Compression molding of glass aspherical lenses has become a viable manufacturing process for precision optics. The widespread use of this process has been hampered by the lack of its fundamental understanding. This research is a part of the ongoing effort to understand some of the issues related to the process. Simple lens molding experiments were performed on a commercial precision lens molding machine. A finite element method (FEM) program was used to create a simple numerical model and analyze the molding process. Experimental results show that this process is capable of producing precision optical components. A comparison of the experimental results with the predicted results indicates that with a more sophisticated numerical model, it is possible to use FEM as a tool for process analysis. 579J ournal

In recent years it has become possible to fabricate free-form optics by use of multiaxis ultraprecision machines. Here a 5 x 5 microlens array is fabricated by using an ultraprecision diamond turning machine equipped with four independent axes. Unlike the conventional process where a single diamond tool is used to machine one lens at a time, this research demonstrates the development of an innovative diamond tool trajectory that allows the entire microlens array to be machined in a single operation. The machined microlens array is measured for both curve conformity and surface roughness. Compared to the conventional approach where indexing the workpiece is difficult and unreliable, this process can produce microlenses with accurate geometry and optical surface finish. This unique process is described in detail from optical measurement to machining process design and development to final results. This research also demonstrates the possibility of fabricating any arbitrary shape with the same approach.

In this research paper, in a major departure from conventional 2D micromachining processes, design and fabrication of a 3D compound eye system consisting of a 3D microprism array, an aperture array, and a microlens array were investigated. Specifically, the 3D microprism array on a curved surface was designed to steer the incident light from all three dimensions to a 2D plane for image formation. For each microprism, there is a corresponding microlens to focus the refracted light on the image plane. An aperture array was also implemented between the microprism array and the microlens array to eliminate cross-talk among the neighboring channels. In this system, 601 individual micro-assemblies consisting of microprisms and microlenses were constructed in a 20 mm diameter area. In this configuration, the maximum light deviation angle was determined to be 18.43 degrees. This research demonstrated an innovative and integrated approach to fabricating true 3D micro and meso scale optical structures. This work also validated the feasibility of using ultraprecision machining process for 3D microoptical device fabrication. The technology demonstrated in this research has high potentials in optical sensing, vision research and many other optical and photonic applications.

In this research, a unique freeform microlens array was designed and fabricated for a compact compound-eye camera to achieve a large field of view. This microlens array has a field of view of 48°×48°, with a thickness of only 1.6 mm. The freeform microlens array resides on a flat substrate, and thus can be directly mounted to a commercial 2D image sensor. Freeform surfaces were used to design the microlens profiles, thus allowing the microlenses to steer and focus incident rays simultaneously. The profiles of the freeform microlenses were represented using extended polynomials, the coefficients of which were optimized using ZEMAX. To reduce crosstalk among neighboring channels, a micro aperture array was machined using high-speed micromilling. The molded microlens array was assembled with the micro aperture array, an adjustable fixture, and a board-level image sensor to form a compact compound-eye camera system. The imaging tests using the compound-eye camera showed that the unique freeform microlens array was capable of forming proper images, as suggested by design. The measured field of view of ±23.5° also matches the initial design and is considerably larger compared with most similar camera designs using conventional microlens arrays. To achieve low manufacturing cost without sacrificing image quality, the freeform microlens array was fabricated using a combination of ultraprecision diamond broaching and a microinjection molding process.

We report what is to our knowledge the first approach to diamond turn microoptical lens array on a steep curved substrate by use of a voice coil fast tool servo. In recent years ultraprecision machining has been employed to manufacture accurate optical components with 3D structure for beam shaping, imaging and nonimaging applications. As a result, geometries that are difficult or impossible to manufacture using lithographic techniques might be fabricated using small diamond tools with well defined cutting edges. These 3D structures show no rotational symmetry, but rather high frequency asymmetric features thus can be treated as freeform geometries. To transfer the 3D surface data with the high frequency freeform features into a numerical control code for machining, the commonly piecewise differentiable surfaces are represented as a cloud of individual points. Based on this numeric data, the tool radius correction is calculated to account for the cutting-edge geometry. Discontinuities of the cutting tool locations due to abrupt slope changes on the substrate surface are bridged using cubic spline interpolation.When superimposed with the trajectory of the rotationally symmetric substrate the complete microoptical geometry in 3D space is established. Details of the fabrication process and performance evaluation are described.

With the recent advances in numerical simulation capabilities and computing technology, finite element method (FEM) can be applied to predict the performance of a precision aspherical lens molding process. In this paper, various stages of the lens molding process have been modeled using a commercial FEM code MSC MARC. Stress relaxation effect during the forming stage has been incorporated into the numerical model by using a generalized Maxwell model. Successful comparison of the predicted results has been made with the experimental data. The various aspects of the simulation that would enable a more realistic modeling of the process have been identified for future research. J ournal

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Cylindrical compression tests were conducted on two different optical glass grades for determining the high-temperature viscosity and elastic parameters. Numerical simulations of the compression tests and the precision lens molding process were performed by incorporating the data obtained from the compression tests using a commercial finite-element method program. Excellent agreement between the viscosity data from the compression test and the beam bending test was obtained, and a good comparison between the measured and predicted deformation load results was also observed. Further issues that have emerged from this research that would be relevant to the ongoing research on the numerical modeling of the precision aspherical lens molding process include determination of hightemperature elastic properties of glass (i.e. elastic and shear modulus) and friction characterization at the glass-mold interface.