CA1216147A - Fiber optic directional coupler - Google Patents
Fiber optic directional couplerInfo
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- CA1216147A CA1216147A CA000466348A CA466348A CA1216147A CA 1216147 A CA1216147 A CA 1216147A CA 000466348 A CA000466348 A CA 000466348A CA 466348 A CA466348 A CA 466348A CA 1216147 A CA1216147 A CA 1216147A
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Abstract
ABSTRACT
Method of determining the depth of fiber cores in a fiber optic directional coupler. The coupler employs generally parallel, inter-secting strands of fiber optic material having the cladding removed on one side thereof to within a few microns owe the fiber cores in the region of intersection to permit light transfer between the strands. The size of the cutaway portion of each strand is measured to determine the position of the strand within the coupler.
Method of determining the depth of fiber cores in a fiber optic directional coupler. The coupler employs generally parallel, inter-secting strands of fiber optic material having the cladding removed on one side thereof to within a few microns owe the fiber cores in the region of intersection to permit light transfer between the strands. The size of the cutaway portion of each strand is measured to determine the position of the strand within the coupler.
Description
go This invention pertains generally to fiber optic systems and more particularly to a method of determining the depth of fiber cores in a fiber optic directional coupler.
According to -this invention there is provided in a method of making a fiber optic directional coupler, -the steps of: pro-voiding two blocks of rigid material each with first and second generally parallel planar faces; forming a slot across the firs-t face of each of the blocks, each said slot having a greater depth -towards the edges owe the block than towards -the center of the block; mounting a strand of single mode fiber optic material in each of the slots so that the strand extends along a path cores-pounding to the bottom wall of the slot, -the strands of fiber optic material each having a central core portion and an outer cladding;
removing material from each of the strands and -the firs-t faces of the blocks in a planar fashion until the cladding portion of each strand is within a few microns of the core portion in the center of -the slot, said removing step comprising: measuring the size of the cutaway portion of each strand; measuring the distance between the firs-t and -the second faces of -the block; utilizing both of these measurements to determine the position of tune core portion of the strand relative to the second face of the block;
and utilizing the second face as a reference for locating the core portion during the removal of material; and placing the blocks together with -the first faces in facing relationship and -the core portions of the strands in close proximity -to each other where the cladding has been removed to form a region in which guided modes of the strands interact through their evanescent fields -to cause light -to be transferred between -the core portions of -the two Lo strands.
This invention also provides a method of manufacturing a fiber optic evanescent field coupler, comprising: removing material from one side of a clad --jingle mode optical fiber to form a face without affecting the core of squid fiber; measuring the size of said face; and utilizing the size measurement to determine -the depth of said core beneath said face.
This invention is divided from Canadian Patent Application Serial No. 375,214 filed April 10, 1981.
The present invention together with that of the alone-mentioned Canadian Patent Application Serial No. 375,21~ will now be further described.
Figure 1 is a centerline sectional view, somewhat schematic, of one embodiment of a coupling device according to -the invention.
Figure 2 is an enlarged fragmentary cross-sec-ional view, somewhat schematic, taken along line 2-2 in Figure 1.
Figure 3 is an enlarged fragmentary view, somewhat schematic, taken along line 3-3 in Figure 1.
Figure is an isometric view of one of the blocks on which the fiber optic strands are mounted in -the embodiment of Figure 1.
Figure 5 is a side elevation Al view, Semite schematic, of a second embodiment of a coupling device according to the - lo -ho I
invention.
Figure 6 is a cross-sectional view, somewhat schematic taken along line 6-6 in Figure 5.
Figure 7 is a block diagram of a dynamically variable fiber optic coupler utilizing a coupling device of the type shown in Figures 1-4.
As illustrated in Figures 1-4, -the coupler 10 includes two strands 11 of a single mode fiber optic material. Each strand comprises a single fiber of quartz glass which is doped to have a central core -lb-~.~
portion 12 and an outer cladding 13. For single mode operation, the core typically has a diameter on the order of 10-15 microns or less, and the cladding has a diameter on the order of 125 microns.
In Figure 1 the diameter of the strands is exaggerated for clarity of illustration, and in Figures 2-3 the diameter of the core is likewise exaggerated. While this particular embodiment employs single mode fibers having a step gradient, the invention is not limited to such fibers and can be employed advantageously with other fibers, e.g., fibers having a more complex w-type doping and graded index multimedia fibers.
