Planar Optical Waveguide Grating Manufacturing via Dual Photomask Exposure
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Solution Overview
Problem
Current planar optical waveguide devices with uniform-pitch or chirped-pitch grating structures struggle to achieve high functionality, such as simultaneous compensation of wavelength dispersion and dispersion slope across multiple channels, and face challenges in processing accuracy, especially when using silicon photonics technology.
Innovation Solution
A manufacturing method for a planar optical waveguide device with a grating structure where core widths of fin and valley portions vary, using a phase-shifting photomask and binary photomask in a two-step exposure process to form a grating structure with discrete pitches, solving the inverse scattering problem using Zakharov-Shabat equations to achieve complex optical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If uniform-pitch or chirped-pitch grating structures are used in planar optical waveguide devices, then the device can be manufactured with conventional processes, but the device cannot achieve high functionality such as simultaneous compensation of wavelength dispersion and dispersion slope across multiple channels
Solution Approach 1:
The patent applies segmentation by dividing the grating structure into discrete pitch regions. Instead of using a continuous uniform-pitch or chirped-pitch grating, the invention segments the grating into multiple sections with discrete pitch values (e.g., PG1, PG2, PG3, PG4), where each segment corresponds to specific optical function requirements. This segmentation enables complex optical characteristics including simultaneous wavelength dispersion and dispersion slope compensation across multiple channels while maintaining manufacturability through standard photolithography processes.
2Adaptability or versatility
If the core widths of fin and valley portions are varied to achieve complex optical characteristics, then high functionality is realized, but processing accuracy becomes difficult to control
Solution Approach 1:
The patent applies local quality by varying the core widths of fin portions (Wf1, Wf2, Wf3, Wf4) and valley portions (Wv1, Wv2, Wv3, Wv4) at different longitudinal positions along the waveguide. Each local region has specifically tailored core width dimensions to achieve the desired optical characteristics for that segment. For example, certain regions have wider fin portions to enhance reflection for specific wavelength channels, while other regions have narrower valley portions to adjust the effective refractive index. This local variation enables complex optical functionality while the discrete nature of the variations maintains compatibility with conventional manufacturing tolerances.
3Productivity
If conventional photolithography is used for manufacturing, then mass production and cost reduction are enabled, but processing accuracy for varied core widths is challenging
Solution Approach 1:
The patent applies parameter changes by utilizing the continuous adjustability of photolithography exposure parameters (exposure time, exposure intensity, development time, development temperature) to precisely control the etched core widths of fin and valley portions. By carefully selecting and adjusting these parameters, the manufacturing process can achieve the desired discrete pitch variations and core width variations within standard process tolerances. This enables mass production of devices with complex optical characteristics using conventional CMOS-compatible photolithography equipment, maintaining both high productivity and adequate manufacturing precision.
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 allows for a compact, high-functional optical waveguide with improved processing accuracy, enabling effective chromatic dispersion compensation and reducing device length, while facilitating mass production and cost reduction through CMOS manufacturing.
Implementation Method 1
forming shaded portions on a photoresist layer using a first photomask, the first photomask being a phase-shifting photomask and the lateral widths of the shaded portions at positions corresponding to the valley portions are substantially equal to the respective core widths of the valley portions
Implementation Method 2
forming shaded portions on the photoresist layer using a second photomask, the second photomask being a binary photomask and the lateral widths of the shaded portions at positions corresponding to the fin portions are substantially equal to the respective core widths of the fin portions
Implementation Method 3
an etching step of etching the high refractive index material layer using the photoresist pattern resulted from the development step to form the fin portions and the valley portions
Data Source
AI summary
A method for manufacturing a planar optical waveguide device of which a core includes a plurality of alternatively arranged fin portions and valley portions to form a grating structure, in which the core widths of the valley portions vary along the longitudinal direction, the method including: a high refractive index material layer forming step of forming a high refractive index material layer; a photoresist layer forming step of forming a photoresist layer on the high refractive index material layer; a first exposure step of forming shaded portions on the photoresist layer using a phase-shifting photomask; a second exposure step of forming shaded portions on the photoresist layer using a binary photomask; a development step of developing the photoresist layer; and an etching step of etching the high refractive index material layer using the photoresist pattern resulted from the development step.