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Photonics
Special Issues
New Advances in Freeform Optics Design
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New Advances in Freeform Optics Design

A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (20 May 2024) | Viewed by 11670

Special Issue Editors

Dr. Zhengbo Zhu

E-Mail Website
Guest Editor
School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, China
Interests: lighting; light emitting diodes free-form; optical design
Dr. Shili Wei

E-Mail Website
Guest Editor
Department of Optics and Electronics Engineering, Huazhong University of Science and Technology, Wuhan, China
Interests: freeform optics for illumination; freeform optics for imaging; laser optics

Special Issue Information

Dear Colleagues,

Freeform surfaces have no rotation symmetry or translation symmetry, a high degree of freedom in optical design, and a flexible spatial layout. It is these characteristics that liberate both designers and engineers from the restrictions of optical surface geometry, enabling them to achieve compact, lightweight, and efficient optics systems with excellent optical performances. In the last 10 years, freeform optics have facilitated compact and high-performing optical systems, including space cameras, illumination optics, helmet displays, and other optical systems. Advancing the theory of optical design for freeform surfaces, improving the manufacturing precision and testing accuracy of freeform optical components, reducing the manufacturing costs, and expanding the application range of freeform optics are thus the goals of both the academic community and the related industry.

This Special Issue invites manuscripts that introduce the recent advances in “Freeform Optics Design”. All theoretical, numerical, and experimental papers are accepted. Possible topics include, but are not limited to, the following:

  • Freeform optics design theory;
  • Freeform optics machining;
  • Freeform optics inspection;
  • Freeform optics installation;
  • Optical freeform surface installation;
  • Freeform surface type characterization;
  • The applications of freeform optics.

Dr. Zhengbo Zhu
Dr. Shili Wei
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • freeform surface
  • freeform imaging
  • freeform illumination

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Further information on MDPI's Special Issue polices can be found here.

Published Papers (5 papers)

