TECHNICAL FIELD The invention relates to a method and a device for mounting optical fibers in ferrules.

BACKGROUND OF THE INVENTION In the use of optical fibers for transmitting signals, i. e. in fiber-optical communication sys- tems, alignment of the fibers is required. Alignment means that the ends of the optical fibers have to be aligned with each other or with input/output areas of optical components. If such an accurate alignment is not made, a too large attenuation can be obtained in splices between optical fibers or in the transition region between an optical fiber and an optical component. When con- necting optical fibers to each other or to components, connectors that are permanently attached to the ends of the fibers can be used. In the typical case, such connectors can comprise a guiding sleeve or socket, also called ferrule, in particular a fiber-optical ferrule, to achieve the accurate positioning of the fibers, in particular an accurate positioning in directions transverse to the fibers.

When mounting fibers in ferrules, end portions of the fibers are introduced in central longitudinal holes in the ferrules so that the fibers project from the front surfaces of the ferrules.

Then, the end portions of the fibers are attached or fixed in the holes using a curable adhesive, usually an adhesive that can be cured by being exposed to heat. After having performed the cur- ing of the adhesive, this being made by placing the ferrules including the fibers, in a batch-wise manner, in an oven and allowing them to stay there during a considerable period of time, the end of the fiber attached in each of the ferrules is polished, so that the end surface of the fiber be- comes positioned in the plane corresponding to or in the front surface of the ferrule. This polishing operation can also require a considerable period of time since it has to be performed in several substeps using successively finer polishing materials, because the ends of the fibers pro- ject a rather long distance from the front surfaces of the ferrules. This assembling method in- cludes plural steps including manual handling and at least the polishing step can require a con- siderable period of time, these facts together implying that the cost of each mounted ferrule will be high.

Thus, it is desirable to find alternative solutions of obtaining assembled ferrules that have a low cost, i. e. to search for methods for simplified mounting of fibers in ferrules.

In U. S. patent No. 6,086, 704 a method for manufacturing an optical connector is disclosed.

By using a curing operation including curing an adhesive in two steps, a connector having a somewhat projecting fiber end can be obtained. In the published International patent application WO 01/71399 a method for positioning an optical fiber in a ferrule is disclosed, the method in- cluding that the fiber is first placed with a somewhat projecting end and thereafter is pushed back. Optical connectors including ferrules are disclosed in U. S. patents Nos. 6,312, 164 and 4,458, 983.

SUMMARY OF THE INVENTION It is an object of the invention to provide a rational method of mounting an optical fiber in a ferrule.

It is another object of the invention to provide a method and a device for mounting an opti- cal fiber in a ferrule giving a low manufacturing cost per assembled ferrule.

It is another object of the invention to provide a method and a device for fixing, in a very short time, an optical fiber in a fiber-optical ferrule using a curable adhesive including one or two components.

It is another object of the invention to provide, for fiber-optical applications, an efficient curing process for adhesives that are curable in heat.

Generally, in a method and in a device for mounting an optical fiber in a ferrule, an ac- tive/passive axial positioning of a cut and stripped optical fiber is used. Thereafter a curing pro- cedure for curing a curable adhesive, for example an adhesive curable in heat, performed in two steps, is used to rapidly fix, in a first step, the optical fiber in a predetermined and well defined position in relation to the mouth of the hole of in the ferrule.

This procedure results in that the optical fiber can with a good accuracy be placed in a position having its end surface in the same level as the tip or peak of the ferrule. This obtained position implies in turn that relatively, only a minimum of machining or working the ferrule and fiber material is required to achieve desired mechanical properties. Thereby, the total working time becomes short and damages created in the polishing of the end surface of the fiber are limit- ed. This means that reflective losses in the connecting surface between two optical fibers are minimized. Because of very good control of relevant parameters short processing times and good optical and mechanical performance are obtained.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods, processes, instrumentalities and combinations particularly pointed out in

