Abstract:
A process for creating an optical and electric connection of electro-optical components that can be implemented inexpensively and has long-term stability and thermal stability, so that information-transmitting light from one or more waveguides of one component can be coupled into one or more waveguides of the other component in an economically feasible manner. An optical and/or electro-optical connection of two optical and/or electro-optical components is created by mounting the two components directly on a single common carrier board by welding with electromagnetic radiation in the wavelength range around 1 μm without using any auxiliary carriers.

Description:
This is a division of U.S. application Ser. No. 08/764,000, filed Dec. 12, 1996 now U.S. Pat. No. 6,181,855. 
    
    
     FIELD OF THE INVENTION 
     The present invention concerns an optical and/or electro-optical connection of two optical and/or electro-optical components. 
     RELATED TECHNOLOGY 
     Traditional optoelectric connections have several disadvantages. The mounting elements had a complicated structure and were bulky and expensive. In most cases, each electro-optical component had to be mounted separately on an auxiliary carrier. This necessitated additional mounting methods, e.g., soldering the laser or gluing the fibers in an assembly tube (adhesive can shrink and become brittle with age). These auxiliary carriers then had to be mounted on the main carrier. Due to the fact that now assembly errors were added (e.g., differences in thickness of the solder between the semiconductor laser and the auxiliary carrier), these arrangements were mechanically inaccurate and bulky but still sensitive to temperature and expensive because of the long assembly times. 
     A first attempt to improve optical and/or electro-optical connections of the type in question is disclosed in unexamined German Patent (Offenlegungsschrift) 4,140,283. However, the connection described in that publication still requires a complicated carrier structure and nothing is said about how the other components are mounted. 
     Fibers spliced together with thermal energy such as an electric arc as done in the past had to be protected from breakage after splicing by a mechanical device. 
     In arrangements where one component is soldered, the melting point of solder (120-250° C.) precludes high-temperature applications, e.g., for sensors. 
     With lasers, modulators, and other electro-optical components, the wire for the electric connection, such as the pump lead-in wire, in previous arrangements has been bonded. This required an extra tool (a bonding machine). 
     SUMMARY OF THE INVENTION 
     The present invention concerns an optical and/or electro-optical connection of two optical and/or electro-optical components, each comprising structures with optical waveguides arranged in parallel or essentially parallel to the substrate surface on a carrier board in the area of the connection. 
     The wavelength range of 0.6 to 1.6 μm is advantageous for transmission of information for such applications as optical communications technology or for sensors because of the low attenuation and low dispersion of glass fibers. Connecting the optical and electro-optical components required for this transmission in the past has been very cost-intensive, especially when the waveguides of the components to be linked to form a system are monomode waveguides. Joining tolerances in the micrometer and submicrometer range must often be maintained for decades despite great temperature fluctuations. A component of such a system is an arrangement for coupling the light from a semiconductor laser transmitter into a monomode fiber because then two beams with spot widths smaller than 1 μm must be aligned so they overlap. Since the fiber has a 5-μm spot, it is advantageous to match the spot widths of the laser and the fiber to each other in a coupling arrangement. This can be accomplished by using a lens between the laser and the fiber, by a lens attached to the end of the fiber or by a spot width taper integrated into the laser chip. Arrangements of components with similarly small spot widths such as semiconductor laser amplifiers or transceivers may also be used. 
     The components may be connected having spot widths adapted to a glass fiber, such as splitters, modulators, switches, wavelength multiplexers and demultiplexers, because here again the 5-μm-spot widths and thus the joining tolerances are small. The same thing is also true of arrangements for coupling two fibers such as splices or plugs. 
     An object of the present invention is to create an optical and electric connection of electro-optical components that can be implemented inexpensively, with long-term stability and thermal stability to make it possible to couple information-transmitting from one or more waveguides of one component into one or more waveguides of the other component in an economically feasible manner. 
     With regard to the process engineering part of the present invention, an inexpensive technology for aligning and mounting components to yield long-term and thermal stability is to be made available. 
     According to the present invention, a connection of the type described above is created in which two components are mounted directly on just one single joint carrier board by welding with electromagnetic radiation in the wavelength range of about 1 μm without using auxiliary carriers. 
