WO1990000260A1

WO1990000260A1 - Optical fiber tap utilizing reflector and cammed closure

Info

Publication number: WO1990000260A1
Application number: PCT/US1989/002542
Authority: WO
Inventors: William David Uken; Thomas D. Ratzlaff
Original assignee: Raynet Corporation
Priority date: 1988-06-30
Filing date: 1989-06-12
Publication date: 1990-01-11
Also published as: EP0422106A1; JPH04503717A; AU3857689A; AU628358B2

Abstract

A tap for withdrawing light from an intermediate portion of an optical fiber core by passing light through a side of the optical fiber comprises an optical coupler in contact with an outside surface of an optical fiber which is bent and disposed in a plane. A light reflector extending transverse to the plane deflects the withdrawn light towards the end surface of a light element disposed completely outside the plane. A similar arrangement may be used to inject light to an intermediate portion of an optical fiber. The tap may be used as a read tap to withdraw light or as a write tap to inject light in optical fiber networks. A spring biased closure member urges the optical fiber to be maintained in bent registration with the optical coupler within the plane. Simple tools and general craft training and knowledge may be applied to insert into, and remove the optical fiber from, the tap.

Description

OPTICAL FIBER TAP UTILIZING REFLECTOR AND CAMMED CLOSURE

BACKGROUND OF THE INVENTION

The present invention relates to an optical fiber tap utilizing a reflector and including a cammed closure member, methods for making same, and networks useable therewith.

Numerous methods have been proposed in the prior art for distributing information using an optical fiber, preferred methods including star, ring and bus architectural networks Generally speaking, star and ring networks utilize point-to-point connections, whereas bus networks are capable of utilizing non- point-to-point connections whereby an optical signal is only partially interrupted by any one connection

For example, Polcyzynski, U.S. Patent No. 4,089,584 discloses a bus network which utilizes an optical fiber having a rectangular core and cladding, and connection or tapping of the fiber is accomplished by removing the cladding and disposing a prism or grading against an exposed rectangular core. Such networks are disadvantageous, since the fiber and taps useable therewith are relatively complex in design and hence unduly expensive, and optical network performance is rather poor in view of relatively low tapping efficiencies that result using such methods.

Miller, United Kingdom Patent document 2,126,749B and an article by Dakin et al. entitled "Experimental Studies into the Non- Invasive Collection and Distribution of Data on a Fiber-Optic Monomode Bus" propose designing a read optical fiber bus using taps whereby light is withdrawn through a side of the optical fiber by passing the light through a coating of the fiber Miller collects the light from the bus fiber by disposing a photodetector at an end of a curved and grooved light pipe disposed around the bus fiber, and Dakin et al. collects the light by tightly pressing a polymeric fiber with part of its cladding removed against a curved portion of the bus fiber. Such techniques are also disadvantageous in that again the taps are complicated in design, require special technician/craft skills and are craft sensitive to install in the field, and are not sufficiently efficient when tight flux budgets are mandated by network design.

Goell et al., U.S. Patent No. 3,982,123 ~t Figures 5A and 5B disclose an optical fiber read tap whereby an exposed glass cladding of a bent optical fiber portion is glued to a top of a photodetector. Such taps are disadvantageous since a strength of the fiber is disadvantageously affected by removal of its outer protective buffer, and rather small coupling light efficiencies are obtained by simply using epoxy to secure a bent optical fiber onto a top surface of a photodetector. In addition, the optical fiber is not releaseable from the tap.

Cross, U.S. Patent No. 4,270,839 discloses a tap for an optical fiber whereby the fiber is bent in air, and downstream from the bent portion of the optical fiber a straight section of the optical fiber is glued within a straight light pipe which thereafter is curved and has a light detector at a remote end thereof Again, such taps are disadvantageous, since they have been found to yield relatively low light coupling efficiencies, and the optical fiber is not releasable from the pipe once glued thereonto.

Campbell et al., U.S. Patent No. 4,728,169; Campbell et al., U.S. Patent Application Serial No. 754,035, filed on July 11, 1985; and Campbell et al., U.S. Patent Application Serial No. 614,884, filed on May 25, 1984, all of which are assigned to the assignee of the present invention, the disclosures of which are all incorporated herein by reference, disclose several advantageous kinds of taps for injecting light into, or withdrawing light from, optical fibers. However, there continues to be a need for yet more efficient taps which are also mechanically simple in structure and reliably useable in the field without special craft skills or extensive training.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to overcome and eliminate the above-noted drawbacks and disadvantages of the prior art approaches and to provide an optical read tap and/or optical write tap and network useable therewith which operates more efficiently than heretofore described.

