The present invention relates generally to a process of manufacturing a ferrule assembly, more specifically, to controlling to fiber protrusion of a ferrule assembly.
Optical fiber connectors are an essential part of substantially all optical fiber communication systems. For instance, optical connectors are used to join segments of fiber into longer lengths, to connect fiber to active devices such as radiation sources, detectors and repeaters, and to connect fiber to passive devices such as switches and attenuators. The principal function of an optical fiber connector is to hold a fiber end such that the core of the fiber is axially aligned with the optical path of the component to which the connector is mated (e.g., another fiber, a planar waveguide, or an opto-electric device). This way, light from the fiber is optically coupled to the other component.
It is well known that to effect optical coupling and minimize Fresnel loss, “physical contact” may be made between the fiber end face and the optical path of the mating device. To effect physical contact, traditionally optical connectors have employed a “ferrule,” which is a well-known component for holding one or more fibers such that the fiber end faces are presented for optical coupling. Ferrule connectors typically bias the ferrule forward such that, when the connector is mated to a mating component, the ferrule urges against the mating component to physically contact the fiber end face with the optical path of the mating component.
To effect such physical contact, a conventional ferrule typically requires polishing. A polished ferrule may best be described by way of contrast to an unpolished ferrule. An unpolished ferrule has a geometry and anomalies on its end face which make it difficult, if not impossible, to bring the end face of fiber housed therein into physical contact with the optical path of the mating component. In addition, when multiple fibers are affixed to an unpolished ferrule, the position of the fiber end faces tend to vary along the mating axis, thereby making it difficult to effect optical coupling with all of the fibers. Polishing the end face of the ferrule with the fibers held therein, shapes and smoothes the ferrule end face while simultaneously polishing the fiber end faces and making them coplanar. To minimize variances in the shape of the ferrule and the coplanarity of the fiber end faces, polishing typically is performed to exacting standards. Polishing therefore tends to be costly and prone to reworking and waste, thereby lowering yields. The problems associated with polishing the ferrule are exasperated in multi-fiber ferrules which are more complicated to polish.
This issue was addressed in U.S. Pat. No. 7,377,700, which discloses an approach for producing a ferrule assembly using an unpolished assembly. Briefly, the approach involves (a) positioning at least one fiber in a ferrule such that a portion of the fiber extends beyond the end face of the ferrule; (b) affixing the fiber relative to the ferrule; and (c) cleaving the portion of the fiber. Such an approach is beneficial because it separates the functions of preparing the fiber's end face for optical coupling and positioning the fiber within the ferrule. By treating these functions separately, the fiber end face can be prepared independently of the ferrule, thereby eliminating the need to polish the ferrule/fiber assembly, while facilitating the precise positioning of the fiber end face relative to the ferrule. This patent recognizes also that it is generally preferred to have the fiber end face protrude from the ferrule to enhance its ability to make physical contact.
Although this approach offers significant advantages, applicants recognize that coplanarity among the fibers tends to become problematic as the number of fibers in the ferrule increases. That is, cleaving fibers and positioning them in the ferrule such that all the fiber end faces are essentially in the same plane is very difficult when the fibers are not polished in situ in the ferrule. This difficulty increases necessarily as the number of fibers increases. The issue of coplanarity is addressed in United States Patent Application No. 20090271126, incorporated by reference.
Therefore, there is a need for a process of producing a ferrule assembly in which precise fiber protrusion is achieved among the fibers without polishing. The present invention fulfills this need among others.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention provides a ferrule assembly in which precise fiber protrusion is achieved without polishing. Specifically, the invention involves using a tool that has a register surface and one or more alignment members that cooperate with one or more alignment members of a ferrule to align the register surface of the tool with the ferrule end face, and thereby provide a register surface against which each fiber can abut to ensure its proper protrusion. Proper fiber protrusion facilitates physical contact among the fibers as described above. It should be understood, however, that the invention is not limited to physical contact applications and may be practiced whenever precise positioning of the fiber end face is required (such as, for example, when optically coupling a fiber across a gap (air or gel-filled) to a lens, active opto electrical device, passive device, or a waveguide). Thus, the invention exploits alignment members that are commonly found in standard ferrules to establish fiber protrusion.
