Patent ID: 12253726

DETAILED DESCRIPTION

In view of the problems described above, there is a need for an improved beam coupling system and a corresponding method, particularly reducing the necessity for ultra-stable opto-mechanics.

Embodiments of the present invention provide a system for coupling at least one optical beam, each having an essentially or exactly elliptical beam cross section, such as one or more optical beams generated by respective semiconductor lasers or laser diodes, into a light receiver, such as an optical fibre, having an essentially or exactly circular light receiving cross section, wherein the system comprises at least one optical beam entry port, each port being configured to provide an entry for each of the at least one optical beam into the system, an optical beam exit port configured to provide an exit for the at least one optical beam out of the system for coupling the at least one optical beam into the light receiver, at least one optical beam deflector, such as a mirror and/or dichroic mirror, for deflection of an optical beam of the at least one optical beam, and an optical base element, such as an optical base plate extending in an (x-y-) plane of the system. In this system, at least one beam deflector of said at least one beam deflector is directly, in other words unintermediately, particularly without using any adjustment device such as the above opto-mechanics or holder, fixed to the base element. Particularly, no adjustment of the thus fixed beam deflector after its fixation is possible. Due to the fixation, especially during or even after the fixation, as will be explained in more detail below, a directly fixed beam deflector typically might rotate—within a small rotation angle range—around a rotation axis which rotation results in an additional deflection of the corresponding optical beam. This “additional” deflection occurs in addition to the normal desired deflection. In this system, the at least one optical beam entry port and/or the at least one optical beam is further configured such that the semi-major axis of the elliptical cross section of the respective optical beam on a deflection surface of the beam deflector is oriented essentially or exactly parallel to the rotation axis. Finally, in this system, the at least one optical beam deflector is oriented such that after having passed the optical beam exit port or at the vicinity of the optical beam exit port, the elliptical cross section of the at least one optical beam overlaps the circular cross section of the light receiver.

Hitherto, in commercial coupling systems, each deflection element/optical beam deflector or at least the one located immediately before the optical beam exit port is delivered with its own opto-mechanics/adjustment device, increasing the costs of the system. It would be advantageous and more user friendly to align the mirrors in a factory, e.g. using special opto-mechanics, and then after having fixed the mirrors to the system release them from the opto-mechanics, which latter can then be used for the production of another system. Embodiments of the present invention achieve this very advantage. A single, some or even all beam deflectors used in the system can be directly fixed onto the base element of the system without delivering corresponding opto-mechanics to the user of the system.

Further, embodiments of the present invention overcome the problems related to the fixing of a mirror to the base element/plate of the system. One could think, for example, of fixing the mirror with some kind of screw or by simply using an adhesive. Each of these processes will unfortunately move the mirror a little bit while fixing it. A screw typically induces a little movement on the mirror while fastening it. On the other hand, an adhesive tends to shrink while hardening and will thus move the mirror. Further, with thermal changes of the environment, adhesives tend to shrink or expand, thus resulting in thermally induced movements of the mirror after its fixation, which can influence the coupling efficiency. Further, there are different ways of fixing a mirror to the base element/plate. The backside of the mirror can be fixed to a holder connected to the base element. Another way would be fixing the mirror with a lateral surface at one of its sides directly to the base element. The fixing could be done by an adhesive. During hardening of the adhesive and later on due to thermal fluctuations, the adhesive moves, moving the mirror and thus leading to different angular orientations. This would typically render the time consuming and cumbersome alignment process void.

In an embodiment, the present invention solves this problem as described in the following disclosure.

The idea of orienting the elliptical cross section of an optical beam in the way described above makes use of the supposed disadvantage of an elliptical beam cross section in order to compensate mirror movements related to a direct fixing of a mirror to the base element. This is described in the following with reference toFIG.3.

FIG.3aschematically shows a beam deflector/mirror310directly fixed via an adhesive314onto a base element300, here a base plate extending in the x-y-plane of the system. The mirror or beam deflector310has a deflection surface311and a backside313opposed to the deflection surface311, and further four lateral surfaces at the four sides of the mirror310, the mirror being directly fixed in this embodiment with one of its lateral surfaces312via the adhesive314to the base element300. It is noted that “directly” or “unintermediately” in the context of fixing a beam deflector to the base element is especially to be understood in the meaning of fixing the beam deflector without an adjustment device allowing free adjustment of the beam deflector after its fixation. Such a “direct” fixing, however, does not exclude that the beam deflector can be fitted onto a holder or into a frame, e.g. irreversibly, or that the beam deflector and the holder/frame are a compound unit acting as a unibody component, and the holder/frame can be fixed to the base element. The fixing itself can be done via an adhesive and/or with the help of at least one screw and/or welding or other fixing means. Again, it is noted that the fixing is particularly done without using any kind of adjustable holders or opto-mechanics as shown inFIG.2by means of which the beam deflector would be indirectly fixed to the base element.

