We propose and experimentally demonstrate a fully hybrid distributed sensing scheme that uses a single narrow-band laser to perform fast measurement of the BFS using BOTDA and simultaneous temperature measurement based on spontaneous Raman scattering over 10 km of single mode fiber. The use of cyclic pulse coding effectively reduces the pump peak power levels required for accurate Raman-based distributed temperature measurement, enhancing at the same time the speed of the BFS measurement in the BOTDA technique.
A simple configuration for achieving a radio frequency transparent 90° hybrid, for broadband QAM wireless systems
using silicon photonics is proposed. The device consists of a high Q ring resonator which induces an optical 90° phase
shift between two adjacent resonant wavelengths. When these optical carriers are modulated by an RF carrier the
resulting device behaves as an RF 90° hybrid. Numerical simulations of the phase shift were performed on a 40 GHz
carrier, and to demonstrate the frequency transparency phase shift simulations was also performed at a carrier frequency
of 60 GHz. One of the main applications of such a device is the generation of millimeter wave 10 Gb/s wireless based on
quadrature amplitude modulation.
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/cm2. Values of net optical gain up to 104dB/cm have been measured at this wavelength.
We present an experimental work on porous silicon-based optical devices. Notch filters and planar waveguides are fabricated and characterized. Three different types of filters are shown, the first one is a stop band filter in the 1.5 micron region, where improvements have been performed (smoothing of the index profile, apodization and index matching). The second is a double Notch filter in the IR range, which blocks two different frequencies. Finally Notch filters in the visible range are shown, where porous silicon has been completely oxidized. Double layer waveguides are fabricated and characterized by atomic force microscopy, luminescence and prism coupling techniques. All the results shown are compared with numerical calculations. The photoluminescence changes and the refractive index variations for different annealing times are modeled in terms of oxidation of silicon and slow condensation of the porous structure.
We report on optical analogues of well-known electronic phenomena such as Bloch oscillations and electrical Zener breakdown. We describe and detail the experimental observation of Bloch oscillations and resonant Zener tunneling of light waves in static and time-resolved transmission measurements performed on optical superlattices. Optical superlattices are formed by one-dimensional photonic structures (coupled microcavities) of high optical quality and are specifically designed to represent a tilted photonic crystal band. In the tilted bands condition the miniband of degenerate cavity modes turns into an optical Wannier-Stark ladder (WSL). This allows an ultrashort light pulse to bounce between the tilted photonic band edges and hence to perform Bloch oscillations, the period of which is defined by the frequency separation of the WSL states. When the superlattice is designed such that two minibands are formed within the stop band, at a critical value of the tilt of photonic bands the two WSLs couple within the superlattice structure. This results in a formation of a resonant tunneling channel in the minigap region, where the light transmission boosts from 0.3% to over 43%. The latter case describes the resonant Zener tunneling of light waves.
We have studied the properties of p+-type doped porous silicon, formed by electrochemical etching, when is left in presence of the electrolyte for different post-etching times. Using an interferometric technique, we monitored the formation of the porous silicon layer during the electrochemical treatment as well as the change of its porosity during the post-etch process due to a chemical dissolution mechanism. These data are complemented with a study of the photoluminescence modification for different post-etching times.