US5058976A — System comprising Er-doped optical fiber

Claim 1

Independent Claim 342 words

Optical fiber communication system comprising a length of optical fiber signal-transmissively connecting signal-generating means at a first location to signal-detecting means at a second location spaced from the first location; the length of optical fiber comprising a length of transmission fiber and a length of Er-doped amplifier fiber; the communication system further comprising means for generating pump radiation and means for coupling pump radiation into the length of optical fiber at a location intermediate the first and second locations; the signal-generating means adapted for generating signal radiation of wavelength λ s (λ s ˜1.5 μm), the means for generating pump radiation adapted for generating radiation of wavelength λ p less than λ s ; the amplifier fiber comprising a first region of relatively high refractive index and a second region, contactingly surrounding the first region, of relatively low refractive index; the first region comprising Ge and Al, and further comprising Er, associated with the amplifier fiber being refractive index difference Δn=(n c -n cl ), where n c is an effective refractive index associated with the first region and n cl is a refractive index associated with the second region, an effective core diameter a, a mode field diameter at wavelength λ p , an Er distribution, an Al distribution, and a Ge distribution, with each of said distributions being associated an effective diameter; CHARACTERIZED IN THAT a) Δn>0.03 and a is less than 3.5 μm; b) the maximum Al concentration in the first region is at least 6 mole %; c) Δn and a are chosen such that the mode field diameter for the pump radiation is less than 5 μm, such that the V-number at λ p is in the range 1.4-2.0, and such that the amplifier fiber has a cut-off wavelength (λ co ) that is less than 1.4 μm; and d) the effective diameter associated with the Er distribution is less than that associated with the Ge distribution, and the effective diameter associated with the Al distribution is not substantially larger than that associated with the Er distribution.

Claim 2

Dependent Claim 342 words

Optical fiber communication system comprising a length of optical fiber signal-transmissively connecting signal-generating means at a first location to signal-detecting means at a second location spaced from the first location; the length of optical fiber comprising a length of transmission fiber and a length of Er-doped amplifier fiber; the communication system further comprising means for generating pump radiation and means for coupling pump radiation into the length of optical fiber at a location intermediate the first and second locations; the signal-generating means adapted for generating signal radiation of wavelength λ s (λ s ˜1.5 μm), the means for generating pump radiation adapted for generating radiation of wavelength λ p less than λ s ; the amplifier fiber comprising a first region of relatively high refractive index and a second region, contactingly surrounding the first region, of relatively low refractive index; the first region comprising Ge and Al, and further comprising Er, associated with the amplifier fiber being refractive index difference Δn=(n c -n cl ), where n c is an effective refractive index associated with the first region and n cl is a refractive index associated with the second region, an effective core diameter a, a mode field diameter at wavelength λ p , an Er distribution, an Al distribution, and a Ge distribution, with each of said distributions being associated an effective diameter; CHARACTERIZED IN THAT a) Δn>0.03 and a is less than 3.5 μm; b) the maximum Al concentration in the first region is at least 6 mole %; c) Δn and a are chosen such that the mode field diameter for the pump radiation is less than 5 μm, such that the V-number at λ p is in the range 1.4-2.0, and such that the amplifier fiber has a cut-off wavelength (λ co ) that is less than 1.4 μm; and d) the effective diameter associated with the Er distribution is less than that associated with the Ge distribution, and the effective diameter associated with the Al distribution is not substantially larger than that associated with the Er distribution.

Claim 3

Dependent Claim 16 words

The system of claim 1, wherein the maximum Al concentration is more than 10 mole %.

Claim 4

Dependent Claim 32 words

The system of claim 1, wherein the concentration of Er in the first region is such that the attenuation of the fiber for 1.53 μm wavelength radiation is greater than 2 dB/m.

Claim 5

Dependent Claim 17 words

The system of claim 1, wherein the length of said amplifier fiber is less than 50 m.

Claim 6

Dependent Claim 17 words

The system of claim 1, wherein the second region of the amplifier fiber comprises fluorine and phosphorus.

Claim 7

Dependent Claim 12 words

The system of claim 1, wherein λ p is about 1.48 μm.

Claim 8

Dependent Claim 57 words

The system of claim 1, wherein the length of optical fiber comprises N lengths of amplifier fibers and a multiplicity of lengths of transmission fibers, with at least one length of transmission fiber between any given two lengths of amplifier fibers, with N≧2; and wherein the system further comprises M means for generating pump radiation, with M≦N.

Claim 9

Dependent Claim 33 words

The system of claim 7, wherein associated with any given amplifier fiber is an amplification threshold, wherein the amplification threshold of at least one length of amplifier fiber is less than 3 mW.

