Classical and linear measurements are bound by the shot noise limit. In optics, the sensitivity increases i) with the square root of the number of photons detected, or ii) with the photons-sample interactions. Case (i) is limited by how safe or efficient is the power level, while (ii) is limited by how to achieve and resolve any number of interactions. We report a versatile interference contrast imaging technique, which extracts more information per photon resource than any linear phase imager to date. It is based on a non-resonant multipass design that allows to efficiently implement case (ii) and extract holographic information by using a single photon camera. It has been designed as a wide-field imaging (i.e., without requiring pixel-scanning) technique, able to image highly transparent/reflective samples, with noise reduction beyond 0.22 in less than 7 rounds.
Polarization-Entangled Photon Sources (EPS) are an important enabling technology in the fields of quantum sensing, quantum communication, and quantum computing. Recently, a need has arisen for efficient sources of entangled photons with high brightness and phase stability, for use in free space and fiber-based quantum communication links. In this work, we present a prototype of EPS based on commercial bulk opto-mechanical components, generating photon pairs via type-0 parametric down-conversion (SPDC). The source is configured in a linear interferometer, where a dual beam displacement is performed by symmetrically disposed birefringent components. The pairs emission can be prepared as an N00N state for quantum sensing, or as a Bell state for entanglement-based Quantum Key Distribution (QKD) protocols. We show a maximal Bell inequality violation, on ⪆99% average visibility, proving the high quality of the generated entanglement. The unique geometry of this interferometer is intrinsically symmetric, thus completely removing any temporal walk-off and decoherence between the two components of the Bell state and enhancing its suitability for various on-field quantum applications.
Quantum technology promises improvements in imaging, computing, and communication, for example using the resource of entanglement between photons with spatial correlations. Detecting spatial correlations, or coincidences, between entangled photons scalably, efficiently, and affordably is therefore an essential capability. However, this task is non-trivial for existing camera technologies, which require low illumination intensities or low detection duty cycles to count coincidences at high signal-to-noise ratios, resulting in long acquisition time, or use expensive custom electronic components. Here, we present an entanglement imaging system based around a novel Single-Photon Avalanche Diode (SPAD) array camera, optimized for sparse illumination with correlated photon pairs. The system is capable of maintaining a duty cycle close to 100%, while simultaneously detecting spatially resolved coincidences with high SNR, enabling the acquisition of real-time entanglement videos at a ~Hz frame rate. We use our system to demonstrate real-time monitoring of entanglement interference visibility, optical system point spread function, as well as real-time widefield entanglement-enhanced phase imaging. Our results show that SPAD array cameras represent a natural choice for scalable entanglement detection and imaging applications.
Interference measurements with undetected photons employ entangled photon pairs in order to overcome classical limitations in measurement sensitivity. With the undetected photon technique, one photon (signal) interacts with an object, and the signature of the interaction is stored in its entangled counterpart (idler): the interacting photon remains undetected, while the detection is performed on the photon that did not interact with the object. While the signal photon can be chosen in any spectral region suitable for the interaction, the idler photon is generated in a spectral region where detectors are efficient, scalable, and cheap. To date, the configurations proposed are in bulk setups. In this work, we propose a novel configuration on an integrated device, with the advantages of the reduced dimension, the lower cost and the robustness to alignment. In our experiment, we pumped a silicon-on-silica integrated circuit with a classical beam at a wavelength of 1.568 μm. Via intermodal spontaneous four-wave mixing, we generated highly non-degenerate time-energy entangled signal and idler photons at 1.99 μm and 1.29 μm, respectively. As we have integrated two identical sources of entangled photons in series, the photon pairs generated in the two sources are indistinguishable, and controlling the phase of the pump beam and the phase of the signal photons after the first nonlinear source, we observed interference patterns with 24% maximum visibility in the idler photon counts. We successfully measured the dephasing induced on the signal photons by measuring only the idler ones.
In this work, we present a novel design and implementation of a lens-free phase imaging system with multi-angle illumination that enhances axial resolution and image quality. The technology, which is based on a common-path shearing interferometer with phase shifting, enables ultra-high sensitivity better than 0.2 nm in optical path difference (OPD), while operating over a wide FoV (>10 mm²) and a large volume (>10 mm³). We show results in several applications, from surface topographies to volumetric structures, including imaging of 10 nm thin transparent topographies and of volumetric laser-written refractive index structures in glass. The high sensitivity and low noise make the proposed technology ideally suited for imaging of low contrast structures on the surface or inside transparent materials, such as defects, impurities, or changes in refractive index.
