Device for tapping radiation from, or injecting radiation into, single made optical fiber, and communication system comprising same

Claim 2

Means for coupling electromagnetic radiation of wavelength Λ o into or from an intermediate portion of an optical fiber, the fiber comprising a core and a cladding surrounding the core and having optical characteristics including an attenuation constant α ij and a propagation constant β ij for each mode LP ij of the radiation that can be present in the fiber, where i is a non-negative integer and j is a positive integer, characterized in that (a) the fiber is a single mode optical fiber at the wavelength λ o ; (b) the coupling means comprise means adapted for forming in the intermediate portion of the fiber a grating consisting of N elements, a grating being a portion of fiber in which one or more fiber parameters are caused to vary as a function of the axial coordinate z of the fiber, the fiber parameters including the core refractive index and the fiber axis geometry, associated with the grating being a nominal repeat distance Λ(z) and a nominal amplitude function g(z); (c) Λ(z) is chosen such that Ω o =(2π/Λ)>β 01 -2πn c1 /λ o , where Λ is the average repeat spacing in the grating, β 01 is the propagation constant of the LP 01 mode of radiation, and n c1 is the refractive index of the cladding of the fiber; (d) Λ(z) furthermore is chosen such that Ω o ˜β 01 -β rs , where β rs is the propagation constant of the LP rs mode of radiation, where LP rs is a tunneling leaky (TL) mode of the radiation of wavelength λ o in the fiber; and (e) the attenuation constant α rs of the LP rs mode is less than about 1 dB/cm.

Claim 3

The coupling means of claim 1, wherein the means adapted for forming a grating comprise means adapted for impressing an undulation upon the fiber axis.

Claim 4

The coupling means of claim 2, wherein the means for impressing an undulation upon the fiber axis comprise at least one corrugated body, and means for urging the corrugated body against the fiber.

Claim 5

The coupling means of claim 1, wherein the means for locally changing the core refractive index comprise a photo-refractively active chemical element present in the core, and means for exposing the fiber core to actinic radiation, whereby the refractive index of the fiber core can be changed by means of the photo-refractive effect.

Claim 6

The coupling means of claim 1, wherein the means for locally changing the core refractive index comprise at least one corrugated body, and means for urging the corrugated body against the fiber, whereby the refractive index of the fiber core can be changed by means of the photo-elastic effect.

Claim 7

The coupling means of claim 2, further comprising means for enhancing the emission of radiation from the cladding of the fiber.

Claim 8

The coupling means of claim 6, wherein the means for enhancing emission of radiation from the cladding comprise a dielectric body contacting the fiber downstream from the grating, the dielectric body being substantially transparent for the radiation of wavelength λ o .

Claim 9

The coupling means of claim 1, wherein the LP rs mode is the LP 11 mode.

Claim 10

The coupling means of claim 1, wherein the nominal amplitude function g(z) is a constant.

Claim 11

The coupling means of claim 1, wherein the nominal amplitude function g(z) is proportional to a Gaussian function of z.

Claim 12

The coupling means of claim 1, wherein the nominal repeat distance Λ(z) is a constant.

Claim 13

The coupling means of claim 1, wherein at least the intermediate portion of the fiber is coated with a material that is substantially transparent for the electromagnetic radiation of wavelength λ o .

Claim 14

The coupling means of claim 1, wherein the means adapted for forming a grating comprise means for locally changing the core refractive index.

Claim 15

An optical communications system comprising a source of first electromagnetic radiation of wavelength λ o , an optical fiber adapted for guiding the first radiation, first means for coupling the first radiation into the fiber at a first fiber location, and means for detecting, at a second fiber location spaced apart from the first fiber location, the first radiation that is transmitted from the first to the second fiber location through the fiber, the fiber comprising a core and a cladding surrounding the core, the fiber having optical characteristics including an attenuation constant α ij and a propagation constant β ij for each mode LP ij of the first radiation that can be present in the fiber, where i is a non-negative integer and j is a positive integer, the optical communications system further comprising second means for coupling first radiation into or from the fiber at a third fiber location intermediate the first and the second fiber locations without breaking or terminating the fiber, characterized in that (a) the fiber is a single mode optical fiber at the wavelength λ o ; (b) the second means comprise means adapted for forming in the intermediate portion of the fiber a grating consisting of N elements, a grating being a portion of fiber in which one or more fiber parameters have a regular variation as a function of the axial coordinate z of the fiber, the fiber parameters including the core refractive index and the fiber axis geometry, associated with the grating being a nominal repeat distance Λ(z) and a nominal amplitude function g(z); (c) Λ(z) is chosen such that Ω o =2π/Λ>β 01 -2πn cl /λ o , where Λ is the average repeat spacing in the grating, β 01 is the propagation constant of the LP 01 mode of radiation, and n cl is the refractive index of the cladding of the fiber; (d) Λ(z) furthermore is chosen such that Ω o ˜β 01 -β rs , where β rs is the propagation constant of the LP rs mode of radiation, and where LP rs is a tunneling leaky (TL) mode of the radiation of wavelength λ o in the fiber; and (e) the attenuation constant α rs of the LP rs mode is less than about 1 dB/cm.

Claim 16

An optical communications system comprising a source of first electromagnetic radiation of wavelength λ o , an optical fiber adapted for guiding the first radiation, first means for coupling the first radiation into the fiber at a first fiber location, and means for detecting, at a second fiber location spaced apart from the first fiber location, the first radiation that is transmitted from the first to the second fiber location through the fiber, the fiber comprising a core and a cladding surrounding the core, the fiber having optical characteristics including an attenuation constant α ij and a propagation constant β ij for each mode LP ij of the first radiation that can be present in the fiber, where i is a non-negative integer and j is a positive integer, the optical communications system further comprising second means for coupling first radiation into or from the fiber at a third fiber location intermediate the first and the second fiber locations without breaking or terminating the fiber, characterized in that (a) the fiber is a single mode optical fiber at the wavelength λ o ; (b) the second means comprise means adapted for forming in the intermediate portion of the fiber a grating consisting of N elements, a grating being a portion of fiber in which one or more fiber parameters have a regular variation as a function of the axial coordinate z of the fiber, the fiber parameters including the core refractive index and the fiber axis geometry, associated with the grating being a nominal repeat distance Λ(z) and a nominal amplitude function g(z); (c) Λ(z) is chosen such that Ω o =2π/Λ>β 01 -2πn cl /λ o , where Λ is the average repeat spacing in the grating, β 01 is the propagation constant of the LP 01 mode of radiation, and n cl is the refractive index of the cladding of the fiber; (d) Λ(z) furthermore is chosen such that Ω o ˜β 01 -β rs , where β rs is the propagation constant of the LP rs mode of radiation, and where LP rs is a tunneling leaky (TL) mode of the radiation of wavelength λ o in the fiber; and (e) the attenuation constant α rs of the LP rs mode is less than about 1 dB/cm.

Claim 17

Communications system of claim 14, wherein the second means form a variable attenuator.

Claim 18

Communications system of claim 14, wherein the second means comprise clamp-on means comprising corrugated means adapted for forming the grating in the fiber, means for urging the corrugated means against the fiber, and means for detecting the first radiation emitted from the fiber at the third fiber location.

Claim 19

Communications system of claim 14, wherein the source of electromagnetic radiation also emits electromagnetic radiation of wavelength other than λ o , wherein the first means are adapted for coupling at least some of the radiation of wavelength other than λ o into the fiber at the first fiber location, and wherein the second means form a filter adapted for selectively coupling at least some of the first radiation from the fiber.