Rene Daendliker

High-accuracy distance measurements with multiple-wavelength interferometry

Multiple-wavelength interferometry is, like classical interferometry, a coherent method, but it offers great flexibility in sensitivity by an appropriate choice of the different wavelengths and it can be operated on rough surfaces. The accuracy of this method depends essentially on the signal processing and on the properties of the source. Practical considerations for distances in the range of several meters with micrometer resolution are given.

Noninvasive optical system for the study of the function of inner ear in living animals

The Hearing Organ has a coiled structure in which the basic geometrical arrangement of the different types of cells is repeated throughout the organ. Hearing organs of different mammalian species also utilize the same arrangement of cells. In order to understand the significance of this arrangement in processing the auditory stimuli it is essential to measure the cellular function in an intact organ of a living animal. The sensory cells in the intact inner ear of a living animal can be visualized in the basal turn of the cochlea through the round window membrane. To achieve this an imaging system is needed to detect the weak reflections from the sensory cells in the inner ear while rejecting strong reflections from structures below and above the region of interest, particularly the round window membrane itself. A confocal microscope/interferometer was developed and built to visualize the sensory cells and to measure their vibration in response to sound applied to the ear. The measuring system and some of its performance characteristics are described.

Design of a nonconventional illumination system using a scattering light pipe

A linear light pipe allowing the transformation of a quasi- point source into an extended lighting device has been developed. The control of the spatial light distribution is of special interest for the uniform illumination of extended surfaces. The distribution of the emitted light is achieved by the combination of scattering and reflective coatings on the light pipe faces. Paint has been used as scattering coating. Paint characterization and introduction of the measured parameters into the ray-tracing program are described. Several light pipe configurations have been simulated and manufactured. The performance of the different configurations are discussed and compared with experimental results.

Illumination light pipe using micro-optics as diffuser

A scattering light pipe has been designed for a non- conventional illumination system. The spatial distribution of the light is controlled by diffusers which are deposited on top of the pipe faces. The first realized samples have used a scattering paint as diffuser which has good optical properties but is unsuited to fabrication. Diffusers based on micro-optics have the potential to replace favorably classical Lambertian diffusers. Micro-optical diffusers (MODs) allow the generation of perfectly defined scattering distributions which are well adapted for the design of an optimized light pipe. A further advantage of such surface relief elements is their potential for cheap mass production. The strengths and limits of micro-prisms, micro- lenses, and gratings are evaluated in view of their use as diffusers. Finally a proposition for an optimized design of the illumination light pipe is presented.

Coherent coupling of an array of Nd3+-doped single-mode fiber lasers using an intracavity phase grating

A method for the coherent coupling of single-mode fiber lasers which produces a single Gaussian output beam is presented. The output and spectral properties of an experimental device composed of three coupled Nd3+ single-mode fiber lasers have been studied. Typically 70% of the total output power have been obtained in a single beam for different coupling conditions. The dynamic behavior of the emission spectrum is discussed.

Multilevel nematic liquid crystal phase gratings

Planar-aligned nematic liquid crystals cells with an array of parallel electrodes can perform phase modulation with profiles going from binary to blazed gratings. A nematic liquid crystal with high birefringence (BL006) allows reducing the thickness of liquid crystal cells and thus reducing switching times. But the discrete electrodes and the small thickness have negative consequences on the shape of the phase profile. Liquid crystal phase gratings with 192 separately controlled electrodes were fabricated. The electrode distances and widths were 3 or 4 micrometers at a cell thickness of 6 micrometers . Perpendicular and parallel alignment of the liquid crystal with respect to the electrode grating were investigated. Far field diffraction measurements and phase measurements with a Mach-Zehnder interferometer were performed to characterize the gratings. The director distribution was modeled in 2 dimension and the resulting phase profiles were calculated with a Jones matrix method. It allows a comparison with the measurements. It was found that in the liquid crystal grating cell the in- plane electric field has a large influence on the optical properties. The in-plane electric field between the high- and low-voltage electrodes forms an unfavorable director deformation that limits the diffraction efficiency to approximately 65% for linear polarized light. Both, the measured and the simulated phase profiles, show a typical structure where valleys appear and worsen the optical performances. The optimization of such a grating is a compromise of large thickness, that smooths the valley structures, and small thickness, that reduces the in-plane switching effect and the switching time.

Concept of modes in optics and photonics

The concept of modes, or eigenfunctions, is fundamental for all wave phenomena in physics like optics, acoustics and quantum mechanics. In optics and photonics, the concept of modes is well suited to describe emission and absorption, coherence and interference, propagation and dispersion. The concept of modes consists of two aspects: first, the modes are solutions for the propagation of the light; second, the number of photons int he different modes describes the transport of energy or information. The energy density of the black body radiation, given by Plancks law, is the production of the density of modes in free space and the average number of photons per mode, given by the Bose- Einstein distribution. The transverse shape of the modes is determined by diffraction and boundary conditions. The longitudinal extension is given by the coherence length.

MICRO- OPTICS FOR SENSOR APPLICATIONS

Our investigation is focused on microlens arrays for microsystems and sensor applications. Arrays of refractive lenses (2 micrometer to 5 mm lens diameter) have been fabricated by melting resist technology. Microlens arrays have been transferred in fused silica (reactive ion etching) and replicated in polycarbonate and polymer (embossing, casting). Lens arrays have been integrated into lithographic systems, sensors and neural networks.

Optical near-field phase singularities produced by microstructures

An electromagnetic field is characterized by an amplitude, a phase and a polarization state. In this paper, we intend to gain an understanding of the interaction of light with microstructures in order to determine their optical properties. Measurements of the amplitude and phase close to gratings are presented using a heterodyne scanning probe microscope. We discuss some basic properties of phase distributions. Indeed, coherent light diffracted by microstructures can give birth to phase dislocations, also called phase singularities. Phase singularities are isolated points where the amplitude of the field is zero. The position of these special points can lead us to information about the structure (shape, surface defects, etc), by comparing with rigorous diffraction calculation using e.g. the Fourier Modal Method (FMM). We present high-resolution measurements of such phase singularities and compare them with theoretical results. Polarization effects have been studied in order to understand the field conversion by the fiber tip.

Coupled Waves: A Powerful Concept in Modern Optics

Coupled waves are used in many fields of modern optics: volume holograms, Bragg reflectors, acousto-optic modulators, waveguide couplers, distributed feedback lasers, polarization effects in optical fibers and liquid crystals, non-linear optics, parametric amplifiers and oscillators, four-wave mixing, etc. First, the general concept of coupled waves is introduced for any kind of perturbation (spatial and temporal) of the dielectric polarization within an optical medium. The result is a general form of coupled wave solutions. Second, the particular topics mentioned above are treated by introducing the special conditions for the basic modes to be considered (plane waves, guided waves, optical polarizations) and the physical effects relating the induced perturbation of the dielectric polarization to the electrical field (spatial and temporal variation of refractive index, absorption or birefringence, non-linear optical effects, etc.). This approach puts the emphasis on teaching concepts rather than presenting particular effects. The fundamental role of phase- matching (Bragg) and the similarities of the solutions for different physical effects emerge clearly.