Abstract:
Presented are structures and methods by which to align fiber optics side-by-side or end-to-end; to align fiber optics to features in supporting substrates or to objects on supporting substrates; and to align substrates to one another. Alignment grooves are included with particular properties that permit the groove to participate in the moving of a fiber into alignment. A fiber is used in a tapered channel as an alignment key enabling accurate tuning of an optical coupling ratio and efficiency of fiber-optic side-polished couplers, multiplexers, taps, splitters, joiners, filters, modulators and switches. Substrates made of crystal are presented having variable-width grooves and in some cases also variable-depth grooves which form guiding and constraining pathways for fiber optics. The reader will readily appreciate the novel structures and methods applicable to realize manufacturable fiber optics to perform all-fiber photonic functions.

Description:
BACKGROUND OF THE INVENTION 
     This invention generally pertains to alignment and assembly methods for fiber optics with supporting substrates, and to fiber optic devices that are implemented with side-polished fiber optics. 
     There are no prior art methods and devices published, or on the market, for utilizing the precision of crystal structure(s) to achieve ultra-precise alignments of interacting side-polished fiber. What is known in the prior art deals with implementation of single-fibers that are side-polished to implement two-port photonic functions requiring no side-by-side critical alignment to other fibers. This known art is taught in the U.S. Pat. Nos. 5,809,188 “Tunable optical filter or reflector” and 5,781,675 “Method for preparing fiber-optic polarizer”, both by Tseng. Tseng&#39;s patents teach the use of a variable-depth V-groove etched in a silicon crystal substrate to achieve both a) precise control of the remaining side-wall thickness left on a side-polished fiber and b) an arcuate path for the fiber which enables the side-polished region to be of a controlled length. Tseng teaches the use of silicon substrates with 100 crystal orientation at the surface to achieve superior precision in the control of remaining sidewall thickness. He does not teach methods or devices for facilitating the placement of a fiber into a groove of width comparable to the diameter of the fiber. He does not teach means by which to align two fibers end-to-end. 
     Earlier art teaches side-polished fiber optics made by retaining the fiber within a groove cut into the surface of a non-crystalline material such as glass or quartz. This art can be found in such U.S. Pat. Nos. as 4,493,528 “Fiber optic directional coupler”, 4,536,058 “Method of manufacturing a fiber optic directional coupler”, 4,556,279 “Passive fiber Optic Multiplexer”, 4,564,262 “Fiber optic directional coupler”, 4,601,541 “Fiber optic directional coupler”, 6,011,881 “Fiber-optic tunable filter”, all by Shaw. This art also teaches the requirement of one side-polished fiber along side of a second side-polished fiber, but fails to disclose any means of mechanical self-alignment. 
     Earlier art also includes devices and methods of aligning optical components using constant-depth V-grooves in the surfaces of silicon substrates. Three examples include U.S. Pat. Nos. 5,633,968 “Face-lock interconnection means for optical fibers and other optical components and manufacturing methods of the same” by Sheem, 4,475,790 “Fiber optic coupler” by Little, and 4,802,727 “Positioning optical components and waveguides” by Stanley. Another U.S. Pat. No., 4,688,882 “Optical contact evanescent wave fiber optic coupler” by Failes, not only references some of the earliest work of constructing substrate-supported, side-polished, fiber-optic devices, but also describes some of the limitations involved. This patent by Failes teaches a method of achieving a fused coupling between side-coupled fibers that doesnt&#39;t require the index-matching coupling fluid of previous works. Failes did not offer any approaches to precisely and rigidly support the fibers through intimate contact with respective hard substrates. 
     Another relevant prior art is that of U.S. Pat. No. 5,187,760 “Wavelength selective coupler for high power optical communications” by Huber. This patent references little of the above prior art, and furthermore, to this inventor&#39;s opinion, seems to be what is called a “non-enabling” patent because it does not provide the reader with information on how to practically implement the structures described and claimed. It describes the use of gratings with which to couple light within a wavelength band between a first fiber and a second fiber. In fact it also describes doing this at more than a single location along the length of the second fiber, wherein the multiple first fibers have respective gratings with different wavelength bands. What is needed is a practicable way in which to implement such structures and devices successfully. 
