Abstract:
Angled fiber terminations and methods of making the same are provided. One aspect relates to an optical fiber support assembly. The assembly comprises a substrate with a hole formed in the substrate. The hole comprises at least one non-circular opening. The hole is configured to receive a tip of a fiber such that an angle between an axis of the fiber tip and a normal of a surface of the substrate is greater than zero.

Description:
INCORPORATION BY REFERENCE  
       [0001]    A co-assigned U.S. Patent Application, entitled “HIGH DENSITY FIBER TERMINATOR/CONNECTOR” (Attorney Docket No. M-9920 US), filed on May 15, 2001, is hereby incorporated by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to fiber optic terminators, and more particularly to an angled fiber terminator.  
           [0004]    2. Description of the Related Art  
           [0005]    Optical fibers are used to transmit signals. Common fiber optic terminations/connectors terminate one fiber at a time. There are several connector styles (e.g., FC/PC, LC), but in all cases, a single fiber is inserted and glued in a precision ferrule, which is typically made of ceramic. The end of the ferrule and fiber are polished together to provide a smooth surface or a desired shape.  
         SUMMARY OF THE INVENTION  
         [0006]    Angled fiber terminations and methods of making the same are provided in accordance with the present invention. In one embodiment, a structural system aligns and holds optical fibers in a substrate prior to a bonding process. When the fibers are glued in position and an optical face of the substrate is polished, the fiber termination will have one or more properties. For example, one property relates to an input/output point of each fiber (i.e., a polished face of the fiber core) that is located with a high degree of accuracy in the optical face of the substrate.  
           [0007]    Another property relates to an optical axis of each fiber core that is positioned at a well-defined angle with respect to a surface normal of the polished face of the fiber and the optical face of the substrate. This property minimizes back-reflection and accurately defines the input/output angle of each fiber.  
           [0008]    Another property relates to a plurality of fibers that are robustly supported by a structure, such that positional changes of their respective fiber bodies or ‘pigtails’ will not cause changes in coupling efficiency, transmission loss, or damage to the fibers.  
           [0009]    Another property relates to scalability of the assembly to support a fiber termination with a large number of fibers.  
           [0010]    In one embodiment, kinematic supports may be implemented in a fiber termination, but a fiber should not be considered a rigid body. The body of a fiber engaged in an alignment assembly should be considered to have more than six independent degrees of freedom (DOF). Degrees of freedom beyond the normal six are deflected shapes that can be considered as normal modes of the fiber, i.e., an orthogonal set of elastically deflected states. One aspect of the present invention provides a support assembly that (1) supports the rigid body degrees of freedom, (2) controls the most dominant elastic modes, and (3) prevents non-negligible elastic modes.  
           [0011]    One aspect relates to an optical fiber support assembly. The assembly comprises a substrate with a hole formed in the substrate. The hole comprises at least one noncircular opening. The hole is configured to receive a tip of a fiber such that an angle between an axis of the fiber tip and a normal of a surface of the substrate is greater than zero.  
           [0012]    In one embodiment, the assembly comprises three structures. A first structure, such as a silicon substrate, locally controls the lateral positions of a plurality of fiber tips and an angle between an axis of each fiber tip and a normal of a surface of the first structure. A second structure, such as a locator plate, controls a lateral position of each fiber body behind the first structure. A third structure, such as a removable alignment fixture, may control a lateral position and a tilt of each fiber body at some location behind the second structure. A part of the assembly may then be bonded. In one embodiment, the bonding comprises filling a space defined by the first structure and the second structure with glue. The first structure, the second structure, and glue fill may control substantially all rigid body motion and all critical elastic modes of each fiber.  
           [0013]    Another aspect of the invention relates to a method of supporting at least one optical fiber. The method comprises inserting a tip of the fiber into a hole in a first structure; and applying a load to a body of the fiber such that an axis of the fiber tip is at an angle with respect to a normal of a surface of the first structure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIGS. 1A and 1B illustrate one embodiment of a substrate that locally controls a lateral position of a fiber tip and an angle between an axis of the fiber tip and a surface normal of the substrate.  
