Which type of optical amplifier is known to produce no measurable distortion to the modulated light wave?

The erbium-doped fiber amplifier (EDFA) is recognized for its ability to amplify light signals in optical communication systems with minimal distortion. This characteristic is crucial because in optical communications, maintaining the integrity of the signal is essential for effective data transmission.

The EDFA works by using a fiber optic medium that is doped with erbium ions. When a pump laser excites these ions, they emit photons in response, thus producing amplification. The key advantage of an EDFA is its capacity to amplify a wide range of wavelengths commonly used in telecommunications without altering the waveform of the incoming light. This means that modulated signals—those that carry information—remain intact, allowing for a clear transmission of data over long distances.

In contrast, other types of optical amplifiers may introduce some level of distortion. For instance, laser diode amplifiers can have non-linear characteristics which might affect signal fidelity. Semiconductor optical amplifiers can also induce distortion due to their dependence on current input, while Raman amplifiers, although beneficial in some contexts, may lead to changes in the waveform due to their reliance on nonlinear optical processes.

Thus, the erbium-doped fiber amplifier is the preferred choice for applications requiring high quality and low distortion in optical signal amplification.