WO2006103512A1

WO2006103512A1 - Optical data tranceiver

Info

Publication number: WO2006103512A1
Application number: PCT/IB2006/000656
Authority: WO
Inventors: Piet De Pauw
Original assignee: Melexis Nv
Priority date: 2005-03-29
Filing date: 2006-03-23
Publication date: 2006-10-05
Also published as: GB0506274D0

Abstract

An optical data transceiver 200 comprises: an integrated circuit 101 having implemented upon it first light sensing means 106, light emitting means 105 and second light sensing means 104. A gel blob 108 is provided on integrated circuit 101. Said gel blob 108 is substantially transparent and allows most of the light emitted by light emitting means 105 to pass through it into an optical fibre 207. In a similar manner most of the light emanating from optical fibre 207 may pass through the gel blob and be incident upon the second light sensing means 104. A proportion of the light emitted by light emitting means 105 is not passed through gel blob 108 but is instead reflected from the surface of gel blob 108 and is then incident upon the first light sensing means 106. The signal generated by the first light sensing means 106 is input to control means (not shown), typically implemented as part of integrated circuit 101. The control means monitors the output of the first light sensing means and controls the power output of the light emitting means 105 in response thereto. In this way, the power output of the light emitting means may be optimised without exceeding safe output levels.

Description

OPTICAL DATA TRANCEIVER

The invention relates to optical data transceivers and in particular to optical data transceivers having means for monitoring and controlling output power levels.

Optical data transmission systems use light to carry digital data along fibre optic cables. The light is generated by a first transceiver, coupled to the fibre, and travels along the fibre to its far end whereupon it is incident upon a second transceiver. The first transceiver acts to convert electrical signals into optical signals and the second transceiver acts to convert the optical signals back into electrical signals. This process may of course be reversed, with signals being sent from the second transceiver to the first transceiver, if desired.

Each transceiver has an optically active element or elements. Typically the optically active elements are a light emitting means and a light sensing means. It is however possible, if data transmission is required in a single direction only, that transceivers may be adapted only to emit light or to sense light i.e. to have a single optically active element being either a light emitting means or a light sensing means as appropriate. In this application, the term transceiver is used to encompass all three possibilities.

Conventionally, optical transceivers are housed in a protective package, said protective package having an aperture through which light may pass between the optically active elements of the transceiver and the exterior of the package and the aperture is adapted such that an optical fibre may be inserted and releaseably retained. The optical fibre is conventionally terminated in a ferrule. To allow the fibre to be inserted and retained, the aperture is adapted to have a cross-section which corresponds to the cross-section of the ferrule. If the ferrule is not aligned correctly with the optically active elements, coupling between the optical fibre and the optical data transceiver is reduced and thus a proportion of the signal is lost. These losses reduce the effective intensity of the transmitted data signals and hence reduce the efficiency, the sensitivity, data rate, Bit Error Rate, and maximum communication range of the signal from their optimum values.

In order to compensate for such losses, it is tempting merely to boost the output power of such transceivers however many optical transmission systems have legal, health and safety, or industrial practice limitations on transmitted power. To be sure that 100 percent of transmitters fall below the limit during their lifetime requires a prediction of variation during life and a consequential downgrading of the nominal power to ensure the power transmitted remains below the limit. When manufacturing tolerances are also allowed for, the nominal power transmitted can be such as to have a detrimental affect on the range of a transmitter. Extensive testing at manufacture and on test adjustments of power output can raise the nominal power output but the cost of testing and adjustment can be prohibitive in low cost applications.

As a result, a number of methods have been proposed wherein the power output of a transceiver is monitored to ensure that power levels remain below permitted limits. In US 6,005,262 this is achieved by mounting an optical emitting element over an optically sensitive element; in US 6,567,435 this is achieved by mounting a half silvered mirror between the optical emitting element and the fibre to reflect part of the emitted light back onto an optical sensor; and in US 2002/0126936 a pair of optical emitters in parallel are provided, one used for data transmission and the other monitored continuously by an optically sensitive element. Each of these systems have additional mechanical or optical elements and thus have increased manufacturing or assembly costs.

