Fiber-Optic Intensity Modulator, 20 GHz, 1064 nm

Both our phase and our amplitude modulators are based upon the Pockel's effect: the electro-optic effect where the refractive index along one or more axes is proportional to an externally applied electric field. Therefore, by applying a voltage across the electrodes of an electro-optic crystal, you can change the phase of light as it passes through the crystal. By placing the crystal between crossed polarizers, this phase modulation can be converted into amplitude modulation.

These intensity modulators use the Mach Zehnder interferometer (MZI) architecture by splitting the waveguide into two paths and recombining them. The elec-trodes are placed around the two waveguide paths to modulate the phase in the light while split. When the paths recombine, the light path undergoes either constructive or deconstructive interference depending on the phase, thereby modulating the light intensity.

Proton Exchange (PE) is one of the common waveguide fabrication techniques in lithium niobate. Compared with Ti in-diffusion, another fabrication method, it can generate higher extraordinary refractive index changes (Δn_e close to 0.1). A subsequent annealing in a controlled atmosphere, hense called Annealed Proton Exchange (APE), permits a high polarization rejection and a high optical power handling capability, especially for applications using a shorter wavelength than in telecommunications. The annealing, in fact, helps in recovering the nonlinear coefficients that are compromised by standard PE processing.