Remote measurement of physical variables with fiber optic systems

Claim 2

1 . An optical fiber adapted to sense physical forces at different points along its length, comprising at least a light-guiding region A into which interrogating light is launched and a second light-guiding region B, and characterized by deflecting under the action of a force at any point, when interrogated by pulsed or AC-modulated light within a pre-selected wavelength region and of pre-selected duration or frequency, a fraction α of the intensity of the interrogating light pulses being transmitted through region A into region B, said region B adapted to automatically process said deflected light and transmit it to as least one fiber end in a form which makes said deflected light resolvable from interrogating light transmitted through region A and from light deflected from region A to region B at other points along the fiber.

Claim 3

2 . An optical fiber as claimed in claim 1 wherein said light-guiding region A is the fiber core, and said light-guiding region B is a cladding around said core and has a fluorescent material dissolved therein and adapted to automatically convert said deflected light into fluorescence light having wavelengths different and separable from the wavelength or wavelengths of the interrogating light.

Claim 4

3 . An optical fiber as claimed in claim 1 wherein said light-guiding region A is a core having an index of refraction n₁ bounded by a first cladding having an index of refraction n₂ lower than n₁, the relative values of n₁ and n₂ being such that the value of (n 2 1 - n 2 2 ) ½ does not exceed 0.15, and said light-guiding region B is a second cladding around and in contact with said first cladding, having a graded index of refraction the highest value of which, n₃, is at least two percent higher than n₁, the higher value of n₃ adapted to cause said light deflected at each sensing point to arrive at the fiber distal end at different, resolvable times from the times of arrival of the undeflected interrogating light and from the times of arrival of the lights deflected from region A to region B at other sensing points along the fiber.

Claim 5

4 . A force-sensing arrangement of the optical fiber claimed in claim 2 and additionally comprising: a) means for generating and launching said pulsed or AC-modulated interrogating light into the fiber core at the launch end of said fiber; b) means located at or near the launch end of the fiber for directing the fluorescence back-emitted from force-sensing points along the fiber to photodetection means for providing force measurements.

Claim 6

5 . A force-sensing arrangement comprising the optical fiber claimed in claim 3 and additionally comprising: a) means for generating and launching said pulsed or AC-modulated interrogating light into the fiber core at the launch end of said fiber; and b) photodetector means for processing the light deflected at each sensing point and for providing force measurements.

Claim 7

6 . A force-sensing arrangement as claimed in claim 5 and adapted to the non-invasive coupling of information into an optical fiber from the side at any point, the arrangement additionally comprising means to convert the information to be coupled into forces applied laterally to the fiber.

Claim 8

7 . An optical fiber comprising: a) a fiber core made of a luminescent material capable of stimulated emission and having an index of refraction desigmnated herein as n₁; said core designated herein as the fiber's first light-guiding region; b) a second light-guiding region around said core, having an index of refraction n₂ not higher than n₁ and an elongated cross-section with a long dimension much greater than the diameter of the core, and a dimension, perpendicular to said long dimension, approximately equal to or not more than a few micrometers greater than the diameter of said core; and c) a cladding around and in contact with said second light-guiding region, said cladding having an index of refraction n₃ lower than n₂.

Claim 9

7 . An optical fiber comprising: a) a fiber core made of a luminescent material capable of stimulated emission and having an index of refraction desigmnated herein as n₁; said core designated herein as the fiber's first light-guiding region; b) a second light-guiding region around said core, having an index of refraction n₂ not higher than n₁ and an elongated cross-section with a long dimension much greater than the diameter of the core, and a dimension, perpendicular to said long dimension, approximately equal to or not more than a few micrometers greater than the diameter of said core; and c) a cladding around and in contact with said second light-guiding region, said cladding having an index of refraction n₃ lower than n₂.

Claim 10

8 . An arrangement for pumping a fiber laser or optical fiber amplifier, comprising: a) an optical fiber as claimed in claim 7; and b) means for launching excitation light into said second light-guiding region, said light having wavelengths within an optical absorption band of said luminescent material.