     Additional prior art on positioning of fiber optics on substrates is found in the technology of Microelectronic Mechanical Systems (MEMS). One reference to such technology is that of “MEMS Packaging for Micro Mirror Switches”, by L. S. Huang, S. S. Lee, E. Motamedi, M. C. Wu, and C. J. Kim, Proc. 48th Electronic Components &amp; Technology Conference, Seattle, Wash., May 1998, pp. 592-597. 
     None of the above art teaches methods or devices for facilitating the placement of a fiber into a groove of width comparable to the diameter of the fiber. And none of the above prior art teaches methods or devices to facilitate bringing two fibers end-to-end using a common substrate. Straight and constant-width V-grooves are commonly used in prior-art fiber optic devices, assemblies, and products, but none provide devices and methods by which, in the first place, to facilitate bringing the fiber easily into alignment with these grooves. And fiber optic connectors are common in the prior art with which to bring two fibers into end-to-end alignment, but not using a common substrate and always involving numerous interrelating parts. For example, see U.S. Pat. No. 5,659,647 “Fiber alignment apparatus and method” by Kravitz, U.S. Pat. No. 4,919,510 “Optical connector and method” by Hoke, and U.S. Pat. No. 4,682,848 “Underwater-mateable optical fiber connector” by Cairns. 
     Practicable methods and devices are needed that manifest a) easy assembly of fibers into precision grooves in supporting substrates; b) easy co-alignment of two independent, precision substrates; and c) easy and precise alignment of fibers end-to-end or of a fiber to a planar waveguide. 
     Practicable methods and devices are needed that easily manifest precision alignment of fibers side-by-side, and with controlled positional tuning as necessary for fiber optic devices with three or more ports (such as fiber-optic couplers, add-drop multiplexers, taps, splitters, joiners, filters, modulators and switches). 
     What is also needed is a means to reduce the stress experienced by a fiber optic where it enters or leaves a substrate groove. 
     BRIEF SUMMARY OF THE INVENTION 
     Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods and devices and combinations particularly pointed out in the appended claims. 
     The object of the invention is to provide new devices and methods by which to align fiber optics to one another, either side-by-side or end-to-end, or to features in supporting substrates (and devices or features on those substrates), and to align substrates to one another. It is also the object of the invention to provide devices that include alignment grooves having particular alignment-facilitating properties that participate in the moving of a fiber into an alignment groove. The object of the invention is also to include properties that may reduce stress to a fiber where it enters or leaves a supporting substrate. And the object of the invention is to provide facilitating means for using an alignment keying fiber to enable accurate tuning of optical coupling ratio and efficiency of 4-port devices (including 3-port devices) such as fiber-optic side-polished couplers, multiplexers, taps, splitters, joiners, filters, modulators and switches. 
     These and other objects of the invention are provided by a novel use tapered grooves in supporting substrates, and particularly in crystal substrates having variable-width grooves and in some cases also variable-depth grooves-which are fabricated by etching to form guiding and constraining pathways for fiber optics. The reader will readily appreciate the novel methods and structures used to realize manufacturable fiber optic (and planar optic) devices for performing needed all-fiber photonic functions. Some of the achievements of this invention include the following: 
     1. A uni-directionally or bi-directionally tapered V-groove for enabling easy positioning of fibers into a precision narrow groove. 
     2. A precise and microscopically small tapered channel for enabling easy insertion and positioning of a fiber into a precision narrow channel. 
     3. Substrates with tapered grooves leading to more narrow linear grooves for enabling a fiber to be used as a means of co-aligning a pair of these substrates over a common surface. 
     4. Substrates with tapered grooves on one surface (face) enabling a fiber to be used as a guide to precisely locate the face of one substrate to the face of another. 
     5. A bi-directionally tapered groove used for easy alignment of two fibers end-to-end. 
     6. Substrates with tapered grooves enabling a first fiber in a first substrate to be located end-to-end with a second fiber in an overlapping second substrate. This also allows for precise control of the rotation of the fibers relative to one another, such as when connecting polarization-maintaining fibers end-to-end. 
     7. Substrates as in 6 above but which also provide for the substrates to cover over the end-to-end fiber interconnection. 
     8. Method of adjusting interaction length and coupling-ratio in a 4-port side-polished fiber optic device (e.g. coupler or add-drop multiplexer) through the use of an easily positioned fiber as a sliding key in a parallel pair of face-to-face, uni-directionally or bi-directionally tapered grooves. 
