Reduced diameter optical fiber and manufacturing method

A method (12) for manufacturing an optical fiber (1) having an optical-fiber diameter of 180 microns or less from a core (2) and a cladding (3) surrounding the core (2) and having an outer diameter of 125 μm, the method (12) comprising:

• Applying (S1) a primary coating directly on the cladding (3), with a thickness t1 between 10 and 18 μm,
• Curing (S2) the primary coating to obtain a cured primary coating (4) with an in-situ tensile modulus Emod1 between 0.10 and 0.18 MPa,
• Applying (S3) a secondary coating directly on the cured primary coating (4), with a thickness t2 lower or equal to 18 μm,
• Curing (S4) the secondary coating (5) to obtain a cured secondary coating (5) with an in-situ tensile modulus Emod2 between 700 and 1200 MPa,
• The preceding steps being performed so that said first and second thicknesses and said first and second in-situ tensile moduli satisfy the following equation:
• 4%<(t1×t2×Emod1×Emod23)/(t1_norm×t2_norm×Emod1_norm×Emod2_norm3)<50%
• Where t1_norm is the thickness of the cured primary coating of a standard 245 μm-diameter optical fiber, which is equal to 33.5 μm,
• t2_norm is the thickness of the cured secondary coating of a standard 245 μm-diameter optical fiber, which is equal to 25 μm,
• Emod1_norm is the in-situ tensile modulus of the cured primary coating of a standard 245 μm-diameter optical fiber, which is equal to 0.4 MPa, and
• Emod2_norm is the in-situ tensile modulus of the cured secondary coating of a standard 245 μm-diameter optical fiber, which is equal to 800 MPa.

An optical fiber (1) having an optical-fiber diameter of 180 microns or less, the optical fiber comprising a core (2) and a cladding (3) surrounding the core (2) and having an outer diameter of 125 μm, the optical fiber (1) comprising a cured primary coating (4) directly surrounding the cladding (3) and a cured secondary coating (5) directly surrounding the cured primary coating (4), said cured primary coating (4) having a thickness t1 between 10 and 18 μm, an in-situ tensile modulus Emod1 between 0.10 and 0.18 MPa, and a cure rate yield after UV curing between 80 and 90% one week after draw, said cured secondary coating (5) having a thickness t2 lower or equal to 18 μm, an in-situ tensile modulus Emod2 between 700 and 1200 MPa, and a cure rate yield after UV curing between 94 and 98%, wherein said first and second thicknesses and said first and second in-situ tensile moduli satisfy the following equation:

• 4%<(t1×t2×Emod1×Emod23)/(t1_norm×t2_norm×Emod1_norm×Emod2_norm3)<50%
• where t1_norm is the thickness of the cured primary coating of a standard 245 μm-diameter optical fiber, which is equal to 33.5 μm,
• t2-norm is the thickness of the cured secondary coating of a standard 245 μm-diameter optical fiber, which is equal to 25 μm,
• Emod1-norm is the in-situ tensile modulus of the cured primary coating of a standard 245 μm-diameter optical fiber, which is equal to 0.4 MPa, and
• Emod2_norm is the in-situ tensile modulus of the cured secondary coating of a standard 245 μm-diameter optical fiber, which is equal to 800 MPa.