Simple production of membrane-based LiNbO3 micro-modulators with integrated tapers.

We report on free-standing electro-optical LiNbO3 waveguides with integrated tapers made by optical grade dicing. Membranes with a calibrated thickness are produced simultaneously with tapers acting as spot-size converters. Thereby, thicknesses from 450 to 500 µm can simply be achieved together with integrated tapers guaranteeing low insertion losses. These developments open the way to the low-cost production of compact and low-power-consuming electro-optical components. As an example, a 200 µm-long free-standing electro-optical Fabry-Perot is demonstrated with a figure of merit of only 0.19 V·cm in a 4.5 µm-thick membrane.

Low-loss LiNbO(3) tapered-ridge waveguides made by optical-grade dicing.

We report on low-loss vertical tapers for efficient coupling between confined LiNbO3 optical ridge waveguides and Single Mode Fibers. 3D-Pseudo-Spectral-Time-Domain calculations and Optical-Coherence-Tomography-based methods are advantageously used for the numerical and experimental study of the tapers. The tapered-section is done simultaneously with the ridge waveguide by means of a circular precision dicing saw, so that the fabrication procedure is achieved in only two steps. The total insertion losses through a 1.6 cm long ridge waveguide are measured to be improved by 3 dB in presence of the taper. These tapered-ridge waveguides open the way to the low-cost production of low-loss phase modulators or resonators.

Optical characterization of ultra-short Bragg grating on lithium niobate ridge waveguide.

In this Letter, we report a technique to etch giant aspect ratio nanostructures in lithium niobate. An 8 µm long Bragg grating on a Ti:LiNbO3 ridge waveguide was fabricated by combining optical-grade dicing and focused ion beam milling. The reflectivity was evaluated using an optical coherence tomography system: it is measured to be 53% for the TM wave and 47% for the TE wave. We study by 2D-FDTD the modeled behavior of the electromagnetic field when an angle exists between two consecutive sidewalls of the grating in order to understand the difference between ideal Bragg grating and experimental samples. These simulations allow us to optimize the parameters in order to increase the reflection of the grating up to 80%.

Integrated temperature sensor based on an enhanced pyroelectric photonic crystal.

In this paper, temperature variations are detected thanks to an enhanced nano-optical pyroelectric sensor. Sensing is obtained with the pyroelectric effect of lithium niobate (LN) in which, a suitable air-membrane photonic crystal cavity has been fabricated. The wavelength position of the cavity mode is tuned 11.5 nm for a temperature variation of only 32 °C. These results agree quite well with 3D-FDTD simulations that predict tunability of 12.5 nm for 32 °C. This photonic crystal temperature sensor shows a sensitivity of 0.359 nm/°C for an active length of only ~5.2 µm.