Optical fiber coupling fitting

An optical fiber coupling fitting includes a clamping member, a central portion of which is removed for receiving an optical fiber holder which is inserted into the central hole portion. Transverse to a slot in the clamping member is a tapped bore for receiving a screw by which the distance between the opposite faces of the slot may be reduced, thereby reducing the area of the central hole portion of the clamping member and causing clamping engagement between the walls of the hole and the outer surface of a larger diameter end of the optical fiber holder. Loosening of the screw releases the clamping engagement between the walls of the hole and the optical fiber holder so that the fiber holder may be adjusted in a direction parallel to the axis of the optical fiber. The clamping member is affixed to a mounting block, which retains the optical element, by means of a plurality of screws passing through holes in the clamping member and engaging threaded holes in the mounting block. Loosening of these plurality of screws permits the position of the clamping member relative to the optical element retained in the mounting block to be adjusted, in order to properly align the optical fiber with the light coupling face of the optical element.

FIELD OF THE INVENTION 
The present invention relates to an arrangement for connecting a light 
conducting fiber or filament to the light coupling face of an optical 
element such as a light receiving photodiode or a light transmitting laser 
diode. In particular, the present invention is directed to an optical 
fiber coupler fitting which facilitates the connection and disconnection 
of both the optical element to which the fiber is coupled and the fiber 
itself, while achieving the required alignment between the fiber and the 
element without the need for adjustment whenever a connection replacement 
is effected. 
BACKGROUND OF THE INVENTION 
The recent development of optical telemetry systems has seen a significant 
reduction in the size of system components, such as light emitting 
devices, light receiving elements, and the optical conductive highways by 
way of which an optical transmitter and an optical receiver may be coupled 
to one another. Typically, the communication path is in the form of an 
optical fiber or filament, the ends of which are coupled with the light 
transmitting and receiving elements, respectively. In order to assure 
maximum optical coupling between the ends of the fiber and the optical 
devices to which they are coupled, it is important to precisely fix the 
axial distance between the end of the optical fiber and the face of the 
optical element to which it must be coupled, and to accurately align the 
end of the fiber with a prescribed location on the surface of the element. 
In addition, it is desirable that the coupling fitting permit rapid 
replacement of the optical fiber relative to the optical element. 
Examples of optical fiber coupler fitting arrangements which have been 
proposed to facilitate alignment and replacement of the coupled components 
are described in U.S. Pat. No. 4,060,309 to LeNoane et al and British Pat. 
No. 1,438,016 to Hennell et al. Basically, each of these arrangements is 
of tubular or cylindrical configuration with an optical fiber retained in 
an inner cylindrical sleeve member which, in turn, is inserted into an 
outer tubular member. A threaded retaining element is frictionally urged 
against the inner member to hold the fiber and inner element within the 
outer member. Alignment is to be achieved by a plurality of set screws 
provided in a tubular body into which the inner and outer cylindrical 
members are inserted, the set screws engaging the outer surface of the 
outer cylindrical member and being adjusted to orient the axis of the 
optical fiber relative to the surface of the light receiving or emitting 
element. Additional disclosures of optical fiber fitting arrangements may 
be found in the U.S. Pat. Nos. to Prochazka 3,803,409, Sato 3,936,143, 
Dakss et al 3,999,841 and IBM Technical Disclosure Bulletin Vol. 18, No. 
2, July 1975, pages 485 and 486 in an article by E. C. Uberbacher, 
entitled "Optical Connection for LSI Electrical Circuits". 
Unfortunately, devices of the type described in the above literature, 
including those which purport to achieve fiber-element alignment, while 
permitting relative replacement between the two, are bulky and complex, 
thereby incurring a high cost of manufacture and departing from the 
compact size needed for practical application to present day optical 
system components. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided an improved 
optical fiber coupler fitting which is both compact and structurally 
simplified, while enabling an optical fiber to be accurately aligned with 
the light transmitting or receiving surface of an optical element, such as 
a light emitting laser diode or photosensitive diode. Moreover, once 
proper alignment of a clamping member portion of the fitting with the 
optical element has been achieved, subsequent rapid replacement of the 
optical fiber can be effected without loss of alignment. 