Another proposal is outlined in US 6,898,219. In this proposal, reflective fragments are dispersed throughout a protective gel blob provided over the optical emitting element. The reflective fragments deflect light output by the light emitting means to light sensing means, the amount of light deflected being related to the amount of light emitted. Accordingly, the light emission levels can be monitored. However, this proposal is not entirely satisfactory as the additional scattering induced by the reflective fragments can reduce the light transmission markedly and providing gel incorporating said fragments increases the expense of the emitting element. As an alternative, also in US 6,898,219, it has been suggested that reflections from the end of an optical fibre coupled to the optical data transceiver can be monitored to provide a indication of the power output. If however the fibre becomes detached, no reflection is detected and the output power is boosted. This can lead to output power exceeding permitted levels.

It is therefore an object of the present invention to provide an optical data transceiver having a new means for monitoring and controlling its power output. According to a first aspect of the present invention there is provided an optical data transceiver comprising: a light emitting means; a light sensing means for detecting incident light and outputting a signal in response thereto; a gel blob provided such that a proportion of the light emitted by the light emitting means is directed to the light sensing means by the gel blob; and control means for controlling the power output by the light emitting means in response to the output of the light sensing means.

This thus provides a low cost optical data transceiver to an optical fibre, which can maintain accurate levels of light output. In this manner, the power output by the light emitting means can be maintained at maximum but safe levels and hence, the sensitivity, data rate, Bit Error Rate, and maximum communication range of the data signals are optimised. The use of a gel blob to reflect a proportion of the output signal enables this to implemented in a low cost manner and additionally provides a measure of additional protection for the optical elements.

Wherein the present invention is described specifically in relation to optical elements operational with light in the visible region of the electromagnetic spectrum, it should be understood that the invention may equally be applied to elements operation in the ultraviolet or infrared regions of the electromagnetic spectrum. Accordingly, the terms 'light' and 'optical' used herein should be understood to cover ultraviolet and infrared radiation in addition to visible radiation. Preferably, the gel blob is provided such that it covers both the light emitting means and the light sensing means and light is directed to the light sensing means from the light emitting means by reflection from the surface of the gel blob.

Li use, the optical data transceiver is typically optically coupled to an optical fibre. The optical fibre may be a plastic optic fibre (POF) and may be terminated by a ferrule.

Preferably, there is a gap between the top of the gel blob and the bottom of the optical fibre or the ferrule terminating the optical fibre. The maximum height of the gel blob above the surface of the light emitting means may be of the order of 150μm.

The volume of the gel blob may be of the order of 260nl. This volume may be varied as required, but typically this variation would not exceed 5-10% of the total volume. Typically, the gel blob will have a refractive index of around 1.5 to 1.6. This is higher than the usual range of refractive indices used for gel blobs in optical applications. The range is chosen because it improves the light coupling efficiency between the light emitting means and the optical fibre and reduces the beam divergence from the light emitting means. As a result, alignment tolerances in respect of the light emitting means maybe larger.

The gel blob may be adapted, by application or otherwise, so as to form a lens to assist in directing light from said light emitting means to said optical fibre. The gel blob may be comprised of a silicone gel or may be comprised of an epoxy gel. In some embodiments, the gel blob may be comprised of a silicone gel blob applied directly over the light emitting means and a quantity of epoxy gel applied over the silicone gel blob so as to form a compound blob. The above features of a single material blob may be complied with by the compound blob as a whole or may be complied with by the silicone blob within the compound blob.

Preferably, the optical transceiver is packaged in a protective housing. The protective housing is preferably provided with an aperture through which light can pass between the light emitting means and the exterior of the package. The aperture may be adapted to retain the optical fibre and align the optical fibre with the light emitting means. If the optical fibre is terminated by a ferrule, the aperture or mounting means may be adapted to receive and retain the ferrule. The aperture may be formed so as to provide a reflector means for directing light between the light emitting means and the optical fibre. Alternatively, a mounting means may be provided within the aperture to provide the retention and reflection functions.

Preferably, said optical transceiver comprises an integrated circuit incorporating said light emitting means and said light sensing means. The light emitting means and said light sensing means may be implemented on a single integrated circuit or may each be implemented on independent integrated circuits, said independent integrated circuits being electrically connected and physically fixed in a desired relative position. Preferably, the packaged optical data transceiver is mounted on a substrate. Most preferably said substrate is an application substrate such as a printed circuit board (PCB) or similar and said packaged optical data transceiver is electrically connected to said substrate.

