High-precision female format multifiber connector Number:6,817,778 from the United States Patent and Trademark Office (PTO) owispatent A female format connector, usable for connection with a male format connector having an alignment pin is described as having a high-precision piece coupled to a low precision piece. The low precision piece has an alignment opening dimensioned to accept the alignment pin of the male format device. The high-precision piece also has an alignment opening. The alignment openings are sized and positioned for accurate alignment between the pieces during coupling and, after coupling, the high-precision piece is modified such that the second alignment opening, after modification, is larger than it was prior to the coupling. A method of forming a female format ferrule involves coupling a high precision piece to a low precision piece, via alignment holes on each, the alignment holes are sized to accept a common alignment pin for maintaining accurate alignment between the pieces during coupling, and, after coupling, removing some of the alignment hole wall.<H multifiber, connector, High, precision, , 6817778.html, Patent, pto, 6817778

Title: High-precision female format multifiber connector

Abstract: A female format connector, usable for connection with a male format connector having an alignment pin is described as having a high-precision piece coupled to a low precision piece. The low precision piece has an alignment opening dimensioned to accept the alignment pin of the male format device. The high-precision piece also has an alignment opening. The alignment openings are sized and positioned for accurate alignment between the pieces during coupling and, after coupling, the high-precision piece is modified such that the second alignment opening, after modification, is larger than it was prior to the coupling. A method of forming a female format ferrule involves coupling a high precision piece to a low precision piece, via alignment holes on each, the alignment holes are sized to accept a common alignment pin for maintaining accurate alignment between the pieces during coupling, and, after coupling, removing some of the alignment hole wall.

Patent Number: 6,817,778 Issued on 11/16/2004 to Kang, et al.

Inventors: Kang; Keith (Hollis, NH); Dudoff; Greg (Amherst, NH)
Assignee: Xanoptix, Inc. (Merrimack, NH)

Appl. No.: 607620

Filed: June 27, 2003

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
098652	Mar., 2002	6609835
098255	Mar., 2002	6619855
098990	Mar., 2002	6629780
896664	Jun., 2001	6773166
896513	Jun., 2001
896196	Jun., 2001
896192	Jun., 2001

Current U.S. Class: 385/60 ; 385/78

Field of Search: 385/52,60,78,89,95-99

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Primary Examiner: Nguyen; Khiem
Attorney, Agent or Firm: Morgan & Finnegan LLP

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of commonly assigned U.S. patent application Ser. No. 10/098,652, (now U.S. Pat. No. 6,609,835), Ser. No. 10/098,255 now U.S. Pat. No. 6,619,855 and Ser. No. 10/098,990 (now U.S. Pat. No. 6,629,780), all filed Mar. 14, 2002 which are continuations-in-part of commonly assigned U.S. patent application Nos. 09/896,513, 09/896,664, (now U.S. Pat. No. 6,773,166) Ser. No. 09/896,196 and 09/896,192, all filed Jun. 29, 2001 and which are all incorporated herein by reference in their entirety.

Claims

What is claimed is:

1. A method of preparing a mating surface and a feature defined by a wall that will mate with the mating surface to a specified sub-micron tolerance, the method comprising: optimizing the size of at least one of the mating surface or at least part of the wall by uniform oxidization in a slow, controlled manner over a period of several hours until the specified sub-micron tolerance is achieved.

2. A method of forming a female format connector comprising: coupling at least one high-precision piece to a low precision piece to form a ferrule, the low precision piece comprising a first and second alignment openings, the at least one high-precision piece comprising a plurality of fiber holes, a first and second removable portions, and a third and fourth alignment openings at least in part disposed on the first and second removable portions, the first, second, third and fourth alignment openings sized and positioned to provide accurate alignment between the high-precision piece and the low precision piece during coupling; and modifying the third and fourth alignment openings after coupling.

3. The method of claim 2 wherein the third and fourth alignment openings before modification are cylinders having a cross section of a first diameter and the third and fourth alignment openings after modification are cylinders having a cross section of a second diameter, larger than the first diameter.

4. The method of claim 2 wherein the modifying the third and fourth alignment openings comprises changing the shape of the third and fourth alignment openings.

5. The method of claim 2 wherein the modifying the third and fourth alignment openings comprises removing the first and second removable portions.

6. A method of forming a female format connector comprising: aligning a low precision piece and a high precision piece using a first and second alignment pins passing through a first, second, third and fourth alignment openings in the low and high precision pieces, the first and second alignment openings being in the low precision piece, the third and fourth alignment openings being in the high precision piece and being disposed at least in part on a first and second removable portions of the high precision piece, the high precision piece further having multiple fiber holes; bonding the low precision piece to the high precision piece to form a ferrule; removing the first and second alignment pins from the alignment openings after bonding the low precision piece and high precision piece; and modifying the third and fourth alignment openings after aligning the low precision piece and high precision piece.