     9. Terminations for fiber optic alignment grooves that provide for minimizing stress and strain at the entry and exit edges of the grooves. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings incorporated in and forming apart of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings: 
     FIGS. 1A and 1B show both a perspective view and a cross-sectional view of a first of two prior arts with structure and means for positioning a fiber within a groove in order to maintain a two-dimensional relationship relative to features in a supporting substrate. 
     FIGS. 2A and 2B show both a perspective view and a cross-sectional view of a second of two prior arts with structure and means for holding a fiber within a groove in order to maintain a two-dimensional relationship relative to features in a supporting substrate. 
     FIG. 3 shows a new structure and means by which to easily guide a fiber into a target groove of a supporting substrate by a structural fixture comprised of a tapered groove in a separate substrate used as a placement guide. 
     FIG. 4 shows a new structure and means by which to more easily locate a fiber into a target groove of a supporting substrate wherein the guiding means is a tapered groove portion located within the same substrate and contiguous with the target groove portion. 
     FIG. 5 shows supporting and guiding substrates that demonstrate alternative shapes for guiding grooves. 
     FIG. 6 shows a guiding channel constructed of two guiding and locating grooves positioned face-to-face. 
     FIG. 7, shows means by which to co-align grooves in two separate substrates end-to-end. 
     FIG. 8 also shows means by which to co-align a first substrate, having a fiber that is itself aligned and held within this first substrate, to a terminated groove within a second substrate. 
     FIG. 9, shows prior art for aligning two fibers end-to-end by using edges and surfaces of their supporting substrates to reference against an alignment fixture. 
     FIG. 10 shows bi-directionally-tapered grooves in a single substrate used to align two fibers end-to-end. 
     FIG. 11 shows both a bi-directionally-tapered groove and a uni-directionally-tapered groove used in combination to align two fibers end-to-end. 
     FIG. 12, similar to FIG. 11, also shows both a bi-directionally-tapered groove and a uni-directionally-tapered groove used in combination to align fibers end-to-end, but wherein the two substrates involved end up covering up the interface between the two fiber ends. 
     FIGS. 13A and 13B show how varying the widths of face-to-face grooves, and alignment with a slidable fiber key, can facilitate the tuning of optical coupling ratio and efficiency in a 4-port fiber optic made with side-polished fibers. This structure permits tuning by way of either or both linear translation and limited rotation. The varying widths allow the limited rotation. FIG. 13 also shows how a varying width and depth groove can reduce stress in a fiber where it enters or leaves the groove. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Having summarized various aspects of the present invention, reference will now be made in detail to the description of the invention as illustrated in the drawings. While the invention will be described in connection with these drawings, there is no intent to limit it to the embodiment or embodiments disclosed therein. On the contrary, the intent is to cover all alternatives, modifications and equivalents included within the spirit and scope of the invention as defined by the appended claims. 
     Reference is now made to FIG. 1, which consists of two parts, FIG.  1 A and FIG. 1B, that illustrates a prior art for placing and positioning a fiber within a groove in the surface of a substrate. The groove is used for positioning the fiber in two dimensions, one within the plane of the surface of the substrate and the other perpendicular to that same surface. In addition, the groove orients the direction of the fiber to lie parallel to the plane of the surface as well as in a particular direction within the surface, that of the direction of the groove. FIG. 1A shows a fixture and fiber arrangement  1  comprised of a fiber  5  and a substrate  2  having a groove  3  located on a planar surface  4 . The fiber S is not easily placed within the groove  3  since the diameter of the fiber is comparable to the width of the groove  3 . In the prior art, the placement of the fiber  5  into the groove  3  involves rolling the fiber  5  along the surface  4 . This is done while attempting to maintain the fiber  5  parallel to the groove  3  and searching for the condition that the fiber will drop into the groove  3 . Once in the groove  3 , the fiber  5  is finally located in two-directions and two rotations relative to the groove  3 , and consequently in relation to both the substrate  2  and its surface  4 . This operation of locating the fiber  5  within the groove  3  is sometimes unduly time-consuming and can additionally require maintaining the fiber  5  in a straight configuration. 
