Erbium-doped fiber devices have been extraordinarily successful due to their broad optical gain around 1.5–1.6 μm. Er-doped fiber amplifiers enable efficient, stable amplification of high-speed, wavelength-division-multiplexed signals, thus continue to dominate as part of the backbone of longhaul telecommunications networks. At the same time, Er-doped fiber lasers see many applications in telecommunications as well as in biomedical and sensing environments. Over the last 20 years significant efforts have been made to bring these advantages to the chip level. Device integration decreases the overall size and cost and potentially allows for the combination of many functions on a single tiny chip. Besides technological issues connected to the shorter device lengths and correspondingly higher Er concentrations required for high gain, the choice of appropriate host material as well as many design issues come into play in such devices. In this contribution the important developments in the field of Er-doped integrated waveguide amplifiers and lasers are reviewed and current and future potential applications are explored. The vision of integrating such Er-doped gain devices with other, passive materials platforms, such as silicon photonics, is discussed.

Erbium-doped integrated waveguide amplifiers and lasers

A series of Er3+-TiO2, Yb3+-TiO2 and Er3+/Yb3+-TiO2 photocatalysts were obtained via sol–gel method, using lanthanides precursor ranging from 0.25 to 10 mol%. The experiments demonstrated that phenol in aqueous solutions was successfully degraded under visible light (λ > 450 nm) using Er/Yb-TiO2. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS), UV–vis absorption measurement, BET surface area analysis and luminescent spectroscopy. XPS analysis revealed that erbium and ytterbium were present in the form of oxides. The sample showing the highest photoactivity was in the form of anatase, its surface area equalled to 125 m2/g, average crystals size was 13 nm, and it was prepared introducing 1 mol% of Yb3+ into reaction medium. 3 h of irradiation resulted in 89% of phenol degradation under visible light. Action spectra analysis performed for the selected Er/Yb-TiO2 samples, revealed that irradiation from 420 to 475 nm is responsible for visible light photoactivity.

Visible light activity of rare earth metal doped (Er3+, Yb3+ or Er3+/Yb3+) titania photocatalysts

Sol-gel silica/titania-on-silicon Er/Yb-doped waveguides for optical amplification at 1.5 μm

Three types of TiO-compound-based nanobelts (Na2Ti3O7, H2Ti3O7, TiO2) are prepared from commercial TiO2 powders via an alkaline hydrothermal process. Nanostructured sheets based on the as-synthesized nanobelts are prepared using a paper-making process. The nanobelts are connected with hydrogen bonds or/and bridge oxygen atoms and packed together, forming a paperlike porous network structure, with an average pore size of ∼500 nm. The electrical properties and gas sensing of the nanostructured sheets are demonstrated to display sensitivity down to sub-ppb levels. H2Ti3O7 nanobelts decorated with Ag nanoparticles have also been applied as an antibacterial agent.

Nanostructured Sheets of TiO Nanobelts for Gas Sensing and Antibacterial Applications

The effects of the erbium concentration, crystal size, crystal phase, and different processing temperatures on the upconverted emission of Er3+ in BaTiO3 and TiO2 nanocrystals are reported. A cw diode laser at 975 nm was used as a pump source for resonant sequential excitation of the 4I11/2 and 4F7/2 levels. Green and red upconversion emission at 550 and 670 nm were observed from these oxide nanocrystals with 975 nm excitation. With the same Er3+ concentration, the upconversion emission intensity from BaTiO3 was higher than that observed in the TiO2 host. In the TiO2 matrix, the maximum upconversion emission intensity of Er3+ was found for samples calcined at 800 °C where both the anatase and the rutile phases were present. The observed emission characteristics and the pump intensity dependence of the luminescence intensity confirm that the upconverted emission in these materials is produced by two-photon excited-state absorption (ESA) processes.

Fluorescence Upconversion Properties of Er3+-Doped TiO2 and BaTiO3 Nanocrystallites

The up-conversion of infrared radiation into blue, green and red fluorescences has been investigated for erbium-doped titanium dioxide (TiO2) optical planar waveguides. These waveguides have been prepared by a sol-gel process and a dip-coating technique. The lifetime measurements of the 4S32 level (green fluorescence) were performed using a pulsed excimer-pumped dye laser operating at 650 nm. They were found to depend strongly on the Er3+ ion concentration.

J. Mugnier

Papers

Up-conversion fluorescence spectroscopy in Er3+: TiO2 planar waveguides prepared by a sol-gel process

Fluorescence of Er3+ ions in TiO2 planar waveguides prepared by a sol-gel process

Sol–gel waveguide thin film of YBO3: preparation and characterization

Structural characterisation of Er3+ doped sol–gel TiO2 planar optical waveguides

IR luminescence decays and radiative lifetime of the level in Er3+ doped sol-gel TiO2 planar waveguides