TESTING OF OPTICAL TRANSMITTER AND RECEIVER MODULES

Abstract: When fabricating electro-optic modules (1) at least one optical transmission module and at least one optical reception module are fabricated on the same substrate. Optical waveguides (9) are arranged on the substrate between a light-emitting component (7) in one module and a light-detecting component (15) in a neighbouring module. The light-emitting component and the light-detecting component are energized and the transmission of light between the components is tested. Then the substrate is split into individual modules along division lines (3). The optical connection between the modules is then broken and the waveguides can be connected to optical fibers by means of a connector. Electronic driver circuits (11, 17) can be mounted on the modules. The modules can also have integrated electric connections between the driver circuits and the optocomponents. The optical testing is in this way executed in a simple and automatic way involving a minimum of manual operations since substantially all transmitter and receiver modules can be tested at the same time in the same testing equipment.

Description: TESTING OF OPTICAL TRANSMITTER AND RECEIVER MODULES TECHNICAL FIELD The present invention relates to testing optical transmitter and receiver modules. BACKGROUND OF THE INVENTION AND STATE OF THE ART Telecommunication systems using light propagating in different waveguides expand more and more today. There is a large interest in extending the optical networks even up to private homes or local business estates, the so called local access network which is also called "Fibre To (In/From) the Home", "Fibre To (In/From) the Customer (Business)", etc. Also, there is a large interest in extending the use of optical networks in LANs, i.e. local area networks, used for interconnecting computers in a business estate and furthermore for communication inside computer equipment and for communication between computers and peripheral devices such as printers etc. In order to achieve this expansion, the costs of the components of the optical networks of course have to be reduced as much as possible. Very important costs are related to producing the optical transmitter and receiver modules including lasers, LEDs, etc. and other active or passive devices. A part of these costs are in turn associated with testing finished optoelectrical modules which are to be mounted e.g. on printed circuit boards. In conventional testing of optical modules manufactured at the surface of a substrate the respective optical device of a module is energized and the light is emitted in the case of an optical transmitter device and the electrical signals output from an optical receiver device are studied when injecting light into the receiver device. Such a method is disclosed in e.g. U.S. patent 5,631,571. General testing methods of electro-optic modules are disclosed in U.S. patents 5,631,759 and 5,546,325 and microlenses for injecting light for such testing is described in Tsai, Yang and Le, "A novel scheme for efficient excitation of high-density channel-waveguide array using ion-milled planar microlens array" , Optoelectronics, Devices and Technologies, Vol. 5, No. 2, Dec. 1990, pp. 317 - 324. SUMMARY OF THE INVENTION It is an object of the invention to provide a method of testing optical modules in a simple way that is suited to be integrated in a process for mass-fabrication of such modules. The problem solved by the invention is that how to arrange optical modules when they are fabricated so that the testing thereof can be facilitated, in particular so that it can be automatically executed requiring a minimum amount of extra connection devices for supplying electrical power and for injecting light of an adapted intensity. Thus, generally at least one optical transmission module and at least one optical reception module are fabricated on the same substrate. An optical connection, i.e. some optical waveguide, is arranged on the substrate between a light-emitting component in one module and a light-detecting component in another module. The light-emitting component and the light-detecting component are energized and the transmission is tested. Then the 2 substrate is split into individual modules, the optical connection then being broken and the waveguide terminating at the edge of such module. There the waveguide can be connected to another optical waveguide such as an optical fiber by means of some connector. The optocomponents on each module may be supplemented with electronic driver circuits mounted on the same module and on the module there may also be electric connections between the driver circuits and the optocomponents. The optical testing can then be made very rational involving a minimum of manual operations since substantially all transmitter and receiver modules can be tested at the same time in the same testing equipment. A substrate can comprise only a single pair of optical transmitter and receiver modules up to thousands of such pairs depending on the sizes of the transmitter and receiver devices and of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in detail by way of non-limiting embodiments with reference to the accompanying drawings in which: Fig. 1 is a plan view of a portion of a substrate covered by a multilayer structure forming electrical signal paths and optical waveguides, the portion in particular illustrating a transmitter module and a receiver module, Fig. 2 is a plan view of a small region of the substrate portion showing optical waveguides having attenuation means at a division border, and Figs. 3 - 6 are plan views of a substrate region showing an optical waveguide having alternative attenuation means. DESCRIPTION OF PREFERRED EMBODIMENTS The multichip module to be described is made of materials as described in M. Robertsson, A. Dabek, G. Gustafsson, O.-J. Hagel, M. Popall, "New Pattemable Dielectric and Optical Materials for MCM-L/D- and o/e-MCM-packaging", First IEEE Int. Symp. on Polymeric Electronics packaging, Oct. 26-30, 1997, Norrkδping, Sweden. In that article photo-patternable polymer materials, ORMOCER, are disclosed which are suitable for optoelectrical multichip modules in order to build optical waveguides. In particular the refractive indices of these materials can be varied for producing cores and claddings of optical waveguide structures. In Fig. 1 a plan view of a portion of a substrate coated with various layers is shown, having optical and electric components mounted thereon and fabricated as disclosed in the simultaneously filed Swedish patent application "Optoelectric multichip module". After manufacturing the substrate and having components mounted thereon it is intended to be divided in square modules 1, the division lines being indicated at 3 and marks for cutting the substrate being shown at 5. At 7 a surface-emitting laser chip is shown, comprising five individual laser units. They emit light into optical waveguides 9 extending perpendicularly to a division line 3 into a neighbouring module 1. On the 3 module of the laser chip 7 an electronic driver circuit chip 11 is located and furthermore electric contact pads 13 are placed in the marginal region of the considered module 1. On the neighbouring module, into which the optical waveguides 9 extend, a photodetector chip 15 is located receiving light from the optical waveguides 9. Three electronic driver s chips 17 are also located on this module and furthermore electrical contact pads are provided. In order to test the substrate of Fig. 1, the driver circuits 11, 17 and the optical chips 7, 15 are energized by e.g. supplying electrical current to a current supply plane, not shown, inside the substrate. Suitable signals can be provided either to the contacts on o the substrate or directly to the respective module, using suitable ones of the contact pads 13. In the testing procedure so called "eye-opening" diagrams can be studied and evaluated. The optical interconnection of the laser units and the light detector chip through the waveguides 9 can be provided with an intentional optical attenuation, e.g. in the region of s the waveguides in which they pass the sectioning lines 3 and which is removed when cutting the substrate into the individual modules. This illustrated in Fig. 2, in which a region of the waveguides 9 at the sectioning line 3 is shown. The waveguides 9 are constituted of cores 19 surrounded by cladding strips 21. When dividing the substrate into modules 1, some material of the substrate will be removed by for instance sawing, such 0 as between the lines shown at 23. "Angular scores" 25 in the waveguide cores 19 and at the module border 3 are produced by letting the cladding strips 21 have corresponding triangular projections at the border 3. These scores 25 are photolithographically defined when making the recesses in a waveguide core layer which will receive material from a top cladding layer also penetrating into these recesses forming the cladding strips 29 at 25 the side of the waveguide cores 19, see the above cited simultaneously filed patent application. These angular scores 25 will act attenuating on light propagating in the waveguides 9 as indicated by the arrows 27. Since the angular scores are located between the lines 23, they will be removed when splitting the substrate into modules and will thus not affect the finished modules. 30 The additional attenuation produced by such attenuating devices can then suitably correspond to a "typical attenuation" or a "maximum acceptable attenuation" as specified for the optical connection of the optical transmitter and receiver, what can be obtained by a proper selection of the magnitude of geometrical dimensions of the incisions 25. If required, several incisions 25 can be arranged at the module border 3 between the lines 35 23, as is shown in Fig. 3. Alternative attenuator geometrical designs are illustrated in Figs. 4 and 5. Here the cladding material in the strips 21 are made to form a straight cutoff 29 of the waveguide cores 19 and an oblique cut-off 31 respectively. The cut-offs 29 and 31 are thus regions or strips having a uniform width which extend from one cladding strip 21 to the neighbouring cladding strip through the waveguide cores 19. 4 In Fig. 6 instead recesses 33 are made from the top surface of the substrate, at the module border 3 as above and cutting off the waveguide cores 19. These recesses can if desired or required be filled with some suitable material, such a liquid having an adapted refractive index, during the testing procedure. Then even liquids having different refractive indices can be used. Such a recess 33 can also be formed interactively during the testing process by having a laser beam ablating material from the surface of the substrate. Then the recess will have a gradually increasing depth and a corresponding increasing attenuation will be obtained at the module border. Generally thus, the additional attenuation which can be required for an accurate testing of components can be obtained by exterior influence such as by deforming, shaping or removing portions of the waveguides for example mechanically. Using an integrated thermoelectric Mach-Zehnder modulator, not shown, in the waveguides 9, which can be produced requiring no extra costs, the attenuation can be electrically controlled by the testing equipment. Also, a thermo-optical evanescent-field coupler can in principle provide the same function. However, such solutions require some space of the module surface and are thus not always feasible. By controlling the attenuation in that way an estimation of Bit Error Rate BER or "eye-opening" to the link losses or dynamic range (often length of the link) can be obtained in a relatively simple way and automatic. Of course, there may be more than one tight emitting chip on a single module and more than one light detecting chip on the other module. A plurality of optical waveguides may then be provided, in the general case including optical splitter or combiners, so that the devices of all modules can be tested.

