We demonstrated a novel two-dimensional photonic crystal (PC) based Symmetric Mach Zehnder type all-optical switch (PC-SMZ) with InAs quantum dots (QDs) acting as a nonlinear phase-shift source. The 600- ?m-long PC-SMZ having integrated wavelength-selective PC-based directional couplers and other PC components exhibited a 15-ps-wide switching-window with 2-ps rise/fall time at a wavelength of 1.3 ?m. Nonlinear optical phase shift in the 500-?m-long straight PC waveguide was also achieved at sufficiently low optical-energy (e.g., ??phase shift at ~100-fJ control-pulse energy) due to the small saturation energy density of the QDs, which is enhanced in the PC waveguide, without using conventional measures such as SOAs with current-injected gain. The results pave the way to novel PC- and QD-based photonic integrated circuits including multiple PC-SMZs and other novel functional devices.

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We investigate the quality (Q) factor and the mode dispersion of single-defect nanocavities based on a triangular-lattice GaAs photonic-crystal (PC) membrane, which contain InAs quantum dots (QDs) as a broadband emitter. To obtain a high Q factor for the dipole mode, we modulate the radii and positions of the air holes surrounding the nanocavity while keeping six-fold symmetry. A maximum Q of 17 000 is experimentally demonstrated with a mode volume of V = 0.39(λ/n) 3 . We obtain a Q/V of 44 000(n/λ) 3 , one of the highest values ever reported with QD-embedded PC nanocavities. We also observe ten cavity modes within the first photonic bandgap for the modulated structure. Their dispersion and polarization properties agree well with the numerical results.

We developed a low-coherence light source based on self-assembled InAs quantum dots (QDs) with controlled emission wavelengths and applied it to optical coherence tomography (OCT) imaging. A current-driven superluminescent diode (SLD) light source including four layers of QDs exhibits a broadband (80-nm-bandwidth) emission centered at approximately 1.2 µm with a Gaussian-like spectral shape at room temperature. Spectral-domain OCT (SD-OCT) using the QD-SLD as a light source was developed and imaging with the SD-OCT was demonstrated. The axial resolution was estimated to be approximately 8 µm in air and no apparent side lobes appeared beside the point spread function, indicating the effectiveness of the QD-SLD for high-resolution, noise-reduced OCT imaging.

We experimentally investigated the excitation power dependence of a strongly coupled quantum dot (QD)-photonic crystal nanocavity system by photoluminescence (PL) measurements. At a low-excitation power regime, we observed vacuum Rabi doublet emission at QD-cavity resonance condition. With increasing excitation power, in addition to the doublet, a third emission peak appeared. This observed spectral change is unexpected from conventional atomic cavity quantum electrodynamics. The observations can be attributed to featured pumping processes in the semiconductor QD-cavity system. Solid-state cavity quantum electrodynamics (QED) based on semiconductor quantum dots (QDs) has been intensively studied as a key tool for quantum information processing 1-3 . In these studies, single QDs are often considered as atomic two-level systems 4 . However, recent experiments on coupled QD-cavity systems 5-8 have reported several strange phenomena unexpected from conventional atomic cavity QED. One of the major oddities is the so-called non-resonant coupling, which describes strong photon feeding to the cavity mode from the QDs with large spectral detuning from the cavity resonance. Another peculiarity is triplet emission in the strong coupling regime at the resonance condition where vacuum Rabi doublet emission is expected. Both peculiar observations were first reported by Hennessy et al 5 , and much effort has been made to understand the observations.With regard to the mystery of non-resonant coupling, several groups have been investigating the mechanisms both experimentally 6,7 and theoretically 9,10 . In contrast, with regard to the spectral triplet, detailed studies have not been conducted so far, and there is little knowledge of the mechanism. The effect of pumping processes on strongly coupled QD-cavity systems is also known little even though photoluminescence (PL) measurements, in which collective carriers are injected around and inside the QDs, are a major experimental tool in semiconductor cavity QED. A theoretical model 11,12 considering incoherent pumping on both the QD and the cavity mode has recently been introduced and applied to explain the pumping power dependence of the vacuum Rabi doublet emission 13 ; however, the spectral triplet was outside its scope. Deeper understanding of the peculiar observations is necessary for developing QD-based cavity QED systems for wide application in quantum information technology.In this paper, we studied the excitation power dependence of a strongly coupled QD-cavity system in the resonance condition by micro-PL measurements. With increasing excitation power, a transition from vacuum Rabi doublet to triplet emission was observed. Quantum correlations of the emitted photons were also investigated and the degradation of the quantum nature along with the increment of the third emission peak were observed. The spectral triplet is attributed to featured pumping processes in semiconductor cavity QED systems, including collective carrier injection inside the host material and incohe...