Fresnel Lens Annular Segmentation for HMD Weight and Image Quality

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Solution Overview

Problem

Existing observation optical systems for head mount displays face challenges in achieving a wide viewing angle and high optical performance while minimizing size and weight, with Fresnel lenses prone to image quality deterioration due to defects and serrated shapes affecting central regions.

Innovation Solution

The proposed observation optical system incorporates a Fresnel lens with a positive refractive power and a lens configuration where the ratio of specific lengths and diameters is optimized, ensuring a balanced refractive power distribution to reduce aberrations and weight, while maintaining a wide viewing angle.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If a Fresnel lens is used to reduce weight and achieve wide viewing angle, then weight is reduced and viewing angle is widened, but image quality deteriorates due to defects and serrated shapes

Engineering Contradiction:

Improveweight of observation optical systemVSAvoidimage quality

Core Design Contradiction:

Weight of moving objectVSReliability

Solution Approach 1:

The Fresnel lens is divided into multiple annular sections (first annular section, second annular section, third annular section) with different grating structures. Each section has optimized parameters (grating width, pitch, depth) to balance weight reduction with image quality maintenance, particularly protecting the central region from degradation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the Fresnel lens are assigned different structural characteristics. The first annular section (central region) has smaller grating width and pitch to maintain high image quality, while outer sections have larger dimensions for weight reduction. The grating depth also varies by region to optimize local optical performance.

Inventive Principle:

Principle #3Local quality

2Weight of moving object

If Fresnel lens with serrated shape is used to reduce weight, then weight is reduced, but image quality deteriorates in central area due to defectively formed parts

Engineering Contradiction:

Improveweight of Fresnel lensVSAvoidimage quality in central area

Core Design Contradiction:

Weight of moving objectVSManufacturing precision

Solution Approach 1:

The central first annular section uses smaller grating dimensions (narrower width, smaller pitch) compared to outer sections. This local optimization reduces the impact of manufacturing defects on central image quality while maintaining weight reduction benefits in outer regions.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The lens is segmented into annular sections with progressively different grating parameters. The first annular section's optimized small-grating structure specifically addresses central region image quality, while subsequent sections provide weight reduction.

Inventive Principle:

Principle #1Segmentation

3Adaptability or versatility

If lens configuration is optimized for wide viewing angle, then viewing angle is widened, but optical performance may deteriorate due to aberrations

Engineering Contradiction:

Improveviewing angleVSAvoidoptical performance

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

Each annular section is optimized for its specific function: the first section maintains central image quality with small gratings, the second section transitions with medium gratings, and the third section provides peripheral coverage with large gratings. This local optimization across zones achieves wide viewing angle while controlling aberrations.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The divided annular structure allows independent optimization of each section's grating parameters. This segmentation enables the lens to simultaneously achieve wide viewing angle coverage and maintain high optical performance by tailoring each zone's characteristics to its specific optical requirements.

Inventive Principle:

Principle #1Segmentation

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 enhances optical performance and reduces weight, preventing image quality deterioration by optimizing the Fresnel lens's shape and refractive power distribution, achieving a high optical performance and wide viewing angle.

Implementation Method 1

a Fresnel lens and a lens LP with a positive refractive power provided on a light incident side or a light emitting side of the Fresnel lens

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

a primary diffraction effect is used by providing a diffractive lens structure around the resin lens to suppress a focal position deviation of the resin lens attributable to a temperature fluctuation

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS11487050B2Observation optical system and observation apparatus including same

Publication Date: 2022.11.01 CANON KK

AI summary

An observation optical system according to the present invention includes a Fresnel lens and a lens LP with a positive refractive power provided on a light incident side or a light emitting side of the Fresnel lens. A length in a direction of an optical axis from a surface vertex of a central annular section of the Fresnel lens to an end portion of the central annular section is defined as h0, and a length in the direction of the optical axis of a grating wall surface of a first annular section adjacent to the central annular section is defined as h1. The lengths h1 and h0 are set to appropriate values, respectively.