A new solid-state Wavelength-Selective Switch (WSS) based on a Programmable Micro-Diffractive Grating (PMDG) fabricated over a Lithium-Niobate (LiNbO3) substrate is presented, and its operation described. The device consists of a periodic arrangement of ridge waveguides whose optical phase delay can be individually or collectively tuned through the electro-optics (Pockels) effect. Each waveguide is patterned with a metal electrode and connected to an external microprocessor-based driving unit. By appropriately programming the phase shift induced on each waveguide, the far-field diffraction pattern of the grating can be shaped in order to implement complex all-optical signal processing functions, such as 1-to-M demultiplexing, beam splitting, beam steering or wavelength-selective filtering. Once integrated within a telecommunications infrastructure, this component can clearly enhance the level of flexibility and robustness of the network optical physical layer.
This work presents and discusses the features of a monolithic Programmable Micro Diffractive Grating (PMDG) fabricated over a lithium niobate substrate, which can be used to synthetize the visible and near-infrared spectra of important analytes, including dangerous materials (chemically aggressive, toxic or explosive gases). The functional core of the device consists of a periodic arrangement (array) of ridge waveguides whose optical delay (phase shift) is controlled electrically via the linear electro-optical (Pockels) effect. By distinctly polarizing every waveguide composing the comb with a suitable voltage, the collective transparency of the grating can be tailored so that the output far-field, at a predetermined diffraction angle, may reproduce a spectral distribution of interest. Therefore, this device can serve as universal reference cell in a correlation spectroscopy set-up, with particular interest for safety and security applications, as it could avoid the direct manipulation of dangerous or explosive materials. Moreover, by using a dual colour InGaAs detector, the sensing system can process optical spectra covering an extremely wide wavelength band, from the near UV, (~380 nm), to the MIR (~2.5 μm). In the present article, a schematic description of the sensing system, together with a detailed description of the PMDG device and its programming, will be provided and compared with some experimental data and the corresponding generated synthetic spectra. Examples of simulation of synthetic spectra generation in the case of some gases of interest for safety and security, together with the modelling of the device performances, as a function of the design parameters will also be discussed.
Ghost imaging is a novel non-conventional technique allowing to generate high resolution images by correlating the intensity of two light beams, neither of which independently contains sufficient information about the spatial distribution and shape of the object. The first demonstration of ghost imaging used light in double photon state, obtained from spontaneous parametric down-conversion. Owing to the entanglement of the source photons, the proposed theory required quantum descriptions for both the optical source and its photo-detection statistics1. However, subsequent experimental and theoretical considerations2,3 demonstrated that ghost imaging can be performed also with thermalized light, utilizing either CCD detector arrays or photon-counting detectors, thus admitting to a semi-classical description, employing classical fields and shot-noise limited detectors. This has generated increasing interest4-6 in establishing a unifying theory that characterizes the fundamental physics of ghost imaging and defines the boundary between classical and quantum domains. In this view, we exploited recent progress obtained through the application of Fourier Transform Techniques to demonstrate ghost imaging in the frequency domain, in order to measure a continuous spectrum by using a highly brilliant and coherent monochromatic source. In particular, we demonstrate the application of this ghost imaging technique to broadband spectroscopic measurements by means of interaction free photon detection. The experimental apparatus and the collected data are described in a dedicated work7. In this paper, we consider the theoretical aspects underlying the proposed Spectroscopic technique. In particular, two alternative theoretical models are presented. In one case, a statistical approach (semi-classical) is applied, where the states of the sampling beam are considered, whereas in the other case a pure quantum treatment is carried on, by describing the interaction of vacuum states generated by photon conversion processes. Both theoretical models, though carried on by means of a complementary formalism, lead to equivalent results and offer a physical interpretation of the collected experimental data. The application of these results offer novel perspectives for remote sensing in low light conditions, or in spectral regions where sensitive detectors are lacking.
