Kenjiro Hamanaka

Multiple imaging and multiple Fourier transformation using planar microlens arrays.

A new type of multiple imaging and multiple Fourier transformation system under coherent illumination using microlens arrays has been developed. The optical system is based on geometrical optics instead of convolution or diffraction. As a result, it has the advantage of design flexibility especially in alignment of the duplicate images. The experimental results of the system, which are implemented using planar microlens arrays fabricated by an ion exchange technique, are also discussed.

High numerical aperture planar microlens with swelled structure

The planar microlens is a 2-D integrated microlens fabricated by the selective ion exchange technique. This paper demonstrates a new class of planar microlens which has a high numerical aperture. The new planar microlens uses a swelling structure and index distribution which comes from replacing ions with different ion volumes. Lens diameters from 10 to 400 microm can be fabricated. A numerical aperture larger than 0.5 is achieved when the lens diameter is smaller than 100 microm. Use of this microlens in light coupling between an LD and a single-mode fiber is also evaluated.

Integration of Free-Space Interconnects Using Selfoc Lenses: Image Transmission Properties

A novel optical interconnection system which consists of cascade arrays of Selfoc lenses, has been proposed. An alignment-free optical mother board which has many comjugate image planes and the Fourier planes composed by the lenses is available for integrating many kinds of free-space optical systems. The system has the advantages of easy assembly and high reliability, in addition to a large space-bandwidth product and flexibility. Its concept, optical designs and image transmission properties evaluated through basic experiments and ray tracing estimations, are discussed.

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.

Multiple imaging and multiple Fourier transformation using microlens arrays

A new type of coherent multiple imaging system using microlens arrays has been developed. The principles, features, basic functions and possible applications are also discussed with some experimental results which are implemented by using a planar microlens array fabricated by an ion exchange technique. An experimental result of the multichannel matched filtering has also been demonstrated.

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.

Light coupling characteristics of planar microlens

The 2-D integrated planar microlens (PML) is expected to be used in connection with various 2-D devices in parallel optical fiber communication systems. In this paper, we demonstrate recent progress of PML and its light coupling characteristics. The coupling characteristics between (1) LD and single-mode fiber, (2) LED and GI-50 fiber, (3) single-mode fiber and single-mode fiber, and (4) single-mode fiber and detector were evaluated.

Light coupling between LD and optical fiber using high NA planar microlens

The planar niicrolens (PML) is a 2-D integrated niicrolens array fabricated by the ion-exchange technique. This paper demonstrates light coupling between LD and optcal fiber using the planar inicrolens. In oder to accept the light power from LD effctively, two classes of High NA planar inicrolens are prepared. A coupled planar inicrolens and new planar inicrolens with swelled structure are evaluated. The minimum coulping loss between LD and single mode fiber was - 5.3 dB using planar muicrolens with the swelled stuctre. (Including 0. 71 dB of Fresnel loss)

Aberration Properties Of The Planar Microlens Array And Its Applications To Imaging Optics

Aberration properties of planar microlens arrays, which are small lenslet arrays fabricated by an ion exchange technique, are described. The optical set-up of the measurement system. is designed to combine a Mach-Zehnder interferometer, a microscope imaging set-up and fringe scanning analysis to obtain precise measurements for microlenses. Many types of planar microlens have been measured, and the spherical aberration, coma in off-axis imaging etc., were evaluated. The experimental results indicate that the planar microlens can perform high quality imaging in a wide image field. Also, by using planar microlens arrays, multiple imaging optical systems in incoherent and coherent illumination are demonstrated..© (1989) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Chapter 5 – Physics of Planar Microlenses

This chapter explains the physics of planar microlenses. Optical processing is based on the light coupling among various optical devices. However, because light emission angles and light acceptance angles are different in the most cases, light couplings between different optical devices are not always easy to achieve. For example, a typical laser diode (LD) emits light under angle of 30° to 40°. On the other hand, a single-mode optical fiber can accept light within 5°. Microlenses are required to achieve effective light coupling between different optical devices. The microlens converts the numerical aperture (NA) of light rays, such that effective coupling is realized. Monolithically integrated microlens arrays were first introduced and demonstrated in 1980. The planar microlens (PML) was the result of the introduction and demonstration of the concept of the integrated microlens array, which is based on the idea of planar technology as demonstrated by Oikawa et al. Using the PML, Iga et al. introduced the concept of stacked planar optics. The light coupling between devices also included diffraction problems. Planar microlenses are fabricated by planar technology, in which a dopant is diffused selectively into a planar substrate. The planar microlens is based on the ion-exchange technique, in which the ions in a glass substrate are exchanged for other ions. The glass substrate is immersed in a molten salt at high temperatures of around a few hundred degrees Celsius.