The correct answer is: B. Pump source.
A bidirectional optical amplifier is an optical amplifier that can amplify light signals in both directions. This is achieved by using a pump source that emits light at a wavelength that is absorbed by the core material of the fiber. The absorbed light energy is then transferred to the signal light, which is amplified as a result.
The core material of the fiber is important for determining the wavelength of light that can be amplified. However, the pump source is more dominant in making a fiber function as a bidirectional optical amplifier. This is because the pump source provides the energy that is necessary to amplify the signal light.
The cladding material and the diameter of the fiber are also important factors in determining the performance of a bidirectional optical amplifier. However, they are not as dominant as the pump source.
The cladding material helps to confine the light to the core of the fiber. The diameter of the fiber affects the amount of light that can be amplified. However, both of these factors can be optimized to achieve the desired performance, regardless of the pump source.
In conclusion, the pump source is the most dominant factor in making a fiber function as a bidirectional optical amplifier. This is because the pump source provides the energy that is necessary to amplify the signal light.