The bandwidth limit of a single-mode fiber optic cable depends on various factors, including the type of fiber, the transmission technology used, and the equipment involved. In ideal conditions, the speed of light in a vacuum is approximately 299,792 kilometers per second, but the speed of light in an optical fiber is slightly slower due to the refractive index of the fiber.
In practice, modern single-mode fiber optic systems can achieve much higher data rates than what you calculated. With advanced modulation techniques, such as dense wavelength division multiplexing (DWDM) and coherent detection, data rates of 100 gigabits per second (Gbps), 200 Gbps, and even 400 Gbps per wavelength are achievable over long distances.
Furthermore, modern fiber optic networks often employ multiple wavelengths (colors of light) transmitted simultaneously over the same fiber, using techniques like DWDM. This allows for the aggregation of multiple data streams, significantly increasing the overall capacity of the fiber.
For example, with 96 wavelengths at 400 Gbps each, a single fiber could support a total capacity of 38.4 terabits per second (Tbps). There are even experimental systems that have achieved data rates of 1 petabit per second (Pbps) over a single fiber, although these are not yet deployed commercially.
It's important to note that achieving these high data rates requires advanced technology, sophisticated equipment, and careful management of factors like signal loss, dispersion, and noise. The actual achievable data rates and the number of wavelengths that can be transmitted over a fiber will depend on the specific implementation and the characteristics of the fiber itself.
In summary, while the speed of light sets an upper limit on the potential data rate over a single-mode fiber, modern fiber optic systems can achieve much higher data rates by utilizing advanced modulation techniques and multiple wavelengths transmitted simultaneously. The actual bandwidth limit of a single fiber optic cable can be in the terabit or even petabit per second range, depending on the implementation.