Claim 11

9 . A temperature measuring arrangement comprising: a) an optical fiber comprising a core with an index of refraction n₁, a first cladding around said core having an index of refraction n₂ lower than n₁, the value of n₂ decreasing in a known manner with an increase in temperature at a greater rate than the decrease in the value of n₁, and a second cladding around said first cladding, having an index of refraction n₃ lower than n₂; b) means for generating and launching interrogating light pulses of submicrosecond duration into the core and the first cladding at the launch end of said fiber; and c) means located at or near the launch end of said fiber for directing light backscattered within the fiber core at temperature measurement points along the fiber to photodetector means, the intensity of said backscattered light at each measurement point being an indicatoe of the temperature at that point.

Claim 12

9 . A temperature measuring arrangement comprising: a) an optical fiber comprising a core with an index of refraction n₁, a first cladding around said core having an index of refraction n₂ lower than n₁, the value of n₂ decreasing in a known manner with an increase in temperature at a greater rate than the decrease in the value of n₁, and a second cladding around said first cladding, having an index of refraction n₃ lower than n₂; b) means for generating and launching interrogating light pulses of submicrosecond duration into the core and the first cladding at the launch end of said fiber; and c) means located at or near the launch end of said fiber for directing light backscattered within the fiber core at temperature measurement points along the fiber to photodetector means, the intensity of said backscattered light at each measurement point being an indicatoe of the temperature at that point.

Claim 13

A force-sensing optical fiber, comprising: (a) a clear core having an index of refraction n₁; (b) a clear first cladding around and in contact with said core, having an index of refraction n₂ lower than n₁; (c) a second cladding around and in contact with said first cladding, having an index of refraction n₃ not significantly lower than n₂ and characterized by a length-­dependent partial absorption of interrogating light of suitable pre-selected wavelenghts λ₁ and a much weaker absorption of light of suitable pre-selected wavelengths λ₂; and (d) a clear third cladding having an index of refraction n₄ substantially lower than n₂; the fiber being so characterized that, when interrogating light composed of light of said wavelengths λ₁ and light of said wavelengths λ₂ is injected into one end (i.e. the injection end) of the fiber and propagated along said core towards the other end (the distal end), a bending force applied at any point along the fiber causes the deflection of a fraction α of the intensity of the interrogating light from the core to said first and said second claddings and the absorption of a fraction β of the intensity of the component of wavelengths λ₁ of said deflected light, the magnitude of β being a known function of the location along the fiber where the force is acting, the relative intensities of the components of wavelengths λ₁ and λ₂ of the deflected light transmitted by said first and said second claddings to said other end being an indicator of the location along the fiber where the force is acting.

Claim 14

A force-sensing optical fiber, comprising: (a) a clear core having an index of refraction n₁; (b) a clear first cladding around and in contact with said core, having an index of refraction n₂ lower than n₁; (c) a second cladding around and in contact with said first cladding, having an index of refraction n₃ not significantly lower than n₂ and characterized by a length-­dependent partial absorption of interrogating light of suitable pre-selected wavelenghts λ₁ and a much weaker absorption of light of suitable pre-selected wavelengths λ₂; and (d) a clear third cladding having an index of refraction n₄ substantially lower than n₂; the fiber being so characterized that, when interrogating light composed of light of said wavelengths λ₁ and light of said wavelengths λ₂ is injected into one end (i.e. the injection end) of the fiber and propagated along said core towards the other end (the distal end), a bending force applied at any point along the fiber causes the deflection of a fraction α of the intensity of the interrogating light from the core to said first and said second claddings and the absorption of a fraction β of the intensity of the component of wavelengths λ₁ of said deflected light, the magnitude of β being a known function of the location along the fiber where the force is acting, the relative intensities of the components of wavelengths λ₁ and λ₂ of the deflected light transmitted by said first and said second claddings to said other end being an indicator of the location along the fiber where the force is acting.

Claim 15

An optical keyboard system, comprising: (a) an arrangement of depressable keys; and (b) two optical fibers as claimed in claim 1, each of them being disposed under said arrangement of keys in such a manner that the two fibers intersect under each key of said arrangement, the depresssion of each key producing said bending forces at both fibers simultaneously.

Claim 16

An optical keyboard system as claimed in claim 2 and additionally comprising: (a) means for generating and injecting interrogating light composed of said wavelengths λ₁ and λ₂ into the cores at the injection end of each of said two fibers; and (b) photodetector means for measuring the relative intensities of the component of wavelengths λ₁ and the component of wavelengths λ₂ of the light deflected from the core to said first and second cladings of each of said two fibers and transmitted by said claddings to the fibers' distal ends.

