Fiber optical modulator and data multiplexer

• US 4,545,253 A
• Filed: 04/05/1984
• Issued: 10/08/1985
• Est. Priority Date: 08/29/1983
• Status: Expired due to Fees

• Current Assignee: Exxon Production Research Company (Exxon Mobil Corporation)
• Original Assignee: Exxon Production Research Company (Exxon Mobil Corporation)
• Inventors: Avicola, Kenneth
• Primary Examiner(s): Kreitman, Stephen A.
• Application Number:
  US06/596,889
• Time in Patent Office: 551 Days
• Field of Search: 73/655, 73/657, 367/140, 367/149, 332/7.51, 250/227, 350/96.15, 350/96.16, 350/96.24
• US Class Current: 73/655
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G01H 9/004 using fibre optic sensors light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125
• CPC Class Codes: G02B 6/264 with optical elements between opposed fibre ends which perform a function other than beam splitting having lens focusing means G02B6/32; utilising prism or grating G02B6/34
• CPC Class Codes: G02B 6/2804 forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
• CPC Class Codes: G02B 6/2821 using lateral coupling between contiguous fibres to split or combine optical signals
• CPC Class Codes: G02B 6/283 couplers being tunable or adjustable

Abstract

A data gathering system comprising a single optical fiber having one or more modulators formed thereon, means for launching into the fiber an interrogating light pulse which propagates in a first direction, means for generating at each modulator an optical return signal which propagates in the fiber in a second direction opposite the first direction and which has an intensity which is variable in response to variations in an external signal incident at the modulator, and means for detecting and processing each such return signal. The return signal comprises a portion of the interrogating light pulse which is coupled into the fiber in the second direction via evanescent coupling. The return signal from each modulator (or array of modulators) is identified via time division multiplexing. A signal processing means may be coupled to the fiber for generating a unique return signal from each of one or more modulator arrays, each array comprising a selected subset of the modulators. In a preferred embodiment, each modulator comprises a looped section of the fiber having a coupling region in which the distance between adjacent fiber segments is variable in response to variations in an external signal incident thereon. In another embodiment, each modulator comprises a short fiber segment positioned adjacent to the main fiber and separated therefrom by a distance variable in response to pressure changes incident on the modulator.

Claims

1. A data gathering system comprising:

an optical main fiber having a first and a second end and including a core and cladding material;

means for transmitting into the first end of the main fiber an interrogating light pulse which propagates in a first direction along the main fiber;

a modulator formed on said main fiber, said modulator comprising an optical fiber segment held substantially parallel to a first section of said main fiber in a manner so that said segment and said main fiber are separated by a distance which is variable in response to variations in an incident external signal, said modulator further comprising means for diverting a return portion of said interrogating light pulse having intensity which varies in response to the distance between said segment and said main fiber, so that the return portion propagates in the main fiber in a direction opposite said first direction; and

means optically coupled to said main fiber for detecting said return portion.

2. The invention of claim 1 wherein:

said segment comprises a second section of said main fiber; and

said return portion diverting means comprises a third section of said main fiber having a first end connected to said second section and a second end connected to said first section, so that said return portion comprises a portion of the interrogating pulse diverted from said first section to said second section via evanescent coupling and a portion of the interrogating pulse diverted from said second section to said first section via evanescent coupling.

3. The invention of claim 2 wherein said external signal is an acoustic signal, and said modulator further comprises:

a hollow structure defining a chamber containing air, which structure encloses said first section and said second section and substantially prevents liquid intrusion into the chamber, said structure comprising a first area and a second area, said first area adapted to move relative to said second area in response to acoustic vibrations incident on said structure;

compliant cladding material positioned between said first section and said second section;

a first pin positioned in said chamber in contact with said first area and said first section; and

a second pin positioned in said chamber in contact with said second area and said second section so that acoustic vibrations incident on the structure will displace said first pin relative to said second pin and vary the distance between said first section and said second section.

