Loss-Reduction in Flexibly Vertical Coupled Ring Lasers Through Asymmetric Double Shallow Ridge and ICP/ICP Cascade Etching

Loss-reduction in flexibly vertical coupled ring lasers is demonstrated through asymmetric double shallow ridge in the main ring area and inductively coupled plasma (ICP)/ICP cascade etching. Compared with the previous counterpart, the reduced threshold current and enhanced output power are obtained; coupling ratio is tuned from 27% to 1.5% when threshold current is varied from 60 to 80 mA. Single-mode lasing with sidemode-suppression ratio of 27 dB and quality factor of 13120 is achieved when $I_{c}=15$ mA, $I_{d}=58$ mA, which are nearly twofolds of that in the previous one. Such strategies can be widely employed to reduce loss in other vertical coupled photonic circuits.