Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Optical fiber – waveguide – or preform
Reexamination Certificate
1998-08-27
2001-03-13
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Optical fiber, waveguide, or preform
C264S001270, C264S001370, C264S001380, C264S002500, C430S321000, C205S070000
Reexamination Certificate
active
06200502
ABSTRACT:
The invention concerns a method for fabrication of optical components with at least one fiber taper receptacle wherein a microstructure body is fabricated, this microstructure body is electroformed and the resulting negative form is used as a form tool for fabricating molded pieces for the optical component by means of molding, as well as optical components fabricated by this method. Such components can be used, for example, in optical telecommunications or in sensors.
The transmission of signals and data in telecommunications and sensor engineering is occurring increasingly on an optical basis. Instead of electrical connections, optical connections are created by means of optical waveguides, the assemblage of which represents an optical network. To build up such a network, one requires the most diverse of components in large numbers at the cheapest possible price: these include connections (connectors, splices), signal dividers (branches), wavelength division multiplexers (WDM) and switches.
Optical waveguides consist of a so-called waveguide core and a waveguide material and are generally made of glass or plastic. The transport of the optical signal occurs essentially in the core of the optical waveguide. Depending on the transmission wavelength and size or index of refraction of the optical waveguide, one or more optical modes are used for the transport. Especially in the area of sensor technology and trunk transmission of data (transmission bandwidth), a single-mode transmission is required, which presupposes the use of so-called single-mode optical waveguides. Such single-mode optical waveguides have core dimensions in the range of 2-10 &mgr;m at the usual wavelengths (0.4-1.6 &mgr;m).
Especially high demands are placed on the connections of single-mode optical waveguides to each other or to optical components, due to the small dimensions of the core. For applications in optical telecommunications, it is necessary to observe a precision of ±1 &mgr;m for the fiber position in lateral direction and ±0.5° for the angular orientation. Such tolerances, for example, for fiber band connectors (fiber ribbon: cable with several optical waveguides), can be achieved in that the connector is fabricated with positioning structures for the optical waveguide in the injection molding technique with the help of a high-precision form tool produced by microtechniques (H. D. Bauer, L. Weber, W. Ehrfeld: “LIGA for Applications for Fiber Optics: High Precision Fiber Ribbon Ferrule”: MST News 10 (1994), p. 18-19)).
Integrated-optical components are also being used increasingly for the passive and active connection of optical signals. For this, an optical waveguide arrangement which fulfills a particular function (signal branching, switching, etc.) is integrated in a substrate. The coupling of optical waveguides to the component (observing the above-given tolerances!) can be done, for example, by an active or semi-active assembly process of the components, in which the position of the fiber is varied by measuring the optical power which is coupled in and measured at the exit, thereby optimizing it to a minimal loss. However, the expense of such a manufacturing technique is relatively high.
A very cost-favorable solution for the fabrication of such components is the use of polymer materials, which are processed in a molding process, such as injection molding, spray stamping, hot stamping, reaction casting, etc. In this connection, in addition to the waveguide regions it is also especially advantageous to integrate fiber guide regions in the component, in which the fibers need only be inserted, without subsequent adjustment. Such a fiber coupling is also known as a self-adjusting or passive fiber-chip coupling.
The use of the LIGA technique is especially advantageous for the fabrication of the components. This technique involves the three process steps of lithography, galvanics, and molding. In the first step, a resist is placed on a substrate and exposed to synchrotron radiation, for example, through a suitable mask. After the development, metal is galvanically deposited in the regions dissolved away from the resist, producing a shaping insert as a negative of the original structure. This shaping insert is used in a molding process (e.g., injection molding) to produce molded pieces of plastic, for example. Thanks to the LIGA technique, molded pieces can be produced with a very high precision (<1 &mgr;m). A detailed description of the LIGA technique will be found, for example, in: W. Ehrfeld, M. Abraham, U. Ehrfeld, M. Lacher, H. Lehr: “Materials for LIGA Products,” Micro-Electrical Mechanical Systems: An Investigation of Microstructures. Sensors. Actuators. ed. by W. Benecke, published by The Institute of Electrical and Electronic Engineers, Piscataway, N.J.: IEEE Press. 1992.
From DE 42 12 208, a method of fabrication of an optical polymer component is known, in which a microstructure body is produced by means of Si-micromechanics and excimer laser machining. From this microstructure body, a shaping insert is created by electroforming, which is used for molding in a polymer material. The microstructure here has a v-shaped fiber receptacle and a trough for the waveguide.
In DE 42 17 526 A1, a method is described for fabrication of components for waveguide networks, in which fiber guide structures and waveguide preforms are fabricated by means of a stepped shaping insert in molding technology. X-ray deep lithography using a stepped substrate with subsequent galvanic forming is mentioned as the preferred manufacturing technique for the shaping insert. The fabrication of the stepped shaping insert is also the subject of Patent Application DE 43 10 296.
The drawback in both techniques from the state of the art is that fiber receptacle and waveguide are situated on two levels, separated by a step. But such a body is completely unsuited for accommodation of fiber tapers, since a definite positioning of the taper tips is not assured. If only because of the slight diameter of the fiber taper in the region of the tip, bending can easily occur when introducing the fiber taper, which would alter the position of the taper tips and thus result in a high insertion loss. Furthermore, the shape of the described receptacles is not adapted to the profile of the fiber taper, so that an overcoupling of the optical wave between fiber taper and fiber taper receptacle is not possible, as in DE 43 44 179.
A device for coupling of fiber tapers to optical waveguides is known from DE 43 44 179. The described device has a fiber taper receptacle which is adapted to the profile of the fiber taper. This ensures that an overcoupling of the optical field between fiber taper and fiber taper receptacle is possible. The cross section of the described fiber taper receptacle is circular or trapezoidal (two V-shapes, one on top of the other).
A method for fabrication of the proposed coupling device is not indicated in DE 43 44 179. Yet the indicated cross sectional shapes of the fiber receptacle are especially ill suited for the fabrication of the device. They cannot be fabricated in the desired precision and with the required low roughness of the walls with known fabrication techniques of precision engineering and microtechnology. Furthermore, the device has the definite disadvantage of specifying the troughs for the fiber taper receptacle in the bottom and top plate. Besides the bottom plate, therefore, a special shaping insert must also be fabricated for the top plate and this used to mold the shaped pieces of the top plate. Furthermore, for a good coupling function, bottom and top plate must be assembled and secured with very high precision (around 1 &mgr;m). But such a demand is only technologically feasible through very high expenditure (active positioning of the plates or self-adjustment through high-precision positioning elements).
EP 0 618 502 A1 describes a method for fabrication of stepped shaping inserts, in which two resist layers and two radiation exposure processes are employed, while in the meant
Paatzsch Thomas
Smaglinski Ingo
Hudak & Shunk Co. L.P.A.
Institut Fur Mikrotechnik Mainz GmbH
Vargot Mathieu D.
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