Concentric core optical fiber with multiple-mode signal transmission

• US 5,627,934 A
• Filed: 08/03/1994
• Issued: 05/06/1997
• Est. Priority Date: 08/03/1994
• Status: Expired due to Fees

• Current Assignee: Martin Marietta Energy Systems, Inc.
• Original Assignee: Martin Marietta Energy Systems, Inc.
• Inventors: Muhs, Jeffrey D.
• Primary Examiner(s): Lee, John D.
• Application Number:
  US08/285,246
• Time in Patent Office: 1,007 Days
• Field of Search: 385/28, 385/29, 385/126, 385/127, 385/128, 385/12, 385/13
• US Class Current: 385/127
• CPC Class Codes: G01D 5/353 influencing the transmission properties of an optical fibre
• CPC Class Codes: G02B 6/02042 Multicore optical fibres
• CPC Class Codes: G02B 6/03633 arranged - -
• CPC Class Codes: G08B 13/186 using light guides, e.g. optical fibres

Abstract

A concentric core optical fiber provides for the simultaneous but independent transmission of signals over a single optical fiber. The concentric optical fiber is constructed of a single-mode or multimode inner optical fiber defined by a core and a cladding of a lower index of refraction than the core and an outer optical fiber defined by additional cladding concentrically disposed around the cladding and of an index of refraction lower than the first mentioned cladding whereby the latter functions as the core of the outer optical fiber. By employing such an optical fiber construction with a single-mode inner core or optical fiber, highly sensitive interferometric and stable less sensitive amplitude based sensors can be placed along the same length of a concentric core optical fiber. Also, by employing the concentric core optical fiber secure telecommunications can be achieved via the inner optical fiber since an intrusion of the concentric optical fiber will first cause a variation in the light being transmitted through the outer optical fiber and this variation of light being used to trigger a suitable alarm indicative of the intrusion.

Claims

1. An optical fiber sensor system for providing simultaneous signals indicative of any change in different conditions occurring in a single body and comprising a concentric core optical fiber assembly with a first sensor means and a second sensor means supported by said body and with said second sensor mean being less sensitive to the changes in the different conditions than said first sensor means, said optical fiber sensor system consisting of first and second concentrically disposed optical fiber means, a single light source means coupled to a common end of said first and said second optical fiber means for simultaneously transmitting a first light signal at a selected frequency through the first optical fiber means and a second light signal at said selected frequency through the second optical fiber means, first detector means coupled to a region of said first optical fiber means spaced from said common end for detecting and measuring any changes in the frequency of the first light signal from said selected frequency transmitted therethrough independent of any light signal being transmitted through the second optical fiber means, and second detector means coupled to a region of said second optical fiber means spaced from said common end for detecting and measuring any changes in the frequency of the second light signal from said frequency transmitted therethrough independent of any light signal being transmitted through the first optical fiber means, said first optical fiber means having an elongated region thereof defining the first sensor means and consisting essentially of a first core with a first index of refraction and a first cladding concentrically disposed about the first core and having a second index of refraction that is lower than the index of refraction of the first core for the transmission of said first light signal at said selected frequency through the first sensor means with any change in the frequency of the first light signal to a frequency different from said selected frequency for reception by said first detector means being in response to a change in a first condition in the body supporting the first and second sensor means with the extent of the change in the frequency from said selected frequency providing a measurement indicative of the extent of the change in the first condition in said body, and said second optical fiber means consisting essentially of a second core defined by said first cladding and a second cladding concentrically disposed about said first cladding and having a third index of refraction lower than the index of refraction of the first cladding, said second optical fiber means having an elongated region substantially co-linear with the elongated region of the first optical fiber means and define, rig the second sensor means for the transmission of said second light signal at said selected frequency through the second sensor means with any change in said selected frequency of the second light signal to a frequency different from said selected frequency for reception by said second detector means being in response to a change in a second condition in said body with the extent of the change in the frequency from said selected frequency providing a measurement indicative of the extent of the change in the second condition in said body.

2. An optical fiber sensor system for providing simultaneous signals indicative of different conditions or changes occurring in a single body as claimed in claim 1, wherein said first condition in said body is defined by a strain imposed upon said body, and wherein the extent of change in frequency of the first light signal from said selected frequency corresponds to the extent of strain imposed on said body.

3. An optical fiber sensor system for providing simultaneous signals indicative of different conditions or changes occurring in a single body as claimed in claim 2, wherein said second cladding contains an E-beam thermographic phosphor, wherein said second condition is defined by a change in the temperature of said body, and wherein the extent of change in the frequency of said second light signal from the selected frequency corresponds to said extent of the change in the temperature of said body.