Preferably, the optical data transceiver comprises a second light sensing means, the second light sensing means being operable to detect light signals sent along said optical fibre to said optical data transceiver. This enables the transceiver to be used in duplex systems or networks. The second light sensing means is preferably adapted such that it does not detect light emitted by the light sensing means. This may be achieved by providing the second light sensing means outside the gel blob. As an alternative, the second light sensing means may be adapted so as not to detect light of the wavelength emitted by the light emitting means. This can be achieved by means of a filter, an interference coating or otherwise.

A further alternative is that the first light sensing means may be adapted such that it does not detect light transmitted along the optical fibre. This can be achieved by positioning the first light sensing means such that light transmitted along the fibre is not incident upon it, by adapting the shape of the gel blob in the appropriate manner or by means of a filter, an interference coating or otherwise.

Preferably the light emitting means is a vertical cavity surface emitting laser (VCSEL). In alternative embodiments however any other suitable light emitting means may be used, for example an LED, or RCLED. Preferably, the light emitting means and the light sensing means are implemented on an integrated circuit along with the control means. Preferably, the control means includes non-volatile memory means. Preferably said non-volatile memory means stores calibration data for use by said control means in controlling the output of said light emitting means. Preferably said calibration data is stored as part of a test and calibration process during manufacturing to accommodate both inherent and manufacturing tolerances.

According to a second aspect of the present invention there is provided an optical network comprising a plurality of optical data transceivers according to the first aspect of the present invention optically coupled to and interconnected by optical fibres.

Such a network may be used in vehicular or automotive control or entertainment systems such as those operating to the MOST OPHY (Optical Physical Layer) or aOPHY (advanced Optical Physical Layer) standards and IEEE 1394 or IDB1394 SlOO, S200, S400, and S800 standards. Another application for such a network is in transmitting data between a digital imaging device and an image processing means for instance, those used in various automotive applications including lane following and parking assist.

In order that the invention is more clearly understood, it will now be described further herein, by way of example only and with reference to the following drawings in which: Figure 1 is a cross-sectional view of an optical data transceiver according to the invention;

Figure 2 is a cross-sectional view of a packaged optical data transceiver according to the invention; and

Figure 3 is a cross-sectional view of an alternative embodiment of a packaged optical data transceiver according to the invention.

Referring now to figure 1, an optical data transceiver 200 comprises: an integrated circuit 101 having implemented upon it first light sensing means 106, light emitting means 105 and second light sensing means 104; a mounting means 102; and bond pads 107, said bond pads being electrically connected to said integrated circuit 101. Mounting means 102 forms a mechanical interface between the optically active means 104, 105, 106 and optical fibre 207. As is shown in figure 1, it may have a curved reflective inner surface to assist in directing light between the optical fibre and the optically active means 104, 105, 106. Mounting means 102 further defines an area encompassing and surrounding the optically active means 104, 105, 106.

A gel blob 108 (typically, the gel may be a silicone gel, such as that supplied under the code number JCR6175 or an epoxy gel, such as that supplied by Kyocera under the code XKE-9529) is dispensed onto integrated circuit 101 into said area defined by mounting means 102. Said gel blob is substantially transparent and allows most of the light emitted by light emitting means 105 to pass through it into the optical fibre 207. In a similar manner most of the light emanating from optical fibre 207 may pass through the gel blob and be incident upon the second light sensing means 104.

As the index of refraction of the gel blob 108 is higher than the index of refraction of air, application of a substantially transparent gel 108 on top of the light emitting means 105 will significantly enhance the amount of light extracted from the light emitting means 105. By choosing a gel material with the optimum value of the index of refraction the light output of the light emitting means 105 can be maximized for a given drive current. The ideal index of refraction of the gel is as close as possible to the square root of the product of the index of refraction of the light emitting means 105 and the material surrounding the gel blob 108, in this case air.

