Glass-ceramic Waveguides Research Articles

Tb 3+/Yb 3+ co-activated Silica-Hafnia glass ceramic waveguides

70SiO 2-30HfO 2 glass ceramic planar waveguides co-activated by Tb 3+/Yb 3+ ions were fabricated by sol gel route using a top-down approach. The energy transfer from Tb 3+ to Yb 3+ ions was investigated as a function of the Tb 3+/Yb 3+ molar ratio as well as of the total amount of rare earth ions. In particular, the conversion of absorbed photons at 476 nm into photons at 980 nm is considered, looking for potential application in photovoltaic systems.

Rare-earth-activated glass–ceramic waveguides

This work presents a short review of the activity performed in developing sol–gel-derived SiO 2–HfO 2 and SiO 2–SnO 2 glass–ceramic waveguides activated by Er 3+ and Eu 3+ ions, respectively. Fabrication by top-down and bottom-up techniques is reported and optical and spectroscopic assessment of glass ceramic waveguides is discussed. Luminescence enhancement is demonstrated. Refractive index modulation upon UV exposure is measured in SiO 2–SnO 2 film.

Controlled Growth of SnO2 Nanocrystals in Eu3+-Doped SiO2−SnO2 Planar Waveguides: A Spectroscopic Investigation

We report on the fabrication of Eu3+-doped SiO2−SnO2 low-loss (0.8 dB/cm at 632.8 nm) glass-ceramic planar waveguides, fabricated by the sol−gel technique and dip-coating processing. The effects of heat treatments on the growth and evolution of SnO2 nanocrystals in the matrix were investigated using different spectroscopic tools. In situ high-temperature X-ray diffraction allowed for the determination of the crystallization temperature and confirmed the formation of tetragonal rutile SnO2 crystals. The effect of crystallization on the optical properties and on the photoluminescence of Eu3+ ions was also studied. Low-frequency Raman scattering was successfully used to determine the crystal size, and the results obtained were found to be consistent with transmission electron microscopy measurements. The breakage of Si−O−Sn linkages during the formation of SnO2 nanocrystals in the matrix was investigated by Fourier-transform infrared spectroscopy.

XRD and EXAFS studies on the structure of Er{sup 3+}-doped SiO{sub 2}-HfO{sub 2} glass-ceramic waveguides: Er{sup 3+}-activated HfO{sub 2} nanocrystals

This paper describes the structure of Er{sup 3+}-doped SiO{sub 2}-HfO{sub 2} waveguides containing nanocrystals of HfO{sub 2}. Pure and 1 mol% Er{sup 3+}-doped 70SiO{sub 2}-30HfO{sub 2} films were deposited by the sol-gel method on amorphous SiO{sub 2} substrates using the dip-coating technique. Each waveguide has experienced a single thermal treatment at temperatures ranging from 900 to 1200 deg. C, for either short (30 min) or long (24 h) durations. Crystallization and microstructure were studied by x-ray diffraction (XRD). The local environments of hafnium and erbium ions were determined, respectively, from Hf and Er L{sub 3}-edges extended x-ray absorption fine structure (EXAFS) experiments. Both XRD and EXAFS results demonstrate the substitution of Hf{sup 4+} by Er{sup 3+} ions in the crystalline structure. XRD shows the nucleation of tetragonal HfO{sub 2} nanocrystals after heat treatment at 1000 deg. C for 30 min in the pure waveguide, and at 900 deg. C for 24 h in the waveguide doped with Er{sup 3+}. In both series, partial transformation from tetragonal to monoclinic HfO{sub 2} nanocrystals starts after heat treatment at 1100 deg. C for 24 h. The average crystallite size and size distribution can be controlled by thermal annealing temperature and duration, respectively, with brief treatment yielding a more homogeneous nanocrystal size.

XRD and EXAFS studies on the structure of Er3+-doped SiO2–HfO2 glass-ceramic waveguides: Er3+-activated HfO2 nanocrystals

This paper describes the structure of Er3+-doped SiO2–HfO2 waveguides containing nanocrystals of HfO2. Pure and 1 mol% Er3+-doped 70SiO2–30HfO2 films were deposited by the sol–gel method on amorphous SiO2 substrates using the dip-coating technique. Each waveguide has experienced a single thermal treatment at temperatures ranging from 900 to 1200 °C, for either short (30 min) or long (24 h) durations. Crystallization and microstructure were studied by x-ray diffraction (XRD). The local environments of hafnium and erbium ions were determined, respectively, from Hf and Er L3-edges extended x-ray absorption fine structure (EXAFS) experiments. Both XRD and EXAFS results demonstrate the substitution of Hf4+ by Er3+ ions in the crystalline structure. XRD shows the nucleation of tetragonal HfO2 nanocrystals after heat treatment at 1000 °C for 30 min in the pure waveguide, and at 900 °C for 24 h in the waveguide doped with Er3+. In both series, partial transformation from tetragonal to monoclinic HfO2 nanocrystals starts after heat treatment at 1100 °C for 24 h. The average crystallite size and size distribution can be controlled by thermal annealing temperature and duration, respectively, with brief treatment yielding a more homogeneous nanocrystal size.

