Fabien Henrot

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.

Acoustic resonator based on periodically poled lithium niobate ridge

The constant improvement of industrial needs to face modern telecommunication challenges leads to the development of novel transducer principles as alternatives to SAW and BAW solutions. The main technological limits of SAW (short-circuit between electrodes) and BAW (precise thickness control) solutions can be overcome by a new kind of transducer based on periodically poled ferroelectric substrate. The approach proposed in this paper exploits a ridge structure combined with a periodically poled transducer (PPT), allowing for the excitation of highly coupled modes unlike previously published results on planar PPTs. High-aspect-ratio ridges showing micrometer dimensions are achieved by dicing PPT plates with a diamond-tipped saw. An adapted metallization is achieved to excite acoustic modes exhibiting electromechanical coupling in excess of 15% with phase velocities up to 10 000 m·s-1. Theoretical predictions show that these figures may reach values up to 20% and 18 000 m·s-1, respectively, using an appropriate design.

Fast-beam self-trapping in LiNbO(3) films by pyroelectric effect.

We report light-beam self-trapping triggered by the pyroelectric effect in an isolated ferroelectric thin film. Experiments are performed in an 8-μm-thick congruent undoped LiNbO(3) film bonded onto a silicon wafer. Response time two orders of magnitude faster than in bulk LiNbO(3) is reported. The original underlying physics specific of this arrangement is discussed.

Ridge-shaped periodically poled transducer for wide band R-F filter

Transducer on Periodically Poled Lithium Niobate (PPLN) exhibiting an electromechanical coupling about 20% and an equivalent phase velocity about 10 km.s-1 were shown in [1]. These transducers are 3D structured to overcome Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) technological limits, such as short circuit between electrodes for SAW and precise thickness control for BAW. The present work shows the use of these 3D structured transducers for Radio Frequency (RF) filtering. An acoustic filter showing a band pass of about 5MHz has been realized on Lithium Niobate at 250MHz. This filter is made of PPLN exhibiting a poling period of 14.9μm.

New radio-frequency resonators based on periodically poled lithium niobate thin film and ridge structures

In this paper, we present new results on the development of an original acoustic waveguides concept based on a Periodically Poled Lithium Niobate transducer. Periodically poled transducers have been investigated recently as an alternative to classical inter-digital transducers for the excitation and detection of guided acoustic waves. We expose here two different structures of RF resonators based on this concept: a “Silicon/Gold layer/PPLN thin film/Gold layer/Silicon” stack and a PPLN-ridge structure. Simulations, fabrication and experimental results of both resonators are presented. “Si/10 μm-thick PPLN/Si” and “PPLN-ridge (11 μm-wide and 250 μm-deep)” resonators with a poling period of 50 μm have been achieved. The experimental admittances of these devices have pointed out the existence of an isolated mode operating at frequencies near 110 MHz for the stack structure and near 160 MHz with an electromechanical coupling of about 19 % for the ridge structure. These results are in agreement with the finite and boundary elements simulations.

Integrated LiNbO3 photonic crystals

We present easy-to-implement technologies to produce LiNbO3 PhCs in confined optical waveguides. Ti-indiffusion or Annealed Proton Exchange (APE) are combined with optical grade dicing to fabricate ridge waveguides with propagation losses that can be lower than 0.2 dB/cm. Firstly we show how a PhC inscribed in a confined ridge waveguide can be exploited as a temperature sensor with an unexpectedly high 8 nm/°C temperature sensitivity. LiNbO3 PhCs with high aspect ratio are also demonstrated. The performance is achieved by properly tilting the ridge before patterning its walls by Focused Ion Beam (FIB). A eight micrometer long 1D-PhC on a Ti:LiNbO3 ridge waveguide has been fabricated and its reflectivity has been evaluated using an optical coherence tomography (OCT) system: it is measured to be 53 % for the TM wave and 47 % for the TE wave. The period can be optimized in order to increase the reflection of the 1D-PhC up to 80 %. These developments open the way to the dense integration of compact dynamic devices such as modulators, spectral filters or electric field sensors.

Integrated LiNbO 3 photonic crystals

We present easy-to-implement technologies to produce LiNbO3 PhCs in confined optical waveguides. Ti-indiffusion or Annealed Proton Exchange (APE) are combined with optical grade dicing to fabricate ridge waveguides with propagation losses that can be lower than 0.2 dB/cm. Firstly we show how a PhC inscribed in a confined ridge waveguide can be exploited as a temperature sensor with an unexpectedly high 8 nm/°C temperature sensitivity. LiNbO3 PhCs with high aspect ratio are also demonstrated. The performance is achieved by properly tilting the ridge before patterning its walls by Focused Ion Beam (FIB). A eight micrometer long 1D-PhC on a Ti:LiNbO3 ridge waveguide has been fabricated and its reflectivity has been evaluated using an optical coherence tomography (OCT) system: it is measured to be 53 % for the TM wave and 47 % for the TE wave. The period can be optimized in order to increase the reflection of the 1D-PhC up to 80 %. These developments open the way to the dense integration of compact dynamic devices such as modulators, spectral filters or electric field sensors.

Integrated LiNbO3photonic crystals

We present easy-to-implement technologies to produce LiNbO3 PhCs in confined optical waveguides. Ti-indiffusion or Annealed Proton Exchange (APE) are combined with optical grade dicing to fabricate ridge waveguides with propagation losses that can be lower than 0.2 dB/cm. Firstly we show how a PhC inscribed in a confined ridge waveguide can be exploited as a temperature sensor with an unexpectedly high 8 nm/°C temperature sensitivity. LiNbO3 PhCs with high aspect ratio are also demonstrated. The performance is achieved by properly tilting the ridge before patterning its walls by Focused Ion Beam (FIB). A eight micrometer long 1D-PhC on a Ti:LiNbO3 ridge waveguide has been fabricated and its reflectivity has been evaluated using an optical coherence tomography (OCT) system: it is measured to be 53 % for the TM wave and 47 % for the TE wave. The period can be optimized in order to increase the reflection of the 1D-PhC up to 80 %. These developments open the way to the dense integration of compact dynamic devices such as modulators, spectral filters or electric field sensors.

Pr3+:YLiF4 epitaxial layers: efficient laser oscillation in the visible spectral region with planar and channel waveguides

Efficient guided laser oscillation in the red, orange and green spectral region is demonstrated with Praseodymium-doped YLiF4 layers grown by liquid phase epitaxy (LPE). Channel waveguides were obtained by using a precision dicing diamond saw.

Highly coupled resonator based on ridge-shaped periodically poled materials for radio-Frequency applications

Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) devices are largely used in telecommunication for radio Frequency (RF) signal processing. Nevertheless, these devices are limited by various factors such as short-circuit between electrodes for SAW and precise thickness control for BAW. This paper shows the interest of a new kind of transducer using Periodically Poled Lithium Niobate (PPLN) developed to overcome SAW and BAW technological limits. A former PPLN-based wave-guide was presented some years ago exploiting planar technologies. The novelty of the present work lies in the 3D structuring of the transducer allowing for very high aspect ratio structures exhibiting a theoretical electromechanical coupling about 20% and a phase velocity up to 20 km.s-1.