     For the fiber  5  to be located precisely relative to features (not shown) on the surface  4 , reference edges  6 , or another surface  7  of the substrate  2 , the geometry of the groove  3  must be precise in relationship to that of the fiber  5 . If it is the intention that the groove  3  holds the fiber  5  in a straight configuration, the groove must be straight and its surfaces  8  and  9  free of bumps, burrs, contaminating objects, and other position-disturbing defects. The best known prior art for achieving these objectives for straightness and precision is to use a V-groove anisotropically wet-etched into the 100 surface of a cubic crystal such as silicon (Si)or gallium arsinide (GaAs). The term used here “100” is a Miller index of crystal orientation. Other crystalline materials can also be used such as, but not. limited to, lithium-niobate (LiNbO3), potassium dihydrogen phosphate (KDP), lithium tantalate (LiTaO 3 ), barium titanate (BaTiO 3 ), silicon germanium (SiGe), indium phosphide (InP), gallium indium arsinide (GaInAs), and crystals of III-V compounds in general, or even some organic crystals. 
     FIG. 1B shows the geometry of a circular cross-section of a perfect fiber  10  situated in a V-groove  11  formed in the surface  12  of a 100 silicon crystal substrate  13 . The surfaces  14  and  15  defining the V-groove  11  are 111 planes of the crystal and form the included angle of approximately 70.53 degrees. The direction of the groove is parallel to 110 planes. It is therefore plain to see that the width and angle at the bottom of the groove determine a depth of the V-groove  11 , and this result, along with the fiber diameter, determines the position of the axis  16  of the fiber  10 . The position of the fiber  10  is thereby precisely determined by simple geometric relationship relative to the groove  11 , and consequently to the surface  12  and therefore the substrate  13 . It is important to note that the flatness of 111 crystal faces defining the V-groove facilitate accurate placement of a fiber. It is equally important to note that the flatness of the 100 crystal plane defining the top surface  12  aids in aligning the fiber with other objects and features also located relative to this surface  12 . These other features may include such items as a light source, a detector, a grating, a diffractive optic, a non-linear material, a reflector, a grin lens, a spherical lens, a refractive prism, a polarizer, a filter, an isolator, a circulator, a modulator, an attenuator, a coupler, a modulator, a multiplexer, a switch, a planar optical circuit, and an integrated circuit. 
     FIG. 2, which is composed of two parts, FIG.  2 A and FIG. 2B, illustrates another prior art means of locating a fiber relative to a surface. The prior art illustrated in both FIG.  2 A and FIG. 2B is similar to that just described and illustrated with FIG.  1 A and FIG.  1 B. What is different is the groove cross-section now is rectilinear instead of V-shaped. What is shown in FIG. 2A is a fixture and fiber  21  comprised of a fiber  25  and a substrate  22  having a groove  23  located on a planar surface  24 . As before, the fiber  25  is not easily placed within the groove  23  since the diameter of the fiber is comparable to the width of the groove  23 . In this prior art also, the placement of the fiber  25  into the groove  23  involves rolling the fiber  25  along the surface  24 . This is done while attempting to maintain the fiber  25  parallel to the groove  23  and searching for the condition that the fiber will drop into the groove  23 . Once in the groove  23 , the fiber  25  is finally located in relation to the groove  23 , and consequently in relation to both the substrate  22  and its surface  24 . This operation of locating the fiber  25  within the groove  23  is also sometimes unduly time-consuming and can additionally require maintaining the fiber  25  in a straight configuration. 
     For the fiber  25  to be located precisely in 2-dimensions relative to features (not shown) along the surface  24 , reference edges  26 , or another surface  27  of the substrate  22 , the geometry of the groove  23  must be precise in relationship to that of the fiber  25 . If it is the intention that the groove  23  holds the fiber  25  in a straight configuration, the groove must be straight and its surfaces  28 ,  29  and  30  free of bumps, burrs, contaminating objects, and other position-disturbing defects. As with V-grooves, rectilinear grooves can be fabricated into crystal substrates, but the etching process steps, wet or dry, are less well defined as for V-grooves that are shaped by  111  surfaces. The sidewall surfaces  28  and  29  are prone to over-etching, while the bottom  30  depends more sensitively on etch-rates and etch times. 
     FIG. 2B shows the geometry of a circular cross-section of a perfect fiber  40  situated in a rectilinear, square-bottomed groove  41  formed in the surface  42  of the substrate  43  by side-wall surfaces  44  and  45  and by the bottom surface  47 . It is therefore plain to see that the width and depth determine, along with the fiber diameter, determine the position of the axis  46  of the fiber  40 . The position of the fiber  40  is thereby less precisely determined than by a V-groove formed by ill crystal planes (which have a relatively slow etch rate) and the single variable of V-groove width (see FIG.  1 B). In the case of a rectilinear, square-bottomed groove  41 , the position of the fiber  40  depends upon groove width and depth, both of which are harder to control than the one V-groove variable of width. 
