GB2064103A

GB2064103A - Testing optical fibres

Info

Publication number: GB2064103A
Application number: GB7941250A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1979-11-29
Filing date: 1979-11-29
Publication date: 1981-06-10
Also published as: GB2064103B

Abstract

An arrangement for testing a plurality of optical fibres, e.g. the individual fibres of a cable. The fibres (134) are illuminated selectively via an indexer mechanism (13) which mechanism is driven at constant speed by a drive motor (132). The light transmission characteristics of the fibres are monitored and stored by a microprocessor (MPU). The sequence of operations of the microprocessor is determined by the activation of a series of light activated switches (LAS 1 to 8) via a set of control fibres (123) illuminated via a coding disc (131) forming part of the indexer mechanism. <IMAGE>

Description

SPECIFICATION Testing optical fibres This invention relates to techniques and to apparatus for the measurement of the optical properties of optical fibres e.g. during cabling operations.

The quality of optical fibres and/or optical fibre cable is routinely assessed following manufacture by observing changes in the light transmission characteristics during e.g. environmental tests at both high and low temperatures, each fibre being tested on an individual basis. Such a process is, of course, time consuming and in some circumstances can limit the rate at which fibres and cables can be produced.

The object of the present invention is to minimise or to overcome this disadvantage.

According to one aspect of the present invention there is provided an apparatus for measuring the optical characteristics of a plurality of optical fibres, including a control unit, a light source, indexing means for coupling the fibres selectively to the light source, and means for measuring the optical transmission properties of each illuminated fibre, and wherein said indexing means is so constructed as to provide the control unit for each said illuminated fibre with a code signal identifying that fibre.

According to another aspect of the invention there is provided a method of measuring the optical properties of a plurality of optical fibres, including arranging the one ends of said fibres in an array, coupling the other ends of said fibres to a photodetector, scanning the array with a light carrying relatively large fibre so as to illuminate selectively the one ends of the fibres, and measuring the light output of each said fibre.

An embodiment of the invention will now be described with reference to the accompanying drawings in which: Fig. 1 is a schematic diagram of an optical fibre multichannel test apparatus.

Fig. 2 is a cross-sectional view of the index mechanism of the apparatus of Fig. 1; Fig. 2a shows a scrap sectional view along the line X-X; Fig. 3 shows the input fibre mounting plate of the index mechanism of Fig. 2; Fig. 4 shows the test fibre mounting plates of the index mechanism of Fig. 2; and Fig. 5a and 5b shows plan and sectional views respectively of the coding plate mechanism of the indexer of Fig. 2.

Referring to Fig. 1, the optical fibre multichannel test apparatus depicted therein is employed for measuring the optical properties of the various individual fibres of an optical cable, or of a plurality of uncabled fibres, under various conditions of temperature, humidity, strain and pressure. The apparatus is controlled from a central control unit 11 and includes a light source 12, an index mechanism 13, a photodetector arrangement 14 and an environmental test chamber 1 5. The light source 12 is coupled to indexer 13 via a relatively large optical fibre 121 and to the central control unit 11 via first and second sets of fibres 122 and 123 respectively.

Each first fibre 122 can be coupled to a respective second fibre 123 via a rotatable perforated coding disc 131 forming part of the indexer mechanism and driven by a motor 132.

The individual fibres 134 of an optical cable 135 to be tested are coupled to the detector 14, and to the indexer 13, where they may be coupled selectively to the fibre 121, the sheathed portion of the cable 135 being led through the test chamber 15. Also, a reference optical fibre 136 is coupled directly between the indexer 13 and detector 14. The detector output is fed back to the central control unit 11.

The control unit 11 advantageously includes a microprocessor MPU suitably programmed for performing the various control, computation and data output functions. The microprocessor is provided with input instructions via a set of light activated switches LAS 1 to LAS 8, and receives input data from the detector 14. The output of the microprocessor can be fed to a display unit VDU, a disc memory M1 and a printer P1.

The sequence of operation of the microprocessor corresponds to the order in which the respective switches LAS 1 to LAS 8 are activated by coupling of the respective fibres 122 and 123 via the coding disc 131. In the embodiment shown in Fig. 1, the first switch LAS 1 when activated initiates an instruction to read the test chamber conditions and store these in the memory Ml. The second switch LAS 2 provides for reading of the detector output for each fibre 134 and storing that reading. The third switch LAS 3 instructs the microprocessor to read the input from the set of fibres 123a coupled to the switches LAS 4 to 8, these fibres being set to supply a five bit code input.

