No abstract

Transverse photonic crystal (TPC) laser arrays are designed by effective index method and transfer matrix method, and fabricated by the process of standard photolithography. The fundamental supermode of the TPC laser array possesses a larger optical confinement factor in the active region than those of high-order supermodes, because the propagation constant of the fundamental supermode lies in the forbidden band of the TPC while all the propagation constants of the high-order supermodes lie in the allowed band of the TPC. Therefore, the fundamental supermode can lase firstly near the threshold when the laser is injected with currents. The fabricated TPC laser achieves a single-lobe horizontal far-field pattern under an injection current of 0.3 A, and the corresponding near-field pattern is well confined to the centre five waveguides injected with currents. The TPC semiconductor laser array may be a good candidate for optical sources with narrow horizontal divergence angles.

Electrically injected Parity-time (PT)-symmetric double ridge stripe semiconductor lasers lasing at 980 nm range are designed and measured. The spontaneous PT-symmetric breaking point or exceptional point (EP) of the laser is tuned below or above the lasing threshold by means of varying the coupling constant or the mirror loss. The linewidth of the optical spectrum of the PT-symmetric laser is narrowed, compared with that of traditional single ridge (SR) laser and double ridge (DR) laser. Furthermore, the far field pattern of the PT-symmetric laser with EP below the lasing threshold is compared with that of the PT-symmetric laser with EP above the lasing threshold experimentally. It is found that when the laser start to lase, the former is single-lobed while the latter is double-lobed. when the current continues to increase, the former develops into double lobe directly while the latter first develops into single lobe and then double lobe again.