6. Optical fiber

6.1 Problem position

Optical delays are produced using single-mode optical fiber coils. A delay of 5 µs corresponds to 1 km of fiber.

Assuming 100 channels in the 1550 nm wavelength range, spaced 0.8 nm apart (100 GHz), the optical band occupied by the signals is 80 nm.

Standard single-mode optical fibers have zero chromatic dispersion around 1,300 nm, which increases with wavelength to reach a typical value of 17 ps · km ^–1 · nm ^–1 around 1,550 nm. For a 1 km length of such a fiber and 80 nm of optical bandwidth used, the maximum differential delay between the different signals is 1,360 ps.

To achieve long delays, it is...