Photonics integration continues to be a main driver for innovation in multiple aspects, including wafer-scale integration, new materials, sub-micron alignment of components and protection from harsh environment. We show cost-effective fabrication technologies of micro-optical components by UV wafer-scale replication into chemically stable polymers. Furthermore, for simplified fiber coupling and packaging, a novel 90° optical interconnect is presented, integrated with self-alignment structures. Replicated, space compliant microlenses on packaged CMOS imagers show improved light sensitivity by a factor 1.8. A laser based, low stress bonding process is explored to generate wafer-scale hermetic enclosures for harsh environment applications ranging from space to implants.
The interest in MEMS based Micro-Spectrometers is increasing due to their potential in terms of flexibility as well as cost, low mass, small volume and power savings.
This interest, especially in the Near-Infrared and Mid- Infrared, ranges from planetary exploration missions to astronomy, e.g. the search for extra solar planets, as well as to many other terrestrial fields of application such as, industrial quality and surface control, chemical analysis of soil and water, detection of chemical pollutants, exhausted gas analysis, food quality control, process control in pharmaceuticals, to name a few. A compact MEMS-based Spectrometer for Near- Infrared and Mid-InfraRed operation have been conceived, designed and demonstrated. The design based on tunable MEMS blazed grating, developed in the past at CSEM [1], achieves state of the art results in terms of spectral resolution, operational wavelength range, light throughput, overall dimensions, and power consumption.
Plasmonics involves the interaction of light with metallic structures at the nanoscale, which enables in particular the generation of strong reflection and absorption effects in the visible and near infrared range. The fabrication of plasmonic nanostructures using ultra-violet (UV) imprint and thin metallic coatings is reported. Wafer-scale fabrication and process compatibility with cost-efficient roll-to-roll production are demonstrated, which paves the road towards an industrial implementation. The color, phase, polarization and direction of the transmitted light are controlled by tuning the process parameters and the symmetry of the nanostructures. A family of devices is presented, for which the potential for sensing, filtering, anticounterfeiting and optical security is evaluated.
Modules consisting of multiple single emitters pose demanding challenges on assembly, production capabilities and cost.
A fiber coupled module has been produced delivering 100 W optical power from a 105 μm, NA 0.15 fiber. The module
consists of two times six vertically stacked single emitters combined by polarization multiplexing. Special attention was
paid to the development of a very robust low cost pigtail. The developed semiautomatic highly accurate process enables
assembly times way faster than possible in a purely manual procedure. The achievable yield in combination with low
material costs proofs the excellent potential for the manufacturing of cost efficient laser modules.
Single-mode-emitting high-power diode laser arrays (SM-HPDLA) are available industrially with more than 50 W
emission power per bar. Based on this platform an expandable prototype solution is realized for fiber coupling of a
stacked array with more than 100 W to an optical fiber with diameter of 200 micron and NA of 0.11. Advanced methods
of controlled assembly of micro-optics by infrared laser-soldering have been developed therefore. We present a compact
and scalable concept with scalability on 2 internal and 2 external factors. Internal factors are the increasing beam quality
and power stability of high-power single-mode-emitting arrays and the improved assembly accuracy for diode bar and
micro-optics. External factors are the interlaced coupling of stacked beam emission from the stacked array and the
further option to use optimized polarisation coupling with several diode laser stacks.
The realization of all-optical switching schemes is mostly hindered by the lack of suitable materials with a refractive index change that is large and fast enough. The characterization of the linear and nonlinear optical properties of potential materials is therefore of prime importance. Various characterization methods have been proposed and are employed, yielding different parameters of the nonlinear optical response at the involved laser frequencies. However, in most techniques the resulting nonlinearities are measured only at one point in the spectral dispersion. To generate the whole nonlinear spectra, the laser source has to be tuned over the desired wavelength range and consecutive measurements have to be taken. We propose and demonstrate here a novel technique to measure the nonlinear optical response for a broad wavelength region in a pump-probe scheme that requires no laser tuning. In order to detect the two-photon absorption at several wavelengths simultaneously, we use a white-light-continuum as the probe beam. As the pump beam is held constant, the Kramers-Kroenig transformation can be used to calculate the dispersion of the nonlinear refractive index from the two-photon spectra. By delaying the probe beam relative to the pump beam, the temporal behavior of the nonlinearity can be obtained.