Light emitting means 105, optical fibre 207 and second light sensing means 104 comprise a duplex data transmission system. A proportion of the light emitted by light emitting means 105 is not passed through gel blob 108 but is instead reflected from the surface of gel blob 108 and is then incident upon the first light sensing means 106. The shape of the curved surface of the transparent gel blob 108, and the refractive index of the gel will determine the distribution of the reflected light. Said shape will be determined by the dimensions of mounting means 102 and the quantity and consistency of the gel blob material dispensed. These parameters may be adjusted during manufacturing for optimum results.

The signal generated by the first light sensing means 106 is input to control means (not shown), typically implemented as part of integrated circuit 101. The control means monitors the output of the first light sensing means and controls the power output of the light emitting means 105 in response thereto. In this way, the power output of the light emitting means may be optimised without exceeding safe output levels. The control means may incorporate non-volatile memory which stores calibration data for use by said control means in controlling the output of said light emitting means. The calibration data is typically stored as part of a test and calibration process during manufacturing to accommodate both inherent and manufacturing tolerances.

If the optical data transceiver 200 is used in a simplex or half duplex system then the light received by first light sensing means 106 will be only that reflected by transparent gel blob 108. If however the optical data transceiver is used in a full duplex system then light received from the optical fibre 207 may also be incident upon the first light sensing means 106. hi such a case the shape of mounting means

102 and/or gel blob 108 may be adapted such that light reflected from the surface of the gel blob 108 is incident upon the first light sensing means but light emanating from the optical fibre 207 is not incident upon the first light sensing means 106.

Referring now to figure 2, the integrated circuit 101 is mounted on and electrically connected to a lead frame 109. The electrical connections are made via wires 208 connected to bond pads 107. The combined assembly may then be packaged in a protective housing 110. This provides protection for the data transceiver 200 during use. Referring now to figure 3, an alternative embodiment of the invention is shown wherein the gel blob 108 is replaced with a compound gel blob 180. The compound gel blob comprises an inner blob 181 formed from a silicone gel and an outer blob 182 formed from an epoxy gel.

Such a compound blob 180 can be used in order to maximise the beneficial qualities of each gel material and overcome the drawbacks of each gel material. In particular, silicone gel material has a tendency to collect dust on its upper surface, which can inhibit the transmission of light and there may be a large difference in coefficients of thermal expansion between epoxy gel and the light emitting means, which can lead to a relatively large thermo-mechanical stress being applied to the light emitting means. A compound blob 180 with a silicone inner blob 181 avoids the problem of thermo-mechanical stress being applied to the light emitting element 105. Additionally, the provision of the epoxy outer blob 182 reduces the amount of dust that can collect on the outer surface of the compound blob.

In the compound blob 180, each gel may have substantially the same refractive index or each gel may have different refractive indices. If the refractive indices are substantially equal, it is the surface of the outer blob 182 that is primarily responsible for the reflection of light and accordingly more care is taken to form this surface at a desired location and to a desired shape. If the refractive indices of the two gels differ then the surfaces of both the inner blob 181 and the outer blob 182 will cause some reflection and accordingly care must be taken to form both at a desirable position and with a desirable shape. Typically, the compound blob 180 would be formed by applying a quantity of silicone gel to form the inner blob 181; curing said silicone gel; cleaning the surface of the inner blob (possibly using UV light or plasma cleaning); applying a quantity of epoxy gel to form the outer blob 182; and curing said epoxy gel.

The light emitting means 105 can be any suitable light source, a particular example being a VCSEL.

It is of course to be understood that the invention is not to be restricted to the details of the above embodiments which are described by way of example only.

Claims

1. An optical data transceiver comprising: a light emitting means; a light sensing means for detecting incident light and outputting a signal in response thereto; a gel blob provided such that a proportion of the light emitted by the light emitting means is directed to the light sensing means by the gel blob; and control means for controlling the power output by the light emitting means in response to the output of the light sensing means.

2. An optical data transceiver as claimed in claim 1 wherein the gel blob is provided such that it covers both the light emitting means and the light sensing means and light is directed to the light sensing means from the light emitting means by reflection from the surface of the gel blob.

3. An optical data transceiver as claimed in any preceding claim wherein the optical data transceiver is optically coupled to an optical fibre.

4. An optical data transceiver as claimed in claim 3 wherein the optical fibre is a plastic optic fibre (POF) terminated by a ferrule.

