Chirped Periodic Poling for Multi-Mode Wavelength Conversion
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Solution Overview
Problem
Conventional wavelength converting elements fail to efficiently perform wavelength conversion on fundamental wave laser beams in high-order modes due to unsatisfied phase matching conditions, resulting in low conversion efficiency and difficulty in configuring thin elements to inhibit high-order mode generation.
Innovation Solution
An optical second harmonic wavelength converting element with a nonlinear optical material having linearly harmonic chirped polarization inversion periods, broadening the phase matching bandwidth to include phase matching conditions for at least two transverse laser oscillation modes, allowing efficient wavelength conversion across multiple modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional QPM wavelength converting element with fixed polarization inversion period is used, then phase matching conditions are satisfied for a specific wavelength, but the phase matching bandwidth is small and cannot accommodate high-order laser oscillation modes
Solution Approach 1:
The patent applies parameter changes by gradually varying the polarization inversion period along the optical propagation direction. Instead of using a fixed period, the period is changed continuously or in steps, allowing the element to satisfy phase matching conditions for multiple wavelengths corresponding to different laser oscillation modes (e.g., fundamental mode and high-order modes). This transforms a single-parameter optimization into a multi-parameter solution that accommodates bandwidth requirements.
Solution Approach 2:
The patent introduces dynamic characteristics by making the polarization inversion period variable along the propagation direction. This creates a distributed phase matching structure where different sections of the waveguide accommodate different modes, effectively transforming a static single-mode matching element into a dynamic multi-mode compatible structure.
2Object-affected harmful factors
If the wavelength converting element is made thin to inhibit high-order mode generation, then high-order mode generation is suppressed, but the element cannot perform efficient wavelength conversion on high-order modes when they do oscillate
Solution Approach 1:
The patent applies local quality by creating different polarization inversion periods in different spatial regions along the waveguide. The structure is designed so that certain regions are optimized for fundamental mode phase matching while other regions accommodate high-order modes. This allows the element to selectively handle different modes with appropriate local characteristics, enabling efficient conversion even when the element is thin.
3Adaptability or versatility
If a chirp-like structure with gradually changed polarization inversion pitch is used to broaden phase matching bandwidth, then bandwidth is increased, but the structure becomes more complex and manufacturing difficulty increases
Solution Approach 1:
The patent applies segmentation by dividing the wavelength converting element into multiple sections, each with a specific polarization inversion period or a controlled gradient. Instead of requiring a continuous complex chirp structure, the element is segmented into discrete regions that can be independently designed and manufactured, simplifying the overall structure while maintaining the bandwidth-broadening effect.
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 enables efficient second harmonic wavelength conversion on fundamental wave wavelengths by broadening the phase matching bandwidth, enhancing conversion efficiency and allowing operation in multiple laser oscillation modes with a simple configuration.
Implementation Method 1
by using a nonlinear material, the fundamental wave laser beams are converted into second harmonic waves each having half the wavelength (twice the frequency) through a Second Harmonic Generation (SHG)
Implementation Method 2
Quasi Phase Matching (QPM) elements in which a periodic structure is used are known. In a QPM wavelength converting element, an optical waveguide is formed in, for example, Periodically Poled Lithium Niobate (PPLN), which is a nonlinear optical crystal, so that polarization is periodically inverted along the waveguide direction
Data Source
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AI summary
A wavelength converting element that is of a planar waveguide type, includes a plate-like nonlinear optical material, and performs a wavelength conversion on a fundamental wave of a laser beam by propagating the fundamental wave in a plurality of laser oscillation modes in a direction perpendicular to a plate-like main surface, the direction being perpendicular to an optical axis, wherein periods of polarization inversions of the nonlinear optical material are changed so that each of the periods has a width of a phase matching band A that includes phase matching conditions of at least two of the plurality of laser oscillation modes and so that a non-polarization-inversion region and a polarization inversion region are formed in the nonlinear optical material.