Patent Application
20180128991
The present invention relates to fabricating optical fiber ferrules, and more particularly a fixture for shaping and sizing grooves in fabricating optical fiber ferrules.
There are many advantages of transmitting light signals via optical fiber waveguides and the use thereof is diverse. Single or multiple fiber waveguides may be used simply for transmitting visible light to a remote location. Complex telephony and data communication systems may transmit digitized data through optical signals within the waveguides. These applications couple fibers in an end-to-end relationship, with the coupling being one source of light loss. Precision alignment of two polished ends of fibers is needed to ensure that optical loss in a fiber link is less than the specified optical loss budget for a system. For single-mode telecommunication-grade fiber, this typically corresponds to connector fiber alignment tolerances that are less than 1000 nm. This means that in both parallel fiber and single fiber links, operating at multi-gigabit rates, the components applied to align the fibers must be assembled and fabricated with sub-micron precision.
In an optical fiber connection, an optical fiber connector terminates the end of a cable that contains one or multiple fibers, and enables quicker connection and disconnection as compared to splicing. The connectors mechanically couple and align the cores of fibers so that light can pass end-to-end. The end of an optical fiber is supported in a ferrule, with an end face of the optical fiber positioned generally flush with or slightly protruding from an end face of the ferrule. When complementary ferrules in connector assemblies are joined together, the optical fiber of one ferrule is aligned with a mating optical fiber of the other ferrule. In some applications, the end faces of mating optical fibers physically contact one another to effect signal transmission between the mating optical fiber pair. Better connectors lose very little light due to reflection or misalignment of the fibers. Connectors, in both parallel/multiple fiber and single fiber links, operating at multi-gigabit rates must be assembled with subcomponents fabricated with sub-micron precision.
U.S. Pat. No. 7,343,770, commonly assigned to the assignee of the present invention, discloses a novel precision stamping system for manufacturing small tolerance parts, including optical fiber ferrules. The disclosed stamping process involves stamping a stock material (e.g., a metal blank) to form the final overall external geometry of a ferrule and geometry of surface features including an optical fiber groove at tight (i.e., small) tolerances of below 1000 nm, whereby the groove is in precise alignment with the external alignment surface of the ferrule, for alignment to another ferrule using an external sleeve.
U.S. Pat. No. 7,311,449, commonly assigned to the assignee of the present invention, discloses various optical fiber ferrule configurations designed to be fabricated by the stamping process in U.S. Pat. No. 7,343,770, which make use of alignment sleeves for end-to-end coupling of two ferrules. Finally, optical fiber connectors incorporating ferrules as fabricated can achieve low insertion loss and low return loss, and which can be fabricated in high throughput and at low costs.
While the process disclosed in U.S. Pat. No. 7,343,770 was a technological breakthrough to achieving low cost, high throughput, precision manufacturing of optical fiber ferrules (including ferrule assemblies), further improvement is desired to develop a process to achieve tighter/smaller tolerances in optical fiber ferrules, e.g., for single mode fiber-optic transmissions, which can be fabricated in high throughput and at low costs.
One object of the present invention is to produce a cylindrical groove within semi-ferrules (or ferrule halves) that is precisely sized and shaped to create a slight compression fit around an optical fiber. The compression fit can hold the fiber within the ferrule assembly (comprising the two semi-ferrules) without the need for an epoxy adhesive. The ferrule assembly thus holds the optical fiber (made of glass) within the cylindrical hole, but this requires that the size and shape of the hole be nearly identical to the diameter of the optical fiber. Unfortunately, the diameters of optical fibers can vary by a few micrometers, which is similar to the amount of elastic compression desired in the compression fit. Therefore, the variability in the diameter of the fiber can adversely cause either too much or too little clamping force on the optical fiber, depending upon the production tolerances of the glass fiber.
The present invention overcomes the consequences from variability in the diameter of the glass fiber by using the glass optical fiber as a tool to establish the size and shape of the cylindrical hole. Squeezing the ferrules together causes plastic deformation of the hole surrounding the fiber. The strength of the glass fiber is sufficient to withstand the compressive stress generated during this fiber-as-a-tool forming operation. Upon relaxing the squeezing force, the material in the hole springs back to produce a hole with a diameter that is slightly smaller than the diameter of the optical fiber. This slight interference produces an elastic interference fit of the optical fiber within the ferrule assembly. The result is a conformal groove that clamps the optical fiber within the ferrule without requiring an adhesive such as epoxy, despite the adverse variability in fiber diameters. Hereinafter, for convenience, a ferrule assembly may be simply referred to as a ferrule, since the disclosed embodiment of a ferrule comprises two ferrule halves.
