Augmented low index waveguide for confining light in low index media

Abstract

Guiding light in the low index region of a high refractive index contrast waveguide can be beneficial for many applications including sensing, nonlinear optics and electro‐optics. Existing methods to achieve this goal suffer from fabrication complexity, large loss, or poor optical confinement. We propose a simple structure to achieve a significant enhancement of light confinement in the low index medium. We explain the guiding principle of this structure using geometrical optics, and suggest a number of applications where this guiding structure can provide significant performance benefits. The combination of simplicity, ease of fabrication, and good confinement makes this waveguide an attractive choice for a wide range of applications. To illustrate this, we consider the integration of a nonlinear polymer with a silicon photonic waveguide, and show that significantly better performance with an easier fabrication process can be achieved using this new scheme.

Review on Optical Waveguides

“…Fabrication of the slot waveguide is cumbersome and hybrid plasmonic waveguide suffers from additional propagation losses due to the presence of metal. Augmented waveguide confines light efficiently in the low-index region by reducing the reflection at the high index-low index interface in a high-index contrast waveguide, which results in enhancement of light confinement in the low-index region [26]. Figure 18 shows the schematic of an augmented low-index waveguide.…”

Numerical investigations of an ultra-compact polarization beam splitter based on augmented low-index guiding and subwavelength grating structures

“…The refractive indices 29 of the Si, Si 3 N 4 , and SiO 2 we used are n Si = 3.4777, n Si3N4 = 1.9963, and n SiO2 = 1.4440, respectively, and the operating wavelength of the device is λ = 1.55 μm. According to the guiding principle for an ALIG structure 18 , the Si layer must be thin enough to push most of the power of the TM mode (for which most of the electric field is in the y direction) into the Si 3 N 4 layer. On other hand, the high-index Si layer is used as a conventional waveguide to confine the TE mode (for which most of the electric field is in the x direction).…”

“…Recently, the augmented low-index guiding (ALIG) mechanism 18 has been utilized to construct a PBS. An ALIG waveguide consists of a two-layer system with a high-contrast index.…”

All-dielectric scale invariant waveguide

“…One of these is related to the spatial distribution of light in waveguides, which is fundamentally limited to the material with the highest refractive index by total internal reflection (TIR). This critical challenge limits the amount of lightmatter interaction with low-refractive-index materials, which in turn restricts their usage.To date, guiding light in low-index materials has been achieved using Bragg reflectors 10 , antiresonant structures [11][12][13][14] , photonic crystals 15-17 , slot-waveguides 18,19 , plasmonic waveguides [20][21][22][23] , and ALIG waveguides 24,25 . However, all of these solutions are either lossy, require periodicity (larger footprint), exhibit narrow bandwidth, are polarization restricted 18,25 , or are limited to subwavelength dimensions 18,20,26 .…”

“…This critical challenge limits the amount of lightmatter interaction with low-refractive-index materials, which in turn restricts their usage.To date, guiding light in low-index materials has been achieved using Bragg reflectors 10 , antiresonant structures [11][12][13][14] , photonic crystals 15-17 , slot-waveguides 18,19 , plasmonic waveguides [20][21][22][23] , and ALIG waveguides 24,25 . However, all of these solutions are either lossy, require periodicity (larger footprint), exhibit narrow bandwidth, are polarization restricted 18,25 , or are limited to subwavelength dimensions 18,20,26 . As an example, consider the slot waveguide that confines light in the low-index media by relying on the discontinuity of the electric field at the dielectric interfaces between the two media.…”