The Bell Laboratories research arm of Lucent Technologies Inc claims to have perfected a means of transmitting 206 channels of digital traffic down a single fiber optic strand by exploiting wavelength division multiplexing and using a single very fast- switching laser in place of the multiple lasers normally used. The laser issues a pulse every femtosecond and the system exploits the fact that a light pulse at the red end of the spectrum travels faster than a pulse at the blue end. Since each wavelength arrives at the end of the fiber at a slightly different time, the data can be encoded sequentially onto the wavelength division multiplexing channels – and when the frequency components of a short-pulse laser are separated temporarily by propagation in a dispersive medium, a single time- division-multiplexed modulator can be used to encode data on all channels. The femtosecond laser meets the requirements that the source generate an extremely broad color spectrum and a short optical pulsewidth as well as eliminating the problem that conventional wavelength division multiplexing are usually limited to dozens of channels because the task of combining and stabilizing a large number of single-frequency lasers becomes increasingly complex and expensive. The femtosecond light source is a mode-locked, or pulse, laser made of a length of optical fiber containing the rare-earth element Erbium. In the experimental system, each channel carries 36.7 Megabits of data per second, and the channel spacing is about 36GHz.
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