The present invention provides a process involving a high-precision alignment fixture to produce a ferrule assembly with an optical fiber precisely held therein in alignment with the external alignment surface of the ferrule assembly. In this connection, the alignment fixture allows for precise reshaping and resizing at least one groove that was pre-formed in an optical fiber ferrule. In one aspect of the present invention, the inventive process is directed to a precision alignment fixture for aligning two ferrule halves and an optical fiber. In one embodiment of the present invention, the high-precision alignment fixture comprises a double-compound flexure supporting a linearly moving body (e.g., a reshaping and resizing jaw), which eliminates parasitic displacement in a direction lateral to the direction of linear motion of the moving body. More specifically, each compound flexure includes a pair of double parallel leaf springs (in series). In the disclosed embodiment, two compound flexures on each side supports the moving body for vertical linear movement, with no or negligible motion in the lateral direction. The double-compound flexure has been referred to also as a double nested compound linear spring flexure.
In one embodiment, the alignment fixture is used for termination of an optical fiber using a ferrule, involving reshaping and resizing at least one groove that was pre-formed in the ferrule, and a fixture to facilitate reshaping and resizing such groove. Alignment of ferrules halve and optical fibers using the inventive fixture for other than termination purposes (e.g., welding of ferrule halves in a fiber termination) are also contemplated, and are well within the scope and spirit of the present invention.
In one embodiment of the present invention, the ferrule comprises a pair of complementary ferrule halves, each corresponding to a semi-ferrule (hereinafter, ferrule halve and semi-ferrule may be used interchangeably), which may be substantially similar in structure. Each ferrule halve has an external geometry such that when the two ferrule halves are joined together to form a ferrule, the overall external geometry of the ferrule is generally cylindrical (e.g., circular or oval cross-section). The external cylindrical surface of the ferrule is used to align with another ferrule in an end-to-end relationship using an external sleeve. Accordingly, each ferrule halve has a generally semi-circular or semi-oval cross-section, with a generally flat surface facing between the ferrule halves. Each ferrule halve is pre-formed with a groove for locating and receiving a bare section at the end of an optical fiber (with cladding exposed, without protective buffer and jacket layers). The groove on each ferrule halve has a semi-circular cross section. When the ferrule halves are joined together at the opposing flat surfaces, the opposing grooves form a cylindrical through-hole receiving a section of the optical fiber.
In one embodiment of the present invention, the ferrule halves are precision formed by high throughput processes, such as stamping a metal blank material. In one embodiment, the ferrule body is made of a metal material, which may be chosen to have high stiffness (e.g., stainless steel), chemical inertness (e.g., titanium), high temperature stability (nickel alloy), low thermal expansion (e.g., Invar), or to match thermal expansion to other materials (e.g., Kovar for matching glass). Each ferrule halve may be stamped to form a unitary or monolithic body, which does not require further attachment of sub-components within the ferrule halve.
In accordance with the present invention, the groove on each ferrule halve is further subject to a separate, subsequent shaping and sizing (i.e., reshaping and resizing) step using a tool or fixture. In one embodiment, the reshaping and resizing step is undertaken using a section of bare optical fiber (i.e., a bare section of optical fiber with cladding exposed, without protective buffer and jacket layers, as a shaping and sizing tool) as a gauge. In other words, the optical fiber is used as a gauge (i.e., a gauge optical fiber) in the tool to precisely shape and size the groove on the ferrule halve. In another embodiment, the reshaping and resizing step is undertaken using a gauge pin having an outer diameter similar to a bare section of optical fiber. The ferrule halves are pre-aligned to each other, and using the pre-formed grooves as guides for the gauge optical fiber or gauge pin, the ferrule halves are pressed together with the gauge optical fiber or gauge pin therebetween, thereby reshaping and resizing the respective grooves on the ferrule halves via plastic deformation of the material inside the cylindrical through-hole. After reshaping and resizing, the groove that is finally formed on each ferrule halve would be precisely shaped, sized and located with respect to the external surface (i.e., the contact surface to the external alignment sleeve) of the ferrule halve.
