Freeform optics has become the most prominent element of the optics industry. Advanced freeform optical designs supplementary to ultra-precision manufacturing and metrology techniques have upgraded the lifestyle, thin...Freeform optics has become the most prominent element of the optics industry. Advanced freeform optical designs supplementary to ultra-precision manufacturing and metrology techniques have upgraded the lifestyle, thinking, and observing power of existing humans.Imaginations related to space explorations, portability, accessibility have also witnessed sensible in today’s time with freeform optics. Present-day design methods and fabrications techniques applicable in the development of freeform optics and the market requirements are focussed and explained with the help of traditional and non-traditional optical applications. Over the years,significant research is performed in the emerging field of freeform optics, but no standards are established yet in terms of tolerances and definitions. We critically review the optical design methods for freeform optics considering the image forming and non-image forming applications. Numerous subtractive manufacturing technologies including figure correction methods and metrology have been developed to fabricate extreme modern freeform optics to satisfy the demands of various applications such as space, astronomy, earth science, defence,biomedical, material processing, surveillance, and many more. We described a variety of advanced technologies in manufacturing and metrology for novel freeform optics. Next, we also covered the manufacturing-oriented design scheme for advanced optics. We conclude this review with an outlook on the future of freeform optics design, manufacturing and metrology.展开更多
Using compressive sensing for imaging has many applications, and it is an important branch of computational imaging.In this Letter, freeform surfaces are introduced in the hardware optical system design of a compressi...Using compressive sensing for imaging has many applications, and it is an important branch of computational imaging.In this Letter, freeform surfaces are introduced in the hardware optical system design of a compressive sensing imager. The system works under the medium wave infrared band and realizes a 16× compression with a field-of-view of 7.5°× 6°. Good imaging performance is achieved in both the entire system and the freeform objective optics. Compared with the system using all spherical lenses, the volume of the freeform system is about 1/3 smaller, and the total transmittance is about 56%higher, which shows the benefits of using freeform surfaces for compressive sensing and computational imaging.展开更多
Current freeform illumination optical designs are mostly focused on producing prescribed irradiance distributions on planar targets.Here,we aim to design freeform optics that could generate a desired illumination on a...Current freeform illumination optical designs are mostly focused on producing prescribed irradiance distributions on planar targets.Here,we aim to design freeform optics that could generate a desired illumination on a curved target from a point source,which is still a challenge.We reduce the difficulties that arise from the curved target by involving its varying z-coordinates in the iterative wavefront tailoring(IWT)procedure.The new IWT-based method is developed under the stereographic coordinate system with a special mesh transformation of the source domain,which is suitable for light sources with light emissions in semi space such as LED sources.The first example demonstrates that a rectangular flat-top illumination can be generated on an undulating surface by a spherical-freeform lens for a Lambertian source.The second example shows that our method is also applicable for producing a non-uniform irradiance distribution in a circular region of the undulating surface.展开更多
Dear Editor Freeform optical surfaces have no axis of rotational invariance,thus providing more design degrees of freedom(DoFs)than conics and aspheres1,2.The additional DoFs can be used for aberration correction in c...Dear Editor Freeform optical surfaces have no axis of rotational invariance,thus providing more design degrees of freedom(DoFs)than conics and aspheres1,2.The additional DoFs can be used for aberration correction in compact folded imaging systems3–6 and for increasing efficiency and irradiance uniformity in illumination systems7–9.However,given their surface form complexity,freeform optics remain challenging to manufacture,test,and assemble1,9.Reference structures(RS)–physical features designed and fabricated in addition to the optical surfaces–are required to define a common coordinate system(CS)during the manufacturing process chain10–13.We present the conclusions of a literature and industry survey on the effective implementation of RS.We then demonstrate the benefits of an automated tool for generating CAD models with accurate NURBS freeform surfaces and effective RS to for use in manufacturing and metrology.We conclude with the design of a test framework for further evaluation and comparison of the effectiveness of various types of RS.展开更多
We present optical designs with freeform optics in the context of hyperspectral imaging.Results show designs that are 5×more compact in volume than similar designs using conventional spherical or aspherical surfa...We present optical designs with freeform optics in the context of hyperspectral imaging.Results show designs that are 5×more compact in volume than similar designs using conventional spherical or aspherical surfaces.We will show how combining the concepts of spatial and spectral-band broadening,which will be introduced in this paper,led to the improvement in compactness that is uniquely enabled by freeform optics.展开更多
