Published papers

We report multi-color visible light generation from photonic crystal nanocavity lasers exhibiting broadband quantum dot gain in the near infrared. The visible emission is produced though self-frequency doubling, which efficiently occurs within the high Q nanocavities. © OSA 2013.

We report multi-color visible light generation from photonic crystal nanocavity lasers exhibiting broadband quantum dot gain in the near infrared. The visible emission is produced though self-frequency doubling, which efficiently occurs within the high Q nanocavities. © 2013 The Optical Society.

We will present our recent advances on single quantum dot-photonic crystal nanocavity coupled systems. Cavity enhanced two-photon emission and large optical Stark effect with extremely low control power in these systems will be mainly discussed. © 2013 IEEE.

We report the demonstration of room-temperature lasing in a single GaAs nanowire embedding 50-stacked In0.22Ga0.78As/GaAs quantum dots at a lasing emission energy of 1.37 eV with a threshold pump pulse fluence of 138 μm/cm2.

We report the demonstration of room-temperature lasing in a single GaAs nanowire embedding 50-stacked In0.22Ga0.78As/GaAs quantum dots at a lasing emission energy of 1.37 eV with a threshold pump pulse fluence of 138 μJ/cm2. ©2015 Optical Society of America.

Self-frequency summing processes in photonic crystal nanocavity quantum dot lasers are observed. High quality factors and small mode volumes of the nanocavities facilitate efficient nonlinear frequency summing processes, generating a variety of visible emission lines. © 2013 IEEE.

We measured the vacuum Rabi splitting of a single quantum emitter through direct free space spontaneous emission. This lays the groundwork for accessing diverse cavity quantum electrodynamics phenomena manifesting themselves only in the spontaneous emission.

We measured the vacuum Rabi splitting of a single quantum emitter through direct free space spontaneous emission. This lays the groundwork for accessing diverse cavity quantum electrodynamics phenomena manifesting themselves only in the spontaneous emission. © OSA 2015.

We report the observation of the vacuum Rabi splitting of a single quantum emitter by measuring its direct spontaneous emission into free space. We use a semiconductor quantum dot inside a photonic crystal nanocavity, in conjunction with an appropriate cavity design and filtering with a polarizer and an aperture, enabling the extraction of the inherently weak emitter's signal. The emitter's vacuum Rabi spectra exhibit clear differences from those measured by detecting the cavity photon leakage. Moreover, we observe an asymmetric vacuum Rabi spectrum induced by interference between the emitter and cavity detection channels. Our observations lay the groundwork for accessing various cavity quantum electrodynamics phenomena that manifest themselves only in the emitter's direct spontaneous emission.

Quantum dots enable strong carrier confinement and exhibit a delta-function like density of states, offering significant improvements to laser performance and high-temperature stability when used as a gain medium. However, quantum dot lasers have been limited to photonic cavities that are diffraction-limited and further miniaturization to meet the demands of nanophotonic-electronic integration applications is challenging based on existing designs. Here we introduce the first quantum dot-based plasmonic laser to reduce the cross-sectional area of nanowire quantum dot lasers below the cutoff limit of photonic modes while maintaining the length in the order of the lasing wavelength. Metal organic chemical vapor deposition grown GaAs-AlGaAs core-shell nanowires containing InGaAs quantum dot stacks are placed directly on a silver film, and lasing was observed from single nanowires originating from the InGaAs quantum dot emission into the low-loss higher order plasmonic mode. Lasing threshold pump fluences as low as ∼120 μJ/cm2 was observed at 7 K, and lasing was observed up to 125 K. Temperature stability from the quantum dot gain, leading to a high characteristic temperature was demonstrated. These results indicate that high-performance, miniaturized quantum dot lasers can be realized with plasmonics.

We discuss our recent progress in photonic crystal nanocavity quantum dot lasers. We show how enhanced light matter interactions in the nanocavity lead to diverse and fascinating lasing phenomena that are in general inaccessible by conventional bulky semiconductor lasers. First, we demonstrate thresholdless lasing, in which any clear kink in the output laser curve does not appear. This is a result of near unity coupling of spontaneous emission into the lasing cavity mode, enabled by the strong Purcell effect supported in the nanocavity. Then, we discuss self-frequency conversion nanolasers, in which both near infrared lasing oscillation and nonlinear optical frequency conversion to visible light are simultaneously supported in the individual nanocavity. Owing to the tight optical confinement both in time and space, a high normalized conversion efficiency over a few hundred %/W is demonstrated. We also show that the intracavity nonlinear frequency conversion can be utilized to measure the statistics of the intracavity photons. These novel phenomena will be useful for developing various nano-optoelectronic devices with advanced functionalities.

The modification of a circularly polarized vacuum field in three-dimensional chiral photonic crystals was measured by spontaneous emission from quantum dots in the structures. Due to the circularly polarized eigenmodes along the helical axis in the GaAs-based mirror-asymmetric structures we studied, we observed highly circularly polarized emission from the quantum dots. Both spectroscopic and time-resolved measurements confirmed that the obtained circularly polarized light was influenced by a large difference in the photonic density of states between the orthogonal components of the circular polarization in the vacuum field.

