Comparison of novel liquid electrodes for silica optical fiber thermal poling

We report experimental analysis of optical fibers thermally poled over long lengths using novel types of internal liquid electrodes to generate effective second-order nonlinearities. Our analysis includes transmission losses, depletion region formation, SHG at telecom pump wavelengths

Erratum: "Ultraviolet poling of pure fused silica by high-intensity femtosecond radiation" [Appl. Phys. Lett. 86, 071106 (2005)]

Erratu

Thermal poling of glass modified by femtosecond irradiation

Thermal poling of silica glass modified by femtosecond laser irradiation is demonstrated. Increase of second-harmonic generation in the irradiated regions is observed. This enhancement is interpreted in terms of structural modifications in silica glass that make the poling process more efficient. Evidence of a change in the distribution of the electrostatic field frozen in glass during poling is obtained. This technique is used for (2) grating fabrication

All-fiber fourth and fifth harmonic generation from a single source

All-fiber fourth and fifth harmonic generation from a single source is demonstrated experimentally and analyzed theoretically. Light from a fully fiberized high power master oscillator power amplifier is launched into a periodically poled silica fiber generating the second harmonic. The output is then sent through two optical microfibers that generate the third and fourth harmonic, respectively, via four wave mixing (FWM). For a large range of pump wavelengths in the silica optical transmission window, phase matched FWM can be achieved in the microfibers at two different diameters with relatively wide fabrication tolerances of up to ±5 nm. Our simulations indicate that by optimizing the second harmonic generation efficiency and the diameters and lengths of the two microfibers, conversion efficiencies to the fourth harmonic in excess of 25% are theoretically achievable

Four-wave mixing UV generation in optical microfibers

UV generation via four-wave-mixing (FWM) in optical microfibres (OMFs) was demonstrated. This was achieved by exploiting the tailorable dispersion of the OMF in order to phase match the propagation constant of the four frequencies involved in the FWM process. In order to satisfy the frequency requirement for FWM, a Master Oscillator Power Amplifier (MOPA) working at the telecom C-band was connected to a periodically poled silica fibre (PPSF), producing a fundamental frequency (FF) at 1550.3nm and a second harmonic (SH) frequency at 775.2nm. A by-product of this second harmonic generation is the generation of a signal at the third harmonic (TH) frequency of 516.7nm via degenerate FWM. This then allows the generation of the fourth harmonic (FH) at 387.6nm and the fifth harmonic (5H) at 310nm via degenerate and nondegenerate FWM in the OMF.The output of the PPSF was connected to a pure silica core fibre which was being tapered using the modified flame brushing technique from an initial diameter of 125µm to 0.5µm. While no signal at any UV wavelength was initially observed, as the OMF diameter reached the correct phase matching diameters, signals at 387.6nm appeared. Signals at 310nm also appeared although it is not phase matched, as the small difference in the propagation constant is bridged by other nonlinear processes such as self-phase and cross phase modulation

Long-term home ventilation of children in Italy: A national survey.

BACKGROUND: Improved technology, as well as professional and parental awareness, enable many ventilator-dependent children to live at home. However, the profile of this growing population, the quality and adequacy of home care, and patients' needs still require thorough assessment. OBJECTIVES: To define the characteristics of Italian children receiving long-term home mechanical ventilation (HMV) in Italy. METHODS: A detailed questionnaire was sent to 302 National Health Service hospitals potentially involved in the care of HVM in children (aged <17 years). Information was collected on patient characteristics, type of ventilation, and home respiratory care. RESULTS: A total of 362 HMV children was identified. The prevalence was 4.2 per 100,000 (95% CI: 3.8-4.6), median age was 8 years (interquartile range 4-14), median age at starting mechanical ventilation was 4 years (1-11), and 56% were male. The most frequent diagnostic categories were neuromuscular disorders (49%), lung and upper respiratory tract diseases (18%), hypoxic (ischemic) encephalopathy (13%), and abnormal ventilation control (12%). Medical professionals with nurses (for 62% of children) and physiotherapists (20%) participated in the patients' discharge from hospital, though parents were the primary care giver, and in 47% of cases, the sole care giver. Invasive ventilation was used in 41% and was significantly related to young age, southern regional residence, longer time spent under mechanical ventilation, neuromuscular disorders, or hypoxic (ischemic) encephalopathy. CONCLUSIONS: Care and technical assistance of long-term HMV children need assessment, planning, and resources. A wide variability in pattern of HMV was found throughout Italy. An Italian national ventilation program, as well as a national registry, could be useful in improving the care of these often critically ill children

