Identification and location of fiber optic cables

• US 20030052258A1
• Filed: 11/06/2002
• Published: 03/20/2003
• Est. Priority Date: 09/21/1998
• Status: Active Grant

• Current Assignee: Radiodetection Limited
• Original Assignee: Radiodetection Limited
• Inventors: Russell, Stuart John, Dakin, John Philip, Lewis, Andrew Biggerstaff
• Granted Patent: US 6,650,798 B2
• Time in Patent Office: Days
• US Class Current: 250/227.17
• CPC Class Codes: G02B 6/562 locatable, e.g. using magnetic means

Abstract

In order to identify a fiber optic cable (10) a beam (14) of polarised light is caused to pass down the cable to a first site (A) at which an electromagnetic field (24) is applied to the cable (10). The electromagnetic field (24) traverses the cable (10) in an essentially transverse direction and has a time-varying component orientated along the length of the cable (10) at the first site (A), with the component varying so that the line integral thereof along the cable (10) is non-zero. This results in a variation in the polarisation of the light, which can the be detected by a polarisation discriminator (20) at a second site (B), thereby to identify the cable (10).

Claims

1. A method of identifying a fiber optic cable (10), comprising:

causing a beam (14) of light to pass down the cable (10);

applying an electromagnetic field (24) to the cable at a first site A, thereby to vary the polarisation of the light; and

detecting (26) the variation in the polarisation at a second site (B), thereby to identify the fiber optic cable;

characterised in that;

the electromagnetic field is applied by causing said electromagnetic field (24) to traverse the fiber optic with (10) in an essentially transverse direction, the electromagnetic field (24) having a time-varying component orientated along the length of the fiber optic cable (1) at the first site (A), said component varying such that the line integral thereof along the cable (10) is non-zero.

2. A method according to claim 1, wherein the electromagnetic field (24) has a frequency in the range 10 kHz to 200 MHz.

3. A method according to claim 1 or claim 2, wherein the electromagnetic field (24) is transmitted to the fiber optic cable (10) from at least one antenna (16) which is aligned in a plane which is substantially parallel to offset from the longitudinal axis of the cable (10) at the first point (A).

4. A method according to any one of the preceding claims, wherein the state of polarisation of the beam of light (14) is modulated prior to the application of said electromagnetic field to the cable.

5. A method according to claim 4 as dependent on claim 2, wherein the frequency of modulation is a factor of at least 10 less than the frequency of electromagnetic field.

6. A method according to claim 4 or claim 5, wherein the beam of light is generated by a light generator (22) to which a modulation signal is applied, thereby to modulate the state of polarisation.

7. A method according to claim 4 or claim 5, wherein the beam of light is generated by a light generator (22) and said state of polarisation is modulated by a modulator (40) which is located between said light generator (22)and said first site (A).

8. An apparatus for identifying a fiber optic cable (10) comprising:

a light generator (22) for causing a beam (14) of light to pass down the cable (10);

an antenna (16) for applying an electromagnetic field (24) to the cable (10) at a first site (A), thereby to vary the polarisation of the light; and

a detector (26) for detecting the variation in polarisation at a second site (B), thereby to identify the fiber optic cable (10);

characterised in that;

the antenna is arranged to cause said electromagnetic field (24) to traverse the fiber optic with (10) in an essentially transverse direction, the electromagnetic field (24) having a time-varying component orientated along the length of the fiber optic cable (1) at the first site (A), said component varying such that the line integral thereof along the cable (10) is non-zero.