Abstract:
The invention disclosed provides an optical switch and optical fiber assembly for the control of optical signals. The optical switch incorporates a mirror mounted on a resilient mirror platform. The mirror and the platform are movable between a first position and a second position. In the first position, the mirror reflects an optical signal emitting from an input optical fiber to a selected output optical fiber. In the second position, the mirror allows the optical signal to pass directly to a coaxially located output optical fiber. The input and output optical fibers are fixedly assembled to the switch. The switch and mirror platform are formed of crystalline silicon material, with the mirrors integral with the mirror platform.

Description:
RELATED APPLICATION  
       [0001]    This application derives priority in part from provisional patent application No. 60/253,115, filed Nov. 27, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to the field of fiber optics and more particularly to the control of electromagnetic signal radiation.  
         BACKGROUND OF THE INVENTION  
         [0003]    The use of light as a carrier of information is increasing exponentially. The multiplicity of wavelengths available from the infra-red to the ultraviolet portion of the electromagnetic spectrum permits the transmission of a plurality of signals in a single fiber at the same time. Certain wavelengths, especially in the range of 1550 nanometers, have proven to be optimal for communication purposes. Fiber optic transmission is quickly replacing copper electric transmission in both short and long distance data and voice transmission.  
           [0004]    Many devices and techniques have been developed to enhance the operational performance and advance the functionality of these optical communication systems. The continuing need to carry more signal traffic drives the telecommunication industry to attain constantly greater bandwidth capacity. Bandwidth essentially defines the divisions of wavelengths to optimize signaling capacity. Development of Wavelength Division Multiplexing (WDM) and Dense Wavelength Division Multiplexing (DWDM) are two significant examples of advances in this field.  
           [0005]    Whenever the light signal must be changed, for example, switching it to a selected path, attenuate it, provide wavelength filtration, or otherwise work on the light beam, the light signal must exit the optical fiber and traverse through the ambient working space. The signal is reinserted into another fiber optic core at the completion of the modification process. Optical fibers are designed to retain the light signal within its core by creating an internally reflective barrier between the core and an outer coating known as cladding. Light naturally diverges once it exits the constraint of the fiber and it is useful to optically redirect it into a parallel beam. This redirection of diverging radiation is termed collimation. After working on, or steering the collimated beam as desired, the collimated beam is then focused so as to converge and enter the receiving optical fiber. Presently, there are several known devices for causing an optical signal to become collimated. A first such device is a Gradient Index (GRIN) lens in which the index of refraction varies as the diameter varies.  
           [0006]    A variation of the GRIN lens is disclosed in U.S. Pat. No. 4,701,011 to Emkey et al., entitled Multimode Fiber-Lens Optical Coupler. This coupler is formed of a length of multimode optical fiber that is fused to the end of a single mode fiber of equal diameter to collimate a light signal. The coupler disclosed has a length equal to one quarter of the wavelength of the optical signal being transmitted.  
           [0007]    A further variation of an optical lens is disclosed by Hirai et al. in U.S. Pat. No. 5,384,874 for an Optical Fiber Rod Lens Device And Method Of Making Same. The lens of the &#39;874 patent is a gradient index lens that is not less in diameter than the single mode transmission fiber.  
           [0008]    Shaped lenses are additional variations for use in conjunction with optical fibers in the manipulation of light. Shaped lenses are available in spherical or semi-spherical configurations. A particular lens employed in an embodiment of the present invention and in the shape of a sphere with a stem is made and supplied by Corning Incorporated of Corning, N.Y.  
           [0009]    Such optical fibers with applied lenses are typically used to collimate emitted light for directional control while the signal is directed to a selected path by an optical switch. However, the optical switches using such designs are over 60 mm long. As in other technologies, large size is undesirable, since smaller devices operate faster and the distance over which a signal travels defines the time for transmission. Also, the assembly time for known optical switches is high and results in a cost level that will be under pressure as increased message traffic demands more cost effectiveness.  
           [0010]    U.S. Pat. Nos. 5,436,986 and 5,642,446 to Tsai for Apparatus For Switching Optical Signals Among Optical Fibers (And Method) teach optical switch configurations. The Tsai switches are described as having mirrors for deflecting a light path from a straight transmission to a diverted transmission. The mirrors are moved in a plane that is parallel to the plane in which the two input and two output optical fibers reside, either by rectilinear or arcuate motion.  
