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Proposes a quasi-steady-state heat transfer/thermal stress model for dislocation generation in the vertical gradient freeze (VGF) growth of III-IV compounds. VGF growth model; Calculation of the temperature distribution; Factors influencing the generation of glide dislocations in III-IV compounds.

Provides information on a study that compared two avenues available to achieve low dislocation densities in gallium arsenide grown by the vertical gradient freeze and liquid-encapsulated Czochralski techniques. Solution for the heat conduction equation; Result of experiments; Origin of dislocations in regions free of thermal stresses.

We describe a new multicore fiber (MCF) having seven single-mode cores arranged in a hexagonal array, exhibiting low crosstalk among them and low loss across the C- and L-band. In order to spatially multiplex and demultiplex optical signals in and out of the MCF, we designed and fabricated a tapered MCF connector (TMC) with ultralow crosstalk and loss for space-division-multiplexing (SDM) transmission. The key crosstalk properties of MCF, including wavelength and distance dependence crosstalk characteristics, and statistical distribution of crosstalk over time, are measured and discussed. Using the MCF and TMC, we experimentally demonstrate a record transmission capacity of 112 Tb/s over a 76.8 km MCF using SDM and dense wavelength division multiplexing. Each core of the MCF carries 160 107 Gb/s polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK) channels on a 50 GHz grid in the C- and L-band, resulting in an aggregate spectral efficiency of 14 b/s/Hz. The system impact of the intercore crosstalk on a 107 Gb/s PDM-QPSK signal is further investigated by transmitting it through the center core while the six outer cores carry same-wavelength 107 Gb/s signals. The system implication of the core-to-core crosstalk on ultralong-haul transmission is also discussed. [ABSTRACT FROM PUBLISHER]

High quality p-type InP is critical for devices ranging from high power injection lasers to space-based solar cells. The growth of 50 mm diameter, low defect density, p-type, Zn:InP substrates has been achieved for the first time at doping levels below 10 cm. The 600 gram 〈111〉 B-seeded crystals were grown by the vertical dynamic gradient freeze technique. Dislocation densities are more than an order of magnitude below those achieved in comparable LEC-growth material. These range from 300 cm at the seed end to 1200 cm in the 50 mm diameter portion of the crystal. Single crystals were grown with carrier concentrations ranging from 1-5 × 10 cm as determined by Hall measurements. Hole mobilities as high as 100 cm volt sec were achieved. The in-corporation of the zinc dopant follows normal freezing and a distribution coefficient of 0.67 ± .09 was determined. Infrared transmission imaging shows a lower level of stria-tion contrast relative to that observed for sulfur doped InP. [ABSTRACT FROM AUTHOR]

We show that frozen-in viscoelasticity has a significant impact on the refractive index profile of optical fibers. Viscoelastic strains can be frozen into an optical fiber during draw, or by cooling down a drawn fiber from its fictive temperature while under tension. The resulting refractive index perturbation is concentrated in the highest viscosity region of the fiber, exhibits minimal birefringence, and can significantly alter critical performance characteristics. Our quantitative theory for the refractive index perturbation is in excellent agreement with measured data. Frozen-in viscoelasticity can also be harnessed to serve as the basis for optical fiber devices. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate new, large-mode area (LMA) gain fibers with ∼25 µm mode-field diameter, and increased higher-order mode loss that enable diffraction limited, pulsed fiber lasers operating at high average power with high pulse energy. We achieved 1.6 mJ, ns pulses, with 1.2 kW average power and 370 kW peak power in one of the new Yb-doped gain fibers. In a second, higher absorption fiber, we demonstrate 2 mJ pulse energy with peak power of >420 kW at an average power of 660 W. To the best of our knowledge these are the highest demonstrated energies, powers and peak powers for any nanosecond diffraction-limited, all-fiber laser. The TMI thresholds of two of these fibers were measured to be 1.8 kW and 1 kW respectively.

We demonstrate scaling of the effective area of higher-order mode, Er-doped fiber amplifiers. Two Er-doped higher-order mode fibers, one with 3800 μm(2) A(eff) in the LP(0,11) mode, and one with 6000 μm(2) effective area in the LP(0,14) mode, are demonstrated. Output beam profiles show clean higher order modes, and S(2) imaging measurements show low extraneous higher order mode content. CW and pulsed amplifier experiments are reported. Nanosecond pulses are amplified to 0.5 mJ pulse energy with 0.5 MW peak power.

We perform detailed measurements of the higher-order-mode content of a low-loss, hollow-core, photonic-bandgap fiber. Mode content is characterized using Spatially and Spectrally resolved (S2) imaging, revealing a variety of phenomena. Discrete mode scattering to core-guided modes are measured at small relative group-delays. At large group delays a continuum of surface modes and core-guided modes can be observed. The LP11 mode is observed to split into four different group delays with different orientations, with the relative orientations preserved as the mode propagates through the fiber. Cutback measurements allow for quantification of the loss of different individual modes. The behavior of the modes in the low loss region of the fiber is compared to that in a high loss region of the fiber. Finally, a new measurement technique is introduced, the sliding-window Fourier transform of high-resolution transmission spectra of hollow-core fibers, which displays the dependence of HOM content on both wavelength and group delay. This measurement is used to illustrate the HOM content as function of coil diameter.

A cladding pumped multicore erbium-doped fiber amplifier for simultaneous amplification of 6 channels is demonstrated. Peak gain over 32 dB has been obtained at a wavelength of 1560 nm and the bandwidth measured at 20-dB gain was about 35 nm. Numerical modeling of cladding pumped multicore erbium-doped amplifier was also performed to study the properties of the amplifier. The results of experiment and simulation are found to be in good agreement.