7. The method of claim 6, wherein the third and fourth alignment openings are modified after aligning and bonding the low precision piece and high precision piece.

8. The method of claim 6, wherein modifying the third and fourth alignment openings comprises making the third and fourth alignment openings larger.

9. The method of claim 6, wherein modifying the third and fourth alignment openings comprises changing the shape of the third and fourth alignment openings.

10. The method of claim 6, wherein modifying the third and fourth alignment openings comprises removing the first and second removeable portions to partially remove the third and fourth alignment openings from the ferrule.

11. The method of claim 6, wherein modifying the third and fourth alignment openings comprises removing the first and second removeable portions to entirely remove the third and fourth alignment openings from the ferrule.

Description

FIELD OF THE INVENTION

This invention relates to components and processes for fiber optic related component fabrication. More particularly, the invention relates to the fabrication of optical coupling and waveguiding elements.

BACKGROUND OF THE INVENTION

Optical Fibers in commercial systems have been traditionally held by using a combination of pieces.

A connector assembly 100, such as shown in FIG. 1 as an exploded view is used to attach various fiber pieces (or fiber pieces and modules) together. A ferrule 102 is the part of the connector 100 into which the fibers 104 themselves are inserted before the ferrule 102 is inserted into the overall connector itself. The ferrule 102 is a `high-precision` piece of the assembly 100. It holds the fiber(s) 104 in a precise position and ensures that when two connector pieces are attached, that the fibers in the two pieces are held in accurate alignment. The remainder of the connector 106 is `low precision` relative to the ferrule 102.

In the multi-fiber connectors available today, most of the connections are for fiber arrays of 2 or more fibers, such as shown in U.S. Pat. No. 5,214,730, up to arrays of 1.times.12 (although some commercial 2.times.12 configurations have been tried). The connectors employed are referred to by various names depending upon who makes them. In 1.times.2 arrays, connectors are referred to as ST, LC, MT-RJ connectors while for 1.times.12 arrays the connectors are referred to as MTP.RTM., MPO, MPX and SMC connectors, among others. In the 1.times.12 or 2.times.12 area, all of the various connectors use a common type of ferrule commercially available from, among others, US Conec Ltd. and Alcoa Fujikura Ltd. In addition, commercial connectors for small arrays (less than 12) fibers have also been proposed, for example, in U.S. Pat. No. 5,743,785.

Fiber holding pieces, such as ferrules 102, can be made by molding plastic or epoxy pieces containing holes 108 into which optical fibers 104 can be inserted. Fibers must be able to be centered in each hole precisely and repeatably.

When an array of holes is made in a material for holding optical fibers, there are two aspects which need to be controlled. The spacing between holes (the "pitch" of the holes) and the diameter of each hole. Both have some margin of error due to the inherent inaccuracies of the fabrication techniques. If inaccuracies introduce errors in either (or both) pitch or size that are too large, then the fibers can be inserted at an angle or will not be positioned correctly in the ferrule. In either case, this negatively affects the ability to couple light efficiently, if at all, from one bundle to another or from an optical or opto-electronic component to a fiber bundle. If the hole pitch is inaccurate, then fibers from one bundle will not line up well with fibers of another bundle. However, even if the center-to-center pitch of the holes is very accurate, because the hole diameter is larger than the fiber (and each hole likely varies across an array) each fiber need not be in the exact same place in the hole as the other fibers in their holes, then that can cause misalignment, leading to inefficiencies or unacceptable losses. For example, if each of the holes in a ferrule piece was accurate to within 4 microns, then adjacent fibers could be off in pitch by up to 4 microns, since one fiber could be pushed to one side by 2 microns and the adjacent fiber could be pushed in the other direction by 2 microns. While this may be acceptable for multi-mode fibers, for single mode fibers this would be a huge offset that could make connections unacceptable or impossible.

In addition, fibers should generally not be placed in a hole at an angle or, if inserted at an angle, the particular angle should be specifically controlled.

FIG. 2 shows an example connector hole 200 and fiber 202. The inner circle, represents an actual fiber 202 while the outer circle, represents the hole 200 in the ferrule. As shown, the difference in sizes is not to scale but is exaggerated for purposes of illustration. Nevertheless, in actuality, the ferrule hole 200 must be larger than the fiber 202 by enough of a margin to allow for easy insertion--ultra-tight tolerances can not be effectively used. While the fiber 202 should ideally be centered with respect to the hole 200, as can be seen in FIG. 3, any individual fiber 202 could also be pushed in any hole 200 to somewhere else in the hole, for example, either the left or right edge (or any other edge) where it would not be centered within the hole 200. Thus, even if the ferrule has an accurate pitch "P" between hole centers 204, adjacent fibers 200 in an array may have an incorrect pitch "P+2.DELTA.P" due to the offset .DELTA.P between the center 206 of each hole 200 and where the fiber 200 lies within the hole 200, in this case, causing an incorrect pitch of P plus 2 times the individual offset .DELTA.P in each hole.