We demonstrate room-temperature lasing oscillation in a plasmonic microring resonator containing InAs/GaAs self-assembled quantum dots. The resonator is composed of a GaAs microring placed on an atomically flat silver surface. Such a structure was fabricated by transfer printing, through which we can pick the dielectric microring and place it on the silver surface at will, hence maintaining a high-quality metal surface without introducing any complex fabrication process. Our result will be important in the development of nanoscale light sources in future densely integrated plasmonic circuits.

We experimentally investigate the emission decay rates of self-assembled single InAs quantum dots (QDs) embedded in sub-wavelength semiconductor waveguides with and without metal side claddings. Compared with as-grown single QDs, we observe a clear suppression (enhancement) in the radiative decay rates of single InAs QDs embedded in the sub-wavelength semiconductor waveguides without (with) metal cladding, respectively. The decay rate for QDs in metal-clad waveguides is >2 times faster than that in waveguides without metal. Numerical calculations using models that include the effects of structural imperfections show good agreement with the experimental results, and reveal that the most important structural imperfection is the gap between the metal and the semiconductor.

We demonstrate large optical Stark shifts in a single quantum dot embedded in a modified H1 photonic crystal nanocavity. We designed the nanocavity to simultaneously possess a high Q factor, a small mode volume, and a high coupling efficiency to the external laser field. This nanocavity enabled the observation of a large Stark shift of 70 μeV even under very weak laser irradiation. The large shift was sustained by only four intracavity photons on average, paving the way for the development of ultralow-power quantum/classical optical devices.

We report the formation of GaAs nanowires (NWs) containing In0.2Ga0.8As/GaAs quantum dots (QDs) on patterned Al0.65Ga0.35As/GaAs distributed Bragg reflectors (DBRs) grown on GaAs(111)B substrates. The growth conditions of both GaAs and Al0.65Ga0.35As layers on GaAs(111)B are optimized for the growth of high-quality Al0.65Ga0.35As/GaAs DBRs with (111) orientation in order to obtain high reflectivity at the NW/DBR interface. Moderately high growth temperature and low V/III ratio can mitigate the formation of pyramidal hillocks, resulting in the formation of high-quality DBRs on GaAs(111)B substrates. Optical characterization at 7 K of single GaAs NW cavities containing 75-stacked InGaAs/GaAs NWQDs grown on patterned such Al0.65Ga0.35As/GaAs DBRs/GaAs(111)B substrates exhibits lasing oscillation at 1.43 eV with a threshold pump pulse fluence of 250 μJ/cm2.

The high-quality factors (Q-factors) of nanocavities in three-dimensional photonic crystals were experimentally demonstrated by increasing the in-plane area of the structure. Entire structures made of GaAs were fabricated by a micro-manipulation technique, and the nanocavities contained InAs self-assembled quantum dots that emitted near-infrared light. The obtained Q-factor was improved to 93,000, which is 2.4 times larger than that in a previous report of a three-dimensional photonic crystal nanocavity. Due to this large Q-factor, a lasing oscillation from this cavity mode was successfully observed.

Strong light matter interactions between semiconductor quantum dots and optical micro/nanocavities are useful resources for developing quantum information processing devices and for exploring diverse quantum optical phenomena. In pursuit of better device performances and novel physics, it is desirable to achieve a larger coupling constant between the quantum dot and the cavity while keeping the high coherence of the coupled system. In this letter, we report the observation of a large vacuum Rabi splitting of ∼328 μeV using a single InAs quantum dot embedded in a GaAs-based H0 photonic crystal nanocavity, which possesses a near-diffraction limited mode volume as well as a high experimental Q factor of ∼52 000. The resulting figure of merit of the strongly coupled systems, defined as a ratio of the coupling constant to the cavity decay rate, reaches 6.4, which is the record high value for semiconductor QD-nanocavity systems reported to date.

Optically induced dynamic nuclear spin polarization (DNP) in a semiconductor quantum dot (QD) requires many cycles of excitation of spin polarized carriers and carrier recombination. As such, the radiative lifetime of the exciton containing the electron becomes one of the limiting factors of DNP. In principle, changing the radiative lifetime of the exciton will affect DNP and thus the nuclear spin polarization. Here, we demonstrate the manipulation of DNP in single QDs through the engineering of the photonic environment using two-dimensional photonic crystals. We find that the achievable degree of nuclear spin polarization can be controlled through the modification of exciton radiative lifetime. Our results show the promise of achieving a higher degree of nuclear spin polarization via photonic environment engineering, with implications on spin-based quantum information processing.

We propose a method to generate path-entangled NOON-state photons from quantum dots and coupled nanocavities. In the systems we considered, cavity mode frequencies are tuned close to the biexciton two-photon resonance. Under appropriate conditions, the system can have the target NOON state in the energy eigenstate, as a consequence of destructive quantum interference. The NOON state can be generated by a resonant laser excitation. This method, first introduced for a two-photon NOON state (N=2), can be extended toward a higher NOON state (N>2) based on our recipe, which is applied to the case of N=4 as an example.