5. An optical data transceiver as claimed in claim 4 wherein there is a gap between the top of the gel blob and the bottom of the ferrule.

6. An optical data transceiver as claimed in any preceding claim wherein the gel blob is adapted so as to form a lens to assist in directing light from said light emitting means to said optical fibre.

7. An optical data transceiver as claimed in any one of claims 1 to 6 wherein the gel has a refractive index of around 1.5 to 1.6.

8. An optical data transceiver as claimed in any one of claims 1 to 7 wherein the gel blob is comprised of a silicone gel.

9. An optical data transceiver as claimed in any one of claims 1 to 7 wherein the gel blob is comprised of an epoxy gel.

10. An optical data transceiver as claimed in any one of claims 1 to 7 wherein the gel blob is comprised of a silicone gel blob applied directly over the light emitting means and a quantity of epoxy gel applied over the silicone gel blob so as to form a compound blob.

11. An optical data transceiver as claimed in claim 10 the compound blob as a whole is adapted so as to form a lens to assist in directing light from said light emitting means to said optical fibre.

12. An optical data transceiver as claimed in claim 10 or claim 11 wherein the silicone blob within the compound blob gel blob is adapted so as to form a lens to assist in directing light from said light emitting means to said optical fibre.

13. An optical data transceiver as claimed in any preceding claim wherein the optical transceiver is packaged in a protective housing provided with an aperture through which light can pass between the light emitting means and the exterior of the package.

14. An optical data transceiver as claimed in claim 13 wherein the aperture is adapted to retain the optical fibre, align the optical fibre with the light emitting means and provide a reflector means for directing light between the light emitting means and the optical fibre.

15. An optical data transceiver as claimed in claim 13 or claim 14 wherein a mounting means is provided within the aperture to retain the optical fibre, align the optical fibre with the light emitting means and to provide a reflector means for directing light between the light emitting means and the optical

fibre.

16. An optical data transceiver as claimed in any preceding claim wherein the optical transceiver comprises an integrated circuit incorporating said light emitting means and said light sensing means.

17. An optical data transceiver as claimed in any preceding claim wherein the packaged optical data transceiver is mounted on an application substrate and said packaged optical data transceiver is electrically connected to said substrate.

18. An optical data transceiver as claimed in any preceding claim wherein the optical data transceiver comprises a second light sensing means, the second light sensing means being operable to detect light signals sent along said optical fibre to said optical data transceiver.

19. An optical data transceiver as claimed in claim 18 wherein the second light sensing means is adapted such that it does not detect light emitted by the light sensing means.

20. An optical data transceiver as claimed in claim 18 or claim 19 wherein the second light sensing means is provided outside the gel blob.

21. An optical data transceiver as claimed in any one of claims 18 to 21 wherein the second light sensing means is adapted so as not to detect light of the wavelength emitted by the light emitting means by means of a filter or an interference coating.

22. An optical data transceiver as claimed in any preceding claim wherein the first light sensing means is adapted such that it does not detect light transmitted along the optical fibre.

23. An optical data transceiver as claimed in claim 22 wherein the first light sensing means is positioned such that light transmitted along the optical fibre is not incident upon it, by adapting the shape of the gel blob.

24. An optical data transceiver as claimed in claim 22 or claim 23 wherein the first light sensing means is adapted so as not to detect light of the wavelength transmitted along the optical fibre by means of a filter or an interference coating.

25. An optical data transceiver as claimed in any preceding claim wherein the light emitting means is a vertical cavity surface emitting laser (VCSEL).

26. An optical data transceiver as claimed in any preceding claim wherein the light emitting means and the light sensing means are implemented on an integrated circuit along with control means and non-volatile memory means, the non-volatile memory means storing calibration data for use by said control means in controlling the output of said light emitting means.

27. An optical network comprising a plurality of optical data transceivers according to any preceding claim, said optical data transceivers optically coupled to and interconnected by optical fibres.

28. An optical network as claimed in claim 27 wherein the network is used in vehicular or automotive control or entertainment systems operating to the MOST standard.

29. An optical network as claimed in claim 27 or claim 28 wherein the network is used in transmitting data between a digital imaging device and an image processing means.