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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.

An electromagnetic (EM) Bloch wave propagating in a photonic crystal (PC) is characterized by the immittance (impedance and admittance) of the wave. The immittance is used to investigate transmission and reflection at a surface or an interface of the PC. In particular, the general properties of immittance are useful for clarifying the wave propagation characteristics. We give a general proof that the immittance of EM Bloch waves on a plane in infinite one-and two-dimensional (2D) PCs is real when the plane is a reflection plane of the PC and the Bloch wavevector is perpendicular to the plane. We also show that the pure-real feature of immittance on a reflection plane for an infinite three-dimensional PC is good approximation based on the numerical calculations. The analytical proof indicates that the method used for immittance matching is extremely simplified since only the real part of the immittance function is needed for analysis without numerical verification. As an application of the proof, we describe a method based on immittance matching for qualitatively evaluating the reflection at the surface of a semi-infinite 2D PC, at the interface between a semiinfinite slab waveguide (WG) and a semi-infinite 2D PC line-defect WG, and at the interface between a semi-infinite channel WG and a semi-infinite 2D PC slab line-defect WG.

We developed a waveguide-integrated Si nano-photodiode (PD) with a surface plasmon (SP) antenna for on-chip optical clock distribution. The interfacial periodic nano-scale metal–semiconductor–metal Schottky electrodes were shown to function as an SP optical antenna and also as an optical coupler between a SiON waveguide and a very thin Si-absorption layer. Furthermore, a very high speed response of 17 ps as well as enhanced photoresponsivity was achieved for a 10-µm coupling length. By using this technology, we fabricated a prototype of a large-scale-integration (LSI) on-chip optical clock system and demonstrated 5 GHz of optical clock circuit operation connected with a 4-branching H-tree structure.