Strands 11 are affixed to bases or blocks 16 having optically flat confronting faces or surfaces 17. The strands are mounted in slots 18 which open through the confronting faces, and they extend along generally parallel, intersecting paths defined by the inner or bottom walls 19 of the slots. The primary function of the bases is to hold the strands, and the bases can be fabricated of any suitable rigid material. In one presently preferred embodiment, the bases comprise generally rectangular blocks of fused quartz glass approximately one inch long, one inch wide and one-quarter inch thick, and slots 18 are aligned with the sagittal planes of the blocks. In this embodiment, the fiber optic strands are secured in the slots by suitable cement 21 such as epoxy glue. One advantage of the fused quartz blocks is that they have a coefficient of thermal expansion similar to that of glass fibers, and this advantage is particularly important if the blocks and fibers are subjected to any heat treatment during the manufact-using process. Another suitable material for the blocks is silicon, which also has excellent thermal properties for this application.
-I i I,, I, ;
Slots 18 are deeper towards the edges of the blocks than toward the center. With one of the blocks mounted on the other in an inverted position, both the bottom walls of the slots and the strands mounted in the slots converge toward the centers and diverge toward the edges of the blocks. In the embodiment illustrated, bottom walls 19 are arcuately curved along their length, but they can have any other suitable contour, preferably one which provides gradual convergence and divergence of the fiber optic strands with no sharp bends or abrupt changes in direction.
In the schematic illustration of the drawings, the bottom walls are illustrated as being elite in cross-section. Ilowever, they may be curved or have any other desired cross-section.
Toward the centers of the blocks, the depth of slots 18 is less than the diameter of strands 11, and the outer portions of the fiber optic material are removed evenly with surface 17. At the edges of the blocks, the depth of the slots is preferably at least as great as the diameter of the strands so that none of the cladding is removed at these points. Thus, the amount of fiber optic removed increases gradually from zero toward the edges of the blocks to a maximum toward the centers of the blocks. Removal of the material permits each core to be positioned within the evanescent field of the other whereby light is transferred between the two fibers. I've evanescent fields extend into the cladding and decrease rapidly with distance outside the core in which they originate.
The tapered removal of material enables the fibers to converge and diverge gradually, and this is important in avoiding backward reflection and excess. loss of the incident light energy.
Applicants have discovered that the amount of material removed I
must be carefully controlled to provide proper coupling between the fiber optic strands. If too little cladding is removed, the strands cannot be brought close enough together, and insufficient coupling will result.
If too much material is removed, the propagation characteristics of the fibers will be altered, and improper operation will result, e.g. back reflection and loss of fight energy. When the spacing between the core portions of the strands is within a certain predetermined "critical zone", however, each of the strands receives a significant portion of the evade-scent energy from the other strand, and optimum coupling is achieved without the undesirable effects associated with removal of too little or too much of the fiber optic material.
'rho extent of the critical zone for a particular coupler is dependent upon a number of interrelated factors such as the parameters of the fiber itself and the geometry of the coupler, and with single mode fiber optic strands having a step index gradient, the critical zone can be quite narrow. In a single mode coupler of the type shown in Figures I for example the required center-to-center spacing between the strands at the center of the coupler is typically less than a few (e.g. 2-3) core diameters.
An interaction region 23 is formed at the junction of the strands, and in this region light is transferred between the two strands. The amount of light transferred is dependent upon the proximity and orientation of the cores, as well as the length of the region of interaction. The length of that region is in turn, dependent upon the radius of curvature of bQtt~ln wall 19~ and the spacing between the cores. In one presently preferred embodiment employing an edge~to-edge core spacing on the order of magnitude of the core diameter, the radius of curvature is on the order of 1 meter, and the interaction region is approximately 2.5 millimeters long. With these dimensions, the light makes only one transfer between the strands as it travels through the interaction region. Louvre, if desired, a longer interaction region can be employed, in which case the light will transfer back and forth between the two strands as it travels through the region. These additional transfers can provide increased sensitivity to motion for some types of switching, e.g. translation or acoustic. If desired, the length of the interaction region can be increased without increasing the number of transfers if the separation between the cores is increased by a corresponding amount.
A film of fluid (not shown) is provided between the confronting surfaces of block 16. This fluid serves the dual function owe matching refractive indexes and preventing the optically flat surcease owe the blocks Eros becoming permanently locked together.
The amount of coupling between the fibers is adjusted by changing the relative positions and/or orientations owe the fiber cores in the interaction region. The primary adjustment is provided by translating the blocks in a direction perpendicular to the axis of the fibers. Additional adjustments can be made by translating the blocks in a direction parallel to the fiber axis and by rotating the blocks about an axis perpendicular to the fiber axis. One of the blocks can be mounted in a fixed position, and the other can be mounted on a carriage havillg micrometer screws for making the translational and rotational aid us,tmentS, The coupler ha four ports labeled A-D in Figure 1, with ports A
B at opposite ends of one of the fibers and ports C, D at opposite ends of the other fiber. In the following discussion, it is assumed that input light of suitable wavelength (e.g. 1.15 micron) is applied to port A. This light passes through the coupler and is delivered to port B and/or port D, depending upon the coupling ratio for which the coupler is set.
