The coupling of an optical fibre and an emitter of laser light requires an accurate alignment between this component and the fibre, usually an alignment close to 10 μm, the accuracy required being even higher for single-mode optical fibres. To couple an optical fibre and a detector component (for example, a VCSEL operating as a photodetector) the same accuracy as for the coupling between the fibre and emitter component is required.
Considering the example of coupling an optical fibre and a laser emitter, a commonly used alignment technique consists of actively aligning the fibre and laser emitter, the latter being powered in order to produce a laser beam. Once the alignment is produced, the fibre is attached to the laser emitter by soldering or using an adhesive.
This active alignment technique leads to a high cost figure for the assembly thus obtained.
For this reason a passive alignment technique has been conceived. In this case, the relative positioning and then the attachment of the fibre and the emitter or receiver component is achieved without voltage (for the component), nor luminous flux. The fibre and the component are locked mechanically with respect to each other then precisely connected.
There exists for example a well-known passive assembly technique for joining an optical fibre and a laser rod that uses lateral emission. This assembly is shown schematically in FIG. 1.
An alignment support 2 in the shape of a V groove, usually made from silicon 4 is used to locate the optical fibre 6. This latter is bonded into the V shaped silicon and the laser rod 8 is precisely hybridised to the fibre using the alignment support.
This technique allows accuracies of the order of 1 μm to 5 μm to be achieved.
As regards this technique there is for example a description [1] that, as with the other documents referred to later, is listed at the end of this description.
The technique described earlier, using a V groove in silicon, is applicable for the assembly of an optical fibre and a laterally emitting laser but not for the assembly of a fibre and a VCSEL device that emits light from a face.
However, this technique has been modified in order to enable such an assembly to be performed. In this case, mechanical or optical means are used to place the VCSEL device at 90° to the optical fibre.
This subject is referred to as an example in document [2].
However, this technique alters the passive alignment and requires the use of complex operations, in particular supplementary alignment means.
Similar disadvantages are also apparent when it is required to connect an optical fibre and a VCSEL as described in document [5] or a VCSEL able to emit light from its inner or rear face, as described in documents [3] and [4].
In this latter case, it is worth noting that it is easier to refer to a vertical cavity laser or VCL since such a laser emits light across its substrate rather than from an upper or forward face.
Also to be noted is the flip chip technique that is described in document [3] in order to connect the VCL device to a silicon control circuit.