the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS While the novel features of the invention are set forth with particularly in the appended claims, a complete understanding of the invention, both as to organization and content, and of the above and other features thereof may be gained from and the invention will be better appre- ciated from a consideration of the following detailed description of non-limiting embodiments presented hereinbelow with reference to the accompanying drawings, in which: -Fig. la is a view from the side of a fiber-optical ferrule having an optical fiber mounted therein, - Fig. lb is a sectional view corresponding to the elevational view of Fig. la, - Fig. 2 is a view similar to Fig. la of a ferrule including a longitudinal hole in which a curable adhesive has been applied, - Fig. 3a is a schematic view from the side of a ferrule holder in which a ferrule is retained that includes an optical fiber placed in it, - Fig. 3b is a sectional, detail view of the region at the end surface of the fiber, - Fig. 4a is a schematic view from the side of a station for longitudinally aligning a fiber end in- cluding a ferrule holder, - Figs. 4b and 4c are sectional, detail views of the region at the end surface of the fiber after pushing the end surface back, longer and longer, for aligning it, - Fig. 4d is a sectional, detail view of the region at the end surface of the fiber after pushing the fiber back and aligning it, - Fig. 5a is a schematic view from the side of a station for cleaning a fiber end and the region of the front surface of a ferrule located around the fiber end, - Figs. 5b and 5c are sectional, detail views of the region at the front surface of the fiber before and after cleaning it, respectively, - Fig 6a is a schematic view from the side of a ferrule holder including a ferrule held therein in an operational step for performing a well defined advancement of a fiber end, - Figs. 6b and 6c are sectional, detail views of the front surface of the fiber before and after an advancement of the fiber end, respectively, - Fig. 7a is a schematic view from the side of a station for performing a first curing step for cur- ing adhesive that is applied to an optical fiber and is located in the front-most portion of a hole in a ferrule, - Fig. 7b is a sectional, detail view of the region at the front surface of the fiber in which a region heated in a curing step is shown, - Fig. 8 is a schematic view from the side of a station for polishing a fiber end,

- Fig. 9 is a schematic view from the side of a station for visual inspection and interferometric measurement of the position of the end surface of a fiber mounted in a ferrule, - Fig. 10 is a schematic view from the side of a station for measuring optical performance of a ferrule having an optical fiber mounted therein, - Fig. 1 la is a sectional view of a device for performing a second curing step, a final curing op- eration, of adhesive in ferrules having optical fibers fixed therein in a first curing step, -Fig. 1 lb is a view from above of the device of Fig. 1 la, - Fig. 11 c is a view from the side, taken in a longitudinal direction, of the device of Fig. 1 la, - Fig. 12 is a view from above of a mounting installation including a plurality of stations for mounting optical fibers in ferrules, - Fig. 13a is a schematic view from the side of an optional station for angular alignment of a ferrule in a ferrule holder, and - Fig. 13b is a schematic view from the front of a ferrule rotator.

DESCRIPTION OF A PREFERRED EMBODIMENT Optical fibers are often provided with ferrules in order to achieve detachable interfaces to optical components.

In Figs. la and lb such a ferrule 1 is shown for connecting an optical fiber and it comprises a circular-cylindrical body 3 having a somewhat rounded, convex front surface 5. In a longitudi- nal direction through the ferrule a centrally placed hole 7 passes which has a circular cross-sec- tion and the front portion of which is adapted to the diameter of a bare optical fiber, having been rid of its protective coating. At the rear end of the body a cylindrical collar or flange like portion 9 may be provided. The optical fiber is mounted in the ferrule 1 with a fiber portion 11, that has no protective coating, passes through the hole 7 and has a flat end surface. This end surface is located perpendicularly to the longitudinal axis of the fiber and the ferrule and is aligned with the axially outermost portion of the convex surface 5 so that the convex surface together with the end surface of the fiber forms a smooth surface having no steps or shoulders. The fiber is fixed in the ferrule hole by an adhesive. The protective coating 11 of the optical fiber passes a distance into the rear portion of the hole 7 that has a larger diameter than the front portion and is there also attached inside a rear portion 13 of the ferrule.

A method and a device for mounting a fiber in a ferrule will now be described. The method is divided in operational steps which are performed in different working stations in the device to which stations the fiber and the ferrule are successively displaced.