4. The invention of claim 2 wherein said external signal is an acoustic signal, and said modulator further comprises:

a hollow structure defining a chamber containing air, which structure encloses said first section and said second section and substantially prevents liquid intrusion into the chamber, said structure comprising a first area and a second area, said first area adapted to move relative to said second area in response to acoustic vibrations incident on said structure;

a layer of gel, having index of refraction substantially the same as that of the cladding material of the optical main fiber, separating said first section from said second section;

a first member positioned in said chamber in contact with said first section and said first area; and

a second member positioned in said chamber in contact with said second section and said second area so that acoustic vibrations incident on the structure will displace said first member relative to said second member and vary the distance between said first section and said second section.

5. The invention of claim 2 wherein said external signal is a voltage signal, and wherein said return portion diverting means comprises:

a housing attached to said first section; and

a pusher element attached to the housing and to said second section in a manner so that the pusher element moves said second section relative to said first section in response to variations in the voltage signal, so as to vary the distance between said first section and said second section in response to variations in the voltage signal.

6. The invention of claim 2, wherein said modulator further comprises:

a sensor for producing a voltage signal in such a manner that a characteristic of said voltage signal will vary in response to variations in an external signal incident on said sensor;

a housing attached to said first section; and

a pusher element electrically coupled to the sensor, and attached to the housing and to said second section in a manner so that the pusher element moves said second section relative to said first section in response to variations in the voltage signal, so as to vary the distance between said first section and said second section in response to variations in the voltage signal.

7. The invention of claim 1 wherein:

said segment is an optical fiber separate from said main fiber, said optical fiber having a highly reflective, flat first end face oriented substantially perpendicular to the axis of said optical fiber, and a highly reflective, flat second end face oriented substantially perpendicular to the axis of said optical fiber; and

said return portion comprises a portion of said interrogating pulse diverted from said main fiber into said optical fiber via evanescent coupling and then diverted via evanescent coupling from said optical fiber back into said main fiber so as to propagate in said main fiber in the direction opposite said first direction.

8. The invention of claim 7 wherein said external signal is an acoustic signal, and said modulator further comprises:

a hollow structure defining a chamber containing air, which structure encloses said optical fiber and said first section of the optical main fiber and substantially prevents liquid intrusion into the chamber, said structure comprising a diaphragm adapted to move relative to said first section of the optical main fiber in response to acoustic vibrations incident on said structure; and

a compliant member attached between said diaphragm and said first section, and including a compliant layer having index of refraction substantially the same as that of the cladding material of the optical main fiber, which compliant layer is positioned between said optical fiber and said first section so that acoustic vibrations incident on the structure will vary the distance between said optical fiber and said first section.

9. The invention of claim 1 wherein said return signal detecting means comprises a first transducer for converting at least part of the return portion into a first electrical signal.

10. The invention of claim 9 further comprising:

a directional coupler optically coupled to said main fiber between said first end of said main fiber and said modulator;

a first optical branch fiber optically coupled to the directional coupler so that light propagating in said main fiber toward said modulator is diverted by said directional coupler into said first optical branch fiber;

monitor means optically coupled to the first optical branch fiber for detecting light diverted into said first optical branch fiber by said directional coupler; and

a second optical branch fiber optically coupled to the directional coupler and to the return signal detecting means so that the return portion propagating in said main fiber is diverted by said directional coupler through said second optical branch fiber to said return signal detecting means.

11. The invention of claim 1 further comprising means attached to the modulator for reducing the effect on the intensity of the return portion due to change in the incident external signal which change has a rate of change below a selected minimum rate.

12. A data gathering system employing time-division multiplexing, comprising:

an optical main fiber having a first end and a second end;

means for transmitting into the first end of the main fiber, at a first instant, an interrogating light pulse which propagates in a first direction along the main fiber;

at least two modulators formed on said main fiber, each of which said modulators comprises an optical fiber segment held substantially parallel to a first section of said main fiber in a manner so that said segment and said main fiber are separated by a distance which is variable in response to variations in an incident external signal, each of said modulators further comprising means for diverting a return portion of said interrogating light pulse having intensity which varies in response to the distance between said segment and said main fiber so that the return portion propagates in the main fiber in a direction opposite said first direction; and

means optically coupled to said main fiber for detecting the return portion from each of said modulators.