One aspect of the invention is a process for producing a ferrule by exploiting a ferrule's alignment member. In one embodiment, the process comprises: (a) positioning one or more fibers in a ferrule having a ferrule end face and at least one first alignment member such that a portion of each fiber extends forward beyond the ferrule end face; (b) after step (a), cleaving the portion of each fiber, thereby forming cleaved fiber end faces; (c) after step (b), interengaging a second alignment member of a fiber-alignment tool with the first alignment member such that a register surface of the fiber-alignment tool is aligned with the ferrule, and registering the cleaved end face of each fiber against the register surface; and (d) affixing the fiber(s) relative to the ferrule.
Another aspect of the invention involves the tool which exploits the alignment members of the ferrule to provide a register against which the fibers can be abutted. In one embodiment, the tool comprises: (a) a body portion having a register surface; and (b) at least one alignment member at a certain angle from the register surface, the alignment member configured to cooperate with a corresponding alignment member of a ferrule.
a)-(d) show schematically various stages of preparing a multifiber ferrule assembly according to one embodiment of the present invention.
a)-(d) show schematically different fiber profiles and their corresponding register surface on the fiber-alignment tool.
a)-(g) show schematically different register surfaces on the fiber-alignment tool for three dimensional fiber arrays.
Referring to
The step depicted in
The first alignment member 104 may be incorporated into the ferrule 102 specifically for interengagement with the second alignment member 151 or it may be inherent in the ferrule design. More specifically, the alignment member may be used to align the ferrule 102 not only with the tool 150, but also with a mating structure (not shown). Such alignment members are well known, and include, for example, alignment pin/alignment hole for receiving the pin, a sleeve, and V-grooves along the sides of the ferrule. In the embodiment shown in
As mentioned above, a conventional ferrule end face is typically polished, which involves abrading the ferrule end face to remove all anomalies therefrom and to smooth the fiber end faces sufficiently for optical coupling. However, the ferrule of the present invention does not require such polishing since the fiber end faces are suitable for optical coupling following the cleaving step (depicted in
As used herein, the term “unpolished ferrule” refers to a ferrule that has not been polished or is not polished to the extent typically required to achieve physical contact. An unpolished ferrule in this context has a number of distinguishing characteristics. First, it has a molded surface rather than a polished or machined surface. A molded surface is characterized typically (although not necessarily) by a rough surface, which may not be precisely oriented with respect to the guiding features of the ferrule. Such a surface also tends not to be reflective. The surface of the ferrule may also contain the impression of features that support the core pins used to mold the ferrule, and may include a parting line where two sides of the mold meet. Second, an unpolished ferrule comprises embedded particles (e.g. glass particles used for imparting hardness) that lack a planar surface. That is, during polishing, the embedded particles at the end face of the ferrule will have planar surface ground into them at the surface of the end face as the end face is abraded away. Obviously, in an unpolished ferrule, the embedded particles at the end face will not have such a ground planar surface. Third, an unpolished ferrule typically (although not necessarily) has surface anomalies on its end face that tend to interfere with the mating surface of the mating connector or device and prevent end faces of fibers from making physical contact with mating optical pathways. For example, ridges or bumps on the end face of an unpolished ferrule prevent the end face from making good physical contact with a perfectly planar surface. Obviously, as the end face of the ferrule becomes larger in area, as with MT ferrules, the probability of surface variations and imperfections increases along with the number of fibers. Polishing the ferrule removes these surface anomalies. Therefore, as used herein, the term “unpolished ferrule” refers to a ferrule having an end face that has a molded finish and not a polished finish, and/or an end face that has embedded particles which do not have a planar surface.
Although the ferrule may be made from any known material, generally MT ferrules are made of polymeric material, such as highly glass-filled polyphenylene sulfide (PPS). Single-fiber ferrules are typically made of a ceramic such as zirconia or metal such as stainless steel or nickel-silver or titanium.