Claim 17

An optical fiber adapted to sense physical variables, comprising at least two light-guiding regions A and B and so characterized that, when interrogated with light of a wavelength or wavelengths within a suitable pre-selected spectral region injected at one fiber end (the injection end) into region A, the intensity of the interrogating light propagating along the fiber is distributed between said regions A and B, the relative distribution varying as a function of the magnitude of the physical variable acting on the fiber, the fiber being adapted to automatically process said relative distribution into two resolvable optical signals the relative intensities of which are an indicator of said relative distribution and, hence, of the magnitude of the physical variable.

Claim 18

An optical fiber adapted to sense physical variables, comprising at least two light-guiding regions A and B and so characterized that, when interrogated with light of a wavelength or wavelengths within a suitable pre-selected spectral region injected at one fiber end (the injection end) into region A, the intensity of the interrogating light propagating along the fiber is distributed between said regions A and B, the relative distribution varying as a function of the magnitude of the physical variable acting on the fiber, the fiber being adapted to automatically process said relative distribution into two resolvable optical signals the relative intensities of which are an indicator of said relative distribution and, hence, of the magnitude of the physical variable.

Claim 19

An optical fiber as claimed in claim 4 and adapted to sense forces, where said light-guiding region A is a core having an index of refraction n₁ bounded by a first cladding having an index of refraction n₂ lower than n₁, and said light-guiding region B is a second cladding around and in contact with said first cladding and having a graded index of refraction the highest value of which, n₃, is substantially higher than n₁, the fiber being so characterized that, when interrotaged with light pulses of suitably short duration injected into said core A at one fiber end (the injection end) and propagating along said core, a fraction α of the intensity of each interrogating light pulse propagating along said core is deflected from the core to said second cladding, said deflected light pulse arriving at the other fiber end (the distal end) at a time measurably different from the earlier time of arrival of the undeflected light pulse, the value of α increasing with increasing magnitude of the force.

Claim 20

An optical fiber as claimed in claim 5 and adapted to sense forces at different points along its length, the fiber being so characterized that, when interrogated with light pulses of suitably short duration injected into said core at the fiber injection end, said fraction α of the intensity of each interrogating light pulse propagating along said core at each sensing point is deflected from said core to said second cladding, said deflected light pulse arriving at the fiber distal end at a time measurably different from the earlier time of arrival of the undeflected light pulse and from the times of arrival of the light pulses deflected at other sensing points along the fiber, said times of arrival identifying the location along the fiber where the force is acting.

Claim 21

A force-sensing arrangement comprising the optical fiber claimed in claim 6 and additionally comprising: (a) means for generating and injecting said light pulses into the fiber core at the injection end of said fiber; and (b) photodetector means and associated electronic means for measuring the times of arrival at the fiber distal end, relative to the time of arrival of the undeflected light pulses, of the pulses of light deflected from the fiber core to said second cladding at each sensing point along the fiber.

Claim 22

An optical keyboard system consisting of a force-sensing arrangement as claimed in claim 7 and additionally comprising an arrangement of depressable keys, where said fiber is disposed under said arrangement of keys in such a manner that each key, when depressed, deflects a fraction of the intensity of the interrogating light injected into said core from said core into said second cladding simultaneously at two different points along the fiber, thus generating from each interrogating light pulse two pulses of deflected light the times of arrival of which at the fiber distal end, relative to the time of arrival of the undeflected pulse, identify the location of said key.

Claim 23

An optical keyboard system consisting of a force-sensing arrangement as claimed in claim 7 and additionally comprising an arrangement of depressable keys, where two optical fibers as claimed in claim 6 are disposed under said arrangement of keys in such a manner that the two fibers intersect under each key of said arrangement, and where the intensity of each interrogating light pulse is distributed between the two fibers, the depression of each key causing the deflection of a fraction of the intensity of the interrogating lights propagating along the cores of each fiber at that point from said cores into said second claddings, thus generating from each interrogating light pulse two pulses of deflected light the times of arrival at the distal ends of the two fibers, relative to the time of arrival of the undeflected pulses, identify the location of each key.