Graphene is emerging as a powerful material for molecular sensors based on surface enhanced infrared absorption (SEIRA), as it exhibits mid-infrared (MIR) plasmonic tunability and extreme light confinement. While MIR probing of biomolecules - such as incubated proteins on graphene nanostructures – was successfully demonstrated in recent years, sensing of gas molecules can be challenging when relying on gas physisorption at the graphene surface. In this work, we employ an ultrathin gas-adsorbing polymer that optimizes gas sensing with graphene plasmons in an unprecedented combination. As a proof-of-concept, we used polyethylenimine (PEI) polymer deposited on top of graphene nanoribbons to selectively adsorb CO2 molecules. The ultrathin PEI layer concentrates the gas close (≤10 nm) to the graphene surface, so that the interaction with the plasmonic near field is significantly enhanced. Critical for the enhancement of graphene plasmon effect is the role of polymer-induced graphene doping. The varying CO2 concentrations can be transduced in changes in the surface optical response by both PEI vibrational mode enhancement and localized surface plasmon resonance (LSPR) modulation related to graphene chemical doping. The latter presents a novel and simpler transduction mechanism with respect to SEIRA effect. Also, we show that the optical response is reversible upon thermal desorption. The proposed hybrid gas sensor can be extended to different functional conductive polymer coatings that adsorb other relevant gases. Moreover, chemical-based doping of graphene plasmonic surfaces opens promising opportunities for gate-free graphene sensors.
In the talk, we will present our recent work on mid-IR gas sensing using highly confined surface modes in graphene and hBN nanoresonators. We have used ultrathin functional coatings to selectively concentrate the target gas molecules in proximity of the 2D nanostructures, just like recognition elements are used in biosensors. As a proof of concept we have demonstrated CO2 sensing using graphene nanoribbons coated with a 10nm polyethylenimine chemisorber. We will discuss the different sensing mechanisms that can be leveraged (e.g. plasmon tuning via polymer-induced chemical doping) and the possibility to extend this platform to other 2D materials like hBN.
In this work we do a brief analysis of some widespread technologies for imaging science and security, while we also propose new techniques to exceed their standard classical limits by using quantum illumination and quantum detection, and exploiting special quantum modulation phenomena.
We propose a disruptive point-of-care (PoC) imaging platform based on lens-free interference phase-contrast imaging for rapid detection of biomarker such as for sepsis and potentially other diseases (e.g. cancer). It enables simultaneous analysis of potentially up to 10,000 functionalized microarray spots with different biomarkers with fast time-to-results (few minutes) and by consuming a small sample volume (~10 μL). The high sensitivity allows direct measurements of the biomarker binding without the use of fluorescent labels (e.g. ELISA) or microbial culture methods. In addition, adhoc plasmonic nano-structuring is utilized to significantly improve the sensitivity for biomarker detection (optical path difference ~Å) to concentration levels relevant for disease diagnosis.
The proposed technology incorporates a portable and low-cost lens-free imaging reader made of consumer electronic components, plasmonic microarrays with distinct functionalization, and user-friendly software based on a novel phaseshifting interferometry method for topography and refractive index analysis. Due to its compactness and cost-efficiency, we foresee a great potential for PoC applications, especially for the rapid detection of infectious diseases or lifethreatening conditions, e.g. sepsis, but also for clinical trials of drugs and food control.
Securing information has been a concern for more than 4,000 years, but in the times in which we are connecting every single aspect of our businesses and lives, developing secure products and infrastructures has become a global priority. Remarkably, quantum technologies bring unique possibilities for the cryptographic world. In this talk, we will describe recent efforts on the development of a highly integrated quantum entropy source, a key component to generate unpredictable cryptographic keys in any connected device. In particular, we will present the integration of two quantum entropy sources, one in Silicon Photonics and the other in Indium Phosphide. The devices are based on the accelerated phase diffusion process observed in pulsed semiconductor lasers, a macroscopic quantum effect resulting from microscopic spontaneous emission events. Both chip implementations enable Gb/s generation rates in form factors below 2mm x 5mm in indium Phosphide and 0.5mm x 1mm in Silicon Photonics. Our results show progress towards the industrialization of quantum devices using standard semiconductor production lines and processes.