For this purpose, the clamping member is configured as a slotted thick 
disc, a central portion of which is removed for receiving an optical fiber 
holder. The holder is cylindrical with one end of larger diameter being 
inserted into the central hole portion of the disc. Transverse to a slot 
in the disc is a tapped bore for receiving a screw. As the screw is 
tightened into the tapped bore, the distance between the opposite faces of 
the slot is reduced, thereby reducing the area or size of the central hole 
portion of the disc and causing clamping engagement between the walls of 
the hole and the outer surface of the larger diameter end of the optical 
fiber holder. Loosening of the screw releases the clamping engagement 
between the walls of the hole and the optical fiber holder so that the 
fiber may be adjusted in a direction parallel to the axis of the optical 
fiber. 
The fiber itself is inserted into a protective ferrule which is held in a 
channel provided along the axis of the holder and retained in the channel 
by way of a set screw provided in the holder. The clamping member is 
affixed to a mounting block, which retains the optical element, by means 
of a plurality of screws passing through holes in the clamping member and 
engaging threaded holes in the mounting block. The diameter of these screw 
holes in the clamping member is larger than the diameter of the screw 
threads, thereby providing a certain degree of play or slop. The axes of 
the screw holes are parallel to and surround the axis of the optical fiber 
channel of the fiber holder when retained in the clamping member. 
Loosening of these plurality of screws permits the position of the 
clamping member relative to the optical element retained in the mounting 
block to be adjusted, in order to properly align the optical fiber with 
the light coupling face of the optical element. Once this proper alignment 
has been achieved and the screws are tightened, proper alignment with an 
optical fiber that may be inserted and held in the clamping member is 
assured without the need for repeating the axis alignment procedure. 
The manner in which the optical element is retained in the mounting block 
may vary depending upon the type of optical element to be used. Where the 
optical element comprises a cylindrically-shaped photodiode, the light 
receiving surface of which constitutes one end face of a cylinder, a 
corresponding cylindrical well or slot may be provided in a surface of the 
block opposite to that receiving the clamping member, so that the 
photodiode may be inserted into and retained in the mounting block and 
abut against the optical fiber. Similarly, where the optical element 
comprises a laser diode configured as a partially flattened cylinder, a 
correspondingly configured partially flattened hole, transverse to the 
clamping member receiving face of the block, may be provided for insertion 
of the laser diode into the block. In either exemplary configuration, a 
rectangular slot is provided in the clamping member receiving face of the 
mounting block to provide a viewing aperture through which visual access 
to the fiber/optical element interface may be achieved, so that proper 
alignment of the end of the optical fiber and the face of the optical 
element may be observed, as by the use of a suitable viewing instrument 
such as a microscope objective.

DETAILED DESCRIPTION 
Referring to FIG. 1 of the drawings, there is shown a partially exploded 
pictorial view of an optical fiber coupler fitting in accordance with the 
present invention for coupling an optical fiber 35 to the light emitting 
face 41 of an injection laser diode. The injection laser diode may be in 
the form of a commercially available diode package 40 typically configured 
as a partially flattened cylindrical package having a cylindrical portion 
43 and a flattened surface portion 42 in which the light emitting face 41 
of an injection laser diode chip is disposed. Affixed to the flattened 
face 42 is a thin glass plate 45 from which light generated by the laser 
diode emerges. The laser diode package 40 is inserted in a partially 
flattened cylindrical slot or hole (not shown in FIG. 1) in the face 16 of 
a mounting fixture 10, of a generally block configuration (and hereinafter 
referred to as a mounting block), with glass lens 45 facing a rectangular 
slot 11, which is formed in face 12 of rectangular block 10 and extends 
from face 16 to opposite face 15. A more detailed explanation of the 
configuration of the mounting block, per se, will be presented below in 
conjunction with a description of FIGS. 2 and 3. 