The 1.times.12 and 2.times.12 ferrule technology currently in commercial use is based upon a glass filled epoxy resin (a high-performance plastic) which is fabricated using a common plastic molding technique called transfer molding. Today, ferrules molded out of epoxies or plastics can be made to the necessary tolerances for multimode fibers, but special care must be taken during fabrication. Plastic molding technology is very process sensitive and molds having the requisite precision are extremely difficult to make. Even so, yields tend to be poor due to the inherent manufacturing process errors that occur in plastics molding. Since the tolerances on these pieces must be very accurate (on the order of about 1 to 2 micrometers), high yield manufacture is difficult. As a result, the cost of terminating fiber bundles into these connectors can be quite expensive, running hundreds of dollars per side. In addition, the process is not scalable to larger numbers of fibers (particularly 30 or more) because of inaccuracies and yield issues associated with molding technology and reliable production of ferrules for similar numbers of single mode fibers is even more difficult.

There has been an increasing need among users in the fiberoptic field for larger groups of fibers, so demand for connectors to handle these groups has been increasing as well. As a result, creation of connectors for larger arrays, such as 5.times.12, have been attempted. One manufacturer is known to have made a 5.times.12 connector array, but achieved such poor yields that they deemed an array of that size unmanufacturable. Moreover, the cost of producing the pieces resulted in their being sold for $500 each, due to poor yield, and the mold for producing the pieces was destroyed during the process.

The problem is that in plastic molding pieces for holding higher fiber counts in small spaces results in less structural integrity for the molded piece. As such, the prior art has been forced to do without commercial connectors for such large arrays, because 5.times.12 arrays can not be reliably created and commercial connectors for larger format arrays (e.g. even a 6.times.12) are considered prohibitively difficult to even attempt.

The ferrule area is very small, since ferrules for the above MTP, MPO, MPX or SMC connectors are about 0.07" high, 0.3" wide and 0.4" deep, so molding or machining of features in the ferrules of the sizes required to hold multiple optical fibers (which typically have about a 125 micron diameter for a multimode fiber and a 9 micron diameter core for a single mode fiber) is very difficult. Since single mode fibers have an even smaller diameter than multimode fibers, molding or machining ferrules to accommodate large arrays of single mode fibers is currently, for all practical purposes, impossible--particularly on a cost effective commercially viable scale.

Additionally, making ferrules for arrays is made more difficult due to process variations during production because, as the holes approach the edge of the ferrule, the structural integrity of the walls decrease causing parts to have poor tolerance at the periphery, become overly fragile causing component collapse in some cases, or prohibiting removal of material from the inside of the piece that impedes or prevents fiber insertion.

Some have attempted to make two-dimensional fiber bundle arrays by creating a dense packing of fibers together, for example, as described in U.S. Pat. No. 5,473,716, and K. Koyabu, F. Ohira, T. Yamamoto, "Fabrication of Two-Dimensional Fiber Arrays Using Microferrules" IEEE Transactions on Components, Packaging and Manufacturing Technology--Part C, Vol 21, No 1, Jan. 1998. However, these attempts have not yielded a solution, particularly for the types of connectors mentioned above, because the inaccuracies of fiber production result in diameters of fibers which fluctuate within a 2 micron range (i.e. plus or minus 1 micron). Hence if 12 fibers are stacked in a row, there could be as much as 12 microns of inaccuracy in fiber alignment. Even with multi-mode fibers (the best of which use 50 micron cores), a misalignment of 12 microns will cause unacceptable light loss for most applications. For single mode fibers, which typically have 9 micron diameter cores, a 7 to 12 micron misalignment could mean that, irrespective of the alignment of the fiber at one end of the row, entire fibers at or near the other end of the row could receive no light whatsoever. For two-dimensional fiber arrays, the problem is even worse because the inaccuracy of the fiber is not limited to one direction. Thus, for example with a 16.times.16 array, a plus or minus 1 micron inaccuracy could result in fiber misalignments by up to 23 microns or more. Compounding the problem is the further fact that fiber inaccuracies stated as plus or minus 1 micron do not mean that fiber manufacturers guarantee that the fiber will be inaccurate by no more than 1 micron. Rather, the inaccuracy statement represents a standard deviation error range. This means that most of the fiber should only be that inaccurate. Individual fibers, or portions thereof, could have larger inaccuracies due to statistical variations.

As a result, the larger the number of fibers, the more likely a problem due to fiber inaccuracy will occur because, for example, using the 16.times.16 array above, the array would have 256 times the chance (because there are 16.times.16=256 fibers) of having at least one of these statistically anomalous fibers in the group.