The coefficient of coupling is defined as the ratio owe power at output port D to the power at input port A. In one example of a coupler having the dimensions given above, as much as 85% of the input lo power at port A has been observed to be delivered to port D. In principle, however, 100% coupling is possible, and the amount of coupling can be adjusted to any desired value between zero and the 100% maxim. Thus, the coupler has a high, widely adjustable coefficient of coupling.
The coupler also has a very low throughput loss and very good directivity. The throughput loss in the above example is less than 0.2 dub. The directivity is defined as the ratio of the power at port D to the power at port C, with the input applied to port A. With -this coupler, the power at port D is greater than 60 dub above the power at port C. Thus, substantially all of the power applied to input port A is delivered to the output ports B and D.
The coupler also has excellent polarization almost equally well.
Thus, the characteristics of the coupler are substantially independent of polarization.
In one presently preread method of manufacture, the coupler Of rogues 1~4 it Ned by first grinding the opposite faces 17, 26 of blocks 16 flat and parallel. Slots 18 are then cut through faces 17 to a I
uniform depth greater than the diameter of the fiber optic strands. The bottom walls of the slots are then shaped to provide the desired contour.
The shaping is preferably such that the depth of the slots at the edges of the blocks is at least one half of a fiber core diameter greater than the depth at the centers of the slots.
Once the slots have been formed, epoxy glue 21 is placed therein, and strands 11 are placed in the slots with the glue. eights are then attached to the ends of the strands to tension the strands and draw them tightly against the bottom walls of the slots. The entire assembly is then heated in an oven to cure the glue, typically at a temperature on the order of 70C for about 10 hours. With the epoxy glue, it is very important that the heat be applied and removed gradually in order to prevent breakage of the fibers within the slots. This can be accomplished by placing tile blocks in the oven before it is energized and leaving them in the oven until it has cooled down to room temperature after the heating process. When the heating is completed, the weights are removed to release the tension in the fibers.
Once the fibers have been mounted in the slots, faces 17 are lapped parallel to faces 26 until they intersect the cladding of the fibers, forming elongated oval shaped flat surfaces on the outer sides of the fibers. The widths of these oval shaped areas are measured to determine the positions of the fibers relative to block surfaces 26, and thereafter these surfaces serve as references for locating the core portions of the swabbers. By measuring the lengths of the oval shaped areas at different depths of cuts, the radii of curvature of the fibers can be determined.
Roy lapping process continues until the cladding has been removed to within about 3 microns of the desired distance from the cores, as determined by direct measurement of the thickness of the blocks. The final three microns are removed by polishing.
The polished surfaces of the blocks are then placed together, with the cut-away portions of the fibers facing each other. The confronting faces of the blocks are separated by a distance on the order of 0.5 micron or less, an optical oil is introduced between the blocks by capillary action.
In the embodiment heretofore described, slots 18 are formed by cutting into the surfaces of the blocks. It should be understood, however, that the slots can be formed by other means such as building up areas on the blocks or joining two or more blocks together and that the slots can have other shapes, e.g. V-grooves. Likewise, techniques other than cementing might be employed to bond the fibers to the blocks, e.g. indium bonding. Similarly, the material can be removed from the blocks and the cladding by other suitable techniques, such as etching and photolithograph.
In the embodiment of figures 5-6, a plurality of eyebrow optic strands 31 similar to strands 11 are affixed to bases or blocks 32 and positioned to provide a plurality of interaction regions 33 between corresponding pairs of the strands on the two blocks. In this embodiment, the cores of the fibers are designated by the reference numeral 36J and the cladding are designated 37.
As illustrated, bases 32 comprise generally rectangular blocks I quartz or other suitable rigid material having confronting faces or surfaces 38 and outer faces or surfaces 39. The central portions I of surfaces 38 are planar and parallel to surfaces 39 and toward the edges of the blocks surfaces 38 curve away from central portions 41. The length of interaction regions 33 is determined by the length of planar central portions 41 and the radius of curvature of the end portions of surfaces 38, as well as the core spacing of the eyebrows.
Fibers 31 are mounted on surfaces 38 and affixed thereto by suitable means such as epoxy glue 42, or other suitable cement. As in the embodiment of Figures 1-4 the material on the outer sides of the fibers is removed gradually, from zero toward the edges of the blocks to within the critical zone toward the centers of the blocks by lapping and polishing in a direction parallel to surfaces 38 39.
