Freeform Three-Mirror Telescope for Compact FSOC Wavefront Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing free space optical communication systems require large collection apertures and are constrained by volume and mass requirements, with central obscuration causing light loss and impractical path lengths, making them unsuitable for space applications.
Innovation Solution
A compact, three-mirror telescope system with at least one freeform mirror and one aspheric mirror, featuring a folded optical path and off-axis arrangement, which corrects wavefront aberrations and maintains polarisation, allowing for a large aperture and reduced volume and mass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large collection aperture is used to maximize photon collection and reduce transmit power requirements, then the optical performance and link budget are improved, but the volume and mass requirements increase making the system impractical for space applications
Solution Approach 1:
The patent implements a folded optical path where the light beam traverses the same physical space multiple times through successive reflections between mirrors. This nesting of the optical path allows a long effective optical path length to be contained within a compact physical volume, resolving the contradiction between large aperture requirements and space constraints.
Solution Approach 2:
The patent uses a three-mirror configuration with off-axis arrangements that fold the optical path into three dimensions. By utilizing multiple spatial dimensions for mirror placement and beam folding, the system achieves a long optical path length equivalent to a much larger physical telescope, thereby maintaining optical performance while reducing the physical volume and mass of the system.
2Measurement precision
If a rotationally symmetric optical system is used to reduce aberrations by increasing optical path length, then the wavefront quality is improved, but the path length becomes impractically long for space-based applications
Solution Approach 1:
The folded optical path design causes the light beam to traverse the same physical region multiple times through sequential mirror reflections. This nesting effect accumulates the optical path length within a compact space, achieving the wavefront quality improvements associated with long path lengths without requiring an impractically long physical telescope structure.
Solution Approach 2:
The patent employs an off-axis three-mirror configuration where the mirrors are positioned and angled to dynamically fold the optical path. This dynamic arrangement of reflective surfaces creates multiple beam bounces within a short physical distance, effectively increasing the optical path length while maintaining a compact form factor suitable for space applications.
3Device complexity
If a central obscuration is present in the optical system, then the rotationally symmetric design is simplified, but light losses of up to 33% occur reducing system efficiency
Solution Approach 1:
The patent removes the central obscuration element from the optical path by using an off-axis mirror configuration. The mirrors are positioned such that the light beam does not need to pass through or around a central support structure, thereby eliminating the source of light loss and blockage while still achieving aberration correction through the freeform mirror surfaces.
Solution Approach 2:
The patent employs asymmetric off-axis mirror positioning and freeform surface geometries that deliberately break rotational symmetry. This asymmetric configuration eliminates the need for central obscuration while providing the degrees of freedom needed to correct wavefront aberrations, thereby maintaining optical simplicity without the penalty of light loss.
4Adaptability or versatility
If the field of view is increased to improve coverage area, then the system versatility is improved, but wavefront aberrations increase degrading optical performance
Solution Approach 1:
The patent uses freeform mirror surfaces with locally varying curvatures and orientations tailored to specific regions of the optical path. These localized surface variations are designed to correct wavefront aberrations that arise at different field angles, enabling the system to maintain diffraction-limited performance across a wide field of view by addressing each region's specific optical quality requirements.
Solution Approach 2:
The freeform mirror surfaces incorporate continuously varying geometric parameters across their surfaces, allowing the optical system to dynamically adjust the wavefront correction for different field angles. This parameter variation in the mirror surfaces enables simultaneous correction of aberrations across a wide field of view, maintaining high optical performance while increasing system versatility.
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 system provides a diffraction-limited performance across a wide field of view, maintaining optical performance in extreme space environments and enabling high data transfer rates for satellite and terrestrial links.
Implementation Method 1
at least one mirror comprises a freeform mirror configured to control the distribution of light in the focal plane to provide correction of wavefront aberrations across a field of view of the system
Implementation Method 2
the telescope is configured to receive an incident light beam and to focus the light beam to a telescope focal plane as input to the optical bench
Implementation Method 3
The telescope comprises an off-axis three-mirror telescope, wherein each mirror has a tilted and decentered local coordinate system with respect to a central axis
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
There is provided a telescope for use in an optical terminal system configured for free space optical communication, FSOC, configured to operate in earth orbit, and/or for terrestrial line-of-sight links. The optical terminal system comprises the telescope and an optical bench. The the telescope (200) is configured to receive an incident light beam (500) and to focus the light beam to a telescope focal plane (250) as input to the optical bench. The telescope comprising: a primary mirror; a secondary mirror; and a tertiary mirror. At least one mirror comprises a freeform mirror configured to control the distribution of light in the focal plane to provide correction of wavefront aberrations across a field of view of the system. Also provided is an optical terminal system comprising the telescope and an optical bench.