Others have attempted to align two dimensional arrays of fibers (e.g. 4.times.4 arrays) in a research setting, but none have applied their techniques to conventional connector technologies. Moreover, the techniques are not suitable or readily adaptable for high yield, low cost, mass production as demanded by the industry. For example, some groups have examined the use of micromachined pieces made out of polyimide as described in J. Sasian, R. Novotny, M. Beckman, S. Walker, M. Wojcik, S. Hinterlong, "Fabrication of fiber bundle arrays for free-space photonic switching systems," Optical Engineering, Vol 33, #9 pp. 2979-2985 September 1994.

Others have attempted to use silicon as a ferrule for precisely holding fiber bundle arrays since silicon can be manufactured with very high precision (better than 1 micron) and techniques for processing of silicon for high yield is, in general, well understood.

Early attempts at silicon machining for two-dimensional array fiber placement were performed with some limited success and one-dimensional fiber arrays, using fibers placed in V-Grooves etched into a piece of silicon, have been created, for example, as shown in FIG. 4A. The approach used the silicon pieces to hold the fibers but no attempt was made to integrate such an arrangement into a commercial connector.

Other groups took the V-Groove approach of FIG. 4A and performed an experiment where they stacked two of pieces together FIG. 4B for insertion into a connector. This resulted in a minimal array with two rows of fibers, as described in H. Kosaka, M. Kajita, M. Yamada, Y. Sugimoto, "Plastic-Based Receptacle-Type VCSEL-Array modules with One and Two Dimensions Fabricated using the self-Alignment Mounting Technique," IEEE Electronic Components and Technology Conference, pp. 382-390 (1997), but the technique was not scalable to larger format two-dimensional arrays, such as shown in FIG. 4C.

Still other groups looked at holding larger format two-dimensional arrays using silicon pieces machined using wet-etching techniques, as described in G. Proudley, C. Stace, H. White, "Fabrication of two dimensional fiber optic arrays for an optical crossbar switch," Optical Engineering, Vol 33, #2, pp. 627-635, February 1994.

While these silicon pieces were able to hold fibers, they were not designed to be, and could not readily be, used with existing ferrule or connector technology. Moreover, they could not be used for single mode fibers with any accuracy.

Thus, none of the above attempts have provided a viable solution to the problem of how to effectively create a large format fiber array which: allows for high precision holding of large arrays of fibers, especially single mode fibers, is compatible with current commercially used connectors that attach two fiber bundles to each other or one fiber bundle to a component containing an array of optical devices, such as lasers and/or detectors, and that allows for easy fiber termination in a rapid fashion at low production cost.

In addition, because of the above problems, there is presently no large format ferrule apparatus that can maintain fibers at a low angle, or at a precisely specified angle, for good optical coupling.

Collimating arrays are conceptually arrays of pipes for light. Mass production of collimating arrays for commercial applications has largely been dominated by the digital photographic camera and digital video camera world. These applications typically use a device called a "faceplate", which is a multi-fiber assembly used to direct light onto optical detectors used for imaging. Since, for cameras, effective imaging requires the maximum amount of light reach the detectors, a faceplate will have several fibers per individual detector. In fact, in the most desirable faceplates, the number of optical fibers exceeds the number of optical detectors by many times. Thus, light being directed to a single detector in such a camera passes through multiple optical fibers arranged in parallel, and a camera has one detector per pixel. For imaging systems like cameras, this collimating technique is sufficient to accomplish its purpose. However, when dealing with optical communication systems, faceplates can not be used because the light loss resulting from such a collimating arrangement is significant. The faceplate technique (sometimes also referred to as oversampling) is also incompatible with the use of single mode fibers or lasers (which are highly desirable for use in high speed, long distance data transmission). Hence, the collimating technique of using a faceplate, such as made for use in cameras, is an unworkable approach for opto-electronic communication devices.

As noted above, for one-dimensional optical device arrays, attempts have been made to create collimators by using a piece of silicon wafer, into which V-Grooves are etched, and laying the fibers into the V-Grooves as shown in FIG. 4A. This is an operational approach for forming a one-dimensional array that is unsuitable for mass production.

Other groups have attempted to stack multiple V-Groove arrays on top of one another (FIGS. 4b, 4c) to create a larger collimating element. Unfortunately, the accuracy of stacking in the second dimension is limited by the accuracy of the thickness of the individual wafers, both on an absolute basis and on a relative basis, due to thickness variations over the area of the wafer. In addition, the stacked V-Groove technique requires such accuracy that individual stacks must be individually built up one at a time; a costly and inefficient process.

Similarly, optical waveguides are also conceptually pipes for light. Presently, there are also no inexpensive two dimensional optical waveguide combiners available for commercial applications or that can be used with a fiber array. In some cases, optical fibers are twist fused to form a 2 to 1 "Y" branch, for example, for coupling a pumping laser to a single, signal carrying, fiber. For one-dimensional arrays of devices, Y branches have been created on the surface of a wafer by patterning, using lithographic techniques, to form waveguides. This technique provides robust control for a one-dimensional array, but cannot be extended into two dimensions since it is inherently a planar process.