In order to improve on-product-overlay, the image placement performance of a photomask can be corrected and improved through a multiphoton absorption process. This is possible with an ultra-short pulse laser focused into the glass substrate of the mask, from its backside. For optical masks, this is a well-established technology by using the RegC system from ZEISS. Applying this technology to EUV mask requires a backside transparent coating, still electrically conductive for chucking (according to SEMI SPEC). Using nanometers thick Cr and Ni, their oxide and nitride forms, in different stoichiometric forms if need be, we have developed a backside coating with the required optical transmission, sheet conductance, and mechanical durability, and demonstrated femtosecond correction through it. The proposed backside transparent coating designs can be extended to other metals, such as Ti, Ta, Mo and compounds, such as carbides and borides.
The peculiar electronic structure of graphene results in a large optoelectronic response that holds great potential for technology. For example, this material exhibits a nearly constant absorption ~2.3% over a broad spectral range [1], which can be electrically modulated in the mid-IR by injecting attainable densities of charge carriers. When doped, graphene can sustain plasmons that radically modify its optical response, enabling complete optical absorption for suitably designed patterns [2]. Graphene nanoribbons constitute one of the simplest geometrical patterns that one can produce. They have been extensively studied and their plasmons accurately explained with simple models [3]. When heated to a large electronic temperature, graphene behaves nearly as if is was highly doped, also giving rise to plasmon modes [4].
In this work, we study the possibility of using ultrashort light pulses together with the natural electronic relaxation mechanisms in graphene nanoribbons as a way to tune their optical response. We first discuss the optically induced plasmons of individual nanoribbons when illuminated with ultrashort pulses and then analyze the evolution of the plasmon frequency as a function of the delay between pump and probe. We study the redshift of these plasmons with increasing delay due to electron relaxation. We also investigate the optical response of the ribbon exposed to a train of optical pulses. We further discuss ribbon arrays illuminated from the substrate under total internal reflection conditions, for which we predict complete absorption for a suitable choice of geometrical and illumination parameters.
References
[1] F. H. L. Koppens, D. E. Chang, and F. J. García de Abajo, Nano Letters 11, 3370-3377 (2011)
[2] S. Thongrattanasiri, F. H. L. Koppens, and F. J. García de Abajo, Phys. Rev. Lett. 108, 047401 (2012)
[3] I. Silveiro, J. M. Plaza Ortega, and F. J. García de Abajo, Light: Science and Applications 4, e241 (2015)
[4] F. J. García de Abajo, ACS Photon. 1, 135 (2014).
Ultrathin materials and nano-structuring are becoming essential for the functionalization of optical surfaces. In the talk we will show how ultrathin metals can be exploited to create competitive transparent electrodes. At the same time they can be used to create nanostructured surfaces through mass scalable dewetting and etching techniques. After presenting the techniques, we will focus on the applications made possible by these materials and technologies, including self-cleaning or easy-to-clean display screens, efficient indium-free light emitting diodes and solar cells, antireflective structures for the laser industry and super-wetting surfaces for biology.
In this paper a simple photonic crystal fiber (PCF) interferometric breathing sensor is introduced. The interferometer consists of a section of PCF fusion spliced at the distal end of a standard telecommunications optical fiber. Two collapsed regions in the PCF caused by the splicing process allow the excitation and recombination of a core and a cladding PCF mode. As a result, the reflection spectrum of the device exhibits a sinusoidal interference pattern that instantly shifts when water molecules, present in exhaled air, are adsorbed on or desorbed from the PCF surface. The device can be used to monitor a person's breathing whatever the respiration rate. The device here proposed could be particularly important in applications where electronic sensors fail or are not recommended. It may also be useful in the evaluation of a person's health and even in the diagnosis and study of the progression of serious illnesses such as sleep apnea syndrome.
