the possible causes for this effect, including meshing effects, back reflections, and finite thickness sidewalls. It is found that since below the light-line the group index becomes very high and the loss becomes very low, strong Fabry-Perot oscillations dominate the cut-back results. The paper also discusses the impact of operating near to the cut-off wavelength of the photonic crystal waveguide Bloch mode and the implications this has for loss calculation.

Label-free porous silicon membrane waveguide for DNA sensing

We report a label-free porous silicon membrane waveguide biosensor based on a 1μm thick freestanding porous silicon film with 100nm diameter pores. The sensor operates in the Kretschmann configuration. A formvar polymer film provides robust adhesion of the porous silicon membrane to a rutile prism and enables confinement of guided modes in the porous silicon membrane. Attenuated total reflectance measurements are performed, along with theoretical calculations, to fully characterize the waveguide. The sensitivity of the sensor is investigated through DNA hybridization in the porous silicon membrane. A detection limit of 42nM was demonstrated for 24-base pair DNA oligonucleotides.