The Coherent Optics Revolution: Transcending The 10G Wavelength Barrier
The Coherent Optics Revolution: Transcending 10G Wavelengths - Part 1 The first stage of optical communication was dominated by what Mark Tinka called the simple optical detection scheme. A pulse of laser light represented a '1' and no light meant a '0' or vice versa. Cisco white papers call this 'on-off signalling'. So this approach is based on the optical power or intensity of light. The stronger a light pulse, the higher its amplitude. See the top diagram. The Achilles of this approach is chromatic dispersion, namely that fact different frequencies of light traverse a solid medium such as fibre glass at different speeds. Now any laser pulse is a band of frequencies. It may be narrow, but it always has non-zero width. So chromatic dispersion is inevitable (like Donald Trump continuously changing tariff rates). As the fibre path distance grows, the probable outcome is that a laser might transmit a '1 0' but the light will spread over time and the opt...
