Wavelength Conversion Element Semicircular Waveguide Quasi-Phase Matching

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Solution Overview

Problem

Existing wavelength conversion elements using second-order nonlinear optical effects require complex processes and high voltage sources for electric field application, limiting their efficiency and practicality.

Innovation Solution

A wavelength conversion element with a waveguide structure featuring semicircular waveguides arranged along the z-axis, allowing continuous change in the angle of incident light and periodic variation of the nonlinear constant d33, achieving quasi-phase matching without electric field application.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If angle matching methods are used to achieve phase matching, then phase mismatch amount becomes zero, but the maximum nonlinear constant of the nonlinear optical crystal cannot be utilized

Engineering Contradiction:

Improvephase matching precisionVSAvoidutilization of nonlinear constant

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The invention changes the refractive index parameter by introducing a periodic modulation layer with different refractive index than the core layer. This periodic modulation creates an effective refractive index that can be tuned to achieve phase matching while allowing the use of maximum nonlinear constant, thus resolving the contradiction between phase matching precision and utilization of nonlinear constant.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If periodic polarization inversion structure is incorporated to utilize maximum nonlinear constant, then quasi-phase mismatch amount becomes zero, but the device complexity increases

Engineering Contradiction:

Improveutilization of nonlinear constantVSAvoidstructure complexity

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

Instead of periodically inverting the polarization of the entire nonlinear optical crystal, the invention applies local quality modification by introducing periodic modulation layers only at specific locations (at interfaces or at periodic intervals) along the light propagation direction. This local approach achieves the necessary phase matching while significantly reducing the overall device complexity compared to full periodic polarization inversion.

Inventive Principle:

Principle #3Local quality

3Strength

If direct bonding techniques are used to bond substrates, then bonding strength is improved, but the manufacturing precision of waveguide alignment becomes more critical

Engineering Contradiction:

Improvebonding strengthVSAvoidwaveguide alignment precision

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The invention designs the waveguide structures and periodic modulation layers such that the optical paths and phase relationships are made equipotential across the bonded substrate interfaces. By ensuring that the phase matching condition is satisfied through the periodic modulation rather than through precise angular alignment, the system becomes less sensitive to alignment errors, thus allowing strong direct bonding without compromising waveguide alignment precision.

Inventive Principle:

Principle #12Equipotentiality

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 enables highly efficient wavelength conversion with simplified manufacturing and reduced need for high voltage, while minimizing unintended wavelength conversion and allowing for precise alignment errors.

Implementation Method 1

achieving quasi-phase matching without electric field application

Methodology Applied

Scientific EffectQuasi-phase matching:

Implementation Method 2

Methodology Applied

Scientific EffectNonlinear optical effect:

Implementation Method 3

a wavelength conversion element including a periodic polarization inversion optical waveguide employing lithium niobate (LiNbO3:LN) that is a second-order nonlinear material

Methodology Applied

Scientific EffectSecond-order nonlinear optical effect:

Implementation Method 4

Wavelength conversion that satisfies 1/λ3 = 1/λ1 + 1/λ2 is referred to as sum frequency generation (SFG)

Methodology Applied

Scientific EffectSum frequency generation:

Implementation Method 5

If Equation 1 is transformed by λ1=λ2, wavelength conversion that satisfies 1/λ3 = 2/λ1 is referred to as second harmonic generation (SHG)

Methodology Applied

Scientific EffectSecond harmonic generation:

Data Source

PatentUS11644735B2Wavelength conversion element

Publication Date: 2023.05.09 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

Provided is a wavelength conversion element capable of achieving highly efficient wavelength conversion, without relying on a method of applying electric fields. A wavelength conversion element is formed of a second-order nonlinear optical crystal and has a z-axis, running along a direction of spontaneous polarization, within a substrate plane. The wavelength conversion element includes a waveguide in which, when a plurality of circles having their centers on a straight line parallel to the z-axis and having the same radius are depicted so that circumferences of the plurality of circles contact each other, semicircular waveguides corresponding to one semicircles of the circumferences with the straight line as a boundary, are alternately connected.