Wei-Yao Hsu

Slow tool servo diamond turning of optical freeform surface for astigmatic contact lens

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.

Study of air-driving fluid jet polishing

In this study, we proposed an air-driving fluid jet polishing (FJP) system which draws slurry utilizing an air/water mixer. The air-driving FJP system is mainly comprised by an air/water mixer, slurry tank with stirrer, compressed air, pressure and flow rate regulators, and a nozzle. The high speed air flow in the air/water mixer draws out the slurry from the slurry tank, and the slurry is guided to mix with air flow inside the nozzle cavity. Then, the combined fluid slurry is emitted from the nozzle. The air-driving FJP system was preliminarily tested on N-BK7 and ZERODUR® plates with different air pressure and processing time. The test results show that the air-driving system could get a Gaussian-like removal shape with 3 kg/cm2 compressed air source and the depth of removal is about 100 nm within 5 seconds processing time. The compressed air improves the kinetic energy of each abrasive, and makes it more efficient in material removal. Furthermore, the Gaussian-like removal shape is more convenient for tool path planning and surface waviness control of corrective polishing.

Study on measurement of 160 mm convex hyperbolic mirror for Cassegrain reflecting system

In this study, the measurement of a 160 mm convex hyperbolic mirror by using the 6 inches phase shifting interferometer and the CGH (computer-generated hologram) in a vertical setup is presented. The wavefront errors of the metrology system including the reference flat and CGH flat due to gravity effect are measured and calibrated by using random testing and null cavity testing with and without CGH. Then, the real form error of each single sub-aperture could be acquired by subtracting the system wavefront errors. In this study, we measured form errors of 10 off-axis sub-apertures with equal angle space and then stitched them to establish the whole irregularity in the shape of the mirror in 160 mm diameter. Finally, we imported the irregularity in the shape of the mirror to the CNC aspheric polishing machine for correction polishing. Combining the aspheric metrology technique and the CNC aspheric polishing technique, a 160 mm secondary mirror for the Cassegrain reflecting system was finished within PV 0.15μm and RMS 17.9 nm.

Design and development of bi-directional viewer

Bi-directional viewer just likes a lens of camera. Unlike conventional camera lens, the bi-directional viewer captures not only front view but also side view around the bi-directional viewer. The barrel of bi-directional viewer was designed to have cuts in the side to allow side light to come through, and we use two aspherical mirrors to receive and change the side light to converge on the main optical path. The front view and side view can be imaged simultaneously on an image sensor. Commercial aspherized achromatic lens and micro video lens were also used to keep the image quality and miniaturize the size of the bi-directional viewer respectively. We report on the development of bi-directional viewer, including optical design, optical simulation, optomechanics design, fabrication techniques, assembly procedure and performance testing. The MTF of the bi-directional viewer is also measured and discussed in this paper. We successfully design and realize a bi-directional viewer, which can perform 100 lp/mm spatial frequency image in detail above 20% contrast in the 7.6 mm front view area. And we keep the dimensions of this device within 35 mm in total length and Φ20 mm in diameter.

Freeform mirror polishing for compensation on non-symmetry system aberrations of remote sensing instrument

Cassegrain optical systems are widely used in remote sensing instrument. Cassegrain telescope is composed of a primary mirror (M1), a secondary mirror (M2), and a set of correction lenses. The system aberrations of telescope could be corrected and balanced by M1 and M2. In the event of deformation of telescope assembly, the non-symmetry aberrations will be induced to the optical system and reduce the optical performance. The non-symmetry aberrations can be measured after completing M1 and M2 assembly and alignment processes. Compensating this identified error to M1 or M2 can improve the optical performance of the telescope system. The error compensation on M2 is more efficient due to its smaller aperture and quickly assembly and de-assembly processes. In this study, we map the system wavefront error caused by deformation of mirror supporting and gravity onto the designed aspheric surface of M2. The surface of M2 becomes a freeform from aspheric. The polishing process combines the techniques of conventional lapping and CNC polishing. We apply the conventional spherical lapping process to quick remove the sub-surface damage (SSD) layer and to get the accurate radius of best fit sphere of the designed aspheric surface with fine surface texture simultaneously. The polishing and metrology processes were performed by using Zeeko IRP1000 polisher and QED ASI. A Φ 150 mm mirror with freeform surface was completed.

Parameter investigation of air-driving fluid jet polishing

Air-driving fluid jet polishing (FJP) technique was first presented in 2011. Slurry was drop out due to Venturi effect inside the atomizer which is the main component of air-driving FJP system, and was guided to mix with air flow by the nozzle. The Venturi effect and the added high speed air flow provide slurry more kinetic energy to impact the optical surface. Therefore, the air-driving FJP system has a rotational symmetrical Gaussian-like removal profile with lower air pressure and normal incidence configuration. In this paper, we investigate oblique incidence polishing to find the optimal material removal performance of the technique, including removal shape and depth and surface roughness. Different oblique angles ranged from 80 to 20 degree were tested. The air-driving FJP system was adapted upon a CNC machine, so not only single point polishing but also straight line polishing with constant feed rate can be carried out. We report on the performance of oblique air-driving FJP in different air pressure and processing time, and also the material removal of dynamic polishing for N-BK7, Fused Silica and ZERODUR®. The results indicate oblique incidence can get a Gaussian-like removal shape, and improve the surface roughness. The air-driving FJP not only has the advantages of conventional fluid jet polishing, such as no tool wears, cutter interference and debris deposition problems, but also has excellent material removal rate with lower energy.