Other methods for making structures for guiding light center around a field known as "photonic integrated circuits" and approaches for making them fall into three general classes.

The first class, shown in FIG. 31, involves patterning waveguides 3102 on top of a substrate 3104. By way of example, the waveguides 3102 can be polyimide and the substrate 3104, glass. The problem with this approach is that it is not applicable for 2-dimensional array formatting since the intended height of the waveguides 3102 can be as much as 30 microns, but must have sub-micron tolerance and uniformity across the substrate 3104. For mass production, this typically means across an 8 inch or larger wafer. Obtaining this level of accuracy is prohibitive if not impossible to achieve for waveguides 3102 patterned above the substrate 3104.

The second class, shown in FIG. 32, involves defining waveguides 3202 within a substrate 3204 using an implant or irradiation technique to change the refractive index of the substrate 3204 in various regions. The problem with this approach is that the typical refractive index change between the implanted or irradiated region is a gradient that is so small relative to the substrate that unacceptable levels of light leakage can occur at bends, turns or tapers in the structure. Thus, this approach is poorly suited for waveguides that are not straight.

A hybrid approach, shown in FIG. 33, using a combination of the first and second class approaches, defines regions 3302 in the substrate 3304 by implant or irradiation and uses pattern etches 3306 on top to bound the light. However, the same loss problems typical of the second class of processes occur. In addition, most substrates that would be used in an etch process, such as in the first and hybrid approaches, are glasses or crystals which are difficult to etch to significant depths, for example, 30 microns or more, with an accuracy of 1 micron or less.

A third class uses voltage to define waveguides. However, this class similarly has problems typical of those occurring with the second class of processes. In addition, this class has the further disadvantage of requiring the application of electric power to define the regions, which is highly undesirable.

In addition, whatever form of waveguide, collimator or coupler is used, if such devices are used in connectors, they must be able to withstand the stresses of repeated connecting to and disconnecting from a mating part without incurring damage or detrimentally affecting the accurate fiber alignment necessary for proper operation.

Thus, there remains a need in the art for high accuracy, low loss waveguides or couplers that can be manufactured on a commercial production scale and can stand up to repeated connectorization.

SUMMARY OF THE INVENTION

We have created a processing and fabrication technique for multi-piece ferrule technology that satisfies the different needs in the art. With our approach, a female format high-precision ferrule piece used in a female side of a device or connector is modified so that alignment pins (also referred to as guide pins) from a male format component, with which the female side will mate, do not damage the high precision piece.

By applying the teachings herein, fabrication of optical coupling and waveguiding elements according to a simple, but highly accurate, processing scheme is made possible. Moreover, these optical coupling and waveguiding elements exhibit extremely low loss of light through the structures, particularly where the light path includes bends, turns or tapers.

Advantageously, the technique is scalable, permitting concurrent manufacturing of multiple such devices on individual wafers, irrespective of wafer diameter, the only limitations being the number and size of the devices that will fit within a wafer's area and/or the number of wafers that can be concurrently etched and/or oxidized. Such limitations however, are independent of the invention.

By using our approach, optical coupling and waveguiding elements can be made at a lower material cost, in a highly accurate manner, on a production scale previously unavailable, and in a manner that is not overly labor intensive.

Moreover, the technique allows the creation of optical elements that provide additional benefits because they can be fit into a connector, may or may not hold optical fibers, and can add a third dimension of freedom. This enables the construction of not only fiber holding elements, but also collimator arrays, Y branch, two-dimensional waveguides, and three-dimensional optical integrated circuits.

One aspect of the invention involves a female format connector, usable for connection with a male format connector having at least one alignment pin. The female format connector has a housing, a ferrule, contained within the housing, comprising at least one high-precision piece coupled to a low precision piece. The low precision piece has a first alignment opening dimensioned to accept the alignment pin of the male format device. Prior to being coupled to the low precision piece, the at least one high-precision piece has multiple fiber holes and a second alignment opening. The first and second alignment openings are sized and positioned to provide accurate alignment between the high-precision piece and the low precision piece during coupling of the high-precision piece and the low precision piece to each other. After coupling, the high-precision piece is modified such that the second alignment opening after modification is larger than the second alignment opening prior to the coupling.

Another aspect of the invention involves a female format connector, usable for connection with a male format connector having at least one alignment pin. The female format connector has a housing, a ferrule, contained within the housing, comprising at least one high-precision piece coupled to a low precision piece. The low precision piece has a first alignment opening dimensioned to accept the alignment pin of the male format device. Prior to being coupled to the low precision piece, the at least one high-precision piece comprises multiple fiber holes and a wall surface defining a second alignment opening. The first and second alignment openings are sized and positioned to provide accurate alignment between the high-precision piece and the low precision piece during coupling of the high-precision piece and the low precision piece to each other. After coupling, a portion of the high precision piece is removed.

