Tapered Fiber Bragg Grating Formation for Reduced Scattering Loss
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Solution Overview
Problem
Existing fiber Bragg gratings in narrow-diameter regions suffer from significant optical power loss due to scattering at concave portions.
Innovation Solution
A method involving the formation of a fiber Bragg grating element by heating and stretching an optical fiber to create a narrow-diameter region with a cladding containing a photosensitive material, followed by irradiation with light to induce a periodic refractive index change in both the core and cladding, reducing optical power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fiber Bragg grating is formed by ablating the narrow-diameter region to create concave portions, then a fiber Bragg grating can be formed in the narrow-diameter region, but optical power loss due to light scattering increases significantly
Solution Approach 1:
The invention changes the physical-chemical state of the optical fiber by heating it to a high temperature state, transforming it into a viscous state that enables uniform refractive index modulation without material removal. This parameter change (temperature-induced state transformation) allows the formation of a fiber Bragg grating without creating scattering-causing concave portions, thereby resolving the contradiction between grating formation and optical power loss reduction
Solution Approach 2:
The optical fiber undergoes a phase transition from solid state to viscous state through heating, enabling the core material to be uniformly modulated by light interference patterns. This phase transition allows refractive index changes without mechanical ablation, eliminating the harmful concave portions while maintaining grating functionality, thus reducing optical power loss
2Reliability
If the optical fiber is heated and stretched to form a narrow-diameter region, then a tapered optical fiber with strong light confinement effect is created, but the manufacturing process becomes more complex
Solution Approach 1:
The invention merges two separate processes (taper formation and grating inscription) into a single integrated process. By heating the tapered fiber to create a viscous state and then applying light interference patterns, both the tapered structure and the grating are formed in one continuous operation, reducing manufacturing complexity while maintaining light confinement effects
Solution Approach 2:
The optical fiber is pre-formed into a tapered structure with controlled diameter variations before the grating inscription process. This preliminary action creates the desired light confinement geometry, and subsequent heating and light exposure complete the grating formation without requiring separate complex manufacturing steps
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 method enables the production of a fiber Bragg grating element with reduced optical power loss by modulating the refractive index of the cladding and core, minimizing light scattering and power loss.
Implementation Method 1
a stretching step of heating and stretching the optical fiber to form a narrow-diameter region having a reduced diameter
Implementation Method 2
an exposure step of irradiating a part of the narrow-diameter region with light to cause a photoinduced refractive index change and to form a fiber Bragg grating in which a refractive index of the outer peripheral layer containing the photosensitive material periodically changes
Data Source
Figure 1
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Figure 4~5
AI summary
The present invention provides a fiber Bragg grating element in which a fiber Bragg grating with reduced optical power loss is formed in a narrow-diameter region, and a method for producing the same. A starting fiber 31 in which a core 21 and a cladding 22 are made of silica-based glass containing a photosensitive material is prepared. Ge (germanium) for increasing a refractive index is used as the photosensitive material, and a concentration of the photosensitive material in the core 21 is set to be higher than a concentration in the cladding 22, and thus the starting fiber 31 in which a refractive index of the core 21 is greater than a refractive index of the cladding 22 is heated and stretched to produce a tapered optical fiber 11. A narrow-diameter region 12 of the tapered optical fiber 11 is irradiated with ultraviolet rays by a phase mask method to form periodic refractive index modulation in the core 21 and the cladding 22.