Optical Fiber Terms
Core diameter
A parameter of multimode optical fibers. It represents the diameter of the circle that best approximates the circumference of the core region. The smaller the value of the core diameter, the broader the services band. Fibers commonly used today have a core diameter of 50μm.
Mode field diameter (MFD)
A parameter of single-mode optical fibers, MFD corresponds to the diameter of the spread of electric field distribution in propagation mode (light path). Light usually passes through the core region. However, in the case of a single-mode optical fiber, the light leaks into the cladding region. Therefore, single-mode optical fibers are specified by MFD rather than core diameter. MFD is slightly greater than the core diameter. The smaller the MFD, the higher the required accuracy of alignment for connection/splicing. Furthermore, the larger the MFD difference of two joined fibers, the greater the connector/splice loss.
Cladding diameter
The diameter of the circle best approximating the cladding surfaces. The larger the cladding diameter difference of two joined fibers, the greater the connector/splice loss.
Cable cutoff wavelength
A parameter of single-mode optical fibers. An optical fiber cannot be a single-mode fiber if it is used at a wavelength shorter than the cable cutoff wavelength, which is determined by optical fiber structure, involving refraction index distribution and core diameter.
Proof test
Screening is a technique intended to remove the glass defects of a fiber and improve its structural reliability. A given level of elongation strain is applied to the overall length of an optical fiber to break the fiber at its low-strength section. The screening level is the value of the elongation strain. The higher the value of screening level, the higher the reliability of the optical fiber.
Transmission loss
Transmission loss is a value that indicates the decrease of optical power of light propagating between two points of optical fiber. It is expressed
The transmission distance becomes short when transmission loss grows.
Transmission band
A parameter of multi-mode optical fibers. The transmission band is the frequency at which the magnitude of the baseband transfer function decreases to a specified value (6 dB). In other words, the value indicates to what frequency the signal is transmitted without distortion. The higher the transmission band, the higher the usable transmission frequency, hence larger-capacity transmission.
Zero-dispersion wavelength
A parameter of single-mode optical fibers. At the zero-dispersion wavelength, the wavelength dispersion decreases to zero. Transmission at a wavelength of a large absolute value of wavelength dispersion results in greater dispersion and therefore higher optical pulse distortion. Optical fibers designed so that the zero-dispersion wavelength is about 1310 nm or 1550 nm are known as the general-purpose SM or the dispersion-shifted optical fiber, respectively.
Zero-dispersion slope
A parameter of single-mode optical fibers. The zero-dispersion slope represents the gradient of dispersion at the zero-dispersion wavelength. In general, the greater the zero-dispersion slope, the higher the absolute value of dispersion at any wavelength.
