Asymmetric Waveguide Grating for Polarization-Independent Wavelength Selection

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Solution Overview

Problem

Conventional waveguide-type optical diffraction gratings exhibit polarization-dependent wavelength selection, making them unsuitable for subscriber optical access systems that handle mixed transverse magnetic (TM) and transverse electric (TE) polarization components.

Innovation Solution

A waveguide-type optical diffraction grating with an asymmetric core thickness and modulated period, combined with a phase adjustment portion to ensure a constant phase sum for both polarizations, and a polarization rotation element that connects in series with the diffraction grating to achieve polarization conversion and wavelength selection independent of polarization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a conventional waveguide-type optical diffraction grating is used, then wavelength selection can be performed, but the wavelength selection exhibits polarization dependency which makes it unsuitable for systems with mixed TM and TE polarization components

Engineering Contradiction:

Improvewavelength selection precisionVSAvoidpolarization independence

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The waveguide core is designed with asymmetric thickness in the thickness direction, creating different effective refractive indices for TM and TE polarizations. This asymmetry enables the phase adjustment portion to compensate for polarization-dependent phase differences, ultimately achieving polarization-independent wavelength selection while maintaining precise wavelength discrimination capability

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The invention modifies the physical parameters of the waveguide structure by introducing asymmetric thickness and periodic modulation. These parameter changes create controlled phase differences between polarizations that can be compensated to achieve polarization independence while preserving wavelength selection precision

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If the waveguide core is made asymmetric with modulated period, then polarization-independent wavelength selection is achieved, but the device structure becomes more complex

Engineering Contradiction:

Improvepolarization independenceVSAvoidwaveguide structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The waveguide structure is segmented into distinct functional portions: the asymmetric waveguide core section and the phase adjustment portion with periodic modulation. This segmentation allows each section to perform its specific function independently, achieving polarization independence through the asymmetric core while the periodic modulation provides phase compensation, thereby managing structural complexity through functional decomposition

Inventive Principle:

Principle #1Segmentation

3Adaptability or versatility

If a phase adjustment portion with periodic modulation is added, then the phase difference between forward and reflected waves is compensated for polarization independence, but the device length increases

Engineering Contradiction:

Improvepolarization independenceVSAvoidgrating length

Core Design Contradiction:

Adaptability or versatilityVSLength of moving object

Solution Approach 1:

The phase adjustment portion utilizes periodic modulation of the waveguide structure to create constructive and destructive interference patterns that compensate for polarization-dependent phase differences. By carefully designing the period and length of this modulation, the device achieves polarization independence while controlling the overall length through optimization of the interference conditions

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 configuration allows for polarization-independent wavelength selection, enabling effective operation in systems with mixed polarization components by converting between TM and TE modes, thereby enhancing wavelength selectivity and polarization plane selectivity.

Implementation Method 1

waveguide-type optical diffraction grating

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

optical wavelength filter which uses the waveguide-type optical diffraction grating of a mode conversion type in a multimode waveguide

Methodology Applied

Scientific EffectMode conversion:

Implementation Method 3

a phase adjustment portion configured to adjust a phase difference between a forward wave traveling in an input direction and a reflected wave traveling in a direction reverse to the input direction

Methodology Applied

Scientific EffectBragg reflection: Bragg Diffraction

Data Source

PatentUS9823418B2Waveguide-type optical diffraction grating and optical wavelength filter

Publication Date: 2017.11.21 OKI ELECTRIC INDUSTRY CO LTD

AI summary

Provided is a waveguide-type optical diffraction grating. A waveguide core includes a waveguide core that is asymmetric with respect to a thickness direction perpendicular to a light propagating direction. In the waveguide core, a phase adjustment portion is configured to adjust a phase difference between a forward wave traveling in an input direction and a reflected wave traveling in a direction reverse to the input direction in the waveguide-type optical diffraction grating, and the phase adjustment portion is provided in a manner that a sum of a phase of the forward wave and a phase of the reflected wave which are generated in the phase adjustment portion becomes a constant value irrespective of a polarization state of input light to the waveguide-type optical diffraction grating.