Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-02-07
2002-08-20
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S089000, C385S090000, C385S137000
Reexamination Certificate
active
06435733
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns an assembly allowing for connection of optical fibres with optical or optoelectronic components and a process for manufacturing this assembly.
The invention has applications in the area of microelectronics, particularly in all cases where optical fibres are to be connected to laser sources or optical modules (for example dividers, multiplexers or sensors) mounted on optoelectronic substrates.
In the case of telecommunications by optical transmission in particular, the invention can be used when a laser diode (or bar of lateral emission laser diodes) must be connected to an optical fibre (or several optical fibres).
STATE OF THE PRIOR ART
In the area of microelectronics, the increase in functioning frequency of electrical systems requires:
designing of new principles of data transmission and particularly paralleling of electric buses allowing for simultaneous transmission of several signals at once and/or
use of light through optical wave guide (integrated wave guides or optical fibres) in order to increase the information rate.
These optical wave guides provide very good immunity to electromagnetic disturbances.
In addition, optical transmission requires the making of emission, reception and luminous signal processing modules. Techniques have been developed for this, particularly on glass or silicon in order to provide:
coupling of the optical fibres
optical and electrical connections of optoelectronic components
electric connection of electronic interface components. The following documents can be consulted:
[1] “Soldering technology for optoelectronic packaging”,
1996
Electronic Component and Technology Conference, p. 26 to 6
[2] “Passive alignment for optoelectronic components, Advances in electronic packaging, EFP-vol. 19-1, 1997, vol. 1, p. 753 to 758.
[3] “Silicon motherboards for multichannel optical module”, IEEE transactions on components, packaging and manufacturing technology, Part A, vol. 19, no. Mar. 1, 1996, p. 34 to 40.
[4] “Flip-chip optical fibre attachment to a monolithic optical receiver chip”, SPIE, vol. 2613, p. 53 to 58.
Each of the assemblies known by documents [1] to [4] is generally in the form of a substrate on which:
optical fibres are connected either facing optical wave guides formed in the substrate or facing laser diodes and/or photodetectors,
optoelectronic components inserted in this substrate or placed on its surface are coupled with optical wave guides and/or optical fibres,
electronic components addressing or collecting information coming from optoelectronic components are positioned.
The optical fibres and optical or optoelectronic components must be perfectly aligned with each other to minimise optical losses.
The degree of precision sought can be less than 0.5 &mgr;m.
Two techniques are primarily used for this.
1) A known technique for active alignment of an optical fibre with a laser diode which ensures alignment by electric measurement with a photodiode in real time.
To do this, the laser diode is supplied and a measurement of the luminous power at the exit of the fibre gives an indication of its alignment relative to the laser diode. Optimisation of the alignment is provided by small movements of this laser diode using mechanical or piezoelectric micro-manipulators. An assembly can then be made by bonding.
This active alignment technique has some drawbacks:
long alignment process
the need for mechanical fixing, with glue for example, of the laser diode after alignment and
that this fixing must not produce mechanical stresses which could modify the alignment.
2) A passive alignment technique for optical fibres is also know. Its main objective is cost reduction.
If the fibre must be connected in parallel to a substrate in silicon for example, the most widespread connection method at present is the making of a V-shaped cavity in the silicon substrate which acts as a optical micro-bench, for example according to the principle of etching along the preferential crystalline planes (100).
The fibre is fixed and glued to the bottom of the cavity facing an optoelectronic component. This optoelectronic component, if it is brought onto the substrate, is generally mounted head down using the flip-chip technique on metallic links providing electrical continuity, mechanical resistance and thermal evacuation to the substrate.
The optoelectronic component facing the fibre must be in absolute alignment in the three directions in space. The following can be used for this:
very precise equipment allowing for positioning and welding of the component, while holding it on the substrate, with precision on the order of 1 &mgr;m,
soldering joints with positioning shims made in the substrate and/or in the component to be assembled,
soldering joint elements without shims using the auto-positioning effect linked to the wettability forces of the solder in the liquid phase, the auto-positioning taking place in parallel on the substrate by wetting on the metallic studs and perpendicular to the substrate by control of the volume of the soldering elements.
In addition to the use of V-shaped cavities in the substrate, there is a method for attaching by gluing fibres in an intermediate support in silicon, also etched into a V-shape, and then put on the substrate upside down (see document [4]). The alignment and soldering of the intermediate support is done with precision equipment. The auto-alignment effect in the liquid phase is not used. The rigidity of the fibres and the weight of the unit do not allow this.
When a fibre is connected perpendicularly to a substrate, there is a method for inserting the fibre into a pierced block which is first soldered and mounted by the flip-chip method using the auto-alignment effect in the liquid phase.
FIG. 5
of document [1] may be consulted for this subject.
There is a problem in the case of passive alignment of an optical fibre facing an optoelectronic component put onto an interconnection substrate.
When the fibre is attached parallel to the substrate in a V-shaped cavity integrated into this same substrate, the optical positioning of the optoelectronic component facing the fibre must be absolute in the three directions in space.
In a plane parallel to the substrate, the metallic studs made, which are soldered, are perfectly aligned with the V-shaped cavity because they are generated by the same lithographic template. The effect of auto-alignment in the liquid phase of the solder microspheres ensures good positioning of the component facing the fibre.
In a direction perpendicular to the substrate however, control of the height of the optical axes requires, for the fibre, control of the width of the V-shaped cavity (variation of burying of the fibre) and of the optoelectronic component, either a mechanical block or a control of the solder volume. These operations depend on the technological manufacturing variations.
SUMMARY OF THE INVENTION
The purpose of this invention is to define an assembly and its manufacturing process, allowing for very precise passive alignment of one or several optical fibres with one or several optical or optoelectronic components in a relative manner.
This assembly is made using microspheres of a meltable material (solder) on a substrate, which can be an interconnection substrate, which acts as an optical micro-bench.
The meltable material of the microspheres is for example indium or a meltable tin and lead-based alloy or any alloy with a low melting point.
Precisely, this invention concerns firstly an assembly including a substrate and, on this substrate, at least one optical fibre support, at least one optical fibre in the support and at least one optical or optoelectronic component, the optical axis of the fibre and the optical axis of the component being aligned, this assembly being characterised in that the support and the component are attached to the substrate using microspheres of a meltable material, allowing the optical axis of the fibre and the optical axis of the
Caillat Patrice
Parat Guy
Puget Christiane
Commissariat a l'Energie Atomique
Pearne & Gordon LLP
Rojas, Jr. Omar
Sanghavi Hemang
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