Operation and use of the embodiment of Figures 5-6 is similar to that of the coupler of Figures 1-4, and the amount of coupling between the aligned pairs of strands on the two blocks can be adjusted by trays-lotion and rotation owe the blocks.
In one presently preread method of manufacture for the coupler of Figures 5-6 the surfaces of blocks 32 are first ground flat and parallel. Thereafter the desired curvatures are formed toward the outer edges of surfaces 38. The glue is then applied to the contoured surfaces, and the fiber optic strands are placed on the blocks and pressed against surfaces 38 while the glue cures. If heating is required to cure the glue the heat should be applied and removed gradually to avoid breakage owe the fibers.
When the glue is cured the material on the outer sides of the strands is removed by lapping and polishing in a direction parallel to surfaces 38~ 39. The distance between the lapped and polished surfaces and the cores of the fibers is determined by measurement of the distances between these surfaces and outer surfaces 39. Removal of the material in this manner provides a gradual tapering of the fibers into and out of the interaction regions. In this embodiment, the adjacent fibers on each block provide lateral support for each other and serve as a guide in the grinding and polishing steps.
When the desired amount of material has been removed, the blocks are superposed with surfaces 38 facing each other and the corresponding strands Oil the two blocks aligned to form a plurality owe coupler pairs.
As illustrated in Figure 7, a coupling device 10 owe the type heretofore described can be utilized to provide dynamically variable coupling in a fiber optic system. In this embodiment, suitable trays-dupers or drivers 51, 52 are connected to upper block 16 for translating that block back and forth relative to the lower block along axes 53, 54 in directions perpendicular and parallel to the axes of the fibers. A similar transducer or driver 56 is also connected to the upper block for moving that block along an axis 57 in a direction perpendicular to axes 53~ I
to vary tile spacing between the blocks. A fourth transducer 58 provides relative rotation of the blocks about axis 57. By varying the relative positions and/or orientations of the blocks and the fiber cores in the interaction region, one or more of the transducers vary the amount of coupling between the fibers in accordance with signals applied to the transducers. These transducers can be of any suitable design, including piezoelectric transducers and other known electromechanical transducers.
Tile system illustrated in Figure 7 can be employed as a variable coupler in which the coefficient of coupling is con-trolled by voltages ~.10~
or other suitable control signals applied to the transducers. The system can also function as a modulator if a time varying voltage or other suitable modulation signal is applied to the transducers.
It is apparent from the foregoing that a new and improved coupler has, been provided for use in both single mode or multimedia fiber optic systems. The coefficient of coupling can be adjusted over a wide range, permitting input light to be divided as desired between two output ports.
The coupler has a low throughput loss and a very high directivity so that substantially all of the light input is delivered to the output lo ports. The operating characteristics of the coupler are substantially independent of polarization. The coupler is mechanically stable and durable so that it can ye employed in a variety of environments. If adjustability is not desired, the blocks can be bonded together to provide a mixed coupler.
According to -this invention there is provided in a method of making a fiber optic directional coupler, -the steps of: pro-voiding two blocks of rigid material each with first and second generally parallel planar faces; forming a slot across the firs-t face of each of the blocks, each said slot having a greater depth -towards the edges owe the block than towards -the center of the block; mounting a strand of single mode fiber optic material in each of the slots so that the strand extends along a path cores-pounding to the bottom wall of the slot, -the strands of fiber optic material each having a central core portion and an outer cladding;
removing material from each of the strands and -the firs-t faces of the blocks in a planar fashion until the cladding portion of each strand is within a few microns of the core portion in the center of -the slot, said removing step comprising: measuring the size of the cutaway portion of each strand; measuring the distance between the firs-t and -the second faces of -the block; utilizing both of these measurements to determine the position of tune core portion of the strand relative to the second face of the block;
and utilizing the second face as a reference for locating the core portion during the removal of material; and placing the blocks together with -the first faces in facing relationship and -the core portions of the strands in close proximity -to each other where the cladding has been removed to form a region in which guided modes of the strands interact through their evanescent fields -to cause light -to be transferred between -the core portions of -the two Lo strands.
This invention also provides a method of manufacturing a fiber optic evanescent field coupler, comprising: removing material from one side of a clad --jingle mode optical fiber to form a face without affecting the core of squid fiber; measuring the size of said face; and utilizing the size measurement to determine -the depth of said core beneath said face.
This invention is divided from Canadian Patent Application Serial No. 375,214 filed April 10, 1981.
The present invention together with that of the alone-mentioned Canadian Patent Application Serial No. 375,21~ will now be further described.
Figure 1 is a centerline sectional view, somewhat schematic, of one embodiment of a coupling device according to -the invention.
