L. Zampedri

Erbium-activated HfO2-based waveguides for photonics

Abstract Silica-based sol–gel waveguides activated by Er 3+ ions are attractive materials for integrated optic devices. 70SiO 2 –30HfO 2 planar waveguides, doped with Er 3+ concentrations ranging from 0.01 to 4 mol%, were prepared by sol–gel route. The films were deposited on v–SiO 2 and silica-on-silicon substrates, using dip-coating technique. The waveguides show a homogeneous surface morphology, high densification degree and uniform refractive index across the thickness. Emission in the C-telecommunication band was observed at room temperature for all the samples upon excitation at 980 nm. The shape is found to be almost independent on erbium content, with a FWHM between 44 and 48 nm. The 4 I 13/2 level decay curves presented a single-exponential profile, with a lifetime ranging between 1.1 and 6.7 ms, depending on the erbium concentration. The waveguide deposited on silica-on-silicon substrate supports one single propagation mode at 1.5 μm with a confinement coefficient of 0.85, and a losses of about 0.8 dB/cm at 632.8 nm.

Sol-gel Er-doped SiO2–HfO2 planar waveguides: A viable system for 1.5 μm application

70SiO2–30HfO2 planar waveguides, doped with Er3+ concentrations ranging from 0.3 to 1 mol %, were prepared by sol-gel route, using dip-coating deposition on silica glass substrates. The waveguides show high densification degree, effective intermingling of the two components of the film, and uniform surface morphology. Propagation losses of about 1 dB/cm were measured at 632.8 nm. When pumped with 987 or 514.5 nm continuous-wave laser light, the waveguides show the 4I13/2→4I15/2 emission band with a bandwidth of 48 nm. The spectral features are found independent both on erbium content and excitation wavelength. The 4I13/2 level decay curves presented a single-exponential profile, with a lifetime between 2.9 and 5.0 ms, depending on the erbium concentration.

Infrared-to-visible CW frequency upconversion in erbium activated silica-hafnia waveguides prepared by sol-gel route

Abstract 70SiO2–30HfO2 mol% planar waveguides, doped with Er3+ with concentrations ranging from 0.3 to 2 mol% were prepared by sol–gel route, using dip-coating deposition on vitreous-SiO2 substrates. Infrared-to-visible upconversion emission, upon excitation at 980 nm, has been observed for all the samples. The upconversion results in green, red and blue emissions. The investigation of the upconversion dynamic as a function of the Er3+ concentration and excitation power, show that processes such as excited state absorption and energy transfer upconversion are effective.

Er-doped silica-based waveguides prepared by different techniques: RF-sputtering, sol-gel and ion-exchange

Erbium-activated silica-based planar waveguides were prepared by three different technological routes: RF-sputtering, sol–gel and ion exchange. Various parameters of preparation were varied in order to optimize the waveguides for operation in the NIR region. Particular attention was devoted to the minimization of the losses and the increase of the luminescence efficiency of the metastable 4I13/2 state of the Er3+ ion. Waveguide properties were determined by m-line spectroscopy and loss measurements. Waveguide Raman and luminescence spectroscopy were used to obtain information about the structure of␣the prepared films and about the dynamical processes related to the luminescence of the Er3+ ions.

Erbium-Activated Silica-Titania Planar Waveguides

Abstract(100 − x)SiO2-(x)TiO2-ErO3/2 planar waveguides, with 7 ≤ x ≤ 20 have been prepared by sol-gel route using the dip-coating technique. The thickness of the films was optimized to support a single propagating mode at 1550 nm, with a confinement coefficient higher than 0.75. The process of densification of the gel and the devitrification with the growth of TiO2 nanocrystals were studied by Raman scattering. Devitrification is important only for x ≥ 15, but it was not possible to obtain full densification of the samples, even at the lowest TiO2 content, without the appearance of nanocrystals.Emission in the C telecom band was observed; the spectral width of the 4I13/2 → 4I15/2 transition of Er3+ slightly increases with the titania content. For x ≤ 12 most of Er3+ ions (about 65%) decay exponentially with a lifetime of about 8 ms.

Nucleation of titania nanocrystals in silica titania waveguides

SiO2(1 − x)-TiO2(x) monomode waveguides at 632.8 nm, with x in the range 0.07–0.2 and thickness of about 0.4 μm, were deposited on silica substrates by a dip-coating technique. Nucleation of TiO2 nanocrystals and the growth of their size by thermal annealing up to 1300°C were studied by waveguided Raman scattering in the SiO2(0.8)-TiO2(0.2) composition. In the low frequency region (5–50 cm−1) of the VV and HV polarized Raman spectra the symmetric and quadrupolar acoustic vibrations are observed. The mean size of the titania particles are obtained from the frequencies of the Raman peaks. The results are compared with those obtained from the measure of the linewidths in the X-ray diffraction spectra. Nanocrystals with a mean size in the range 4–20 nm are obtained by thermal annealing in a corresponding range of 700–1300°C.