Metrology challenges have increasingly been the bottleneck in the manufacturing of freeform optics.On-machine metrology has emerged as a potential solution to bridge the gap between measurement and machining processes...Metrology challenges have increasingly been the bottleneck in the manufacturing of freeform optics.On-machine metrology has emerged as a potential solution to bridge the gap between measurement and machining processes.It is widely recognised that metrology systems integrated with manufacturing platforms are affected by the dynamic characteristics of the host platform.However,there is a limited understanding of how these dynamic disturbances contribute to measurement error,primarily due to a lack of comprehensive system-level analysis.This paper aims to depict the relationship between mechanical vibration and measurement error in an on-machine surface measurement(OMSM)system and proposes a method to mitigate this error through system calibration.A dynamic error model of the OMSM system is developed,incorporating feed disturbances,machine dynamics,and the compliance of the measurement units.Our analysis identifies phase lag in the measurement unit as a primary contributor to the distortion of the measured surface figure.To address this issue,a calibration procedure is performed based on system transfer function identification.The proposed calibration method effectively reduces the residual error in high-speed measurements.Experimental results demonstrate a reduction of the peak-to-valley(PV)error from 6μm to 0.5μm,and a decrease in the root mean square(RMS)error from 2.3μm to 20 nm.Using this system,a high-density point cloud of 290,000 points was measured in 6 minutes,successfully meeting the challenges of measuring freeform surfaces on the manufacturing platform with both high accuracy and high efficiency.The proposed calibration method,which compensates for the absence of an independent metrology frame,can be adapted for other similar on-machine systems.This approach offers a cost-effective and timeefficient solution for the rapid prototyping of freeform optical components using integrated surface metrology.展开更多
基金the UK’s Engineering and Physical Sciences Research Council(EPSRC)funding of Future Metrology Hub(Ref.:EP/P006930/1)the UK’s Science and Technology Facilities Council(STFC)Innovation Partnership Scheme(IPS)project under Grant Agreement No.ST/V001280/1the European Union’s Horizon 2020research and innovation programme under Grant Agreement No.767589。
文摘Freeform optics has become the most prominent element of the optics industry. Advanced freeform optical designs supplementary to ultra-precision manufacturing and metrology techniques have upgraded the lifestyle, thinking, and observing power of existing humans.Imaginations related to space explorations, portability, accessibility have also witnessed sensible in today’s time with freeform optics. Present-day design methods and fabrications techniques applicable in the development of freeform optics and the market requirements are focussed and explained with the help of traditional and non-traditional optical applications. Over the years,significant research is performed in the emerging field of freeform optics, but no standards are established yet in terms of tolerances and definitions. We critically review the optical design methods for freeform optics considering the image forming and non-image forming applications. Numerous subtractive manufacturing technologies including figure correction methods and metrology have been developed to fabricate extreme modern freeform optics to satisfy the demands of various applications such as space, astronomy, earth science, defence,biomedical, material processing, surveillance, and many more. We described a variety of advanced technologies in manufacturing and metrology for novel freeform optics. Next, we also covered the manufacturing-oriented design scheme for advanced optics. We conclude this review with an outlook on the future of freeform optics design, manufacturing and metrology.
基金This work was supported by the National Key Research and Development Program of China(No.2017YFA0701200)National Natural Science Foundation of China(No.61805012)Young Elite Scientist Sponsorship Program by CAST(No.2019QNRC001)。
文摘Using compressive sensing for imaging has many applications, and it is an important branch of computational imaging.In this Letter, freeform surfaces are introduced in the hardware optical system design of a compressive sensing imager. The system works under the medium wave infrared band and realizes a 16× compression with a field-of-view of 7.5°× 6°. Good imaging performance is achieved in both the entire system and the freeform objective optics. Compared with the system using all spherical lenses, the volume of the freeform system is about 1/3 smaller, and the total transmittance is about 56%higher, which shows the benefits of using freeform surfaces for compressive sensing and computational imaging.
基金We are grateful for financial supports from National Key Research and Development Program(Grant No.2017YFA0701200)National Science Foundation of China(No.11704030).The author Z X Feng thanks the valuable discussions with Xu-Jia Wang and Rengmao Wu.