Another object of the present invention is to provide a more efficient optical fiber tap into and from which an optical fiber may be installed and removed by ordinarily skilled crafts persons without special tools, skills or training.

These objects are achieved by utilizing a tap which bends an optical fiber in a plane, preferably the plane being flat, and which utilizes a light reflector for directing light withdrawn from a core of the optical fiber towards a light collection end surface or for directing light from a light emitting end surface into a core of an optical fiber, the light reflector preferably having a reflectance greater than 0.5, preferably greater than 0.7 or 0.8, and more preferably greater than 0.85 or 0.90, most preferably greater than 0.95, a polished light reflector being most preferred. Preferably the light is coupled through a side of the optical fiber utilizing an optical coupler which has an index of refraction which optimally matches an outer surface of the optical fiber, and preferably the optical coupler is disposed so as to contact a bent portion of the optical fiber, though it can be disposed downstream of the bent portion of the optical fiber for reading, and upstream of the bent portion of the optical fiber for writing, if desired.

The reflecting surface is formed in a vicinity of the optical coupler and in close proximity therewith, and it deflects light out of the plane of the bent optical fiber portion and towards the end surface of a light element, the light element either constituting ultimately a photodetector for light detection or a light emitter for light injection. In any case the light emitter or the light detector can be substantially displaced from the tap of the present invention by utilizing a pigtail optical fiber light element which facilitates testing of the apparatus prior to permanent installation and after disposing a bus optical fiber within the tap. The tap further includes means for bending the optical fiber which is releaseable therefrom which also facilitates testing and repairs.

Since the light element is disposed outside the plane of the optical fiber bend, the bend profile of the optical fiber can be optimized for optimum optical efficiency. The bend profile is not required to be unnecessarily further modified so as to accommodate mechanical size constraints imposed by a size of the light element, which is generally much larger than the fiber core.

A cammed closure when open enables the optical fiber to be loaded into and unloaded from the tap without difficulty or damage, and when closed urges the optical fiber against the optical coupler in proper alignment and registration therewith. The cammed closure is operable with a simple hand-held rotating tool and without special craft training.

The tap of the present invention is most suitable for use in a serial connection with an optical fiber for creating either a read bus or a write bus.

In addition, the tap of the present invention may be manufactured in a much more cost efficient way, since thermoplastic materials and simple molding techniques may be utilized to form a single component which incorporates both the bend profile features necessary to control and to register the optical fiber with the optical coupler, and focusing elements required optimally to transfer the light between the light emissive/receptive element and the core of the optical fiber at the bend. Also a thickness of the component can be made sufficiently uniform to allow it to cool and harden in a stable manner incident to the molding process.

These and other objects, advantages, features and aspects of the present invention will be more fully understood and appreciated upon consideration of the following detailed description of preferred embodiments, presented in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings:

Fig. 1 illustrates a preferred embodiment of a tap embodiment incorporating the principles of the present invention which includes a curved reflection surface. Fig. 2 illustrates a tap embodiment of the present invention utilizing a planar reflection surface.

Fig. 3 illustrates another preferred embodiment of the invention which includes a closure member for releasably pressing the optical fiber so as to maintain a constant bend attitude therein.

Fig. 3A is a bottom plan view of an adaptation of the closure member depicted in Fig. 3 provided in order to achieve a cammed closure member for releasably pressing the optical fiber.

Fig. 3B is a side view in elevation and section of the cammed closure member adaptation as taken along line 3B-3B in Fig. 3.

Fig. 4 illustrates an alternative embodiment of the invention which includes a waveguide for transmitting light to and from an optical fiber core.

Fig. 5 illustrates a tap geometry whereby an end surface of a light element is disposed in a plane of an optical fiber bend.

Fig. 6 illustrates another preferred embodiment of the present invention which utilizes a series of microbends for bending an optical fiber.

Fig. 7 illustrates yet a further embodiment of the present invention whereby a macrobend includes a series of microbends therein for bending an optical fiber.

Fig. 8 illustrates one preferred embodiment of a network employing taps of the present invention. DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig 1, an optical fiber 1 has a portion 2 thereof bent about a radius of curvature sufficiently small so as to cause light 3 to leak or radiate therefrom. The light 3 is then deflected by reflector 4 towards a light collection end surface 5 which in this figure is part of a photodetector 6.