     For more information about crystal geometry, crystal-plane orientations, Miller indices, and etching, reference can be made to standard text books known in the integrated circuit processing industry. For information on prior.art for orienting photolithographic masks precisely to crystal planes, see for example: “MEMS Packaging for Micro Mirror Switches”, by L.S. Huang, S. S. Lee, E. Motamedi, M. C. Wu, and C. J. Kim, Proc. 48th Electronic Components &amp; Technology Conference, Seattle, Wash., May 1998, pp. 592-597. 
     FIGS. 3 through 6 illustrate the use of new crystalline structures and methods that facilitate the placement of a fiber into an alignment groove to locate it relative to the substrate surface that contains the groove. As above, this achieves location of the fiber along two translational dimensions and about two rotational axes, but with greater ease and precision. 
     FIG. 3 shows a fiber being positioned from a first position  51  to a second position  51 A within a tapered groove  53  formed in the top surface  54  of a first substrate  55 . Pre-aligned with the substrate  54  is a second substrate  56  having a targeted (i.e. destination) groove  57  formed in its top surface  58  with a constant groove width. In this situation, the first substrate  55  and tapered groove  53  are being used as a tool for facilitating the placement of the fiber  50  into the groove  57  on the second substrate. The groove  57  is of constant width and cross-section, and is sized to hold a fiber partially above the surface  58  by having a width only slightly larger than the diameter of the fiber  51 . It is easy to understand that with the small cross-sectional dimensions of a fiber  51  and the groove  57 , it would be difficult to lay the fiber  51  into such a groove without the aid of a tool, such as comprised of the tapered groove  53  in the substrate  55 . 
     Referring still to FIG. 3, the preferred process for placing a fiber  50  into a targeted alignment groove  57  involves the steps of: 
     a) pushing the side of the fiber  50  against the edge  59  of the surface  54  containing the tapered groove  53 ; 
     b) sliding (or rolling) the fiber  50  along the edge  59  toward the largest opening of the tapered groove  53 , 
     c) when the fiber  50  falls within the opening to the groove  53 , which in this example is seen to have a V-shaped contour to the cross-section perimeter of the groove, and while still pushing the fiber  50  against the edge  59  which is seen to include this contour, tilting the fiber  50  toward parallelism with the groove-containing surface  54 ; and 
     d) pressing the fiber  50  into the targeted alignment groove  57 . 
     FIG. 4 shows a device and method similar to that just described in FIG.  3 . Although here the two substrates  55  and  56  of FIG. 3 are combined into a single substrate  64 . And an initial part of the groove  63  is tapered from a larger width at its opening to a smaller-width, followed by a section  65  of constant width at the other end of the surface  66 . Here the fiber  60  is initially in a tilted-up orientation  6   1 . It is then moved into the wider opening of the tapered section of the groove  6 , and then rocked downward before being finally pressed into the later portion  65  of the groove where it is in the position  61  A parallel to the surface  66 . Preferably, the length-wise contour of the groove  63 , in changing from the wider portion to the narrower portion  65 , is a smooth one. Also shown in FIG. 4, under-etching can create grooves still having accurately sloped sides but having a flat bottom  68  where the groove widths are larger than a desired threshold. 
     If in FIGS. 3 and 4, the substrates  55 ,  56  or  64  are made of cubic crystal having respectively their top surfaces  54 ,  58  and  66  comprised each of 100 surfaces, variable or fixed width and depth V-grooves can be patterned and etched with great precision. The general lengthwise directions of these V-grooves are parallel to 110 planes. The sidewalls comprising the V-shape of a constant-width groove will be of constant depth also, and will lie in, and be defined by, planes of 111 orientation. The sidewalls of a variable width V-groove will not wholly lie in 111 crystal planes, but the V-shape, in any cross-sections taken perpendicular to the groove axis, will be defined by a pair of intersecting 111 crystal planes. It is very important to observe that this constraint by the crystal planes on the shape of the V-grooves, whether they be of constant width or not, is an important property. This constraint by the crystal planes can be exploited by the current invention to achieve accurate and precise location of a fiber on a surface and in relationship to other objects and features also located on the same surface. Tapered-width and depth V-grooves can be accomplished with a large variety of contour profiles, including segmented and smooth profiles. The lithographic pattern used as the etch mask can be constructed with any of a variety of contours including linear, parabolic, hyperbolic, elliptical, and arcuate. 
