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Thin films of BaFCl:Sm nanocrystals prepared using a polymer binder were used to create fluorescence images. The phosphor films were exposed to a UV-C mercury lamp light source via chromium-coated quartz greyscale masks to create 4 μm resolution greyscale fluorescence images. The mechanism relies on the highly efficient conversion of Sm³⁺ to Sm²⁺ ions upon exposure to UV-C light which displays a large linear dynamic range. The red fluorescence around 688 nm of the Sm²⁺ is then read-out using blue-violet illumination under a laser scanning confocal microscope. The greyscale images with 16 greyscale levels had a resolution equivalent to ∼125 line pairs per mm or ∼6400 dpi. Improvements in the resolution would be possible using collimated UV-C laser exposure of the film or the use of higher resolution photomasks. Ultra-high resolution binary fluorescence images were also created with resolutions down to 2 μm (∼250 line pairs per mm, ∼12 700 dpi). Downstream applications of the technology could include tailored covert or overt anti-counterfeiting labelling. Refereed/Peer-reviewed

Refereed/Peer-reviewed The generation of Mn4+ in α-Al2O3:Mn3+ by soft X-ray exposure is demonstrated with a large dynamic range of the X-ray generated Mn4+ luminescence signal, indicating the potential use of α-Al2O3:Mn3+ for multilevel optical data storage. Samples with a range of Mn concentrations (0.05, 0.1, 0.2, 0.4, 0.6 and 1.2 atom%) were prepared via a facile combustion method and the sample with 0.4 atom% was found to display the highest luminescence intensity. The stored information can be read out via the R-lines (2E -> 4A2) under ∼470 nm (4A2 -> 4T2), or ∼630 nm (4A2 -> 2T1) excitation with the latter being preferred since photobleaching is minimized. Interestingly, the Mn4+ valence state can be fully switched back to Mn3+ by blue light exposure (e.g., 462 nm laser diode). The stored information could be repeatedly written and erased, showing no significant deterioration over five consecutive cycles, with less than 5% uncertainty.

Annealing of mechanochemically prepared nanocrystalline BaLiF3 yields F3+ colour centres that exhibit unique singlet (excited state) to triplet (ground state) luminescence in the NIR.

We report photoluminescence and photoionization properties of Sm2+ ions generated by X-irradiation of nanocrystalline CaF2:Sm3+ prepared by coprecipitation. The nanocrystals were of 46 nm average crystallite size with a distribution of ±20 nm and they were characterised by XRD, TEM and SEM-EDS. At room temperature, the X-irradiated sample displayed broad electric dipole allowed Sm2+ 4f55d (A1u) → 4f6 7F1 (T1g) luminescence at 725 nm that narrowed to an intense peak at 708 nm on cooling to ∼30 K. The narrow f–f transitions of Sm3+ were also observed. The X-irradiation-induced reduction of Sm3+ + e− → Sm2+ as a function of X-ray dose was investigated over a very wide dynamic range from 0.01 mGy to 850 Gy by monitoring the photoluminescence intensities of both Sm2+ and Sm3+ ions. The reverse Sm2+ → Sm3+ + e− photoionization can be modelled by employing dispersive first-order kinetics and using a standard gamma distribution function, yielding an average separation of 13 A between the Sm2+ ions and the hole traps (e.g. oxide ion impurities). The present results point towards potential applications of Sm doped CaF2 nanocrystals in the fields of dosimetry and X-ray imaging.

Coupling characteristics between a single mode fiber (SMF) and a waveguide embedded in a glass chip via a graded index fiber (GIF) tip are investigated at a wavelength of 976 nm. The GIF tips comprise a coreless fiber section and a GIF section. A depressed cladding waveguide in a ZBLAN glass chip with a core diameter of 35 μm is coupled with GIF tips that have a range of coreless fiber and GIF lengths. An experimental coupling efficiency as high as 88% is obtained while a numerical simulation predicts 92.9% for the same GIF tip configuration. Since it is measured in the presence of Fresnel reflection, it can be further improved by anti-reflection coating. Additionally, it is demonstrated that a gap can be introduced between the chip waveguide and the GIF tip while maintaining the high coupling efficiency, thus allowing a thin planar optical component to be inserted. The results presented here will enable miniaturization and simplification of photonic chips with integrated waveguides by replacing bulk coupling lenses with integrated optical fibers.