As shown in
As depicted in
Cleaving the fibers may be performed either mechanically or by laser cleaving. With respect to mechanical cleaving, this is a well-known technique and involves essentially shearing the fibers cleanly to provide an end face. It may be preferred to polish a mechanically cleaved end face of the fiber. Methods of performing this polishing are well-known and may include, for example, physical grinding/polishing and “laser polishing” in which a laser is used to melt and thereby smooth the end face of the fiber. Although mechanical cleaving is certainly contemplated in the present invention, the preferred method of cleaving is laser cleaving, which is the embodiment shown in
With respect to laser cleaving, suitable processes are described, for example, in U.S. Pat. Nos. 6,246,026; 6,963,687; and 7,377,700, incorporated herein by reference. In the laser cleaving process, optical fiber material is typically ablated rather than melted. This requires a laser 107 to produce a beam 108 having sufficient energy to effect the fiber's immediate sublimation. Suitable results have been achieved using a laser with a wavelength between 0.1 and 1.5 μm and 8.5 μm to 10.6 μm. Suitable lasers include, for example, CO2 and excimer lasers, although a CO2 laser is generally, although not necessarily, preferred. CO2 lasers have proven particularly advantageous due to the high speed at which they can be operated and resulting cost effectiveness.
Balancing the objective of delivering high energy to fiber to ablate the glass is the need to minimize the energy absorbed by the glass surrounding the cut so as to minimize melting adjacent the cut. For this reason, the laser is preferably operated in a pulse mode for cutting the fiber. In the pulse mode, the laser transmits short high-energy pulses of laser light so that the material of the fiber is sublimated. The pulses are very short and have very steep edges, thus, the maximum pulse energy is achieved very rapidly. For example, suitable results have been achieved in which the peak power of the pulse is between about 0.1 and about 1000 watts and the pulse length is greater than about 50 fs. Good results are achieved with a CO2 laser (wavelength 10.6 μm) having a pulse length of 35 μs and a peak power of 600 watts.
Although operating the laser in pulse mode is preferred generally, particularly with high power lasers such as a CO2 laser, some application may favor operating the laser in a continuous wave mode. For example, if the contact time between the laser and fiber is decreased, i.e., the laser cuts across the fiber more quickly, it may be desirable to operate the laser in continuous wave mode.
Directing the laser beam on the fiber to effect the cut is subject to several variables involving the angle of the beam to the fiber, the axial position of the beam along the fiber, the angle of convergence of the beam, the cutting time/energy level of the beam, and the desired end face geometry. These variables are considered in detail in U.S. Pat. No. 7,377,700, which is incorporated by reference herein.
The way in which the fibers and laser beam are moved relative to each other to effect the cuts described above can vary and it is anticipated that any approach which is precise, accurate and repeatable will suffice. In one embodiment, a device is used which maintains a certain angle between the beam and the fiber and moves the fibers at one or more predetermined angles relative to the laser beam. It is within the scope of the present invention, however, to move the laser beam relative to the fiber. Alternatively, a stationary elliptical beam can be used to cut stationary fibers as is done in the commercially-available system sold by OpTek Systems Inc., Greenville, S.C.
As shown in
Referring to
The geometry of the register surface depends on the application. For example, in the embodiment shown in
Referring to
It should be appreciated that the profiles described above with respect to a single row of fibers can be combined, mixed and matched to form a variety of different three dimensional fiber profiles in embodiments having three or more rows of fibers. In other words, each profile along a row (x-axis) can be applied across rows (y-axis) as well. For example, Referring to
To ensure the register surface is oriented properly with respect to the ferrule, the tool 150 comprises at least one second alignment member 151 at a certain angle from the register surface 152. The second alignment member is configured to cooperate with the first alignment member of the ferrule. As mentioned above, the alignment members may be any known alignment means. In the embodiment shown in
Because the tool 150 comprises a register surface 152 for urging against the cleaved fiber end faces and pushing them backward in the ferrule, it should comprise a material having suitable toughness and abrasion resistance. Suitable materials include for example, stainless steel, tool steel, Stavax®, and sapphire. Furthermore, the surface may be treated or coated to improve durability.