Figure 2 is an enlarged fragmentary cross-sec-ional view, somewhat schematic, taken along line 2-2 in Figure 1.
Figure 3 is an enlarged fragmentary view, somewhat schematic, taken along line 3-3 in Figure 1.
Figure is an isometric view of one of the blocks on which the fiber optic strands are mounted in -the embodiment of Figure 1.
Figure 5 is a side elevation Al view, Semite schematic, of a second embodiment of a coupling device according to the - lo -ho I
invention.
Figure 6 is a cross-sectional view, somewhat schematic taken along line 6-6 in Figure 5.
Figure 7 is a block diagram of a dynamically variable fiber optic coupler utilizing a coupling device of the type shown in Figures 1-4.
As illustrated in Figures 1-4, -the coupler 10 includes two strands 11 of a single mode fiber optic material. Each strand comprises a single fiber of quartz glass which is doped to have a central core -lb-~.~
portion 12 and an outer cladding 13. For single mode operation, the core typically has a diameter on the order of 10-15 microns or less, and the cladding has a diameter on the order of 125 microns.
In Figure 1 the diameter of the strands is exaggerated for clarity of illustration, and in Figures 2-3 the diameter of the core is likewise exaggerated. While this particular embodiment employs single mode fibers having a step gradient, the invention is not limited to such fibers and can be employed advantageously with other fibers, e.g., fibers having a more complex w-type doping and graded index multimedia fibers.
Strands 11 are affixed to bases or blocks 16 having optically flat confronting faces or surfaces 17. The strands are mounted in slots 18 which open through the confronting faces, and they extend along generally parallel, intersecting paths defined by the inner or bottom walls 19 of the slots. The primary function of the bases is to hold the strands, and the bases can be fabricated of any suitable rigid material. In one presently preferred embodiment, the bases comprise generally rectangular blocks of fused quartz glass approximately one inch long, one inch wide and one-quarter inch thick, and slots 18 are aligned with the sagittal planes of the blocks. In this embodiment, the fiber optic strands are secured in the slots by suitable cement 21 such as epoxy glue. One advantage of the fused quartz blocks is that they have a coefficient of thermal expansion similar to that of glass fibers, and this advantage is particularly important if the blocks and fibers are subjected to any heat treatment during the manufact-using process. Another suitable material for the blocks is silicon, which also has excellent thermal properties for this application.
-I i I,, I, ;
Slots 18 are deeper towards the edges of the blocks than toward the center. With one of the blocks mounted on the other in an inverted position, both the bottom walls of the slots and the strands mounted in the slots converge toward the centers and diverge toward the edges of the blocks. In the embodiment illustrated, bottom walls 19 are arcuately curved along their length, but they can have any other suitable contour, preferably one which provides gradual convergence and divergence of the fiber optic strands with no sharp bends or abrupt changes in direction.
In the schematic illustration of the drawings, the bottom walls are illustrated as being elite in cross-section. Ilowever, they may be curved or have any other desired cross-section.
Toward the centers of the blocks, the depth of slots 18 is less than the diameter of strands 11, and the outer portions of the fiber optic material are removed evenly with surface 17. At the edges of the blocks, the depth of the slots is preferably at least as great as the diameter of the strands so that none of the cladding is removed at these points. Thus, the amount of fiber optic removed increases gradually from zero toward the edges of the blocks to a maximum toward the centers of the blocks. Removal of the material permits each core to be positioned within the evanescent field of the other whereby light is transferred between the two fibers. I've evanescent fields extend into the cladding and decrease rapidly with distance outside the core in which they originate.
The tapered removal of material enables the fibers to converge and diverge gradually, and this is important in avoiding backward reflection and excess. loss of the incident light energy.
Applicants have discovered that the amount of material removed I
must be carefully controlled to provide proper coupling between the fiber optic strands. If too little cladding is removed, the strands cannot be brought close enough together, and insufficient coupling will result.
If too much material is removed, the propagation characteristics of the fibers will be altered, and improper operation will result, e.g. back reflection and loss of fight energy. When the spacing between the core portions of the strands is within a certain predetermined "critical zone", however, each of the strands receives a significant portion of the evade-scent energy from the other strand, and optimum coupling is achieved without the undesirable effects associated with removal of too little or too much of the fiber optic material.
'rho extent of the critical zone for a particular coupler is dependent upon a number of interrelated factors such as the parameters of the fiber itself and the geometry of the coupler, and with single mode fiber optic strands having a step index gradient, the critical zone can be quite narrow. In a single mode coupler of the type shown in Figures I for example the required center-to-center spacing between the strands at the center of the coupler is typically less than a few (e.g. 2-3) core diameters.
