Yonghang Shen

Photonic nanowires directly drawn from bulk glasses

High-uniform nanowires with diameters down to 50 nm are directly taper-drawn from bulk glasses. Typical loss of these wires goes down to 0.1 dB/mm for single-mode operation. Favorable photonic properties such as high index for tight optical confinement in tellurite glass nanowires and photoluminescence for active devices in doped fluoride and phosphate glass nanowires are observed. Supporting high-index tellurite nanowires with solid substrates (such as silica glass and MgF2 crystal) and assembling low-loss microcoupler with these wires are also demonstrated. Photonic nanowires demonstrated in this work may open up vast opportunities for making versatile building blocks for future micro- and nanoscale photonic circuits and components.

Compact dual-wavelength Nd:GdVO 4 laser working at 1063 and 1065 nm

We report a compact diode-laser pumped Nd:GdVO(4) laser with stable dual-wavelength output at 1063 nm and 1065 nm simultaneously. Two types of resonant cavity configurations were presented to support the stable dual-wavelength operation of the laser. Using a polarization beam splitter(PBS) included T-shaped cavity, we obtained a total power output over 5 W in two orthogonal polarized beam directions with 4 W in sigma polarization (1065.5 nm) and 1 W in pi polarization (1063.1 nm). By combining a half-wave-plate with the PBS in the laser cavity, a new configuration favoring one beam direction dual-wavelength output with same polarization direction was realized. A phenomenon of further line splitting was observed in both 1065 nm and 1063 nm.

Sapphire-fiber thermometer ranging from 20 to 1800 °C

A novel, to our knowledge, sapphire-fiber thermometer ranging from 20° to 1800 °C is presented that combines the radiance detection and the fluorescent lifetime detection schemes into one system. The thermal probe is a sapphire fiber grown from the laser-heated pedestal growth method. Its end part is doped with Cr3+ ion and coated with some radiance material to constitute a minifiber cavity. The sapphire fiber is coupled with a Y-shaped silica fiber bundle for signal transmission. Radiance and fluorescence signal processing schemes are also set up within one thermometer system. A sandwich two-band p-i-n detector is used that may respond to both the radiation and the fluorescence. Preliminary experimental results show that the thermometer is suitable for practical application with potential long-term stability and a high-temperature resolution.

Novel sapphire fiber thermometer using fluorescent decay

Abstract A novel sapphire fiber thermometer using fluorescent decay is presented. The thermal probe is simply a sapphire fiber grown from the laser heated pedestal growth (LHPG) method, with its end doped with Cr 3+ ion. The sapphire fiber is coupled with a normal Y-shape silica fiber bundle for signal transmission. Signal processing system for the fluorescent lifetime detection is set up. Relationship of the fluorescent lifetime and intensity with the temperature for the doped sapphire fiber is carefully measured and presented. The thermometer has good thermal response characteristics due to its specific thermal probe structure. The coupling efficiency between the fiber probe and the guiding fiber bundle is also high and stable. Experimental result shows that the thermometer has an average temperature resolution of 1°C between 20 and 450°C.

Short cavity single frequency fiber laser for in-situ sensing applications over a wide temperature range

A novel Er-doped silica fiber, with heavy Er doping, was specially developed for application to a single frequency fiber laser. Two high temperature-sustainable fiber Bragg gratings, written into Bi-Ge codoped photosensitive fiber, were chosen for the application and spliced to the specialist Er doped silica fiber to form a compact, linear cavity, fiber laser. The fiber laser retained single mode oscillation over a wide temperature range, from room temperature to 400 degrees C. The wavelength of the laser output could be tuned smoothly, without mode hopping being observed, when the temperature was changed. A narrow linewidth of less than 1 kHz was measured at the output of fiber laser and this indicates the potential of the fibre laser sensing system with extremely high sensitivity and resolution over this wide range.

Thermal decay characteristics of strong fiber Bragg gratings showing high-temperature sustainability

Strong fiber Bragg gratings (FBGs) with high-temperature sustainability were fabricated by writing the gratings into several specially developed photosensitive fibers. The thermal decay characteristics of these gratings were investigated over a temperature range from room temperature to 950°C. A cation-hopping model is presented to account for the obvious differences between the FBGs in terms of their thermal properties. A related cation-oriented trap distribution model is also used to simulate the decay properties of the gratings during high-temperature annealing and is found to yield a good fit to the experimental data. An accurate operating lifetime of these specially fabricated gratings can be predicted by using the cation-oriented trap distribution simulation.

High-efficiency semi-external-cavity-structured periodically poled MgLN-based optical parametric oscillator with output power exceeding 9.2 W at 3.82 μm

We report a high-efficiency and high-power mid-IR laser generation by a periodically poled (PP) MgLN-based optical parametric oscillator (OPO) working at room temperature, from which 9.23 W of output was obtained at 3.82 microm when pumped by a linearly polarized acousto-optic Q-switched Nd:YVO(4) laser of 48.2 W output. A semi-external-cavity structure was applied in the OPO system to avoid the conversion saturation caused by the thermal lens effect of the PPMgLN crystal and thus to maintain the high conversion efficiency and the high beam quality under the high power level. It was computed that 29.4% slope efficiency and 19.2% total efficiency were realized for the 1.063-3.82 microm conversion.

PPMgLN-Based High-Power Optical Parametric Oscillator Pumped by Yb

We report a periodically poled magnesium-oxide-doped lithium niobate (PPMgLN) based optical parametric oscillator (OPO) pumped by a diode-seeded, linearly polarized, high-power, pulsed, ytterbium fiber master oscillator power amplifier (MOPA). Using adaptive pulse shaping of the seed laser (using an external modulator), we demonstrate a reduction in the impact of dynamic gain saturation and optical Kerr/Raman nonlinearities within the fiber MOPA, obtaining shaped signal and idler pulses at the OPO output and reduced spectral bandwidths. A maximum average output power of 26.5 W was obtained from the MOPA at 1062 nm. An output power as high as 11 W from the OPO at an overall slope efficiency of 67% was achieved, with 2.7 W of output power obtained at a wavelength of 3.5 mum. Our experiments were pump-power-limited and considerable scope remains for further power scaling of such OPOs using this approach.

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Conventional sapphire fibre-optic sensors show excellent performance in high-temperature applications, but they cannot be used for contact measurement of temperatures above 1900 °C. In order to extend the operating temperature of fibre-optic sensors, a radiation-based zirconia single-crystal fibre-optic sensor has been developed. This novel sensor can be operated up to 2300 °C. A 60 mm long and 0.45 mm thick yttria-stabilized zirconia single-crystal fibre with one end coated with a layer of BeO ceramic is used to generate and transmit radiation signals at high temperature. Another 520 mm long and 0.80 mm thick sapphire fibre is used as a sub-high-temperature waveguide. Experimental results from 1200 °C to 2300 °C demonstrate that the developed sensor is very promising for applications beyond 2000 °C.

-Doped Fiber Amplifier Incorporates Active Pulse Shaping

A highly photosensitive Sb/Er/Ge-codoped silica fiber for fabricating fiber Bragg gratings (FBGs) with strong high-temperature sustainability is presented. The photosensitivity and the high-temperature sustainability of FBGs created in this fiber are examined and compared with those produced in a Sn-doped silica fiber. The results show that the Sb/Er/Ge fiber has a much higher level of photosensitivity than the Sn-doped silica fiber and that the FBGs have a similar high-temperature sustainability of 800 degrees C. The strong fluorescence properties observed from this fiber are also examined.