Andrea Chiappini

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.

High quality factor Er3+-activated dielectric microcavity fabricated by rf sputtering

The authors report on one-dimensional dielectric photonic crystals activated by Er3+ ion and fabricated by rf-sputtering deposition. The cavity was constituted by an Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of six pairs of SiO2∕TiO2 layers. Near infrared transmittance spectra evidence the presence of a stop band from 1350to1850nm and a cavity resonance centered at 1537nm. Intensity enhancement and narrowing of the I13∕24→I15∕24 emission band of Er3+ ion, due to the cavity effect, were observed. A cavity quality factor of 171 was achieved.

Glass optical waveguides: a review of fabrication techniques

Abstract. Glasses, either pure or suitably doped, constitute an excellent material for the development of integrated optical circuits. A brief review is presented of the most widely used processes for the fabrication of passive and active glass waveguides. Brilliant prospects of glass-based platforms for the development of photonic integrated circuits are outlined.

Femtosecond laser direct writing of gratings and waveguides in high quantum efficiency erbium-doped Baccarat glass

The femtosecond laser direct writing technique was employed to inscribe gratings and waveguides in high quantum efficiency erbium-doped Baccarat glass. Using the butt coupling technique, a systematic study of waveguide loss with respect to input pulse energy and writing speed was performed to achieve the best waveguide with low propagation loss (PL). By pumping at 980 nm, we observed signal enhancement in these active waveguides in the telecom spectral region. The refractive index change was smooth and we estimated it to be ~10−3. The high quantum efficiency (~80%) and a best PL of ~0.9 dB cm−1 combined with signal enhancement makes Baccarat glass a potential candidate for application in photonics.

High quality factor Er-doped Fabry?Perot microcavities by sol?gel processing

An optimized sol–gel process was developed to fabricate 1D photonic bandgap structures. Several erbium-doped Fabry–Perot microcavities were prepared and characterized. The thickest sample contained two Bragg mirrors, each having 12 distributed Bragg reflector periods of alternating silicate glass and titania layers. The total thickness of this sample reached ~12 µm. The Er3+ photoluminescence spectra at 1.5 µm were measured for the microcavities. A quality factor of 250 and an Er3+ photoluminescence enhancement of 96 times at 1.5 µm have been reached. The sol–gel processing details, the crystallization of the titania films and the refractive index of the deposited materials are discussed in detail. The simulated optical spectra of the microcavities were found to agree well with the actually measured curves. These results demonstrate that the present sol–gel processing technique is of potential interest for low cost fabrication of 1D photonic bandgap devices.

Er3+ activated silica-hafnia glass-ceramics planar waveguides

Silica-hafnia glass-ceramics waveguides activated by Er3+ ions were fabricated by sol-gel route. X ray diffraction and optical spectroscopy showed that after an adapted heat treatment, the resulting materials showed a crystalline environment. Analysis of the luminescence properties has demonstrated that erbium ions are, at least partially, trapped in a crystalline phase. Losses measurements at different wavelength highlight a very low attenuation coefficient indicating that this nanostructured material is suitable for a single band waveguide amplifier in the C band of telecommunication.

Experimental investigation of photonic band gap influence on enhancement of Raman-scattering in metal-dielectric colloidal crystals

A simple chemical technique is implemented to fabricate a metal-dielectric colloidal crystal structure (MDCS) in order to enhance the otherwise weak Raman signals by combining the effects of localized surface plasmon resonance (LSPR) enhancement due to gold nanoparticles, precise field confinement of dielectric and air bands in the periodic dielectric structure and field enhancements at the photonic band gap (PBG) edges. The higher density of electromagnetic modes (DOS) near these band edges is explained as due to the reduced group velocity at the photonic band gap edges. Intense electric field strength due to the excitation of high DOS at the edges of PBG of MDCS and the LSPR excitation through field confinement in the dielectric medium of MDCS are employed to study the Raman-scattering signals of adsorbed benzenethiol (BT) molecule on the MDCS. Large enhancement for the Raman signal in MDCS in comparison to the Raman spectra observed for BT molecule dispersed on sputtered gold film shows the effectivene...

Erbium-activated silica–titania planar waveguides on silica-on-silicon substrates prepared by rf sputtering

Abstract Erbium-activated silica–titania planar waveguides were prepared by radio-frequency (rf) sputtering technique. Silica-on-silicon substrates obtained by plasma-enhanced chemical vapor deposition (PECVD) and rf sputtering (RFS) were employed. The refractive indices, the thickness and the propagation losses of the waveguides were measured. The refractive index and the roughness of the silica substrates produced by RFS appear to be dependent on the thickness. Thermal annealing, which is a necessary condition to obtain light propagation, induces a decrease of the refractive index in the silica substrates. The waveguide deposited on PECVD substrate exhibits several propagating modes with an attenuation coefficient 1.7 dB/cm compared with 12.2 dB/cm measured for the waveguide deposited on silica substrate produced by RFS technique. Emission of the 4 I 13/2 → 4 I 15/2 transition with a 53 nm bandwidth was observed.

Diamond photonics platform enabled by femtosecond laser writing

Diamond is a promising platform for sensing and quantum processing owing to the remarkable properties of the nitrogen-vacancy (NV) impurity. The electrons of the NV center, largely localized at the vacancy site, combine to form a spin triplet, which can be polarized with 532 nm laser light, even at room temperature. The NV’s states are isolated from environmental perturbations making their spin coherence comparable to trapped ions. An important breakthrough would be in connecting, using waveguides, multiple diamond NVs together optically. However, still lacking is an efficient photonic fabrication method for diamond akin to the photolithographic methods that have revolutionized silicon photonics. Here, we report the first demonstration of three dimensional buried optical waveguides in diamond, inscribed by focused femtosecond high repetition rate laser pulses. Within the waveguides, high quality NV properties are observed, making them promising for integrated magnetometer or quantum information systems on a diamond chip.

Photonic crystals for monitoring fatigue phenomena in steel structures

This paper introduces the concept and development of a strain sensing system for structural application based on the properties of photonic crystals. Photonic crystals are artificially created periodic structures, usually produced in the thinfilm form, where optical properties are tailored by a periodicity in the refractive index. The idea of using the crystal as a sensor is based on the observation that a distortion in the crystal structure produces a change in the reflected bandwidth. When a photonic crystal is designed to operate in the visible part of the spectrum, a permanent distortion of the film results in a change in its apparent color. This property makes photonic crystals suitable for permanent monitoring of structural elements, as any critical changes in the strain field can be promptly and easily detected by visual inspection. A simple and low-cost example of photonic crystals consists of opals synthesized by vertical deposition. In this contribution we introduce a target application for the fatigue monitoring of wind turbines, and then provide the reader with some basic information concerning modeling of the crystal architecture and fabrication of these structures. Next we discuss their application to strain measurement, specifying how reflection and transmission properties of the opals have to be designed to satisfy the expected strain response of the sensor. Finally, we present the preliminary results of a laboratory validation carried out on thin films applied to a rubber support.