Group-III-nitride nanophotonics on silicon is a booming field, from the near-IR to the UV spectral range. The main interest of III-nitride nanophotonic circuits is the integration of active structures and laser sources. Laser sources with a small footprint can be obtained with microresonators formed by photonic crystals or microdisks, exhibiting quality factors up to a few thousand down to the UV-C. So far, single microdisk laser devices have been demonstrated, mostly under optical pumping. Combining microdisk lasers under electrical injection with passive devices represents a major challenge in realizing a viable III-nitride nanophotonic platform on silicon. As a first step to realize this goal, we have separately demonstrated electroluminescence from microdisks and side-coupling of microdisks to bus waveguides with outcoupling gratings in the blue spectral range. We have developed the fabrication of electrically injected microdisks with a circular p-contact on top of the disk that is connected to a larger pad via a mechanically stable metal microbridge. Blue electroluminescence is observed under current injection at room temperature. We also demonstrated high Q factor (Q > 2000) WGMs in the blue spectral range from microdisks side-coupled to bus waveguides, as measured from the luminescence of embedded InGaN quantum wells. The WGM resonances are clearly observed through outcoupling gratings following propagation in partially etched waveguides to remove quantum well absorption. Small gaps between microdisks and bus waveguides of around 100 nm are necessary for efficient coupling in the blue spectral range, which represents a major fabrication challenge. We will discuss the progress brought by these building blocks to generate future III-nitride photonic circuits.
We demonstrate sub-wavelength electromagnetic resonators operating in the THz spectral range, whose resonant properties and optical response can be engineered using lumped elements, similarly to what is done in electronic circuits and antennas. We discuss the device concept, and we experimentally study the tuning of the resonant frequency as a function of variable capacitances and inductances. The advantages of this ‘circuit-tunable’ platform to realize novel THz meta-devices featuring an ultra-small semiconductor core are then discussed. As an application, we show that these micro-resonators have a strong potential for ultra-fast THz detection, when combined to a tiny quantum well photodetector active core.
We demonstrate strong light-matter coupling at room temperature in the terahertz (THz) spectral region using 3D meta-atoms with extremely sub-wavelength volumes.
Using an air-bridge fabrication scheme, we have implemented sub-wavelength 3D THz micro-resonators that rely on suspended loop antennas connected to semiconductor-filled patch cavities. We have experimentally shown that they possess the functionalities of lumped LC resonators: their frequency response can be adjusted by independently tuning the inductance associated the antenna element or the capacitance provided by the metal-semiconductor-metal cavity. Moreover, the radiation coupling and efficiency can be engineered acting on the design of the loop antenna, similarly to conventional RF antennas.
Here we take advantage of this rich playground in the context of cavity electrodynamics/intersubband polaritonics. In the strong light−matter coupling regime, a cavity and a two-level system exchange energy coherently at a characteristic rate called the vacuum Rabi frequency ΩR which is dominant with respect to all other loss mechanisms involved. The signature, in the frequency domain, is the appearance of a splitting between the bare cavity and material system resonances: the new states are called upper and a lower polariton branches.
So far, most experimental demonstrations of strong light−matter interaction between an intersubband transition and a deeply sub-wavelength mode in the THz or mid-infrared ranges rely on wavelength-scale or larger resonators such as photonic crystals, diffractive gratings, dielectric micro-cavities or patch cavities. Lately, planar metamaterials have been used to enhance the light-matter interaction and strongly reduce the interaction volume by engineering the electric and magnetic resonances of the individual subwavelength constituents. In this contribution we provide evidence of strong coupling between a THz intersubband transition and an extremely sub-wavelength mode (≈λ/10) within our recently developed 3D meta-atoms. A GaAs/AlGaAs parabolic quantum well is used as semiconductor active core to observe the strong coupling regime up to room temperature, as the structure ensures by design a sufficiently large useful electron population irrespective of temperature. In contrast with the previous metamaterial paradigm, the electrical dipoles responsible for the light-matter excitation are now exactly confined in the capacitive region of each meta-atom. Remarkably, we will show that we can modulate the light-matter interaction solely via the external inductor/antenna element while keeping the interaction volume (i.e. the capacitor size) unvaried. Perspectives about the exploitation of this metamaterial peculiar features (reconfigurability, dynamic tuning, …) for polaritonic devices will be discussed.