Optical microsystems, which can be fabricated using replication technology and assembled using optical surface mounting techniques, can offer compact, cost-effective solutions for applications in optical communication, metrology, sensors, illumination and displays. Especially adapted to the needs of mid-size volume production of a few hundred to thousands modules is wafer-scale replication.
The fabrication of single micro lenses or lenslet arrays on wafer substrates and the wafer-scale replication of such lens arrays for optical microsystems in sol-gel materials is under development as a cost-effective alternative to lens fabrication in glass. For an optical microsystem with a compact module for laser beam forming, wafer-scale, singlesided and double-sided replication has been developed to fabricate refractive or diffractive optical elements onto glass substrates. Combined opto-mechanical modules have been UV-cast-replicated from a sol-gel master in a single step. In addition, step & repeat replication can be employed for the fabrication of large arrays of custom specific lenses. Replication accuracy of better than a wavelength has already been achieved for refractive lenses with 50 μm SAG. Finally, diced optical components from the replicated wafers will be used for the manufacturing of micro-optic systems. A six-axis robot motion, automated optical alignment and laser-reflow soldering method is used to assemble the photonics modules. This method, called TRIMO-SMD (three-dimensional miniaturized optical surface-mounted device), is currently being made commercially available by Leica Geosystems AG.
Tandem chirped grating couplers for spectral measurement applications in optical communications are developed. The current devices are designed to monitor data/telecom dense wavelength-division multiplexing (DWDM) channels in the spectral range from 1528 to 1561 nm (C-Band). A replication process provides the diffractive structures, on the gratings a high-index waveguide material is deposited. Design parameters and fabrication tolerances are discussed in detail, and measurement results of the fabricated devices are presented.
Transparent polymer elements, containing both 3D-positioning structures and planar optical elements made by surface structuring, open the way for the mutual passive alignment of optical elements with respect to fibers, detectors and light sources in micro-optical benches with sub-micron precision. A fabrication process is presented for polymer inserts in micro-optical benches, which combines the mechanical precision of the LIGA-process with the wide variety of optical functions offered by diffractive optical elements. For this purpose, metal masters with lens elements made by surface structuring, and frame structures made with deep X-ray lithography and electroplating were used in a combined molding tool, and precision micro-optical elements were replicated by injection molding. The fabrication of the different parts of the mold insert and the alignment and fixing schemes for metal plates forming the micro cavity is described in detail. Injection molding experiments have been carried out using polycarbonate, a polymer known for its good optical properties. We discuss the different designs of mold inserts and injection geometries used for the mold, which were chosen in order to control the shrinkage of the molded element, to restrict damages during demolding, and to avoid inhomogeneities in the area of the lenses due to flow anisotropies and seam lines. We report on the characterization of the molded lens components. Injection molded lens structures are compared with hot embossed replicas, and used for the purpose of collimation applications. The imaging properties of these optical elements from single mode fibers onto single mode fibers is discussed. The miniature optical elements are arranged in arrays with 250 micrometers pitch which make them well suited for applications with fiber ribbons. Various positioning schemes and bench arrangements are under development.
We report on the fabrication of lens components, based on diffractive optical elements, for the purpose of imaging laser-diode emission onto fibers or photodetectors, or for collimation applications. The miniature optical elements are arranged in arrays with 250 micrometer pitch which make them well suited for applications with fiber ribbons. Test optical plates were made of polycarbonate using hot stamper replication technology. The imaging properties of these optical plates from single-mode fibers onto single-mode fibers or from lasers onto single-mode fibers are discussed. The addition of 3D-marker structures to the outline borders of such plates made them suitable for use in micro-optical benches with built-in mechanical registration structures. We fabricated the optical bench inserts with built-in passive alignment elements using deep x-ray LIGA technology (LIGA is a German acronym for 'lithographie, galvanik und abformung' meaning lithography, electroforming and molding). This technology offers high mechanical precision even for the 500 micrometer thick optical bench inserts which we fabricated by injection molding out of transparent and thermally stable polycarbonate. We report on first arrangements of plastic optical bench inserts into micro-optical benches. With the aim towards a fully replicated micro-optical bench made out of plastic we also report on a mounting concept for laser-didoes with built-in alignment trenches. The fabrication process and important properties of these special lasers which we recently developed for transceiver applications are described. We use these lasers for imaging onto single-mode fibers applying the diffractive optical element plates already mentioned.
A grating fabrication technology has been established for producing DFB- /DBR-grating structures in Er-doped Ti:LiNbO3 waveguide lasers. It is based on holographically defined resist gratings transferred into the surface of LiNbO3 waveguides using reactive ion etching with SF6 gas as the dry etching technique. For a sample with a 24 mm long surface relief grating of 346 nm period, a transmission drop of -11.7 dB, a filter bandwidth as small as 0.08 nm, a Bragg resonance wavelength at 1528.4 nm very close to the Erbium absorption line at 1531 nm and excess losses attributed to the grating of only 1 to 2 dB were measured.