Patent Application
20080253423
This invention relates to a compact opto-electronic device including at least one Vertical Cavity Surface Emitting Laser or VCSEL, which operates with another opto-electronic component.
It applies in particular to a surface emitting laser with monitoring of the power that it emits or that works with another transmitter to carry out optical multiplexing in an optical wave guide.
The development of surface emitting laser opto-electronic components has opened up a wide range of applications from the detection of gas to the creation of opto-electronic modules for optical fibre networks for short distance networks. The surface emitting lasers have a certain number of advantages compared with edge emitting lasers or EEL, in particular their aptitude to be tested collectively on the common substrate on which they are manufactured and their easier coupling in standard optical fibres.
These surface emitting lasers are used once they are placed in a case, traditionally TO (Transistor Outline) case or TOSA (Transmitter Optical Sub Assembly) cases, respectively fitted with a window allowing the light beam emitted to pass or a device which permits the electrical connection of an optical fibre connector.
Most applications which use these surface emitting lasers need the power emitted by the laser to be measured constantly, by means of a photo-detector placed inside the case. The photo-detector is typically a PIN type photodiode also called a monitoring photodiode. Therefore the aim is to illuminate the photo-detector with a fraction of the light emitted by the laser before it leaves the case.
Contrary to the edge emitting lasers, it is not possible to place the photo-detector on the face of the laser opposite to that which produces the light as this face is that of a substrate on which the epitaxial growth of the intrinsic structure of the laser has been made and that said substrate is opaque to the light produced by the laser.
The currents required for this monitoring are approximately of the order of 100 to 500 micro amperes with processes capable of detecting very small current variations. Consequently, with photodiodes whose typical sensitivity is less than approximately 1 A/W and surface emitting lasers whose power is around 1 to 2 mW, it may be necessary to sample up to approximately 50% of the light emitted by the laser to monitor it, and the other 50% may be used for the chosen application.
The monitoring is carried out conventionally by using parasite reflections of the light beam emitted by the laser on the outlet window of the case. In fact, a fraction of the beam is reflected and a monitoring photodiode may be placed in the path of the portion of beam after reflection.
In the U.S. Pat. No. 5,905,750, the photo-detector and the emission surface of the laser are next to one another, they are placed substantially in a same plane.
In the patent application GB-A-2 351 180, the laser is mounted on the chip on which the photo-detector is located, wherein the laser and the photo-detector are offset laterally with respect to one another.
In the American U.S. Pat. No. 5,737,348 the laser is mounted on the photo-detector, it is placed in a central zone of the photo-detector. The collection may only be made in a peripheral zone of the photo-detector.
In the patent application WO-A-99/34487 the laser and the photo-detector are fitted as in the patent application GB-A-2 351 180 and the window is inclined with respect to the emission axis of the laser beam so as to redirect the part of the beam that is reflected onto the photo-detector.
In the U.S. Pat. No. 5,943,357 the photo-detector and the laser are stacked on one another and the photo-detector only receives the light emitted by the rear of the laser.
In the American U.S. Pat. No. 5,757,836 the photo-detector is positioned next to the laser, its sensitive face is substantially transversal to the front face of the laser.
In the patent EP-A-0 869 590, the patent application WO-A-03/000019 and the patent application US-A-2003/0109142, the photo-detector is either in the path of the direct beam emitted by the laser, or in the path of a reflected fraction, wherein the front face of the laser and the sensitive face of the photo-detector are in distinct planes.
One disadvantage of these structures is that their base takes up a lot of space, as the photo-detector is positioned laterally to the front face of the laser. This disadvantage also exists in opto-electronic devices comprising a surface emitting laser that is associated to another opto-electronic component that is not a photo-detector but a transmitter. Such an opto-electronic device further comprises a multiplexer to combine the beams emitted by the two sources of light and carry out multiplexing.
The last three structures mentioned are also quite thick.
The structures on which the monitoring is carried out on a fraction of the beam emitted by the laser, wherein this fraction is reflected by a window, are not satisfactory as the power monitored is not high enough and the signal to noise ratio is too low.
Furthermore, when the device comprises several lasers in a same case, and the monitoring is made on reflected beams, it is not possible to discriminate between the respective powers of the different lasers.
The purpose of this invention is precisely to propose an opto-electronic device that does not have the disadvantages mentioned above.
One purpose is in particular to propose such an opto-electronic device that is very compact with respect to the prior art.
Another purpose of this invention is to propose an opto-electronic device that comprises a surface emitting laser that operates together with a component that is a monitoring photo-detector, in which the power that is monitored by the photo-detector is increased with respect to the prior art, wherein this monitoring permits any dysfunctioning laser to be detected and/or to regulate the mean power emitted.
Another purpose of the invention is to provide an opto-electronic device with a surface emitting laser that operates together with a photo-detector in which the representativity of the power level is increased with respect to the prior art.
To achieve these purposes the invention concerns more precisely an opto-electronic device comprising at least two opto-electronic components which work together, among which a first one that is a surface light emitting laser and another opto-electronic component, characterised in that each of the opto-electronic components is mounted on a main face that is different and opposite an intermediate layer incorporating a grating coupler coupled to an optical wave guide designed to transport part of the light emitted by the surface emitting laser, wherein the grating coupler is sandwiched between the emissive face of the surface emitting laser and the other opto-electronic component.