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Research

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13 pages, 5982 KiB  
Article
Comparative Study on the Interest in Non-Uniform Rational B-Splines Representation versus Polynomial Surface Description in a Freeform Three-Mirror Anastigmat
by Clément Freslier, Guillaume Druart, Alice Fontbonne, Thierry Lépine, Christophe Buisset, Tibor Agocs, Arnaud Heliere, Fanny Keller, Jean-Baptiste Volatier, Stéphane Beaussier and Paul Jougla
Photonics 2024, 11(9), 875; https://doi.org/10.3390/photonics11090875 - 18 Sep 2024
Viewed by 883
Abstract
Novel freeform optical design methods can be classified in two categories, depending on whether they focus on the generation of a starting point or the development of new optimization tools. In this paper, we design a freeform three-mirror anastigmat (TMA) and compare different [...] Read more.
Novel freeform optical design methods can be classified in two categories, depending on whether they focus on the generation of a starting point or the development of new optimization tools. In this paper, we design a freeform three-mirror anastigmat (TMA) and compare different surface representations using either a differential ray tracer as a new optimization tool or a commercial ray tracer (ANSYS-ZEMAX OpticStudio). For differential ray tracing, we used FORMIDABLE (Freeform Optics Raytracer with Manufacturable Imaging Design cApaBiLitiEs), an optical design library with differential ray tracing and Non-Uniform Rational B-Splines (NURBS) optimization capabilities, available under the European Software Community License (ESCL). NURBS allow a freeform surface to be represented without needing any prior knowledge of the surface, such as the polynomial degree in polynomial descriptions. OpticStudio and other commercial optical design software are designed to optimize polynomial surfaces but are not well-suited to optimize NURBS surfaces, requiring a custom optical design library. In order to demonstrate the interest in using NURBS representation, we designed and independently optimized two freeform telescopes over different iteration cycles; with NURBS using FORMIDABLE or with XY polynomials using OpticStudio. We then compared the resulting systems using their root mean square field maps to assess the optimization quality of each surface representation. We also provided a full-system comparison, including mirror freeform departures. This study shows that NURBS can be a relevant alternative to XY polynomials for the freeform optimization of reflective three-mirror telescopes as it achieves more a uniform imaging quality in the field of view. Full article
(This article belongs to the Special Issue New Advances in Freeform Optics Design)
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15 pages, 13360 KiB  
Article
Design Method for Freeform Off-Axis Three-Mirror Anastigmat Optical Systems with a Large Field of View and Low Error Sensitivity
by Chengming Ren and Qingyu Meng
Photonics 2024, 11(3), 211; https://doi.org/10.3390/photonics11030211 - 26 Feb 2024
Cited by 1 | Viewed by 1752
Abstract
A freeform off-axis three-mirror anastigmat (TMA) optical system with a large field of view (FOV) can obtain target image information with a larger spatial range and more spatial details, which is a development trend within the realm of space optics. The optical aberration [...] Read more.
A freeform off-axis three-mirror anastigmat (TMA) optical system with a large field of view (FOV) can obtain target image information with a larger spatial range and more spatial details, which is a development trend within the realm of space optics. The optical aberration increases exponentially with the FOV, resulting in a significant increase in error sensitivity for large-FOV optical systems. To address this issue, a method for designing optical systems with a large FOV and low error sensitivity is proposed. The FOV is gradually expanded from a small initial value in equal-length increments until it reaches the full FOV. At each step, the error sensitivity is recalculated and controlled to a lesser extent than in the previous step. In this design process, the freeform surface is used to correct the aberration and obtain low error sensitivity. An optical system with a focal length of 1000 mm and an F-number of 10 is used as an example, and the FOV is enlarged from 5° × 1° to 20° × 4°. The design results show that the modulation transfer function (MTF) of the optical system can reach 0.45@50 lp/mm, and the average wavefront aberration is 0.029λ. After four rounds of FOV expansion and error sensitivity optimization, the error sensitivity is reduced by 37.27% compared to the initial system, which verifies the correctness and practicality of the method. Full article
(This article belongs to the Special Issue New Advances in Freeform Optics Design)
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16 pages, 4358 KiB  
Article
Design of a Spaceborne, Compact, Off-Axis, Multi-Mirror Optical System Based on Freeform Surfaces
by Baohua Wang, Xiaoyong Wang, Huilin Jiang, Yuanyuan Wang, Chao Yang and Yao Meng
Photonics 2024, 11(1), 51; https://doi.org/10.3390/photonics11010051 - 3 Jan 2024
Cited by 1 | Viewed by 1551
Abstract
Based on the application requirements of high spectral resolutions, high spatial resolutions and wide swatches, a new-generation, high-performance, spaceborne, hyperspectral imaging spectrometer (NGHSI) with a spatial resolution of 15 m and a swatch of 90 km is proposed. The optical system of the [...] Read more.
Based on the application requirements of high spectral resolutions, high spatial resolutions and wide swatches, a new-generation, high-performance, spaceborne, hyperspectral imaging spectrometer (NGHSI) with a spatial resolution of 15 m and a swatch of 90 km is proposed. The optical system of the NGHSI has a focal length of 1128 mm, an F-number of three, a field of view (FOV) of 7.32° and a slit length of 144 mm. A new off-axis, multi-mirror telescope structure with intermediate images is put forward, which solves the design problem that realizes secondary imaging and good telecentricity at the same time. And a new off-axis lens-compensation Offner configuration is adopted to address the challenge of the high-fidelity design of spectral imaging systems with long slit lengths. The relationship between X-Y polynomials and aberration coefficients is analyzed, and the X-Y polynomial freeform surfaces are used to correct the off-axis aberrations. The design results show that the image quality of the telescope system is close to the diffraction limit. The smile, known as the spectral distortion along the line, and keystone, which is the magnification difference for different wavelengths, of the spectral imaging system are less than 1/10 pixel size. The complete optical system of the NGHSI, including the telescope system and the spectral imaging system, has excellent imaging quality and the layout is compact and reasonable, which realizes the miniaturization design. Full article
(This article belongs to the Special Issue New Advances in Freeform Optics Design)
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16 pages, 13878 KiB  
Article
Design of Dual-Focal-Plane AR-HUD Optical System Based on a Single Picture Generation Unit and Two Freeform Mirrors
by Chengxiang Fan, Lingbao Kong, Bo Yang and Xinjun Wan
Photonics 2023, 10(11), 1192; https://doi.org/10.3390/photonics10111192 - 26 Oct 2023
Cited by 6 | Viewed by 2964
Abstract
Augmented reality heads-up displays (AR-HUDs) have a much richer display than traditional heads-up displays. An ideal AR-HUD requires two or more focal planes to display basic and interactive driving information to the car driver separately. We present an off-axis reflective optical structure for [...] Read more.
Augmented reality heads-up displays (AR-HUDs) have a much richer display than traditional heads-up displays. An ideal AR-HUD requires two or more focal planes to display basic and interactive driving information to the car driver separately. We present an off-axis reflective optical structure for dual-focal-plane displays using a single projection-type picture generation unit (PGU) and two freeform mirrors. The dual-focal-plane AR-HUD system designed in this paper can simultaneously generate high-quality far-field image (13° × 4°, 10 m) and near-field images (13° × 1.4°, 3.5 m) in a 130 mm × 60 mm eyebox. A fully automated analysis program is written to analyze the modulation transfer function (MTF) and distortion values of the optical system over the entire eyebox range. The analysis results show that the maximum distortion values of the far-field image and near-field image in the eyebox range are 3.15% and 3.58%, respectively. The MTF was greater than 0.3 at 7.2 lp/mm for both near-field images and far-field images. We also designed a projection lens for the projection-type PGU used in this system. The projection lens uses three plane mirrors to fold the image plane of the projection system into different positions to serve as the image source for the AR-HUD. This research provides a new solution for realizing the dual-focal-plane AR-HUD, which not only satisfies the need for simultaneous display of near-field basic information and far-field interactive information, but also has a larger display screen. Full article
(This article belongs to the Special Issue New Advances in Freeform Optics Design)
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Review

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15 pages, 9217 KiB  
Review
Advanced Study of Optical Imaging Systems for Virtual Reality Head-Mounted Displays
by Zhongju Ren, Xiuhua Fu, Keyan Dong, Ying Lai and Jingjing Zhang
Photonics 2023, 10(5), 555; https://doi.org/10.3390/photonics10050555 - 10 May 2023
Cited by 6 | Viewed by 3406
Abstract
Driven by the rapid innovation of science and technology and industrial manufacturing technology, virtual reality display technology has developed rapidly. At present, the application of virtual reality display technology is expanding in many fields such as military, medical, aviation and education. This paper [...] Read more.
Driven by the rapid innovation of science and technology and industrial manufacturing technology, virtual reality display technology has developed rapidly. At present, the application of virtual reality display technology is expanding in many fields such as military, medical, aviation and education. This paper analyzes the imaging principle of the human vision system and the optical performance requirements of VR heads-up display, summarizes the current design scheme of VR heads-up optical imaging system, focuses on the principle and index parameters of each optical system, and compares the advantages and disadvantages of different schemes. The development prospects and directions of virtual reality headset displays are also prospected. Full article
(This article belongs to the Special Issue New Advances in Freeform Optics Design)
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