Takaaki Miyashita

Comparing glass and plastic refractive microlenses fabricated with different technologies

We review the most important fabrication techniques for glass and plastic refractive microlenses and we quantitatively characterize in a systematic way the corresponding state-of-the-art microlenses, which we obtained from selected research groups. For all our measurements we rely on three optical instruments: a non-contact optical profiler, a transmission Mach–Zehnder interferometer and a Twyman–Green interferometer. To conclude, we survey and discuss the different fabrication techniques by comparing the geometrical and optical characteristics of the microlenses, the range of materials in which the lenses can be produced, their potential for low-cost fabrication through mass-replication techniques and their suitability for monolithic integration with other micro-optical components.

Wavefront aberration measurement technology for microlens using the Mach-Zehnder interferometer provided with a projected aperture

We have carried out wavefront aberration measurement with the reduction projection of an aperture on the pupil of the test microlens set in the interferometer optics. The size of the image of the aperture determines the effective aperture of the microlens, and proposes aperture restriction methods to reduce the influence of the Fresnel diffraction. Wavefront aberrations were measured and evaluated by the use of phase shift method applied to the Mach-Zehnder interferometer. We studied if we can form an image of an aperture stop on the pupil plane of the test microlens. The evaluation of the effect of the aperture on the fringe quality was evaluated through the prototype equipment using the microlens of less than 30 micrometers in diameter. In this paper, we describe the method of reducing the measurement error of wavefront aberration using the effective diameter of the microlens.

Comparative study of glass and plastic refractive microlenses and their fabrication techniques

In this paper we review the most important fabrication techniques for glass and plastic refractive microlenses and we quantitatively characterize in a systematic way the corresponding state-of-the-art microlenses which we obtained from selected research groups. For all our measurements we rely on three optical instruments: a non-contact optical profiler, a transmission Mach-Zehnder interferometer and a Twyman-Green interferometer. To conclude we survey and discuss the different fabrication techniques by comparing the geometrical and optical characteristics of the microlenses.

International standards for metrology of microlens arrays

The standardization of a microlens brings the merit for both users and suppliers, but which has issues to be solved in the characterization and evaluation due to the small lens size, caused from difficulty to apply the definition of conventional optical systems. Japan has the leading position of the international standardization activities in ISO for characterization of microlens since the early stage. Additionally, the recent development activities of wavefront aberration testing technologies are described.

Equivalence between the software-determined and the hardware-determined effective numerical aperture in the interferometrical measuring of microlens

We describe here characteristic properties relating to the interferometrical measuring of microlens with an effective numerical aperture determined by the software or the hardware. Starting from the wave equation, both of the amplitude and the phase of propagating optical beams can be calculated using Hankel transformation anywhere through the interferometer. First introducing the effective aperture determined by the hardware including the method of projecting the effective aperture on the pupil of the microlens, the effect of truncation or diffraction with the effective aperture on the beam propagation is shown. Next using Mach-Zehnder interferometer combined with the effective aperture, the measurement of the wavefront aberration of test microlens is simulated to show that the imaginary aperture by the software settled on the image sensor which is located at the conjugate position of the test microlens is equivalent to the hardware determined effective aperture including projected one. Numerical results are presented to show the measurement errors stay within λ/100 for two typical test microlens of 38 μmΦ and 125 μmΦ with 1 λ wavefront aberration for aberration-free measuring optics with large enough numerical aperture.