Generally, as used throughout herein the invention is described with reference to "a light element", and it should be hereinafter understood that the light element may constitute any one of a variety of apparatuses useful for detecting light withdrawn from an optical fiber; alternatively any one of a number of apparatuses for generating light for injection into an optical fiber; or simply a waveguide (e.g. pigtail optical fiber) connecting a light detector, light emitter, or further waveguide to the tap of the present invention.

Preferably the taps of the present invention are constructed so that light is withdrawn from a core of an optical fiber, as opposed to its cladding, and alternatively light is injected into a core of the optical fiber as opposed to being simply injected into a cladding of the optical fiber According to preferred embodiments of the present invention, the light is injected or withdrawn by passing through one or more coatings of the fiber (e.g. buffers or jackets) and the cladding. Nothing expressed herein should be understood as suggesting that the practice of the present invention calls for or requires that either the buffer/jackets or the cladding be removed or peeled away from the fiber at the situs of the tap. Such prior procedures are made obsolete by the present invention. Fig. 2 illustrates a case where the light is injected into the optical fiber 1, and particularly its core, at the bend 2 using a reflection surface 14 which deflects light originating from a light source 8 after being focused by lens 9 so as to exit lens end surface 12. The lens 9 may comprise a pigtail optical fiber, or a specially formed waveguide. In both Figs. 1 and 2 the reflection surface 4, 14 deflects the light between a core of a bent optical fiber portion 2 and a light element 5, 9.

Fig.3 illustrates a geometry of a preferred tap embodiment which includes the concept of Figs. 1 and 2 and whereby it is evident that in all cases a light element 6, 8, 68 has a respective end surface 11, 12, 13 which is disposed in a plane which is parallel with plane 24 and whose optical axis is not parallel to plane 24 (but is preferably normal or perpendicular to that plane)~ the plane including the bent optical fiber portion 2, as illustrated by the crisscrossing arrows 24 in Fig. 3.

In Fig. 3 a substrate 16 has formed thereon a groove 17 sized to accept an optical fiber 1 (not shown in Fig. 4) to be tapped, the groove 17 including a bent portion 22. The substrate 16 includes first and second flanges 18 which define first and second grooves 19 along which a closure member 20 can slide along in parallel in the plane 24 which includes therein the bent portion 22 and the bent optical fiber portion 2. An end face 25 of the closure member 20 has a profile 26 which is complementary with the curved profile of the groove 17 such that the optical fiber 1 may be securely maintained in a constant bent attitude and registration within the groove 17 when the end face 25 of the closure member 20 is urged against the optical fiber 1 in its closed position. As shown in Figs. 3A and 3B a bias force, indicated by arrow 28 in Fig. 3 A, is generated by providing the closure member 20 with a transversely mounted leaf spring 32 seated in two oppositely facing notches 33 formed in outer sidewalls 34 of the closure member 20. The leaf spring 32 is placed in a recess 35 formed in outer sidewalls 34 of the closure member 20. The leaf spring 32 is placed in a recess 35 formed within the closure member 20. Central longitudinal dependent ribs 36 cooperate with the sidewalls 34 and endwalls 37 and 38 to reinforce the closure member 20.

A rotatable locking pin 40 is seated in a suitable opening defined in the substrate 16 and is rotatable about an axis of rotation denominated by the axis line pointed to by reference numeral 41. A screwdriver groove 42, or e.g. a central hexagonal recess (Allen wrench compatible) may be formed in the top of the pin 40 to enable a craftsperson to rotate the pin with a suitable mating tool (not shown).

The pin 40 is preferably provided with at least one cam portion 43 which engages and causes the leaf spring 32 to become deflected and thereby urge the closure member 20 resiliently against the optical fiber 1 which is in turn forced against the substrate 16 with a bias force selected to be adequate to maintain the optical fiber 1 in proper alignment and registration with respect to the groove 17, and particularly its bent portion 22.

The closure member 20 is formed to define a longitudinal slot 44 which provides a central opening through which the pin 40 freely, yet snugly passes. The slot 44 enables the cam portions 43 of the pin 40 to pass through the closure member 20 in one axial orientation of the pin 40 relative to the closure 20 during assembly of the tap. A bottom stem portion of the pin 40 is hollow and slotted and is provided with an outwardly extending skirt 45. This skirt 45 seats with a peripheral annular flange formed into the lower face of the substrate 16 at the opening sized and placed to form a journal for and accommodate the pin 40. Slots 46 enable the bottom stem portion of the pin 40 to be sufficiently resilient to pass through the opening in the substrate 16, notwithstanding the presence of the skirt portion 45. Thus, it will be appreciated that the pin 40 snap-locks into the substrate 16 through the closure member 20.