         SUMMARY OF THE INVENTION  
         [0011]    The invention disclosed hereinbelow provides a switch for altering the path of an optical signal from an input optical fiber for transmitting via a selected output optical fiber. A length of multimode optical fiber is mounted as a lens to each input and output optical fiber. The fiber and lens assemblies are then mounted in a support channel formed on the optical switch with a gap left between the input and output lens ends. A mirror is interposed between the ends of the input and output lenses so as to be movable between a first position to intersect the light path and a second position out of the light path. The switch is substantially small and formed by etching a crystalline silicon chip.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention is described below with reference to the following drawings in which like features are identified with like numbers, and wherein:  
         [0013]    [0013]FIG. 1 is an exploded perspective view of an optical fiber and fiber lens as used according to the present invention.  
         [0014]    [0014]FIG. 2 is an enlarged perspective view of the optical fiber and fiber lens of FIG. 1 in assembled condition and showing an optical signal being transmitted therethrough.  
         [0015]    [0015]FIG. 3 is a bottom plan view of a pair of input fibers and a pair of output fibers as shown in FIGS. 1 and 2 and mounted to a fiber locating chip.  
         [0016]    [0016]FIG. 4 is a top plan view of a mirror chip with the input and output fibers superimposed thereon for descriptive purposes.  
         [0017]    [0017]FIG. 4A is an enlarged view of the portion within the circle of FIG. 4 showing the mirrors in position and the optical signal paths between the ends of the input and output optical fibers.  
         [0018]    [0018]FIG. 5 is a top plan view of the switch of the invention including the fiber locating chip of FIG. 3 with input and output fibers mounted thereto assembled and mounted to the mirror chip of FIG. 4.  
         [0019]    [0019]FIG. 5A is a cross sectional view taken along line  5 - 5  of FIG. 5 and showing the assembled switch of the invention with the optical signal mirrors interposed between the ends of the input and output optical fibers.  
         [0020]    [0020]FIG. 5B is a cross sectional view taken along line  5 - 5  of FIG. 5 and showing the assembled switch of the invention with the optical signal mirrors out of the line between the ends of the input and output optical fibers.  
         [0021]    [0021]FIG. 5C is a cross sectional view taken along line  5 - 5  of FIG. 5 and showing the assembled switch of the invention with the optical signal mirrors interposed between the ends of the input and output optical fibers and a spring mounted therebelow.  
         [0022]    [0022]FIG. 6 is a perspective schematic diagram of a second embodiment of the invention with a pair of input optical fibers and a pair of output optical fibers bearing spherical optical lenses and the two mirrors mounted on individual mirror platforms.  
         [0023]    [0023]FIG. 7 is a top plan view of a mirror chip according to a third embodiment of the invention with the input and output fibers superimposed thereon for descriptive purposes.  
         [0024]    [0024]FIG. 7A is an enlarged view of the portion within the circle of FIG. 7 showing the mirrors in position and the optical signal paths between the ends of the input and output optical fibers. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    Referring now to FIG. 1, an optical fiber  10  according to the invention is illustrated in perspective view with an optical lens  20  positioned for assembly thereto. Optical fiber  10  comprises core  12 , on which cladding  14  is coated, and which is contained in coating  16 . As is known in the art, core  12 , preferably a single mode fiber, carries optical signals along its length, the optical signals being reflected inwardly by the addition of cladding  14  having a different index of refraction than core  12 . Coating  16  is coated onto cladding  14  to improve the fiber&#39;s handling characteristics and resistance to damage. For mounting to an optical switch or for splicing the fiber together, coating  16  is removed from a selected length of cladding  14 .  