A further aspect of the invention involves a method of forming a female format ferrule involves coupling a high precision piece, having a first wall defining a first alignment hole, to a low precision piece, having a second alignment hole, the first and second alignment holes being sized to accept a common alignment pin for maintaining accurate alignment between the high precision piece and the low precision piece during the coupling, and after the coupling, removing at least some of the first wall.

These and other aspects described herein, or resulting from the using teachings contained herein, provide advantages and benefits over the prior art. For example, one or more of the many implementations of the inventions may achieve one or more of the following advantages or provide the resultant benefits of: longevity through repeated connectorizations, ease of insertion into a large format ferrule, high yield, low cost assembly, high precision, design scalability, application scalability, integration into standard commercial connectors, compatibility with commercial connector through-hole pin-placement, manufacturability in a mass-production wafer scale process, compatibility with the thermal coefficient of expansion of silicon chips used for transmission and reception of data, lower material cost, lower labor cost, high two- and three-dimensional accuracy (since etches can be placed with lithographic precision and oxidation further increases this precision), pieces can be stacked arbitrarily and/or large numbers to make waveguides which change in two- or three dimensions along their length, collimated couplers, optical routers, etc . . . , individual wafer thickness is irrelevant, so cheaper, less controlled material can be used, stacking on a wafer basis rather than on a piece basis to allow for integration on a massive scale.

Additional advantages achievable in some variants include: the ability to easily create highly accurate two-dimensional and three-dimensional light directing structures inexpensively, through the use of commercially available silicon wafers, since silicon wafers of exacting thickness are widely available; ease of manufacture, since patterning and etching of silicon can be accomplished to very accurate sizes and depths; wafer scale manufacturability, because the processes used are all compatible with current wafer scale fabrication techniques; and, creation of very high-confinement optical structures, having smooth sidewalls of a highly uniform, extremely controllable refractive index material, so that almost all light entering the resultant guide structure will be transmitted through it.

The advantages and features described herein are a few of the many advantages and features available from representative embodiments and are presented only to assist in understanding the invention. It should be understood that they are not to be considered limitations on the invention as defined by the claims, or limitations on equivalents to the claims. For instance, some of these advantages are mutually contradictory, in that they cannot be simultaneously present in a single embodiment. Similarly, some advantages are applicable to one aspect of the invention, and inapplicable to others. Thus, this summary of features and advantages should not be considered dispositive in determining equivalence. Additional features and advantages of the invention will become apparent in the following description, from the drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded view of a commercial connector assembly;

FIG. 2 shows an example connector hole and fiber;

FIG. 3 shows fibers not centered within holes of FIG. 2;

FIG. 4A shows a one-dimensional fiber array having fibers placed in V-Grooves etched into a piece of silicon;

FIG. 4B shows a stack of two one-dimensional fiber arrays of FIG. 4A;

FIG. 4C shows a hypothetical large format stack of three one-dimensional fiber arrays of FIG. 4A;

FIG. 5 shows an example of a low-precision piece in accordance with the invention;

FIG. 6 shows an example of a low-precision piece that is also part high precision piece;

FIG. 7 shows an example wafer created using one variant of the technique described herein;

FIG. 8, shows a silicon wafer created using another variant of the technique described herein;

FIG. 9 shows a silicon wafer created using another variant of the technique described herein having a feature for accurate alignment of the wafer relative to another wafer and/or holding of the wafer;

FIG. 10A shows an example high precision piece made using one variant of the technique described herein;

FIG. 10B shows an example high precision piece incorporating microlenses, made using another variant of the technique described herein;

FIG. 11 shows a high-precision piece set up to mount flush on a face of a low-precision piece;

FIG. 12 shows a tapered piece having a potentially large angle of insertion;

FIG. 13 shows one approach to ensuring that an angle of insertion is minimized;

FIG. 14 shows a second approach to ensuring that an angle of insertion is minimized;

FIG. 15 shows a third approach to ensuring that an angle of insertion is minimized;

FIG. 16 shows a variant comprising two high precision pieces and a chamber;

FIG. 17 shows another variant comprising two high precision pieces and a chamber;

FIG. 18 shows one hole for a high-precision piece superimposed over an optical fiber;

FIG. 19 shows two fiber holes of the same size as in FIG. 18 on different high precision pieces according to a variant of the invention;

FIG. 20 shows the holes of FIG. 19 holding the optical fiber of FIG. 18 where the offset is equally divided between both pieces;

FIG. 21 shows one example of a three piece holder approach;

FIG. 22A shows four wafer pieces or slices with a two dimensional array of holes in the center of each slice;

FIG. 22B shows the wafer slices of FIG. 22A in stacking order;