FIG.3afurther shows an optical beam320such as a laser beam travelling in an x-y-plane and being reflected by a deflection surface311of the mirror310. The illuminated area on the deflecting surface311is also shown. The arrows320denote the propagation direction of the laser beam, not the beam shape.

Fixing the mirror310by a layer of adhesive314to the base element300, the adhesive will typically create a layer between the lateral surface312and the base plate300, which layer is never really perfectly uniform, but could, for example, be in the form of a slight wedge. This wedge of adhesive will lead to a rotation of the mirror310around an axis parallel to the x-axis upon shrinkage or expansion of the wedge due to hardening or thermal changes. This situation is illustrated inFIG.3b. A rotation of the mirror310around an axis parallel to the x-axis, however, does not influence the direction of the reflected beam320, in other words, does not lead to an “additional” deflection as defined above.

Additionally or alternatively, the wedge of adhesive can be formed as shown inFIG.3c. Again, during shrinkage or expansion of the adhesive due to hardening of the adhesive or due to thermal changes, the thicker side of the wedge will expand further than the thinner side of the wedge, leading to a tilt or a rotation of the mirror310around a rotation axis y′ parallel to the y-axis. A movement of the mirror310around the y′-axis, however, leads to a deflection of the beam upon reflection out of the x-y-plane as illustrated inFIG.3cand thus to an additional undesired deflection. As explained below, embodiments of the present invention, however, are to a large extent insensitive to such a deflection of the beam out of the x-y-plane as long as the elliptical cross section overlaps the circular cross section of the light receiver.

As mentioned above, another possibility of fixing the mirror310to the base element300would be to use a holder which is fixed to the base element, the mirror310being fixed with its backside313at least partly to such a holder. As can be seen fromFIG.3, such a fixing might lead to a slight rotation of the mirror310around an axis parallel to the z-axis upon shrinkage or expansion of the adhesive. In this case, it would have to be made sure that the semi-major axis of the elliptical cross section of the optical beam on the deflection surface311is oriented (essentially) parallel to the rotation axis/z-axis.

As explained further below in connection with embodiments of the present invention, the situation ofFIG.3c, i.e. a rotation of the mirror310around the y′-axis leads to a shift of the elliptical cross section with its semi-major axis along the z-direction as illustrated inFIG.3dby the arrow next to the elliptical beam cross section330. Such a shift hardly influences the coupling efficiency as long as the elliptical cross section330overlaps the circular cross section340of the light receiver.

It is noted that each focussing lens performs a Fourier transformation of the beam cross section of the beam passing the lens. In case of an elliptical shape such a Fourier transformation essentially results in a rotation of the elliptical shape of 90°. Thus, for example, the lens170as shown inFIG.1rotates the elliptical shape of the optical beam120,121comprising an elliptical cross section being oriented essentially parallel to the x-y-plane between the dichroic beam deflector130and the lens170such that the semi-major axis of the optical beam at the vicinity of the optical beam exit port190/at the light receiver160is oriented along the z-direction as illustrated inFIG.3dby the arrow next to the elliptical beam cross section330.

It should be noted that “essentially or exactly elliptical” or “elliptical or at least essentially elliptical” is meant to describe an elliptical form which may vary as a result of interaction with optical elements, such as (dichroic) mirrors, optical lenses etc. The same applies to the expression “essentially or exactly circular” and to the definitions of “essentially or exactly parallel” and “essentially or exactly perpendicular”. Further, deviations are allowed within typical tolerances.

