Abstract: A laser welding method for a stator coil forms an abutting surface by abutting a side face of a first lead portion of a first rectangular wire to a side face of a second lead portion of a second rectangular wire. A laser beam is focused on a position more inward than a surface of an upper end of the abutting face between the first lead portion and the second lead portion, and the laser beam is moved in a helical loop on the upper end of the abutting face between the first lead portion and the second portion so as to melt the conductor wires to form a molten pool. The molten pool is then moved along the abutting face while the molten pool is continuously formed.

Abstract: A laser welding method for coil wires includes welding two coil wires by irradiating a laser beam to an upper end edge of butted surfaces of side surfaces of tip end portions of the two coil wires. At this time, a molten pool is formed at the center of a welding portion on the upper end edge by scanning the laser beam in a plurality of continuous loop shapes from one or both welding end portions, and welding is performed to make the molten pool at the center portion of the welding portion greater in welding depth than other molten pools by controlling at least one among a movement pitch, a loop area, a laser scanning speed, and a laser power of loops of the laser beam.

Abstract: A part of a wavelength division multiplexed optical signal output from a multiplexing area is extracted as a check signal, and then the extracted signal is guided to a multiplexing area. A reentered check signal is detected at a facet located opposite a facet from which the check signal has been reentered, and the state of the detected check signal is determined. Furthermore at need, on the basis of the result of the determination, a control signal is output that controls operations of a plurality of optical signals input to the multiplexing area.

Abstract: A part of a wavelength division multiplexed optical signal output from a multiplexing area is extracted as a check signal, and then the extracted signal is guided to a multiplexing area. A reentered check signal is detected at a facet located opposite a facet from which the check signal has been reentered, and the state of the detected check signal is determined. Furthermore at need, on the basis of the result of the determination, a control signal is output that controls operations of a plurality of optical signals input to the multiplexing area.

Abstract: A heterojunction bipolar transistor includes an emitter layer of a first conductivity type, a base layer of a second conductivity type adjacent to the emitter layer, a collector buffer layer of the first conductivity type, and a collector layer arranged between the collector buffer layer and the base layer. The collector layer includes a first collector layer formed at the side of the base layer and a second collector layer arranged at the side of the collector buffer layer. The first collector layer is a semiconductor layer having an impurity concentration lower than that of the base layer. The second collector layer is a semiconductor layer of the second conductivity type having an impurity concentration higher than that of the first collector layer.

Abstract: A plurality of parallel-connected surface acoustic wave (SAW) resonators, having different oscillation frequencies and different turnover temperatures, are connected to an active element containing circuit to form a SAW oscillator. The oscillator frequency deviation due to temperature is kept within a small allowable range .DELTA. fa by satisfying the following formulas:f.sub.H -f.sub.L .ltoreq..DELTA.faT.sub.p1 <T.sub.p2. . .<T.sub.pnwheref.sub.H : a maximum frequency among those frequencies of a plurality of SAW resonators connected to the active element-containing circuit which are produced at turnover temperatures on a temperature curve;f.sub.L : a minimum frequency among those of the plurality of SAW resonators; andT.sub.p1 to T.sub.p2 : the turnover temperatures corresponding to the individual SAW resonators.