Fig. 1. (a) Schematic diagram of the epitaxial structure of OQD devices. (b) Optical confinement as functions of passive GaAs WG thickness.

Fig. 2. (a) Schematic diagram of OQD MLL above the bottom cladding. The rendering is not to scale. The WG spiral termination is not illustrated here for simplicity. Scanning electron microscope (SEM) images of (b) mesa cross section after the nonselective GaAs etch, (c) passive GaAs WG cross section with 1 μm thick silicon dioxide upper cladding, (d) GaAs WG with gratings etched on the sidewall, and (e) taper transition from the active to the passive WG section.

Fig. 3. (a) Reflectivities and (b) group delay responses of several grating designs simulated with the transmission matrix technique. Red: uniform grating, κ=162  cm−1. Pink: linearly chirped grating, CR=−0.032  nm/μm. Blue and green: chirped and apodized gratings, CR=−0.032  nm/μm. For pink and blue, κ=162  cm−1 at the half length of the grating. For green, κ=243  cm−1 at the half length.

Fig. 4. (a) CW LIV curves for 20 GHz OQD MLL with SA in a floating state. Blue: laser A. Pink: laser B. Green: laser C. (b) Optical spectra under the bias conditions Igain=129  mA, 179 mA, 94 mA and VSA=5.6  V, 2.7 V, 4.3 V for lasers A–C, respectively. (c) RF spectrum for laser C under the same bias condition in 50 GHz span view.

Fig. 5. Pulse width mapping as a function of gain section current and SA section reverse bias voltage under passive mode-locking operation for laser C. Regions marked by white indicate unsuccessful PML.

Fig. 6. (a) Autocorrelator traces of the narrowest pulses of OQD MLLs with various grating designs. Blue, red, green, pink, and brown circles represent lasers A–E, respectively. Sech2 fitting gives pulse widths of 12.8, 14.4, 5.3, 7.6, and 4.5 ps. The bias conditions for narrowest pulses are Igain=129  mA, 179 mA, 94 mA, 108 mA, 101 mA and VSA=5.6  V, 2.7 V, 4.3 V, 0 V, 6.2 V, for lasers A–E, respectively.