CO 2 laser annealing on erbium-activated glass–ceramic waveguides for photonics

Silica-based sol–gel waveguides activated by Er 3+ ions are one of the most important materials for integrated optics devices. In this paper, we present an alternative method combining sol–gel route and CO 2 laser annealing for planar optical waveguides processing. The effects of pulsed and continuous CO 2 laser irradiation on the optical and spectroscopic properties of SiO 2–ZrO 2 and SiO 2–HfO 2 planar waveguides are evaluated and the thermal conventional annealing effects for these systems are reported for comparison. All the planar waveguides, doped with 0.5 and 5 mol% Er 3+, were prepared by sol–gel route using dip-coating deposition on v-SiO 2 substrates. An increase of the refractive index of approximately 0.04 at 1.5 μm has been observed on 70SiO 2–30HfO 2 planar waveguide after continuous CO 2 laser annealing. A similar refractive-index variation was detected in all SiO 2–ZrO 2 planar waveguides after CO 2 laser irradiation. We have observed, moreover, that continuous CO 2 laser annealing can lead to waveguides with a lower attenuation coefficient with respect to the attenuation coefficient measured for thermal annealed waveguides. Upon excitation at 514.5 nm continuous-wave laser light, on the irradiated sample, the shape is found to be almost independent on the time and irradiation power with CW laser annealing but a decrease of the FWHM of approximately 46–12 nm has been observed on planar waveguides after pulsed laser annealing. Before and after conventional thermal annealing, the 4 I 13 / 2 level decay curves present a single-exponential profile with a lifetime of 4.0 and 5.7 ms, respectively, but the lifetime increases up to 7.0 ms, after pulsed laser annealing treatment. X-ray diffraction and optical spectroscopy showed that after an adapted pulsed CO 2 laser annealing, the resulting materials showed a crystalline environment.

X-ray photoelectron spectroscopy of Er3+-activated SiO2–HfO2 glass-ceramic waveguides

xHfO2–(100 − x) SiO2 (x = 10, 20, 30 mol%) glass-ceramic planar waveguides doped with 0.3 mol% Er3+ ions, prepared by the sol–gel route and heat treated at 1000 °C to nucleate HfO2 crystals, were analysed by x-ray photoelectron spectroscopy, x-ray diffraction, high resolution transmission electron microscopy and photoluminescence spectroscopy. Formation of tetragonal HfO2 nanocrystals has been evidenced in all the samples. Spectroscopic parameters concerning the 4I13/2 metastable state of Er3+ion are revisited as a function of XPS analysis.

Raman and Er 3+ spectroscopy of hafnia single crystals and nanocrystals

In this work, we report on the spectroscopic characterization of erbium doped HfO 2 nanocrystals in SiO 2–HfO 2 glass–ceramic waveguides, fabricated by sol–gel process. The results are compared with those of single crystals grown using the flux growth technique. XRD and Raman measurements showed that the single crystals are monoclinic, while in the glass–ceramic waveguides, depending on the heat treatment, the nanocrystals are present in both tetragonal and monoclinic phases. The size distribution of nucleated nanocrystals was studied by transmission electron microscopy. The Raman peaks of the nanocrystals are broadened and shifted with respect to those observed in the bulk samples. The luminescence measurements in monoclinic nanocrystals and bulk single crystals of the same structure are quite dissimilar, evidencing that the rare earth ions are subjected to a different crystal field.

Enhanced fluorescence from Eu3+ in low-loss silica glass-ceramic waveguides with high SnO2 content

We report on the sol-gel fabrication and characterization of (100−x)SiO2–xSnO2 (x=8, 16, and 25mol%) glass-ceramic waveguides doped with 1mol% Eu3+. A suitable top-down thermal process led to the formation of SnO2 nanocrystals ∼4nm embedding Eu3+ ions. The excitation spectra evidence the role of interband electronic transition of SnO2 nanocrystals on the luminescence of Eu3+. Monitoring the D05→F27 Eu3+ emission, we observe about 15 times increase in the intensity of SnO2 absorption band, moving from x=8to25mol%. These waveguides also exhibit low losses, making them quite promising for development of high-gain integrated optical amplifiers.

Low-loss optical Er3+-activated glass-ceramics planar waveguides fabricated by bottom-up approach

A low-loss optical erbium activated silica-hafnia glass-ceramic planar waveguide was fabricated using a bottom-up approach. Hafnia nanoparticles were first prepared by colloidal route and then mixed in a silica-hafnia:Er3+ sol. The resulting sol was deposited on SiO2 substrate. Analysis of the photoluminescence has demonstrated that erbium ions are embedded in a crystalline phase. A lifetime enhancement of the I13∕24 metastable level was observed. Losses measurements at 1542nm highlight a very low attenuation coefficient (0.3dB∕cm) making this nanostructured material suitable for single band waveguide amplifier in the C band of telecommunications.

Are low-loss glass–ceramic optical waveguides possible?

The results of a cutback measurement of a glass-ceramic optical waveguide with single-mode fiber geometry have demonstrated that sub decibels per kilometer losses can be achieved. Difference spectra show that the limit of intrinsic scattering in these two-phase structures ought to be tens of decibels per kilometer.

Design and performance of a multiple element slab waveguide spectrograph for multimode fiber-optic WDM systems

A new type of compact (<7 cm/sup 2/) multiple element slab waveguide spectrograph suitable for medium resolution fiber-optic wavelength division multiplexing (WDM) applications in the 700 nm to 900 nm optical band is described. The spectrograph consists of a replicated diffraction grating formed on the convex edge of a multilayer glass-ceramic slab waveguide stack The grating design, based on an aberration corrected derivative of the classic Rowland spectrometer, was first verified holographically, and then implemented by replication from a ruled master grating. A combination of thick-film solder glass glazing, lamination, optical finishing and grating replication was chosen to produce a multiple element spectrograph that enables accurate spectral referencing, and can be interfaced by a passive optical fiber array and detector array alignment procedures.< >