FIG. 22C shows the stack of FIG. 22B being aligned on alignment pins;

FIG. 22D shows the stacked wafer slices of FIG. 22C connected to form a high precision waveguide piece;

FIG. 23 shows a series of semiconductor wafer pieces fabricated with holes nearly the same size along with cutaway views of two variants thereof;

FIG. 24 shows one example tapering waveguide variant;

FIG. 25 shows an example of a two dimensional array of optical Y branches created using one variant of the techniques described herein;

FIG. 26A shows a more complex, combination application of the techniques described herein;

FIG. 26B shows a microlens array stacked with two high precision pieces and a low precision piece to create an ferrule compatible with an MTP, MPO, MPX or SMC style connector;

FIG. 26C shows a single optical device focussing light between a device and a single mode fiber using the arrangement of FIGS. 26A and 26B;

FIG. 27 is a photograph of a high precision piece created according to one variant of the techniques described herein;

FIG. 28 is a photograph of the piece mounted in a low precision piece as described herein showing the alignment pins;

FIG. 29 is a photograph, in 3/4 view of a ferrule for use in an MTP connector superimposed against a penny;

FIG. 30 is a photograph of a fully assembled MTP connector as described herein having 72 light carrying fibers;

FIG. 31 shows one class of waveguide;

FIG. 32 shows another class of waveguide;

FIG. 33 shows a hybrid of the classes of waveguides of FIG. 31 and FIG. 32;

FIGS. 34A-34C are example variants for avoiding stressing a high precision piece in a female connector;

FIG. 35 is an alternative example of a variant for avoiding stressing a high precision piece in a female connector;

FIG. 36 is an additional alternative example of a variant for avoiding stressing a high precision piece in a female connector;

FIG. 37 is a further alternative example of a variant for avoiding stressing a high precision piece in a female connector;

FIG. 38 is a top and side view of a portion of a wafer where the openings of holes have been reduced by plating, or treatment with a reactive gas;

FIG. 39 is a set of thickness vs. time curves for the oxidation of silicon based upon the Deal-Grove equation;

FIG. 40 is an example of the through-hole format light guiding structures;

FIG. 41 is an example of a waveguide format light guiding structures;

FIG. 42 is an example of a piece combining through-hole and waveguide formats;

FIG. 43 is an example of a more complex geometry light guiding structure combining through-hole and waveguide formats; and

FIG. 44 is a photograph of a cross section of a guide structure made using the through-hole format.

DETAILED DESCRIPTION

Overview

In overview, the technique uses one or more high-precision pieces that can be combined with a low precision piece to form a ferrule-like unit and then integrated into a commercial connector as the ferrule the connector is designed to receive.

Low Precision Piece Creation

An example of a low-precision piece 500 is shown in FIG. 5. As shown, this particular shape piece is designed in the shape of a ferrule opening in an industry standard connector apparatus so it can be inserted into a commercial connector, for example, in place of the ferrule 102 of FIG. 1. In practice, this currently means the piece should typically be shaped to dimensionally fit into at least one of an MTP or MPO or MPX or SMC style connector. Depending upon the particular variant, the low-precision piece 500 is manufactured by, for example, a polymer molding technique, for example, injection molding, transfer molding, or by some other molding, milling or forming technique. In some variants, the material used for injection molding is a glass filled epoxy, although other epoxies or plastics can be used. Alternatively, in other variants, the material is either metal or some other moldable or millable material.

The low-precision piece is manufactured to the outer dimensions to allow it to be properly inserted into the desired connector. In addition, it typically has an opening 502 that is large enough to receive the high precision piece(s).

In some variants, the "low precision" piece may also be, in part, a high precision piece, for example, as shown in FIG. 6, if the low precision piece 600 is made out of metal and has a thin face 602 that can be processed with holes 604 as described below. However, it is expected that such variants will lack many of the advantages of using separate low- and high precision pieces, but may achieve other advantages or benefits due to the particular application it is being used for or in.

High Precision Piece(s) Creation

By way of representative example, the technique for creating the high-precision piece(s) will now be described using a wafer of silicon as the starting point.

While in some variants, silicon is used as the starting material for forming the high-precision piece(s), in other variants, materials such as quartz, sapphire, ceramics, glass, other insulators, other semiconductor wafer compounds, polymers such as polyimide, or metals, such as aluminum or tungsten or alloys, can be used.

The overall manufacturing process for the high-precision piece(s) proceeds as follows:

a) The wafer is processed into a series of chips by etching holes through the wafer using either an etching or drilling process. In some variants, this is done through a semiconductor lithography process combined with an etching technique. In other variants, laser drilling is used. The holes are each of specific sizes and, where appropriate, axially offset at a specific angle relative to the plane of the wafer (or piece once cleaved). Features such as holes for alignment pins or bumps and recesses for precision mating are also created, where appropriate. The wafer contains many copies gf the chips that will be needed to make a particular high precision piece, for example, fiber holding piece, a collimator, many-to-one taper or Y branch. The pieces to build up an element of a particular type can be processed on a single wafer or by making several wafers, each having some of the pieces needed to make the component. In either case, the resultant wafer scale batch processing is the same and saves costs.

