Fluorescent nanocellulose films fabricated via 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose nanofibers were prepared using two methods. In the first process, fluorescent particles were added halfway through the last vacuum filtration step of film fabrication. Three different particles were used: micro-pSi, micro-pSi with COOH, and Si-COOH nanocrystals. Several optical techniques were employed to characterize resulting films: UV-Vis spectrophotometry, fluorescence spectrophotometry, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) microscopy. All techniques revealed that particles retained their intrinsic properties after deposition on the film. Photoluminescence spectra of resulting films at λ<sub>excitation</sub> = 350 nm exhibited the following fluorescence peaks: λ<sub>micro-pSi</sub> = 600 nm, λ<sub>micro-pSi</sub> <sub>with COOH</sub> = 596 nm, λ<sub>Si-COOH nanocrystals</sub> = 618 nm. A blue shift of at most 20 nm was observed when comparing particle fluorescence peak emission before and after deposition on the film. The peak shift was attributed to oxidation, as the particles remained in an aqueous solution during film fabrication. Continued observation of film fluorescence spectra showed that peak emission values are maintained for a month. A second method of fluorescent film fabrication involved the immersion of a dry, transparent nanocellulose film in a chlorophyll in acetone solution. Fluorescence spectra of the resulting hybrid film were taken using a UV laser as the excitation source (λ<sub>excitation</sub> = 355 nm). The fluorescence peak was found to be λ<sub>chlorophyll</sub> = 683.21 nm. Both methods of film hybridization were effective in preparing nanocellulose films that show promise as stable fluorescent media.
We present a post-processing free quantum random number generator (QRNG) based on silicon nanocrystals (Si-NCs) LEDs as a source of randomness. The relatively simple setup for data extraction, a negligible bias measured from the datasets and applying no post-processing operations to the raw data are the main advantages of this QRNG . The obtained bit sequences pass all the NIST tests and the highest bit-rate achieved is 0.6 Mbps.
In this article we describe the fabrication of free standing n-type porous silicon microcavity (MC) and their properties as liquid sensors. We have optimized the etching recipe to keep both large pore size and high quality factor (Q-factor). Thus the fabricated porous layers have pore size in the range of 40 to 110 nm and are thus compatible with mass transport across the porous layer. We found that MC with a Q-factor of 60 can measure down to 1.1*10<sup>-5</sup> refractive index variations. Furthermore we analyze the role of non specific binding by comparing flow through versus flow over geometries. We compare these two approaches using different techniques and we show that flow over assay systematically overestimates the sensitivity of the device because of an inefficient rinse of the sample. Our work clearly indicates a limit in the reliability of measurements performed in flow over geometry unless specific controls are taken into account.
Reconfigurable optical band interleavers based on interference in coupled racetracks are experimentally investigated.
The full reconfigurability, including a "splitter" state, is demonstrated by means of thermal tuning. A novel three
components interleaver design is presented.
The modeling, fabrication and characterization of PSi fabricated from both (110) and (100) surface oriented silicon for
optical sensing is thoroughly reported. First, based on the generalized Bruggeman method, the birefringence and
sensitivity of the fabricated membranes were calculated as a function of the fabrication parameters such as porosity and
pore sizes; and external effects, such as the pores surface oxidation. Thereafter we report on the fabrication of PSi
membranes from (110) and (100) surface oriented silicon with pore sizes in the range of 50 - 80 nm, and the
characterization of their birefringence using a polarimetric setup. Their sensitivities were determined by filling the pores
with several liquids having different refractive index. As a result, sensitivities as high as 1407 nm/RIU were obtained for
the (110) samples at a 1500 nm wavelength and 382 nm/RIU for the (100) samples at the same wavelength.
Silicon photonics is the emerging optical interconnect technology where integrated nanophotonic components allow reaching high device density and improved optical functionalities. One key component is the optical microresonator. A particular kind of microresonator is the racetrack resonator where straight waveguide sections are used to achieve a large value of the coupling coefficient with a bus waveguide for any light polarization state. It is our aim to study the performances of racetrack resonators fabricated on silicon on insulator via CMOS processing. We experimentally investigated different multiple resonator designs where box-shaped filter characteristic, Vernier effect, and coupled resonator induced transparency effects are obtained. We demonstrate that racetrack resonators are instrumental to several different functions in nanophotonics and that the actual lithographic process is fully capable of building these structures.
We report on a novel organic/inorganic hybrid waveguide approach, which is composed of a cladding of extremely low
refractive index oxidized porous silicon formed on a bulk silicon substrate and of it, a polymeric
(polymethylmethacrylate) core doped with a visible laser dye (Nile-Blue) was deposited by spin coating.
The waveguiding properties of the structures have been characterised by means of the m-line technique, demonstrating
that the use of oxidized porous silicon as a cladding can considerably improve the mode confinement factor of single-mode
waveguides. The low refractive index achievable in the cladding (n=1.16) allows forming waveguides with a low
index polymer cores.
Variable stripe length (VSL) measurements have been also performed in order to characterise the amplification
properties of the waveguides. We demonstrate a clear transition from losses to gain at 694nm with a pump threshold of
28mJ/cm<sup>2</sup>. Values of net optical gain up to 104dB/cm have been measured at this wavelength.