         [0015]    [0015]FIG. 2 illustrates one embodiment of an assembly configured to support the fiber body in FIG. 1 prior to a bonding process.  
         [0016]    FIGS.  3 A- 3 D illustrate examples of possible elastic displacement modes of an elongated body.  
         [0017]    FIGS.  3 E- 3 F illustrate examples of possible elastic displacement of an elongated body, such as the fiber body in FIG. 2.  
         [0018]    [0018]FIG. 4 illustrates one embodiment of a bonding process involving the substrate, the locator plate and the fiber body in FIG. 2.  
         [0019]    [0019]FIG. 5A illustrates one embodiment of the substrate, the fiber body and the locator plate in FIG. 2.  
         [0020]    [0020]FIG. 5B illustrates one embodiment of the substrate, the fiber body and the alignment fixture in FIG. 2.  
         [0021]    [0021]FIG. 6 illustrates one embodiment of a substrate, such as the substrate in FIG. 2, with a plurality of etched holes and a plurality of recesses formed on one side of the substrate.  
         [0022]    [0022]FIG. 7 illustrates one embodiment of an angled fiber array with a plurality of fibers. 
     
    
     DETAILED DESCRIPTION  
       [0023]    [0023]FIGS. 1A and 1B illustrate one embodiment of a substrate  100  that locally controls a lateral position of a fiber tip  102 B and an angle between an axis  114  of the fiber tip  102 B and a normal vector of a surface  104  of the substrate  100  (also called ‘substrate face  104 ’ or ‘optical face  104  of the substrate  100 ’). FIG. 1A is a front view of the substrate face  104 , and FIG. 1B is a cross-sectional side view of the substrate  100 .  
         [0024]    A ‘fiber’ comprises a fiber tip  102 B (FIG. 1B) and a fiber body  102 C (FIG. 1B). As shown in FIG. 1A, the fiber tip  102 B comprises a fiber end  102 A, a core  102 D and a cladding  102 E. The core  102 D comprises an inner portion of the fiber, and the cladding  102 E comprises a portion around the core  102 D. In one embodiment, the core  102 D and the cladding  102 E comprise a substantially similar material, such as glass, but have one or more different optical properties, such as indices of refraction. In another embodiment, the core  102 D and the cladding  102 E comprise different types of materials. The fiber body  102 C comprises the core  102 D and the cladding  102 E of the fiber tip  102 B plus an exterior buffer or shielding  102 F around the cladding  102 D. In general, a fiber can have multiple claddings, as well as multiple cores.  
         [0025]    In FIGS. 1A and 1B, the substrate  100  may comprise silicon, glass or some other suitable material. The substrate  100  comprises an elongated hole  106 . The substrate  100  and the hole  106  may be formed by one or more processes described in a co-assigned U.S. Patent Application, entitled “HIGH DENSITY FIBER TERMINATOR/CONNECTOR” (Attorney Docket No. M-9920), which is hereby incorporated by reference in its entirety. In one embodiment, the hole  106  is formed by deep reactive ion etching (DRIE) and photolithography. In one embodiment, the hole  106  is fabricated with a lithographic micromachining process where the machining is done from the optical side  104  of the substrate  100  so that a high level of accuracy is obtained.  
         [0026]    The hole  106  in the substrate  100  comprises a first opening  112 A on the optical face  104  of the substrate  100  and a second opening  112 B on an opposite side of the optical face  104 . In one embodiment, the cross-sectional shape of the hole  106  comprises two half circles and an elongated portion between the two half circles. In other embodiments, the cross-sectional shape of the hole  106  may comprise an oval, a rectangle, a triangle, a pentagon, a hexagon or some other shape.  
         [0027]    In one embodiment, the first opening  112 A and the second opening  112 B may have different shapes and/or sizes. In one embodiment, the first opening  112 A is shaped and/or sized to fit a fiber tip  102 C snuggly, while the second opening  112 B is elongated to allow the fiber tip  102 C to enter the hole  106  at an angle. In one embodiment, the different shape and/or size of the first and second openings  112 A,  112 B gradually become equal in the hole  106  close to the front substrate surface  104  of the substrate  100 .  
