Optical Waveguide Slit Loss Reduction via Thin Film Lens

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Solution Overview

Problem

Optical waveguide elements with high relative refractive index differences experience significant light loss due to slits, which increases with wider slit widths and higher refractive index differences, making it difficult to reduce losses, especially in the height direction.

Innovation Solution

Incorporating a thin film lens element with a photonic crystal structure into the slit of the optical waveguide element, which includes a half-wavelength plate and thin film elements with lenses that adjust the beam diameter to minimize light loss by rotating polarization and optimizing the alignment of optical axes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the relative refractive index difference is increased to reduce the minimum bending radius and enable high-density integration, then the size and integration density improve, but the slit loss increases significantly

Engineering Contradiction:

Improveintegration densityVSAvoidslit loss

Core Design Contradiction:

Volume of moving objectVSLoss of energy

Solution Approach 1:

A taper portion is introduced as an intermediary structure between the optical waveguide and the slit. This taper portion gradually transforms the mode field distribution, acting as a transition zone that mediates between the confined mode in the waveguide and the broader mode required at the slit, thereby reducing reflection and improving coupling efficiency

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The solution extends the problem from two-dimensional plane optimization to three-dimensional space optimization by introducing the taper portion that utilizes the depth dimension. Instead of only adjusting parameters in the waveguide cross-section, the invention creates a gradual transition structure along the propagation direction, effectively using the third dimension to solve the coupling problem

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of manufacture

If the slit width is increased to facilitate optical filter insertion, then the ease of manufacture improves, but the slit loss increases

Engineering Contradiction:

Improveoptical filter insertionVSAvoidslit loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The taper portion serves as a mediator that decouples the relationship between slit width and loss. By introducing this gradual transition structure, the invention allows wider slits to be used for easier filter insertion while the taper compensates for the increased discontinuity, maintaining acceptable coupling efficiency

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If a half wavelength plate is inserted into the slit to convert polarization, then the functional versatility improves, but the device complexity and alignment precision requirements increase

Engineering Contradiction:

Improvepolarization conversion functionVSAvoidslit structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The taper portion is designed to serve multiple functions simultaneously: it acts as a mode field transformer to reduce reflection loss, serves as a structural support for inserting the half wavelength plate, and provides a gradual transition zone that facilitates easier alignment. This multi-functionality reduces the need for additional separate components

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 effectively reduces slit loss by up to 50% compared to conventional designs, achieving a desirable 0.5 dB loss even at high refractive index differences, while maintaining high coupling efficiency and reducing the risk of optical axis misalignment.

Implementation Method 1

Incorporating a thin film lens element with a photonic crystal structure into the slit of the optical waveguide element

Methodology Applied

Scientific EffectPhotonic crystal: Photonic Crystal

Implementation Method 2

when the TE polarized light propagates through one optical waveguide of the divided optical waveguides into the half wavelength plate, the polarization direction rotates by 90° so that the light becomes the TM polarized light by the half wavelength plate

Methodology Applied

Scientific EffectPolarization rotation: Polarisation

Implementation Method 3

a first thin film element which is inserted into the slit along with the optical filter and is provided with a first thin film lens, wherein the first thin film lens provided in the first thin film element converges light that has propagated through the first optical waveguide and outputs into the slit into the second optical waveguide

Methodology Applied

Scientific EffectLight convergence: Lens

Data Source

PatentUS10564355B2Optical waveguide element

Publication Date: 2020.02.18 FURUKAWA ELECTRIC CO LTD

AI summary

A disclosed optical waveguide element includes a cladding portion formed on a substrate; an optical waveguide which is formed inside the cladding portion and has a refractive index higher than that of the cladding portion; an optical filter which is inserted into a slit formed in the cladding portion to divide the optical waveguide into a first optical waveguide and a second optical waveguide; and a first thin film element which is inserted into the slit along with the optical filter and is provided with a first thin film lens, wherein the first thin film lens provided in the first thin film element converges light that has propagated through the first optical waveguide and outputs into the slit into the second optical waveguide.