The section of the optical fiber used for reshaping and resizing is replaced with the bare end section of the optical fiber to be terminated with a ferrule. The ferrule halves are aligned and attached to each other with the end section of the optical fiber held in the grooves therebetween. The opposing ferrule halves are joined together, e.g., by laser welding using the alignment fixture. The end of the optical fiber is thus terminated by the ferrule, with the tip/end face of the optical fiber protruding slightly beyond the end face of the ferrule. The end face/tip of the optical fiber is polished (e.g., mechanically or using a laser) (the end face of the ferrule may be polished as well). The ferrule may be assembled with other components (e.g., ferrule housing, preload spring, boot, etc.) to form an optical fiber connector terminating the end of the optical fiber cable.
The ferrule has an external surface for alignment with a complementary surface of an external alignment sleeve (i.e., the inside surface of a generally cylindrical or tubular sleeve). The external surface of the ferrule is generally cylindrical, having a contact surface profile with a cross-section that is generally circular or oval. Two similarly terminated optical fibers can be optically coupled end-to-end by the alignment sleeve. In use, two similar ferrules are inserted into the alignment sleeve, with the opposing end faces of the optical fibers in the ferrules abutting against each other. In one embodiment, one of the ferrules may be a demountable terminal ferrule attached to an optical device (e.g., a housing of a hermetically sealed optoelectronic module OM).
In accordance with the present invention, given the subsequent precision reshaping and resizing step, the groove that was initially formed (or preformed) may not need to maintain a high tolerance with respect to shape (e.g., roundness) and size (e.g., width) of the groove, as long as the axis of the pre-formed groove had been accurately located with respect to the external alignment surface of the ferrule halve. From another perspective, a groove that was preformed at high tolerance will be further subject to precision reshaping and resizing, to thereby achieve even higher tolerance than the early preform step (e.g., by stamping).
The ferrule fabricated in accordance with the present invention further improves over the prior art, resulting in an optical fiber connector with low insertion and return losses, which provides ease of use, and which can be fabricated at low cost.
Accordingly, the present invention is directed to the features at least covered by the appended claims, which are incorporated by reference herein.
For a fuller understanding of the nature and advantages of the invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings. In the following drawings, like reference numerals designate like or similar parts throughout the drawings.
This invention is described below in reference to various embodiments with reference to the figures. While this invention is described in terms of the best mode for achieving this invention's objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the invention.
By way of illustration and not limitation, the inventive process involving reshaping and resizing pre-formed fiber grooves will be disclosed below in reference to an embodiment of a termination process for optical fiber ferrules, and further an embodiment of a ferrule or ferrule assembly having a pair of ferrule halves or semi-ferrules. In the present invention, it is understood that the term “ferrule” generally refers to a structure having a body structured and configured with at least a groove for supporting and/or aligning a section of optical fiber. In the embodiments disclosed herein below, the ferrule is configured with two ferrule halves that are joined together to terminate an optical fiber for making a demountable connection to another ferrule and/or a connection terminal (e.g., a pigtail) on an optical device.
A—stripping the protective jacket and buffer to expose the cladding, and preparing a fiber-optic cable;
B—pre-aligning a pair of pre-formed semi-ferrules and placing a gauge tool between the pre-formed grooves in the semi-ferrules, and grasping the pre-aligned pair of pre-formed semi-ferrules in a gripper;
C—performing reshaping and resizing using the gauge tool (e.g., a fiber or a pin); in the illustrated embodiment, the gauge is a section of bare optical fiber, thus the optical fiber is used as a tool for reshaping and resizing the grooves; hence this step is referred to as a “fiber as tool” (“FAT”) process step;
D—aligning semi-ferrules and holding in the gripper;
E—with the aligned semi-ferrules held in the gripper, welding the semi-ferrules together;
F—cleaving the optical fiber (mechanically or using a laser);
G—assembling connector components to complete an optical connector;
H—polishing the tip/end face of the optical fiber held in the ferrule;
I—inspecting finished part and quality control; and
J—packing part that passed inspection.
