Ion-implanted Lithium Niobate Research Articles

Step-index optical waveguide produced by multi-step ion implantation in LiNbO_3

The refractive indexes, material attenuation and damage fractions of a multi-step ion implanted Lithium Niobate (LiNbO3) waveguide were analyzed as functions of the annealing temperatures. An almost flat damage depth profile was designed to reduce the uncertainties related to the indexes profile shape, thus providing a better test-case for the characterizations. The measurements performed on the fabricated optical waveguides confirmed the predicted step-index profiles showing that the light is confined inside the damaged layer. The low measured attenuation (less than 0.8 dB/cm @ 632.8 nm) makes the obtained waveguide attractive for device fabrication.

Theoretical analysis of the TE mode Cerenkov type second harmonic generation in ion-implanted X-cut lithium niobate channel waveguides

Optical second harmonic generation (SHG) in the form of Cerenkov radiation from ion-implanted lithium niobate (LiNbO 3) channel waveguides is analyzed by directly resolving the wave equations. Useful formula of the SHG efficiency is derived and expressed in terms of waveguide parameters. Numerical examples are plotted for LiNbO 3 crystals. The results enable the optimization of waveguide design for efficient second harmonic generation in the Cerenkov configuration.

Engineering of thermo-optic properties in ion implanted lithium niobate waveguides by electronic stopping power

The thermo-optic (TO) properties of the lithium niobate waveguide fabricated by oxygen ion implantation at three different energies (2, 3 and 6 MeV) have been investigated. It is found that, as the electronic stopping power (Se) of the O ions is below a threshold ∼2.2 keV nm−1, the TO features are well preserved in the waveguide regions. When Se is above this value, the TO coefficients of the waveguides are considerably modified, which is attributed to the increased defect generation in the crystal.

Enhanced photonic bandgap in ion-implanted lithium niobate waveguides by improving index contrast

We report on utilizing focused ion beam milling and selective wet-etching techniques to enlarge the optical barrier in helium ion-implanted lithium niobate single crystals. We realized a high-efficiency narrow-bandwidth photonic band filter by introducing an air cavity as the optical barrier on a waveguide portion. The air cavity was created beneath the Bragg gratings (1-D photonic crystals) to strengthen the light confinement and optical response. The experimental performance of photonic crystals with and without air cavity is presented and compared with the theoretical modeling. These photonic crystal devices with high refractive-index contrast make a further step towards ultracompact optical circuit integration and applications based on single crystals.

Refractive index tailoring in congruent Lithium Niobate by ion implantation

Refractive index profiles of ion-implanted Lithium Niobate waveguides are investigated. Z + and z − congruent Lithium Niobate samples have been implanted with C 3+ ions at a fluence of 4 × 10 14 ions/cm 2. Dark m-lines measurements have been performed on ordinary ( n o ) and extraordinary ( n e ) indexes for three different wavelengths (532 nm, 632.8 nm, 818 nm) before and after the annealing process. A reconstruction of refractive index profiles by Reflectivity Calculation Method (RCM) is presented and commented. The literature data for nuclear damage regime have been collected and critically examined. n o and n e curves as function of the density of energy released in nuclear collisions, E d , describing the effects of ion implantation on LN refractive indexes has been obtained on the basis of literature data. n o depth profile, predicted according to n o ( E d ) curve, is in good agreement with the RCM reconstructed one. In the case of n e , a satisfactory agreement has been reached only slightly modifying the n e ( E d ) curve and considering an alternative RCM profile structure.

Study of Er+ ion-implanted lithium niobate structure after an annealing procedure by RBS and RBS/channelling

Abstract Erbium-doped lithium niobate (Er:LiNbO3) is a prospective photonics component, operating at λ = 1.5 μm, which could be used as an optical amplifier or waveguide laser. We have focused on the structure of Er:LiNbO3 layers created by 330 keV erbium ion implantation (fluences 1.0 × 1015, 2.5 × 1015 and 1.0 × 1016 cm−2 1) in the X, Z and two various Y crystallographic cuts of LiNbO3. Five hours annealing at 350 °C was applied to recrystallize the as-implanted layer and to avoid clustering of Er. Depth distribution of implanted Er has been measured by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He+ ions. Defects distribution and structural changes have been described using the RBS/channelling method. Data obtained made it possible to reveal the relations between the crystallographic orientation of the implanted crystal and the behaviour during the restoration process. The deepest modified layer has been observed in the perpendicular Y cut, which also exhibits the lowest reconstruction after annealing. The shallowest depth of modification and good recovery after annealing were observed in the Z cut of LiNbO3. Since Er-depth profiles changed significantly in the perpendicular Y cut, we suppose that the crystal structure recovery inhibits Er mobility in the crystalline structure.

Quantification of nuclear damage in high energy ion implanted lithium niobate

We show that the approximations used to extract the damage depth profiles from the RBS-channeling spectra of high energy ion implanted lithium niobate lead to incorrect results when two defective regions containing damage generated by electronic and nuclear energy deposition are produced. We demonstrate by high resolution X-ray diffraction analysis that the end-of-range defects formation is not influenced by the onset of different defects in the surface region and it is thus independent of the implantation energy. We propose universal curves, valid for ions Z⩽14, for the end-of-range defective fraction and the maximum strain as a function of the density of energy deposited by nuclear processes.

Complementary X-ray topography and near-surface diffraction for investigations into the structure of ion-implanted optical waveguides

Ion implantation is now a well established technique for the production of optical waveguides for integrated optics applications. However, in some materials, such as lithium niobate, it leads to anomalous optical properties in the waveguiding region. We have investigated the structure of the waveguide and the damaged region in ion-implanted lithium niobate by carrying out complementary X-ray topography and near surface X-ray diffraction on etched crystals. The results indicate radiation enhanced annealing in the waveguide itself and the upper region of the substrate, as well as a high degree of amorphisation in the damaged layer.

Second Harmonic Generation in Ion Implanted Lithium Niobate Planar Waveguides

Abstract We report the first demonstration of second harmonic generation (SHG) in ion implanted lithium niobate optical waveguides. For both ordinary and extraordinary index profiles a computer program was developed to simulate the positions of the modes within the optical well. With the help of this program the theoretical possibility of SHG using mode matching conditions within the guide was then studied as a function of the guide depth and temperature, and from these predictions, practical guides were constructed. Initially, SHG Cerenkov radiation was observed with leaky single implanted guides. Mode matched SHG from m = 0 to m = 2 was subsequently achieved by means of a multiple energy implant which was able to confine both fundamental and harmonic waves. Allowing for coupling and transmission losses, the corrected conversion efficiency is 0–018% W−1 which compares favourably to a theoretical prediction for this guide of 0–020% W−1. In this case a wide temperature tuning range was obtained.