Method for the production of an optical fibre, preform, and an optical fibre

A method of manufacturing an optical fibre, which method comprises the following steps:

• i) providing a hollow substrate tube,
• ii) passing doped or undoped reactive, glass-forming gases through the interior of the hollow substrate tube,
• iii) depositing glass layers onto the interior of the hollow substrate tube, wherein a non-isothermal plasma is reciprocated between two reversal points along the substrate tube, wherein the velocity of movement of the plasma decreases to zero from a deceleration point to each reversal point,
• iv) collapsing the substrate tube thus obtained so as to form a solid preform, and
• v) drawing an optical fibre from said solid preform,
• wherein the power of the plasma and the velocity at which the plasma moves between the two reversal points along the hollow substrate tube is maintained at a substantially constant value during step iii), with the plasma power being changed as a function of time in an end region adjacent to a reversal point, which change marks the starting point of the end region, which plasma power is lower than the plasma power outside the end region at the beginning of step iii) and is gradually increased as a function of time during the deposition process to a plasma power having a value which, at the end of step iii), is higher in the end region than the plasma power in the region outside the end region, and
• a velocity profile at which the plasma is moved along the hollow substrate tube is changed for each succeeding glass layer.

A method of manufacturing an optical fibre, which method comprises the following steps:

• i) providing a hollow substrate tube,
• ii) passing doped or undoped reactive, glass-forming gases through the interior of the hollow substrate tube,
• iii) depositing glass layers onto the interior of the hollow substrate tube, wherein a non-isothermal plasma is reciprocated between two reversal points along the substrate tube, wherein the velocity of movement of the plasma decreases to zero from each deceleration point to each reversal point,
• iv) collapsing the substrate tube thus obtained so as to form a solid preform, and
• v) drawing an optical fibre from said solid preform,
• wherein the supplied amount of reactive, glass-forming gases according to step iii) is maintained at a substantially constant value during a passage of the plasma between the two reversal points, with the composition of the reactive, glass-forming gases being changed as a function of time in the end region adjacent to a reversal point during the deposition process, which change marks the starting point of the end region, and
• a velocity profile at which the plasma is moved along the hollow substrate tube is changed for each succeeding glass layer.

A method of manufacturing an optical fibre, which method comprises the following steps:

• i) providing a hollow substrate tube,
• ii) passing doped or undoped reactive, glass-forming gases through the interior of the hollow substrate tube,
• iii) depositing glass layers onto the interior of the hollow substrate tube, wherein a non-isothermal plasma is reciprocated between two reversal points along the substrate tube, wherein the velocity of movement of the plasma decreases to zero from each deceleration point to each reversal point,
• iv) collapsing the substrate tube thus obtained so as to form a solid preform, and
• v) drawing an optical fibre from said solid preform,
• wherein the velocity at which the plasma is moved along the hollow substrate tube between the two reversal points is maintained at a substantially constant value, with the pressure in the hollow substrate tube being changed as a function of time in an end region adjacent to a reversal point, which change marks the starting point of the end region, and
• a velocity profile at which the plasma is moved along the hollow substrate tube is changed for each succeeding glass layer.

A method of manufacturing an optical fibre, which method comprises the following steps:

• i) providing a hollow substrate tube,
• ii) passing doped or undoped reactive, glass-forming gases through the interior of the hollow substrate tube,
• iii) depositing glass layers onto the interior of the hollow substrate tube, wherein a non-isothermal plasma is reciprocated between two reversal points along the substrate tube, wherein the velocity of movement of the plasma decreases to zero from each deceleration point to each reversal point,
• iv) collapsing the substrate tube thus obtained so as to form a solid preform, and
• v) drawing an optical fibre from said solid preform,
• wherein the velocity at which the plasma is moved along the hollow substrate tube is changed in a first end region adjacent to a reversal point during step iii), both as a function of time in the deposition process and as a function of position in the first end region, which change marks the starting point of the first end region, wherein the end point of the first end region coincides with the reversal point and wherein the starting point is located further away from the reversal point than the deceleration point, said first end region having a length that suffices to reduce the taper in the perform, and
• at the beginning of step iii) the velocity at which the plasma is moved along the hollow substrate tube in the first end region is lower at all positions than the velocity at which the plasma is moved along the hollow substrate tube outside the end region, and at the end of step iii) velocity values are reached which are higher than the velocity at which the plasma is moved along the hollow substrate tube outside the first end region.