Modulate a laser's wavelength? What are the inner workings of a laser, and is it possible to change the wavelength mechanically? Are there any lasers that can change wavelength?
No, it is not possible to modulate the wavelength of a laser. The particular wavelength of light is determined by the amount of energy released when an excited electron drops to a lower orbit, which in turn is defined by the specific glass/crystal/gas used in the laser.
Even if you could design some sort of mechanism to swap in/out different emission media to make step-changes in wavelength, you would not be able to reproduce a meaningful signal.