Abstract:
A coupling apparatus for coupling a light emitting element with an optical fiber, wherein the light emitting element and a coupling lens are secured within a holder. The apparatus includes a ferrule which holds the optical fiber and which is inclined at a predetermined inclination angle with respect to the optical axis of the coupling lens, and a support member which is secured to the holder and which holds the ferrule so as to move in a direction parallel with the optical axis of the coupling lens.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a coupling apparatus (receptacle) of a light emitting element such as a laser diode and an optical fiber. The present invention also relates to a method for adjusting optical fiber position using the same. 
     2. Description of the Related Art 
     Recently, laser drawing apparatuses using multi-laser beams have been proposed in which a group of light sources consisting of a plurality of laser emitters and a plurality of optical fibers are provided to increase the drawing speed. 
     In a multi-laser beam drawing apparatus using optical fibers as a light source, the laser beam emitted from the semiconductor laser and made incident upon the incident surface of the optical fiber is partly reflected by the incident surface. If the reflected light is made incident upon the semiconductor laser, the laser emission is disturbed, thus resulting in a change in the intensity of the laser beams, etc. To avoid this, the incident surface of the optical fiber is cut along a plane inclined with respect to the center axis of the optical fiber to form an oblique incident surface, so that the light reflected thereby does not reach the semiconductor laser, as shown in FIG.  4 . 
     In the prior art shown in FIG. 4, a laser diode (LD)  156  is secured to a lens holder  116  which holds a coupling lens  136  through an LD holder  126 . The lens holder  116  is provided with an adjusting ring  166  secured thereto. The optical fiber  20  is held by a ferrule  196  so that the center axis of the optical fiber at the incident surface thereof is inclined with respect to the optical axis of the coupling lens  136  at a predetermined inclination angle. The ferrule  196  is press-fitted in the adjusting ring  166  which is secured to the lens holder  116 . The incident surface of the optical fiber  20  is defined by an oblique surface  20   a  inclined at a predetermined inclination angle with respect to a plane perpendicular to the center axis thereof. The optical fiber  20  is held in such a way that the incident surface  20   a  thereof is not normal to the optical axis O 1 . 
     The ferrule  196  which holds the optical fiber  20  is not parallel with the optical axis O 1  of the coupling lens  136  and is moved in the direction parallel with the center axis of the optical fiber  20  to adjust the position of the incident surface (core surface)  20   a  of the optical fiber  20 . However, since the direction of the movement of the optical fiber  20  is inclined with respect to the optical axis O 1 , if the ferrule  196  is slid to move the incident surface  20   a  to the focal point of the coupling lens  136 , not only does the distance between the incident surface  20   a  and the coupling lens  136  in the optical axis direction change, but also the distance between the center of the incident surface  20   a  and the optical axis O 1  also varies. Consequently, it is difficult to adjust the incident surface  20   a  of the optical fiber  20  to the focal point f of the coupling lens  136 . 
     Moreover, to establish a highly precise positional relationship between the laser diode  156  and the optical fiber  20  at the connection therebetween, the LD holder  126  and the adjusting ring  166  are independently moved along the contact surfaces thereof with the lens holder  116  in the prior art. Upon completion of the adjustment, the LD holder  126  and the adjusting ring  166  are welded to the coupling lens holder  116 , for example, by a YAG laser to prevent the accidental movement thereof. Therefore, if the laser diode  156  is broken, it is difficult to replace the laser diode alone. Upon replacement of the broken LD  156 , if the LD holder  126  is detached from the lens holder  116  without detaching the adjusting ring  166  to which the ferrule  196  and the optical fiber  20  are secured from the lens holder  116 , it is difficult to readjust the position of the incident surface  20   a  of the optical fiber  20 , as mentioned above. 
     The emission surfaces of the light sources are united in the form of a fiber array. Therefore, if a laser diode of one of the light sources is broken, it is difficult to repair or replace the LD since the laser receptacle cannot be disassembled. Furthermore, since the fiber array cannot be disassembled, the entirety of the laser sources must be replaced in spite of the fact that the remaining fibers are normal. 
     It is possible to secure the adjusting ring  166  to the lens holder  116  by means of screws in place of welding. However, the relative position therebetween may be changed due to the force produced in the rotation direction or forward movement direction of the screws when the screws are fastened or loosened. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a coupling apparatus for a light emitting element and an optical fiber in which the position of the optical fiber can be easily adjusted during the assembling operation. 
