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Spiral-waveguide amplifiers in erbium-doped amorphous aluminum oxide are fabricated by RF reactive co-sputtering of 1-mu m-thick layers onto a thermally-oxidized silicon wafer and chlorine-based reactive ion etching. The samples are overgrown by a SiO2 cladding. Spirals with several lengths ranging from 13 cm to 42 cm and four different erbium concentrations between 0.5-3.0x10(20) cm(-3) are experimentally characterized. A maximum internal net gain of 20 dB in the small-signal-gain regime is measured at the peak emission wavelength of 1532 nm for two sample configurations with waveguide lengths of 13 cm and 24 cm and erbium concentrations of 2x10(20) cm(-3) and 1x10(20) cm(-3), respectively. The obtained gain improves previous results by van den Hoven et al. in this host material by a factor of 9. Gain saturation as a result of increasing signal power is investigated. Positive net gain is measured in the saturated-gain regime up to similar to 100 mu W of signal power, but extension to the mW regime seems feasible. The experimental results are compared to a rate-equation model that takes into account migration-accelerated energy-transfer upconversion (ETU) and a fast quenching process affecting a fraction of the erbium ions. Without these two detrimental processes, several tens of dB/cm of internal net gain per unit length would be achievable. Whereas ETU limits the gain per unit length to 8 dB/cm, the fast quenching process further reduces it to 2 dB/cm. The fast quenching process strongly deteriorates the amplifier performance of the Al2O3:Er3+ waveguide amplifiers. This effect is accentuated for concentrations higher than 2x10(20) cm(-3)., QC 20150612

The development in the field of erbium-doped integrated waveguide amplifiers for the generation of broadband and high-speed optical amplification around 1.5 - 1.6 μm is discussed and current and future potential applications are explored. In erbium-doped amorphous aluminium oxide on a silicon wafer, an internal net gain per unit length of 2.0 dB/cm at the wavelength of 1533 nm and internal net gain over a bandwidth of 80 nm has been demonstrated. Spiral-waveguide amplifiers of different lengths and erbium concentrations have been studied and an internal net gain of 20 dB in the small-signal-gain regime has been achieved. Currently, a highly promising crystalline host material, potassium double tungstate, which provides high emission cross sections to rare-earth ions and has generated an internal net gain per unit length of > 1000 dB/cm when exploiting the ytterbium transition at 1 μm, is doped with erbium ions and tested for amplification around 1.5 - 1.6 μm., QC 20151214 QC 20160922

A potassium double tungstate layer with the composition KY0.40Gd0.29Lu0.23Tm0.08(WO4)(2) was grown onto a pure KY(WO4)(2) substrate by liquid-phase epitaxy, microstructured by standard lithography and Ar-ion etching, and overgrown by a pure KY(WO4)(2) layer. The end-facets were polished. Laser experiments were performed on these buried, ridge-type channel waveguides in a resonator with one butt-coupled mirror and Fresnel reflection from the other endfacet, resulting in a high output-coupling degree of 89%, compared to intrinsic round-trip losses of only 2%. By pumping with a Ti:Sapphire laser at 794 nm, 1.6 W of output power at 1.84 mu m with a maximum slope efficiency of similar to 80% was obtained. To the best of our knowledge, this result represents the most efficient 2-mu m channel waveguide laser to date. We determined the optimum Tm3+ concentration in double tungstate channel waveguides to be at least 8at.% for efficient lasing. The theoretical limit of the slope efficiency depends on the Stokes efficiency which here is 43.2%, the outcoupling efficiency which here is 99%, and the pump quantum efficiency. The pump quantum efficiency of a 2-mu m Tm3+ laser pumped around 800 nm hinges on the efficiency of its cross-relaxation process. By fitting the macroscopic cross-relaxation parameter which linearly depends on the Tm3+ concentration to concentration-dependent luminescencedecay data, calculating the overall decay rate of the pump level, and deriving the concentration-dependent pump quantum efficiency, we obtain a theoretical limit for the slope efficiency of 83% for the chosen Tm3+ concentration. The experimental slope efficiency of similar to 80% closely approaches this limit., QC 20150612

Fibromyalgia typically presents with spontaneous body pain with no apparent cause and is considered pathophysiologically to be a functional disorder of somatosensory processing. We have investigated potential associations between the degree of self-reported clinical pain and resting-state brain functional connectivity at different levels of putative somatosensory integration. Resting-state functional magnetic resonance imaging was obtained in 40 women with fibromyalgia and 36 control subjects. A combination of functional connectivity-based measurements were used to assess (1) the basic pain signal modulation system at the level of the periaqueductal gray (PAG); (2) the sensory cortex with an emphasis on the parietal operculum/secondary somatosensory cortex (SII); and (3) the connectivity of these regions with the self-referential "default mode" network. Compared with control subjects, a reduction of functional connectivity was identified across the 3 levels of neural processing, each showing a significant and complementary correlation with the degree of clinical pain. Specifically, self-reported pain in fibromyalgia patients correlated with (1) reduced connectivity between PAG and anterior insula; (2) reduced connectivity between SII and primary somatosensory, visual, and auditory cortices; and (3) increased connectivity between SII and the default mode network. The results confirm previous research demonstrating abnormal functional connectivity in fibromyalgia and show that alterations at different levels of sensory processing may contribute to account for clinical pain. Importantly, reduced functional connectivity extended beyond the somatosensory domain and implicated visual and auditory sensory modalities. Overall, this study suggests that a general weakening of sensory integration underlies clinical pain in fibromyalgia.