We present new experimental results on second-harmonic generation in highly conjugated organic molecules and molecular crystals recently developed in our group, as well as on electro-optic eftects in thin-film polymers. A large value of the molecular hyperpolarizability of a new hydrazone-type molecule crystallizing in a noncentrosymmetric point group is reported. Large nonlinear optical coefticients of up to 840 ± 200 pmN were measured in crystals of 4'-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). The new experimental results are compared with theoretical calculations of limiting values of nonlinear optical coefticients. Computer modeling of crystal structures shows good agreement with experimental results. Measurements on electro-optic polymers with high thermal stability are presented.
We give an overview of the current status of research in the field of molecular crystals with respect to frequency-conversion, electro-optic modulation, and photorefractive effects. Applications of organic materials for nonlinear optics will depend on the development of waveguide devices and bulk crystals. Up to now the most advanced integrated optical organic devices use polymers. Thin crystalline films would also be very attractive if suitable techniques for high quality film deposition would become available. Organic molecular beam epitaxy offers new possibilities for fabricating low loss waveguides based on crystalline materials.
Electro-optic effects in single crystals of 2-cyclooctylamino-5-mitropyridine and 2-(N- prolinol)-5-nitropyridine have been investigated. The measured wavelength dependence of the electro-optic coefficients can be well explained with the quantum-mechanical two-level model. Enhancements of these coefficients near acoustic phonon resonances of up to a factor of 25 were observed when scanning the modulation frequency of the applied electric field. A comparison between measured second-order polarizabilities and electro-optic coefficients revealed that optic phonons may still contribute considerably to the electro-optic effects in the investigated molecular crystals. A simple expression to estimate the limiting values of electro- optic coefficients is proposed and compared with values of known molecular crystals.
Molecular second-order nonlinear optical properties of a series of interesting nitropyridine derivatives, namely 2-cyclooctylamino-5-nitropyridine (COANP), 2-docosylamino-5- nitropyridine (DCANP), and 2-(N-prolinol)-5-nitropyridine (PNP) were investigated with two different methods: electric field-induced second-harmonic generation (EFISH) and a solvatochromic method. Both techniques yield the same values within the experimental errors, showing that the main contribution of the microscopic nonlinearity arises from a single intramolecular charge transfer transition. The measured values were shown to follow the theoretical two-level dispersion. A comparison of the hyperpolarizabilities and the macroscopic nonlinear optical coefficients shows a good quantitative agreement. This illustrates that intramolecular contributions are the main source for the large nonlinear optical responses observed in these crystals.
We report for the first time phase-matched second-harmonic generation by mode conversion in nonlinear optically active Langmuir-Blodgett (LB) film waveguides. Phase-matched frequency- doubling was observed in LB films of 2-docosylamino-5-nitropyridine (DCANP) by conversion of a fundamental TE0-mode into a second-harmonic TE1-mode. The experiments were done in four-layer optical waveguides. For DCANP this four-layer configuration improves the theoretical conversion efficiency more than 100 times compared to a conventional three-layer waveguide. In the preliminary experiment infrared to blue light conversion efficiencies up to 0.5% W-1 cm-2 (0.02% W-1) were measured.
We demonstrate phase-matched frequency-doubling in Langmuir-Blodgett film waveguides of 2-docosylamino-5-nitropyridine (DCANP). Using the Cerenkov-type configuration we can generate light in the absorption region of DCANP (at least down to 410 nm). The largest nonlinear optical coefficient d33 could be used by exciting TE modes propagating in the film. Coupling of the fundamental beam into the waveguide is demonstrated by means of gratings and prisms.
Read-out of volume phase holograms in photorefractive crystals with a wavelength that is different from the wavelength of hologram formation imposes the difficulty to match the Bragg condition for all spatial frequencies of the object to be stored. Therefore, the quality of the reconstructed image decreases and resolution and image field losses are observed. Experimental and theoretical examinations of these effects reveal that the geometrical configuration of the writing experiment determines the reconstructed image field. Depending on the wavelength of read-out an appropriate reconstructing wave can be formed with the help of lenses diminishing image field and resolution losses considerably.
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