     Another object of the present invention is to provide a simple coupling apparatus of a light emitting element and an optical fiber in which the assembling and disassembling thereof can be easily carried out. 
     According to an aspect of the present invention, there is provided a coupling apparatus for coupling a holder, to which the light emitting element and a coupling lens are secured, with the optical fiber. This coupling apparatus includes a ferrule which holds the optical fiber and is inclined at a predetermined angle with respect to the optical axis of the coupling lens. Preferably, the incident end surface of the optical fiber is inclined at a predetermined angle with respect to a plane that is normal to the optical axis of the coupling lens. 
     Also provided is a support member that includes: an adjustable ring which is movable and adjustable in a plane perpendicular to the optical axis of the coupling lens and which is secured to the lens holder; a ferrule ring supported within the adjusting ring, wherein the ferrule ring is movable in a direction parallel with the optical axis of the coupling lens; and a ferrule holder which is detachably press-fitted into the ferrule ring so as to be movable in a direction parallel with the optical axis of the coupling lens. The ferrule is held by the ferrule holder at an inclined position with respect to the optical axis and is movable together with the ferrule holder in a direction parallel with the optical axis. 
     Alternatively, the support member can include: an adjustable ring which is movable and adjustable in a plane perpendicular to the optical axis of the coupling lens and which is secured to the lens holder; a ferrule ring supported within the adjusting ring, wherein the ferrule ring is movable in a direction parallel with the optical axis of the coupling lens; and wherein the ferrule is held in the ferrule ring at an inclined position with respect to the optical axis and is movable together with the ferrule ring in a direction parallel with the optical axis. The ferrule holder and the adjusting ring can be made of metal and can be secured to the lens holder by laser welding. Alternatively, the ferrule holder is made of metal and the adjusting ring is made of a ceramic material, so that the ferrule holder and the adjusting ring are secured to each other by an adhesive. 
     According to another aspect of the present invention, there is provided a coupling apparatus for a light emitting element and an optical fiber which includes: a lens holder to which the light emitting element, a coupling lens and the optical fiber are to be secured; an adjusting ring which is movable and adjustable in a plane perpendicular to the optical axis of the coupling lens and which is secured to the lens holder upon completion of the positional adjustment between the adjusting ring and the lens holder; a ferrule ring which is fitted inside the adjusting ring, movable in a direction parallel with the optical axis of the coupling lens and which is secured to the adjusting ring upon completion of positional adjustment between the ferrule ring and the adjusting ring; and a ferrule member which is fitted in the ferrule ring and which holds the optical fiber in a position so that the optical fiber is inclined at a angle with respect to the optical axis of the coupling lens. Preferably, the incident end surface of the optical fiber is inclined at a predetermined angle with respect to a plane that is normal to the optical axis of the coupling lens. Preferably, the ferrule member is movable within the ferrule ring in a direction parallel with the optical axis. Preferably, the ferrule member includes a ferrule ring fitted inside the adjusting ring (the ferrule ring being movable in a direction parallel with the optical axis of said coupling lens) and a ferrule holder which is press-fitted inside the ferrule ring (the ferrule holder supporting the optical fiber). Preferably, the ferrule member includes a single ferrule holder fitted inside the adjusting ring, the ferrule holder being movable in a direction parallel with the optical axis of the coupling lens. The ferrule holder and the adjusting ring can be made of metal and can be secured to the lens holder by laser welding. The lens holder can be made of metal and the adjusting ring can be made of a ceramic material, so that the lens holder and the adjusting ring can be secured to each other by an adhesive. 
     According to another aspect of the present invention, there is provided a method for adjusting the position of an optical fiber in a coupling apparatus wherein the coupling apparatus includes: a lens holder, one end of which a light emitting element and a coupling lens are secured, and the other end of which the optical fiber is connected; an adjusting ring to be secured to the lens holder; a ferrule ring which is fitted inside the adjusting ring (the ferrule being movable in a direction parallel with the optical axis of said coupling lens); and a ferrule member which is fitted inside the ferrule ring and which holds the optical fiber in a position so that the optical fiber is inclined at a predetermined angle with respect to the optical axis of the coupling lens. The method includes: moving the adjusting ring in a plane perpendicular to the optical axis of the coupling lens and securing the adjusting ring to the lens holder upon completion of position adjustment between the adjusting ring and the lens holder; and moving the ferrule ring in the adjusting ring in a direction parallel with the optical axis of the coupling lens and securing the ferrule ring to the adjusting ring upon completion of position adjustment between the ferrule ring and the adjusting ring. 
