Bayer filter arrays are commonly added to visible detectors to achieve multicolor sensitivity. To extend this approach to the infrared range, we present frequency selective surfaces that work in the mid-infrared range (MWIR). They are easily integrated in the device fabrication process and are based on a simple operating principle. They consist of a thin metallic sheet perforated with apertures filled with a high-index dielectric material. Each aperture behaves as a separate resonator. Its size determines the transmission wavelength λ. Using an original approach based on the temporal coupled mode theory, we show that metallic loss is negligible in the infrared range, as long as the filter bandwidth is large enough (typically <λ/10). We develop closed-form expressions for the radiative and dissipative loss rates and show that the transmission of the filter depends solely on their ratio. We present a prototype infrared detector functionalized with one such array of filters and characterize it by electro-optical measurements.
Multicolor detection capabilities, which bring information on the thermal and chemical composition of the scene, are desirable for advanced infrared (IR) imaging systems. This communication reviews intra and multiband solutions developed at CEA-Leti, from dual-band molecular beam epitaxy grown Mercury Cadmium Telluride (MCT) photodiodes to plasmon-enhanced multicolor IR detectors and backside pixelated filters. Spectral responses, quantum efficiency and detector noise performances, pros and cons regarding global system are discussed in regards to technology maturity, pixel pitch reduction, and affordability. From MWIR-LWIR large band to intra MWIR or LWIR bands peaked detection, results underline the full possibility developed at CEA-Leti.
Superconducting single photons detectors (SSPDs) have emerged in recent years as a promising alternative for
fast and sensitive infrared detectors working in the photon counting mode. In particular, those detectors combine
very low dark count rates (below 1 Hz), high speed (above 1 GHz), photon number resolution and reasonable
quantum efficiency (10% at telecom wavelengths). They already found applications in quantum cryptography
systems and integrated circuit failure analysis, but could also be used as ultimate sensors in matrix configurations.
We show here the optimization of SSPD fabrication and their optical metrology at CEA. SSPD are fabricated
by patterning a 80 nm wide nanowire in a very thin (4 nm) NbN film on sapphire, forming a pixel of several
microns size. A cryogenic all-fibered optoelectronic system has been developed and allows precise metrology of
the optical performances of SSPD. When biasing near the critical current of the nanowire, we demonstrate a
detection quantum efficiency of 8% at 1.55 µm, which is also found to be strongly polarization dependent. This
quantum efficiency being limited by optical absorption, we propose a prism coupling based absorption enhancing
structure that allows reaching 100% quantum efficiency.