A single-mode optical cable supports only one mode of light.

Single-mode optical fibers are engineered with a very narrow core, typically around 8 to 10 micrometers in diameter, which allows only a single transverse mode of light to propagate through the fiber . This design minimizes modal dispersion, ensuring that all light pulses travel essentially the same distance, which preserves signal integrity over long distances .

Key Characteristics

• Single Propagation Path: The narrow core restricts light to a single spatial distribution, or mode, meaning the electromagnetic oscillations occur in a uniform transverse pattern .
• Long-Distance Transmission: Because only one mode propagates, single-mode fibers can transmit data over tens to hundreds of kilometers without significant signal degradation .
• High Bandwidth: The absence of multiple modes reduces interference and allows for extremely high data rates, limited primarily by the electronic equipment rather than the fiber itself .
• Core Size and Wavelength: The fiber's core diameter is smaller than the cutoff wavelength, which ensures that only one mode is supported . In contrast, multimode fibers have larger cores (50–62.5 micrometers) and support multiple modes of light, which makes them suitable for shorter distances but more prone to modal dispersion . In summary, a single-mode optical cable is specifically designed to carry exactly one mode of light, making it ideal for long-haul, high-bandwidth communication applications.