     Preferably, the method further includes the moving of the ferrule member in the ferrule ring in a direction parallel with the optical axis and securing the ferrule member in the ferrule ring upon completion of positional adjustment between the ferrule member and the ferrule ring. 
     The present disclosure relates to subject matter contained in Japanese Patent Application No.9-138472 (filed on May 28, 1997) which is expressly incorporated herein by reference in its entirety. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be discussed below in detail with reference to the accompanying drawings, in which; 
     FIG. 1 is an enlarged longitudinal sectional view of a first embodiment of A coupling apparatus for a light emitting element and an optical fiber, according to the present invention; 
     FIG. 2 is an enlarged longitudinal sectional view of a second embodiment of A coupling apparatus for a light emitting element and an optical fiber, according to the present invention; 
     FIG. 3 is an enlarged longitudinal sectional view of a third embodiment of A coupling apparatus for a light emitting element and an optical fiber, according to the present invention; 
     FIG. 4 is an enlarged longitudinal sectional view of a known coupling apparatus of a light emitting element and an optical fiber; 
     FIG. 5 is a schematic perspective view of a multi-laser drawing apparatus to which A coupling apparatus for a light emitting element and an optical fiber according to the present invention is applied; and, 
     FIG. 6 is an exploded perspective view of a light emission end structure of a multi-laser source using optical fibers. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 5 and 6, a multi-laser drawing apparatus to which a coupling apparatus of optical fibers according to the present invention by way of example is applied will be discussed below. 
     A multi-laser drawing apparatus shown in FIG. 5 is composed of a multi-laser source having a plurality of laser sources  10  to which optical fibers  20  are coupled. The laser sources  10  are secured in the form of an array. The optical fibers  20  are held at their emission ends by a fiber array structure (not shown) within a fiber holder block  44 , so that the emission ends of the optical fibers  20  are aligned along a line at an equi-pitch (distance) smaller than the distance (pitch) of the remaining portions of the optical fibers. 
     The laser beams emitted from the laser sources  10  are transmitted through the optical fibers  20  and are emitted from the fiber holder block  44 . The laser beams emitted from the fiber holder block  44  are emitted toward a polygonal mirror  37  which is rotated, through a collimating lens  31 , a reflection mirror  33 , and a beam shaping optical system  35 . The laser beams reflected and deflected by the polygonal mirror  37  are transmitted through an fθ lens group  39 ; are reflected by a mirror  41 ; and are made incident upon an outer peripheral surface of a photosensitive drum to scan the same. In the illustrated embodiment, the polygonal mirror  37  is driven at a constant speed by a spindle motor  38 , and the laser sources  10  are turned ON or OFF in synchronization with a pixel clock which is in turn synchronized with the rotation of the spindle motor  38  and in accordance with drawing data. 
     As can be seen in FIG. 6, the emission ends  20   b  of the optical fibers  20  are spaced at a predetermined distance and are interconnected to form a fiber array so that the laser beams emitted from the emission ends  20   b  reach respective points on a drawing surface, which are spaced at a predetermined distance from one another in the main scanning direction and sub-scanning direction. Namely, the optical fibers  20  are received in respective parallel V-shaped grooves  45   a  of a V-groove block  45  and are pressed by a retainer block  46 . The optical fibers  20 , the V-groove block  45  and the retainer block  46  are adhered together. The emission ends  20   b  of the optical fibers  20  are polished together with the ends  45   b  and  46   b  of the blocks  45  and  46  on the emission side to define a plane normal to the central axes of the fibers  20 . 
     The present invention can be applied to a multi-laser beam drawing apparatus constructed as above. FIGS. 1,  2  and  3  show enlarged longitudinal sectional views of first, second and third embodiments of the present invention. In these embodiments, according to the features of the present invention, the ferrule  19 ,  192  or  193  is moved in a direction parallel with the optical axis of the coupling lens  13 ,  132  or  133  to adjust the position of the optical fibers  20  at the incident surfaces  20   a  thereof. 
