Experimental demonstration of second-harmonic generation in high χ2 metasurfaces.

Metasurfaces able to concentrate light at various wavelengths are promising for enhancing nonlinear interactions. In this Letter, we experimentally demonstrate infrared second-harmonic generation (SHG) by a multi-resonant nanostructure. A 100 GaAs layer embedded in a metal-insulator-metal waveguide is shown to support various localized resonances. One resonance enhances the nonlinear polarization due to the transverse magnetic (TM)-polarized pump wavelength near 3.2µm, while another is set near the TE-polarized generated wavelength (1.6µm). The measured SHG efficiency is higher than 10-9W-1 for pump wavelengths ranging from 2.9 to 3.3µm, which agrees with theoretical computations. This is typically 4 orders of magnitude higher than the equivalent GaAs membrane.

MTF measurements of a type-II superlattice infrared focal plane array sealed in a cryocooler.

In operational electro-optical systems, infrared focal plane arrays (IR FPA) are integrated in cryocoolers which induce vibrations that may strongly affect their modulation transfer function (MTF). In this paper, we present the MTF measurement of an IR FPA sealed in its cryocooler. The method we use to measure the MTF decorrelates operational constraints and the technological limitations of the IR FPA. The bench is based on the diffraction properties of a continuously self imaging grating (CSIG). The 26 µm pixel size extracted from the MTF measurement is in good agreement with the expected value.

Multi-frame linear regressive filter for the measurement of infrared pixel spatial response and MTF from sparse data.

A challenging point in the prediction of the image quality of infrared imaging systems is the evaluation of the detector modulation transfer function (MTF). In this paper, we present a linear method to get a 2D continuous MTF from sparse spectral data. Within the method, an object with a predictable sparse spatial spectrum is imaged by the focal plane array. The sparse data is then treated to return the 2D continuous MTF with the hypothesis that all the pixels have an identical spatial response. The linearity of the treatment is a key point to estimate directly the error bars of the resulting detector MTF. The test bench will be presented along with measurement tests on a 25 µm pitch InGaAs detector.

Mason's rule and signal flow graphs applied to subwavelength resonant structures.

Widely used for the design of resonant electronic devices, Mason's scalar rule is adapted here to the study of resonant subwavelength optical structures. It turns out to be an efficient formalism, especially when dealing with multiple wave interference mechanisms. Indeed it allows to comprehend the underlying physical mechanisms of the structure in a straightforward way and fast analytical formulae can be retrieved. As an illustration, we apply it to the study of dual metallic gratings, which appear to be promissing optical filters as their spectral shape can be tailored according to needs.

Perfect extinction in subwavelength dual metallic transmitting gratings.

We investigate the strong electromagnetic coupling that settles in dual metallic grating structures. This coupling is evidenced to lead to a perfect optical extinction in the transmission spectrum. The behavior of this perfect extinction that strongly depends on the longitudinal space and the lateral displacement between the two gratings can be explained by a simple model that describes the interference between a propagating mode and a couple of evanescent modes. The results show that the electromagnetic transmission of the structure can be tuned by controlling the position of this perfect transmission extinction and thus pave the way to new types of infrared tunable filters.