Vratislav Perina

A study of the preparation and properties of copper-containing optical planar glass waveguides

Abstract We have studied the fabrication and properties of the Cu + -containing waveguides. These waveguides were fabricated in a special soda-lime silicate glass as well as in commercial optical glass substrates, by using an ion exchange in the melts containing either Cu + or Cu 2+ , at temperatures from 350°C to 500°C, and for periods from 5 min to 21 h. The optical properties of the fabricated waveguides were characterized using both mode and photoluminescence spectroscopy. The composition of waveguiding layers was studied using Rutherford Backscattering Spectrometry (RBS) and ESCA. The presence of divalent copper was determined using Electron Paramagnetic Resonance (EPR). After ion exchange, the refractive index increased, depending on the fabrication conditions, up to Δ n =+0.0693, and the waveguides supported up to 16 TE and TM modes. The depths of the fabricated waveguides varied between 6.0 and 27.5 μm. The most intensive blue-green luminescence was achieved with the samples that were ion-exchanged in the Cu 2 Cl 2 ·ZnCl 2 melt, where the presence of Zn 2+ strongly impeded the oxidation of Cu + to Cu 2+ . Both oxidation states of copper (Cu + as well as Cu 2+ ) were found in the waveguides fabricated in the pure Cu 2 Cl 2 . The main advantage of the copper-containing waveguides is the possibility of integrating the passive and active functions of the waveguides on the same substrate.

Novel low-temperature Er3+ doping of lithium niobate

Low temperature doping procedure is employed to make erbium doped lithium niobate substrates. The doping process is studied for X-, Y- and Z-cuts in both virgin and proton exchanged wafers. The amount as high as 9 weight percent of erbium was found in X-cuts when the doping was performed from a mixture of molten nitrates containing 10 weight percent of erbium slat after 5 hours diffusion at 400 degrees C. The content of erbium in Z- and Y-cuts as well as in the proton exchanged X-cuts was found to be much lower, below 0.5 percent. In-diffused erbium ions concentration is localized in a very thin layer, which can be extended by a subsequent annealing. Annealed proton exchanged waveguides were fabricated in the erbium doped wafers without any deterioration of the samples surfaces.

Localized moderate-temperature Er3+doping into optical crystals

Possibility of localized doping by Er3+ diffusion at moderate (less than 500 degree(s)C) temperature is demonstrated for lithium niobate and sapphire. The doping is achieved by immersing the substrate wafers into reaction melt containing small amounts of erbium salt. A crucial point of the presented technology is a crystallographic orientation of the used wafers. Though in the Z- and Y-cuts of lithium niobate the content of incorporated erbium did not exceed the concentration achieved using standard high temperature (or high energy) approaches, lithium niobate X-cuts contained up to 10 weight % of erbium. Similar results were obtained also for the corresponding cuts of sapphire. This strong anisotropy of the doping is explained on the basis of crystal structure of the particular cuts. The in-diffused layers in all the cuts are rather shallow, however, erbium can be diffused deeper into the substrates by post-diffusion annealing in air. The moderate-temperature approach enabled us to fabricate APE waveguides in erbium doped lithium niobate without deteriorating the samples surfaces. The samples were characterized by RBS, SEM, NDP and mode spectroscopy.

Investigation of GaN layers doped with Er3+ and Er3+ + Yb3+ ions using the transmittance measurement

We report about fabrication and properties of Gallium Nitride (GaN) layers doped with erbium or mixture of erbium and ytterbium ions. Transmission spectra in the spectral range from 280 to 800 nm taken by the spectrometer Varian Cary 50 showed that the increasing concentration of the dopants shifts the absorption edge to the lower wavelengths. Optical band gap Eg was determined from the absorption coefficient values using Taucs procedure and the obtained values varied from 3.08 eV to 3.89 eV depending on the erbium or erbium plus ytterbium doping. Photoluminescence emission at 1 530 nm due to the Er3+ intra-4f 4I13/2 → 4I15/2 transition was observed by using excitation of semiconductor lasers operating at 980 nm.