Referring again toFIG.3, an adhesive wedge between a lateral surface312of the beam deflector310and the base element300will only have a relevant influence if movement of the wedge results in a rotation of the beam deflector around the y′-axis (seeFIG.3c). As already discussed above, this will lead to a deflection of the beam in z-direction and thus to movement of the focal spot in z-direction on the light receiving element (seeFIG.3d). The beam deflector will almost never significantly rotate around the z-axis if the adhesive shrinks or expands. Bearing this understanding in mind, the elliptical shape of the laser beam cross section can even help to stabilise the laser coupling into the light receiver/fibre, if the beam is correctly oriented. By orienting the beam such that the semi-major axis of the elliptical cross section lies in the x-y-plane after having entered the optical beam entry port of the system, the focal spot of the optical beam will show its semi-major axis oriented parallel to the z-axis after having passed the exit port including a lens as shown inFIG.3d. Thus, if the beam moves in z-direction, the circular light receiving cross section340will still be significantly illuminated due to the elongation of the elliptical focal spot330in this direction.

In an advantageous embodiment, the at least one optical beam entry port or every optical beam entry port comprises a collimator lens. According to an embodiment, the optical beam exit port comprises a lens performing a Fourier Transform, in particular a condenser lens. While the collimator lens generates a beam of parallel light bundles, the condenser lens focuses a beam of parallel light bundles into a focal spot. A coupling end of the light receiver/optical fibre should be located at this focal spot.

In another advantageous embodiment, the optical beam exit port is further configured to receive an optical fibre as the light receiver, such that an optical fibre can be mounted to the optical beam exit port. Similarly, it is advantageous if a laser, particularly a laser diode, can be mounted to an optical beam entry port.

Typically, the lateral surface of a beam deflector is essentially or exactly perpendicular to the deflection surface of the optical beam deflector for deflecting the optical beam.

Embodiments of the present invention are particularly advantageous for coupling two or more optical beams into a light receiver such as an optical fibre. In this case, at least one of the optical beam deflectors is a dichroic beam deflector which allows a first optical beam to pass through the dichroic beam deflector and deflects a second optical beam, e.g. due to the wavelength characteristic of the dichroic beam deflector. Such a dichroic beam deflector is particularly suited for superimposing two optical beams. In case of more than two optical beams, more than one dichroic beam deflectors may be used. Such a dichroic beam deflector is advantageously arranged for directing the first and the second optical beams to the optical beam exit port.

In an advantageous embodiment, at least the optical beam deflector which is located immediately before the optical beam exit port is directly fixed to the base element. Typically, the system is set up starting to adjust the beam deflectors in the direction from the entry port to the exit port. Any deviations of the preceding mirrors/beam deflectors can, to a certain degree, be balanced out by adjusting the beam deflector/dichroic beam deflector located immediately before the optical beam exit port correspondingly. To this end, hitherto the last beam deflector/dichroic beam deflector is usually provided with opto-mechanics, i.e. an adjustment device. With embodiments of the present invention, however, even these opto-mechanics can be rendered superfluous. In this context, it is particularly advantageous if each of the at least one optical beam deflector is directly fixed to the base element without using any opto-mechanics.

In a second aspect of the present invention, a method for coupling at least one optical beam into a light receiver is provided. The method for coupling at least one optical beam, each having an elliptical or at least essentially elliptical beam cross section into a light receiver having a circular or at least essentially circular light receiving cross section, comprises the steps of: providing at least one optical beam deflector for deflection of an optical beam of the at least one optical beam, and providing an optical base element, particularly extending in a plane, wherein at least one beam deflector of said at least one beam deflector is, after an orientation step for orienting the at least one beam deflector, directly fixed to the base element, particularly without an adjustment device allowing adjustment of the directly fixed deflection element after its fixation, wherein due to the fixation the respective directly fixed optical beam deflector is allowed—within a small range—to rotate around a rotation axis which rotation results in an additional (undesired) deflection of the corresponding optical beam, and orienting the semi-major axis of the elliptical cross section of the respective optical beam on a deflection surface of the respective optical beam deflector parallel or at least essentially parallel to the rotation axis, wherein the orientation step for orienting the at least one beam deflector comprises orienting the at least one optical beam deflector such that the elliptical cross section of the at least one optical beam overlaps the circular cross section of the light receiver.

In a preferred embodiment, the method comprises the steps of: providing at least one optical beam deflector for deflection of an optical beam of the at least one optical beam, and providing an optical base element extending in an x-y-plane, wherein at least one beam deflector of said at least one beam deflector is, after an orientation step for orienting the at least one beam deflector, directly fixed with a lateral surface of the beam deflector to the base element, such that a deflection surface of the beam deflector extends at least essentially perpendicular to the surface of the base element/x-y-plane, and orienting the semi-major axis of the elliptical cross section of the respective optical beam parallel or at least essentially parallel to the x-y-plane when striking/hitting the deflection surface of the respective optical beam deflector.