Before the ferrule is applied to station 1 in the device, a defined quantity of an adhesive that is curable in heat is applied in the longitudinal hole 7 of the ferrule, see Fig. 2. The quantity

of adhesive is adapted so that the adhesive in all of the following procedure will substantially fill all the space between an introduced fiber and the wall of the hole. Applying the adhesive can be made manually or automatically using a syringe or pipette 15. When operating the syringe, un- cured adhesive is from the syringe point 17 squirted into the rear portion of the hole 7 having a larger diameter. It is then in some way accomplished that the end of the fiber projects from the front surface 5 of the ferrule by a relatively well defined distance of for example about 0.5 mm, such as by the method that the protective coating of the fiber is removed over a region at the fiber end and thereafter the optical fiber is cut at a predetermined distance from the end of the remaining protective coating. Thereby, an end surface located approximately perpendicularly to the longitudinal direction or longitudinal axis of the fiber is obtained. Thereupon, the bare fiber end is introduced in the ferrule 1 up to the position in which the protective coating of the fiber is stopped at a surface located at the transition to the front, narrower portion of the hole 7 intended for the very fiber, i. e. generally stopped by a rear engagement surface in the ferrule. The prede- termined distance can be selected so that it somewhat exceeds the distance between the corre- sponding surfaces in the ferrule, i. e. between the front surface of the ferrule and the surface in the hole at the transition between the two different diameters, or generally so that the outermost portion of the optical fiber will project from the ferrule the intended distance of about 0.5 mm.

Uncured adhesive accompanies the fiber 11 to be located along the cylindrical surface of the fi- ber and up to the front surface 5 of the ferrule, where it can form a string or bead 19 of adhesive located at the fiber, see the detail view of Fig. 3b.

The ferrule together with the fiber introduced therein is then placed in a ferrule holder 21, see Fig. 3a, in a suitable hole or recess in a front upstanding portion 23 thereof and is firmly held therein. The ferrule 1 obtains an accurately determined position by the flange 9 of the ferrule coming in contact with the rear surface of the upstanding part. The ferrule holder 21 includes a base part 25 to which a fiber holder 27 is connected. The fiber holder can be standard type and holds the fiber at a portion thereof located a distance from the front support 23 and from the fer- rule 1. The fiber holder can be fixed or maintained in this position using some suitable device 28, that for example can use a vacuum or include an electromagnet. Such a fixing can be made at an intermediate part which in the illustrated procedure is a unit for performing a well determined micro displacement in the direction of the fiber, the unit for example comprising a piezo-electri- cal block 29 that can be supplied witch electrical voltage from a control unit 31. The unit for micro displacement can alternately include a step motor or similar device having for example a mechanical reduction of a linear or rotating movement.

The ferrule holder 21 together with the ferrule held thereby is thereafter placed or located

in the position of station 1 in the device.

Station 1. Active/Passive positioning of the optical fiber in relation to the front surface of the ferrule In this station, see Fig. 4a, an active/passive positioning of the optical fiber 11 is performed by pressing, using a suitable tool, against the free end surface of the fiber to mode the fiber back into the ferrule 1. Then, the fiber holder 27 can freely slide longitudinally on the intermediate part 29. The tool can for example have a very smooth and rounded surface with e. g. approxi- mately the same radius as the front surface of the ferrule, such as a radius of about 15 mm. For example, as is illustrated in the figure, a cylindrical roller 31 can be used, mounted to have a horizontal axis perpendicular to the longitudinal direction of the fiber 11 and mounted on a moveable frame 33. The frame is mounted to slide in the longitudinal direction of the fiber along mechanical guides such as a rail, not shown, in a fixedly arranged base part 33. The frame 33 is activated by a linear motor 37, that through a compression spring 39 is connected to the frame 33. For example, also tools having a flat surface, not shown, such as a knife blade, can be used.

The elastic pushing-back operation of the fiber end appears from Figs. 3b and 3c. The pushing- back movement stops when the surface that presses against the end of the fiber reaches a position of contact with the front surface 5 of the ferrule and thereby the fiber obtains the position having its surface in level with the front surface of the ferrule. The pushing-back tool is then retracted from contact with the fiber end in the ferrule so that the fiber obtains its desired position, see Fig.