     The present invention provides a process for producing a connection as discussed above where at least one of the components ( 10 ,  13 ) to be mounted is made of a transparent material. The electromagnetic radiation ( 19 ,  20 ,  40 ) is selected and matched with the material of the components ( 10 ,  13 ) to be mounted on the carrier board ( 15 ) so that it penetrates the components ( 10 ,  13 ) on its path to the weld ( 18 ) without altering their function. A process for producing a connection as discussed above where the components ( 10 ,  13 ) to be joined are made of a non-transparent material is also provided. The electromagnetic radiation ( 19 ,  20 ,  40 ) is selected and matched with the material of the components ( 10 ,  13 ) to be mounted on the carrier board ( 15 ) so that it penetrates through the components ( 10 ,  13 ) on its path to the weld ( 17 ), forming holes ( 21 ) without altering the function of the components (FIG.  6 ). 
     Electro-optical components in the sense of the present invention are understood to be structures with optical waveguides aligned essentially parallel to the respective contact surface of the carrier board in the area of the coupling site. Examples include: 
     Cubic integrated optical or integrated electro-optical chips made of InP, GaAs, PbS, tantalate, glass, germanium, or silicon, e.g., semiconductor lasers, semiconductor detectors, splitters, directional couplers, switches, modulators, multiplexers and demultiplexers, flat spectrographs. 
     Cylindrical structures such as glass fibers. 
     With regard to the electromagnetic radiation to be used according to the present invention, radiation from Nd-glass lasers or Nd-YAG lasers with an output wavelength in the range of λ=1 μm, for example, can be used. Other sources having similar radiation properties in the wavelength range of λ=0.2 μm to λ=2.0 μm are also possible. 
     An advantage of the present invention includes the fact that only a single mounting element with a simple structure is used, namely the carrier board on which all the electro-optical components plus the optional imaging arrangement, e.g., a spherical lens are mounted directly, i.e., without an intermediate carrier or an extra carrier, by a single method, namely welding with electromagnetic radiation. 
     Various embodiments of the present invention with regard to the object part of the present invention include that the carrier board ( 15 ) has a contact face ( 38 ), and the optical and/or electro-optical components ( 10 ,  13 ) are arranged on the flat contact face ( 38 ) and mounted there (FIGS. 1,  2 ,  5  and  7 ). The carrier board ( 15 ) also may have two parallel stepped contact surfaces ( 29 ,  30 ) with one of the two components ( 10 ,  13 ) arranged and mounted on each surface (FIG.  3 ). A semiconductor on which the carrier board ( 15 ) is mounted by angled input of the electromagnetic radiation ( 23 ,  24 ) may serve as one ( 10 ) of the two components ( 10 ,  13 ) (FIG. 5) and one ( 10 ) of the two components ( 10 ,  13 ) may be an electro-optical component having a current lead-in wire ( 39 ) connected by electromagnetic radiation ( 40 ) (FIG.  7 ). One ( 13 ) of the two components ( 10 ,  13 ) also may be a fiber ( 13 ) that is connected to the carrier board ( 15 ) by utilizing its cylindrical lens effect on the electromagnetic radiation ( 20 ) (FIGS.  1  and  3 ). Moreover, both of the electro-optical components ( 10 ,  13 ) may be fibers that are not only attached to the carrier board ( 15 ) by the electromagnetic radiation ( 19 ,  20 ) but are also spliced together (FIG.  2 ). In addition, one ( 10 ) of the electro-optical components ( 10 ,  13 ) may be a semiconductor laser and the other ( 13 ) a fiber. 
     An optical imaging element ( 36 ) may be inserted between the two components ( 10 ,  13 ) to improve the optical transmission properties, and also may be mounted on the carrier board ( 15 ) by means of electromagnetic radiation ( 37 ). Optionally an (other) carrier board level ( 34 ) that is stepped with respect to the carrier board level(s) ( 33 ,  35 ) used for mounting the components ( 10 ,  13 ) is provided for mounting the imaging element ( 36 ) (FIG.  4 ). 