It is pointed out that the features described above in relation to the system according to the first aspect represent an analogous description of the corresponding features of the method according to the second aspect. Some or all of the method steps may be executed by (or using) a hardware apparatus, like for example, a processor, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, one or more of the most important method steps may be executed by such an apparatus.

As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”.

It should be noted that features of the above examples as well as of the examples explained below can—wholly or in part—be combined to other examples not explicitly mentioned herein, nevertheless being part of the present disclosure.

InFIG.1, two optical beams120,121, each having an elliptical beam cross section are coupled into a light receiver160having a circular light receiving cross section. The system is designated100. System100comprises two optical beam entry ports180,181, each port being configured to provide an entry for each of the optical beams120and121into the system100. In the embodiment shown, optical beam entry port180comprises a collimator lens150and is configured for mounting a laser diode140for generating the optical beam120. Same applies to optical beam entry port181which comprises a collimator lens151and is configured to receive a laser diode141for generating the optical beam121.

The system100further comprises an optical beam exit port190configured to provide an exit for the merged two optical beams120and121out of the system100for coupling the beams into the light receiver160which is an optical fibre in the embodiment shown. The optical beam exit port190further comprises a condenser lens170and is further configured to receive the optical fibre160. Usually, the system100comprises not only the elements shown e.g. inFIG.1as well as an optical base element preferably in the form of a base plate300(see e.g.FIG.3or4), but also at least one side wall and in particular with a top cover element, such that the system may have a box-shape. The at least one optical beam entry port180,181and the optical beam exit port190are in such a case formed in a side wall.

The system100further comprises a number of beam deflectors110,111,112, and130, e.g. fitted into corresponding frames or onto corresponding holders, for deflection of the optical beams120,121in order to direct them to the optical beam exit port190. Optical beam deflectors110,111,112may be in the form of simple mirrors, while beam deflector130may be a dichroic beam deflector which allows optical beam121to pass through it and which deflects optical beam120in order to merge the two optical beams120,121onto the same optical path and preferably essentially propagating in a co-axially manner in the direction of the optical beam exit port190.

System100may comprise further optical elements and may comprise more than two optical beam entry ports. A person skilled in the art may easily adapt system100to a system for coupling more than two optical beams into a light receiving element160.

The system100further comprises an optical base element extending in an x-y-plane of the system, which plane corresponds to the drawing plane ofFIG.1. At least one beam deflector, especially the dichroic beam deflector130and advantageously also the mirrors110,111,112, are directly fixed with a lateral surface to the base element. This is further described with regard toFIG.3. The deflection surfaces of the fixed beam deflectors extend essentially or exactly perpendicular to the base element/drawing plane ofFIG.1. The such fixed beam deflectors are advantageously fixed via an adhesive. Alternatively or additionally, the fixing can be achieved by at least one screw and/or by welding.

System100may advantageously be set up in a factory, first aligning mirrors110and111, second, aligning mirror112and finally aligning dichroic mirror130and fixing each of the aligned mirrors with an adhesive layer to the base element. The pre-built system100can then be delivered to a user without the need of a user alignment by means of opto-mechanics.

FIG.2shows an opto-mechanical holder or opto-mechanics200for a beam deflector typically used hitherto as an adjustment device for aligning and fixing a beam deflector. The mirror-mounting surface of the opto-mechanics200is designated210. The opto-mechanics200comprises a ball bearing220, a spring240and an adjustment screw230. At least two supporting points of the mirror-mounting surface210can be moved back and forth by corresponding screws230with a fine thread. Thus, the vertical and horizontal tilt can be set independently. This allows a highly precise movement of the beam deflector. Such opto-mechanics200are high in costs and the alignment process is time consuming.

