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We investigate strong excitonic absorption and large nonlinear wavelength shifts in buried multiple-quantum-well photonic crystal L3 nanocavities that well confine the carriers. The confined carriers can survive as long as the radiative lifetime because carrier diffusion is negligible and surface recombination is well suppressed. In addition, strong optical confinement and small mode volume provided by photonic crystals can enhance excitonic nonlinearity. Therefore, our structure shows a strong excitonic effect that induces large refractive index changes by exciton bleaching and exhibits a large cavity-frequency shift. Our results will contribute to the development of ultralow energy all-optical switching devices in the future. [ABSTRACT FROM AUTHOR]

We demonstrate a high signal-to-noise ratio (SNR) for a photonic-crystal nanophotodetector (PD). The ultralow-capacitance nano-PD can be terminated with a load resistor with a resistance as high as 59 kΩ for efficient light-to-voltage conversion, and its strong thermal-noise suppression leads to an SNR that is 30 dB higher than that of the conventional p-i-n PD terminated with a 50-Ω load. The noise equivalent power is only 500 fW/√Hz, while a gigahertz-level bandwidth can be maintained when considering that the PD capacitance is only 1 fF. Theoretically, this allows optical reception at less than 100 aJ to obtain a bit error rate of 10–9. The resistor-loaded nano-PD requires a small electrical biasing energy comparable to the optical energy, which is remarkably energy saving compared with avalanche PDs or other PDs integrated with amplifiers. Such a receiver promises a dense optical interface with CMOS electronics in photonic networking and processing chips. [ABSTRACT FROM AUTHOR]

Generally, reverse-biased photodetectors (PDs) are used for high-speed optical receivers. The forward voltage region is only utilized in solar-cells, and this photovoltaic operation would not be concurrently obtained with high efficiency and high speed operation. Here we report that photonic-crystal waveguide PDs enable forward-biased high-speed operation at 40 Gbit/s with keeping high responsivity (0.88 A/W). Within our knowledge, this is the first demonstration of the forward-biased PDs with high responsivity. This achievement is attributed to the ultracompactness of our PD and the strong light confinement within the absorber and depleted regions, thereby enabling efficient photo-carrier generation and fast extraction. This result indicates that it is possible to construct a high-speed and ultracompact photo-receiver without an electrical amplifier nor an external bias circuit. Since there is no electrical energy required, our estimation shows that the consumption energy is just the optical energy of the injected signal pulse which is about 1 fJ/bit. Hence, it will lead to an ultimately efficient and highly integrable optical-to-electrical converter in a chip, which will be a key ingredient for dense nanophotonic communication and processors. [ABSTRACT FROM AUTHOR]