     Advantageous refinements of the process part of the present invention include that all the joining steps required for mounting the two electro-optical components ( 10 ,  13 ) are carried out in a vacuum. The first component ( 10 ) also may be gripped by an auxiliary device, preferably a precision manipulator or a precision xy translation table, and may be placed with its contact surface ( 16 ) on the carrier board ( 15 ) and then shifted into its final position on the carrier board ( 15 ) by means of the auxiliary device. The second component ( 13 ) as well may be gripped by an auxiliary device, preferably a precision manipulator or a precision xy translation table, and it may be placed with its contact surface ( 16 ) on the carrier board ( 15 ). The information-transmitting light from the waveguide ( 11 ) of the first component ( 10 ) is then used for positioning (final position) the second component ( 13 ) on the carrier board ( 15 ) (active adjustment). Moreover, the second component ( 13 ) may be gripped by an auxiliary device, preferably a precision manipulator or a precision xy translation table, and placed with its contact face ( 16 ) on the carrier board ( 15 ). The external shape of the components ( 10 ,  13 ) or auxiliary marks then is used to locate the final position of the second component ( 13 ) on the carrier board ( 15 ) (passive adjustment). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The figures illustrate embodiments of the present invention that are described below. They show (greatly enlarged): 
     FIG.  1 : a vertical section through an embodiment of an optical and/or electro-optical connection using a flat carrier board. 
     FIG.  2 : a sectional diagram according to FIG. 1 of a slightly modified variant of a connection of two fibers in comparison with FIG.  1 . 
     FIG.  3 : another embodiment of a connection where the components are arranged on a carrier board having steps, shown here in a sectional diagram according to FIGS. 1 and 2. 
     FIG.  4 : another embodiment of a connection using a carrier board with two steps and a spherical lens, shown here in a sectional diagram according to FIGS. 1 through 3. 
     FIG. 4 a : a sectional diagram according to FIG. 4 of another variant of a connection where a special lens is used but with a flat carrier board in contrast to FIG.  4 . 
     FIG.  5 : a front view of the mounting of a semiconductor laser on a carrier board. 
     FIG.  6 : a top view of the mounting of a semiconductor laser with a laser-active zone on a carrier board. 
     FIG.  7 : a sectional view according to FIGS. 1 through 4 of the mounting of a pump lead-in wire on a semiconductor laser. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows an electro-optical component  10  having a waveguide  11 , such as a semiconductor laser. The first component  10  works together with a second component, such as a fiber, which is labeled as  13  on the whole and has a waveguide  14 . Waveguides  11  and  14  of components  10  and  13  are connected to and by means of carrier board  15 . For this purpose, the two components  10  and  13  each have a contact face  16 . Fusion points  17  and  18  mark the connection points of the first component  10  and the second component  13 , respectively, with carrier board  15 . 
     Arrows  19  and  20  in FIG. 2 indicate an electromagnetic radiation that is used to produce the welds (at  17 ,  18 ) and is in the wavelength range around 1 μm (preferably 1.06 μm). 
     If one of the two components, such as the first component  10  in FIG. 1, or both components  10 ,  13  in FIG. 2, are transparent to electromagnetic radiation  19  or  19  and  20 , then the radiation can be supplied through the respective component  10  and/or  13  itself However, the radiation must not impair the electro-optical function of electro-optical components  10  or  10  and  13 . 
     Furthermore, the imaging properties of components  10  and/or  13  for radiation  19  and/or  20  are to be taken into account in producing the weld in question. If the components are designed as fibers (e.g., component  13  in FIG. 1 or components  10  and  13  in FIG.  2 ), then the fibers act as cylindrical lenses that result in linear fusion zones (e.g.,  18 ). 
     However, if the material used for components  10 ,  13  is not transparent to radiation  19 ,  20 , these components can be mounted on carrier board  15  by having radiation  19 ,  20  fuse a hole (labeled as  21  in FIG. 6) in components  10 ,  13  and thus reach interfaces  16  of components  10 ,  13  with carrier board  15 . If one of components  10  or  13  is designed as a semiconductor laser, then holes  21  must be fused next to laser-active zone  11 ,  14  so as not to impair the laser function (FIGS.  1  and  6 ). In FIG. 6,  11  is the laser-active zone of component  10 . Fusion spots  17  for mounting component  10  on carrier board  15  are located beneath holes  21 . both components  10  and  13  are designed as fibers, as in the embodiment according to FIG. 2, and are to be spliced together, the electromagnetic radiation must be supplied in the direction of arrow  22  for this purpose (FIG.  2 ). 
     To mount a component such as the first component  10  on carrier board  15 , the electromagnetic radiation can also be supplied diagonally at the side, as an alternative to the radiation path illustrated in FIGS. 1 and 2. This variant of the process is diagramed in FIG. 5, where the electromagnetic radiation is indicated by arrows  23 ,  24 , and the connection spots (welds) are labeled as  25 ,  26 . 
