Graded Index Rod Lens Comprising Light-Wave Conductors

The invention relates to a graded index rod lens (GRIN lens) comprising several coupled light-wave conductors for optical data communication systems. Gradient index rod lenses (GRIN lenses) provided with light-wave conductors (LWC's) are used, for example, in multiplex devices for optical broadband transmission.

In an optical multiplexer, GRIN lenses are known, on the end face of which at least two LWC's are coupled (DE-AS 27 45 940). The areas provided for coupling can be calculated with reference to the imaging properties of the GRIN lens. The calculated position of a coupling area can be found only with difficulty, however, laborious measurements being required by fine-mechanical positioning auxiliaries.

The invention has for its object to make it simpler to find calculable areas for coupling light-wave conductors on the end face of a GRIN lens in order to be able to establish rapidly and reliably couplings which are accurately positioned.

In a GRIN lens of the kind mentioned in the opening paragraph, this is achieved in that an end face of the GRIN lens is provided with a profile in which coupling areas for the light-wave conductors are formed.

The invention is based inter alia on the recognition of the fact that due to the dependence of the imaging properties of GRIN lenses upon the wave length, coupling areas can be located in different planes--with respect to the plane of an end face.

An advantageous embodiment of the invention consists in that the area calculable for each coupling is defined by a funnel-shaped recess. Another advantageous embodiment is obtained in that several concentric GRIN lens disks of different thicknesses are adhered to the end face of the GRIN lens to be connected to the LWC's.

The invention will now be described more fully for further advantageous embodiments defined in the claims with reference to the examples shown diagrammatically in the drawing. In the drawing:

FIG. 1 shows in sectional view a GRIN lens having a funnel-shaped end face structure;

FIG. 2 shows in sectional view another embodiment of a GRIN lens having a terraced end face structure;

FIG. 3 shows in sectional view another embodiment with disks secured on the end face.

The GRIN lens 1 shown in FIG. 1 forms part of an optical transmission system. Starting from its end face 2, different radiation paths are indicated in broken lines, in dotted lines and in dot-and-dash lines, which may originate from an optical system (not shown) coupled to this end face or which are produced upon reflection at the end face 2 when this face is covered with corresponding reflective layers.

Without taking into account the dimensional accuracy, it is shown that various radiation beams have points of intersection at different distances from the opposite end face 3.

The end face of the GRIN lens 1 has a profile of funnel-shaped recesses 10, 11, 12. The tips of the funnels are located at the points of intersection 4,5,6 of the radiation beams shown to which the LWC's 7,8 and 9 are coupled. For coupling purposes, the LWC's are introduced into the relevant funnel and adhered there to each other. On GRIN lenses of this configuration, LWC's can thus be coupled in a simple and accurate manner to the relevant radiation path.

Such funnels can be formed by photoetching or by precision vibration boring operations so that the funnel tip is located at the relevant point of intersection of the radiation beams. LWC's 7,8 and 9 to be coupled on the end face 3 are by these recesses 10-12 guided to the relevant precalculated coupling areas, at which they are adhered to the GRIN lens 1.

Other forms (not shown) of the recesses are possible and can be defined by the relevant manufacturing method. Thus, regular profile patterns may also be provided on the end faces, in which the relevant recesses are suitable to be used as coupling areas.

FIG. 2 shows a further profile of a GRIN lens 20, in which the same elements are designated by the same reference symbols. The end face 23 of the GRIN lens 20 has a stepped profile, which is obtained when the end face 23 is covered with GRIN lens disks of different diameters.

The plane of the relevant calculated point of intersection is freely accessible for the LWC. In order to facilitate the orientation in finding the coupling area, the diameter of each of the disks 24 and 25 to be placed on the end face 23 is dimensioned in accordance with the distance of the intersection point of the radiation beams from the center. The coupling areas of the LWC's 7 and 9 are located on concentric circles.

FIG. 3 shows a further version of a profile, To GRIN lenses are now adhered GRIN lens disks 24, 25 and 26, the outer diameter of which corresponds to the diameter of the GRIN lens and which have bores for the relevant coupling area of the LWC's. For calculation of the position of the coupling areas, the material of the disks is also taken into account, which is preferably glass or another radiation-transparent material, for example, synthetic resin. As a matter of course, prismatic disks with obliquely positioned surfaces may also be used, in which bores define the relevant coupling areas.