Claim 10

Dependent Claim 204 words

Method of making a silica-based Er-doped optical fiber comprising a core and a cladding and adapted for use as an amplifier fiber for radiation of wavelength in the range 1.5-1.6 μm; the method comprising a) providing a silica-based substrate tube; b) forming a vitreous deposit on the inner surface of the tube; c) collapsing at least a portion of the tube such that a rod-like preform results; the preform comprising core material and cladding material; and d) drawing the optical fiber from the rod-like preform; CHARACTERIZED IN THAT step b) and c) comprise e) forming a first quantity of vitreous deposit on the inner surface, the first quantity comprising a portion of the core material, whereby a tubular preform is produced f) partially collapsing at least a portion of the tubular preform such that the inner diameter of the at least portion of the tubular preform is reduced; g) forming a second quantity of vitreous deposit on the inner surface of the partially collapsed at least portion of the tubular preform, the second quantity comprising the remainder of the core material; h) collapsing at least a part of the partially collapsed at least portion of the tubular preform, such that the rod-like preform results.

Claim 11

Dependent Claim 204 words

Method of making a silica-based Er-doped optical fiber comprising a core and a cladding and adapted for use as an amplifier fiber for radiation of wavelength in the range 1.5-1.6 μm; the method comprising a) providing a silica-based substrate tube; b) forming a vitreous deposit on the inner surface of the tube; c) collapsing at least a portion of the tube such that a rod-like preform results; the preform comprising core material and cladding material; and d) drawing the optical fiber from the rod-like preform; CHARACTERIZED IN THAT step b) and c) comprise e) forming a first quantity of vitreous deposit on the inner surface, the first quantity comprising a portion of the core material, whereby a tubular preform is produced f) partially collapsing at least a portion of the tubular preform such that the inner diameter of the at least portion of the tubular preform is reduced; g) forming a second quantity of vitreous deposit on the inner surface of the partially collapsed at least portion of the tubular preform, the second quantity comprising the remainder of the core material; h) collapsing at least a part of the partially collapsed at least portion of the tubular preform, such that the rod-like preform results.

Claim 12

Dependent Claim 28 words

Method of claim 9, wherein the portion of the core material comprises Si, Ge and Er, and wherein the remainder of the core material comprises Si and Al.

Claim 13

Dependent Claim 56 words

Method of claim 10, wherein the at least portion of the tubular preform is partially collapsed such that the inner diameter of the at least portion of the tubular preform is reduced to a value that is selected such that the collapse of step h) can be accomplished in a single pass of a heating means.

Claim 14

Dependent Claim 75 words

Method of claim 9, wherein after step h) and before step d) at least a part of the rod-like preform is maintained at a temperature above 500° C. and said part of the rod-like preform is stretched such that the diameter of the region that consists of the core material (the core region) is reduced below a critical value a c that is associated with cracking of the rod-like preform upon cooling to room temperature.

Claim 15

Dependent Claim 12 words

Method of claim 12, wherein a c is at most 1 mm.

Claim 16

Dependent Claim 164 words

Method of making a silica-based Er-doped optical fiber adapted for use as an amplifier fiber for radiation of wavelength in the range 1.5-1.6 μm; the method comprising a) providing a silica-based substrate tube; b) forming a vitreous deposit on the inner surface of the tube; c) collapsing at least a portion of the tube such that a rod-like preform results; the preform comprising core material and cladding material and d) drawing the optical fiber from the rod-like preform; CHARACTERIZED IN THAT the method further comprises stretching at least a part of the rod-like preform such that the diameter of the region that consists of the core material (the core region) is reduced below a critical value a c that is associated with cracking of the rod-like preform upon cooling to room temperature, with the temperature of at least the part of the rod-like preform not being permitted to drop below 500° C. during the time from completion of step c) to completion of stretching.

Claim 17

Dependent Claim 164 words

Method of making a silica-based Er-doped optical fiber adapted for use as an amplifier fiber for radiation of wavelength in the range 1.5-1.6 μm; the method comprising a) providing a silica-based substrate tube; b) forming a vitreous deposit on the inner surface of the tube; c) collapsing at least a portion of the tube such that a rod-like preform results; the preform comprising core material and cladding material and d) drawing the optical fiber from the rod-like preform; CHARACTERIZED IN THAT the method further comprises stretching at least a part of the rod-like preform such that the diameter of the region that consists of the core material (the core region) is reduced below a critical value a c that is associated with cracking of the rod-like preform upon cooling to room temperature, with the temperature of at least the part of the rod-like preform not being permitted to drop below 500° C. during the time from completion of step c) to completion of stretching.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1994-10-21	1995-04-22	1995-10-22	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1998-10-21	1999-04-22	1999-10-22	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2002-10-21	2003-04-22	2003-10-22	$7700.00	Window Closed / Lapsed

System comprising Er-doped optical fiber

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