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Ideal ring resonators are characterized by travelling-wave counterpropagating modes, but in practice travelling waves can only be realized under unidirectional operation, which has proved elusive. Here, we have designed and fabricated a monolithic quantum cascade ring laser coupled to an active waveguide that allows for robust, deterministic and controllable unidirectional operation. Spontaneous emission injection through the active waveguide enables dynamical switching between the clockwise and counterclockwise states of the ring laser with as little as 1.6% modulation of the electrical input. We show that this behavior stems from a perturbation in the bistable dynamics of the ring laser. In addition to switching and bistability, our novel coupler design for quantum cascade ring lasers offers an efficient mechanism for outcoupling and light detection., 13 pages, 6 figures, submitted to journal

Opto-electronic integration in the mid-infrared may unlock new implementations of miniaturized imaging and sensing systems. We demonstrate a small mid-infrared system composed of a laser, bus waveguide and photodetectors fabricated on a single conventional quantum cascade laser wafer.

While metal-halide perovskite light-emitting diodes (PeLEDs) hold the potential for a new generation of display and lighting technology, their slow operation speed and response time limit their application scope. Here, high-speed PeLEDs driven by nanosecond electrical pulses with a rise time of 1.2 ns are reported with a maximum radiance of approximately 480 kW sr-1 m-2 at 8.3 kA cm-2 , and an external quantum efficiency (EQE) of 1% at approximately 10 kA cm-2 , through improved device configuration designs and material considerations. Enabled by the fast operation of PeLEDs, the temporal response provides access to transient charge carrier dynamics under electrical excitation, revealing several new electroluminescence quenching pathways. Finally, integrated distributed feedback (DFB) gratings are explored, which facilitate more directional light emission with a maximum radiance of approximately 1200 kW sr-1 m-2 at 8.5 kA cm-2 , a more than two-fold enhancement to forward radiation output.

We demonstrate a novel method of inducing a gradual change in semiconductor conductivity by combining grayscale processing of photoresist and proton implantation. This method is flexible and lends itself to many applications in semiconductor-based optical and electrical devices.

The performance of lead-halide perovskite light-emitting diodes (LEDs) has increased rapidly in recent years. However, most reports feature devices operated at relatively small current densities ( 10% to current densities as high as 2000 mA cm-2 ), and tenfold increase in operational lifetime (when driven at 100 mA cm-2 ). Furthermore, with proper thermal management, a maximum current density of 2.5 kA cm-2 and an EQE of ≈1% at 1 kA cm-2 are shown using electrical pulses, which represents an important milestone toward electrically driven perovskite lasers.

We report on 8 μm quantum cascade superluminescent emitters. Doping in the active region contributed to higher SL power of 7.5 mW; we obtained a coherence length of ∼346 μm at maximum SL power.