An interaction region 23 is formed at the junction of the strands, and in this region light is transferred between the two strands. The amount of light transferred is dependent upon the proximity and orientation of the cores, as well as the length of the region of interaction. The length of that region is in turn, dependent upon the radius of curvature of bQtt~ln wall 19~ and the spacing between the cores. In one presently preferred embodiment employing an edge~to-edge core spacing on the order of magnitude of the core diameter, the radius of curvature is on the order of 1 meter, and the interaction region is approximately 2.5 millimeters long. With these dimensions, the light makes only one transfer between the strands as it travels through the interaction region. Louvre, if desired, a longer interaction region can be employed, in which case the light will transfer back and forth between the two strands as it travels through the region. These additional transfers can provide increased sensitivity to motion for some types of switching, e.g. translation or acoustic. If desired, the length of the interaction region can be increased without increasing the number of transfers if the separation between the cores is increased by a corresponding amount.
A film of fluid (not shown) is provided between the confronting surfaces of block 16. This fluid serves the dual function owe matching refractive indexes and preventing the optically flat surcease owe the blocks Eros becoming permanently locked together.
The amount of coupling between the fibers is adjusted by changing the relative positions and/or orientations owe the fiber cores in the interaction region. The primary adjustment is provided by translating the blocks in a direction perpendicular to the axis of the fibers. Additional adjustments can be made by translating the blocks in a direction parallel to the fiber axis and by rotating the blocks about an axis perpendicular to the fiber axis. One of the blocks can be mounted in a fixed position, and the other can be mounted on a carriage havillg micrometer screws for making the translational and rotational aid us,tmentS, The coupler ha four ports labeled A-D in Figure 1, with ports A
B at opposite ends of one of the fibers and ports C, D at opposite ends of the other fiber. In the following discussion, it is assumed that input light of suitable wavelength (e.g. 1.15 micron) is applied to port A. This light passes through the coupler and is delivered to port B and/or port D, depending upon the coupling ratio for which the coupler is set.
The coefficient of coupling is defined as the ratio owe power at output port D to the power at input port A. In one example of a coupler having the dimensions given above, as much as 85% of the input lo power at port A has been observed to be delivered to port D. In principle, however, 100% coupling is possible, and the amount of coupling can be adjusted to any desired value between zero and the 100% maxim. Thus, the coupler has a high, widely adjustable coefficient of coupling.
The coupler also has a very low throughput loss and very good directivity. The throughput loss in the above example is less than 0.2 dub. The directivity is defined as the ratio of the power at port D to the power at port C, with the input applied to port A. With -this coupler, the power at port D is greater than 60 dub above the power at port C. Thus, substantially all of the power applied to input port A is delivered to the output ports B and D.
The coupler also has excellent polarization almost equally well.
Thus, the characteristics of the coupler are substantially independent of polarization.
In one presently preread method of manufacture, the coupler Of rogues 1~4 it Ned by first grinding the opposite faces 17, 26 of blocks 16 flat and parallel. Slots 18 are then cut through faces 17 to a I
uniform depth greater than the diameter of the fiber optic strands. The bottom walls of the slots are then shaped to provide the desired contour.
The shaping is preferably such that the depth of the slots at the edges of the blocks is at least one half of a fiber core diameter greater than the depth at the centers of the slots.
Once the slots have been formed, epoxy glue 21 is placed therein, and strands 11 are placed in the slots with the glue. eights are then attached to the ends of the strands to tension the strands and draw them tightly against the bottom walls of the slots. The entire assembly is then heated in an oven to cure the glue, typically at a temperature on the order of 70C for about 10 hours. With the epoxy glue, it is very important that the heat be applied and removed gradually in order to prevent breakage of the fibers within the slots. This can be accomplished by placing tile blocks in the oven before it is energized and leaving them in the oven until it has cooled down to room temperature after the heating process. When the heating is completed, the weights are removed to release the tension in the fibers.
Once the fibers have been mounted in the slots, faces 17 are lapped parallel to faces 26 until they intersect the cladding of the fibers, forming elongated oval shaped flat surfaces on the outer sides of the fibers. The widths of these oval shaped areas are measured to determine the positions of the fibers relative to block surfaces 26, and thereafter these surfaces serve as references for locating the core portions of the swabbers. By measuring the lengths of the oval shaped areas at different depths of cuts, the radii of curvature of the fibers can be determined.
Roy lapping process continues until the cladding has been removed to within about 3 microns of the desired distance from the cores, as determined by direct measurement of the thickness of the blocks. The final three microns are removed by polishing.
The polished surfaces of the blocks are then placed together, with the cut-away portions of the fibers facing each other. The confronting faces of the blocks are separated by a distance on the order of 0.5 micron or less, an optical oil is introduced between the blocks by capillary action.