     In contrast with FIGS. 1,  2 , and  6 , carrier board  15  is designed with a step (at  28 ) in the embodiment according to FIG. 3, thus creating two planes  29  and  30  at different levels. Contact faces  16  and  16   a  of components  10  and  13 , respectively, that interact with carrier board  15  are also parallel and have different levels accordingly. Otherwise, the parts in FIG. 3 that correspond to those in the embodiments according to FIGS. 1 and 2 are labeled with the same reference numbers. In the embodiment according to FIG. 4, carrier board  15  is again designed with a step, but in contrast with FIG. 3, in this case it has two steps, labeled as  31  and  32 . This results in three parallel planes  33 ,  34 ,  35  at different levels on carrier board  15 . The two outer carrier board levels  33  and  35  work together with the respective contact surfaces  16  and  16   a  of the two components  10  and  13 , respectively. 
     Another special feature of the embodiment according to FIG. 4 includes the fact that a lens such as a spherical lens  36  is arranged and mounted on the third (middle) plane  34  of the carrier board. This is an imaging lens for adjusting the spot widths of waveguides  11  and  14  of components  10  and  13 . The fusion spot for mounting spherical lens  36  on carrier board  15  (plane  34 ) is labeled as  27 . 
     As in FIG. 2, arrows  19  and  20  in FIG. 4 again indicate the directions of input of the electromagnetic radiation for mounting component  10  and  13 , respectively. Arrow  37  indicates the direction of input of the electromagnetic radiation for mounting spherical lens  36 . 
     The shape of carrier board  15  is very simple in all the embodiments illustrated here. Only those surfaces of carrier board  15  on which electro-optical components  10  and  13  and optionally  36  are to be mounted require special attention. However, all other areas of carrier board  15  may have practically any desired design. If waveguides  11  of component  10  and semiconductor  14  of component  13  are the same distance from the contact face on carrier board  15  as in the embodiments according to FIGS. 1 and 2, then it is sufficient for carrier board  15  to have a single flat mounting surface (labeled as  38  in FIGS.  1  and  2 ). 
     FIG. 1 shows specifically a typical laser-fiber coupling arrangement, but it is also possible to couple a laser to a splitter, just as it is also possible to couple two lasers, such as a multi-section laser or for injection locking. Another possible application would be a series connection of splitters, where a 1-to-4 splitter is produced from three identical 1-to-2 splitters. However, a series connection of several Mach Zehnder interferometer chips to form a multiplexer or a demultiplexer is also possible. 
     The arrangement of a connection of two fibers illustrated in FIG. 2 permits another advantage. The electric arc energy customarily used to splice the two fibers can be replaced here by a beam (arrow  22 ) from an Nd-glass laser or an Nd-YAG laser, so that optical and mechanical connections can be produced with just one tool. 
     If waveguide  11  of component  10  and waveguide  14  of component  13  are not the same distance from the respective contact surface on carrier board  15  (this is the case in the embodiments according to FIGS. 3 and 4, for example), then carrier board  15  must be designed with steps as described above to compensate for the differences in distance from the respective contact surfaces ( 29 ,  30  in FIG. 3 or  33 ,  35  in FIG.  4 ). Step height h (FIG. 3) or h 1 -h 2  (FIG. 4) is thus equal to the difference between the distance from waveguide  11  to contact surface  29  and the distance from waveguide  14  to contact surface  30  (FIG. 3) or the difference between the distance from waveguide  11  to contact surface  33  and from waveguide  14  to contact surface  35  (FIG.  4 ). 
     Spherical lens  36  provided in the embodiment according to FIG. 4 serves to adjust the light guided in waveguides  11  and  14 . Spherical lens  36  is mounted with electromagnetic radiation  37  (at  27  on surface  34  of carrier board  15 ). 
     Other lenses such as cylindrical lenses can also be used. FIG. 4 a  shows an advantageous embodiment of such a design, where a cylindrical lens  41  that is used for adjusting the spot width, as is already known, is connected first to one of components  10  or  13  ( 13  here). Only then are components  10  and  13  connected to each other according to the present invention. Other known embodiments of components  10  and/or  13 , where component  13  has a fiber end in the form of a lens, for example, can also be connected with the measures according to the present invention. 
     The arrangements according to FIGS. 5 and 6 show specifically a semiconductor laser ( 10 ,  11 ) mounted on carrier board  15 . In the variant according to FIG. 5 (front view), electromagnetic radiation  23 ,  24  is guided laterally to fusion zones  25 ,  26 , as explained above. In the variant according to FIG. 6, the radiation is supplied directly from above (normal to the plane of the drawing) and cuts a hole  21  to reach fusion zones  17 . 
