Likely some kind of Electro-Optic Modulator. You could use their wavelength comb to separate the light and then use a Mach–Zehnder interferometer to perform On-

Likely some kind of Electro-Optic Modulator. You could use their wavelength comb to separate the light and then use a Mach–Zehnder interferometer to perform On-Off-Keying as an example