In the embodiment heretofore described, slots 18 are formed by cutting into the surfaces of the blocks. It should be understood, however, that the slots can be formed by other means such as building up areas on the blocks or joining two or more blocks together and that the slots can have other shapes, e.g. V-grooves. Likewise, techniques other than cementing might be employed to bond the fibers to the blocks, e.g. indium bonding. Similarly, the material can be removed from the blocks and the cladding by other suitable techniques, such as etching and photolithograph.
In the embodiment of figures 5-6, a plurality of eyebrow optic strands 31 similar to strands 11 are affixed to bases or blocks 32 and positioned to provide a plurality of interaction regions 33 between corresponding pairs of the strands on the two blocks. In this embodiment, the cores of the fibers are designated by the reference numeral 36J and the cladding are designated 37.
As illustrated, bases 32 comprise generally rectangular blocks I quartz or other suitable rigid material having confronting faces or surfaces 38 and outer faces or surfaces 39. The central portions I of surfaces 38 are planar and parallel to surfaces 39 and toward the edges of the blocks surfaces 38 curve away from central portions 41. The length of interaction regions 33 is determined by the length of planar central portions 41 and the radius of curvature of the end portions of surfaces 38, as well as the core spacing of the eyebrows.
Fibers 31 are mounted on surfaces 38 and affixed thereto by suitable means such as epoxy glue 42, or other suitable cement. As in the embodiment of Figures 1-4 the material on the outer sides of the fibers is removed gradually, from zero toward the edges of the blocks to within the critical zone toward the centers of the blocks by lapping and polishing in a direction parallel to surfaces 38 39.
Operation and use of the embodiment of Figures 5-6 is similar to that of the coupler of Figures 1-4, and the amount of coupling between the aligned pairs of strands on the two blocks can be adjusted by trays-lotion and rotation owe the blocks.
In one presently preread method of manufacture for the coupler of Figures 5-6 the surfaces of blocks 32 are first ground flat and parallel. Thereafter the desired curvatures are formed toward the outer edges of surfaces 38. The glue is then applied to the contoured surfaces, and the fiber optic strands are placed on the blocks and pressed against surfaces 38 while the glue cures. If heating is required to cure the glue the heat should be applied and removed gradually to avoid breakage owe the fibers.
When the glue is cured the material on the outer sides of the strands is removed by lapping and polishing in a direction parallel to surfaces 38~ 39. The distance between the lapped and polished surfaces and the cores of the fibers is determined by measurement of the distances between these surfaces and outer surfaces 39. Removal of the material in this manner provides a gradual tapering of the fibers into and out of the interaction regions. In this embodiment, the adjacent fibers on each block provide lateral support for each other and serve as a guide in the grinding and polishing steps.
When the desired amount of material has been removed, the blocks are superposed with surfaces 38 facing each other and the corresponding strands Oil the two blocks aligned to form a plurality owe coupler pairs.
As illustrated in Figure 7, a coupling device 10 owe the type heretofore described can be utilized to provide dynamically variable coupling in a fiber optic system. In this embodiment, suitable trays-dupers or drivers 51, 52 are connected to upper block 16 for translating that block back and forth relative to the lower block along axes 53, 54 in directions perpendicular and parallel to the axes of the fibers. A similar transducer or driver 56 is also connected to the upper block for moving that block along an axis 57 in a direction perpendicular to axes 53~ I
to vary tile spacing between the blocks. A fourth transducer 58 provides relative rotation of the blocks about axis 57. By varying the relative positions and/or orientations of the blocks and the fiber cores in the interaction region, one or more of the transducers vary the amount of coupling between the fibers in accordance with signals applied to the transducers. These transducers can be of any suitable design, including piezoelectric transducers and other known electromechanical transducers.
Tile system illustrated in Figure 7 can be employed as a variable coupler in which the coefficient of coupling is con-trolled by voltages ~.10~
or other suitable control signals applied to the transducers. The system can also function as a modulator if a time varying voltage or other suitable modulation signal is applied to the transducers.
It is apparent from the foregoing that a new and improved coupler has, been provided for use in both single mode or multimedia fiber optic systems. The coefficient of coupling can be adjusted over a wide range, permitting input light to be divided as desired between two output ports.
The coupler has a low throughput loss and a very high directivity so that substantially all of the light input is delivered to the output lo ports. The operating characteristics of the coupler are substantially independent of polarization. The coupler is mechanically stable and durable so that it can ye employed in a variety of environments. If adjustability is not desired, the blocks can be bonded together to provide a mixed coupler.