In the embodiment shown in
The embodiment of the tool 150 shown in
Alternatively, referring to
The tool 150 can be manufactured by molding or machining. In one embodiment, the register surface is produced on a lathe. Prior to the tool being removed from the chuck of the lathe, the alignment hole 154 for receiving the pin may be formed. Such a procedure ensures that the alignment hole (and hence the alignment pin) is perpendicular to the register surface 152.
In one embodiment, the tool 150 is also configured to control the degree to which the register surface 152 is pushed back toward the ferrule end face. For example, it may be advantageous to fashion the register surface 152 with stops (not shown) that project toward the ferrule end face such that they contact the ferrule end face when the register surface is the desired distance from the fiber end face. Alternatively, a washer or similar device may be placed around the alignment pin 151a to act as a spacer to position the register surface 152 the desired distance from the ferrule end face. Still other stops and spacers for positioning the register surface precisely relative to the ferrule end face will be obvious to those of skill in the art in light of this disclosure.
As shown in
The ferrule assembly of the present invention is uniquely suited to facilitate fiber protrusion since the fiber end face and ferrule end face are not polished simultaneously as in the prior art. Polishing a ferrule and fiber assembly together necessarily requires differential wearing of the ferrule and fiber to obtain fiber protrusion. Such differential wearing, however, can be difficult to control, and moreover it does not facilitate varying the protrusion of the fibers across the ferrule. The approach of the present invention, on the other hand, prepares the fiber end face independent from the ferrule end face (in fact, preferably, the ferrule is not even polished). Thus, the fiber end face position and shape with respect to the ferrule end face is fully configurable. For example, in one embodiment, the fibers may optically couple with a lens which images light onto the end faces of an array of fibers that are arranged along a non-planar surface.
Once the ferrule assembly is prepared it may be assembled into an optical package. As used herein, the term “optical package” refers broadly to an assembly comprising a fiber-terminated ferrule assembly and may include, for example, a ferrule-containing connector (e.g., multi-fiber connectors such as the Lightray MPX® connector, MT-RJ connector, and MPO connector, or a ferrule-containing device (e.g., passive devices, such as, add/drop filters, arrayed wave guide gratings (AWGs), splitters/couplers, and attenuators, and active devices, such as, optical amplifiers, transmitters, receivers and transceivers). As is well known, the ferrule assembly in the optical package holds a fiber's end such that the core of the fiber is axially aligned with the optical path of the mating component to which the connector or device is mated. This way, light from the fiber is optically coupled to the other component. The term “optical pathway” as used herein refers to any medium for conducting optical signals, and includes, for example, a fiber or waveguide, a silica or polymeric structure in a substrate, or a silica or polymeric optical component. The term “mating component” refers to an optical package that contains or comprises the optical pathway, and may include, for example, optical connectors and optical devices as mentioned above. A mating component typically comprises a mating surface which is adapted to receive the end face of the ferrule to optically couple the fiber(s) with the mating optical pathway(s). Such mating surfaces are well known in the art.
Optical packages comprising the ferrule assembly of the present invention have a number of advantages over traditional ferrule-containing packages. First, as mentioned above, the ferrule assembly of the present invention obviates the need for polishing. This results in significant simplification of the assembly process and a significant reduction in costs. Aside from this advantage, however, the package of the present invention also has performance related advantages over traditional connectors and packages. Perhaps the most significant performance advantage is derived from the configurability of the fibers' protrusion from the ferrule end face. The protrusion not only allows for the use of an unpolished ferrule, but also facilitates mating with an unpolished ferrule. Thus, the ferrule assembly of the present invention does away with the need for polished ferrules entirely, thereby reducing costs among various optical packages. Furthermore, the fiber's protrusion can even be exploited to compensate for undercut of a polished or unpolished ferrule.
It should be apparent from the above description that the ferrule assembly of the present invention provides for significant advantages over conventional polished ferrule configuration such as lower cost and simplicity in manufacturing and enhanced versatility with respect to the type of mating components with which it can effect optically coupling. Still other advantages of the ferrule assembly are anticipated.