         [0026]    A piece of multimode optical fiber is provided as optical lens  20 . Optical lens  20  comprises core  22  and cladding  24 . According to the preferred embodiment, the diameter d of optical fiber  10  and diameter d′ of optical lens  20  are substantially equal to one another. Referring now to FIG. 2, optical lens  20  is shown assembled to optical fiber  10  at interface  26  by any method known in the art, wherein core  12  of optical fiber  10  and core  22  of optical lens  20  are coaxial and contiguous. A preferred method for assembly of lens  20  to fiber  10  is known as fusing, accomplished by heating one or both ends before placing them in contact. The optical signal exits from optical fiber  10  and enters optical lens  20  at interface  26 . Whereas core  22  of optical lens  20  is of a larger diameter than core  12  of optical fiber  10 , and core  22  is formed of multimode optical fiber, the optical signal undulates sinusoidally along its length, in waveform W. One full sinusoidal wave of waveform W has a length L. The invention recognizes that the projection of the optical signal at the peak of waveform W is substantially parallel to the axis of core  20  and that the waveform peak occurs at the first and third quarter cycle. Thus, by cleaving optical lens  20  at a length equal to any odd multiple of a quarter of the waveform cycle, the light will emit in a parallel beam. The invention further recognizes that although the beam is initially parallel, light naturally diverges over distance. Therefore, once the light beam has emerged from the controlled confinement of an optical fiber, in order to retain the maximum signal strength, the distance of free air exposure is preferably minimized. In the illustration of FIG. 2, optical lens  20  is cleaved at 1.25 sine cycles (1.25×L), resulting in beam B emerging from optical lens  20  as a Gaussian light bundle, i.e. substantially parallel as emitting from and entering respective optical fibers and slightly more compact at the mid-point therebetween.  
         [0027]    Referring now to FIG. 3, a fiber locating chip  30  is shown in bottom plan view. When assembled as is described below, fiber locating chip  30  will be inverted from the orientation shown. Chip  30  is formed substantially planar with a pair of parallel, rectilinear, channels  32   a  and  32   b  formed as guiding means across the visible surface thereof. Channels  32   a  and  32   b  are formed to securely nest an end portion of optical fibers  10   a,    10   b,    10   c  and  10   d  from which the coating has been stripped. Optical lenses  20   a - 20   d  have been assembled to the end of each optical fiber  10   a - 10   d  as described above. In the preferred embodiment of the invention, channels  32   a  and  32   b  are “V” shaped so as to accurately support input optical fibers, e.g.  10   a  and  10   b  coaxially with output optical fibers  10   c  and  110   d.  A gap  34  is provided between the ends of optical lenses  20   a  and  20   c  and between the ends of optical fibers  20   b  and  20   d.  In this orientation, an optical signal being transmitted along the length of optical fiber  10   a  will enter optical fiber  10   c  and an an optical signal being transmitted along the length of optical fiber  10   b  will enter optical fiber  10   d.  Chip  30  is further formed with a pair of windows  36   a  and  36   b  that are symmetrically located on either side of channels  32   a  and  32   b  and centered on gap  34 .  
         [0028]    The illustration of FIG. 4 shows mirror chip  40  with optical fibers  10   a - 10   d  superimposed thereon for purposes of description. Mirror chip  40  is substantially planar. A mirror platform  42  is formed integrally with mirror chip  40  and connected thereto at flex line  44  in a configuration for enhancing the resiliency thereof. The other three edges of mirror platform  42  is surrounded by window  46 . As will be described more fully below, when a force is applied to mirror platform  42 , mirror platform  42  is deflected angularly out of the plane of mirror chip  40  along flex line  44 . Mirror platform  42  returns to its initial position when force F is released. A pair of mirror blocks  50   a  and  50   b  are formed integrally on the surface of mirror platform  42  to be located between the ends of optical fibers  10   a  and  10   c  and optical fibers  10   b  and  10   d,  respectively. In the preferred embodiment, mirror blocks  50   a  and  50   b  are formed as a rhombus, with its opposed acute apexes parallel to the optical fiber axes.  
         [0029]    [0029]FIG. 4A shows an enlarged view of the portion of FIG. 4 shown in a circle with mirror blocks  50   a  and  50   b  arranged to redirect optical signals to a diagonally opposed output optical fiber. The end of optical fiber  10   a  is shown opposed to the end of optical fiber  10   c  with mirror block  50   a  located in the intervening gap. Mirror block  50   a  is located so that the acute apexes of the rhombus are in a line parallel to and slightly offset from the axis of optical fibers  10   a  and  10   c,  and a light signal emitting from input optical fiber  10   a  hits the approximate center of mirror face  54   a.  The end of optical fiber  10   b  is shown opposed to the end of optical fiber  10   d  with mirror block  50   b  located in the intervening gap. Similarly, mirror block  50   b  is located so that a light signal emitting from input optical fiber  10   b  hits the approximate center of mirror block  50   a.  Mirror faces  54   a  and  54   c  of mirror block  50   a  and mirror faces  54   b  and  54   d  on mirror block  50   b  are coated with a highly reflective material, preferably gold. In this arrangement, when mirror block  50   a  is positioned between optical fibers  10   a  and  10   c,  and mirror block  50   b  is positioned between optical fibers  10   b  and  10   d,  a first optical signal travels in the form of electromagnetic energy along light path  52   a  from input fiber  10   b  to reflect off mirror faces  54   b  and  54   c  to enter output fiber  10   c  as a second optical signal travels along light path  52   b  from input fiber  10   a  to reflect off mirror faces  54   a  and  54   d  to enter output fiber  10   d.  This optical signal manipulation effectively re-routes the optical signals to alternate output optical fiber paths. When mirror blocks  50   a  and  50   b  are not in the path of the light signals, a light signal exiting from input optical fiber  10   a  transmits directly to output fiber  11   c  and a light signal exiting from input optical fiber  10   b  transmits directly to output optical fiber  10   d.    