Design and verifications of an eye model fitted with contact lenses for wavefront measurement systems

Contact lenses are typically measured by the wet-box method because of the high optical power resulting from the anterior central curvature of cornea, even though the back vertex power of the lenses are small. In this study, an optical measurement system based on the Shack–Hartmann wavefront principle was established to investigate the aberrations of soft contact lenses. Fitting conditions were micmicked to study the optical design of an eye model with various topographical shapes in the anterior cornea. Initially, the contact lenses were measured by the wet-box method, and then by fitting the various topographical shapes of cornea to the eye model. In addition, an optics simulation program was employed to determine the sources of errors and assess the accuracy of the system. Finally, samples of soft contact lenses with various Diopters were measured; and, both simulations and experimental results were compared for resolving the controversies of fitting contact lenses to an eye model for optical measurements. More importantly, the results show that the proposed system can be employed for study of primary aberrations in contact lenses.

Fabrication of ф 160 mm convex hyperbolic mirror for remote sensing instrument

In this study, efficient polishing processes with inspection procedures for a large convex hyperbolic mirror of Cassegrain optical system are presented. The polishing process combines the techniques of conventional lapping and CNC polishing. We apply the conventional spherical lapping process to quickly remove the sub-surface damage (SSD) layer caused by grinding process and to get the accurate radius of best-fit sphere (BFS) of aspheric surface with fine surface texture simultaneously. Thus the removed material for aspherization process can be minimized and the polishing time for SSD removal can also be reduced substantially. The inspection procedure was carried out by using phase shift interferometer with CGH and stitching technique. To acquire the real surface form error of each sub aperture, the wavefront errors of the reference flat and CGH flat due to gravity effect of the vertical setup are calibrated in advance. Subsequently, we stitch 10 calibrated sub-aperture surface form errors to establish the whole irregularity of the mirror in 160 mm diameter for correction polishing. The final result of the In this study, efficient polishing processes with inspection procedures for a large convex hyperbolic mirror of Cassegrain optical system are presented. The polishing process combines the techniques of conventional lapping and CNC polishing. We apply the conventional spherical lapping process to quickly remove the sub-surface damage (SSD) layer caused by grinding process and to get the accurate radius of best-fit sphere (BFS) of aspheric surface with fine surface texture simultaneously. Thus the removed material for aspherization process can be minimized and the polishing time for SSD removal can also be reduced substantially. The inspection procedure was carried out by using phase shift interferometer with CGH and stitching technique. To acquire the real surface form error of each sub aperture, the wavefront errors of the reference flat and CGH flat due to gravity effect of the vertical setup are calibrated in advance. Subsequently, we stitch 10 calibrated sub-aperture surface form errors to establish the whole irregularity of the mirror in 160 mm diameter for correction polishing. The final result of the Fabrication of ф160 mm Convex Hyperbolic Mirror for Remote Sensing Instrument160 mm convex hyperbolic mirror is 0.15 μm PV and 17.9 nm RMS.160 mm convex hyperbolic mirror is 0.15 μm PV and 17.9 nm RMS.

High-performance illumination module of RGB LEDs pico-projector with dual double side micro lens array

In this research, we propose a high performance non-image illumination module of pico-projector which includes light source, collimator and liquid crystal on silicon (LCoS) panel. The light source is RGB LED. The collimator consists of two glass collimator lenses and two double sides micro lens array (MLA) for light homogenizer. MLAs play a critical role in the LED illumination module. Dual double-side MLAs have been adopted for the homogenizer to satisfy the numerical aperture in the optical design. The good uniformity and high accuracy MLA structure was generated by ultra precision diamond shaping method and the MLA plate is subsequently fabricated by injection molding. Finally, a non-image illumination module with power efficiency 30.87 lm/w and uniformity of 56% on LCoS panel in a very compact size, less than 1.6 cm3 in volume, has been developed.

The fabrication of high filling factor double side micro lens array with high alignment accuracy

The high filling factor double side micro lens array (MLA) for laser beam shaping has been widely applied in optoelectrical applications. In this paper, we demonstrated the double side MLA for the laser beam shaping process. The point laser source has been successfully transformed into a two dimension uniformity light imaging. The ultra-precision slow tool servo (STS) diamond shaping and plastic injection method for MLA fabrication had been studied. The complexity micro structure of high filling factor MLA via the planning of cutting tool path is used in this research. The high alignment accuracy of both sides MLA is obtained by artful fixture design. The form accuracy and surface roughness are less than 0.1μm and 10nm, respectively. The alignment error of both sides MLA is less than 10μm.