Terminology related to Optical Fibers

Core-cladding concentricity error is defined as the distance of the center position between the core and cladding. Smaller core-cladding concentricity error is preferable for minimizing splice/connector loss.

Cladding diameter is defined as the outer diameter of the optical fiber's glass section, which is the vertical red line in the diagram.

Cladding non-circularity is defined in the figure.

Fiber curl describes a tendency of optical fiber to curve along their length when released from winding on a spool, which affects the splice quality.
Fiber curl radius is defined as the radius of curvature.

Coating diameter is the outer diameter of optical fiber’s protecting layer which is made of acrylates which is the vertical blue line in the figure.

Coating-cladding concentricity error is the relative position of the cladding against the coating in an optical fiber.

Attenuation describes the reduction of optical signal power, and is defined as ratio of the optical power at two points, typically expressed as the logarithm of the ratio in decibel (dB).
For optical fiber, attenuation per unit length, e.g. dB per kilometer (dB/km), is typically used as the attenuation coefficient.
Lower attenuation can directly improve the optical signal ratio (OSNR) for large capacity and long distance transmission systems.
Sumitomo Electric offers ultra-low attenuation optical fibers.

The wavelength at which the chromatic dispersion becomes zero. For ITU-T G.652 and G.657 fibers, zero-dispersion wavelength is within 1300-1324 nm.

Slope of the chromatic dispersion versus wavelength curve.

Zero dispersion slope is the chromatic dispersion slope at the zero dispersion wavelength.

The cut-off wavelength of single-mode optical fiber is defined as the shortest wavelength at which only a single mode can propagate. 
Two approaches can be used to determine the cut-off wavelength:
- Fiber cut-off wavelength: This is measured on a short, uncabled fiber, typically around 2 meters in length.
- Cable cut-off wavelength: This is measured on a substantially straight 22 meters cable prepared by exposing 1 meter of decabled fiber at both ends. Alternatively, cable cut-off wavelength can be measured on 22 meters of uncabled fiber loosely coiled with > 140mm radius, incorporating a 40 mm radius loop at each end.
Cable cutoff wavelength is preferred to be specified. The recommended cable cut-off wavelength is ≤1260 nm for ITU-T G.652 and G.657, while it is ≤1530 nm for ITU-T G.654.

The proof stress level refers to the specified value of tensile stress or strain applied along the entire length of the fiber for a short period of time. Sumitomo Electric sets the proof stress level higher than international standards, such as ITU-T Recommendations and IEC Standards, to enhance the resistance of our fiber products to failure.