3d. The adhesive residues 19 on the front surface of the ferrule have now been spread over this surface.

An active positioning of the fiber end can also be made using a camera, not shown, for capturing pictures of the front surface of the ferrule comprising interference flanges and subse- quent image processing in a suitable electronic circuit unit, compare Fig. 9, the result of the image processing being used to control a linear motor. Such a linear motor can be a modified intermediate part 29, designed to perform somewhat larger movements, for displacing the fiber holder 27, which in this case must be attached to the intermediate part 29.

In any case, after the positioning procedure the end surface of the cut fiber 11 should have an axial position that well agrees with the tip 5 of the ferrule. Generally, after a pushing-back operation using for example the curved surface according to the description above, the difference between the position of the end surface of the fiber and the portion of the front surface of the fer- rule close to the mouth of the hole 7 is less than an few um and can even be smaller than 1 urn.

This position is fixed by fixing the fiber or a detachable fiber holder 27, as is shown in the figure, which holds the fiber at its projecting portion including the remaining protecting coating, in the

obtained position. This fixing can be achieved, as has been indicated above, by retaining or at- taching the fiber or fiber holder using a vacuum in a fixture, in the figure at the intermediate part 29. Other mechanical methods of fixing, for example using an electromagnet, can also be used as has been mentioned above.

This processing step in station 1 is important in order to obtain a well defined reference position for the further processing. Then, the ferrule holder 21 including the held ferrule and the well positioned fiber is transferred to the next station.

Between station 1 and station 2 the ferrule holder passes an intermediate station for remov- ing adhesive from the front surface of the ferrule.

As has been described above, the fiber presses, when it is pushed into the hole 7 of the fer- rule, at the same time out a little quantity of the adhesive which is curable in heat and with which the hole has been filled, before the fiber was pushed into the ferrule. This adhesive is in station 1 spread over the front surface of the ferrule and is removed in an intermediate station by a clean- ing operation using alcohol or another solvent when the optical fiber has been fixed as to its po- sition. A front surface of the ferrule and an end surface of the fiber are obtained which are com- pletely free of adhesive.

This processing step for removing all excessive adhesive before curing the adhesive is very important. If all excessive adhesive is not removed, a longer and rougher polishing operation must be performed in a successive step for removing this adhesive. The procedure then takes a longer time and more used valuable material, i. e. primarily grinding and polishing abrasives, is consumed.

Different washing or cleaning methods exist for removing adhesives, possible particles and dirt from the front surface 5 of the ferrule. As is illustrated in Fig. 5a, a cleaning cloth 41 at- tached to a rotating plate 43 can be used. The plate is rotated by a motor 45 that is mounted to slide along a base part 47 and can be elastically advanced against the ferrule using a linear mo- tor, not shown, in the same way as the frame 33 in station 1. Also, if necessary, the motor 45 can be displaced laterally or transversely, for example periodically, using a suitable mechanism, not show, in order that different portions of the cleaning cloth 41 soaked with alcohol, in the rotation in the plate 43, will come in contact with the front surface 5 of the ferrule. The appearance of the front surface of the ferrule close to the end surface of the fiber before and after the washing step appears from Fig. 5b and 5c, respectively. After finishing the washing step the cleaning plate 43 is moved away from contact with the ferrule 1 and thereupon, the ferrule holder 21 including the held ferrule is transferred to station 2.

After the washing step, in the transition from the washing station to station 2, it is in some

way accomplished that the optical fiber will project with some predetermined distance, of the magnitude of order of 10 um, for example between 5 ad 15 um, see Figs. 6a, 6b and 6c, from the front surface 5 of the ferrule. It is made to ensure that some"fiber protrusion"exists that is larger than possible errors in the position of the end surface of the fiber. Such errors can have been pro- duced by the fact that the end surface of the fiber is not always completely perpendicular to the longitudinal direction of the fiber. It is also made to compensate for process variations that can have been produced in station 1. Such an advancement of the fiber 11 can in the embodiment shown be achieved by activating, by the control unit 31, the piezo-electric intermediate part 29 for micro displacement using a fixed applied electric voltage, whereafter a very short fiber por- tion projecting from the front surface 5 is obtained, as appears from Fig. 6c.

