Hybrid Laser Waveguide Layout for Bragg Grating Uniformity
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Solution Overview
Problem
The existing fabrication processes for hybrid laser sources with integrated waveguides and Bragg gratings face challenges in maintaining the desired performance and optical coupling due to non-uniform thickness and surface finish issues, leading to optical losses and degradation of the Bragg grating's performance.
Innovation Solution
A hybrid laser source design where the Bragg grating is located on the upper face of the first portion of the integrated waveguide, covered by a second portion, with a thin continuous layer of low refractive index material filling the troughs, and the second portion forming a longitudinal rib, which is fabricated using a combination of etching and damascene processes to maintain uniformity and prevent dishing and optical losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the integrated waveguide thickness is locally decreased in the coupling region to optimize optical coupling, then optical coupling efficiency is improved, but manufacturing precision deteriorates due to difficulty in controlling thickness and surface finish
Solution Approach 1:
The integrated waveguide is segmented into two distinct portions: a first portion with constant thickness (e.g., 300 nm) formed from the SOI substrate, and a second portion (longitudinal rib) with different thickness (e.g., 200 nm) formed by localized etching. This segmentation allows the constant-thickness region to maintain manufacturing precision while the localized region optimizes optical coupling, resolving the contradiction between coupling efficiency and thickness uniformity.
Solution Approach 2:
The waveguide structure implements local quality by having different thickness characteristics in different regions: the first portion maintains constant thickness for manufacturing precision, while the second portion has localized thickness variation in the coupling region to optimize optical coupling. This spatial differentiation of properties resolves the contradiction between uniformity and coupling efficiency.
2Reliability
If the Bragg grating is located on the upper face of the longitudinal rib, then optical coupling is optimized, but the Bragg grating performance degrades due to non-uniform surface finish from localized etching
Solution Approach 1:
The Bragg grating is extracted from the localized coupling region and placed on the first portion of the waveguide that maintains constant thickness. This separation removes the Bragg grating from the region affected by localized etching and surface finish degradation, preserving its performance while maintaining optimized optical coupling through the second portion.
Solution Approach 2:
The first portion of the waveguide acts as an intermediary structure that provides a stable, uniform platform for the Bragg grating, while the second portion serves as the coupling-optimized region. This intermediary structure resolves the contradiction by decoupling the Bragg grating location from the localized etching region.
3Reliability
If localized etching is used to create the longitudinal rib, then optical coupling is improved, but optical losses increase due to surface finish degradation
Solution Approach 1:
The waveguide is segmented into a first portion that maintains constant thickness and smooth surface finish (reducing optical losses) and a second portion with localized etching for optimized coupling. This segmentation confines the surface finish degradation to a minimal region, reducing overall optical losses while maintaining coupling efficiency.
Solution Approach 2:
The structure implements local quality by restricting localized etching to only the necessary coupling region of the second portion, while the first portion and most of the second portion maintain uniform thickness and smooth surface finish. This minimizes the area affected by surface degradation, reducing optical losses.
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 configuration preserves the performance of the Bragg grating and the laser source by ensuring uniform dimensions and maintaining optical coupling, reducing optical losses and maintaining the desired emission wavelength.
Implementation Method 1
the optical cavity is bounded by two Bragg gratings located in the integrated waveguide, which form wavelength-selective mirrors
Implementation Method 2
integrated photonic circuit comprises a waveguide, coupled to the laser source
Data Source
AI summary
A laser source includes a semiconductor pad containing an active waveguide arranged on a functionalized substrate having an integrated waveguide. The integrated waveguide is formed from a stack of a first portion and of a second portion. A Bragg grating is arranged in the first portion and is covered by the second portion.