Nanophotonic structures with narrow optical resonances, such as high-quality factor photonic crystal cavities, in principle enable spectral sensing with high resolution. This can also result in high-sensitivity displacement and/or acceleration sensing if a part of the cavity is compliant. However, the control of the resonance and its optical read-out are complex and usually not integrated with the sensing part. In this talk we will introduce a novel nano-opto-electromechanical system (NOEMS), where actuation, sensing and read-out are integrated in the same device. It consists of a double-membrane photonic crystal cavity, where the resonant wavelength is tuned by electrostatically controlling the separation between the membranes. The output current signal provides direct information about either the wavelength of the incident light or the cavity resonance. This nanophotonic sensing system can be employed to measure the spectrum of incident light, to determine the wavelength of a laser line with pm-range resolution, or equivalently to measure tiny displacements.
The generation, manipulation and detection of single photons enable quantum communication, simulation and potentially computing protocols. However scaling to several qubits requires the integration of these functionalities in a single chip. A promising approach to the integration of single-photon sources in a chip is the use of single quantum dots embedded in photonic crystal waveguides or cavities. To this aim, efficient coupling of the emission from single quantum dots in photonic crystal cavities to low-loss ridge-waveguide (RWG) circuits is needed. This is usually hampered by the large mode mismatch between the two systems. In this work the emission of a photonic crystal (PhC) cavity realized on a GaAs/AlGaAs membrane and pumped by quantum dots has been effectively coupled and transferred through a long RWG (~1mm). By continuous tapering in both horizontal and vertical direction, transmission values (fiber-in, fiber-out) around 0.16 and 0.08% for RWG and coupled PhC waveguide-RWG have been achieved, respectively. This corresponds to about 2.8% coupling efficiency between the center of the PhC waveguide and the single-mode output fiber, a value much higher than what is achieved by top collection. It further shows that around 70% of the light in the PhC waveguide is coupled to the RWG. The emission from quantum dots in the cavity has been clearly identified by exciting from the top and collecting the photoluminescence from the cleaved facet of the device 1mm away from the cavity which enables the efficient coupling of single photons to RWG and detector circuits.
We report the electromechanical control of spontaneous emission of single InAs quantum dots (QDs) embedded in wavelength-tunable double-membrane photonic crystal cavities (PCC). The tuning is achieved by modulating the distance between two parallel GaAs membranes by applying electrostatic forces across a p-i-n diode under reverse bias. The spontaneous emission rate of single dots has been modified by over a factor of ten, tuning the cavity reversibly between on- and off-resonant conditions without altering the emission energy of the dots. We also discuss a possible approach to integrate the double membrane structure with ridge waveguides, for the transmission of light within a photonic chip.