Teem Photonics (France)

Far-field terahertz imaging is limited by diffraction to resolutions in the tens of micrometers range. On the other hand, near-field optical microscopy is a technique that shows permittivity contrasts at the nanoscale. We present here images of HgTe nanocrystals grown by chemical synthesis in liquid phase. The images are obtained by scattering scanning near-field microscopy at 2.52 THz and show a high contrast compared to the silicon substrate.

One of the most problematic points in THz-TDS is the absorption induced by water lines. This absorption complicates and biases the fitting algorithms. We propose here an approach to eliminate water from TDS data. The 1-parameter model can eventually be used to quantify water present in different samples.

On behalf of the Organizing Committee, it is our great pleasure to invite you to the 27th European Microwave Week (EuMW), which will take place between 22 and 27 September 2024 at Paris Expo Porte de Versailles in Paris, France.

We present an optoelectronic mixer for the terahertz (THz) frequency-domain based on an iron-doped InGaAs layer integrated in a plasmonic microcavity. We show that this structure, under 1550-nm-wavelength illumination, allows for more than 70% absorption efficiency in a 220 nm-thin InGaAs absorber and very high Roff/Ron >1000. It leads to THz mixers driven by 1550-nm lasers showing conversion loss as low as ~30 dB at 300 GHz. Therefore, this design is very promising for application as receivers in high-data-rate wireless telecom, in cw-THz spectrometers, or in photonic-senabled THz spectrum analyzers.

The realization of integrated active optical systems is crucial for the use of components such as amplifiers, lasers or photodetectors on a chip. Alumina (Al₂O₃) doped with erbium is a promising material for the realization of various active functions. Indeed, the low propagation losses of Al₂O₃, the rare earth compatibility and its wide transmission band makes Al₂O₃ suitable for a wide range of applications. Nevertheless, current methods for producing such waveguides are often costly and difficult, requiring complex and potentially loss-making processing steps like etching. In this context, Pulsed Laser Deposited (PLD) combined with lift-off is a relevant method for avoiding etchings. The process is composed of three main steps: photolithography, PLD and lift-off. In this work, we present how the different steps have to be optimized to make suitable waveguides for light propagation. Notably, photolithography needs a precise cross-section profile to obtain smooth sidewall, to ease lift-off and get high resolution patterning. For PLD, SEM images showed the importance of plume directivity and orientation in the PLD chamber to achieve a good control of the waveguide shapes. Finally, we also have shown that the Erbium photoluminescence is dependent on the annealing temperature. These results highlight the essential parameters which need to be precisely controlled to achieve accurate microstructures by liftoff processing performed in PLD layers, paving the way for the demonstration of low-loss waveguides and fully integrated erbium laser without etching.

The selective spatial mode excitation of a bi-dimensional grating-coupled micro-cavity called a cavity resonator integrated grating filter (CRIGF) is reported using an incident beam shaped to reproduce the theoretical emission profiles of the device in one and subsequently two dimensions. In both cases, the selective excitation of modes up to order 10 (per direction) is confirmed by responses exhibiting one (respectively two) spectrally narrowband resonance(s) with a good extinction of the other modes, the latter being shown to depend on the parity and order(s) of the involved modes. These results pave the way toward the demonstration of multi-wavelength spatially selective reflectors or fiber-to-waveguide couplers. Also, subject to an appropriate choice of the materials constituting the CRIGF, this work can be extended to obtain mode-selectable laser emission or nonlinear frequency conversion.