D. Prongué

Two-wavelength laser interferometry using superheterodyne detection

In two-wavelength interferometry, synthetic wavelengths are generated in order to reduce the sensitivity or to extend the range of unambiguity for interferometric measurements. Here a novel optoelectronic technique, called superheterodyne detection, is presented, which permits measurement of the phase difference of two optical frequencies that cannot be resolved by direct optoelectronic heterodyne detection. This technique offers the possibility for operation of two-wavelength interferometry in real time with arbitrary synthetic wavelengths from micrometers to meters in length. Preliminary experimental results are reported. An optical arrangement for absolute range-finding applications using tunable-laser sources (e.g., semiconductor lasers) is proposed.

Optimized kinoform structures for highly efficient fan-out elements

We discuss the realization of highly efficient fan-out elements. Laser-beam writing lithography is available now for fabricating smooth surface relief microstructures. We develop several methods for optimizing microstructure profiles. Only a small number of parameters in the object plane are necessary for determining the kinoform. This simplifies the calculation of M x N arrays also for large M and N. Experimental results for a 9-beam fan-out element are presented.

Continuous-relief diffractive optical elements for two-dimensional array generation

Continuous surface-relief diffractive optical elements for two-dimensional array generation (fan-out) are designed and fabricated. Separable and nonseparable solutions for the two-dimensional element design are compared. The phase-grating microstructures are generated by laser-beam writing lithography in a single exposure step and converted to nickel shims by electroplating, enabling low-cost replicas to be produced by using laboratory and commercial replication processes. Results are presented for a 9 x 9 fan-out diffractive optical element with a measured efficiency of 94% and an overall uniformity within +/-8%; replicas in epoxy have the same efficiency and a uniformity of +/-15%.

Design and fabrication of highly efficient fan-out elements

This paper reports the calculation and fabrication of periodic phase structures for fan-out elements with a theoretical conversion efficiency close to 100% and perfect uniformity. We have measured an efficiency of 92% for a smooth kinoform structure fabricated in photoresist by laser beam writing lithography.

High-efficiency continuous surface-relief gratings for two-dimensional array generation

Continuous surface-relief phase gratings for two-dimensional (2-D) array generation have been realized by laser-beam writing lithography. For a 9 × 9 fan-out element, a diffraction efficiency of 94% and a uniformity of better than ±8% have been achieved. These are, to our knowledge, the best published results for 2-D surface-relief fan-out elements. Separable and nonseparable solutions for the design of 2-D fan-out elements are discussed.

Fabrication of kinoform structures for optical computing

The fabrication of kinoform micro-optical elements for applications in optical computing is described. The elements are recorded as continuous microrelief structures by programmable laser beam writing in photoresist with a computer-controlled precision xy stage and a modulated, focused laser beam. Kinoform structures can be programmed to any desired profile that is required for reproducing complex, optimized structures that are found by computer design techniques.

Two-Wavelength Laser Interferometry Using Super-Heterodyne Detection

Two-wavelength interferometry is well known since years and often used for ranging and contouring at reduced sensitivity 1. Recently, two-wavelength heterodyne interferometry has been reported, which can be applied for both, smooth and rough surfaces 2. However, this method is limited to large wavelength differences, which can be optically separated (prism, grating). By the availability of tunable diode-lasers as light sources, multiple wavelength interferometry with small wavelength differences is getting increased practical interest 3. It is the purpose of this paper to present a novel method, based on super-heterod e detection, which allows to make high resolution measurements at 241-- I effective difference wavelengths Λ = λ1 λ2λ1- shorter than 30 cm, without being obliged to have interferometric stability at the optical wavelengths Xi and1. itse and to separate these wavelengths optically. This is of great importance for range finding and industrial distance measuring with submillimeter resolution.

Fan-out elements recorded as volume holograms: optimized recording conditions

The recording of efficient fan-out elements as volume holograms is investigated by using the coupled-wave theory. In contrast to the results published in the standard literature, we find that the efficiency and the uniformity of regular fan-out elements depend strongly on the relative phases of the object waves, at least, if the thickness of the hologram is less than ~50 wavelengths. High efficiency and uniformity can be achieved by optimized recording conditions. At the same time, the required dynamic range of the holographic material becomes minimum.

HOE for clock distribution in integrated circuits: experimental results

This paper reports the design and fabrication of transmission holographic optical elements (HOEs) for clock distribution. First, we have studied and fabricated a multi-focus doublet HOE. The aberrations due to the wavelength shift between recording ( = 488 nm) and reconstruction ( = 780 nm) have been minimized by an appropriate recording and readout geometry. The diffraction efficiency has been optimized by a copying technique. Second, we have investigated the near-field internal reflection (TIR) holographic recording technique to solve the problems of miniaturization. With this method, we have recorded a lOOxlOO lenlet array with focal lengths of f =400 μm.

Total internal reflection holography for optical interconnections

We applied near-field total internal reflection holography to solve the problems of miniaturization of lenslet arrays. A regular 100 x 100 lenslet array with a 390-μm focal length and a nonregular lenslet array for clock distribution to a specially designed VLSI circuit were recorded in a planar-optics configuration. We also developed an appropriate recording technique to satisfy both the low-aberration condition and the Bragg condition, despite a wavelength shift between the recording and readout.