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An all-fiber type, CW, linearly polarized thulium-doped fiber laser is reported. Highly linear polarization was achieved by a special management of fiber Bragg gratings, which performs as the laser cavity reflectors. The laser generated 28 W signal output at 1949 nm with a slope efficiency of 47.3%. The polarization extinction ratio of the laser was measured to be around 20 dB. The beam quality of the laser was near diffraction-limited, with M2 of 1.1. The laser’s output features make it to be a potential light source for some important applications such as for pumping holmium-doped solid state lasers.

We have experimentally investigated a stably tunable multiwavelength erbium-doped fiber ring laser based on phase modulation of a semiconductor optical amplifier with lasing wavelength and spacing tunability at room temperature. Stable multiwavelength operation is obtained by direct modulation of the bias current in the amplifier. We demonstrate such a laser incorporating a tunable Lyot-Sagnac filter with two segments of polarization-maintaining fibers with wavelength-spacing and lasing wavelength tunability. We successfully achieved 1.0-nm-spacing eight-channel and 0.8-nm-spacing ten-channel lasing wavelengths at room temperature. The lasing wavelength of the laser can be also controlled by a polarization controller.

The systematic analysis of the relationship between temperature sensitivity of long-period fiber gratings and the doping concentrations of GeO 2 and B 2 O 3 in the core and cladding regions, depending on their structure ofthe refractive index profile, is investigated. Based on this analysis, the temperature sensitivities of fiber gratings are suppressed and enhanced to 0.002 and -0.44 nm/°C, respectively. We also discuss the versatile applications of long-period fiber gratings to gain-flattening filters of optical amplifiers and strain/temperature sensors, corresponding to their temperature sensitivity. The theoretical and experimental results are very useful for the design of optical communication devices and mechanical sensors based on long-period fiber gratings.

InGaAs/InP multiple quantum well (MQW) PnpN depleted op- tical thyristors (DOTs) operating at 1.55 mm are proposed and fabricated. To analyze their switching characteristics, we simulate nonlinear s-shape current-voltage curves using the finite difference method (FDM) associ- ated with the current-oriented method. Using the FDM, we calculate the effects of such parameters as doping concentration and the thicknesses of the outer and inner layers of the thyristor to determine an optimized structure in the view of fast and low-power-consuming operation. With these results, we fabricate waveguide- and vertical-type InGaAs/InP MQW PnpN DOTs. The waveguide-type DOT shows sufficient nonlinear s-shape I-V characteristics with a switching voltage of 4.03 V and a holding voltage of 1.77 V, and spontaneous emission along the wave- guide. The current-voltage characteristics of the vertical-type DOT are shown very well under 150 mW of input power, while the s-shape disap- pears at 200 mW. © 2003 Society of Photo-Optical Instrumentation Engineers.