The holes are classified into two groups: those which are made for fiber insertion and/or receiving an optical epoxy, and those that are for alignment and/or placement into a connector. Although in the ideal case, the holes are perfectly cylindrical, frustoconical, obconic or funnel shaped, in practice the holes may only be substantially cylindrical, frustoconical or funnel shaped. However, those deviations, for purposes of the processes described herein, are considered negligible since they are either a) much smaller than the optical fiber diameter and hence have no meaningful effect on placement or performance in the case of fiber holding embodiments, or (b) virtually irrelevant in the case of waveguide embodiments.

In addition, for the variants described herein, to facilitate fiber placement or create certain waveguide arrangements, in some cases it may be desirable to intentionally use cylindrical, frustoconical, obconic or funnel shaped holes that have a substantially oval, substantially egg shaped or substantially elliptical cross section perpendicular to their axes (i.e. they are not round). In other variants, different shaped grooves or grooves in some combination with holes are used.

FIG. 7 shows an example wafer 700 created using one variant of the technique described herein. Each piece 702 (also called a slice) contains a central group of small holes 704 (in this case 72 per piece) for fibers and larger holes 706 on the left and right sides of each piece for alignment of the piece relative to some other piece. Typically, the number of holes will be equal to or some multiple of the number of fibers in a commercial optical fiber bundle, for example, bundles of 6, 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132 or 144 fibers.

FIG. 8, shows a silicon wafer 800 created using another variant of the technique described herein. As shown in FIG. 8, there are small holes 802 in each piece 804 within the central area of the wafer for fibers or optical epoxy and large holes 806 near the edge of the silicon wafer for alignment on a wafer basis.

Additionally, or alternatively, the alignment holes can be part of each piece and specifically be spaced so that the piece may be inserted into an MTP, MPO, MPX, or SMC or other widely available style commercial connector, such as shown in FIG. 1, as part of or in place of a ferrule and also aligned using alignment pins 110 that are on a part 112 of the connector itself.

Additionally, other holes or features may be etched into the piece to allow the insertion of epoxies, solder, or some other fastening agent to hold the piece to the low precision piece or so that two or more of the pieces can interlock with each other.

Depending upon the particular variant, in some cases, one or more of the alignment holes on one or more of the components may optionally have an oblong or oval shape to allow some freedom of movement.

Depending upon the particular variant, the particular grooves or holes may have straight or tapered sidewalls.

In some variants using straight holes, the holes are created by laser drilling. In other variants, the straight holes are formed using an etching process, for example, anisotropic hole etching. By way of example, for a silicon wafer, anisotropic deep/via hole etching of silicon is performed by photoresist patterning the wafer according to the desired hole placement and etching using the Bosch process in a high-density plasma reactor such as either an electron cyclotron resonance (ECR) or inductively coupled plasma (ICP) reactor. The Bosch process is based off of a time multiplexing scheme separating the etch (SF6) and passivation (C4F8 sidewall protection) cycles. The etch causes scalloping on the silicon sidewalls and sharp edges at the base of the via but the profile produces nice straight holes/vias. Since the scalloping creates edges that are too sharp for fiber insertion without a guiding structure to help the fiber avoid the edges at the base of the structure, clean-up etching is required.

Both the clean up etching process and the process of creating tapered holes is essentially the same. In addition to the Bosch process, for clean up and creating tapered holes, an isotropic (non-directional) silicon wet etch (HF:HNO.sub.3, 1:1) is used. This produces smooth, damage free tapered surfaces. In addition, the isotropic wet etch eliminates and/or reduces the scalloping and sharp edges created from the Bosch process, making fiber insertion easier and more reliable.

Alternatively, holes/vias can be made with a combination of etching with KOH and the Bosch process. Both KOH etching and Bosch process etching are well understood and used widely. Etching of silicon using KOH is also well known and is used in the micro-machining industry and the micro electro mechanical systems (MEMS) area.

In the alternative variants, a Bosch etch is used on the front side of the (100) silicon wafer. Then a SiN.sub.X stop layer for the KOH is deposited in the Bosch etched front side hole. The back side of the wafer in then photoresist patterned in alignment with the front side of the silicon wafer. The back side is then wet etched with KOH. The SiN.sub.X is then removed. The scalloping and sharp edges are then smoothed with HF:HNO.sub.3, (1:1). This process produces a via hole that is both sloped and anisotropic with a sidewall profile that facilitates fiber insertion.

The process is similar to create the pieces using other materials except, the specific etch process used will differ based upon the particular material being used. Since techniques for etching and/or drilling of holes in other materia