Station 2. First step of the two step curing procedure In this station the adhesive is cured in a first step to achieve a sufficient permanent fixing or retaining of the fiber 11 in the ferrule 5 in order that it will be possible to directly continue with the first polishing step in the next station. It is not until after all of the complete process has been finished that the final and second curing step is performed, see the description below. Using a curing procedure including two steps is a condition that it will be possible to perform the dif- ferent step of the process successively after each other without requiring too long time periods in any of the stations.

Only that amount of adhesive that is located in the hole very close to the front surface of the ferrule, i. e. within a relatively short region from the front surface of the ferrule, generally within a distance that advantageously can be less than 1 mm from the surface, is cured in the first curing step. Curing the remaining adhesive staying in the hole 7 of the ferrule is made after all stations having been passed, by placing the ferrule in a heating oven in the conventional way.

Generally, the purpose of the primary curing step is that to sufficiently fix, in the shortest pos- sible time period, the optical fiber for allowing different forms of mechanical working.

Thus, the first curing process is made by locally heating the outermost portion of the front surface of the optical fiber 1. The local heating can be produced by e. g. directing a gas flame to- wards the front surface of the ferrule and towards the optical fiber during a short time period.

Alternative ways of locally heating the front surface of the ferrule includes placing a resistively heated filament, an electric arc or a volume that has been heated in some other way close to the center part of the front surface 5 of the ferrule. Another method of local heating the ferrule tip is to illuminate the region using e. g. a C02 laser.

As is illustrated in Fig. 7a, in station 2 a small heating oven or heating unit 51, for example using electrical resistive heating, can be attached to the free end of an arm 53 that is mounted to

swing at a base part 55. The heating unit has in a front surface a recess 57, that in the swung-up position of the arm and the advanced position of the heating unit obtained thereby, surrounds the front end of the ferrule including its front surface 5. The heating unit can be designed in such way that the highest temperature exists at the bottom of the recess. Thereby the adhesive is cured only in a small area 58 at the mouth of the hole 7 at the front surface 5, see Fig. 7b. As is shown, the cured region can have a length along the fiber of a few fiber diameters, such as 0.5-1 mm.

Advancement of the heating unit 51 is in the embodiment shown accomplished by swinging the arm 53 up using a linear motor 59, that is elastically connected to the arm. After this curing step having been finished, after the heating unit has surrounded the front surface of the ferrule during a predetermined time, the heating unit 51 is returned from its advanced position and thereupon, the ferrule holder 21 including the held ferrule is transferred to the next step.

Station 3. First polishing step Since the ferrule 1 and thereby the fiber 11, held by the fiber holder 27, have a well defined position, the polishing procedure can be rapidly and simply performed without requiring mount- ing/dismounting in a special polishing fixture. In currently used production procedures a plural- ity of ferrules are mounted in a special fixture to thereby reduce the production time per ferrule.

Since certain variations exist as to the lengths of the ferrules this means that if stations 1-2 ac- cording to the description above are used and then the conventional manufacturing procedure is used, too high pressing forces will be applied on some ferrules and too low pressing forces on other ferrules in the polishing fixture used. Then, a large distribution of mechanical characteris- tics, i. e. characteristics indicating how fast and how well the end surface can be polished in the intended way, can be expected.

Since only polishing steps with relatively fine grinding abrasives are used, they will not remove very much material from the ferrule implying that the radius that the front surface of the ferrule has as given by the manufacturer thereof and that should be within currently valid speci- fications, remains relatively unchanged. Also, there is almost no risk at all of obtaining a high offset value, where offset is a value which indicates the position of the end surface of the fiber core in relation to the highest point of the ferrule, i. e. to the outermost point on the front surface of the ferrule taken in the longitudinal direction of the ferrule and the fiber, and which should be smaller than 50 um, since very little material has been removed. Generally, this offset value should be smaller than 50 jjm. No problems at all exist of having the ferrule polished too much so that the ferrule could be too short. This happens sometimes using the manufacturing proce- dures of today.