Claims (3)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method of making a fiber optic directional coupler, the steps of:
providing two blocks of rigid material each with first and second generally parallel planar faces;
forming a slot across the first face of each of the blocks, each said slot having a greater depth towards the edges of the block than towards the center of the block;
mounting a strand of single mode fiber optic material in each of the slots so that the strand extends along a path corresponding to the bottom wall of the slot, the strands of fiber optic material each having a central core portion and an outer cladding;
removing material from each of the strands and the first faces of the blocks in a planar fashion until the cladding portion of each strand is within a few microns of the core portion in the center of the slot, said removing step comprising:
measuring the size of the cutaway portion of each strand;
measuring the distance between the first and the second faces of the block;
utilizing both of these measurements to determine the position of the core portion of the strand relative to the second face of the block; and utilizing the second face as a reference for locating the core portion during the removal of material; and placing the blocks together with the first faces in facing relationship and the core portions of the strands in close proximity to each other where the cladding has been removed to form a region in which guided modes of the strands interact through their evanescent fields to cause light to be transferred between the core portions of the two strands.
providing two blocks of rigid material each with first and second generally parallel planar faces;
forming a slot across the first face of each of the blocks, each said slot having a greater depth towards the edges of the block than towards the center of the block;
mounting a strand of single mode fiber optic material in each of the slots so that the strand extends along a path corresponding to the bottom wall of the slot, the strands of fiber optic material each having a central core portion and an outer cladding;
removing material from each of the strands and the first faces of the blocks in a planar fashion until the cladding portion of each strand is within a few microns of the core portion in the center of the slot, said removing step comprising:
measuring the size of the cutaway portion of each strand;
measuring the distance between the first and the second faces of the block;
utilizing both of these measurements to determine the position of the core portion of the strand relative to the second face of the block; and utilizing the second face as a reference for locating the core portion during the removal of material; and placing the blocks together with the first faces in facing relationship and the core portions of the strands in close proximity to each other where the cladding has been removed to form a region in which guided modes of the strands interact through their evanescent fields to cause light to be transferred between the core portions of the two strands.
2. A method of manufacturing a fiber optic evanescent field coupler, comprising:
removing material from one side of a clad single mode optical fiber to form a face without affecting the core of said fiber;
measuring the size of said face; and utilizing the size measurement to determine the depth of said core beneath said face.
removing material from one side of a clad single mode optical fiber to form a face without affecting the core of said fiber;
measuring the size of said face; and utilizing the size measurement to determine the depth of said core beneath said face.
3. A method of manufacturing a fiber optic evanescent field coupler, as defined by claim 2, additionally comprising:
mounting said clad single mode fiber on a substrate to provide support for said fiber during said removing step;
measuring the thickness of said substrate, subsequent to the step of measuring the size of said face, to provide a reference for locating the core of said clad single mode fiber; and further removing said material from said clad fiber to a desired depth utilizing the step of measuring the thickness of said substrate to locate the core of said fiber relative to the face of said fiber.
mounting said clad single mode fiber on a substrate to provide support for said fiber during said removing step;
measuring the thickness of said substrate, subsequent to the step of measuring the size of said face, to provide a reference for locating the core of said clad single mode fiber; and further removing said material from said clad fiber to a desired depth utilizing the step of measuring the thickness of said substrate to locate the core of said fiber relative to the face of said fiber.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000466348A CA1216147A (en) | 1980-04-11 | 1984-10-25 | Fiber optic directional coupler |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/139,511 US4493528A (en) | 1980-04-11 | 1980-04-11 | Fiber optic directional coupler |
| US139,511 | 1980-04-11 | ||
| CA000375214A CA1253375A (en) | 1980-04-11 | 1981-04-10 | Fiber optic directional coupler |
| CA000466348A CA1216147A (en) | 1980-04-11 | 1984-10-25 | Fiber optic directional coupler |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000375214A Division CA1253375A (en) | 1980-04-11 | 1981-04-10 | Fiber optic directional coupler |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1216147A true CA1216147A (en) | 1987-01-06 |
Family
ID=25669301
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000466348A Expired CA1216147A (en) | 1980-04-11 | 1984-10-25 | Fiber optic directional coupler |
| CA000516221A Expired CA1242909A (en) | 1980-04-11 | 1986-08-18 | Fiber optic directional coupler |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000516221A Expired CA1242909A (en) | 1980-04-11 | 1986-08-18 | Fiber optic directional coupler |
Country Status (1)
| Country | Link |
|---|---|
| CA (2) | CA1216147A (en) |
-
1984
- 1984-10-25 CA CA000466348A patent/CA1216147A/en not_active Expired
-
1986
- 1986-08-18 CA CA000516221A patent/CA1242909A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CA1242909A (en) | 1988-10-11 |
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| MKEX | Expiry |