The fibres 134 are tested in sequential order in a continuous cycle. Each fibre is coupled selectively to the large fibre 121 via the indexer which is driven from the motor 132. The coding disc 131 is synchronised with the indexer. Thus, as each fibre 134 is coupled with the fibre 121 the microprocessor receives its operating instructions via switches LAS 1 to LAS 3 together with a five bit code identifying the fibre under test via switches LAS 4 to 8. The motor 132 drives the indexer mechanism at a constant speed. As each fibre 134 is illuminated its output is sampled frequently e.g. every 10 msec, by the microprocessor MPU, the maximum output signal for each measurement being selected by a reiterative comparative process and stored.

Advantageously the fibre 136 is included in the measurement cycle to provide a reference standard.

Fig. 2 shows the indexer mechanism of the apparatus of Fig. 1. As shown in Fig. 2 the indexer includes a mounting block 21 supporting a body member 22 provided with a bearing 23 for carrying a drive shaft 25. Test fibre mounting plate 26 is secured to one face of the body, member 22 and an input fibre mounting plate 27 secured to the drive shaft 25 is rotatable adjacent the opposite face of the body member 22.

The test fibre mounting plate 26 is shown in further detail in Fig. 4, and comprises a truncated circular body 260 provided with an arcuate array of bores 261 parallel to the body axis and each being of such a size as to receive a plastics coated optical fibre. A plurality of L-shaped wire spring members 262, one for each bore 261 are disposed on the inward facing surface of the body 260 and in register with the bore 261. The free end of each spring member 262 is encased in a plastics sleeve 263 to prevent fibre damage and abuts a corresponding groove 264 (Fig. 2a) in the surface of the body member 22 whereby a bared fibre 265 may be secured adjacent the input fibre mounting plate 27 (Fig. 2).

The mounting plate 27, also shown in Fig. 3 comprises a circular body provided near its periphery with a bearing 271 in which a relatively large aperture fibre termination 272 is mounted.

This termination receives the relatively large input fibre 121, the bearing 271 being so disposed that the termination 272 can be brought into register with any one of the fibre ends 265 by rotation of the plate 27. Thus, a stepped rotation of the plate 27 by the motor illuminates each fibre end 265 in turn, the bearing 271 preventing twisting of the fibre 121.

Figs. 5a and 5b show the coding disc assembly of the indexer mechanism. This assembly indudes a perforated disc 51 mounted on the drive shaft 25 and which thus rotates together with the input fibre mounting plate 27. On either side of the disc 51 and disposed in register with each other are first and second optical fibre termination blocks 510 and 511 respectively. These termination blocks each have a corresponding array of fibre termination (not shown) for receiving the first and second sets of optical fibres 122 and 123. As shown in Fig. spa the disc 51 has a plurality of radially disposed arrays of apertures 512, these apertures being so arranged that, as each fibre is illuminated, a selected pair of the fibres 122 and 123 are coupled via the apertures 512 lying along one radius. The apertures 512 provide a code which initiates the operating sequence of the microprocessor MPU (Fig. 1) and identifies the particular fibre under test.

Claims

1. An apparatus for measuring the optical characteristics of a plurality of optical fibres, including a control unit, a light source, indexing means for coupling the fibres selectively to the light source, and means for measuring the optical transmission properties of each illuminated fibre, and wherein said indexing means is so constructed as to provide the control unit for each said illuminated fibre with a code signal identifying that fibre.

2. An apparatus as claimed in claim 1, and wherein said indexer includes a rotatable perforated disc whereby said code signal is provided.

3. An apparatus as claimed in claim 1 or 2, and wherein said control unit includes a microprocessor.

4. An apparatus as claimed in claim 3, wherein the instruction input of said microprocessor is provided via an array of light activated switches.

5. An apparatus as claimed in any one of claims 1 to 4 and which includes an environmental test chamber in which at least some of said fibres are disposed.

6. An optical fibre test apparatus substantially as described herein with reference to the accompanying drawings.

7. A method of measuring the optical properties of a plurality of optical fibres, including arranging the one ends of said fibres in an array, coupling the other ends of said fibres to a photodetector, scanning the array with a light carrying relatively large fibre so as to illuminate selectively the one ends of the fibres, and measuring the light output of each said fibre.

8. A method as claimed in claim 7, and wherein at least some of said fibres are disposed in an environmental test chamber.

.9. An optical fibre measurement process substantially as described herein with reference to the accompanying drawings.