Wavelength Conversion Device Polarization Inversion Structure

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Solution Overview

Problem

High-order quasi-phase matching in wavelength conversion devices leads to unintended wavelength conversion, reducing the intensity of the intended converted light due to parasitic wavelength generation, as the nonlinear constant can only take discrete values, causing odd-order sine components that result in energy transfer to shorter wavelengths.

Innovation Solution

A wavelength conversion device with a second-order nonlinear optical medium featuring a polarization inversion structure where the polarization inversion period is divided into regions with specific width ratios to form an average polarization profile closer to a sine wave, limiting higher-order sine wave components and reducing parasitic wavelength conversion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a periodic polarization inversion structure is used to achieve quasi-phase matching, then wavelength conversion efficiency is improved, but unintended wavelength conversion occurs due to higher-order quasi-phase matching

Engineering Contradiction:

Improvewavelength conversion efficiencyVSAvoidparasitic wavelength generation

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The polarization inversion period is divided into multiple regions with different inversion states. Instead of a simple binary inversion pattern, the structure segments the period into regions with varying polarization inversion states, which suppresses higher-order sine wave components and reduces parasitic wavelength conversion while maintaining first-order quasi-phase matching efficiency

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions within the polarization inversion structure are assigned different local properties (inversion or non-inversion states) to optimize performance. By locally controlling the polarization state in each region, the structure achieves suppressed higher-order components while maintaining effective first-order wavelength conversion

Inventive Principle:

Principle #3Local quality

2Productivity

If the nonlinear optical crystal is used with maximum nonlinear constant orientation, then conversion efficiency is improved, but angle matching requirements increase device complexity

Engineering Contradiction:

Improveconversion efficiencyVSAvoidangle matching requirement

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The invention changes the structural parameter of the polarization inversion period to suppress higher-order components. By carefully designing the period length and inversion pattern, the device achieves both high conversion efficiency and suppression of parasitic wavelengths without requiring precise angle matching, thus reducing device complexity

Inventive Principle:

Principle #35Parameter changes

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 effectively limits the generation of converted light at unintended wavelengths, maintaining the intensity of the original target wavelength by reducing energy transfer to parasitic wavelengths, thus enhancing the efficiency of wavelength conversion.

Implementation Method 1

using lithium niobate (LiNbO3:LN) or lithium tantalate (LiTaO3:LT) which is a material exhibiting a second-order nonlinear optical effect

Methodology Applied

Scientific EffectSecond-order nonlinear optical effect:

Implementation Method 2

Wavelength conversion that satisfies equation (1) is called sum frequency generation (SFG)

Methodology Applied

Scientific EffectSum frequency generation (SFG):

Implementation Method 3

Wavelength conversion satisfying equation (2) is called second harmonic generation (SHG) because it generates light (of the second harmonic) having a wavelength that is half that of the input light

Methodology Applied

Scientific EffectSecond harmonic generation (SHG): Second Harmonic Generation

Implementation Method 4

Wavelength conversion that satisfies equation (3) is called difference frequency generation (DFG) because light corresponding to the difference in the wavenumber

Methodology Applied

Scientific EffectDifference frequency generation (DFG):

Implementation Method 5

the amount of phase mismatch can be set to 0 in a quasi manner (quasi-phase matching can be achieved) by constructing a structure in which the polarization direction of a second-order nonlinear optical material is periodically inverted along the light propagation direction

Methodology Applied

Scientific EffectQuasi-phase matching:

Data Source

PatentUS11768421B2Wavelength conversion device

Publication Date: 2023.09.26 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

A wavelength conversion device includes a second-order nonlinear optical medium with a polarization inversion structure, wherein the wavelength conversion device performs wavelength conversion between three wavelengths according to a relationship of 1/λ1=1/λ2+1/λ3, a polarization inversion period Λ of the polarization inversion structure is divided into 2a regions, and when the 2a regions divided from the polarization inversion period Λ each has a width ratio of an inverted region and a non-inverted region of r to 1−r (where 0≤r≤1), a ratio value r is set such that, when one period in phase of a sine function from 0 to 2π is divided into 2a regions, a value of the sine function in a center of each divided region is (1−2r)±0.1.