We report on a functional, highly reproducible and cost effective sensing platform based on photonic crystal fibers
(PCFs). The platform consists of a centimeter-length segment of an index-guiding PCF fusion spliced to standard single
mode fibers (SMFs). The voids of the PCF are intentionally sealed over an adequate length in the PCF-SMF interfaces.
A microscopic collapsed region in the PCF induces a mode field mismatch which combined with the axial symmetry of
the structure allow the efficient excitation and recombination or overlapping of azimuthal symmetric modes in the PCF.
The transmission or reflection spectrum of the devices exhibits a high-visibility interference pattern or a single, profound
and narrow notch. The interference pattern or the notch position shifts when the length of the PCF experiences
microelongations or when liquids or coatings are present on the PCF surface. Thus, the platform here proposed can be
useful for sensing diverse parameters such as strain, vibration, pressure, humidity, refractive index, gases, etc. Unlike
other PCF-based sensing platforms the multiplexing of the devices here proposed is simple for which it is possible to
implement PCF-based sensor arrays or networks.
A simple and compact photonic crystal fiber (PCF) interferometer that operates in reflection mode is proposed for
refractive index (RI) sensing. The device consists of a ~12mm-long stub of commercially available PCF (LMA-10)
fusion spliced to standard optical fiber (SMF-28). The device reflection spectrum exhibits interference patterns with
fringe contrast up to 40 dB. One of the excited modes in the PCF is sensitive to external RI therefore the device can
be useful for refractrometry. The shift of the interference pattern can be monitored as a function of the external
index. In the operating range, from 1.33 to 1.43, the maximum shift is less than the interferometer period, so there is
no-ambiguity in the measurements. The maximum sensitivity and resolution achieved were 735 nm per RI units and
7×10-5, respectively. Another approach to measure the external RI consists of monitoring the reflection power
located at the quadrature point of the inference pattern in a properly selected wavelength. Consequently the
measuring range is narrower but the resolution is higher, up ~7×10-6, thanks to the high fringe contrast.
In this paper we have studied the performance of a high-temperature packaged sensor based on Regenerated
Fiber Bragg Gratings (RFBGs). The packaging consists of a two-bore ceramic tube and a 1.5 mm-thick metal
casing. The optical response of packaged and unpackaged RFBG sensors for temperature measurements up to
1100°C have been evaluated and compared to each other. Especial attention has been placed on possible
residual hysteresis in the thermo-optical response after several temperature cycling tests. The response and
recovery times of the packaged sensor has been also measured. The former has been found to be comparable
to that of commercial thermometers based on conventional thermocouples.
We report on mode interferometers built with photonic crystal fibers (PCFs) and optical micro/nano fibers (MNFs). This
type of mode interferometers exploit the beating between two modes, are very compact and highly stable over time for
which they are suitable for a myriad of sensing applications. Moreover, their fabrication is simple since it can be carried
out by means of cleaving and splicing or tapering techniques. The transmission spectrum of these interferometers
typically exhibits truly sinusoidal interference patterns which simplifies their analysis. PCF-based mode interferometers
may have niche applications since they are capable of operating at extreme temperatures (up to 1000ºC). To make these
interferometers functional and competitive, our group has placed emphasis on the design of the PCF microstructure,
minimizing the insertion losses, and on the elaboration of ad-hoc packaging for both harsh environment and biosensing
applications. MNF-based interferometers, on the other hand, are extremely compact, require minimal amount of sample
and can be combined with microfluidics for which they may be adequate for refractometric or biosensing applications.
Adequate protection of the MNFs and ad-hoc microfluidics are being implemented to make MNF interferometers
practical.
We have successfully created Chemical Composition Gratings (CCGs) into two different types of optical fiber: standard
telecommunications Germanium doped fibers and photosensitive Germanium/Boron co-doped fibers. We have
performed temperature cycles for analyzing the sensing properties and degradation or hysteresis with respect to the CCG
sensors. The results show that CCG sensors based on Germanium/Boron co-doped photosensitive fiber have an almost
linear response and negligible hysteresis effects, with a response of almost 100°C/s.
We have successfully created Chemical Composition Gratings (CCGs) into two different types of fiber: standard
telecommunications Germanium doped fibers and photosensitive Germanium/Boron co-doped fibers. We will present
results on the regeneration process, the sensing properties and also the high temperature decay and maximum operative
temperature for the CCGs created in both types of fiber.