         [0030]    Referring now to FIG. 5, the optical fiber and switch assembly of the invention is shown in top plan view with fiber locating chip  30  having optical fibers  10   a - 10   d  mounted thereon and fiber locating chip  30  being mounted upon mirror chip  40 . FIGS. 5A and 5B show a side view cross section of the assembly, clearly portraying the nesting of the beveled outer edge of fiber locating chip  30  into the beveled inner edge of window  46  (see FIG. 4) of mirror chip  40 . The mounting of the named components one to another is accomplished preferably by use of an adhesive, most preferably by use of an epoxy adhesive. As is known in the art, epoxy adhesives provide durable adhesion that resist heat and chemical degradation.  
         [0031]    A force transfer member, for example balls  60   a  and  60   b,  are positioned in each window  36   a  and  36   b,  respectively. Balls  60   a  and  60   b  are of a diameter that is able to move freely through windows  36   a  and  36   b,  respectively. Balls  60   a  and  60   b  are preferably formed of a substantially rigid material so as to transmit forces efficiently. Balls  60   a  and  60   b  may be glass balls, which are readily available and substantially inelastic.  
         [0032]    Referring now to FIGS. 5A, 5B and  5 C, the operation of the invention is depicted. Arrow F illustrates the direction of a force to be applied and ball  60   b  resides within window  36   b  and extends upwardly above the upper surface of fiber locating chip  30 . FIG. 5B illustrates the arrow F representing a force having been applied to ball  60   b,  with ball  60   b  repositioned downward into window  36   b  and only a small portion thereof seen above the upper surface of fiber locating chip  30 .  
         [0033]    In the relaxed condition shown in FIG. 5A, mirror block  50   b  remains in its normal position between input fibers  10   a,    10   b  and output fibers  10   c  ,  10   d  , reflecting the light signal into a new path. As seen in FIG. 5B, when ball  60   b  (and ball  60   a,  not seen in this view) is pressed down through window  36   b  on the surface of mirror platform  42  causing mirror platform  42  to deflect arcuately along line α about flex line  44  so as to pivot mirror block  50   b  downwardly. In the condition shown in FIG. 5B, mirror block  50   b  does not intersect the signal emitting from input optical fiber  10   b  and thus the light signal is transmitted in a straight line to output optical fiber  10   d.    
         [0034]    Referring now to FIG. 5C, a further biasing member, for example spring  62 , is positioned so as to cause mirror platform  42  to be biased upwardly against the underside of fiber locating chip  30 . Additional components portrayed in FIG. 5C are similar to the illustration and description of the optical switch in relation to FIG. 5A. While shown in the form of a leaf spring, spring  62  can be any form of resilient member. The addition of spring  42  provides greater security and speed of operation in moving mirror chip  42  from its downward position seen in FIG. 5B to position mirror block  50   b  between optical fibers  10   b  and  10   d.    
         [0035]    Fiber locating chip  30  and mirror chip  40  are each formed of crystalline silicon that has been chemically etched to create a desired shape. By virtue of the substrate material of the switch components being crystalline in nature, natural planes of demarcation exist. By selection of and etching to specific natural planes, a highly precise and repeatable shape can be created. In addition, the planes provide an extremely flat surface which can be coated to enhance its reflectivity. The choice of plane angle and location can be advantageously employed to produce the optical switch of the invention. In reference to FIG. 4A, the planes of mirror blocks  50   a  and  50   b  on which optical signal beams  52   a  and  52   b  impinge are preferably located so that signal beams  52   a  and  52   b  contact the approximate middle of the reflective surface. The distance between mirror block  50   a  and  50   b  is thus a function of the distance between the axes of optical fibers  10   a,    10   c  and  10   b,    10   d.  The reflective surfaces  54   a - 54   d  are each oriented at an angle of between 30° and 40° relative to the optical fiber axes, most preferably an angle of about 35°.  
