Multiple-Port InP/InGaAsP Square-Resonator Microlasers

Multiple-port semiconductor microlasers can be used as the light sources in photonic integrated circuits through on-chip waveguide connection. By directly jointing two and four coupling waveguides at vertices, two- and four-port electrically pumped InP/InGaAsP square-resonator microlasers are proposed and fabricated by standard photolithography and inductively coupled plasma etching techniques. The mode characteristics of square resonators with two and four coupling waveguides are investigated by 2-D finite-differences time-domain (FDTD) simulation. The influences of the thickness of insulating layer SiO₂ and the width of coupling waveguides on the mode Q factors are studied for the square resonators laterally confined by an insulating layer SiO₂ and p-electrode layers Ti/Au. Room-temperature continuous-wave operations are achieved for a square microlaser with a side length of 15 μm and two 1-μm-wide coupling waveguides at threshold current of 26 mA. In addition, a 20-μm-side microlaser connected with four 1-μm-wide bus waveguides is realized at 270 K. At last, the four-port square resonator with the same size as the fabricated lasers is studied by FDTD simulation, which yields the mode Q factors at the same magnitude as that measured result of 1.34 × 10⁴.