Zero-energy topological states, which are protected by chiral symmetry against certain perturbations topologically, localize at interfaces between trivial and non-trivial phases in the Su–Schrieffer–Heeger (SSH) chain model. Here, we propose and demonstrate a method to manipulate chiral symmetry itself to improve the localized interfaces and enlarge the mode volume of topological states in the SSH model, thus optimizing the lasing performance of localized interfaces. As multiple defects corresponding to off-diagonal perturbations in an eigenmatrix are introduced, the topological state expands and extends to extra defects at the topological interface without breaking chiral symmetry. We apply the proposed method in electrical pumping semiconductor laser arrays to verify our theoretical prediction and optimize the output characteristics of the devices. The measured results of the proposed multi-defect SSH laser array show that the output power has been increased by 27%, and the series resistance and far-field divergence have been reduced by half compared to the traditional SSH laser array, establishing a high-performance light source for integrated silicon photonics, infrared light detection and ranging, and so on. Our work demonstrates that the proposed method is capable of improving topological localized interfaces and redistributing zero-energy topological states. Furthermore, our method can be applied to other platforms and inspire optimizations of more devices in broader areas.
TiAlN-coated carbide tools have been used to machine Ti-6Al-4V alloys in aviation workshops. However, the effect of TiAlN coating on surface morphology and tool wear in the processing of Ti-6Al-4V alloys under various cooling conditions has not been reported in the public published literature. In our current research, turning experiments of Ti-6Al-4V with uncoated and TiAlN tools under dry, MQL, flood cooling, and cryogenic spray jet cooling conditions were carried out. The machined surface roughness and tool life were selected as the two main quantitative indexes for estimating the effects of TiAlN coating on the cutting performance of Ti-6Al-4V under various cooling conditions. The results showed that TiAlN coating makes it hard to improve the machined surface roughness and tool wear of a cutting titanium alloy at a low speed of 75 m/min compared to that achieved by uncoated tools. The TiAlN tools presented excellent tool life in turning Ti-6Al-4V at a high speed of 150 m/min compared to that achieved by uncoated tools. From the perspective of obtaining finished surface roughness and superior tool life in high-speed turning Ti-6Al-4V, the selection of TiAlN tools is feasible and reasonable under the cryogenic spray jet cooling condition. The dedicative results and conclusions of this research could guide the optimized selection of cutting tools in machining Ti-6Al-4V for the aviation industry.
By fabricating patterned electrodes on a dumbbell-shaped cavity semiconductor laser, the coherence of the laser can be switched by only changing the injection current. The threshold current and the peak power of the laser are 0.75 A and 1.41 W @ 3 A. Under the injection of small and large currents, the measured speckle contrasts are 40.0% @ 0.8 A and 7.0% @ 3 A. And the corresponding horizontal far-field divergence angles are 4.05°and 8.7°, respectively, showing a high directionality. Such a laser with a wide range of adjustable coherence and a high directionality has a great potential in the field of bioimaging.
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