The latest results on the preparation and characterization of Er3+-doped fluoride glass channel waveguides are presented. The waveguides are prepared by means of ion exchange between fluoride and chloride ions, through a silica mask, on ZBLA (ZrF4-BaF2-LaF3-AlF3) fluoride glass substrate. Single mode propagation is demonstrated at 1.55 μm for a 10-mm long, 5-μm wide waveguide. Propagation losses are found to be not greater than 0.28 dB/cm. An "on/off' gain of 3.9 dB is measured at the output of a 1% Er3+-4% Ce3+-doped fluoride waveguide, with about 240 mW incident pump power at 980 nm. Modelisation studies show that net gain could be achieved in (Er3+, Ce3+) doubly-doped and (Er3+, Ce3+, Yb3+) triply doped fluoride waveguides.
SU-8, negative-tone epoxy base, photoresist has a great potential for ultra-thick high aspect ratio structures in low cost micro-fabrication technologies. Commercial formulation of NanoTM SU-8 2075 is investigate, process limitations are discuss. Good layer uniformity (few %) for single layer up to 200 μm could be obtained in a covered RC8 (Suss-MicroTec) spin coater, but for ultra-thick microstructures it is also possible to cast on the wafer a volume controlled of resist up to 1.5 mm without barrier. Long baking times are necessary for a well process control. The layout of the photo-masks design and process parameters have great impact on residual stress effects and adhesion failures, especially for dense SU-8 patterns on metallic under layer deposited on silicon wafers. A specific treatment applied before the resist coating definitely solved this problem.
Bio-fluidic applications of on-wafer direct prototyping (silicon, glass, plastics) are presented. An example will be given on prototyping dielectophorectic micro-cell manipulation component. The SU-8 fluidic structure is made by a self planarized multi-level process (application for 2,5 to 3D microstructures). Biotechnology applications of integrated micro-cells could be considered thanks to the SU-8 good resistance to PCR (Polymerase Chain Reaction).
Future developments are focusing on the SU-8 capabilities for Deep Reactive Ion Etching of plastic and 3D shaping of microstructures using a process called : Multidirectional Inclined Exposure Lithography (MIEL).
Microchip lasers are used as pulse generators in the LMJ front end. These lasers are made with Nd:YLF using collective fabrication processes. A linearly polarized, single-frequency, 1053 nm pulsed emission has been achieved with very good efficiency. Prototypes of fiber-coupled microchip lasers have been fabricated.
The microchip laser is the most compact and the simplest diode pumped solid state laser, with a typical dimension of 0.5 mm3. In spite of the extreme simplicity of this concept which was described in sixties, the first devices have been realized much later in eighties, in different laboratories in the world. The main advantage of the microchip laser is its ability to be fabricated with collective fabrication processes, using techniques such as currently used in microelectronics, allowing a low cost mass production with a good reproducibility and reliability. The microchip lasers are very simple to use without any optical alignment and any maintenance. They foretell a true technical revolution in the domain of solid state lasers which should be opened to high volume and low cost markets. They have many different industrial applications in large markets such as: automotive, laser marking and material processing, environmental and medical applications, public works, telecommunications, etc.
Microchip lasers are used as pulse generators in the LMJ front end. These lasers are made with Nd:YLF using collective fabrication processes. A linearly polarized, single-frequency, 1053 nm emission has been achieved with very good efficiency. The beam of the microchip lasers has been coupled into a polarization-maintaining single mode fiber using microlenses, with coupling efficiencies better than 70%.
LETI has developed new reliable and low cost diode pumped solid state microchip lasers using a collective fabrication approach. Very compact microchip lasers consist in small cubes (typically 1 mm3), cut in a wafer of laser crystal with plane parallel polished faces on which dielectric mirrors are deposited. In order to reduce the threshold of plane parallel microchip lasers we have achieved microspherical shapes on laser materials by using a two step micro-optic fabrication technique based on photolithography and melting of photoresist followed by a selectively controlled etching process. These spherical shapes such as microlenses were transferred into the substrate by ion beam milling (IBM), forming microspherical mirrors on the laser cavities. By this way we have also produced large arrays of microlenses of low numerical aperture in silica substrate by using a selectively controlled reactive ion etching (RIE) process. In both etching techniques the selectivity, defined as the ratio between the etching rate of the substrate and the resist, can be adjusted (from 0.1 to 3 in our experiments) by controlling the fraction of oxygen in the gas. Low numerical aperture microlens arrays of 100 to 200 micrometer in diameter and 110 to 250 micrometer in pitch have been made with limits of f/15 in photoresist and f/100 after etching In YAG and f/40 in silica. The laser threshold of stabilized microchip lasers in Nd:YAG with spherical shape of 3 mm in radius of curvature and 150 micrometers in diameter, is then lowered from 40 to 2 mW.