         [0028]    Regardless of the cross-sectional shape of the hole  106 , a first dimension, such as an elongated height H of the hole  106  (as shown in FIG. 1A), is greater than a second dimension, such as a width W of the hole  106 . In one embodiment, the elongated height H of the hole  106  may range from about 160 micrometers to about 195 micrometers. In other embodiments, the elongated height H of the hole  106  is less than 160 micrometers or greater than 195 micrometers. In one embodiment, the width W of the hole  106  is about 127 micrometers. In other embodiments, the width W of the hole  106  is greater than or less than 127 micrometers. In one embodiment, the diameter D of the fiber tip  102 C (i.e., diameter of the fiber cladding  102 E) is about 125 micrometers.  
         [0029]    The shape and the size (e.g., height H and width W) of the hole  106  are configured to precisely constrain the position of the fiber tip  102 B and an angle between the axis  114  of the fiber tip  102 B and the normal vector of the substrate surface  104 . In one embodiment, the height H of the hole  106  is equal to the diameter D of the fiber tip  102 B plus the product of a thickness T of the substrate  100  and the tangent of a desired angle (theta) between the fiber tip axis  114  and the surface normal of the substrate surface  104 .  
           H=D   fiber tip +( T   substrate ×TAN(theta))  
         [0030]    In one embodiment, the angle (theta) is about 4 degrees, the thickness T of the substrate  100  is about 500 micrometers, the diameter D of the fiber tip  102 B is about 25 micrometers, and the height H of the hole  106  is about 60 micrometers. In another embodiment, the angle (theta) is about 8 degrees, the thickness T of the substrate  100  is about 500 micrometers, the diameter D of the fiber tip  102 B is about 25 micrometers, and the height H of the hole  106  is about 95 micrometers. In other embodiments, the angle (theta), the thickness T of the substrate  100  and the diameter D of the fiber tip  102 B may comprise other values.  
         [0031]    The fiber tip  102 B is placed into the hole  106  of the substrate  100  with a preloaded force (also called a ‘preload’). A preloaded force is a force applied to a body, such as the fiber body  102 C, in the absence of any other forces on the body. The preloaded force in FIG. 2 is directed upward to ensure contact of the fiber tip  102 B with first and second control points  108 ,  110  on opposite sides of the first and second openings  112 A and  112 B of the hole  106 . The control points  108 ,  110  define in-plane locations of the fiber tip  102 B. The preload and the hole  106  can accurately set (1) the lateral position of the fiber tip  102 B at the optical face  104  of the substrate  100  and (2) the angle between the optical axis  114  of the fiber tip  102 B and the normal of the substrate surface  104 . In one embodiment, the size of the hole  106  does not need to be precisely controlled because of the preload. The preload in FIG. 1 may be applied by a locator plate  206 , as shown in FIG. 2.  
         [0032]    [0032]FIG. 2 illustrates one embodiment of an assembly  200  configured to support a fiber body  102 C prior to a bonding process. The assembly  200  in FIG. 2 comprises a substrate  100 , a connector plate  202 , a locator plate  206  and an alignment fixture  214 . The connector plate  202  may be glued, bonded, or otherwise attached to the substrate  100  and the locator plate  206 .  
         [0033]    In another embodiment, the substrate  100 , the connector plate  202  and the locator plate  206  comprise a single integrated structure. In another embodiment, the connector plate  202  and the substrate  100  comprise a single integrated structure. In another embodiment, the connector plate  202  and the locator plate  206  comprise a single integrated structure. In one embodiment, the spacing between the substrate  100  and the locator plate  206  is about 1 mm. In other embodiments, the spacing between the substrate  100  and the locator plate  206  may be greater or less than 1 mm. In one embodiment, the alignment fixture  214  is removable from the locator plate  206 .  