13. The invention of claim 12 wherein:

said segment comprises a second section of said main fiber; and

said return portion diverting means comprises a third section of said main fiber having a first end connected to said second section and a second end connected to said first section, so that said return portion comprises a portion of the interrogating pulse diverted from said first section to said second section via evanescent coupling and a portion of the interrogating pulse diverted from said second section to said first section via evanescent coupling.

14. The invention of claim 12 wherein:

said segment is an optical fiber separate from said main fiber, said optical fiber section having a highly reflective, flat first end face oriented substantially perpendicular to the axis of said optical fiber, and a highly reflective, flat second end face oriented substantially perpendicular to the axis of said optical fiber; and

said return portion comprises a portion of said interrogating pulse diverted from said main fiber into said optical fiber via evanescent coupling and then diverted via evanescent coupling from said optical fiber back into said main fiber so as to propagate in said main fiber in the direction opposite said first direction.

15. The invention of claim 12 wherein said return portion detecting means comprises a first transducer generating a first electric signal having instantaneous amplitude which varies in response to the instantaneous amplitude of the return portions detected by the return portion detecting means.

16. The invention of claim 15 wherein said first electrical signal has instantaneous amplitude substantially proportional to the instantaneous amplitude of the return portions detected by the return portion detecting means.

17. The invention of claim 15 further comprising:

a directional coupler optically coupled to said main fiber and positioned so that the interrogating pulse will reach the directional coupler prior to reaching any of the modulators;

a first optical branch fiber optically coupled to the directional coupler so that a portion of the interrogating pulse propagating in said main fiber toward said modulators is diverted by said directional coupler into said first optical branch fiber;

monitor means optically coupled to the first optical branch fiber for detecting the portion of the interrogating pulse diverted into said first optical branch fiber by said directional coupler; and

a second optical branch fiber optically coupled to the directional coupler and to the return portion detecting means so that the return portion propagating in said main fiber is diverted by said directional coupler through the second optical branch fiber to said return portion detecting means.

18. The invention of claim 17 wherein the monitor means comprises a second transducer for converting at least part of the portion of the interrogated pulse diverted into said first optical branch fiber into a second electrical signal, and further comprising:

signal processing means electrically coupled to the first transducer and to the second transducer for converting said first electric signal and second electrical signal into an array signal representing the total power of the return portions returned from a selected subset of said at least two modulators.

19. The invention of claim 18 wherein the signal processing means further comprises:

means for generating a third electrical signal having amplitude at any second instant after said first instant substantially proportional to the time integral of said first electrical signal, integrated from said first instant to said second instant; and

means for applying said third electrical signal to said first electric signal so as to reduce the effect on said first electric signal due to upstream modulator losses on the return portion from each of the modulators in said selected subset, and to reduce the effect on said array signal due to said upstream modulator losses.

20. The invention of claim 18 wherein the transmitting means is adapted to transmit successively a plurality of substantially identical interrogating pulses into the first end of the main fiber, and wherein the signal processing means further comprises:

means for generating a fourth electrical signal having amplitude following the peak amplitude of said second electrical signal; and

means for applying said fourth electrical signal to said first electrical signal so as to reduce the effect on said first electrical signal due to differences between the interrogating pulses and to reduce the effect on said array signal due to differences between the interrogating pulses.

21. The invention of claim 20 wherein the signal processing means further comprises:

means for sampling the first electric signal prior to application of said third electric signal to said first electric signal during selected periods when the data gathering system is in a quiet state;

means for holding the sampled signal; and

means, including a differential amplifier, for applying the held signal to said first electric signal in a manner so as to reduce the effect on the intensity of said first electric signal due to changes in the average external conditions affecting the modulators between successive interrogating pulse transmissions.

22. The invention of claim 12 further comprising means attached to each of the modulators for reducing the effect on the intensity of the return portion due to change in the external signal incident on the modulator which change has a rate of change below a selected minimum rate.