         [0036]    [0036]FIG. 6 illustrates one of many variations on the basic inventive concept represented in the present invention in perspective view of a mirror chip  70  with optical fibers  80   a - 80   d  superimposed thereupon. In practice, optical fibers  80   a - 80   d  are supported in channels on a mating fiber locating chip as described above in respect of the preferred embodiment of the invention. In a second embodiment of the invention, optical fibers  80   a - 80   d  each terminate in an assembly with respective spherical lenses  82   a - 82   d.  Other radially symmetrical lenses could be used. Spherical lenses  82   a - 82   d  and the like are available from Corning Incorporated of Corning, N.Y. Mirror chip  70  comprises a pair of identical and opposed segments, typical of which is mirror platform  72   b  on which mirror block  76   b  is formed. In its relaxed position, mirror platform  72   b  is substantially parallel to and planar with mirror platform  72   a  and rests in tangential contact against the surface of spherical lenses  82   b  and  82   d.  An optical signal emitting from lens  82   b  is thus reflected off mirror face  78   b  to mirror face  78   c  on mirror block  76   a  and to lens  82   c.  When mirror platform  72   b  is deflected substantially as described above with respect to the preferred embodiment, mirror platform  72   b  flexes about flex line  84   b  and mirror block  76   b  is displaced out of the path of a signal from lens  82   b.  In this situation, a signal from lens  82   b  is transmitted directly into lens  82   d  and optical fiber  80   d.  Flexure may be accomplished by forming mirror platforms  72   a  and  72   b  with a thin portion adjacent flex lines  84   a  and  84   b,  respectively, or by forming flex lines  84   a  and  84   b  as a torsion spring, configured to bias and control the orientation of mirror platforms  72   a  and  72   b.    
         [0037]    Referring now to FIGS. 7 and 7A, a third embodiment of the invention is illustrated. Optical fibers  90   a,    90   b,    90   c  and  90   d  are superimposed over mirror chip  88 , with the optical fiber chip and optical fiber guide channels not shown here. Optical fibers  90   a - 90   d  are each faced with a form of spherical lens  93   a - 93   d.  Spherical lens geometry permits the emitted light signal to maintain integrity over a greater distance in air. Mirror block  94  is formed with four mirror faces  96   a - 96   d  which, according to the third preferred embodiment of the invention, are formed at respective angles of 45° to the axes of optical fibers  90   a - 90   d.  With this mirror configuration, a signal emitting from optical fiber lens  93   a,  when mirror block  94  is positioned between the optical fibers  90   a - 90   d,  follows path  98   a  to mirror face  96   a,  is reflected to mirror face  96   b  and further reflected to optical fiber lens  93   b  to enter optical fiber  90   b.  Thus the input and output optical fibers are positioned adjacent one another, rather than across from one another as described above. Since the spherical lenses  93   a - 93   d  permit a greater optical path length, the spacing is greater between the axes of fibers  90   a  and  90   c  and the axes of fibers  90   b  and  90   d  than in the earlier described embodiments. This spacing allows a flat portion  95  to be formed between the two symmetrical halves of mirror block  94 , and a single force-applying member (not shown) to bear on flat  95 . This configuration thus eliminates the need for dual, equal, force-applying members as shown in the first and second embodiments of the invention. As in the previously described embodiments, mirror platform  92  and mirror block  94  are deflected downward in a direction substantially perpendicular to the plane in which the axes of the optical fibers lie. The resiliency of the silicon of which the optical switch is formed, optionally increased by an auxiliary biasing member (not shown), returns optical platform  92  to its relaxed position in alignment with mirror chip  88 , and mirror block  94  intercepts light signals  98   a  and  98   b.    
         [0038]    While the present invention is described with respect to specific embodiments thereof, it is recognized that various modifications and variations may be made without departing from the scope and spirit of the invention, which is more clearly and precisely defined by reference to the claims appended hereto.