A generating device includes at least one pulsed laser source that delivers primary photons having at least one wavelength in a single spatial mode and in pulses having a high pump energy, forming means that act on the primary photons to deliver an input beam, and at least one optical fiber having at least ten modes between which the pump energy is initially distributed, and able to relocate the latter via a non-linear effect into a fundamental mode, before generating secondary photons of various wavelengths by wavelength conversions from the wavelength of the primary photons in the fundamental spatial mode.