Off-axis Freeform Mirror Mode Conversion
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Solution Overview
Problem
Existing mode conversion apparatuses for laser systems face challenges in preserving polarization and optimizing optical design, particularly in off-axis optical systems where linear astigmatism and polarization changes occur, leading to inefficiencies and light loss.
Innovation Solution
A mode conversion apparatus utilizing two freeform-surface mirrors, where the surface shapes are determined by specific optical parameters and freeform-surface coefficients, to convert incident light while preserving polarization and eliminating linear astigmatism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an on-axis optical system is used in a reflective telescope, then the structure is simple and easy to manufacture, but the central portion of the primary mirror is obscured by the secondary mirror causing significant light loss
Solution Approach 1:
The patent applies asymmetry by transitioning from an on-axis to an off-axis optical system. The off-axis configuration eliminates the central obscuration problem by positioning the secondary mirror away from the optical axis, allowing the laser beam to pass through the central region of the primary mirror unobstructed. This asymmetric arrangement resolves the contradiction by sacrificing some structural simplicity to eliminate light loss.
2Loss of energy
If an off-axis optical system is used to avoid shielding, then light loss is reduced, but linear astigmatism occurs degrading image quality
Solution Approach 1:
The patent employs parameter changes by optimizing the off-axis angle and mirror surface curvatures to control and minimize linear astigmatism. By carefully selecting specific optical parameters (off-axis angle, radius of curvature, mirror spacing), the system achieves a balance where light loss is reduced while image quality degradation from astigmatism is kept within acceptable limits.
3Loss of energy
If conventional mirrors are used in off-axis configuration, then shielding is avoided, but polarization is not preserved
Solution Approach 1:
The patent applies local quality by using polarization-preserving mirrors with specific surface coatings and orientations at different locations in the optical path. The first and second mirrors are configured with particular incident angles and surface properties that maintain polarization states locally, ensuring that the overall system preserves polarization despite the off-axis configuration.
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 apparatus effectively converts the mode of incident light while maintaining polarization, optimizing optical parameters, and suppressing higher order modes, making it suitable for applications such as squeezed vacuum light, gravitational wave detection, and laser interception systems.
Implementation Method 1
a first freeform-surface mirror configured to reflect incident light provided from a front-end optical system and output the reflected light in a first direction
Implementation Method 2
a second freeform-surface mirror configured to reflect the reflected light and output mode-converted light in a second direction corresponding to a rear-end optical system
Data Source
AI summary
A mode conversion apparatus includes a first freeform-surface mirror to reflect incident light provided from a front-end optical system and output the reflected light in a first direction, and a second freeform-surface mirror to reflect the reflected light and output mode-converted light in a second direction where surface shapes of the first and second mirrors are determined based on a freeform-surface coefficient determined by at least five optical parameters of a distance from the first mirror to a confocal point of the first mirror and the second mirror, a distance from the confocal point to the second mirror, a distance from a waist of the incident light to the first mirror, a distance from the second mirror to a waist of the mode-converted light, and an incident angle of the incident light for the first mirror and an incident angle of the reflected light for the second mirror.