As is illustrated, the polishing station can include a rotating plate or disc 61 at the front sur-

face of which a polishing cloth 63 is attached. The polishing cloth can be soaked with a suitable polishing liquid, for example water. The disc 61 is rotated by a motor 65 attached to or included in a frame 67 that is mounted to slide at a base part 69 along suitable mechanical guides. The frame can be displaced by a linear motor 71 that is rigidly attached to the base part and is elasti- cally connected to the actuating rod of the linear motor. Also, if required or desired the frame 67 or the rotary motor 65 can be moved laterally or transversely, for example periodically by a suit- able mechanism, not shown, in order that the contact between the polishing cloth 63 and the front surface 5 of the ferrule will be at varying radii of the polishing cloth. For using the polish- ing device, the disc 61 is advanced towards the front surface of the ferrule by activating the linear motor 71 acting on the frame. Due to the elastic connection 73 between the linear motor and the accurately determined positions of the front surface of the ferrule and the end surface of the fiber, the rotating plate 61 including the polishing cloth is with a predetermined pressing force applied against these surfaces. After finished polishing operation the plate 61 is retracted by a suitable activation of the linear motor 71. Thereupon, the ferrule holder including the held ferrule is transferred to station 4.

Station 4. Second polishing step In this step polishing is performed in the same way as in the preceding step but a polishing film or cloth having a finer polishing material is used. It is not necessary to use this station if the polishing in the preceding step can be made sufficiently fine. The same kind of device as is used in station 3 can be used, see Fig. 8.

Station 5. Optical inspection including visual inspection and interferometric measurement In this station image processing of images of the end of the fiber is used, which have been taken using a camera connected to a microscope, and interferometric information to detect sur- face damages. Mechanical parameters are defined by interferometric methods. This can be achieved because the position of the ferrule is well defined.

In Fig. 9 a device is illustrated that can be used in this station. In the same way as in several preceding stations a frame 81 is provided that is mounted to slide along mechanical guides on a base part 83. The movement of the frame is determined by a linear motor 85 rigidly attached to the base part and connected to the frame. The frame carries an optical unit including a light source 91, that emits parallel light in a downwards vertical direction. The light is de- flected to a horizontal direction by a semitransparent mirror 93 so that the light comes to pass in a direction parallel to the longitudinal direction of the fiber 11, towards the end surface of the fiber. The horizontal light is focused by a lens system 95 of the type microscope objective to- wards the end surface of the fiber. The focusing is made so that interference patterns are formed.

The light reflected by the end surface of the fiber and by adjacent areas of the front surface 5 of the ferrule is refracted by the lens system 95 to a parallel light beam propagating away from the fiber and the ferrule. It passes without changing its direction through the mirror 93 to hit the light sensitive area of a CCD camera 97. The signal provided by the camera is supplied to a computer 99 connected to a display 101. On the display the end surface of the fiber and adjacent portions of the front surface of the ferrule can be observed in detail and in particular interference patterns can be observed indicating how well these surfaces are located in the same plane as each other.

An inspector can on a keyboard, not shown, or another input unit of the computer 99 indicate whether the fiber end surface is accepted or not. Thereupon, the ferrule holder 21 including the held ferrule is displaced to station 6.

Station 6. Optical characterizing step In this station optical parameters such as contact attenuation and contact reflection are automatically measured. A device therefor is schematically shown in Fig. 10. A frame 111 is in the same way as above mounted to slide along mechanical guides on a base part 113. The dis- placement of the frame is determined by a linear motor 115 rigidly attached to the base part and connected to this frame. The frame carries a reference ferrule 117 or some similar connector in- cluding a reference fiber 119 that is very accurately mounted in the reference ferrule. The other end of the reference fiber is connected to a combined laser/measuring unit 121 for light power.

When using the optical characterizing device, the frame 111 is advanced so that the reference ferrule comes in contact with the fiber 1 in the ferrule holder 21 or is located at a very small dis- tance from it. A material for enhanced optical contacting applied between the end surfaces of the light guiding fibers can be used. The light from the laser/measuring unit 21 is conducted by the reference cable 119 and is reflected by among other things, the end surface of the fiber 11 mounted in the ferule. The reflected light is conducted back to the laser/measuring unit in which it is detected. From the received light parameters can be determined indicating how well the light transmission is to/from the fiber 11. After this station, first the fiber holder 21 is detached from the intermediate portion 29 and then the ferrule 1 including the fiber 11 attached therein is de- tached from the front upstanding part 23 of the ferrule holder 21.