Optical properties of Er3+ + Yb3+ doped gallium nitride layers

We report about properties of Gallium Nitride layers doped by Erbium and Erbium/Ytterbium ions. The GaN layers were fabricated by Metal Organic Chemical Vapor Deposition on sapphire substrate, and Er3+ and Yb3+ ions were incorporated into the deposited layers by using ion implantation. After the implantation the samples were annealed in nitrogen atmosphere. The structures of the GaN samples were examined by the X-Ray Diffraction analysis; composition of the samples was measured by Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis. The GaN layers had single crystalline hexagonal wurtzite structure and content of Er3+ and Er3+\Yb3+ ranged from 0.05 to 3.38 at. %. The photoluminescence measurement was carried out at excitation of λex = 632.8 nm (temperature 4 K) and λex = 980 nm (room temperature). Photoluminescence spectra taken at 4 K showed typical erbium 4I13/2→4I15/2 emission bands. Some of our samples exhibited the desired emission even at the room temperature, which indicated that the samples were of a good quality what concerned their crystallographic homogeneity, as well as distribution and appropriate concentration of the Er3+ and Yb3+.

Photoluminescence study of (Er3+ + Yb3+) doped gallium nitride layers fabricated by magnetron sputtering

Erbium (Er3+) and Ytterbium (Yb3+) ions doped Gallium Nitride (GaN) layers were deposited by RF magnetron sputtering. Deposition was carried out in Ar + N2 gas mixture using Ga and Ga2O3 target as the source of Gallium. For the erbium and ytterbium doping, the Er2O3, Yb2O3 pellets, or Er and Yb powder were laid on the top of the Ga2O3 target. The GaN layers were deposited on silicon and Corning glass substrates. The properties of the GaN layers were investigated by using X-ray diffraction, Raman spectroscopy, absorption spectra and photoluminescence spectra. Prism coupling mode spectroscopy was used to measure the waveguiding properties. The composition of the fabricated samples was determined by using nuclear chemical analysis as Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection Analysis (ERDA). The results of the experiments were evaluated in terms of the relations between the technology approaches and the composition and luminescence properties of the fabricated thin films. Up to now the best results, which can be utilized for a structure operating at 1550 nm (when pumped at 980 nm), were obtained when using (erbium plus ytterbium) metallic powder and Corning glass as the substrate for the deposition.

Properties of erbium-doped gallium nitride films prepared by RF magnetron sputtering

We report on fabrication of the GaN layers deposited onto silicon, silica-on-silicon and quartz glass substrates by RF magnetron sputtering. The GaN layers were also doped with erbium ions to achieve active optical properties. The fabricated layers were characterized by a number of methods and the results are discussed on the bases of quality of the deposited GaN structures.

Properties of the APE waveguides fabricated in Er:LiNbO3 and (Er+Yb):LiNbO3

We present a study of the annealed proton exchanged waveguides fabricated in erbium and in a mixture of erbium and ytterbium (RE) bulk doped lithium niobate. Waveguiding properties and composition of the RE doped waveguides were not substantially changed compared with those fabricated in pristine lithium niobate. However, presence of the doping ions decreases the r33, but a carefully designed APE technology can increase the r33 almost to the value of the pristine LiNbO3. According to our results the proton exchange need not necessarily change the efficiency of the 1,5 μm emission and certainly does not lower the concentrations of the RE.

Optical spectroscopic properties of Er3+ ions in LiNbO3 planar waveguides produced by annealed proton exchange

We investigated the optical properties of Er3+ ions in LiNbO3 planar waveguides produced by annealed proton exchange (APE) using the site-selective method of combined excitation-emission spectroscopy at low temperature. The spectroscopic results obtained for the luminescence in the green spectral region (≈ 550nm) under the direct laser excitation at 450 nm and under two step laser excitation at 980 nm (up-conversion process) are compared with bulk material and LiNbO3 waveguides produced by Ti-diffusion. Notable differences have been found in the kind of defect sites, in their number distribution, and in the inhomogeneous broadening of the optical transitions.

Erbium localized doping into various cuts of lithium niobate and sapphire: a comparative study

Medium temperature (350 °C) localized doping of Er3+ was studied in lithium niobate (LN) and sapphire single crystal wafers that were cut in various crystallographic directions. It was found that the efficiency of the doping was connected with orientations of the substrate wafers of both LN and sapphire, and with the presence of mobile lithium ions in the structure of LN. The basic interstitial mechanism of erbium incorporation into the structure of sapphire and LN is in the latter accompanied with erbium for lithium ion exchange. While the rate of the interstitial diffusion was higher in the wafers oriented perpendicularly towards the cleavage planes of the crystals, ion exchange process was significant in the wafers cut in cleavage planes. Waveguiding properties in erbium doped lithium niobate originated rather from presence of erbium in the structure of the crystals than being a consequence of a weak proton exchange. Luminescence properties of the fabricated samples are also presented.