Apparatus for measuring the protrusion of an end of an optical fiber terminated in a connector

Abstract: An apparatus (10) is provided for measuring the distance an optical fiber (12) terminated in a connector protrudes from a component (14) of the connector such as a ferrule or the like. A fixed abutment member (16, 24) defines an abutment surface (24a) against which the connector component can be moved into engagement. A movable measuring member (18, 20) is mounted for movement relative to the fixed abutment member and is engageable by a distal end (12a) of the optical fiber as the connector component is moved into engagement with the abutment surface of the fixed abutment member. Therefore, the amount of relative movement between the movable measuring member and the fixed abutment member directly corresponds to the distance the optical fiber protrudes from the connector component. Calculating electronics (44-56) are operatively associated with at least the movable measuring member for calculating its amount of movement and, thereby, the protruding distance of the optical fiber. The electronics includes providing a portion (16) of the movable measuring member and a portion (18) of the fixed abutment member as capacitor plates and the capacitance thereof is utilized to calculate the protruding distance of the optical fiber.

Description: The invention relates to an apparatus for measuring the distance an optical fiber end terminated in a connector protrudes from, or is recessed by a small amount in a planar end surface of a connector component, particularly a ferrule. Optical fiber connectors are known (US-A-4 892 178) where the optical fiber end has a desired distance from a planar end surface of the connector. It is also known (US-A-4 218 113) to have a length of the optical fiber protruding from the connector into a tunnel member where the fiber end meets and abuts a further fiber end which protrudes from a second connector. Most kinds of mating connectors do not show an arrangement of the optical fiber relative to the connector as referred to above, but the fiber end is flushed to or protrudes slightly from the planar end surface of the connector. The ends of the fibers conventionally are flat and polished. When a pair of connectors are mated the ends of the fibers are in abutment with each other to minimize transmission losses between the fibers. One of the problems in fiber optic connectors of the character described is to maintain a particular protruding length of the fibers beyond the connector components or ferrules. If the protruding end of a fiber is too long, the fiber can break due to high stresses created in the mated connectors. If the fiber protrusion is too short, physical contact between the fiber ends can be difficult, resulting in a decrease in performance/transmission quality, i.e. an increase in transmission losses. For instance, it has been found that the fiber protrusion in a given fiber optic abutting ends of the optical fibers. Presently, there are no known instruments which can accurately measure such small protruding distances in production or field environments. Heretofore, laboratory-type equipment of a complex and expensive nature has been the only means known to perform such measurements. This invention is directed to providing a relatively simple apparatus for accurately measuring the fiber protrusion distance in conventional fiber optic connectors. An object of the invention is to provide a novel apparatus for measuring the distance between an optical fiber end and a planar end surface of a connector component. The invention is defined by claim 1. In the exemplary embodiment of the invention, generally, the measuring apparatus includes a fixed abutment member against which the connector component can be moved into engagement. A movable measuring member is mounted for movement relative to the fixed abutment member and is engageable by a distal end of the optical fiber as the connector component is moved into engagement with the fixed abutment member. Therefore, the amount of relative movement between the movable measuring member and the fixed abutment member directly corresponds to the distance the optical fiber protrudes from the connector component. Calculating means are provided, operatively associated with at least the movable measuring member of the apparatus, for calculating its amount of movement and, thereby, the protruding distance of the optical fiber. As disclosed herein, the fixed abutment member of the apparatus is provided in the form of a ferrule-like member shaped complementarily to the connector component or ferrule. An alignment sleeve surrounds the fixed abutment member and projects from an end thereof for guiding the connector component into abutment therewith. The movable measuring member is provided in the form of a needle-like member telescoped within a passageway through the fixed abutment member, with a distal end of the needle-like member engageable by the distal end of the optical fiber. The passageway is configured such that the distal end of the optical fiber is movable thereinto as the fiber moves the needle-like member. Generally, the invention contemplates that the calculating means include means for sensing relative movement between the movable measuring member and the fixed abutment member, means coupled to the sensing means for generating an electrical signal, and means responsive to the electrical signal for determining the protruding distance of the optical fiber. In the illustrated embodiment of the invention, the means for sensing relative movement between the movable measuring member and the fixed abutment member are provided as capacitor means including one capacitor plate coupled to the movable measuring member and another capacitor plate fixed to the fixed abutment member. Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings. Brief Description Of The Drawings The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with its objects and the advantages thereof, may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the figures and in which: FIGURE 1 is a schematic illustration of an apparatus embodying the concepts of the invention; FIGURE 2 is a section, on an enlarged scale, through the measuring area of the apparatus; FIGURE 3 is a schematic illustration of an apparatus using a capacitive sensor means; and FIGURE 4 is a block diagram of the electronics involved in using the capacitive sensor means. Detailed Description Referring to the drawings in greater detail, and first to Figure 1, an apparatus, generally designated 10, is shown for measuring the distance an optical fiber 12, terminated in a connector, protrudes from a component 14 of the connector. As is conventional in fiber optic connectors, component 14 often is a ceramic or metal ferrule having a generally planar end 14a beyond which a protruding distal end 12a of the optical fiber protrudes. The protruding distal end of the optical fiber is intended to engage or make physical contact with the distal end of another optical fiber of a mating connector, all of which is known in the art. Fiber end 12a often protrudes from ferrule 14 a small distance on the order of 0.1 to 2.5 microns. This range is acceptable for establishing a good physical contact with the fiber end of a mating connector. Apparatus 10 is designed to measure the distance of fiber end 12a from the planar end surface 14a to insure that the distance the fiber end 12a protrudes from planar end 14a of connector component 14 is in the acceptable range. More particularly, apparatus 10 includes a fixed abutment member 16 and a movable measuring member which includes a holder 18 and a needle 20 fixed to the holder whereby the needle can move with the holder in the direction of double-headed arrow "A" relative to fixed abutment member 16. Needle 20 extends through a passageway 22 in a ferrule-like portion 24 of fixed abutment member 16. Ferrule-like portion 24 is shaped correspondingly to connector component or ferrule 14, and an alignment sleeve 26 surrounds the ferrule-like portion 24 and the connector component 14 so that, upon insertion of the connector component into the sleeve 26 in the direction of arrow "B", fiber end 12a will be in alignment with needle 20 and passageway 22. Generally, a position sensing means 28 is provided for sensing movement of holder 18 and needle 20 relative to fixed abutment member 16 and its depending ferrule-like portion 24. Various forms of position sensing means can be employed, a specific capacitor sensing system being shown in Figures 3 and 4 which will be described in greater detail hereinafter. Figure 2 shows an enlarged depiction of connector component or ferrule 14 and the ferrule-like portion 24 of fixed abutment member 16 in alignment within alignment sleeve 26. It can be seen that protruding end 12a of optical fiber 12 is in alignment with and, in fact, is shown already projecting into passageway 22, with needle 20 being reciprocal within the passageway in the direction of double-headed arrow "C". The simplicity of operation of apparatus 10 is one of its major attributes. In operation, a user simply inserts connector component 14 into the bottom of alignment sleeve 26 in the direction of arrow "B". Needle 20 extends downwardly through passage 22 at least to the bottom surface 24a so that initial engagement is between fiber end 12a and the end 20a of the needle 20. Further movement of the connector component causes the needle 20 and its holder 18 to move upwardly relative to fixed abutment member 16 and its ferrule-like portion 24, until connector component 14 abuts against the ferrule-like portion 24. Further movement of the connector component 14 is stopped, and the relative movement between fixed abutment member 16 and holder 18 of the movable measuring member can be measured by using an appropriate position sensing device. It should be understood that a variety of position sensing devices could be used, such as capacitive sensors, variable reluctance sensors, sensors of the fiber optic reflective type, or the like. A capacitive sensing scheme will be described below, in relation to Figures 3 and 4. It also should be understood that the amount of movement of needle 20 and holder 18 of the movable measuring member does not have to be precisely equal to the distance fiber end 12a protrudes from connector component 14, because measurements can be made based on a particular position of movable measuring member 18 and needle 20. In other words, referring to Figure 2, abutment interface 30 between connector component 14 and ferrule-like portion 24 of fixed abutment member 16, defines a reference surface for measurement. The distance which fiber end 12a projects beyond planar surface 14a of connector component 14 defines the position of needle 20 relative to abutment interface 30. Of course, this protruding distance also is defined by the position of holder 18 of the movable measuring member (which is fixed to the movable needle) and fixed abutment member 16 (which is fixed to ferrule-like portion 24). With that understanding, reference is made to Figure 3 wherein a capacitive position sensing arrangement is shown. Like numerals have been applied to like components as described above in relation to Figures 1 and 2, except that the movable measuring member is now generally referenced as 18. More particularly, Figure 3 shows connector component 14 moved