     FIG. 5 shows how the choice of the profile shapes for etch masks can provide for smoother interaction between a fiber and the edges of a tapered groove as the fiber is moved into place. Fibers  70  and  71  are located in linear groove portions  72  and  73  respectively. Fiber  70  enters its linear groove-portion  72  via a linearly tapered groove-portion  74 ; whereas fiber  71  enters its linearly tapered groove-portion  73  via a curvilinear tapered groove-portion  75 . It can be appreciated from FIG. 5 that the fiber  71  can be bent through a larger angle  76  than the angle  77  of fiber  70 . Whereas fiber  70 -is bent about sharp corners  78  and even  79 , fiber  71  has yet to be bent about corner  80 . Thus preferred embodiments, for minimizing potential handling stress on a fiber, would select a smoothly contoured taper. 
     FIG. 6 shows a fiber  81  as it enters a channel  82  whose entrance is large compared to the fiber diameter and shrinks deeper within the channel  82  to a section  84  of constant size comparable to the fiber size. A face-to-face pair  83  of substrates  85  and  86  forms the channel  82 . Thus a crystal structure is created that forms a precisely formed funnel that necks down to a size that can constrain and locate the fiber in two dimensions very accurately. It should be clear that this structure provides an efficient means to easily locate a fiber within a position-constraining channel. 
     FIGS. 7 and 8 describe by way of illustration that the use of tapered grooves is not limited to the easy placing and precise locating of a fiber along two translational dimensions and about two orientation axes. 
     FIG. 7 shows how a fiber can be used to bring together and align two substrates that are configured with grooves each having both tapered and linear portions, and with groove axes at least approximately perpendicular to the substrate edges that are to touch. (Let it be defined that a groove axis is a line lying in the plane of the surface containing the groove and bisecting the groove boundaries that are at this surface.) In FIG. 7, the two substrates  100  and  101  are of similar thickness and are placed on a common work-surface (not shown). In addition, these two substrates  100  and  101  each have a respective groove  102  and  103  located on their top surfaces  104  and  105 . The groove  102  is composed of a tapered portion  106  and a linear portion  107 . The groove  103  is composed of a tapered portion  108  and a linear portion  109 . The fiber  99  is bowed slightly in order to first place it within the tapered sections  106  and  108  as shown. Then it is brought down deeper into the two grooves  102  and  103 , becoming less bowed in the process. As the fiber  99  is forced downward into the grooves  102  and  103 , the substrates  100  and  101  are made by the fiber  99  to move into alignment with one-another, that is, to align the two linear portions  107  and  109  co-linear with one-another. It is then an easy matter, maintaining downward pressure on the fiber  99  to also urge the two substrates  100  and  101  together end-to-end such that the two linear portions  107  and  109  of the grooves  102  and  103  come together. Note that this operation could be performed also without the grooves having linear portions, wherein the tapered portions would span the entire distance across the respective substrate surfaces. 
     FIG. 8 shows how precision V-grooves can be used to locate a fiber in three translational dimensions. Furthermore it shows how precision V-grooves can be used to either or both locate one substrate surface in two translational dimensions against another or to locate a fiber in three translational dimensions on a substrate and at the same time control its angle of rotation about its own axis. In FIG. 8, a fiber  110  is shown being located into a precise position on a surface  111  of a substrate  112  by using a V-groove comprising a tapered portion  113  and a linear portion  114  according to previously described aspects of this invention. However, FIG. 8 also shows that one end  115  of the fiber  110  can then be shoved against a closed end  116  of the groove portion  114 . 
     Although not shown in FIG. 8, this example of a closed end  116  could just as well represent the placement of the fiber end  115  against a port of a planar waveguide constructed in the same surface  111 , or to alternative optical devices including a light source, detector, filter. Although also not shown in FIG. 8, this example of a closed end  116  could just as well represent placement of the fiber end  115  at a desired location relative to electrical or optical circuitry on surface  111 . Such an operation positions the fiber  110  in two translational dimensions within the plane of the surface  111 . It also positions the fiber  111  to lie at a determined depth in the groove relative to the surface as defined by the geometry of the fiber  110  and the groove portion  114 . The fiber  110  can be first fixed within an initially supporting substrate  117  by a groove  118  in the surface  119  of that substrate  117 . Then when the surface  119  of this substrate  117  is brought into parallelism and close proximity with the surface  111  of substrate  112 , the fiber is additionally aligned rotationally about its own axis with a predetermined value. Such rotational orientation is important when dealing with polarization-maintaining fiber optics. 
