Optical Fiber Filter Stop Band Selectivity

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Solution Overview

Problem

Conventional solid PBGF optical filters face challenges in achieving high wavelength selectivity due to saturation of transmission loss in the stop band as light propagates, leading to constant intensity in the core section, limiting their ability to filter specific wavelengths effectively.

Innovation Solution

Incorporating a light loss region between two fiber regions with identical optical fiber structures, each comprising a core and clad section with high refractive-index sections arranged periodically, to enhance mode coupling and increase transmission loss within the stop band by redirecting and losing light in the high refractive-index sections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the PBGF length is increased to improve wavelength selectivity, then the transmission loss in the stop band saturates and light intensity becomes constant, limiting further improvement in filter performance

Engineering Contradiction:

Improvewavelength selectivityVSAvoidtransmission loss saturation

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

The optical fiber is divided into multiple sections with different refractive index distributions. Specifically, the clad section is segmented into regions with different periodic structures (different pitch values), creating distinct photonic band gap characteristics in each section. This segmentation allows the light to experience cumulative transmission loss across multiple sections rather than saturating in a single uniform structure, thereby improving wavelength selectivity without requiring excessive fiber length.

Inventive Principle:

Principle #1Segmentation

2Loss of energy

If the periodic structure is made more aggressive to increase transmission loss, then mode coupling increases causing light to diffuse to clad sections, but this also creates balance points where intensity becomes constant

Engineering Contradiction:

Improvetransmission lossVSAvoidlight intensity balance

Core Design Contradiction:

Loss of energyVSStability of the object's composition

Solution Approach 1:

Different sections of the optical fiber are designed with locally optimized refractive index distributions. Each section has a specific pitch value tailored to its position in the light propagation path. The first section has a different pitch than the second section, creating locally varying coupling characteristics that prevent the formation of intensity balance points while maintaining high transmission loss in the stop band.

Inventive Principle:

Principle #3Local quality

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 significantly increases the transmission loss of light within the stop band traveling in the core section, allowing for improved wavelength selectivity and filter performance by maintaining a balance between light intensity in the core and clad sections.

Implementation Method 1

The periodic structure of the refractive-index distribution forms photonic band gaps. The formation of the photonic band gaps realizes a selective wavelength characteristic, thereby keeping light with a specific wavelength corresponding to the periodic structure within a core section

Methodology Applied

Scientific EffectPhotonic band gap: Photonic Crystal

Implementation Method 2

due to mode coupling to couple a waveguide mode in which light intensity is concentrated in the core section and a waveguide mode in which the light intensity is also distributed (present) in the high refractive-index sections in the clad section, light guided in the core section diffuses to the high refractive-index sections in the clad section

Methodology Applied

Scientific EffectMode coupling:

Implementation Method 3

a light loss region between mutually-facing end surfaces of the two fiber regions, for coupling a radiation mode with a waveguide mode in which light intensity is observed in the high refractive-index sections in the clad section

Methodology Applied

Scientific EffectMode coupling (radiation to waveguide):

Data Source

PatentEP2369377B1Optical fiber-type optical filter

Publication Date: 2017.03.01 FUJIKURA LTD

AI summary

An optical fiber-type optical filter includes: two fiber regions, namely, the first and second PBGF regions, each of which includes: a core section extending in a waveguide direction of incident light; and a clad section extending in the waveguide direction and surrounding the core section, wherein the clad section includes a plurality of high rods which have a refractive index higher than that of a base material of the clad section, extend in the waveguide direction, and are arranged periodically in a cross section perpendicular to the waveguide direction , and a light loss region between mutually-facing end surfaces of the first and second fiber regions, for coupling a radiation mode with a waveguide mode in which light intensity is observed in the high refractive-index sections in the clad section.