When the optical fiber 1 is disposed in the tap of Fig. 3 and is transmitting light in a direction from right to left in the drawing, light radiates outward from the fiber core, through its cladding, through its outer coating(s), and into the portion 14 of the substrate defining the groove bent portion 22 which functionally acts as an optical coupler 22 so as to facilitate light transfer between the coupler 22 so as to facilitate light transfer between the outer coating of the fiber and the substrate portion 14. If desired, a wetting preferably stable agent, such as a partially cross-linked gel having finite elongation properties, such as an ultimate elongation in excess of 200 or 500% can be used to facilitate optical coupling.

The light entering the optical coupler is deflected by the reflecting surface of the substrate portion 4 out of the plane 24 of the bent portion 2 of the fiber 1 and groove 17 and towards the light element 68 having an end surface 13 entirely disposed out of the plane 24, even though the end surface 13 can be in very close proximity to the bent portion 22. The reflection surface can simply be a smooth surface exposed to air shaped such that the withdrawn light hits the smooth surface at angles such that total internal reflection occurs off this surface with little or no light being refracted therethrough into the air.

Preferably, the smooth surface has a reflective coating thereon as well. It is preferred to form the surface so as to have a reflectance greater than 0.5, preferably greater than 0.6 or 0.7, most preferably greater than 0.8 or 0.85, and optimally greater than 0.9 or 0.95.

Preferably, although not necessarily, the reflection surface 4 is curved in one or preferably two directions so as to optimize focusing between the fiber core and the light element, such as for example being curved along a direction of axis X and Y (e.g. along a line 34 and a line 35) as schematically illustrated in Fig. 1. A parabolic or an elliptical reflector are two preferred embodiments. According to particularly preferred embodiments, the actual shape of the reflecting surface is optimized so that optimum focusing into the optical fiber core or onto a photodetector or the light collecting surface is achieved. To this end, the surface 4 is shaped and positioned such that preferably more than 30% of the light withdrawn for the fiber core is reflected, more preferably more than 40%, 50% or 60%, most preferably more than 70% or 80%.

For light injection, the surface is shaped and positioned such that as much light as possible emitted by the light source is injected into the fiber core as a guided mode, e.g. preferably more than 0.05%, more preferably more than 0.1%, 0.5% or 1%, most preferably more than 10%, 30% or 40%. Differences in phase- space area between the end surface of the light emitting source and the core of the fiber necessarily result in lower light injection efficiencies than are possible with a similar geometry for withdrawing light. The present invention produces several new and unexpected advantages. First, as graphically illustrated in Figs. 1-3, 3A, and 3B, by disposing the light element 6, 8, 68 and its end surface 11, 12, 13 completely out of the plane 24 of the bend, the bend profile of the optical fiber portion 2 may be optimized as desired to achieve optimum optical detection or injection efficiency without being unduly further modified due to a physical size of the light element or its end surface.

This advantage is more clearly illustrated by reference to Fig. 5 where a light element 71 is disposed so that its collection surface 72 is in the plane of the bend, the bend beginning at point 73 and ending at point 74. The difference between the physical size of the light element 71 and the optical fiber 1 including its bent profile 2 requires that the end surface 72 of the light element 71 be disposed an undesirably large distance away from the beginning of the fiber bend 73 which tends to decrease coupling efficiency.

In addition, to allow the fiber 1 to clear a lowermost edge 75 of the end surface 72, the fiber bend portion must necessarily extend past point 76 of the bend so as to include arc 77, which is particularly disadvantageous since very little of the light escaping the fiber within the arc 77 will be collected by the end surface 72. Also, disposing the light element 71 so that its end surface 73 is in the plane of the bend requires that a thickness of a substrate housing the light element must be unduly thick in a region of the substrate which contains a groove for defining the bend profile of the fiber thus complicating manufacturing of the substrate as molding tolerances become difficult to control. In comparison, with the present invention, the reflection surface 4, 14 may be disposed as close as desired to the bent optical fiber portion 2 and may be made as large and shaped as desired so as to deflect as much light as is required as may be escaping from the fiber or from the light source in order to achieve the highest light coupling efficiency. As mentioned, for highest efficiency light withdrawal, since the end surface of the light collection element is out of the plane 24 of the bend, preferably the bent portion 2 or 22 of the optical fiber is disposed entirely upstream of the reflection surface 4. For highest efficiency light injection the bent portion is disposed entirely downstream of the reflection surface 14.