Within the space bordered by the flat surface 13, a cavity 14 is provided, which includes a wider groove 19 to relatively loosely accommodate the optical fiber 20 behind the groove 18. The groove 19 is not used for alignment of the optical fiber 20, hence it does not need to be formed at high tolerance. The cavity 14 extends to the crimp section 15, with an internal geometry that accommodates the cable jacket 21. Reference is made to U.S. Pat. No. 9,091,833 (which had been commonly assigned to the assignee of the present invention, and which is fully incorporated by reference herein), which discloses a cable retention structure defining a castellated fiber cable clamping surface. The castellated surface has a series of alternating small and large cavities distributed along the axial direction. The cable jacket is securely held by the retention structure to prevent slipping of the cable jacket.
The pre-formed groove 18 on each ferrule halve has a generally semi-circular cross section. When the ferrule halves 12a and 12b are attached by mating at the opposing flat surfaces 13, the opposing grooves 18 form a generally circular cylindrical through hole receiving the end section of the optical fiber 20.
In one embodiment of the present invention, the ferrule halves 12 are precision pre-formed by high throughput processes, such as stamping a metal stock material (e.g., a metal blank). Reference is made to the precision stamping process disclosed in U.S. Pat. No. 7,343,770, which had been commonly assigned to the assignee of the present invention, and which was fully incorporated by reference herein. The disclosed stamping process involves stamping a stock material (e.g., a metal blank) to form the final overall external geometry of a ferrule and geometry of surface features including an optical fiber groove at tight (i.e., small) tolerances of below 1000 nm, whereby the groove is in precise alignment with the external alignment surface of the ferrule, for alignment to another ferrule using an alignment sleeve. U.S. Pat. No. 7,311,449, which had been commonly assigned to the assignee of the present invention, and which was fully incorporated by reference herein, discloses embodiments of ferrules that could be formed by the precision stamping process disclosed in U.S. Pat. No. 7,343,770.
The ferrule halves 12 may be pre-formed by similar processes. It is noted that the pre-formed ferrule halve 12 would include the external curved alignment surface precisely formed in relation to the axis of the groove 18, so that after the groove 18 is subject to reshaping and resizing, and the ferrule halves 12 have been assembled to produce the ferrule 10, the axis of the resultant groove conforms to the optical axis of the optical fiber 20, which would be in precise positional relationship to the exterior cylindrical alignment surface of section 11 of the ferrule 10. The reshaping and resizing procedures discussed herein below does not alter the external alignment surfaces of the ferrule halves 12 and the axis of the preformed groove 18. In other words, the axis of the preformed groove 18 as well as the axis of the resultant reshaped and resized groove would be in the same precise positional relationship to the external alignment surfaces of the ferrule halves 12.
In one embodiment, the ferrule body is made of a metal material, which may be chosen to have high stiffness (e.g., stainless steel), chemical inertness (e.g., titanium), high temperature stability (nickel alloy), low thermal expansion (e.g., Invar), or to match thermal expansion to other materials (e.g., Kovar for matching glass). Each ferrule halve may be stamped to form a unitary or monolithic body, which does not require further attachment of sub-components within the ferrule halve.
The operation of the tool 30 is best understood by reference to
In
In
In particular, in the embodiment of the termination process disclosed in
In step B in
After the ferrule halves 12 are pre-aligned to each other in step B, and using the pre-formed grooves as guides for the gauge optical fiber or gauge pin, the ferrule halves 12 are pressed together with the gauge optical fiber 20 or gauge pin 23 therebetween, thereby reshaping and resizing the respective grooves on the ferrule halves.
Referring to
Referring more closely the drawings, the series connected beams 53 are as follows: (a) one end or edge of the beam 53a is connected to the stationary base 51a of the frame 51, and the opposing edge of the beam 53a is connected to the intermediate body 54; (b) one edge of the beam 53b is connected to the intermediate body 54, and the opposing edge of the beam 53b is connected to the central body 55; (c) one edge of the beam 53c is connected to the central body 55, and the opposing edge of the beam 53c is connected to the intermediate body 54; and (d) one edge of the beam 53d is connected to the intermediate body 54, and the opposing edge of the beam 53d is connected to the stationary top portion 51b of the frame 51.
The two compound flexures 52a and 52b thus symmetrically support the respective side of the central body for vertical linear motions with respect to the frame stationary frame 51, with no or negligible motion in the lateral (horizontal) direction, given the nature of a double-compound flexure as shown. Any lateral motion is expected to be well within, e.g., 100-200 nm, or less, in the lateral direction. The double-compound flexure has been referred to also as a double nested compound linear spring flexure. As configured, the central body 55 is suspended by the double-compound flexure 52, for vertical linear motions. The travel distance of the intermediate body 54 is about half the travel distance of the central body 55.