For providing energizing electrical contact and retaining laser diode 
package 40 within mounting block 10, a thin contact disc 50 made of a 
suitable insulator material such as epoxy board may be provided. Contact 
disc 50 has a circumferential shape corresponding to that of laser diode 
package 40 so that it may properly fit in the slot provided in mounting 
block 10. A circular layer 52 of a suitable conductor such as copper is 
formed on the side of the disc 50 facing laser diode package 40 to provide 
one of the energizing electrical connections to the diode. This conductive 
layer 52 extends through a thru-hole 53 to the opposite side of the epoxy 
board 51 to receive an external connection. Pressing against the face of 
disc 50 opposite that abutting against laser package 40 is a suitable 
pressure pad 60, again of a circumferential shape corresponding to that of 
laser diode package 40 and disc 50, so as to fit within the laser diode 
retaining slot in mounting block 10. Finally, a rectangularly-shaped 
retainer 61 having a hole 62 and a screw 63 are provided to press against 
pad 60 when screw 63 is inserted through hole 62 and tightened in a 
suitable tapped hole (not shown in FIG. 1) in mounting block 10, to 
thereby retain laser diode package 40 at a fixed position at one end of 
the laser package receiving well or slot in block 10. 
A more detailed illustration of the mounting block 10 is shown in FIGS. 2 
and 3. As is shown therein, face 12 of mounting block 10 has a rectangular 
slot 11 extending from face 15 to face 16. A first circular hole or well 
131 extends from face 16 to a prescribed depth in block 10 terminating at 
a flattened annular land 139. From land 139 a second circular hole 132, 
the surface 136 of which has a slightly smaller diameter than the surface 
137 of first circular hole 131, coaxially extends partially towards face 
15, terminating at a flat bottom portion 135. FIG. 3 shows the manner in 
which laser diode package 40 may be inserted into hole 132 with the flat 
lens portion 45 facing rectangular slot 11 and being parallel with face 12 
of mounting block 10. Also shown in FIG. 3 is tapped hole 138 which 
receives screw 63 (FIG. 1) for urging retainer 61 against pad 60 for 
securing the laser diode package 40 in hole portion 132. Tapped holes 133 
and 134 may be provided to receive set screws to securely retain laser 
diode package 40 in place to assure proper alignment. Tapped holes 13 and 
14 may be provided for suitably affixing mounting block 10 to a support 
housing or table, while tapped holes 141, 142, and 143 are provided to 
receive respective clamp retaining screws, such as 28 and 29, shown in 
FIG. 1, by way of which clamp 20 is securely fastened to face 12 of 
mounting block 10. 
Referring again to FIG. 1 and also to FIGS. 4, 5, and 6, the fastening 
component parts for the optical fiber will be described. As is shown 
pictorially in FIG. 1, and in more detail in FIG. 6, an optical fiber 35 
is inserted into a ferrule 34 which extends into a channel 33 of 
ferrule/fiber holder 30. Ferrule/fiber holder 30 includes a first 
cylindrical body portion 31 at one end of which is a large diameter 
cylindrical body portion 32. Optical fiber 35 is surrounded by ferrule 34 
and extends through channel 33 to extend a specified distance beyond face 
110 of the large diameter body portion 32 of holder 30 that optimizes 
optical coupling between the face of the photoelement and the end of fiber 
35. A set screw 36 is inserted into a tapped hole 120 provided in 
cylindrical body portion 31 to secure the optical fiber 35 within the 
holder 30. The axial thickness of the large diameter portion 32 of holder 
30 is less than the thickness of a central hole 27 provided in a thick 
slotted disc clamp 20. The diameter of hole 27 is only slightly larger 
than the diameter of larger diameter portion 32 of holder 30, so that 
holder 30 may be easily inserted into hole 27. Slot 24 extends from hole 
27 to the outer surface of disc-shaped clamp 20 so as to effectively sever 
the essentially annular shaped clamp 20. 
As is shown in detail in FIGS. 4 and 5, a tapped hole 26 extends from slot 
24 into portion 107 of clamp 20, while a hole 108, coaxial with hole 26, 
extends from slot 24 to a flat land portion 106 of a bored-out portion 
105. A suitable screw (not shown) may be inserted at bored-out portion 105 
to pass through hole 108 and tightened into the tapped hole 26. 