     In the embodiment according to FIG. 7, a semiconductor laser having a waveguide  11  is mounted by means of fusion spots  17  on a carrier board  15  having a continuous flat contact surface  38 . So far, this all corresponds to the embodiment according to FIG. 1 (see left side there). The special feature of the variant according to FIG. 7 includes the fact that a pump lead-in wire  39  is connected to semiconductor laser  10  by electromagnetic radiation  40 . In this case, as indicated by an arrow, radiation  40  is supplied perpendicularly from above. 
     In any case, in all the embodiments illustrated and described here, the electromagnetic radiation must be supplied in such a way that it causes the material of joining partners  10  and  15  or  13  and  15  or  39  and  10  (FIG. 7) or  39  and  13  (not shown) or  36  and  15  (FIG. 4) to melt in zones  17  and  18  (FIGS. 1 to  4  and  7 ),  25  and  26  (FIG.  5 ),  27  (FIG. 4) and  21  (FIG.  6 ), respectively, so a joint based on fusion of the joining partners is obtained after cooling. 
     Suitable materials for carrier board  15  include all materials that can be welded with electromagnetic radiation, specifically metals, preferably copper and Kovar, but also silicon or glass. Suitability of these materials for the purposes of the present invention has been demonstrated experimentally. 
     Supplying radiation  19  through component  10  (FIGS. 1 and 2) permits the following procedure: Component  10  is gripped by an auxiliary device (not shown) such as a precision manipulator or a precision xy translation table and is placed with its contact surface  16  on carrier board  15  and then shifted into its final position by the auxiliary device. Then it is secured in this position by turning on radiation  19 . 
     Component  13  can be mounted in the same way, optionally using the information-carrying light from waveguide  11  of component  10  to locate the position of component  13  (active adjustment). As an alternative, the desired position of component  13  can also be located by the external shapes of components  10  and  13  or with auxiliary markings (not shown) without using the information-carrying light from component  10  or component  13  (passive adjustment). In both cases, alignment is necessary in only two coordinate directions, because the third coordinate is determined by surface  38  or  29 ,  30  or  33 ,  34 ,  35  of carrier board  15 . If one of components  10  or  13  is a laser, the electromagnetic radiation ( 54 ) used for mounting can also be used to attach wire  39  for supplying the pump current to the laser (see FIG.  7  and the relevant discussion above). 
     Welding in vacuo is advantageous because the heat introduced by the electromagnetic radiation is dissipated more slowly in a vacuum and thus a lower radiation power can be used, and gases evolved from the materials of the joining partners in the welding plasma will diffuse away more rapidly in vacuo than in air. This minimizes negative effects on the joining partners ( 10 ,  15  or  13 ,  15  or  36 ,  15  or  39 ,  10 ) due to deposition of such gases on the reflective surface of a laser, for example. 
     In summary, the following advantageous effects can be achieved by the present invention: 
     An inexpensive carrier board  15  with a simple structure is used: only one flat contact face ( 38  or  29 ,  30  or  33  to  35 ) is required, optionally with a step ( 28  or  31 ,  32 ). No mounting grooves are required on carrier board  15 . Except for carrier board  15 , no additional mounting element is needed. Requirement: The distances between waveguides  11  and  14  and the respective contact faces on carrier board  15  must be known with sufficient accuracy. 
     The joining partners ( 10 ,  13 ,  36 ) are mounted directly on carrier board  15 , so the possibility of assembly errors is eliminated. 
     Alignment is required in only two coordinate directions, thus permitting a great variability in placement of the components ( 10 ,  13 ). 
     Compact design (module size for laser-fiber coupling not including casing &lt;1 mm 3 ). 
     Little distortion in mounting, because the volume of fused material can be minimized. 
     Simple and inexpensive mounting of all parts to be joined (Nd-glass lasers are available for only DM 10,000, about $6700 at current exchange rates). 
     No soldering, gluing or bonding tools needed. 
     Long lifetime (no adhesive or solder required). 
     Can be used at high temperatures (in test runs an InP laser would deliver light even at 250° C., so temperatures up to 400° C. seem possible). 
     Versatility in use (e.g., laser-fiber coupling, replacement for mechanical or thermal splicing, series connection of splitters or Mach Zehnder interferometer chips).