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OVD process: 185mm G.657.A1 Optical Fiber Preform

    Preform Specifications

    Preform Dimensions

    The preform dimensions shall be as in the Table 1.1 below.

    Table 1.1 Preform Dimensions

    Item Requirements Remark
    1 Average Preform Diameter (O.D.) 135 ~ 160 mm (Note 1.1)
    2 Maximum Preform Diameter (ODmax) ≤ 160 mm
    3 Minimum Preform Diameter (ODmin) ≥ 130 mm
    4 Tolerance of O.D. (within a Preform) ≤ 20 mm ( in straight part )
    5 Preform Length (including handle part) 2600 ~ 3600 mm (Note 1.2)
    6 Effective length ≥ 1800 mm
    7 Taper length ≤ 250 mm
    8 Diameter at the end of taper ≤ 30
    9 Preform Non-circularity ≤ 1 %
    10 Concentricity Error ≤ 0.5 μm
    11 Appearance (Note 1.4&1.5)

    Note 1.1:  The preform diameter shall be measured continuously in straight part with 10mm interval by the Laser Diameter Measurement System and to be defined as the average of measured values. Taper part shall be defined as the position between A to B. Straight Part shall be defined as the position between B to C. A is the position at end of preform. B is the start position having effective core. C is the end position having effective core. D is the end side of preform.
    Note 1.2:  “ Preform Length” shall be defined as shown in the Figure 1.1.
    Note 1.3:  Effective Part shall be defined as the position between B to C.
    Chargeable Length = Effective Length -  ∑Unusable Length at Defect (LUD)

    Figure 1.1 Shape of a Preform

    OVD Process

    Note 1.4:  The bubbles in the outer cladding region (see Figure 1.2) shall be permitted, depending on the size; the number of bubbles per unit volume shall not exceed these stipulated in the Table 1.2 below.

    Table 1.2 Bubble in a Preform

    Location and Size of Bubble

    Number / 1,000 cm3

    Core Region (=core + inner cladding)

    (See Note 1.5)

    Outer Cladding Region

    (=interface + outer cladding)

    ~ 0.5 mm

    No Count

    0.5 ~ 1.0 mm

    ≤ 10

    1.0 ~ 1.5 mm

    ≤ 2

    1.5 ~ 2.0 mm

    ≤ 1.0

    2.1 mm ~

    (See Note 1.5)

    Figure 1.2 Cross-sectional View of a Preform

    OVD Process2

    Note 1.5:  If there are any defects, which are defined below, in the core region and/ or the outer cladding region, the area that covers 3 mm from each side of defect shall be defined as the unusable part (Figure 1.3). In this case, the effective length shall be defined excluding the length of the unusable part. The unusable part will be indicated by “ Defect MAP”, which shall be attached to the inspection sheet. 
    1. a bubble of larger than 2 mm in the outer cladding,
    2. a cluster of a few bubbles in the outer cladding,
    3. a bubble in the inner cladding or the core,
    4. a foreign substance in a preform,

    Figure 1.2 Cross-sectional View of a Preform

    OVD Process3

    Chargeable Weight

    Chargeable weight shall be calculated as follows;
    Chargeable weight[g] =Total weight of preform-Not effective weight at taper part and handle part-Defect weight
    1. Total weight of preform is the weight tested by equipment.
    2. “ Not effective weight at taper part and handle part” is a fixed value determined by experience.
    3. Defect weight = Volume of Defect part[cm3]) × 2.2[g/cm3]; “2.2[g/cm3]” is the density of quartz glass.
    4. “Volume of Defect part” = (O.D.[mm]/2)2 ×Σ(LUD)×π; LUD =Unusable Length at defect=Defect Length+ 6[mm].
    5. The preform diameter shall be measured continuously in straight part with 10mm interval by the Laser Diameter Measurement System.

    Target Fiber Characteristics

    When the drawing conditions and the measurement conditions are optimum and stable, the preforms shall be expected to meet the target fiber specifications as shown in Table 2.1.

    Table 2.1 Target Fiber Characteristics






    Attenuation at 1310 nm

    ≤ 0.35 dB/km


    Attenuation at 1383 nm

    ≤ 0.35 dB/km

    (Note 2.1)

    Attenuation at 1550 nm

    ≤ 0.21 dB/km


    Attenuation at 1625 nm

    ≤ 0.23 dB/km


    Uniformity of Attenuation

    ≤ 0.05 dB/km at 1310&1550 nm



    Mode  Field Diameter at 1310 nm

    9.0 ± 0.4 µm



    Cable Cutoff Wavelength  (λcc)

    ≤ 1260 nm



    Zero Dispersion Wavelength  (λ0 )

    1300 ~ 1324 nm



    Dispersion at 1285~1340 nm

    -3.8 ~ 3.5 ps/(nm·km)



    Dispersion 1550 nm

    13.3 ~ 18.6 ps/(nm·km)



    Dispersion 1625 nm

    17.2 ~ 23.7 ps/(nm·km)



    Dispersion Slope at λ0

    0.073 ~0.092 ps/(nm2·km)



    Core/Cladding Concentricity Error

    ≤ 0.5 µm



    Macro Bending Induced Loss

    (Note 2.2)

    30mm diameter, 10turns, at 1550nm

    ≤ 0.25 dB

    30mm diameter, 10turns, at 1625nm

    ≤ 1.0 dB

    20mm diameter, 1turn, at 1550nm

    ≤ 0.75 dB

    20mm diameter, 1turn, at 1625nm

    ≤ 1.5 dB

    Note 2.1: The attenuation  at 1383  nm after hydrogen  aging test shall not be included  in the Table 2.1 because it highly depends on the fiber drawing conditions.

    Note 2.2: To ensure output ratio of G.657.A1 fibre, the drawing conditions should be controlled effectively to make fiber cut-off wavelength more than 1270 nm. Cable cutoff wavelength  should be tested when fibre cutoff wavelength is larger than 1300nm.