Space Division Multiplexing in Optical Fibres

Optical communications technology has made enormous and steady progress for several decades, providing the key resource in our increasingly information-driven society and economy. Much of this progress has been in finding innovative ways to increase the data carrying capacity of a single optical fibre. In this search, researchers have explored (and close to maximally exploited) every available degree of freedom, and even commercial systems now utilize multiplexing in time, wavelength, polarization, and phase to speed more information through the fibre infrastructure. Conspicuously, one potentially enormous source of improvement has however been left untapped in these systems: fibres can easily support hundreds of spatial modes, but today's commercial systems (single-mode or multi-mode) make no attempt to use these as parallel channels for independent signals.Comment: to appear in Nature Photonic

Optical Characterizations of Polarization-Sensitive Millimeter-Wave Silicon Bolometers

International audienceIn this paper, we investigate two bolometer detectors with a pixel size of 500 µm and 1200 µm to address, respectively, the 0.6 mm and 1.5 mm wavelengths in order to study the temperature and polarization of cosmic microwave background (CMB). The pixels are polarization sensitive using Ti/TiN superconducting absorbers. They are deposited on suspended doped Silicon thermometers operating at low temperature, typically in the range 50–100 mK. A quarter-wavelength optical cavity formed between absorbers and metal reflector of these pixels is adapted for an absorption around 100 µm. In order to address the millimeter band, we have used a dielectric (Silicon) superstrate placed above the absorbers to shift the absorption band to larger wavelengths. In this paper, we have conducted finite-element (FEM) electromagnetic simulations to optimize the pixel design. The optical absorption measurements of the pixels were performed at room temperature using a terahertz time-domain spectrometer (THz-TDS) and at 300 mK with a Fourier-transform spectrometer (FTS). Finally, an estimation of pixels performances is discussed showing, an expected high responsivity of around 10$^{11}$ V/W and a low noise equivalent power (NEP) of 10$^{–18}$ W/Hz$^{1/2}$

Physicochemical properties and electrochemical behavior of Ebonex/Pt-based materials

Physicochem. properties and electrochem. behavior of Ebonex/Pt-based electrodes obtained with the use of a combined electrochem. method by electrodeposition of a thin platinum layer on substoichiometric titanium oxides (Ebonex) followed by heat treatment are studied. Phase compn. is found to depend substantially on the temp. of the electrode treatment. At temps. above 230°, a titanium-dioxide-hollandite phase is formed and facilitates thermal diffusion of platinum deep into the substrate. A previously unknown titanium-oxygen phase (310°) that affects the electrochem. behavior of the electrodes is discovered. Ebonex/Pt-based materials are n-type semiconductors, the flat band potentials and the no. of charge carriers of which are detd. by the formation conditions