The other opto-electronic component may be a photo-detector for monitoring the light emitted by the laser.
As a variant, the other opto-electronic component may be a transmitter designed to carry out multiplexing with the surface emitting laser.
The grating coupler is semi-transparent for the light emitted by the surface emitting laser, especially when the other opto-electronic component is a photo-detector.
The intermediate layer may be flanked on each of its main faces by electrical connection tracks.
At least one electrical connection track is ended with a pad fitted with a collapse chip before the laser or the other opto-electronic component is mounted.
An electrical connection track of a face of the intermediate layer may be connected to an electrical connection track on the other face of the intermediate layer by at least one metallised hole passing through the intermediate layer.
A case may accommodate the intermediate layer and at least one pair formed by the laser and the other opto-electronic component.
When several pairs are accommodated in the case, the opto-electronic components mounted on one face of the intermediate layer may be individual or grouped into linear array.
This invention also concerns a manufacturing process for an opto-electronic device comprising at least two opto-electronic components which work together including a first component that is a surface light emitting laser and another opto-electronic component comprising the following steps:
In the process, the assembly may use collapse chip connection, thermo-compression of pads or bonding with conductive glue.
Glue may be inserted between the intermediate layer and at least one of the opto-electronic components.
The grating coupler and the optical wave guide may be made on the surface of the base substrate.
The optical wave guide may have a core which is made, like the grating coupler, from silicon, doped silica, a material obtained by sol-gel, resin, polymer.
The base substrate may be eliminated by selective chemical etching.
This invention will be more clearly understood upon reading the description of examples of embodiments provided, purely by way of illustration and in no way restrictively, in reference to the appended drawings in which:
Identical, similar or equivalent parts of the various figures described below bear the same numerical references so as to facilitate switching from one figure to another.
The different parts shown in the figures are not necessarily to a uniform scale, to make the figures easier to read.
It is to be understood that the different variants shown are not necessarily mutually exclusive.
Structures that are found in the prior art are not shown in detail in order to avoid this invention more difficult to be read.
In the following description, other opto-electronic components 2 will be mentioned in general.
The surface emitting laser 1 and the other opto-electronic component 2 are mounted on either side of an intermediate layer 3 incorporating an optical wave guide 4 and a grating coupler 5. The face of the laser 1 which emits the light has the reference 1.1, it is located on the intermediate layer 3 side.
The optical wave guide 4 is designed to transport part of the light emitted by the surface emitting laser 1 to a user device (not shown). The optical wave guide 4 has one end coupled to the grating coupler 5 and one free end from which the light transported by the optical wave guide 4 leaves. The grating coupler 5 is positioned upstream of the optical wave guide 4, opposite the emitting face 1.1 of the laser 1. The grating coupler 5 may be for example a diffraction network, a Bragg's grating or other. The network couplers are known as optical structures. They feature a periodic network type structure which permits part of the light they receive to be injected substantially perpendicularly or inclined into the optical wave guide that is coupled to them and which is located in the extension of the grating coupler, substantially in the same plane. The periodic structure can be seen clearly in
Typically the coupling rate of the light emitted by the laser 1 in the optical wave guide 4 is approximately 50 to 80%.
When the other opto-electronic component 2 is another surface emitting laser, it is symmetrical to the first laser 1 with respect to the grating coupler 5. Its face which emits the light is opposite the grating coupler 5.
Reference 7 shows a coated material which surrounds the surface emitting laser 1. Its use will be described below.
The surface emitting laser 1 and the other opto-electronic component 2 are mounted or hybridised onto the intermediate layer 3, sandwiching the grating coupler 5. The assembly may use collapse chips 8 with a fusible material to be applied onto the bond pads 6.1, 6.2 (visible in
As a variant, it is possible to thermo-compress connector metallic pads 126 or bond using conductive resin pins deposited for example by screen printing. It is supposed that in
The collapse chips 8 may be carried either by the laser or by the other opto-electronic component or by the intermediate layer 3 prior to hybridisation.
The surface emitting laser 1 and the other opto-electronic component 2 need to be connected to electrical connection tracks 6, 6′ for their energy supply and for their command or to collect the electrical signals that they generate in the case of a photo-detector 2. It is provided that on each of the main faces 3.1, 3.2 of the intermediate layer 3 on which the surface emitting laser 1 and the other opto-electronic component 2 are mounted, these conductive tracks are fitted, for example fitted out in a network. An electrical connection track 6 of one face 3.1 may be connected to a electrical connection track 6′ of the other face 3.2 by means of a metallised hole 9 or via. These electrical connection tracks 6, 6′ may be ended with bond pads 6.1, 6.2 on which the collapse chips 8 are made for the hybridisation of the surface emitting laser 1 and the other opto-electronic component 2.
The intermediate layer 3 may be made from a silicon or silica base for example, as will be described below.
