teristics and, especially, changes in lasing characteristics for laser diode. The effect of parameters influencing on the lasing characteristics and reliability of the laser diode are discussed previously in Refs. 7 and 8. CONCLUSIONSWe fabricated loss-coupled 1.55 m DFB laser diode having an automatically buried absorptive InAsP layer and performed the reliability test for it. The use of the automatically buried InAsP layer achieved by a single step growth makes the device fabrication process step simpler than that of conventional loss-coupled DFB LDs. High reliability was achieved for the LD, in which operating at high temperature under constant output power for 2800 h without serious device degradation and the expected meantime-to-failure was more than 10 6 h. In this article a conformal slotted array is designed in millimeter band. The work frequency band is 36.7-37 GHz. Omnidirectional azimuth radiation pattern has been achieved, as well as, a Ϫ10°to ϩ30°over the horizon elevation coverage. A short-circuit ended circular waveguide has been used to feed the slot array. Only one mode has been excited to generate the desired circular polarization (TM 01 ). Furthermore, the generated vertical currents over the waveguide walls feed each single element of the array: a pair of noncrossed slots with a separation of g /4 ( g is the waveguide wavelength in the propagated mode). The elevation radiation pattern is achieved by properly placing the slot array in the circular waveguide, which is also the surrounding ground plane of the slot array. The manufacturing antenna process is simple, precise, and lightweight. ANTENNA STRUCTUREAs Figure 1 shows the antenna is composed by eight slot pairs placed on the walls of a circular waveguide. The waveguide is finished with an inner short-circuit at a distance of d s ϭ g /4 from the centre of each slot pair. The waveguide inner diameter D g is 10 mm, so the separation between slot pairs is 0.49 0 at 36.85 GHz ( 0 is the free space wavelength). The slot array is used to generate the omnidirectional radiation pattern with low ripple in azimuth plane. The external surface from the short-circuit to the end of the circular waveguide (h s Ϸ 0 /8), can be used to slightly configure the elevation radiation pattern in the upper angles.The circular waveguide is excited in the TM 01 mode. Fundamental TE 11 and the lower losses TE 01 modes are cancelled by the modified coaxial to waveguide transition in the bottom of Figure 1 scheme. This transition is implemented by the inner conductor of a coaxial cable and an annular disc discontinuity over the inner face of the waveguide wall. By optimizing the height of the discontinuity (h d ϭ 0. A circular waveguide prototype has been manufactured to verify the return losses response of the TM 01 coaxial to waveguide transition [ Fig. 2(b)]. As measurement result in Figure 3 shows, the transition is optimized in 36.85 GHz. A below Ϫ20 dB response is obtained in the edge points of the band. SINGLE ELEMENT-SLOT PAIR AND CIRCULAR POLARIZATIONA Ϫ6 dB a...

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The lasing characteristics and dynamic properties of partly gain-coupled 1.55-pm DFB lasers with a gain corrugation in the strained-layer MQW active region are. presented. Narrow spectral linewidth, which is associated with the low linewidth enhancement factor, was experimentally measured. By analyzing data from RIN measurements, the damping rate, the damping factor, the intrinsic bandwidth and the effective differential gain were obtained. From the small-signal frequency response, a measured -3 dB bandwidth of 22 GHz at 10 mW output power was achieved. The high bandwidth is believed to be related to the high differential gain, resulting from the combination of longitudinal gain-and index-coupling mechanisms and the reduction of the carrier transport time, which is due to an efficient lateral carrier injection along the longitudinal interface. Experimental results show that under 10 Gbit/s pseudorandom NRZ modulation, the devices have small wavelength chirp and clear eye openings making them suitable for long haul and high bit-rate applications.

An approach for single mode operation of 1.3 pm distributed feedback (DFB) lasers with a large side mode suppression ratio over a wide temperature range of -40 "C to 100 "C is reported. The lasers utilize an optimized strained-layer multiquantum well (MQW) active region in combination with indedgain-coupling and detuning effect. A high characteristic temperature To (90-100 K) was obtained in 1.3 pm InGaAsPhnP strained-layer MQW Fabry-Perot lasers when the number of QW's exceeded 10. In gain-coupled DFB lasers, a very low temperature dependence of the thrmhold current has been obtained when there is no detuning or positive detuning of the lasing wavelength at room temperature with respect to the material gain peak. An infinite To can be realized over certain temperature ranges, in which the threshold current exhibits a minimum, depending on the amount of dctuning. The physical mechanism responsible for the appearance of this minimum, as well as the high side mode suppression ratio, are explained theoretically.

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