In the vicinity of tapped hole 26 is a removed portion 23' defining a 
reduced thickness portion 23 of clamp 20 that permits portion 107 of clamp 
20 to flex about the reduced thickness portion 23 in accordance with the 
application of a force parallel to the axis of hole 26, and thereby adjust 
the size of circular hole 27. Once the head of the inserted screw comes in 
contact with land portion 106, further tightening of the screw will cause 
the opposite faces of clamp 20 defining the width of slot 24 to come 
closer together as portion 107 flexes about reduced thickness portion 23 
and thereby, in turn, reduces the size of circular hole 27. With larger 
diameter body portion 32 having been inserted into circular hole 27, the 
result of the tightening of this screw therefore causes a tight pressure 
frictional engagement of the walls of hole 27 with the outer surface of 
larger diameter body portion 32 of holder 30, so that ferrule/fiber holder 
30 is held fast within hole 27 of clamp 20. Loosening of the screw, 
conversely, releases the annularly directed compression of clamp 20 so 
that the area of circular hole 27 is no longer reduced, whereby 
ferrule/fiber holder 30 may be adjusted toward or away from face 109 of 
clamp 20 or be completely removed from hole 27. 
For securing clamp 20 to mounting block 10, clamp 20 is provided with a 
plurality of holes 101, 102, and 103 which are generally aligned with 
holes 141, 142, and 143, respectively, so that the axis of ferrule/fiber 
holder 20, and thereby the axis of the fiber retained therein, will 
intersect the light emitting face of laser diode 40 when clamp 20 is 
affixed to mounting block 10 by respective screws inserted through holes 
101, 102, and 103 and screwed into tapped holes 141, 142, and 143 
respectively. The diameter of holes 101, 102, and 103 is somewhat larger 
than the screw diameter so as to permit a slight amount of play or slop 
between the inner walls of holes 101 through 103 and the outer diameter of 
the threads of the screws used to secure clamp 20 to mounting block 10. 
This slight amount of play is provided to permit adjustment of the 
position of clamp 20 upon mounting block 10 during the original alignment 
of the fiber retained within holder 30 with the face of laser diode 40. 
During initial fabrication and alignment, laser diode 40 is inserted and 
secured in mounting block 10, with the face of lens 45 parallel with the 
face 12 of mounting block 10, as described previously. An optical fiber 35 
and its surrounding ferrule 34 are inserted into holder 30 with the end of 
the fiber 35 extending beyond face 110 of holder 30 a specified distance, 
and set screw 36 is tightened to retain fiber 35 in this position. Holder 
30 is then inserted into hole 27 of clamp 20 with face 110 of holder 30 
flush with face 109 of clamp 20 and a screw threaded into tapped hole 26 
of clamp 20 is tightened, to reduce the size of hole 27 and cause the 
walls of hole 27 to come into slidable pressure engagement with the flared 
portion 32 of holder 30. By means of a suitable X-Y-Z positioning 
mechanism that engages cylindrical body portion 31 of holder 30, clamp 20 
is then placed into position with face 109 resting flush against face 12 
of mounting block 10 and holes 101 through 103 in alignment with holes 141 
through 143. Screws with washers are inserted through holes 101 through 
103 of clamp 20 and screwed into respective tapped holes 141 through 143 
of mounting block 10. By appropriate positioning of the X-Y-Z system, 
clamp 20 may then be adjusted within the degree of play permitted by holes 
101 through 103 for maximum optical coupling between laser diode 40 and 
optical fiber 35, using a microscope objective to look into slot 11 and 
appropriate measuring equipment coupled to the free-end of fiber 35. Once 
maximum optical coupling is achieved to thereby define the desired proper 
alignment, the screws are tightened into holes 141 through 143 with the 
screw heads urging clamp 20 into a fixed pressure engagement with mounting 
block 10. Once proper alignment of clamp 20 upon mounting block 10 has 
been achieved, fiber/ferrule holder 30 may be adjusted relative to the 
face of the optical element to maximize optical coupling. Then the screw 
threaded into tapped hole 26 is tightened, thereby reducing the size of 
hole 27 so as to firmly grip optical fiber holder 30. Once fiber/ferrule 
holder 30 is secured into hole 27 of clamp 20, alignment of optical fiber 
35 with laser diode 40 is already assured by virtue of the original 
alignment procedure described above and the manner in which fiber/ferrule 
holder 30 is held with precision within circular hole 27 in clamp 20 by 
the pressure gripping action created by reducing the distance between the 
opposing faces of slot 24. Optical fiber 35 may then be removed by 
loosening set screw 36 in tapped bore 120 and a new fiber slipped into 
place, without suffering a loss of proper alignment. In this regard, it is 
to be noted that there may be a slight amount of offset, in a direction 
parallel to the optical fiber axis, of the end of fiber 35 from the face 
of the optical element, when a new fiber is inserted. However, this offset 
is substantially insignificant and does not adversely affect the 
originally achieved and still maintained alignment of the fiber in 
directions orthogonal to the fiber axis. Advantageously, in accordance 
with the present invention, the area of contact between the clamp 20 and 
mounting block 10 is considerable, extending over face 109 of clamp 20 and 
face 12 of mounting block 10, thereby preventing offset between the fiber 
retaining channel of holder 30 and the light emitting face of laser diode 
package 40 when holder 30 has been secured in place within compressed 
circular hole 27 and with face 110 of holder 30 flush with face 12 of 
mounting block 10. 
