W. Margulis

Characterization of efficient dual-wavelength (1050 + 800 nm) pumping scheme for thulium-doped fiber amplifiers

We report on the characterization of a recently introduced dual-wavelength pumping scheme for thulium-doped fiber amplifiers using 800 and 1050 nm. Using a counterpropagating pump configuration, 180 mW of total pump power yielded 27-dB small-signal gain and less than 5-dB noise figure. Furthermore, using optical frequency domain reflectometry, the distributed gain in this configuration was evaluated, allowing for optimization of the doped fiber length.

Preparation of frequency-doubling fibers under UV excitation

Germanium-doped silica fibers were prepared for frequency doubling of 1.06-microm wavelength radiation under the simultaneous presence of the first, second, and fourth harmonics of the laser light. It was found that the preparation rate for frequency doubling was dramatically increased by the presence of the fourth harmonic. The experiments also showed that a metastable excited state plays a significant role in the process.

Heat scan: a simple technique to study gratings in fibers.

A simple and powerful technique to characterize gratings in fibers is described. It is based on scanning a small heating element along the fiber so as to disturb the phase relationship of the waves in a controlled way.

Low-pump-power, short-fiber copropagating dual-pumped (800 and 1050 nm) thulium-doped fiber amplifier

Using optical frequency-domain reflectometry to reveal the gain distribution and allow us to optimize a thulium-doped fiber amplifier, we have demonstrated 18-dB gain by employing only 5 m of a 2000-parts-in-10(6)-Tm-doped fiber pumped with 145 mW of power at dual wavelengths of 800 and 1050 nm. The role of the 800-nm pump, which by itself does not permit population inversion, was clearly observed experimentally.

Novel dual wavelength (1050nm + 800nm) pumping scheme for thulium doped fiber amplifiers

We demonstrate that simultaneously pumping a thulium doped fiber amplifier with 800nm and 1050nm significantly reduces the required pump powers. 180mW total pump power yielded 27dB gain and less than 5dB noise figure.

Efficient frequency upconversion of 1.064- and 1.319-μm Nd:YAG laser pulses into intense visible light in silica-based optical fibers

Single-pass efficient frequency upconversion of 1.064- and 1.319-μm Q-switched and mode-locked Nd:YAG laser pulses into visible-wavelength light in the range 450–600 nm in silica-based monomode optical fibers is reported. The visible upconverted signal propagates in the LP02 fiber mode and exhibits an asymmetrical wide-bandwidth spectrum of several nanometers with a long tail toward high frequencies. At both pump wavelengths the upconversion process presents a critical fiber length of a few meters and a threshold power that depends on the fiber length and the pump wavelength. It is also observed that the visible light signal has its peak wavelength centered on higher frequencies for fibers with longer minimum dispersion wavelengths. In pure SiO2-core fibers pumped at 1.319 μm, conversion efficiencies of approximately 0.5% were obtained, and a 20-W peak power upconversion signal was generated at 580 nm.

Near-infrared transillumination of teeth: measurement of a system performance

Transillumination (TI) of dental enamel with near-infrared light is a promising nonionizing imaging method for detection of early caries lesion. Increased mineral loss (caries lesion) leads to increased scattering and absorption. Caries thus appear as dark regions because less light reaches the detector. The aim of this work was to characterize the performance of a TI system from the resolution of acquired images using the modulation transfer function at two wavelengths, 1.28 and 1.4 mum. Test charts with various values of spatial periods, mimicking a perfect caries lesion, were attached to tooth sections, followed by capture of the transmitted image, using both wavelengths. The sections were then consecutively reduced in thickness, and a sequence of all sizes of the test charts were used for repeatedly imaging procedures. The results show that the TI system can detect feature size of 250 mum with 30% modulation. From the information about how the image degrades as it propagates through enamel, we also examined the possibility of estimating the position of a simulated approximal caries lesion by comparing images obtained from the two sides of a tooth section.

Low pump power, short-fiber dual-pumped (800 nm+1050 nm) TDFA

A 5-m long 2000-ppm Tm-doped fiber pumped with 145-mW total at 800 nm+1050 nm wavelengths produced 18-dB gain. Optical frequency domain reflectometry revealed the gain distribution and permitted optimizing the system.

Grating evolution in frequency-doubling fibers.

The position and the width of the chi((2)) grating in a frequency-doubling fiber were studied during the preparation process. The peak of the grating moves several centimeters from the input end to the output end of the fiber before the conversion efficiency saturates. On saturation, the grating moves toward the input end and becomes narrower.

Frequency doubling in erbium-doped fibers

Abstract Erbium-doped fibers have been prepared for frequency doubling with various input powers. Annealing experiments were carried out, and a single exponential decay in time was found for the conversion efficiency. An activation energy of ~ 0.2 eV was measured for two fibers with different Er 3+ concentrations. A peculiar modal evolution was also observed in a scale of minutes.