Fig. 1. (a) Illustration of the investigated spatiotemporal isolator in LNOI. (b) Cross-section of the SiN loaded LNOI waveguide. (c) Purple curve shows the simulated spectral response of the add-drop racetrack resonator with an FSR of 55 GHz. Black line is the simulated spectral response for light propagating in the forward direction for a modulation index of 0.77π/2 when the device meets the condition of Eq. (2). (d) Black line is the simulated spectral response for the reverse direction assuming a modulation index of 0.77π/2. The response of the add-drop racetrack resonator is shown in (c) and (d) for reference and is not considered in the black curves.

Fig. 2. (a) Optical microscope image of the fabricated isolator. (b) Magnified view of the racetrack resonator coupling region. (c) The traveling wave electrode alignment to the waveguide. (d) SEM image of the fabricated SiN loaded LNOI waveguide.

Fig. 3. (a) The blue curve shows the measured transmission spectrum of the racetrack resonator. The red curve shows the measured spectrum of the cascaded phase modulators for light travelling in the reverse direction; Measured spectra of the isolator when operating the device in the (b) reverse direction and (c) forward direction, when using the racetrack resonator to suppress sidebands.

Table 1. Comparison of isolators performance that uses spatiotemporal modulation and operates a C-band wavelength.