Fig. 4 illustrates another preferred embodiment of the present invention. In this embodiment, the light 3 withdrawn from the optical fiber 1 at the bent portion 2 is confined within a waveguide 30 which forms part of the substrate 16 and forms the bend profile 26 for the bent optical fiber portion 2, with the reflection surface 14 being disposed at an end of the waveguide 30.

Fig. 6 illustrates yet a further embodiment of the invention wherein both coupling in or out of the optical fiber 1 is accomplished by utilizing a series of complementary microbend surfaces 80 between first and second substrates, the optical fiber 1 being disposed between the first and second substrates by a resilient force denoted by the arrow 28. In this embodiment, it is preferable for one of the members 81, 82 to have a reflective surface on the portion thereof forming the microbend surface so that light is preferentially coupled through the other member which is transparent, with the reflecting surface of the invention being disposed on that other member. As used throughout this specification, the term "microbend" means any kind of bend profile whereby an amplitude of the bend is less than two diameters of the fiber cladding, and is typically of the order of 10 to 20% of the diameter of the outer cladding of the fiber 1. By "macrobend" is meant as any bend having an amplitude greater than twice the diameter of the outer cladding of the fiber.

Fig. 7 illustrates yet a further embodiment of the present invention wherein a substrate 86 has formed therein a microbend having an amplitude equal to the height 85; and, within the surface of the macrobend a series of microbends are formed, with the reflecting surface being formed at an appropriate place within the substrate 86. A member having a curved reflective surface shaped complementary to the bend 84 so as to maintain the optical fiber appropriately bent is not shown but is required in operation.

Fig. 8 illustrates one practical embodiment for using taps having reflecting surfaces as described herein, Fig. 8 illustrating an optical fiber network 90 having first and second bus fibers 91, 92 interconnecting a plurality of terminals 93 in a bus architecture. The optical fiber 91 constitutes a read optical fiber, and the optical fiber 92 constitutes a write optical fiber The network 90 so formed is controlled by a CPU or central processing unit 94.

According to the present invention, the light is withdrawn from the read optical fiber 91 in a serial manner by using a plurality of read taps disposed in series and constructed according to any combination of the embodiments described above with the terminals 93 writing onto the write bus 92 via a plurality of taps 95 disposed in series and constructed in accordance with any of the tap embodiments described hereinabove. Preferably, signals going to any one or more of the terminals 93 are multiplexed in time rather than being controlled by a token passing algorithm. According to a particularly preferred embodiment, any one or more of the terminals 93 is connected to one or more telephones, personal computers, mainframe computers, or similar data assembling, processing and generating equipment.

The present invention is useful for tapping both single mode and multimode fiber, including both step index and graded index, and is usable with both glass-on-glass and plastic clad silica fiber. According to a presently preferred embodiment, the invention includes the use of glass-on-glass fiber including a polymeric coating (e.g. buffer), the coating preferably having an index of refraction higher than the cladding. Examples include an acrylate or silicone buffer, and/or any thin additional layers (e.g. jackets) surrounding the buffer layer Typical preferred glass-on-glass fibers include single mode fibers having a core diameter of about 10 microns, and a cladding diameter of about 125 microns, and a buffer diameter in a range between about 250-500 microns, with multimode glass-on- glass fiber including a core/cladding diameter of roughly 50/125 microns, 100/140 microns, and 85/125 microns, for example. Preferred fibers include those having cylindrical cores, cylindrical claddings and cylindrical coatings (e.g. buffers and/or jackets). Preferably, at least the buffer layer is maintained intact so as not to detrimentally degrade the strength of the fiber by exposing a glass surface thereof to moisture.

Although the invention has been described by reference to certain preferred embodiments thereof, it is not to be limited thereby and is to be limited only by the appended claims.