     FIGS. 9 through 12 depict various means for aligning two fibers end-to-end. FIG. 9 shows some prior art for aligning two fibers end-to-end. This prior art accomplishes end-to-end fiber alignment by using edges and surfaces of supporting substrates to reference against an alignment fixture. But the device and method suffers from the dimensional errors of imperfect substrate shapes and tolerance build-ups due to the number of parts involved and due to inaccuracies in fabricating the fiber-supporting grooves cut into the substrate surfaces. What is shown is a planar reference surface  300  of a supporting substrate  301 . Resting on this supporting substrate  301  is a second reference substrate  303  having a second reference surface  302  that is made perpendicular to the first reference surface  300 . Two fibers  304  and  305  are aligned within grooves  306  and  307  located in top surfaces  308  and  309  of fiber-supporting substrates  310  and  311 . The fiber-supporting substrates  310  and  311  are cut to reference simultaneously against both the reference surfaces  300  and  302 . Furthermore the top surfaces  308  and  309  are cut parallel to and equidistant from the plane of the supporting surface  300 . And, of the two fiber-supporting substrates  310  and  311 , the two surfaces  314  and  315  that face one-another need to be co-parallel. The grooves  306  and  307  should be accurately placed in and parallel to their respective surfaces  308  and  309 , and they should both be located an identical distance and parallel from both reference surfaces  300  and  302 . The fibers  304  and  305  should be located in their respective grooves  306  and  307 , with their ends  312  and  313  intersecting the respective planes that include the surfaces  314  and  315  of their respective fiber-supporting substrates  310  and  311 . Then the fiber ends  312  and  313  can be brought into end-to-end alignment along a common axis (common axis not shown) by simply moving the two fiber-supporting substrates  310  and  311  together, while maintaining contact between the fiber-supporting substrates  310  and  311  and the reference surfaces  300  and  302 . 
     FIG. 10 shows another device and method of the current invention, which reduces the number of parts required to bring two fibers together end-to-end along a common axis. Two fibers  320  and  321  are placed within a common groove  322  constructed from the surface  323  of a substrate  324 . The groove  322  is comprised of two end sections  325  and  326  that are tapered inward toward a common mid-section  327 . The substrate is preferably of cubic crystalline material with surface  323  being a  100  crystal plane, and the sides of the mid-section  327  of the groove  322  being defined by 111 crystal planes that form a V-cross-section to the groove. By under-etching, the groove can be made with the otherwise deeper portions having a flat bottom (not shown) instead of a sharp concave vertex. The axis of the groove  322  (as defined above in discussion of FIG. 7) is a straight line that is directed parallel to  110  crystal planes. The fibers  320  and  321  are fit into the groove from opposite end sections  325  and  326  with the method described above in describing FIG.  3  and FIG.  4 . Once the fibers are aligned in midsection  327 , they can be pushed (one or the other or both) together by sliding along the groove so that their ends  328  and  329  meet. 
     FIG. 11 shows a similar device and method as just described for FIG. 10, but the fiber  329  is first installed, rotated and fixed within a supporting substrate  330  with methods of the current invention already described as in FIG. 3 or FIG.  4 . The rotation of the fiber  321  is to orient it in a particular orientation about its fiber axis (not shown) as may be important for use of polarization maintaining fibers. The function of this additional supporting substrate  330  is to provide a reference surface  331  that can be brought flat against the supporting surface  323  and thereby determine a particular rotational orientation for fiber  321  about its own axis (axis not drawn), relative to the other fiber  320 . The end  329  of the fiber  321  can be located in the plane of the front surface  332  of the supporting substrate  330 , but this is optional. 
     FIG. 12 shows a similar device and method as just described for FIG. 11 above, but the front surface  334  of the supporting substrate  333  is, in this case, located beyond the end  328  of the fiber  321 . The advantage of thus extending the supporting substrate  323  beyond the end of its fiber  321  is that this supporting substrate  333  will end up covering both fiber ends  328  and  329 , allowing the region of fiber-to-fiber contact (not shown) to be sealed. 