         [0034]    The alignment fixture  214  may comprise any material that has a low coefficient of thermal expansion. For example, one embodiment of the alignment fixture  214  comprises stainless steel. In one embodiment, the alignment fixture  214  comprises a shallow groove  212 . In one embodiment, the length of the groove  212  is equal to several fiber tip diameters to support the fiber body  102 C and prevent elastic displacement, as described below with reference to FIGS.  3 A- 3 F. In one embodiment, the length of the groove  212  is equal to four fiber tip diameters. In one embodiment, the length of the groove  212  is equal to 20 fiber tip diameters. In other embodiments, the alignment fixture  214  comprises a channel, a hole or some other feature, instead of a groove  212 .  
         [0035]    The groove  212  is configured to align the fiber body  102 C as the fiber body  102 C is inserted through the hole  210  in the locator plate  206  and the fiber tip  102 B is inserted through the hole  106  in the substrate  100 . In one embodiment, the shallow groove  212  supports the fiber body  102 C at a desired angle. In one embodiment, the angle of an axis of the fiber body  102 C along the shallow groove  212  to a normal of the substrate surface  104  is 8.5 degrees. In another embodiment, the angle is 8.25 degrees. In another embodiment, the angle is 4.0 degrees. In other embodiments, the angle may comprise any desired value.  
         [0036]    In one embodiment, the alignment fixture  214  is positioned at a distance away from the locator plate  206  to allow space for a bonding agent to be applied to the locator plate  206 , as described below with reference to FIG. 4.  
         [0037]    In one embodiment, the fiber body  102 C in FIG. 2 has six degrees of freedom. A first degree of freedom for the fiber body  102 C may point up in FIG. 2, a second degree of freedom may point to the left, and a third degree of freedom may point out of the page toward the reader. Fourth, fifth and sixth degrees of freedom may be rotations (i.e., rotational degrees of freedom) around the first, second and third degrees of freedom, respectively.  
         [0038]    As the fiber body  102 C is translated to the left along the shallow groove  212  and inserted into the locator plate  206 , the shallow groove  212  may control two translational degrees of freedom (e.g., first and third degrees of freedoms) and two rotational degrees of freedom (e.g., fourth and sixth degrees of freedom).  
         [0039]    The locator plate  206  in FIG. 2 comprises a material, such as silicon, with a hole  210  formed in the material. The hole  210  comprises a first opening  208  facing the substrate  100  and a second opening  204  facing the alignment fixture  214 . The hole  210  in the locator plate  206  may be formed by one or more processes described in the U.S. Patent Application, entitled “HIGH DENSITY FIBER TERMINATOR/CONNECTOR.”In one embodiment, the hole  210  is an ‘elongated’ hole, which comprises a cross-sectional shape similar to the hole  106  (FIG. 1A) in the substrate, except the hole  210  in the locator plate  206  may be larger than the hole  106 .  
         [0040]    The length and diameter of the hole  210  in the locator plate  206  are configured to position the fiber body  102 C at a desired angle with respect to a normal of the substrate surface  104 . The angle may be 8.5 degrees, 8.25 degrees, 4 degrees or any other desired value. In addition, the vertical and horizontal position of the locator plate  206  may be adjusted to position the fiber body  102 C at a desired angle with respect to a normal of the substrate surface  104 .  
         [0041]    In one embodiment, the locator plate  206  also applies the preload (FIG. 1B) at the fiber tip  102 B by positioning the hole  210  to be slightly higher in the first degree of freedom than the hole  106  in the substrate  100 . As the fiber body  102 C is translated to the left in FIG. 2, the position of the hole  210  with respect to the hole  106  causes the fiber tip  102 B to deflect elastically somewhat as the fiber tip  102 B enters the hole  106 . The positions of the holes  106  and  210  create a prying action on the fiber tip  102 B in the substrate hole  106 . The substrate hole  106  seats the fiber tip  102 B against the control points  108 ,  110 , as shown in FIG. 1B. Thus, in one embodiment, the preload causes the angle between of the fiber tip axis  114  (FIG. 1B) with respect to the normal of the substrate surface  104  to be 8 degrees, while the angle of the fiber body  102 C with respect to the normal of the substrate surface  104  is 8.5 degrees.  
         [0042]    In one embodiment, the preload is configured such that the difference between (1) the angle of the fiber tip axis  114  (FIG. 1B) with respect to the normal of the substrate surface  104  and (2) the angle of the fiber body  102 C with respect to the normal of the substrate surface  104  is less than 1 degree.  