Er3+/Yb3+ Co-Activated Silica-Alumina Monolithic Xerogels

Monolithic silica xerogels doped with different concentrations of Er3+, Yb3+ and Al3+ were prepared by sol-gel route. Densification was achieved by thermal treatment in air at 950°C for 120 h with a heating rate of 0.1°C/min. We studied the luminescence properties of the 4I13/2 → 4I15/2 emission band of Er3+ as a function of the Al/Er/Yb concentration and we paid particular attention to the alumina effects. Raman spectroscopy and Vis-NIR absorption were used to monitor the degree of densification of the glasses and the residual OH content.

Spectroscopic assessment of silica–titania and silica–hafnia planar waveguides

Silicate glasses remain the most investigated systems for optical planar waveguides, since they offer a reasonable solubility for rare-earth ions, they are transparent in the near-infrared–visible region and they are compatible with integrated optics (IO) technology. In the last decade, various technologies have been employed for the fabrication of silica (SiO2)-based IO components and a broad variety of silicate glass systems have been investigated. Besides the SiO2–titania (TiO2) system, which has been widely studied, it has recently been shown that SiO2–hafnia (HfO2) could be a further viable system for 1.5 µm applications. This paper compares spectroscopic results, in particular infrared and Raman spectra, in order to assess the structural and optical properties of erbium-activated SiO2–TiO2 and SiO2–HfO2 planar waveguides, prepared by two different techniques: rf sputtering and the sol–gel method. Particular attention is devoted to the homogeneity of the material structures obtained in each case.

Enhanced spectroscopic properties at 1.5 μm in Er3+/Yb3+-activated silica–titania planar waveguides fabricated by rf-sputtering

Two Er 3+ /Yb 3+ -codoped 94SiO 2 -6TiO 2 planar waveguides were fabricated by the rf-sputtering technique. One sample was doped with 1 mol% Er and the other was also doped with ytterbium, with a molar ratio Yb/Er = 2. The thickness and the refractive index of the waveguides were measured by an m-line apparatus operating at 632.8 and 543.5 nm. The losses, for the TE 0 mode, were evaluated at 632.8 and 1300 nm. The structural properties were investigated with several techniques, such as secondary ion mass spectrometry, energy dispersive spectroscopy and Raman spectroscopy. All waveguides were single-mode at 1300 and 1550 nm. An attenuation coefficient of 0.5 dB/cm at 632.8 nm and a lifetime of the 4 I 13/2 metastable state of 7.2 ms were measured. Upon cw excitation at 978 nm, an increase of the 1.53 μm luminescence intensity larger than two-fold was detected in the Yb 3+ /Er 3+ -codoped waveguide with respect to the waveguide doped only with Er 3+ .

Erbium-activated monolithic silica xerogels and silica-titania planar waveguides: optical and spectroscopic characterization

Recent results obtained for Er2O3-SiO2 monolithic xerogels and erbium activated SiO2-TiO2 planar waveguides are presented. Monolithic erbium-activated silica xerogels with erbium content ranging from 0 up to 40000 ppm were prepared by the sol-gel technique. Samples were densified by thermal treatment in air at 950 degrees C for 120 hours. The densification degree and the relative content of hydroxyl groups were studied by NIR absorption and Raman spectroscopies. Emission at 1.5 micrometers , characteristic of the 4I13/2 yields 4I15/2 transition of Er3+ ions, was observed at room temperature for all monolithic samples upon continuous wave excitation at 980 nm. For the 5000 Er/Si ppm doped xerogel, an intense photoluminescence was observed with a lifetime of 8 ms for the metastable 4I13/2 level. Passive and erbium-activated SiO2-TiO2 planar waveguides, monomode at 632.8 nm, were prepared by a dip-coating technique. Some parameters such as H2O content, intermediate and final thermal treatments, and the molar ratio TiO2/SiO2 were modified during the preparation of the solution in order to minimize the final content of residual hydroxyl groups and the phase separation between silica and titania. Raman spectroscopy was used to check the structural properties of the waveguides. A lifetime of 7 ms was measured for the metastable 4I13/2 level in a 93SiO2-7TiO2 planar waveguide activated by 10000 ppm Er/(Si + Ti). The best value of the attenuation coefficient was of 0.5 dB/cm at 632.8 nm.