Claims

1. A tap for withdrawing light from an intermediate portion of an optical fiber core by passing the light through a side of the optical fiber, comprising:

a light element having an end surface;

means for maintaining the intermediate portion of the optical fiber bent and disposed in a plane, the end surface of the light element being completely outside the plane;

an optical coupler in contact with an outer surface of the optical fiber;

a light reflector extending transverse to the plane so as to deflect the withdrawn light toward the light element end surface, the maintaining means including a substrate means

a closure member slideably mounted along said substrate means for movement along a locus in parallel with the plane and the bent optical fiber portion disposed therein;

spring means;

the substrate means including a rotatable locking pin journalled in a suitable opening defined in the substrate means and being rotatable about an axis of rotation, the locking pin being provided with at least one cam portion for engaging the spring means thereby to cause the spring means to become deflected and thereby urge the closure member resiliently against the optical fiber with a bias force selected to maintain the bent portion of the optical fiber in alignment and registration with respect to the optical coupler.

2. The tap of claim 1, the closure member having an end face with a profile which is complementary with the profile of the optical coupler such that the optical fiber may be securely maintained in a constant bent attitude and registration at the optical coupler when the end face of the closure member is urged against the optical fiber.

3. The tap of claim 1 or 2, the closure member having a longitudinal slot providing a central opening through which the pin freely passes, thereby to enable the cam portion to pass through the closure member during fabrication and to permit the closure member to move slideably along its locus of movement relative to the substrate when the cam portion of the pin engages the spring as the pin is rotated.

4. The tap of claim 1, 2 or 3, the pin defining rotating hand tool engagement means for enabling a hand tool to engage the pin thereby facilitating its rotation and consequent movement of the closure member along its locus of movement relative to the substrate means.

5. The tap of any one of claims 1-4, the pin including a bottom stem portion defining a hollow central portion and having a slotted, outwardly extending skirt, the substrate including a peripheral annular flange formed into the lower face thereof, the hollow central portion of the pin thereby being adapted to snap-lock to the substrate means thereby to provide the journal for rotation of the pin relative to the substrate means.

6. A tap for injecting light into an intermediate portion of an optical fiber core by passing the light through a side of the optical fiber, comprising:

a light source having an end surface;

an optical coupler in contact with an outer surface of the optical fiber;

a light reflector extending transverse to the plane so as to deflect at least 20% of the light from the light source end surface toward the optical fiber bent portion, a reflectance of the light reflector being greater than 0.50, the maintaining means including a substrate means

a closure member slideably mounted along said substrate means for movement along a locus in parallel with the plane and the bent optical fiber portion disposed therein

spring means;

th e substrate means including a rotatable locking pin journalled in a suitable opening defined in the substrate means and being rotatable about an axis of rotation, the locking pin being provided with at least one cam portion for engaging the spring means thereby to cause the spring means to become deflected and thereby urge the closure member resiliently against the optical fiber with a bias force selected to maintain the bent portion of the optical fiber in alignment and registration with respect to the optical coupler.

7. The tap of claim 6, the closure member having an end face with a profile which is complementary with a profile of an optical coupler such that the optical fiber may be securely maintained in a constant bend attitude and registration at the optical coupler when the end face of the closure member is urged against the optical fiber.

8. The tap of claim 6 or 7, the closure member having a longitudinal slot providing a central opening through which the pin freely passes, thereby to enable the cam portion to pass through the closure member during fabrication and to permit the closure member to move slideably along its locus of movement relative to the substrate means when the cam portion of the pin engages the spring means as the pin is rotated.

9. The tap of claim 6, 7, or 8, the pin defining rotating hand tool engagement means for enabling a hand tool to engage the pin, thereby facilitating its rotation and consequent movement of the closure member along its locus of movement relative to the substrate means.

10. The tap of any one of claims 6-9, the pin including a bottom stem portion defining a hollow central portion and having a slotted, outwardly extending skirt, the substrate including a peripheral annular flange formed into the lower face thereof, the hollow central portion of the pin thereby being adapted to snap- lock to the substrate means thereby to provide the journal for rotation of the pin relative to the substrate means.

11. An optical fiber tap, comprising:

first and second engaging members which include means for bending an optical fiber about a radius sufficiently small such that an optical signal can be injected into or withdrawn from a core of the optical fiber by passing the signal through a side of a cladding of the fiber, the engaging members being slideable relative to one another such that the bending means can be opened and closed so as to release and bendingly engage the optical fiber respectively;

means for biasing the engaging members together so as to bendingly engage the optical fiber, the biasing means including a spring and rotatable cam having first and second positions, in the first position the cam biasing the spring so as to urge the engaging members together so as to bendingly engage the fiber, in the second position the cam being separated from the spring so as to cause the engaging members to disengage an amount sufficient such that the optical fiber is not bendingly engaged by the first and second members.