         [0043]    In another embodiment, there is no elastic deflection of the fiber tip  102 B. In this embodiment, the angle of the fiber tip axis  114  with respect to the normal of the substrate surface  104  is substantially equal to the angle of the fiber body axis with respect to the normal of the substrate surface  104 .  
         [0044]    The first and second openings  208 ,  204  of the hole  210  in the locator plate  206  may control two lateral degrees of freedom (e.g., first and third degrees of freedom). Thus, the first and second openings  208 ,  204  of the locator plate  206  constrain the angle of the fiber body  102 C and the fiber tip  102 B with respect to the normal of the substrate surface  104 . The locator plate  206  may also remove some undesired elastic deflections of the fiber body  102 C.  
         [0045]    In one embodiment, the hole  106  in the substrate  100 , alone or in combination with the first and second openings  208 ,  204  in the locator plate  206 , may control the first, second, third, fourth and sixth degrees of freedom. The fifth degree of freedom may be controlled by friction between the fiber tip  102 B and the substrate  100  and friction between the fiber body  102 C and the locator plate  206  and the alignment fixture  214 . Thus, in one embodiment, the position of the holes  106 ,  210 , the groove  212 , the substrate  100 , the locator plate  206  and the alignment fixture  214  control five or six degrees of freedom and control some or all significant elastic displacement modes of the fiber body  102 C.  
         [0046]    FIGS.  3 A- 3 D illustrate examples of generalized elastic displacement modes of an elongated body, such as the fiber body  102 C of FIG. 2. In FIGS.  3 A- 3 D, the straight horizontal line  300  represents the fiber body  102 C when there are no loads applied. ‘W’ represents the elastic displacement or deflection of lines  302 A- 302 D, which represent the fiber body  102 C as various loads are applied. In FIGS. 3A and 3B, ‘W’ may be expressed as:  
           W=A *Cos( nπ×/L )  
         [0047]    where ‘A’ represents a peak amplitude of displacement, ‘n’ represents an integer constant from 1 to infinity that defines an order of the elastic mode, ‘x’ represents a distance along the line  302 , and ‘L’ represents the total length of the fiber body  102 C.  
         [0048]    In FIGS. 3C and 3D, ‘W’ may be expressed as:  
           W=A *Sin( nπ×/L )  
         [0049]    Because ‘n’ can vary from 1 to infinity, there are a theoretically infinite number of elastic displacement modes.  
         [0050]    In reality, the number of distinguishable modes has an upper limit where L/n approaches the diameter of the fiber body  102 C. Also, forces that create these displacements are almost universally low-order, which means only a few lowest order modes typically exist. Actual shapes encountered in the real world most likely comprise two or more mode shapes in FIGS.  3 A- 3 D superimposed on each other. But only the lowest spatial frequencies will most likely be encountered. Some typical shapes of the fiber body  102 C are shown in FIGS. 3E and 3F.  
         [0051]    FIGS.  3 E- 3 F illustrate examples of possible elastic displacement of an elongated body, such as a fiber body  102 C in FIG. 2. In FIGS.  3 E- 3 F, a straight line  312  represents an ideal position of the fiber body  102 C with no loads applied. FIG. 3E illustrates a displacement mode of the fiber body  102 C in FIG. 2 as a lateral downward load, such as gravity or a manually-applied force, is applied on a part  310  of the fiber body  102 C somewhere to right of the locator plate  206 .  
         [0052]    [0052]FIG. 3F illustrates a displacement mode of the fiber body  102 C in FIG. 2 as a first lateral load is applied at a first part  316  of the fiber body  102 C and a second lateral load is applied at a second part  314  of the fiber body  102 C. The first and second loads may be gravity.  
         [0053]    Displacement modes due to the weight of the fiber body  102 C, and any higher modes, may be neglected by configuring a separation between the substrate  100  (FIG. 2) and the locator plate  206  to be about 4 to about 8 fiber diameters. The addition of the alignment fixture  214  eliminates modes due to applied external loads on the fiber body  102 C. After the fiber body  102 C is bonded as described below with reference to FIG. 4, and rotational DOF are controlled at the locator plate  206 , all displacement modes may be eliminated.  