     FIG. 13 is composed of two parts: FIG.  13 A and FIG.  13 B and shows how varying the widths of face-to-face grooves, as well as alignment with a sliding fiber-key, can facilitate the tuning of optical coupling ratio (and efficiency) between two fibers within a 4-port device. This device can be any of the group including couplers, add-drop multiplexers, taps, splitters, joiners, filters, modulators or switches. This tuning is accomplished by adjusting the interaction length between two evanescently coupled fibers. 
     FIG. 13A shows a tunable 4-port fiber optic device  400 , such as a coupler or add-drop multiplexer. This 4-port device  400  is comprised of two half-couplers  401  and  402  comprised in turn-of respective side-polished fibers  403  and  404  installed within respective varying-width V-grooves  405  and  406  etched into 100 crystal surfaces  407  and  408  respectively (shown face-to-face) of respective substrates  409  and  410 . The two substrates can be slid over one another in the direction parallel to the long axes (not shown) of the two side-polished areas  411  and  412 . The two side-polished areas  411  and  412  are shown at a position where they fully overlap one another. The side-polished areas  411 . and  412  of the fibers  403  and  404  have an elliptical shape with long axes parallel to the groove axes (not shown). The arrows  413  and  414  indicate the direction of motion desired for tuning coupling ratio (or coupling efficiency). 
     As illustrated in FIG. 13A, the device  400  is additionally comprised of a third fiber  415 . Fiber  415  is in a bi-directionally tapered channel  416  constructed of two additional varying-width V-grooves  417  and  418  etched into the surfaces  407  and  408 , parallel to grooves  405  and  406  but offset from them. Fiber  415  serves as an alignment key within this channel  416 , but allows for the motion described with which to tune the optical coupling ratio and efficiency of the 4-port assembly. By eliminating most of any linear portion to the channel  416 , the two half-couplers  401  and  402  may also be allowed some rotation about the region of narrowest constriction  419 . This rotation is easy to control with the substrates being of a significant scale larger than the side-polished areas and provides a tuning method alternative to strict translation  413  and  414  described above. 
     FIG. 13A illustrates yet another advantage of the bi-directionally tapered channels  416  and that formed by grooves  405  and  406 , is that the fibers  415 ,  403  and  404  will experience less chance to be bent and stressed entering or leaving the channel  416  than were the channel  416  of constant cross-section. The taper at the ends of these channels can be accentuated to help achieve additional avoidance of stress on the fibers  415 ,  403  and  404  from otherwise being bent about a sharp edge. It is important in high-bandwidth fiber optic applications, such as in modern data- and tele-communications networks, to avoid stressing or straining fibers. This is because strain-induces birefringence in the fiber and this causes polarization mode-dispersion that can result in high bit-error-rates. 
     FIG. 13B shows an end-view of the device illustrated in FIG. 13A with all similar parts identified by the same numbers, except the view is as though the fibers  415 ,  403  and  404  were terminated at the midpoints of the channels. In addition, the cores  419  and  420  to fibers  403  and  404  are depicted as shaded disks or spots. Note how in this view, one can see the interface between the two side-polished areas  411  and  412  as the region of contact between them. And one can perceive how the side-polish has allowed the cores  419  and  420  of the two fibers  403  and  404  to lie closer to one another to effect better evanescent coupling of light waves between the two cores  419  and  420 . 
     Also note in FIG. 13B that the interfacing surfaces  407  and  408  between the two half-couplers  401  and  402  is shown along with the areas  411  and  412  of the optics being optically coupled, in this case two side-polished optical fibers  403  and  404 . One or both of these side-polished optical fibers along with their respective grooves  405  and  406  could just as well be replaced with planar waveguides from planar optical circuitry embedded in the surfaces  407  and  408 . Also not shown, all or a portion of the surfaces  407  and  408 , or all or a portion of areas  411  and  412 , could be coated with one or more thin films, or with a thin film of fluid. And electrical or optical circuitry could be embedded in the neighboring regions in either or both of the surfaces  407  and  408 . 
     Although the invention is described with respect to preferred embodiments, modifications thereto will be apparent to those skilled in the art. Therefore, the scope of the invention is to be determined by reference to the claims that follow.