To understand the difference between re-generators and optical amplifiers, along with some current design rules, is important to designing cost-effective optical networks.

To demonstrate the difference between regeneration and amplification, Fig.1 shows that amplification only increases the size (power) of the original signal, whereas regeneration reproduces the original signal. Amplification does not discriminate between signal (good) and noise (bad). As amplification is performed on both the original signal and the noise, the signal noise is amplified.

As the signal noise accumulates, the optical signal-to-noise ratio (OSNR) is negatively impacted, and overall signal quality degrades. It is logical that if a signal (original signal and noise) is amplified a number of times, the original signal (without noise) might eventually become distorted to the point that it cannot be recognized and interpreted. So, why not always just regenerate only the signal?

An optical amplifier is a cost-effective method for extending the distance between end devices, or re-generators. Typically, optical amplifiers are placed in line every 80 to 120 km, but a signal re-generator is required every 600 to 1000 km . With respect to cost, an optical amplifier works in the optical domain and can amplify all the wavelengths.

A re-generator must convert the optical signal to electrical to perform the reshape, retime, and re-transmit functions, and the conversion back to optical. This optical-to-electrical-to-optical process can create excessive signal delay - our enemy in long haul transport. In addition, a re-generator is required per wavelength. Cost-effective and low-power optical re-generators are a continual target for optical component design companies.