         [0054]    [0054]FIG. 4 illustrates one embodiment of a bonding process involving the substrate  100 , the locator plate  206  and the fiber body  102 C in FIG. 2. In one embodiment, the fiber tip  102 B is bonded to the substrate  100 , and the fiber body  102 C is bonded to the locator plate  206  by a bonding agent  400 . The bonding process may involve any suitable bonding agent and bonding process. In one embodiment, the bonding process uses a bonding agent that is stable and adapted to withstand certain environmental conditions. In one embodiment, the bonding process comprises ultraviolet cured epoxies. Some suitable bonding processes are described in the U.S. Patent Application, entitled “HIGH DENSITY FIBER TERMINATOR/CONNECTOR.” After the bonding process and a curing process, the alignment fixture  214  may be removed. After the bonding process, the substrate  100 , the fiber tip  102 B and body  102 C and the locator plate  206  may be referred to as a “fiber termination.” 
         [0055]    After the bonding process, the degrees of freedom of the fiber tip  102 B and body  102 C controlled by the substrate  100  and/or locator plate  206  may be different. After the bonding process, the substrate  100  may locally control all six degrees of freedom. Similarly, the locator plate  206  may locally control all six degrees of freedom after the bonding process.  
         [0056]    After the bonding process, the locator plate  206  may provide other functions, such as strain isolation or buffering of the fiber tip  102 B. By constraining all degrees of freedom of the fiber at the locator plate  206  after bonding, the fiber body  102 C may tolerate loads of any direction applied to the fiber body  102 C to the right of the locator plate  206 . The bonding process may fulfill desired constraint conditions of the fiber tip  102 B and/or the fiber body  102 C and remove significant elastic modes shown in FIGS.  3 E- 3 F.  
         [0057]    In one embodiment, any external loads (e.g., gravity) applied to the right end of the fiber body  102 C after the alignment fixture  214  is removed will not induce any strain at the fiber tip  102 B, at least not a first order strain. Thus, no local curvature or stress-induced birefringence will affect the light coupling efficiency of the fiber tip  102 B. A local curvature or stress-induced birefringence would likely change the light diffractive properties of a glass medium, such as the fiber tip  102 B.  
         [0058]    In one embodiment, the elongated holes in the substrate  100  and the locator plate  206  set the position and angle of the fiber tip  102 B to a high accuracy regardless of how the bonding agent may distort with time. In an embodiment where the substrate  100 , the locator plate  206  and the connector plate  202  are made of silicon, the substrate  100 , the locator plate  206  and the connector plate  202  form stable points for fiber location because silicon exhibits a low coefficient of thermal expansion (CTE) and negligible creep.  
         [0059]    After the bonding process, a part of the fiber tip  102 B that protrudes from the substrate face  104  may be removed by one or more processes, as described in the U.S. Patent Application, entitled “HIGH DENSITY FIBER TERMINATOR/CONNECTOR.”The optical face  104  of the substrate  100  (FIG. 1) and the ends  102 A of all fiber tips  102 B mounted in the substrate  100  may be simultaneously polished.  
         [0060]    In addition, a coating, such as an anti-reflection coating, may be applied to the substrate surface  104 . Examples of coatings are described in the U.S. Patent Application, entitled “HIGH DENSITY FIBER TERMINATOR/CONNECTOR.” The fiber tip  102 B in FIG. 4 may conduct light to and from free space or a component on the left of the fiber tip  102 B. The devices described herein may be used in free space or wave guide optical systems.  
         [0061]    [0061]FIG. 5A illustrates one embodiment of the substrate  100 , the fiber body  102 C and the locator plate  206  in FIG. 2. FIG. 5B illustrates one embodiment of the substrate  100 , the fiber body  102 C and the alignment fixture  214  in FIG. 2. As shown in FIGS. 5A and 5B, the substrate  100 , locator plate  206  and alignment fixture  214  may comprise a plurality of holes to support a plurality of fiber bodies, such as the fiber body  102 C shown in FIGS. 5A and 5B.  
