Waveguide-to-Slab Coupler Grating Design
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Solution Overview
Problem
Conventional methods for transitioning light from integrated photonics waveguides to free-space optics are inefficient, requiring significant spatial expansion, resulting in diverging Gaussian beams, which are not suitable for applications like magneto-optic traps, and lack flexibility in beam profiles.
Innovation Solution
A waveguide-to-slab coupler with a grating structure that diffracts light at a controlled angle, allowing for the generation of collimated beams with uniform intensity distribution, independent of propagation length, by varying the grating width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If light is directed into a slab and allowed to diverge naturally, then a wide slab mode is achieved, but significant propagation length is required which takes up valuable chip surface area
Solution Approach 1:
The patent transitions the light propagation from a one-dimensional waveguide mode to a two-dimensional slab mode by introducing a grating coupler that diffracts light at approximately 90 degrees. This dimensional change allows the light to expand in the lateral direction (y-axis) immediately upon coupling into the slab, achieving wide beam width without requiring long propagation distances along the chip surface.
Solution Approach 2:
The grating coupler acts as an intermediary element between the waveguide and the slab. It mediates the coupling process by diffracting the confined waveguide mode into the broader slab mode at a controlled angle, enabling efficient mode transformation and immediate spatial expansion without requiring the light to propagate long distances through the slab.
2Shape
If light diverges naturally in a slab, then spatial distribution is increased, but only a Gaussian profile is realized whereas uniform intensity distribution is often more desirable
Solution Approach 1:
The patent applies local quality by using a grating with spatially varying properties (different grating periods or depths in different regions) to locally control the diffraction of light. This allows different regions of the slab to receive light with different intensity characteristics, enabling the synthesis of uniform or other desired intensity distributions through controlled spatial variation of the grating structure.
Solution Approach 2:
The patent changes the physical parameters of the grating structure (grating period, depth, width, or orientation) to control the diffraction characteristics and resulting intensity distribution. By adjusting these parameters, the system can transform the natural Gaussian profile into uniform or other customized intensity distributions, providing flexibility in beam profile generation.
3Area of moving object
If light is allowed to diverge naturally, then a wide beam is achieved, but the beam is diverging whereas a collimated beam is often more needed
Solution Approach 1:
The patent performs preliminary collimation action by designing the grating coupler to diffract light into the slab at a specific angle (approximately 90 degrees) that produces a collimated output beam. This preliminary angular control ensures that the light maintains its collimation upon entering the slab, eliminating the need for additional propagation distance to achieve collimation while simultaneously achieving wide beam width.
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
Enables the production of collimated beams with customizable intensity profiles, reducing chip surface area requirements and improving compatibility with out-of-plane grating couplers, suitable for generating free-space beams for magneto-optic traps.
Implementation Method 1
A light beam propagating along the waveguide of the waveguide-to-slab coupler can be made to diffract off of the grating and into the slab at an angle, such as about 90 degrees
Data Source
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AI summary
An optical coupler device (100) comprises an optical waveguide (120) having a first edge (122) and an opposing second edge (124) that extend in a direction substantially parallel to a propagation direction (x-axis) of an input light beam injected into the optical waveguide (120). A grating structure (130) is on a portion of the optical waveguide (120), with the grating structure (130) having a first side and an opposing second side. The first and second sides of the grating structure (130) extend in the same direction as the first and second edges (122, 124) of the optical waveguide (120). An optical slab (140) adjoins with the first side of the grating structure (130) and is in optical communication with an output of the grating structure (130). The grating structure (130) includes an array of grating lines (132) configured to diffract the input light beam (150) into the slab (140) at an angle with respect to the propagation direction, such that a diffracted light beam (152) is output from the slab (140).