Antoni Picard

Compact self-aligning assemblies with refractive microlens arrays made by contactless embossing

The hybrid integration of microlenses and arrays of microlenses in micro-optical systems is simplified using contactless embossing of microlenses (CEM) in combination with LIGA microfabrication. CEM is anew fabrication technique for the production of precise refractive microlens arrays. A high precision matrix of holes made by LIGA technique is used as a compression molding tool to form the microlenses. The tool is pressed onto a thermoplastic sample which is heated close to the glass transformation temperature of the material. The material bulges into the openings of the molding tool due to the applied pressure and forms lens-like spherical structures. The name refers to the fact that the surface of the microlens does not get in contact with the compression molding tool during the shaping process and optical quality of the surface is maintained. Microlenses and arrays of microlenses with lens diameters from 30 micrometers up to 700 micrometers and numerical aperture values of up to 0.25 have been fabricated in different materials. Cost-effectiveness in the production process, excellent optical performance and the feature of easy replication are the main advantages of this technique. The most promising feature of this method is the possibility to obtain self- aligned assemblies then can be further integrated into a micro-optical bench setup. The CEM fabrication method in combination with LIGA microfabrication considerably enhances the hybrid integration in micro-optical devices which results in a more cost-effective production of compact micro-opto-electro-mechanical systems.

Parallel optical interconnection using self-adjustung microlenses on injection-molded ferrules made by LIGA technique

Prototypes of compact lensed fiber connectors have been fabricated by LIGA technique that provide multimode connections for parallel optical interfaces. Contactless embossed microlens arrays were introduced as collimating and focusing elements in order to achieve a simplified connector assembly. As an alternative ball lenses were inserted in a second type of expanded-beam connector ferrule. Fibers, microlens arrays or respectively single microlenses, and two metal guiding pins are possibly adjusted in high precision alignment structures. The ferrules are injection modeled and the modular mold insert has been fabricated by means of microtechnology: LIGA technique and electro-discharge machining. Insertion loss values of 4.5 dB have been measured for assembled mated couples of ferrules with contactless embossed microlens arrays and 2.3 dB for ferrules with ball lenses, both at 1310 nm including reflection losses of typical 1 dB. Even though commonly used butt-coupling connector show lower insertion loss values, the introduced compact expanded-beam connectors could offer an attractive solution for applications in harsh or dirty environments of for micro-optical components e.g. compact 90 degrees optical interfaces for backplane connectors or switches by deflecting the expanded optical beam by a mirrors or prisms.

Contactless embossing of microlenses: a new technology for manufacturing refractive microlenses

Contactless embossing of microlenses (CEM) is a new fabrication technique for the production of refractive microlens arrays. The basic idea is that the surface of the microlenses has no contact with the compression molding tool during the shaping of the surface relief. A high precision matrix of holes made by LIGA microfabrication is used as a compression molding tool. This tool is pressed onto a thermoplastic sample which is heated close to the materials transformation temperature. The material bulges into the openings of the molding tool due to the applied pressure. It process conditions are properly set, the material forms lens-like spherical structures. Microlenses and arrays of microlenses with lens diameters between 30 micrometers and 500 micrometers have been fabricated in thermoplastic material. Besides highly accurate microlens arrays, CEM also provides the potential of cost-effective production and high precision mounting concepts.

Refractive microlens arrays made by contactless embossing

Contactless embossing of microlenses (CEM) with LIGA molding tools is a new fabrication techniques for the production of refractive microlens arrays which combines high accuracy in the micrometer range, cost-effective production of the devices, and cost-effective high precision mounting concepts. The name refers to the fact that the surface of the microlenses has no contact with the embossing die during the shaping of the surface relief. A high precision matrix of holes made by LIGA microfabrication is pressed onto a thermoplastic sample which is heated. The material bulges into the openings of the molding tool due to the applied pressure and forms lens-like spherical structures. The embossing die touches the lens material only outside the lens area. High-speed microlenses with f/ < f/4 and diameters of the lens aperture between 30 micrometers and 500 micrometers have been fabricated in PMMA and PC. Excellent uniformity within the microlens arrays are achieved by using LIGA microfabricated embossing dies. In addition to the excellent optical performance of the microlenses, the CEM method assists hybrid integration in micro-opto-electro- mechanical systems by providing precise auxiliary structures for easy and cost-effective mounting and adjusting.

Miniaturized fiber optical switches with nonmoving polymeric mirrors for tele- and data-communication networks fabricated using the LIGA technology

Fiber optical switches for telecom and datacom purposes become more and more important with the growth of fiber- based networks. This paper proposes a new principle for manipulating optical light paths through switchable, but non-moving polymeric mirrors in free-space optical interconnects. To achieve this a polymeric body and a thin liquid film are moved within a cavity. By moving the body up and down perpendicular to the light path the cavity wall can be switched from total reflective to transmissive state while the liquid film remains between body and wall due to capillary forces. The body can be moved with integrated electro-magnetic actuators and so the whole concept allows the realization of very compact switching elements. The coupling of single mode optical fibers requires a lateral and angular alignment precision in the micron and millirad range for both direct coupling and expanded beam coupling concepts. To meet these requirements, the LIGA technology provides a promising approach with respect to the high precision and also low-cost fabrication by mass replication processes. The combination of LIGA technology with other precision machining technologies allows the fabrication of miniaturized systems with both micro-optic and micromechanic components which fulfill the required tolerances for optical coupling. First demonstrators of 1 X 2 and 2 X 2 switches with bistable electro-magnetic actuators have been fabricated to show the feasibility of the proposed principle. The measured insertion loss is less than 2 dB at 1300 nm with -40 dB crosstalk. The switching time was measured 100 ms. The capabilities of the proposed non-moving mirror principle can be applied to 1 X 2 repair switches for the access area as well as to FDDI-switching-nodes up to compact N X M cross-connect switches for reconfiguration purposes or parallel interconnects to optical backplanes for the office area.