into alignment sleeve 26 into abutment with ferrule-like portion 24 depending from fixed abutment member 16. The fixed abutment member is fabricated in the form of a magnetic steel disc. Movable measuring member 18 is a laminated structure fabricated of an aluminum disk 32 sandwiched between a magnet washer 34 and a dielectric film 36. Needle 20 is fixed by an appropriate fastening means 38 to the laminated movable measuring member 18. Fixed abutment member 16 and movable measuring member 18, in essence, form capacitor plates connected by electrical contacts or leads 40 and 42, respectively, to a variable oscillator, as will be described below in relation to Figure 4. In operation of the arrangement described above in relation to Figure 3, when no connector component 14 is inserted into alignment sleeve 26, movable measuring member (capacitor plate) 18 is maintained in contact with fixed abutment member (capacitor plate) 16 either by gravity, by an appropriate spring, by a magnetic washer 34 as shown in Figure 3, or by any other appropriate means. This contacting position establishes a basic capacitance. When a connector component 14, having a protruding fiber end to be measured, is inserted into alignment sleeve 26, the fiber end will engage the distal end of needle 20 and move measuring member (capacitor plate) 18 away from fixed abutment member (capacitor plate) 16, and the capacitance between the two plates changes. In essence, this change is a function of the fiber protrusion and can be detected by electrical means described below. Specifically, conductors or leads 40 and 42 are connected to a variable oscillator circuit 44. The variable oscillator circuit generates a pulse train signal, shown at 46, having a frequency varying as a function of the capacitance of the capacitor plates 16 and 18. The oscillator circuit 44 is connected to an input of an AND gate 48. Another input of the AND gate 48 is connected to a time base oscillator circuit 50. The time base oscillator circuit 50 generates a fixed frequency signal, shown at 52, at a frequency significantly lower than the variable oscillator 44. As a result, the AND gate 48 outputs the variable frequency signal 46 during the time base determined by the fixed frequency signal 52. This provides a fixed time base during which pulses in the variable frequency pulse train 46 are counted by a counter 53 to provide a total count. This total count, which is proportional to the frequency of the pulse train, represents capacitance. The count total from the counter 53 is then converted into microns or any other appropriate unit by interpolation on a calibration curve by a calibrating device 54, the result being displayed on a display device 56. It should be understood that a microprocessor could be used to perform most of these functions. It should be understood that the measuring apparatus can also be used to measure small negative protrusions of the fiber end 12a, i.e. recess of the fiber end below the planar end 14a of the ferrule due to over polishing.

Claims: An apparatus (10) for measuring the distance an optical fiber end (12a) terminated in a connector protrudes from, or is recessed by a small amount in a planar end surface (14a) of a connector component (14), particularly a ferrule, comprising a fixed abutment member (16, 24) which has a passageway (22) therethrough and an abutment reference surface (24a) to be engaged by said planar end (14a), said passageway (22) being of a width larger than the thickness of the optical fiber (12) within said connector component (14), a movable measuring member (18, 20) which has a telescoping portion (20) within said passageway (22) of said fixed abutment member (16, 24) and a distal end (20a) eventually protruding from said reference surface (24a), alignment means (26) surrounding a portion (24) of said fixed abutment member (16, 24) near said reference surface (24a) and projecting therefrom and being dimensioned for guiding the end of said connector component (14) in engagement with said reference surface (24a), thereby aligning the optical fiber end (12a) with the telescoping portion (20) of the movable measuring member (18, 20) and position sensing means (28) operatively associated with at least the movable measuring member (16, 24) for sensing its amount of relative movement and, thereby, the distance of the optical fiber end (12a) from the planar end (14a) of the connector component (14). The apparatus of claim 1 wherein said fixed abutment member (16, 24) has a ferrule-like portion (24) which is shaped correspondingly to the connector component (14), and wherein said alignment means (26) is an alignment sleeve. The apparatus of claim 1 or 2 wherein said telescoping portion (20) is a needle having a needle end as said distal end (20a). The apparatus of any of claims 1-3 wherein said fixed abutment member (16, 24) has a plate-like member (16) and said movable measuring member (18, 20) also has a plate-like member (18), said position sensing means (28) including means for sensing the relative movement between these plate-like members (16, 18). The apparatus of claim 4 wherein said position sensing means (28) includes capacitor means operatively associated with said plate-like members (16, 18). The apparatus of claim 4 or 5 wherein said position sensing means (28) includes electrical signal generating means (44). The apparatus of claim 6 also comprising calculating means (48, 50, 52, 54) which is responsive to electrical signals from said electrical signal generating means (44).

Inventors: SALZBERG JOSE B, SALZBERG, JOSE B.
Applicants: MOLEX INC, MOLEX INCORPORATED
Application year: 1993
Main classification: G01B7
IPC codes: G01B7, G01B11, G02B6, H01R43