Development of non-linear waveguide devices for optical signal processing

Reported in this thesis are advances in glass poling, a technique which produces second-order optical nonlinearity in glass. Poling of glass has drawn much attention because frequency conversion and electro-optic modulation, operations which are typically restricted to crystals, becomes feasible in glass fibres and waveguides which are widely spread media in photonics thanks to their excellent optical properties and mature manufacturing technology. Poled silica glass, despite showing about 10 times lower second-order nonlinearity than nonlinear crystals, can be competitive with them because longer interaction lengths are possible in glass fibres, owing to the lower chromatic dispersion. -gratings in fibres. This technology led to the first demonstration of an all-fibre frequency doubler of a fibre laser. Milliwatts of red light in the fundamental mode were produced by frequency doubling in a quasi-phase matched periodically poled silica fibre which was directly spliced to the output of the laser source. Efficiency up to 2.5% has been demonstrated in 11.5 cm long device with only about 100W of pump power, which means that 50% conversion efficiency is expected for a 2kW input power

Numerical analysis using 2D modeling of optical fiber poled by induction

Thermal poling, a technique to introduce effective second-order nonlinearities in silica optical fibers, has found widespread applications in frequency conversion, electro-optic modulation, switching and polarization-entangled photon pair generation. Since its first demonstration around 25 years ago, studies into thermal poling were primarily based on anode-cathode electrode configurations. However, more recently, superior electrode configurations have been investigated that allow for robust and reliable thermally poled fibers with excellent second order nonlinear properties. Very recently, we experimentally demonstrated an electrostatic induction poling technique that creates a stable second-order nonlinearity in a twin-hole fiber without any direct physical contact to internal fiber electrodes whatsoever. This innovative technique lifts a number of restrictions on the use of complex microstructured optical fibers (MOF) for poling, as it is no longer necessary to individually contact internal electrodes and presents a general methodology for selective liquid electrode filling of complex MOF geometries. In order to systematically implement these more advanced device embodiments, it is first necessary to develop comprehensive numerical models of the induction poling mechanism itself. To this end, we have developed two-dimensional (2D) simulations of space-charge region formation using COMSOL finite element analysis, by building on current numerical models

Fabrication of photonic devices in heavy metal oxide glass by femtosecond laser direct writing

Femtosecond laser can induce a permanent refractive index change inside various transparent materials via multiphoton absorption. This technique also opens up new possibilities for fabricating photonic devices in highly nonlinear glasses such as heavy metal oxide glass (HMO) which will be key to the development of all-optical switches and, in combination with thermal poling, to frequency converters and electro-optic modulators. Since self-focusing occurs in HMO glasses before reaching the optical breakdown threshold owing to the large n2, waveguide writing by femtosecond laser is challenging and so far waveguides at 633 nm have been achieved in HMO glass only outside of the region of filamentary propagation. In this paper, for the first time to our best knowledge, we report on the fabrication of high quality, low loss, channel waveguides and passive waveguide components at 1.5µm in bulk 12.5Bi glass without introducing self-focusing

Ultraviolet poling of pure fused silica by high-intensity femtosecond radiation

We demonstrate UV poling of a pure fused silica sample by applying to it an electric field of 200 kV/cm and irradiating it with high-intensity (~40 GW/cm) femtosecond (220 fs) laser pulses at 264 nm