Waveguide Polarization Beam Splitter Using Asymmetric Couplers

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Solution Overview

Problem

Conventional waveguide-type polarization beam splitters suffer from significant wavelength dependence and temperature-induced deterioration of polarization extinction ratio due to the use of directional couplers and quarter wave plates, leading to suboptimal performance in optical communications.

Innovation Solution

A waveguide-type polarization beam splitter design featuring orthogonal quarter wave plates and specific optical couplers, such as Y-branch or multimode interference couplers, is implemented to minimize wavelength and temperature dependencies, eliminating the need for delay portions with inherent wavelength dependence, and ensuring symmetric waveguide arms.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If directional couplers are used for the first and second optical couplers, then the waveguide-type polarization beam splitter can be manufactured with standard components, but wavelength dependence occurs leading to deterioration of polarization extinction ratio

Engineering Contradiction:

ImprovemanufacturabilityVSAvoidpolarization extinction ratio

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the coupling ratio parameter of the optical couplers from standard 50:50 to asymmetric ratios (e.g., 70:30 or 80:20). This parameter change eliminates the wavelength dependence issue while maintaining ease of manufacture, as the asymmetric couplers are still standard components that can be manufactured with conventional techniques.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If quarter wave plates are inserted in the waveguide arms to provide phase difference, then temperature characteristics are improved, but a delay portion of quarter wavelength is required causing wavelength dependency

Engineering Contradiction:

Improvetemperature characteristicsVSAvoidwavelength dependence

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent extracts and eliminates the delay portion from the waveguide arm structure. By using asymmetric optical couplers instead of quarter wave plates with delay portions, the invention removes the component causing wavelength dependency while maintaining temperature stability through the coupler design.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent substitutes the mechanical/optical delay portion structure with an asymmetric coupling field distribution approach. Instead of using physical delay lines (mechanical/optical path length differences), the invention uses the electromagnetic field coupling characteristics of asymmetric couplers to achieve the same phase difference function without wavelength dependency.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If the waveguide arms are made asymmetric to compensate for manufacturing tolerances, then manufacturing flexibility is improved, but the wavelength dependence is exacerbated

Engineering Contradiction:

Improvemanufacturing flexibilityVSAvoidwavelength dependence

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent changes the design approach from geometric asymmetry (asymmetric arm lengths) to coupling parameter asymmetry (asymmetric coupling ratios). This allows manufacturing flexibility to be achieved through controllable coupling parameters rather than precise geometric dimensions, thereby avoiding exacerbation of wavelength dependence.

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 design significantly reduces wavelength dependence and maintains a high polarization extinction ratio of 30 dB or more, even considering manufacturing tolerances, thereby enhancing the stability and performance of the polarization beam splitter.

Implementation Method 1

one of the first optical coupler and the second optical coupler is an optical coupler which gives a phase shift of about 90° or about −90° between coupled or split light beams

Methodology Applied

Scientific EffectPhase shift:

Implementation Method 2

a first optical coupler optically coupled to the one or two input optical waveguides and having one input and two outputs or two inputs and two outputs

Methodology Applied

Scientific EffectOptical coupling:

Data Source

PatentUS9235003B2Waveguide-type polarization beam splitter

Publication Date: 2016.01.12 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

Provided is a waveguide-type polarization beam splitter in which deterioration of a polarization extinction ratio due to temperature change and wavelength change is suppressed. A groove is formed to extend across a pair of optical waveguide arms and two quarter wave plates are provided in the groove to extend respectively across the arms. Polarization axes of the quarter wave plates are orthogonal to each other. A first optical coupler which gives a phase difference of 0° or 180° between coupled or split light beams and a second optical coupler which gives a phase difference of 90° or −90° between coupled or split light beams are used in combination.