     In the first embodiment shown in FIG. 1, the LD holder  12  which holds the laser diode  15  as a laser source  10  is secured to the lens holder  11  which holds the coupling lens  13 . The laser diode  15  is inserted and secured in the cylindrical LD holder  12 . The coupling lens  13  is secured to an opening formed in the center of the bottom of the lens holder  11 . The LD holder  12  abuts against the outer side surface  11   a  of the lens holder  11  to adjust the alignment of the axes of the laser diode  15  and the coupling lens  13 . After the completion of the adjustment, the contact portion between the LD holder  12  and the lens holder  11  are welded, for example, by means of a YAG laser. The cylindrical adjusting ring  16  is secured to the end surface  11   b  of the cylindrical portion of the lens holder  11  by laser welding. 
     The incident end surface of the optical fiber  20  is extended linearly and secured to the ferrule  19 . The ferrule  19  and the incident end surface (core surface)  20   a  of the optical fiber  20  are polished so as to define a planar surface which is inclined at a predetermined inclination angle with respect to the direction perpendicular to the center axis O 2  of the optical fiber  20  within the ferrule  19 . The ferrule  19  is inserted and secured in an oblique through-hole  18   a  formed in a ferrule holder  18  and inclined at a predetermined angle with respect to the optical axis O 1 . Namely, the axis O 2  of the oblique through-hole  18   a  is inclined with respect to the axis O 1  of the ferrule holder  18  whose outer surface is defined by a cylindrical surface. The cylindrical ferrule holder  18  is press-fitted in a ferrule ring  17  which is inserted in the adjusting ring  16 . 
     The ferrule holder  18  (outer surface thereof), the ferrule ring  17  and the adjusting ring  16  are concentric to each other and constitute a concentric annular structure. 
     The ferrule ring  17  is slidably inserted in the adjusting ring  16  to move in the optical axis direction O 1 . The ferrule ring  17  is secured to the adjusting ring  16 , for example, by YAG laser welding, after the distance between the incident surface  20   a  and the coupling lens  13  is adjusted (i.e., the focusing operation is completed). The ferrule holder  18  is press-fitted in the ferrule ring  17  so as to move in the optical axis direction O 1 . Namely, the ferrule  19  is held by the lens holder  11  so as to move in the optical axis direction O 1  while keeping a predetermined angle between the axis O 2  of the ferrule  19  and the optical axis O 1 . 
     In the first embodiment, the assembling and disassembling operations are carried out as follows. 
     The laser diode  15  is secured in a predetermined position in the LD holder  12 . Thereafter, the coupling lens  13  is secured to the lens holder  11  by means of an adhesive or the like, so that the optical axis O 1  is substantially identical to the axis of the lens holder  11 . The LD holder  12  abuts against the lens holder  11  and the laser diode  15  and the coupling lens  13  are aligned (axis adjustment in two orthogonal directions). Thereafter, the LD holder  12  is secured to the lens holder  11 , for example, by YAG welding. 
     The optical fiber  20  is inserted and secured in the ferrule  19  and is polished together with the ferrule  19 , so that the incident surface  20   a  forms a planar surface which is inclined at a predetermined inclination angle with respect to a direction perpendicular to the center axis O 2 . The ferrule  19  is thereafter inserted or press-fitted and adhered in the oblique through-hole  18   a  of the ferrule holder  18 . The axis of the oblique through-hole  18   a  is not parallel with but is inclined with respect to the axis of the ferrule holder  18 . The ferrule holder  18  is press-fitted into the ferrule ring  17  which is inserted in the adjusting ring  16 . The adjusting ring  16  is brought into contact with the lens holder  11  and thereafter, the position of the adjusting ring  16  in a plane perpendicular to the optical axis O 1  is adjusted so that the incident surface  20   a  is located on the optical axis O 1 . Namely, the adjusting ring  16  is moved in the direction perpendicular to the optical axis O 1  while keeping the same in contact with the end surface of the lens holder  11 . Upon completion of the adjustment, the adjusting ring  16  is secured to the lens holder  11 , for example, by YAG welding. 
     Thereafter, the ferrule ring  17  is moved along the inner peripheral surface of the adjusting ring  16  so that the incident surface  20   a  is located at the focal point f of the coupling lens  13 . Thus, the focus adjustment is carried out. Note that since the movement of the ferrule ring  17  occurs in the direction parallel with the optical axis O 1 , the incident surface  20   a  moves in parallel with the optical axis O 1 . However, no movement of the ferrule ring  17  in the direction perpendicular to the optical axis takes place, and hence the incident surface  20   a  is always located on the optical axis O 1 . After the focus adjustment is completed, the ferrule ring  17  is welded to the adjusting ring  16  to prevent the incident surface  20   a,  whose position has been adjusted, from being deviated from the focal point of the coupling lens in use. 