Ghost imaging is an active technique that implies using a time-varying structured illumination source to image a target without spatially-resolving measurements of the light beam that interacts with the target. Traditionally, a beam splitter is used to create two highly correlated beams, such that the signal interacts with the target and is then measured by a single pixel detector, while the reference is directly measured by a spatially resolving detector. This approach allows to implement ghost imaging in the space domain, nevertheless also temporal and frequency domains can be addressed1,2, allowing to extract the pertinent information. In particular, ghost imaging in the frequency domain has been recently applied to extract spectral information from a target object by means of Fourier Transform Interferometry3,4. In this work we illustrate and discuss the results of interaction-free measurements on an Er3+ doped nonlinear crystal, placed in one arm of an interferometer, obtained by using only non-interacting photons. Our equipment is a wave-guided solid state device, exploiting an integrated quantum photonic circuit that is equivalent to an Asymmetric Nonlinear Mach-Zehnder Interferometer. The experiment was performed by using a 250mW monochromatic 980 nm laser source that allowed exciting an Er:LiNbO3 waveguide, placed in one of the arms of the asymmetric interferometer. The interferograms were obtained by varying the signal in the time domain by using a LiNbO3 undoped waveguide in the opposite branch of the interferometer and recorder with a standard Si p-i-n detector, provided with a pass band filter (975nm ± 25nm) thus blocking all photons except the pump ones. The data were analyzed with conventional Fast Fourier Transform Techniques. The application of this approach allowed to recover information in the frequency domain, in particular, despite the monochromatic characteristics of the detected signal, we could recover the whole spectroscopy of the energy levels of the Er3+ doped crystal. The role of the converted photons was evidenced by the fact that, by using a radiation source that does not interact with the dopant (1320nm Laser), only the line of the source is recovered by the FFT handling of the interferograms. An important aspect to remark is that the obtained spectral distribution addressed also the IR part of the spectrum where the applied detector (Si p-i-n) is blind. In this view, this methodology opens the possibility to extend sensitive spectral measurements in spectral regions where detectors show poor responsivity.
Quantum optics has become a key field of development for investigations of quantum physics principles, leading to novel quantum technologies. In this view Integrated Optics allows implementing complex quantum circuits that can give rise to significant outcomes, difficult to reach using traditional approaches based on discrete components. In this framework, a non-linear Mach-Zehnder Interferometer (MZI) was implemented by using two commercial 50:50 directional fibre couplers. One of the MZI arms was equipped with a single mode Er:LiNbO3 optical waveguide, acting as non-linear component whereas the other MZI arm was provided with an undoped LiNbO3 single mode optical waveguide, used to obtain a phase shift through the application of a controlled voltage ramp. The injection in the MZI of a 980nm wavelength laser radiation allowed to collect structured interferogrammes, that could be ascribed exclusively to the pump photons, as all frequency conversion events are localized only in one arm of the Interferometer. The Fourier Transform elaboration of such interferogrammes, produces multiple peak spectra that tightly match the typical transition spectrograms of Er:LiNbO3 when excited by a 980nm radiation. Thus it is possible to perform a spectrometry of the noninterfering converted photons only by using the interfering pump photons. In this work, the experimental apparatus and the most interesting results, obtained in different experimental conditions, are described. Finally, a possible interpretation is outlined.
A surface micromachining technique of LiNbO3 substrates, based on an improved implantation-assisted wet etching process, will be presented and discussed. 2.3 μm high relief structures with optical quality surfaces were fabricated on LiNbO3 by 5 MeV Cu ion implantation through an SU-8 10 μm thick photoresist masking layer patterned by a standard photolithographic process. The LiNbO3 regions amorphized by implantation were etched in a 49% HF aqueous solution at a rate of 100 nm/s exploiting the high differential etching rate between damaged and undamaged LiNbO3 (100 nm/s against 1 nm/s). The process can be repeated to obtain higher aspect ratios. In this work the results of both single and double step processes will be presented. The sidewalls morphology of the microstructures will be also discussed. Both the surface quality and features of the manufactured structures make this technology highly promising for integrated optics and acousto/opto-fluidics.
G. Bentini, A. Parini, M. Chiarini, M. Bianconi, A. Cerutti, A. Nubile, S. Sugliani, G. Pennestrì, G. Bellanca, S. Trillo, S. Petrini, M. Gallerani, P. De Nicola, F. Bergamini
In the last few years Programmable Micro Diffraction Gratings (PMDG) have shown the possibility to be applied in many areas, spanning from imaging, to telecommunication, to spectroscopy. These devices were mainly based on Micro-Electro-Mechanical Systems (MEMS) techniques and realized by moveable mirrors and pop-up structures. Although this approach have held a central stage in Micro-Opto-Electro-Mechanical-Systems (MOEMS), they made the realized devices delicate and not useful for some critical environments. In this work we discuss the possibility to fabricate a fully integrated electrically driven PMDG device where, to avoid the presence of moving parts, the electro-optical properties of a suitable substrate material are used. The theoretical approach and the design procedure of a miniaturized PMDG apparatus useful as a generator of synthetic spectra are illustrated and discussed in details.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.