Athermalized Beam Expander Using Folded Optical Path
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Solution Overview
Problem
Current beam expanders are large, difficult to manufacture, and struggle with maintaining diffraction-limited performance across a wide temperature range, particularly from −40 degrees Celsius to +75 degrees Celsius, and often obscure the laser beam or require external pupils, making them unsuitable for compact applications.
Innovation Solution
A compact, all-refractive Keplarian telescope beam expander design using Silicon and Cleartran lens groups with a Titanium alloy housing, which maintains diffraction-limited performance over the 1460-1675 nm wavelength range and operates effectively across harsh thermal conditions through athermalization, minimizing overall length and peak-to-valley wavefront error.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional beam expanders are used to achieve 5x magnification, then beam expansion is achieved, but the overall length becomes very long (275-375 mm)
Solution Approach 1:
The patent employs a folded optical path design where the beam travels through lens groups in a nested configuration. The beam enters the first lens group, reflects off a mirror, passes through a second lens group, and exits, creating a compact folded path that achieves 5x magnification in less than 85 mm length by nesting optical components within each other's spatial envelope.
Solution Approach 2:
The patent transitions from a linear one-dimensional optical path to a multi-dimensional folded path by introducing mirrors and angled beam paths. This allows the optical train to fold back on itself, utilizing three-dimensional space efficiently and reducing the overall length from the conventional 275-375 mm to less than 85 mm while maintaining 5x magnification.
2Volume of moving object
If beam expanders are designed for compact size, then space is saved, but diffraction limited performance over wide temperature ranges cannot be maintained
Solution Approach 1:
The patent selects lens materials with specific thermal-optical parameters (dn/dT values) that compensate for thermal expansion effects. By carefully choosing materials whose refractive index changes with temperature in a controlled manner, the design maintains diffraction-limited performance across the -40°C to +75°C temperature range despite the compact form factor.
Solution Approach 2:
The patent uses a composite material approach by combining different lens materials (e.g., silicon, germanium, zinc selenide) with complementary thermal-optical properties in the lens groups. This allows the optical system to compensate for thermal effects through the combined behavior of different materials, maintaining performance consistency over wide temperature ranges in the compact design.
3Ease of manufacture
If refractive beam expanders are used, then beam expansion is achieved, but the system becomes large and difficult to manufacture
Solution Approach 1:
The patent divides the beam expander into separate lens groups (first lens group, second lens group) that can be independently manufactured and then assembled. This segmentation allows each group to be optimized and fabricated separately using standard optical manufacturing techniques, reducing overall manufacturing difficulty while achieving the compact form factor and 5x magnification.
4Length of moving object
If reflective beam expanders are used, then compact size is achieved, but laser beam obscuration occurs
Solution Approach 1:
The patent applies local quality by using reflective surfaces (mirrors) only in specific locations where they do not intersect or obscure the main laser beam path. The mirrors are positioned to fold the beam path at angles that avoid blocking the beam, allowing compact size to be achieved without the harmful effect of beam obscuration that plagues conventional reflective designs.
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 a compact, diffraction-limited beam expander that maintains performance across a wide temperature range without adjustments, reducing the overall length and ensuring minimal obscuration of the laser beam, suitable for applications requiring high resolution and thermal stability.
Implementation Method 1
The change in focus position due to the dn/dt of the lens materials compensates for the change in housing length due to the housing coefficient of thermal expansion
Implementation Method 2
a receive lens group having at least a first, a second, and a third lens comprising materials that have a change of index of refraction over change in temperature
Implementation Method 3
Beam expanders are a type of optical device that expands the size of a collimated beam of light
Data Source
AI summary
A passive 5x athermalized afocal beam expander comprising a housing integrally formed of a single material. Using titanium for the housing as well as lens materials having a minimal change of index of refraction over changes in temperature provides for a 5x athermalized afocal beam expander constructed to operate in a wavelength range from about 1460 nm to about 1675 nm at temperatures ranging from about −40 degrees Celsius to about +75 degrees Celsius.