Claims: 5 CLAIMS 1. A method of testing optical transmitter and receiver modules, comprising the steps of providing a substrate, applying optical waveguides to or in the surface of the substrate, mounting an optical transmitter device in one module region of the substrate and an optical receiver device in another module region of the substrate, supplying power to an optical transmitter device or to an optical receiver device, detecting light generated by the optical transmitter to which power is supplied, or emitting light into the receiver device to which power is supplied and detecting signals issued by the receiver device, cutting the substrate along division lines between the module regions to form tested, optical modules, characterized in that in applying optical waveguides they are applied to pass from a first module region into a neighbouring second module across a division line, that in mounting the optical transmitter device it is mounted to the first module region and in mounting the optical receiver device it is mounted to the second module region, so that light generated by the optical transmitter device when energized is transmitted in the waveguides to propagate therein up to the optical receiver device, in which the light when the optical receiver device is energized is received, energizing the optical transmitter device and the optical receiver device, light propagating therebetween, detecting signals issued by the receiver device. 2. A method according to claim 1, characterized in that in applying waveguides they are provided with tight attenuators located in regions of the waveguides at the division line, which the waveguides pass. 3. A method according to claim 2, characterized in that the light attenuators comprise incisions or scores in an optical waveguide core of an optical waveguide. 4. A method according to claim 2, characterized in that the light attenuators comprise a portion of an optical waveguide core of an optical waveguide having a reduced cross-section area compared to adjacent portions of the optical waveguide core. 5. A method according to claim 2, characterized in that the light attenuators comprise an interruption of an optical waveguide core of an optical waveguide. 6. A method according to claim 5, characterized in that the interruption of an optical waveguide core is produced by making a strip-shaped recess extending through the waveguide core.

Inventors: ROBERTSSON MATS, ROBERTSSON, MATS
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Application year: 1999
Main classification: H04B10
IPC codes: G01M11, H04B10