We report the multiplexing of photonic crystal fiber interferometric sensors that exhibit sinusoidal interference pattern.
The frequency division multiplexing technique combined with a simple fast Fourier transform demodulation method was
used to multiplex several devices in a single channel. To avoid crosstalk between the sensors, we calculate the optimal
relationship between their periods. The technique is validated experimentally by multiplexing two-mode PCF
interferometers but it can be adapted to multiplex any other optical fiber sensors that exhibit sinusoidal patterns. The
technique and results reported here may allow the development of PCFI-based sensor networks.
We report a simple and highly versatile photonic crystal fiber (PCF) interferometer that operates in reflection mode. The
device consists of a short section of PCF fusion spliced at the distal end of a standard single mode fiber. The air-holes of
the PCF are intentionally collapsed over a microscopic region around the splice. The collapsed region broadens the
propagating mode because of diffraction. This allows the coupling and recombination of two PCF modes. Depending on
the PCF structure two core modes or a core and a cladding mode can be excited. In either case the devices exhibit
sinusoidal interference patterns with fringe spacing depending on the PCF length. The interferometers are highly stable
over time and can operate at high temperatures with minimal degradation. The interferometers are suitable for highresolution
sensing of strain, refractive index (biosensing), gases, volatile organic compounds, etc.
We report an in-reflection photonic crystal fiber (PCF) interferometer which exhibits high sensitivity to different volatile
organic compounds (VOCs), without the need of any permeable material. The interferometer is compact, robust, and
consists of a stub of PCF spliced to standard optical fiber. In the splice the voids of the PCF are fully collapsed, thus
allowing the excitation and recombination of two core modes. The device reflection spectrum exhibits very regular
interference pattern which shifts differently when the voids of the PCF are infiltrated with VOC molecules. The volume
of voids responsible for the shift is around 500 picoliters whereas the detectable levels are in the nanomole range.
Recent advances in electro-optic transmitters for improved transmission performances are presented, with special focus on lithium niobate based devices for extended reach applications.
Various material and functional properties have been measured in lithium niobate crystals (LiNbO3) with different compositions, starting from conventional congruent composition, up to off-congruent and quasi-stoichiometric ones. The UV absorption edge has been measured and correlated with the crystal composition, showing the edge shift towards shorter wavelengths. The ferroelectric transition Curie temperatures have been determined by differential scanning calorimetry, and it increases with Li2O content in the crystal. The surface composition has been checked by micro-Raman spectroscopy. A narrowing of the linewidths has been observed for quasi-stoichiometric crystal, showing an ordered structure, if compared with congruent composition. The coercive field has been measured as a function of temperature for two different crystal compositions, and it has been found lower in the off-congruent substrate. The Ti-indiffusion process has been studied and compared in congruent and off-congruent LiNbO3 substrates by secondary ion mass spectrometry. The main diffusion process parameters have been determined. The Ti diffusion process has been found considerably slower in off-congruent substrates, if compared with conventional congruent LiNbO3, and resulted almost isotropic. The Li-outdiffusion phenomenon has been observed and correlated wit the Ti concentration profile. A careful control on LiNbO3 composition and material properties allows one to find the proper compositional window for the realization of various advanced optical and electro-optical devices.
Ferroelectric materials, e.g. lithium niobate (LN), are widely used for the realization of second-order nonlinear (SON) optical devices, including electro-optic (EO) modulators and switches, frequency converters and all-optical switches based on cascading effects. Glass is a centrosymmetric material and does not show any macroscopic SON properties. However, by appropriate poling techniques significant SON values can be induced, e.g. in silica and silica fibres/waveguides. In fact efficient EO modulation, quasi-phase-matched second-harmonic conversion efficiencies exceeding 20% and parametric fluorescence have been demonstrated in poled silica fibres. Compared to ferroelectric waveguides, poled silica fibres/waveguides, despite having a lower SON, offer longer interaction length for the same bandwidth (due to a lower dispersion), higher damage intensity threshold, lower loss and refractive index, thus keeping high values for the EO and frequency conversion efficiency figure of merits. We will review recent progress on those SON materials, highlighting their advantages and disadvantages.
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