Referring now to FIGS. 7 through 9, the optical fiber coupler fitting of 
the present invention is shown in conjunction with a mounting arrangement 
for a cylindrically shaped photodiode package, the light sensitive surface 
of which may be disposed at one end of the cylindrically shaped package. 
More specifically, as is illustrated in FIG. 9, a photodiode package 71 may 
be of a generally cylindrical configuration encasing a photodiode on the 
light receiving face 77 of which is disposed a window 75. The opposite end 
of package 71 is flared at 76. The flared portion 76 of cylindrical 
package 71 fits within the interior portion of a cylindrically shaped 
clamping ring 72, the tapered surface 78 of which is urged against the 
bottom of flared portion 76 of package 71 when package 71 is inserted into 
mounting block 10. A spring washer 73 and snap ring 74 are further 
provided in a serially stacked fashion and inserted into mounting block 10 
to properly secure photodiode package 71 therein. 
The interior configuration of mounting block 10 is shown in detail in FIGS. 
8 and 9. In place of a partially flattened cylindrical slot extending 
transverse to face 12, (as was described above and as is illustrated in 
FIGS. 2 and 3 in conjunction with the laser diode package retaining 
configuration) for receiving the cylindrically-shaped photodiode package 
71, mounting block 10 is bored out substantially coaxially with the axis 
of channel 34 of holder 30 when the latter is held by clamp 20, clamp 20 
being affixed to face 12 of block 10 just as in the embodiment shown in 
FIGS. 1 through 3. A first bored or hollowed-out cylindrical portion 158 
has its cylindrical wall 153 terminating at land 155. A second cylindrical 
hollowed-out portion 159 coaxial with the first portion 158 extends from 
land portion 155, having side wall 154 and terminating at land portion 
156. Rectangular slot 11 extends across face 12 from face 15 to face 16 of 
mounting block 10 and intersects the second cylindrical portion 159. The 
diameter of clamping ring 72 and circular bored portion 158 of mounting 
block 10 substantially coincide so that clamping ring 72 properly urges 
and retains photodiode package 71 in position within block 10. Once 
photodiode package 71 has been secured within mounting block 10, 
fiber/ferrule holding clamp 20 may be affixed to face 12 of mounting block 
10 in exactly the same manner as in the laser diode embodiment described 
above. 
In either embodiment, the configuration of clamp 20 and the adjustable 
manner by which it may be properly aligned with the light coupling face of 
the photo element held within mounting block 10 assures continued accurate 
alignment between an optical fiber and the photo element, while permitting 
rapid replacement of optical fibers without suffering a loss of the 
original alignment. 
As will be appreciated from the foregoing description of the optical fiber 
coupler fitting of the present invention, both accurate alignment and 
rapid replacement of an optical fiber with a light emitting or light 
receiving element may be effected through an arrangement which is compact 
and having a structural configuration that permits simplified mounting of 
the element containing package. Due to the large area of planar contact 
between the fiber holder clamp and the mounting block, relative rotation 
of the fiber channel axis and the light coupling face of the element is 
prevented. Moreover, the turning of a single screw 36 in fiber holder 30 
is all that is necessary to enable rapid removal of the fiber from the 
face of the optical element retained in the mounting block. 
While I have shown and described several embodiments in accordance with the 
present invention, it is understood that the same is not limited thereto 
but is susceptible of numerous changes and modifications as known to a 
person skilled in the art, and I therefore do not wish to be limited to 
the details shown and described herein but intend to cover all such 
changes and modifications as are obvious to one of ordinary skill in the 
art.