Fiber Optic Bundle Concave Core Micro-Lens Bonding

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Solution Overview

Problem

Conventional image intensifier systems experience modulation transfer function (MTF) degradation due to light spreading at the interface between the fiber optic bundle and the image sensor, caused by refractive index differences between the core, cladding, and bonding material, leading to increased spot size and reduced image quality.

Innovation Solution

The output surface of the fiber optic bundle is shaped to focus light into a smaller spot size by creating concave recesses in each core, with a bond layer having micro-lenses that conform to these recesses, reducing light spreading and improving MTF by manipulating the angles of light exit and using a bonding material with a higher refractive index than the core or cladding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a flat output surface is used for the fiber optic bundle, then the structure is simple and easy to manufacture, but light spreading occurs due to refractive index differences causing increased spot size and reduced MTF

Engineering Contradiction:

Improveease of manufactureVSAvoidMTF

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The output surface of the fiber optic bundle is shaped with concave recesses in each core, creating a curved surface that focuses light. This curvature compensates for the refractive index differences between core, cladding, and bonding material, reducing light spreading and improving MTF while maintaining manufacturing feasibility through standardized shaping processes

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The refractive index of the bonding material is optimized to be higher than both the core and cladding materials. This parameter change in the bonding material's optical properties, combined with the curved surface geometry, reduces refraction-induced light spreading and improves the modulation transfer function

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If the output surface is shaped to focus light into a smaller spot size, then MTF and image quality are improved, but the structural complexity increases

Engineering Contradiction:

ImproveMTFVSAvoiddevice complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

Concave recesses are formed in each fiber core at the output surface, creating a systematic curved geometry that focuses light. This approach uses a regular pattern of recesses rather than individual complex lens elements, achieving MTF improvement while keeping the overall device structure relatively simple and manufacturable

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Manufacturing precision

If the bond layer has micro-lenses conforming to the recesses, then light spreading is reduced, but the manufacturing process becomes more complex

Engineering Contradiction:

Improvespot sizeVSAvoidease of manufacture

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The bond layer is designed to simultaneously serve as both the bonding medium and the micro-lens structure. The micro-lenses are formed directly within the bond layer material, combining the bonding function with the light-focusing function into a single integrated component, thereby reducing the need for separate manufacturing steps

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The micro-lenses in the bond layer are shaped with curved surfaces that conform to the concave recesses in the fiber cores. This curvature is achieved through standardized bonding processes that allow the bond layer material to take the shape of the underlying recesses, maintaining ease of manufacture while achieving the desired optical focusing effect

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 reduces the spot size of light exiting the fiber optic bundle, enhancing the modulation transfer function (MTF) and image quality by minimizing light spreading and etaloning effects, achieving a spot size reduction from approximately 19 μm to less than 13 μm with optimal refractive index and protrusion depth settings.

Implementation Method 1

The output surface of the fiber optic bundle is shaped to focus light into a smaller spot size by creating concave recesses in each core

Methodology Applied

Scientific EffectLight focusing: Focusing

Implementation Method 2

caused by refractive index differences between the core, cladding, and bonding material

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

using a bonding material with a higher refractive index than the core or cladding

Methodology Applied

Scientific EffectLight refraction: Refraction

Implementation Method 4

minimizing light spreading and etaloning effects

Methodology Applied

Scientific EffectEtaloning: Interference

Data Source

PatentUS9201193B1Textured fiber optic coupled image intensified camera

Publication Date: 2015.12.01 ELBIT SYSTEMS OF AMERICA LLC

AI summary

A fiber optic bundle couples light from an image intensifier (I2) to an image sensor. The fiber optic bundle includes multiple cores for directing the light from the I2 to the image sensor, and each core has an output surface shaped into a recessed concave surface for focusing the light toward the image sensor. A bond layer is interposed between the output surface of the core and the image sensor. The bond layer is shaped into multiple micro-lenses, each micro-lens configured to conform to the recessed concave surface of each respective core.