Ultra-low power stress-based phase actuation in TriPleX photonic circuits

We present ultra-low power stress optic actuators for high-speed switching in photonic integrated circuits using the standard silicon nitride TriPleX (TM) platform. The stress-optic actuator is created by a piezoelectric layer (lead zirconate titanate, PZT) on top of a Si3N4-based TriPleX (TM) waveguide in our standard Asymmetric Double Stripe (ADS) cross section. The top cladding thickness in between the actuator and the waveguide is chosen to achieve minimal optical loss (<= 0.01dB/cm). The electrodes are placed on the top of- and directly below the PZT layer allowing the generation of a vertical electric field across the layer. This electrical field deforms the PZT layer by means of the piezoelectric effect. As a consequence of the PZT deformation stress is induced in the underlying waveguide. In this way, the refractive index of the waveguide is controlled by the stress-optic effect brought about by actuating the PZT layer. To demonstrate the stress-optic based phase actuation experimentally, a Mach-Zehnder Interferometer (MZI) is employed. The MZI is designed for operation at a wavelength of 1550 nm. We measure a half-wave voltage-length product (V pi center dot cm) of 16 V center dot cm, while the half-wave-voltage length loss product (V-pi center dot L center dot alpha) is 1.6 V center dot dB only. The 2 pi phase shift would be at 42 V. The measured response time is 4.25 mu s. The quasi-DC power dissipation is able to go down to 1 mu W. Compared with conventional thermo-optic actuators these characteristics show a dramatic improvement, being a factor of 50 faster in terms of switching speed and a factor of 100 000 lower in terms of quasi-DC power dissipation. This makes stress-optic actuators an attractive choice for the next generation integrated photonic circuits where ultra-low quasi-DC power dissipation and/or fast switching time and operation in the MHz range are required.