Single-mode Bragg ring laser diodes.

We have designed and fabricated a monolithic semiconductor ring laser based on a Bragg waveguide structure. Through careful control of the waveguiding, we have overcome the inherent "leaky" nature of this waveguide mode and demonstrated a ring laser lasing in the Bragg mode. Best behavior was obtained from lasers with a diameter of 400 µm, where they exhibited output power ${ \gt }{1}\;{\rm mW}$>1mW, in continuous wave (CW) operation. A tangent waveguide provided access to the ring cavity using two ports through evanescent coupling. To meet the stringent waveguiding requirements imposed by the Bragg structure, a two-step etching process, consisting of a shallow-etched coupler and a deep-etched bend section of the ring, was developed in order to reduce the bend and scattering losses. The laser showed a threshold current density of ${\sim}{2.2}\;{{\rm kA/cm}^2}$∼2.2kA/cm2 in CW operation with single longitudinal mode operation with a signal-to-noise ratio of 30 dBm obtained at 1.5 ${I_{\rm th}}$Ith. Broadband phase-matching of $\chi ^{(2)}$χ(2) nonlinearity is observed, offering self-pumped parametric C-band conversion ${ \gt }{40}\;{\rm nm}$>40nm with efficiency of ${142}\% \;{{\rm W}^{ - 1}}\;{{\rm cm}^{ - 2}}$142%W-1cm-2.