All-Fiber Optical Isolator Using Long Period Grating
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional optical isolators for high-power lasers are costly and require large crystals and magnets, making them inefficient for high-volume production, especially in consumer electronics and marking applications, where size and cost are critical, and they struggle to manage reflections effectively in applications like welding, cutting, and drilling.
Innovation Solution
An all-fiber optical isolator using a helical long period grating with perturbations that reject back-reflected skew modes, eliminating the need for expensive crystals and magnets, and allowing for adjustable mode coupling through a bending mechanism with periodic surfaces, enabling effective optical isolation without free space optics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical isolators use large crystals and magnets to prevent laser induced damage, then reliability is improved, but cost and device complexity increase
Solution Approach 1:
The patent replaces the mechanical/optical system of crystals and magnets with an all-fiber optical system using long period gratings. The isolator uses fiber-optic components including a first optical fiber with a long period grating, mode filter, and second optical fiber, eliminating the need for bulk crystals and magnetic fields while maintaining optical isolation functionality.
Solution Approach 2:
The patent changes the operating parameters by using mode coupling between fundamental and higher-order modes through the long period grating. The grating period is specifically designed to couple the fundamental mode to higher-order modes, creating directional optical isolation through modal transformation rather than physical blockage by crystals.
2Device complexity
If optical isolator size is reduced to lower cost, then cost decreases, but isolation performance deteriorates
Solution Approach 1:
The patent transitions from spatial dimension isolation (physical size of crystals) to modal dimension isolation (higher-order modes). The long period grating couples light into higher-order modes that propagate in different spatial distributions, providing isolation through modal differentiation rather than physical separation, thus achieving effective isolation in a compact form factor.
3Reliability
If light beam is focused through optical isolator to optimize isolation, then isolation performance improves, but laser induced damage risk increases
Solution Approach 1:
The patent replaces the free-space optical path requiring focusing with an all-fiber integrated system. The fiber-optic structure guides light through the long period grating without requiring external focusing optics, eliminating the concentration of laser energy at optical surfaces that would cause damage while maintaining isolation functionality.
4Reliability
If conventional isolators are used for high power lasers, then isolation effectiveness improves, but cost and manufacturing complexity increase
Solution Approach 1:
The patent replaces expensive conventional isolator components (large crystals, magnets, precision mounting hardware) with fiber-optic components that can be manufactured using standard fiber fabrication techniques. The long period grating can be written into optical fibers using established processes, enabling high-volume production at lower cost while maintaining effectiveness for high-power laser applications.
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 provides cost-effective optical isolation for high-power lasers by rejecting back-reflected light efficiently, reducing the risk of laser damage and destabilization, and allowing for flexible design and wavelength range adjustment, suitable for industrial processing applications.
Implementation Method 1
the period is selected to couple the fundamental mode to the higher order mode of the optical fibre
Implementation Method 2
Conventional optical isolators are based on Faraday rotation in crystals through which a strong magnetic field is applied
Data Source
Figure 1~2
Figure 3~6
Figure 7~10
AI summary
Apparatus for optically isolating a laser (1) from external reflections, which apparatus comprises a mode filter (19) and a first optical fibre (1), wherein: the first optical fibre (1) is a multimode optical fibre that supports a fundamental mode (3) and at least one higher order mode (4); the mode filter (19) is defined by an optical attenuation which is higher for the higher order mode (4) than for the fundamental mode (3); the mode filter (19) is configured to pass the fundamental mode (3) into the first optical fibre (1); and the apparatus being characterized in that: the first optical fibre (1) comprises a long period grating (10); and the long period grating (10) is defined by a period (13) selected to couple the fundamental mode (3) to the higher order mode (4) of the first optical fibre (1); whereby if the fundamental mode (3) and the higher order mode (4) are reflected back into the first optical fibre (1) as back-reflected fundamental and higher order modes (25), (26), then the mode filter (19) optically attenuates the back-reflected higher order mode (26) more than the back-reflected fundamental mode (25) thereby isolating the external reflection.