We introduce multiple series of uncoupled and coupled surface nanoscale axial photonics (SNAP) microresonators along the 30 micron diameter germanium-doped photosensitive silica optical fiber and demonstrate their permanent trimming and temporary tuning with a CO2 laser and a wire heater. Hydrogen loading allows us to increase the introduced variation of the effective fiber radius by an order of magnitude compared to the unloaded case, i.e., to around 5 nm. It is demonstrated that the CO2 laser annealing of the fabricated microresonator chain can be used to modify the fiber radius variation. Depending on the CO2 laser beam power, the microresonator effective radius variation can be increased in depth up to the factor of two or completely erased. In addition, we demonstrate temporary tuning of a microresonator chain with a wire heater.

We demonstrate 2688-km multi-span transmission using wavelength-division multiplexing (WDM) of ten 50-GHz spaced 128-Gb/s PDM-QPSK signals, space-division multiplexed (SDM) in a low-crosstalk 76.8-km seven-core fiber, achieving a record net aggregate per-fiber-spectral-efficiency-distance product of 40,320 km·b/s/Hz. The demonstration was enabled by a novel core-to-core signal rotation scheme implemented in a 7-fold, synchronized recirculating loop apparatus.

We demonstrate the generation of a 1.12-Tb/s superchannel based on coherent optical orthogonal frequency-division multiplexing with polarization-division multiplexed 32-QAM subcarriers, achieving a net intrachannel-spectral-efficiency (ISE) of 8.6 b/s/Hz. Using space-division multiplexing (SDM), we transmit this superchannel over a 76.8-km low-crosstalk multi-core-fiber (MCF) with a record aggregate ISE of 60 b/s/Hz per fiber. We also discuss the impact of core-to-core crosstalk on transmission performance, as well as future perspectives of MCF-based SDM transmission., (© 2011 Optical Society of America)

We describe a new multicore fiber (MCF) having seven single-mode cores arranged in a hexagonal array, exhibiting low crosstalk among the cores and low loss across the C and L bands. We experimentally demonstrate a record transmission capacity of 112 Tb/s over a 76.8-km MCF using space-division multiplexing and dense wavelength-division multiplexing (DWDM). Each core carries 160 107-Gb/s polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK) channels on a 50-GHz grid in the C and L bands, resulting in an aggregate spectral efficiency of 14 b/s/Hz. We further investigate the impact of the inter-core crosstalk on a 107-Gb/s PDM-QPSK signal after transmitting through the center core of the MCF when all the 6 outer cores carry same-wavelength 107-Gb/s signals with equal powers, and discuss the system implications of core-to-core crosstalk on ultra-long-haul transmission., (© 2011 Optical Society of America)

A multicore erbium-doped fiber (MC-EDF) amplifier for simultaneous amplification in the 7-cores has been developed, and the gain and noise properties of individual cores have been studied. The pump and signal radiation were coupled to individual cores of MC-EDF using two tapered fiber bundled (TFB) couplers with low insertion loss. For a pump power of 146 mW, the average gain achieved in the MC-EDF fiber was 30 dB, and noise figure was less than 4 dB. The net useful gain from the multicore-amplifier, after taking into consideration of all the passive losses, was about 23-27 dB. Pump induced ASE noise transfer between the neighboring channel was negligible., (© 2011 Optical Society of America)

We demonstrate the first erbium-doped fiber amplifier operating in a single, large-mode area, higher-order mode. A high-power, fundamental-mode, Raman fiber laser operating at 1480 nm was used as a pump source. Using a UV-written, long-period grating, both pump and 1564 nm signal were converted to the LP(0,10) mode, which had an effective area of 2700 microm(2) at 1550 nm. A maximum output power of 5.8 W at 1564 nm with more than 20 dB of gain in a 2.68 m long amplifier was obtained. The mode profile was undistorted at the highest output power.

We design and fabricate a novel multicore fiber (MCF), with seven cores arranged in a hexagonal array. The fiber properties of MCF including low crosstalk, attenuation and splice loss are described. A new tapered MCF connector (TMC), showing ultra-low crosstalk and losses, is also designed and fabricated for coupling the individual signals in-and-out of the MCF. We further propose a novel network configuration using parallel transmissions with the MCF and TMC for passive optical network (PON). To the best of our knowledge, we demonstrate the first bi-directional parallel transmissions of 1310 nm and 1490 nm signals over 11.3-km of seven-core MCF with 64-way splitter for PON.

We present an all-fiber supercontinuum source based on a passively mode-locked erbium fiber laser and a small-effective-area, germanium-doped silica fiber. The parallels between this system and the continuum generated in microstructured fibers with 800-nm pulses are discussed, and the role of dispersion is investigated experimentally. We construct a hybrid fiber by fusion splicing lengths of different-dispersion fiber together, generating more than an octave of bandwidth.

A new technique using spectral interferometry to measure optical fiber dimensions with interferometric accuracy better than 0.01 micrometer is presented. The method can potentially be used for online monitoring and control during fiber draw.

The optical and photorefractive properties of Ti-doped InP are investigated. Four-wave mixing at wavelengths of 1.06 and 1.32 microm has been observed for the first time to our knowledge in semi-insulating InP:Ti. Room-temperature diffraction efficiencies for zero applied bias are larger than efficiencies measured previously for InP:Fe because of the absence of bipolar photoconductivity. Photoconductivity is observed out to 2 microm, which raises the possibility of photorefractive mixing at longer wavelengths than previously explored.