FIG.3schematically shows a beam deflector310directly fixed to an optical base element300as part of an embodiment of the system100shown inFIG.1. The beam deflector310can be any one of the beam deflectors110,111,112,130ofFIG.1. Beam deflector310is directly fixed with its lateral surface312to the base element300via an adhesive layer314. As shown inFIG.3a, the semi-major axis of the elliptical cross section330of the optical beam320is oriented parallel to the x-y-plane in which the optical base element300extends and in which the beam320travels in direction of the deflecting surface311. Further details ofFIGS.3ato3dhave already been discussed above. As already explained above, the fixing process and any possible thermal changes afterwards may lead to mirror movements. While movements around a z-axis are very unlikely, movements around an x-axis are not relevant for the coupling efficiency. The only relevant movement is the movement around the y′-axis as shown inFIG.3c. Such a movement leads to a deflection of the reflected beam320out of the x-y-plane, which results in a movement of the focal spot330in the z-direction as shown inFIG.3d. As long as the elliptical cross section330of the optical beam320overlaps the circular cross section340of the optical fibre160, a movement of the semi-major axis along the z-direction hardly influences the coupling efficiency.

FIG.4schematically shows in a perspective view e.g. a part of a system shown inFIG.1together with a light receiver160according to an embodiment of the present invention. The optical beam deflector310can be a mirror especially in case of only one beam being coupled into a light receiver, or can be a dichroic beam deflector in case of coupling two or more optical beams into a light receiver (as shown inFIG.1for two optical beams). In the latter case, optical beam320inFIG.4corresponds to the optical beam120inFIG.1and the beam deflector310corresponds to the dichroic beam deflector130ofFIG.1. Again, the arrows320illustrate the laser beam propagation directions and the elliptical shapes illustrate the corresponding beam cross sections. The optical beam320, after being reflected by the beam deflector310, is directed to the condenser lens170, the elliptical illuminated area being shown inFIG.4(on the surface of the beam deflector310and at a side of the condenser lens170facing the beam deflector310). The condenser lens170focuses the beam onto the front side of the light receiver, here an optical fibre160which is arranged with its front side in the focal plane of lens170. This arrangement results in coupling of the optical beam having an elliptical beam shape330into the optical fibre160having a circular light receiving section340as shown inFIG.3d. The elliptical shape of the optical beam320between the beam deflector310and the condenser lens170is oriented with its semi-major axis essentially parallel to the x-y-plane. Lens170turns the elliptical shape of the optical beam320about 90 degrees by the Fourier Transform function of the lens170, thus resulting in a (focused) elliptical shape of the optical beam320whose semi-major axis is oriented essentially parallel to the z-axis (as shown inFIG.3d).

As can be seen from, for example,FIGS.3aand4, it should be made sure that the mirror dimension in the y-direction or more generally the mirror breadth is sufficient to cover the elliptical beam shape to its full extent. As the semi-major axis of the elliptical beam shape is oriented parallel to the x-y-plane, the semi-major axis is enlarged on the mirror surface, if the beam hits the mirror non-perpendicularly. (For illustration purposes, e.g., a circular beam profile would generate an elliptical illuminated area on a mirror surface, if the beam hits the mirror non-perpendicularly.) Thus, according to an embodiment of the present invention, an elliptical beam profile with its semi-major axis parallel to the x-y-plane may need a mirror with a larger dimension in the y-direction (as shown inFIGS.3aand4), a fact which would normally prevent a person skilled in the art from choosing such a beam profile orientation and would rather lead to choosing a preferred orientation of the semi-major axis parallel to the z-direction. As explained above, however, the present embodiment offers significant advantages such as a better light coupling stability.

While subject matter of the present disclosure has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Any statement made herein characterizing the invention is also to be considered illustrative or exemplary and not restrictive as the invention is defined by the claims. It will be understood that changes and modifications may be made, by those of ordinary skill in the art, within the scope of the following claims, which may include any combination of features from different embodiments described above.

The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B and C” should be interpreted as one or more of a group of elements consisting of A, B and C, and should not be interpreted as requiring at least one of each of the listed elements A, B and C, regardless of whether A, B and C are related as categories or otherwise. Moreover, the recitation of “A, B and/or C” or “at least one of A, B or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B and C.

LIST OF REFERENCE SIGNS

100system110beam deflector, mirror111beam deflector, mirror112beam deflector, mirror130beam deflector, dichroic beam deflector120optical beam121optical beam140laser diode141laser diode150collimator lens151collimator lens160light receiver, optical fibre170condenser lens180optical beam entry port181optical beam entry port190optical beam exit port200opto-mechanical holder, opto-mechanics210mirror-mounting surface220ball bearing230adjustment screw240spring300optical base element, base plate310optical beam deflector, mirror, dichroic beam deflector311deflecting surface312lateral surface313backside314adhesive layer, adhesive320optical beam330elliptical cross section340circular cross system