     FIG. 2 shows a second embodiment of the present invention. The main difference between the first embodiment and the second embodiment resides in the point that the ferrule holder  18  and the ferrule  19  are made of separate pieces in the first embodiment and are made of one piece  192  in the second embodiment, respectively. The structures of the lens holder  112 , the LD holder  122 , the coupling lens  132  and the laser diode  152  are same as those in the first embodiment shown in FIG.  1 . 
     In the second embodiment, the ferrule  192  is provided with a linear fiber hole  192   a  which is inclined at a predetermined inclination angle with respect to the axis of the ferrule  192 . The optical fiber  20  is press-fitted or inserted and secured in the fiber hole  192   a.  The incident surface  20   a  of the optical fiber  20  is polished together with the end face of the ferrule  192 , so that the incident surface  20   a  is inclined at a predetermined inclination angle with respect to the center axis of the optical fiber  20  and the center axis of the ferrule  192  passes through the center of the incident surface  20   a  of the optical fiber  20 . The ferrule  192  is press-fitted in the ferrule ring  172  which is in turn inserted in the adjusting ring  162 . 
     To secure the adjusting ring  162  to the lens holder  112 , first, the adjusting ring  162  is moved in a plane perpendicular to the optical axis O 1  to align the axis of the incident surface  20   a  with the optical axis O 1 . Upon completion of the alignment, the adjusting ring  162  and the lens holder  112  are secured to each other by laser welding. 
     Thereafter, the ferrule ring  172  is moved along the inner peripheral surface of the adjusting ring  162  to move the incident surface  20   a  to the focal point f of the coupling lens  132 . Thus, the focus adjustment is effected. The movement of the ferrule ring  172  occurs in the optical axis direction, and hence the incident surface  20   a  is moved in the optical axis direction O 1 . However, since no movement of the ferrule ring  172  in the direction perpendicular to the optical axis O 1  takes place, the incident surface  20   a  is not deviated from the optical axis. After the completion of the focus adjustment, the ferrule ring  172  is secured (welded) to the adjusting ring  162 . 
     FIG. 3 shows a third embodiment of the present invention. The main difference between the first embodiment and the third embodiment resides in the point that the LD holder  123  and the adjusting ring  163  are made of a material such as a ceramic material, which can be adhered to the lens holder  113 , so that they can be adhered upon completion of the adjustment, in the third embodiment. The structures of the ferrule ring  173 , the ferrule holder  183  and the ferrule  193  and the position adjustment process are same as those of the ferrule ring  17 , the ferrule holder  18  and the ferrule  19  in the first embodiment shown in FIG.  1 . 
     In the above-mentioned embodiments, the ferrule is adjustable independently in the directions perpendicular to and parallel with the optical axis O 1 . Consequently, the alignment of the fiber can be simplified and the time necessary for the alignment operation can be shortened. 
     In the above-mentioned embodiments, if the laser diode  15 ,  153  or  152  is broken, the ferrule holder  18  or  183  is detached or removed from the ferrule ring  17  or  173  or the ferrule  192  is detached or removed from the ferrule ring  172  by means of a detaching tool. Thereafter, a new ferrule ring  17 ,  173  or  172  is press-fitted in the ferrule holder  18  or  183 , or the ferrule  192 . Consequently, the assembling operation and the adjustment can be carried out, using a new laser diode and new parts (LD holder  12 ,  123  or  122 ; adjusting ring  16 ,  163  or  162 ; and lens holder  11 ,  113  or  112 ) in accordance with the above-mentioned assembling and adjustment processes. Thus, the replacement of the laser diode can be facilitated. 
     As may be understood from the above discussion, according to the present invention, since the ferrule which holds the optical fiber which is inclined at a predetermined inclination angle with respect to the optical axis of the coupling lens is held to move in a direction parallel with the optical axis of the coupling lens, not only can the alignment of the fiber be easily carried out but also the time necessary therefor can be reduced. 
     Moreover, according to the present invention, since the ferrule holder is detachably press-fitted in the ferrule ring, the replacement of the laser diode, the coupling lens or the lens holder can be facilitated and the realignment of the fibers after the replacement can be easily carried out.