         [0062]    Also shown in FIGS. 5A and 5B, the substrate  100 , the locator plate  206  and the alignment fixture  214  may be circular in shape. In other embodiments, the substrate  100 , the locator plate  206  and the alignment fixture  214  may comprise other shapes, such as oval or rectangular.  
         [0063]    [0063]FIG. 6 illustrates one embodiment of a fiber termination or substrate  608 , such as the substrate  100  in FIG. 2, with a plurality of etched holes  610  and a plurality of recesses  604  formed on one side  606  of the substrate  600 . The holes  610  are etched with one or more processes as described the U.S. Patent Application, entitled “HIGH DENSITY FIBER TERMINATOR/CONNECTOR.” Each hole  610  in FIG. 6 may comprise an elongated hole as described above with reference to FIGS. 1A and 1B. Thus, FIG. 6 may be a cross-sectional view where the tip of each fiber  602  is at an angle coming out of the page.  
         [0064]    The recesses  604  are formed by removing material from selected parts of the ‘front’ face or side  606  of the substrate  600 . The recesses  604  may be formed by wet etching, plasma etching, laser ablation, sand blasting or some other suitable method. In one embodiment, substrate material is removed everywhere on the front side  606  of the substrate  600  except a ring of substrate material around each hole  610 . In one embodiment, the recesses  604  are formed before a plurality of fibers  602  are inserted in the holes  610 .  
         [0065]    In one embodiment, after the fibers  602  are inserted in the holes  610 , the front side  606  of the substrate  600  and the ends of the fibers are polished. With the recesses  604  on the front side  606 , a relatively small amount of substrate material (e.g., the rings) located around the fibers  602  is polished with the fiber ends. Thus, the substrate  600  with recesses  604  allows more uniform polishing of the ends of the fibers  602  and less wear of the polishing surface.  
         [0066]    In addition, the substrate  600  with recesses  604  facilitates the physical connection of two fiber connectors, as shown in FIGS. 10 and 11 in the U.S. Patent Application, entitled “HIGH DENSITY FIBER TERMINATOR/CONNECTOR.” When pressure is applied between the two connectors, the pressure is located near the fiber ends to provide low insertion loss.  
         [0067]    [0067]FIG. 7 illustrates one embodiment of an angled fiber array  700  with a plurality of fibers  718 . The angled fiber array  700  comprises a plurality of micromachined structures. In one embodiment, the angled fiber array  700  comprises a first layer  702 , a second layer  712  and a third layer  708 . In other embodiments, there are less than three or more than three layers. The layers  702 ,  712 ,  708  are held together by connector plates  704 ,  706 ,  714  and  710  that are glued, bonded or otherwise attached to the layers  702 ,  712 ,  708 .  
         [0068]    The fibers  718  may be arranged in any desired pattern and with any desired angle by configuring (1) the size of the holes in the layers  702 ,  712  and  708 , (2) the shape of the holes in the layers  702 ,  712  and  708 , (3) the horizontal position of the layers  702 ,  712 ,  708 , and (4) the distance between each layer  702 ,  712 ,  708 . The fibers  718  may be arranged at the same angle as shown in FIG. 7 or at different angles.  
         [0069]    In a device with multiple fibers, such as the substrate  100  in FIG. 5A, a plurality of fiber ends  102 A (FIGS. 1A and 1B) may be simultaneous polished by polishing one face of the substrate through which all fiber ends protrude. Polishing multiple fiber ends provides accurate positioning of the fiber tip face normal to the optical face  104  of the substrate  100  (i.e., the fiber tip face  102 A and the substrate surface  104  are coincident). The optical face  104  of the substrate  100  may be the last degree of freedom (direction  2  in FIG. 2) used to completely define the location of the fiber tip face. Angle polishing each fiber face may greatly reduce back-reflection. The polishing, in conjunction with lithographic micromachining fabrication, may be scaled to large devices.  
         [0070]    The above-described embodiments of the present invention are merely meant to be illustrative and not limiting. Various changes and modifications may be made without departing from the invention in its broader aspects. The appended claims encompass such changes and modifications within the spirit and scope of the invention.