Finally, since only the adhesive staying in the front most portion of the hole 7 of the ferrule has been cured, the remaining adhesive must be cured. The ferrule can in the conventional way be placed in a heating oven or heated in some other way. As is illustrated in Figs. l la, l lb and 11 c the ferrule together with other ferrules that have passed the stations 1-6 and been found to have acceptable performance are placed in suitably designed holes 131 in a block 133 of a heat conducting material. The ferrules can be retained in the holes by elastically biased devices 135.

The block can at the surface parallel to the holes carry a resistive heating element 137 that is supplied with electric current from a controlled power supply 139. The power supply is con- trolled to supply suitable electric current/voltage in accordance with a signal obtained from a temperature sensor 141 mounted in the block 133. After all holes 131 in the block have been provided with the ferrules, the heating of the block is started and then the final curing of the ad- hesive in the ferrules is started. After a predetermined time the heating is interrupted, the ferrules and the block are allowed to cool, whereupon the ferrules are detached from the holes 131 and are ready to be used.

The stations 1-6 can be mounted evenly distributed along the periphery of a circle so that they can by a rotating movement be reached by a ferrule holder 21 including a held ferrule. Thus, in Fig. 11 an inner table part 151 designed as a circular plate having the stations 1-6 symmetric- ally placed at the periphery of the plate is illustrated. Between stations 1 and 2 an intermediate station is provided for washing/cleaning. Optionally, a similar station, not shown, can be ar- ranged between the two polishing steps 3 and 4 to ensure that no rough polishing material re- mains on the front surface of the ferrule and this end surface of the fiber in the fine polishing step in station 4. The inner table part is surrounded by an outer table part 153 designed as a rotatable ring on which ferrule holders 21 are attached in a number corresponding to the number of sta- tions, the ferrule holders being, like the stations, evenly distributed over the periphery. Thus, in the embodiment shown six ferrules are simultaneously processed. After all ferules have been completely processed in the respective station, the outer table part is rotated by a corresponding angle, in the embodiment shown 60°, whereby all ferrules except that in station 6 arrive to the next respective station. In this rotating movement, the ferrule is removed that has just passed sta- tion 6 including an optical characterization and instead, a new ferrule having applied adhesive and an introduced fiber is placed in its ferrule holder.

Optionally, also the following stations can be used.

Minimizing contact attenuation In this station that can also be passed before the first curing step, i. e. before the stations 1 and 2, the fact is used that the optical fiber has a position, before the curing and polishing pro- cesses have been performed, that well agrees with the position that it will have after finished processing. It means that if the contact attenuation is measured at the same time as the ferrule is rotated, the ferule can be locked in the angular position which gives the lowest measured at- tenuation. The process is then performed as has been described above.

Mounting polarizing maintaining fibers (PM-fibers) In this station a procedure is performed that is similar to that used in minimizing contact

attenuation as has been described above, but the ferrule is aligned in relation to a reference line on the ferrule by measuring the angular orientation of the fiber that is to be contacted. The fer- rule is then rotated by an angle that is equal to the difference between the angular position of the reference line and the angular orientation of the fiber that is to be mounted.

In these two optional procedures that can be performed in an additional station, an optical installation including image processing can be used, see Fig. 13a, that is similar to that in station 5, compare Fig. 9. To the ferrule holder 21 a unit 161 is added for rotating the ferrule 1 around the axis thereof according to a signal provided by the computer 99 in which a suitable image processing is performed. As appears from Fig 13b, the rotating unit 161 can include a linear motor 163 that displaces a gear rack 165 in a direction perpendicular to the fiber direction and the axis of the ferrule. The gear rack can be engaged with teeth provided on the flange 9 of the ferrule.

While specific embodiments of the invention have been illustrated and described herein, it is realized that numerous additional advantages, modifications and changes will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the spe- cific details, representative devices and illustrated examples shown and described herein. Ac- cordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within a true spirit and scope of the invention.