Yohan Desieres

Subwavelength optical absorber with an integrated photon sorter

We provide the experimental and theoretical evidence that several nano-patch antennas assembled within a wavelength-scale region may constitute an efficient and easily tunable multi-band photodetector. The system uses highly confined localization states of light and exhibits a robust spectral sorting capability, paving the way to highly integrated hyperspectral imaging.

Plasmon-based photosensors comprising a very thin semiconducting region

We theoretically investigate an elementary subwavelength plasmonic sensor comprising a very thin active region. High quantum efficiency (QE), broad spectral band and nearly no sensitivity to the incidence angle and polarization can be achieved. We particularly discuss different examples based on HgCdTe for infrared detection: QEs of 75% are obtained for active layers λ/(8n) thin, corresponding to a tenfold absorption enhancement.

Optical anisotropy and light extraction efficiency of MBE grown GaN nanowires epilayers

The use of nanowires as active medium seems very promising for the development of high brightness LEDs. With a lower effective refractive index than bulk, semiconductor nanowire layers may lead to a high light extraction efficiency. We hereafter discuss the anisotropic properties of dense arrays of molecular beam epitaxy (MBE) grown gallium nitride (GaN) nanowires and the consequences on the optical design of nanowire based LEDs. In particular we show numerically that light extraction efficiency as high as 72% can be expected for GaN nanowires layer grown on a low cost Si substrate.

Nanoplasmonic filters for image sensors

As pixels shrink in CMOS detectors, scaling effects could lead to potential issues with existing colored filters because of their thickness (approx. 1μm). In this paper, we propose to investigate a new generation of filters that are potentially thinner by approximately a decade. Several years ago [1], nanometric metallic gratings have been found to have very unusual transmission properties. Especially, unexpected high transmission has been measured at specific wavelengths. Since these first experiments, studies have shown that very different optical processes can be responsible for these resonant transmissions, depending on the geometry of the grating. This has led to the demonstration of first applications in imaging[2]. With our designs, we show that such components are suitable for RGB color filters. We first discuss the theoretical performances and the integration of these components through modeling with rigorous electromagnetical techniques (RCWA and FDTD) in 2D and in 3D. As an example we evaluate the impact of the pixelization, the technological errors and the illumination conditions on the filter performances. Thanks to an algorithm that can optimize color correction matrix, we show that we have a satisfactory color rendering (dE=4.3). In a second part we realize these samples. We sputter Al layers on glass substrates and structure them with Focused Ion Beam technology that enables approximately 30 nm resolution. These structures are compatible in size with pixel dimensions (1.5 μm X 1.5 μm) and are tested with a dedicated micro-spectrometer.