The opto-electronic device that is the subject of the invention is especially well suited to the case where it comprises, in a same case 10, several surface emitting lasers 1 which work together each with an opto-electronic component 2 of the photo-detector type. Each of the photo-detectors 2 monitors the power emitted by the laser 1 that operates together with it through the intermediate layer 3. The lasers 1 and the opto-electronic components 2 may be presented unitarily and be assembled individually on the intermediate layer 3 as illustrated in
Based on
Now an example of the manufacturing process of an opto-electronic device of the invention will be examined.
Using a base substrate 100, for example made of silicon, on which the optical wave guide 4 and the grating coupler 5 are to be formed. This formation is made by a series of steps for depositing or forming and micro structuring. If the optical wave guide 4 is made on the surface, it is possible to start by depositing, on the base substrate 100, for example by Plasma enhanced chemical vapour deposition—PECVD—a lower cladding layer 101, for example made of silica, for the optical wave guide (
For multimode optical wave guide applications, the optical wave guides of which at least the core is obtained by the sol-gel, resin and polymer process are preferred.
The intermediate layer 3 is thus created. It has a main face 3.1 that is free and another main face 3.2 that is attached to the base substrate 100 and that will be subsequently revealed.
Then on the free main face 3.1 of the intermediate layer 3, the electrical connection tracks 6 are created that are appropriated to the opto-electronic component that will be assembled to this free face 3.1 of the intermediate layer 3, and possibly the bond pads 6.1 which end these electrical connection tracks 6 and are used for the assembly of the opto-electronic component. The opto-electronic component may be the surface emitting laser 1 but it may be envisaged that it is the other opto-electronic component 2 that is assembled onto this free face 3.2. In the following description, it is supposed that it is the laser that is to be assembled first but this is not restrictive.
The electrical connection tracks 6 may be made conventionally with a metal base such as aluminium, which is the most commonly used metal, copper, gold or silver for example by PVD—plasma vapour deposition. The metal 60 is deposited by photolithography and etching is used to define the contour of the electrical connection tracks 6 and that of the bond pads 6.1 (
This assembly is then covered by an electrically insulating passivation layer 118, for example SiO2 or Si3N4, by PECVD (
It is supposed that in the example described, the tracks 6 are made at the same time as the pads 6.1 fitted with collapse chips 8.
Now we will cover the creation of connector pads 6.1 equipped with collapse chips 8 to assemble the laser 1 onto the intermediate layer 3 by collapse chip connection (flip-chip process). By calling the collapse chips “fusible”, this means that they are made from a material that can melt at temperatures that are low enough to avoid damaging the component to be assembled using collapse chips.
The bond pads 6.1 equipped with collapse chips 8 are positioned either on the surface of the intermediate layer 3, or on the laser 1 or on the other opto-electronic component 2. If they are made on the intermediate layer 3, they are placed in electrical contact with the electrical connection tracks 6, 6′.
When assembling, the emissive face of the laser 1 is opposite the grating coupler 5. As concerns the other opto-electronic component 2, if it is a photo-detector, its sensitive face is opposite the grating coupler 5 and if it is a transmitter, it is its emissive face that is opposite the grating coupler 5.
The opto-electronic component 1, 2 also comprises bond pads that may or may not be equipped with collapse chips, as the collapse chips 8 are located either on the intermediate layer 3 or on the opto-electronic component 1, 2 prior to the hybridisation.
In the example described in
The collapse chips 8 are made at the level of the connector pads 6.1. A continuous base 122 is deposited on the surface (
Photolithography is then used to make recesses using the resin 120, at the level of the connector pads 6.1, which are to hold the fusible material of the collapse chips (
The recesses are filled with fusible material 123 (
The hybridised laser 1 also comprises metallic bond pads which need to be attached to the collapse chips 8. They have the references 124 on
It is possible to attach another component 20 to the same free face 3.1 of the intermediate layer 3 as that which accommodates the laser 1. This may be for example a piloting device 20 for the laser 1 shown in
Instead of using a traditional collapse chip connection technique, an assembly technique using metallic pads 126 and thermo-compression may be used as illustrated in
In both cases, glue 125 may be added between the laser 1 and the intermediate layer 3 to avoid problems of thermal expansion.
As a variant, it is possible that bond pads made of electrically conductive resin are used for the assembly instead of using metallic pads and possibly the collapse chips. These resins may be loaded with silver, palladium or platinum for example. Transparent glue may also be placed between the laser and the intermediate layer.
It is possible to provide an interconnection between the electrical connection tracks 6 of one of the main faces 3.1 of the intermediate layer 3 and the electrical connection tracks 6′ of the other main face 3.2 of the intermediate layer 3. This interconnection may be achieved by means of metallised holes 9 which pass through the thickness of the intermediate layer 3. These metallised holes may be formed prior to the coating step (
With such a manufacturing process, it is possible to manufacture opto-electronic devices of the invention, collectively by using the usual micro-electronic means and to obtain the accuracy required for this type of opto-electronic device.
Even though several embodiments of this invention have been shown and described in detail, it can be understood that various changes and modifications may be made without this leaving the scope of the invention. It is especially possible to hybridise the opto-electronic components by all means familiar to a person skilled in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07 54458 | Apr 2007 | FR | national |
