Tapered Waveguide Coupler for Surface-Normal Optical Integration
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Solution Overview
Problem
Conventional waveguides face challenges in efficient coupling between external beams and planar waveguide modes, particularly due to the complexity of fabricating vertically tapered core thickness and the need for in-plane orientation of free-space beams, which limits the use of tapered waveguides in coupling applications.
Innovation Solution
A tapered waveguide with a multilayer stack of light guiding layers, where the stack is delaminated to form a channel with converging sides, enabling surface-normal coupling by reducing the reflectance of cladding mirrors at specific points, allowing for efficient coupling of guided modes with normally incident free-space beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional total internal reflection waveguides are used with mode cutoff couplers, then coupling can be achieved, but the fabrication of planar waveguides with vertically tapered core thickness becomes complex and the free-space beam must be oriented in-plane
Solution Approach 1:
The patent inverts the conventional coupling approach by using surface-normal (out-of-plane) coupling instead of in-plane coupling. The multilayer stack with selective delamination creates a coupling structure that accepts beams perpendicular to the substrate surface, reversing the traditional beam orientation requirement and simplifying integration with vertical optical components
Solution Approach 2:
The patent transitions from two-dimensional in-plane coupling to three-dimensional out-of-plane coupling by introducing a vertically tapered channel through selective delamination of the multilayer stack. This dimensional change allows beams to couple into the waveguide from the vertical direction, eliminating the need for complex in-plane beam steering
2Ease of operation
If vertically tapered core thickness is implemented in planar waveguides, then mode cutoff coupling is achieved, but the fabrication process becomes non-trivial
Solution Approach 1:
The patent segments the multilayer stack by selectively delaminating specific layers to create the tapered channel. Instead of fabricating a continuously tapered structure in a single complex process, the waveguide is constructed from discrete layers that are separated in specific regions, simplifying the fabrication while achieving the desired tapered geometry for mode cutoff coupling
Solution Approach 2:
The multilayer stack is pre-formed with alternating high and low index layers before delamination. This preliminary structuring allows the tapered channel to be created through selective removal of layers, rather than requiring complex direct-write or lithographic patterning of the taper itself, thereby reducing fabrication complexity while maintaining coupling efficiency
3Ease of operation
If surface-normal coupling is proposed in symmetric hollow-core waveguides with Bragg reflector claddings, then coupling efficiency improves, but experimental demonstration has not been achieved
Solution Approach 1:
The patent applies local quality changes by creating regions of increased transmissivity at specific locations in the multilayer stack where delamination occurs. This localized modification of optical properties at the taper region enables surface-normal coupling to be achieved at specific points along the waveguide, allowing experimental demonstration while maintaining overall waveguide integrity
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 enables efficient out-of-plane coupling with improved manufacturability and control over coupling positions, facilitating applications in spectroscopy and wavelength division multiplexing by spatially dispersing spectral signals without the need for moving parts or broad-area illumination.
Implementation Method 1
In conventional total internal reflection waveguides, input/output couplers based on mode cutoff in a taper were proposed and demonstrated in the 1970s
Implementation Method 2
Bragg mirrors called omnidirectional dielectric reflectors (ODRs), have recently been used as claddings for hollow fibers and integrated waveguides
Data Source
AI summary
A method of forming a waveguide, the method comprising the steps of: forming a multilayer stack of light guiding layers; and delaminating the multilayer stack between at least two of the light guiding layers to form a waveguide between the light guiding layers; in which the patterned region has converging sides and the waveguide is tapered, the multilayer stack having increased transmissivity at a region corresponding to a selected thickness of the waveguide. A tapered waveguide is also disclosed, comprising: a multilayer stack of light guiding layers; the multilayer stack defining a channel between at least a first waveguiding layer and a second waveguiding layer; the channel having a diminishing thickness in a first direction; and at least one of the first waveguiding layer and the second waveguiding layer having a region of increased transmissivity adjacent a selected thickness of the core. Methods for the use of the tapered waveguide as an optical coupler or spectrometer are also disclosed. Methods for enhancing the optical resolution of the taper waveguide when operated as a spectrometer are also disclosed.