A stationary lower jaw assembly 57 is attached to the base 51a of the frame 51, which includes a lower jaw 61 having a semi-circular groove 65 provided at its upper edge. The central body 55 suspends/supports an upper jaw assembly 72 having an attached upper jaw 62, which has a semi-circular groove 66 provided at its edge (see also
When the actuator 59 is operated to impart a force against the top part of central body 55 with an input force Fin, the central body 55 moves vertically downwards. The opening 63 between the jaws 61 and 62 is in a state conforming to the outside diameter of the cylindrical section 11 of the ferrule 10. Upon releasing the force Fin by the actuator 59, the flexure 52 lifts the central body 55 upwards, to thereby pull the upper jaw 62 away from the lower jaw 61. The opening 63 is thereby relaxed, allowing insertion/removable of a pair of ferrule halves 12a and 12b.
As shown in
After reshaping and resizing, the groove 18 that is finally formed on each ferrule halve 12 would be precisely shaped, sized and located with respect to the external surface (i.e., the contact surface to the external alignment sleeve) of the ferrule halve. Upon completion of reshaping and resizing operation, the actuator 59 is operated to release the force Fin, thus relaxing the opening 63 to release the ferrule halves 12. The ferrules halves 12 are removed from the opening 63 using the gripper 40.
The section of the optical fiber used for reshaping and resizing is replaced with the bare end section of the optical fiber to be terminated within the assembled ferrule comprising the two ferrule halves 12. The optical fiber 20 and the ferrule halves 12 are removed from the gripper 40. The portion of the bare section of optical fiber that was used as a gauge tool for the FAT operation is cleaved. The remaining optical fiber and the ferrule halves are cleaned, to prepare for subsequent operations (e.g., alignment for welding operations in step D and E).
In step D in
Post welding, the gripper is no longer necessary to maintain alignment of the ferrule halves 12, which have been assembled into a ferrule 10, but it serves as a convenient tool for handling the ferrule for subsequent operations, such as cleaving, polishing, assembly of connector components, inspection and/or packaging in steps F to J in
To complement the inventive FAT operation in the overall inventive termination process in
While the above disclosed embodiment of the FAT operation makes use of a bare section of the optical fiber as a gauge for reshaping and resizing the grooves of the ferrule halves, a hard metal or glass pin 23 (
The ferrule 10 has an external surface for alignment with a complementary surface of an external alignment sleeve (i.e., the inside surface of a generally cylindrical or tubular sleeve). The external surface of the ferrule is generally cylindrical, having a contact surface profile with a cross-section that is generally circular (or oval). Two similarly terminated optical fibers can be optically coupled end-to-end by the alignment sleeve. In use, two similar ferrules are inserted into the alignment sleeve, with the opposing end faces of the optical fibers in the ferrules abutting against each other. In one embodiment, one of the ferrules may be a demountable terminal ferrule attached to an optical device (e.g., a housing of a hermetically sealed optoelectronic module OM).
According to the present invention, the double-compound flexure provides ultra-linear motion of the central body. Lateral/transverse stiffness is 1,000 times higher than vertical stiffness. Stiffness and travel range can be optimized by beam geometrical dimensions (length, width, and thickness), and materials. By varying beam length, width, thickness, and position, moving portion stiffness, including vertical stiffness, transverse stiffness, and rotational stiffness, can be determined by beam geometry dimension (length, width, thickness), and materials. The beams may be preloaded (e.g., using a die spring biased on the central body) to maximum total travel range of central body. Different inserts (not shown) can be press-fit into T-grooves and interchanged to provide different alignment features for different ferrule configurations. Passive alignment of the ferrule halves 12 are achieved, with no active alignment required.
The ferrule in accordance with the present invention further improves the prior art, resulting in an optical fiber expanded beam connector with low insertion and return losses, which provides ease of use and high reliability, and which can be fabricated at low cost.
While the invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit, scope, and teaching of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.
This application claims the priority of (a) U.S. Provisional Patent Application No. 62/384,148 filed on Sep. 6, 2016, which is fully incorporated by reference as if fully set forth herein. All publications noted below are fully incorporated by reference as if fully set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| 62384148 | Sep 2016 | US |
