Recently, freeform surfaces have been widely used in various optical systems because of their high flexibility and ability to correct aberrations when off-axis optical components are considered. Among freeform optics there are the head-up displays (HUDs) for vehicles, HUDs are increasingly used in new vehicles as they keep the driver’s head up and eyes focused on the road for the sake of improved safety. Fora compact size in the limited space of the vehicle, an HUD is typically an off-axis mirror system (including the windshield). The freeform mirror is not only employed to correct the off-axis aberrations caused by the windshield but also is used to provide an optical power for system magnification. This paper focuses on the design, fabrication, and measurement of a freeform mirror developed for a vehicle HUD system. We herewith report the design of the freeform surface including extended its polynomials description and its optimization. Using an ultra-high precision manufacturing and metrology strategy that is based on the use of a multi-axis machining center and advanced nano-metric profiler, the form error of the freeform mirror was precisely controlled according to system requirement. The fabricating method was realized on a machine equipped with a servo tool servo (STS) a and the combination of CXZ coordinates was programmed,. Finally, the freeform surface is fabricated and measured experimentally by ultrahigh accurate 3D profilometer.
The design of the ultra miniaturized camera using 3D-printing technology directly printed on to the complementary metal-oxide semiconductor (CMOS) imaging sensor is presented in this paper. The 3D printed micro-optics is manufactured using the femtosecond two-photon direct laser writing, and the figure error which could achieve submicron accuracy is suitable for the optical system. Because the size of the micro-level camera is approximately several hundreds of micrometers, the resolution is reduced much and highly limited by the Nyquist frequency of the pixel pitch. For improving the reduced resolution, one single-lens can be replaced by multiple-aperture lenses with dissimilar field of view (FOV), and then stitching sub-images with different FOV can achieve a high resolution within the central region of the image. The reason is that the angular resolution of the lens with smaller FOV is higher than that with larger FOV, and then the angular resolution of the central area can be several times than that of the outer area after stitching. For the same image circle, the image quality of the central area of the multi-lens system is significantly superior to that of a single-lens. The foveated image using stitching FOV breaks the limitation of the resolution for the ultra miniaturized imaging system, and then it can be applied such as biomedical endoscopy, optical sensing, and machine vision, et al. In this study, the ultra miniaturized camera with multi-aperture optics is designed and simulated for the optimum optical performance.
In this paper we propose an intuitive concept for manufacturing and inspecting of aspherical components. Two types,
parabolic and cylinder, of plano-convex and plano-concave aspherical lenses were made by LOH 120S form generation
machine. Three form error measurement methods were used known as coordinate measuring machine (CMM),
interferometer with CGH null lens and inspection with combined pair lenses. Ultra high accuracy CMM from Panasonic
Co., CGH cylinder null and CGH aspheric null from Diffraction International and OWI 150 ASPH CGH interferometer
from OptoTech GmbH play the roll for measurement. CMM was used as a surface profiler to inspect the surface shape,
and the software GRAPHER was also used as analysis tool to exam asphere numerical datum. The difference between
theoretical and practical is as a surface polishing revised reference. The finished plano-convex and plano-concave
aspherical lenses can be combined to be a plane lens. The individual and combined lenses were inspected on
OPTOTECH OWI 150 ASPH CGH interferometer. The compared interference patterns have shown with the Diffration
International CGH Aspheric Null "ASPHERIC 1" and CGH Cylinder Null "H80F2C". Through the procedure, the
combined plano-convex and plano-concave aspherical lenses should be a perfect match plane lens and the individual lens
might be an aspherical test standard element for quick inspection.
Three ultra-precision machining processes namely fast tool servo, slow tool servo and diamond milling, are frequently
used to produce optical freeform surface. Slow tool servo machining has the advantages of no extra attachment and fast
setting-up, however the three dimensional tool shape compensation and tool-path generation must be conducted carefully
for getting high form accuracy and fine surface finish. This research aimed to develop a model of three dimensional tool
shape compensation for generating 3D tool path in slow tool servo diamond turning of asymmetrically toric surface for
astigmatic contact lens. The form accuracy of freeform surface was measured by ultra-high accuracy 3D profilometer
(UA3P) with user define function. After correction, the form error is less than 0.5μm both in X- and Y-direction and the
surface roughness is less than 5nm.
A new process that improves the surface roughness of microlens array after the excimer laser machining is studied. The results show that the smoother surface has been fabricated by this innovatory method. The excimer laser with mask projection machining has been successfully applied for the fabrication of 2.5D micro parts. Furthermore, the workpiece dragging machining is capable of manufacturing microstructure array with curved surface by using various shape of mask. But during the machining process, the laser is cutting shoot by shoot and the material is gradually removed layer by layer. The laser marks on the curved surface of micro lens array is obvious and inevitable. This defect limits the product of dragging in real optical application. To overcome this drawback, an improved process is studied. When the desired shape of lens array was machined by the excimer laser machining, the attaching photo resist with the thickness of several micro meter is coated on the rough surface by spin coating or spraying. Then the lens array is baked to get the mirror surface. This original method combines the advantage of the higher fill factor and the smoother surface for the fabrication of micro lens array.
PMMA (polymethyl methacrylate) has been widely used as x-ray LIGA material for its good features of electrical acid plating of all common metals to industrial applications. Unlike the tough characteristics of polyimide in almost all alkaline and acid solutions, PMMA is easily removed in chemical etchants after electroplating process. For this reason, ablation- etching characteristics of PMMA material for 3D microstructures fabrication using a 248 nm KrF excimer laser were investigated. Moreover, the uses of the laminated dry film were also studied in this work. Experimental results show that PMMA microstructures can produce the near-vertical side- wall profile as the laser fluence up to 2.5 J/cm2. PMMA templates with high aspect ratio of around 25 were demonstrated, and the sequential electroplating processes have realized the metallic microstructures. Moreover, the microstructures fabricated in dry film show the perfect side- wall quality, and no residues of debris were found.