Hollow Core Waveguide Using High-Contrast Gratings
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Solution Overview
Problem
Chip-based waveguides suffer from high optical losses due to direct band-edge absorption, free carrier absorption, and interaction with optical phonons, exceeding the acceptable limits for most applications, while hollow-core waveguides with distributed Bragg reflectors (DBRs) have insufficient reflectivity, leading to high losses.
Innovation Solution
The use of high contrast gratings (HCGs) with subwavelength periodicity, comprising high refractive index segments surrounded by low index material, creates a hollow core for light confinement through glancing reflections, achieving low loss propagation by destructive interference between grating harmonics, and allowing for arbitrary incidence and azimuth configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If chip-based waveguides are used, then compact size and integration capability are improved, but optical loss increases significantly
Solution Approach 1:
The patent extracts the core material from the waveguide structure, creating a hollow-core waveguide where light propagates through air rather than through solid semiconductor material. This removes the source of absorption losses (direct band-edge absorption, free carrier absorption, and optical phonon interaction) while maintaining the compact chip-based form factor.
Solution Approach 2:
The patent employs a composite structure combining semiconductor materials for the cladding layers with air as the core medium. The high-refractive-index semiconductor cladding layers surround an air core, creating a composite waveguide that leverages the optical confinement properties of semiconductors while eliminating their absorption losses in the propagation region.
2Reliability
If distributed Bragg reflectors (DBRs) are used in hollow-core waveguides, then light confinement is improved, but reflectivity remains insufficient leading to high losses
Solution Approach 1:
The patent changes the structural parameters of the cladding from conventional DBR designs to high-contrast gratings with specific geometric configurations. The grating period, duty cycle, and depth are optimized to achieve ultra-high reflectivity (>99.9%) at the operating wavelength, significantly improving upon standard DBR performance and enabling ultra-low loss propagation.
3Loss of energy
If optical fibers are used, then ultra-low loss is achieved, but bulkiness and lack of flexibility are worsened
Solution Approach 1:
The patent creates a chip-based hollow-core waveguide that copies the ultra-low loss propagation characteristics of optical fibers by guiding light through an air core. This solid-state implementation replicates the fiber-optic low-loss performance while achieving compact integration and mechanical flexibility suitable for on-chip applications.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in extremely low loss waveguides, such as 0.006 dB/m, with reduced nonlinearity and dispersion, enabling compact, flexible, and efficient light guidance without the need for optical fibers or hollow-core fibers.
Implementation Method 1
light confinement through a hollow core between opposing HCG faces... providing lateral confinement in response to glancing reflections from grating segments
Implementation Method 2
The optical confinement within the core is in response to destructive interference which arises between multiple grating harmonics in a subwavelength periodic structure
Data Source
AI summary
Optical waveguides using segmented periodically-spaced high contrast gratings bounding a hollow core propagation region on at least two sides. Incident light is received in a hollow waveguide (HW) region (core) between opposing HCG faces which provide lateral confinement in response to glancing reflections of the incident light beam from high refractive index segments of the HCG as it traverses the core. Embodiments are described for planar waveguides (1D) having a planar core between two planar HCGs, as well as 2D waveguides, such as having rectangular segments of the HCG through which light is propagated. Additionally, other configurations of HCG-HW, including those having arbitrary incidence and azimuth, angled HCG segments, propagation in a direction which is transverse, or alternatively parallel, to the segments of the HCG.