文摘Current freeform illumination optical designs are mostly focused on producing prescribed irradiance distributions on planar targets.Here,we aim to design freeform optics that could generate a desired illumination on a curved target from a point source,which is still a challenge.We reduce the difficulties that arise from the curved target by involving its varying z-coordinates in the iterative wavefront tailoring(IWT)procedure.The new IWT-based method is developed under the stereographic coordinate system with a special mesh transformation of the source domain,which is suitable for light sources with light emissions in semi space such as LED sources.The first example demonstrates that a rectangular flat-top illumination can be generated on an undulating surface by a spherical-freeform lens for a Lambertian source.The second example shows that our method is also applicable for producing a non-uniform irradiance distribution in a circular region of the undulating surface.
基金supported by the industry members of the Center for Freeform Optics(CeFO)and the National Science Foundation(IIP-1822049 and IIP-1822026,EEC-2310640,EEC-2310681).
文摘Dear Editor Freeform optical surfaces have no axis of rotational invariance,thus providing more design degrees of freedom(DoFs)than conics and aspheres1,2.The additional DoFs can be used for aberration correction in compact folded imaging systems3–6 and for increasing efficiency and irradiance uniformity in illumination systems7–9.However,given their surface form complexity,freeform optics remain challenging to manufacture,test,and assemble1,9.Reference structures(RS)–physical features designed and fabricated in addition to the optical surfaces–are required to define a common coordinate system(CS)during the manufacturing process chain10–13.We present the conclusions of a literature and industry survey on the effective implementation of RS.We then demonstrate the benefits of an automated tool for generating CAD models with accurate NURBS freeform surfaces and effective RS to for use in manufacturing and metrology.We conclude with the design of a test framework for further evaluation and comparison of the effectiveness of various types of RS.
基金supported under the NSF I/UCRC Center for Freeform Optics(IIP-1338877 and IIP-1338898)。
文摘We present optical designs with freeform optics in the context of hyperspectral imaging.Results show designs that are 5×more compact in volume than similar designs using conventional spherical or aspherical surfaces.We will show how combining the concepts of spatial and spectral-band broadening,which will be introduced in this paper,led to the improvement in compactness that is uniquely enabled by freeform optics.
基金UK’s Engineering and Physical Sciences Research Council(EPSRC)funded programmes EP/P006930/1,EP/Z53285X/1UK’s STFC-IPS funding ST/W005263/1+1 种基金the Innovation Launchpad Network+programme RIR26E230613-1the UK’s Royal Academy of Engineering(RAEng)and Renishaw PLC who cosponsor Prof.Jiang’s RAEng/Renishaw Research Chair.
文摘Metrology challenges have increasingly been the bottleneck in the manufacturing of freeform optics.On-machine metrology has emerged as a potential solution to bridge the gap between measurement and machining processes.It is widely recognised that metrology systems integrated with manufacturing platforms are affected by the dynamic characteristics of the host platform.However,there is a limited understanding of how these dynamic disturbances contribute to measurement error,primarily due to a lack of comprehensive system-level analysis.This paper aims to depict the relationship between mechanical vibration and measurement error in an on-machine surface measurement(OMSM)system and proposes a method to mitigate this error through system calibration.A dynamic error model of the OMSM system is developed,incorporating feed disturbances,machine dynamics,and the compliance of the measurement units.Our analysis identifies phase lag in the measurement unit as a primary contributor to the distortion of the measured surface figure.To address this issue,a calibration procedure is performed based on system transfer function identification.The proposed calibration method effectively reduces the residual error in high-speed measurements.Experimental results demonstrate a reduction of the peak-to-valley(PV)error from 6μm to 0.5μm,and a decrease in the root mean square(RMS)error from 2.3μm to 20 nm.Using this system,a high-density point cloud of 290,000 points was measured in 6 minutes,successfully meeting the challenges of measuring freeform surfaces on the manufacturing platform with both high accuracy and high efficiency.The proposed calibration method,which compensates for the absence of an independent metrology frame,can be adapted for other similar on-machine systems.This approach offers a cost-effective and timeefficient solution for the rapid prototyping of freeform optical components using integrated surface metrology.
