Definition of modal bandwidth

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Photonics Dictionary

modal bandwidth: Modal bandwidth is a crucial parameter in optical fiber communication systems, particularly in multimode fiber (MMF) systems. It quantifies the ability of a fiber optic link to transmit data at high speeds without suffering from modal dispersion, which occurs when different modes of light travel at different speeds through the fiber, causing distortion and degradation of the transmitted signal.

Modal bandwidth represents the frequency range over which the fiber optic link can support high-speed data transmission without significant degradation due to modal dispersion. It is typically expressed in terms of bandwidth-distance product, measured in MHz·km or GHz·km.

The modal bandwidth of a multimode fiber depends on various factors, including the fiber's core diameter, numerical aperture, refractive index profile, and wavelength of operation. Generally, larger core fibers with optimized refractive index profiles have higher modal bandwidths, as they can support a larger number of modes and reduce modal dispersion effects.

Modal bandwidth is a critical consideration when designing and deploying multimode fiber optic links, especially for high-speed data transmission applications such as local area networks (LANs), data centers, and backbone networks. It helps ensure that the fiber link can support the desired data rates over the specified distance while maintaining signal integrity and minimizing transmission errors.

In practical terms, modal bandwidth is often specified by fiber manufacturers and system integrators to ensure compatibility with the intended application and transmission requirements. It is typically characterized using standardized test methods, such as differential mode delay (DMD) measurements or bandwidth-distance product measurements, to assess the fiber's performance under various operating conditions and configurations.