Single-mode optical fiber

A method for manufacturing an optical-fiber preform, comprising the steps of:

• depositing layers inside a deposition tube, the layers forming a central core and a first depressed cladding;
• completely removing the deposition tube;
• providing a second depressed cladding around the first depressed cladding;
• and
• providing an outer optical cladding around the second depressed cladding;
• wherein the ratio of the cross-sectional area of the central core to the cross-sectional area of the outer optical cladding is between about 0.0047 and 0.015;
• wherein the ratio of the cross-sectional area of the first depressed cladding to the cross-sectional area of the outer optical cladding is between about 0.019 and 0.11;
• wherein the central core has a refractive-index difference with the outer optical cladding (Dnco−Dnout) of between about −1×10−3 and 3×10−3;
• wherein the first depressed cladding has a refractive-index difference with the outer optical cladding (Dncl1−Dnout) of between about −5.5×10−3 and −2.5×10−3;
• and
• wherein the second depressed cladding has a refractive-index difference with the first depressed cladding (Dncl2−Dncl1) of between about −0.5×10−3 and 0.5×10−3.

A method for manufacturing an optical-fiber preform, comprising the steps of:

• depositing layers inside a fluorine-doped-silica deposition tube, the layers forming a central core and a first depressed cladding;
• providing a second depressed cladding around the deposition tube, the deposition tube forming a third depressed cladding;
• and
• providing an outer optical cladding around the second depressed cladding;
• wherein the ratio of the cross-sectional area of the central core to the cross-sectional area of the outer optical cladding is between about 0.0047 and 0.015;
• wherein the ratio of the cross-sectional area of the first depressed cladding to the cross-sectional area of the outer optical cladding is between about 0.019 and 0.11;
• wherein the ratio of the cross-sectional area of the second depressed cladding to the cross-sectional area of the outer optical cladding is between about 0.31 and 0.77;
• wherein the ratio of the cross-sectional area of the third depressed cladding to the cross-sectional area of the outer optical cladding is less than about 0.27;
• wherein the central core has a refractive-index difference with the outer optical cladding (Dnco−Dnout) of between about −1×10−3 and 3×10−3;
• wherein the first depressed cladding has a refractive-index difference with the outer optical cladding (Dncl1-Dnout) of between about −5.5×10−3 and −2.5×10−3;
• wherein the second depressed cladding has a refractive-index difference with the first depressed cladding (Dncl2−Dncl1) of between about −0.5×10−3 and 0.5×10−3;
• and
• wherein the third depressed cladding has (i) a refractive-index difference with the first depressed cladding (Dncl3−Dnout) of between about −0.5×10−3 and 0.5×10−3 and (ii) a refractive-index difference with the second depressed cladding (Dncl3−Dncl2) of between about −0.5×10−3 and 0.5×10−3.

A method for manufacturing an optical-fiber preform, comprising the steps of:

• providing at least two successive cladding layers around a core rod, the core rod forming a central core and the successive cladding layers forming a first depressed cladding and a second depressed cladding;
• and
• providing an outer optical cladding around the second depressed cladding;
• wherein the ratio of the cross-sectional area of the central core to the cross-sectional area of the outer optical cladding is between about 0.0047 and 0.015;
• wherein the ratio of the cross-sectional area of the first depressed cladding to the cross-sectional area of the outer optical cladding is between about 0.019 and 0.11;
• wherein the central core has a refractive-index difference with the outer optical cladding (Dnco−Dnout) of between about −1×10−3 and 3×10−3;
• wherein the first depressed cladding has a refractive-index difference with the outer optical cladding (Dncl1-Dnout) of between about −5.5×10−3 and −2.5×10−3;
• and
• wherein the second depressed cladding has a refractive-index difference with the first depressed cladding (Dncl2−Dncl1) of between about −0.5×10−3 and 0.5×10−3.