Tapered Ridge Waveguide Grating for Wavelength Stability
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Solution Overview
Problem
Existing external resonator type lasers face challenges in maintaining wavelength stability and suppressing mode hopping due to temperature changes, which leads to fluctuations in optical power, and current control methods increase module size and cost.
Innovation Solution
A grating element with a ridge optical waveguide and Bragg grating is designed, featuring a tapered portion to ensure single-mode propagation, with specific dimensions and materials to enhance wavelength stability and tolerance to axial misalignment, while reducing the length of the resonator to minimize mode hopping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resonator length is reduced to minimize mode hopping, then wavelength stability is improved, but the tolerance to axial misalignment deteriorates
Solution Approach 1:
The waveguide structure is designed with varying cross-sectional dimensions along its length. The incident portion has larger dimensions (width Win and thickness Tr) to provide tolerance for axial misalignment, while the grating portion has smaller dimensions to maintain single-mode propagation and wavelength stability. This local variation in geometric properties resolves the contradiction between misalignment tolerance and wavelength stability.
2Reliability
If temperature control elements are added to suppress mode hopping, then wavelength stability is improved, but module size and cost increase
Solution Approach 1:
The laser device achieves wavelength stability through its inherent structural design rather than external temperature control systems. The optimized waveguide geometry and Bragg grating configuration create a resonator that naturally suppresses mode hopping without requiring additional temperature control elements, thereby maintaining compact size and low cost while ensuring reliable wavelength stability.
3Manufacturing precision
If the waveguide width is increased to improve axial misalignment tolerance, then coupling efficiency is improved, but single-mode propagation is compromised
Solution Approach 1:
The waveguide is segmented into distinct functional portions: an incident portion with larger dimensions for misalignment tolerance and a grating portion with smaller dimensions for single-mode propagation. This segmentation allows each portion to optimize its local function without compromising the overall system performance.
Solution Approach 2:
The transition from the incident portion to the grating portion is achieved through a tapered section that gradually changes the waveguide dimensions. This dimensional transition in the longitudinal direction allows the system to maintain both large dimensions at the input for misalignment tolerance and small dimensions at the grating for single-mode propagation.
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
The solution achieves stable wavelength operation with reduced temperature dependency and optical power fluctuations, allowing for compact design without additional temperature control elements, and increased tolerance to axial misalignment, thereby improving the reliability and efficiency of the laser module.
Implementation Method 1
part of the laser light is returned to the lasers by mirrors with the wavelength selectivity using Bragg reflection to achieve a stable wavelength operation
Implementation Method 2
a propagating light propagates through at least in the Bragg grating in a single mode
Data Source
AI summary
A grating element includes: a support substrate; an optical material layer; a ridge optical waveguide having an incidence surface on which a laser light is incident and an emission end from which an emission light with a desired wavelength is emitted; and a Bragg grating including concave and convex portions formed within the optical waveguide. The optical waveguide includes an incident portion between the incidence surface and the Bragg grating, and a tapered portion between the incident portion and the Bragg grating. In the Bragg grating, a propagation light propagates in single mode. The width Win of the optical waveguide in the incident portion is larger than the width Wgr of the optical waveguide in the Bragg grating. The width Wt of the optical waveguide in the tapered portion is decreased from the incident portion toward the Bragg grating. The relationships represented by formulas (1) to (3) are satisfied.