Graded-index optical fiber probes suitable for focusing or collimating the output of an optical fiber at a wavelength of 1.3 µm have become an enabling technology in optical coherence tomography imaging applications for in vivo bioimaging. Such fiber tips however remain uncommon in other photonics applications. This paper provides the first numerical study of graded-index fiber tips covering a broad range of wavelengths spanning from the UV to short-infrared. The wavelength dependency and the influence of probe geometry on performance characteristics such as far-field divergence angle, spot size and working distance are analyzed. The paper yields easily accessible design guidelines for the fabrication of collimating or focusing fiber tips. Fiber collimators have considerable potential for use in free-space systems and could benefit a range of devices such as variable attenuators, dynamic wavelength equalisers and large 3D optical cross-connect switches, whereas focusing fiber tips have applications in high-resolution imaging. Refereed/Peer-reviewed

In recent decades, storage phosphors have found widespread applications in the fields of dosimetry and computed radiography due to their impressive properties including large dynamic range and passive storage mode. Despite this success, further development of highly efficient X-ray and UV sensitive luminescent materials is still desirable, in par-ticular for applications in dosimetry. In this Article we report X-ray and UV storage properties of nanocrystalline Ba-LiF3 doped with Sm3+. Nanocrystalline BaLiF3:Sm3+ was prepared mechanochemically by ball milling and the resulting product was characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The re-sponse of the phosphor to X-ray and UV radiation was investigated by measuring room temperature photolumines-cence spectra before and after irradiation for a wide range of doses. The lifetime of the Sm2+ emission at 694 nm was determined for both the X-ray and UV irradiated powder samples. The results indicate a potential fo...

This paper extends a recent demonstration of 1.2 Pb/s transmission using a few-mode multi-core fiber with a cladding diameter of 160 μm. The fiber was a 3.37 km, 4-core, 3-mode few-mode multi-core fiber with spatial multiplexing and demultiplexing performed with especially designed mode-selective couplers. We transmitted 368 wavelength division multiplexed spatial super channels across the C and L bands. We selected polarization-division-multiplexed-256-quadrature amplitude modulation format to maximize the generalized mutual information of the transmitted signals, which were decoded using punctured soft-decision forward error correction with a code rate granularity of 0.01. The maximum crosstalk of the system was -31 dB between LP 11 modes of adjacent cores, leading to a Q-factor penalty of approximately 0.5 dB. We estimated the system mode-dependent loss values ranging from 3 dB to 5 dB across C and L bands with negligible wavelength dependence. Refereed/Peer-reviewed

We report on the potential of BaLiF3 as a host matrix for the upconversion sensitizer (Yb3+)-activator (Er3+) pairs as prepared by ball milling. Specifically, the infrared (980 nm)-excited upconversion luminescence (UCL) of BaLiF3:Yb3+, Er3+ samples before and after annealing in air is reported, and it is demonstrated that the upconversion efficiency is enhanced by similar to 2 orders of magnitude via a postannealing treatment. The UCL of BaLiF3:Yb3+, Er3+ compared favorably with that of the efficient NaYF4:Yb3+, Er3+ UCL nanophosphors. In addition, the X-ray storage capability of BaLiF3:Yb3+, Er3+ was explored. It was observed that the photoluminescence intensities of Yb3+ (similar to 980 nm) and Er3+ (similar to 650 nm) ions decrease gradually with cumulative X-ray doses due to X-ray-induced reduction of Yb3+ to Yb2+ and Er3+ to Er2+, and as a result, the upconversion luminescence decreases. The Yb2+ photoluminescence spectrum upon X-irradiation was observed at 480 nm in accord with earlier reports for the BaLiF3 host. In a unique development, 2D X-ray imaging based on the UCL signal is reported for the first time. These results demonstrate the X-ray recording capability of mechanochemically synthesized BaLiF3:Yb3+, Er3+ nanocrystals and point to possible applications in combining X-ray dosimetry and bioimaging. Refereed/Peer-reviewed

Persistent spectral hole-burning is shown to be suitable for multiple bit per point optical data storage at room temperature. In a novel approach employing bespoke tailoring of the effective inhomogeneous line width and line shape, by using a physical mixture of chemically different matlockite nanocrystals, a relatively broad fluorescence emission line with a top-hat distribution can be realized at the diffraction limit and at room temperature. This top-hat profile enables multiple spectral holes to be burnt, all having the same baseline. We demonstrate this with two spectral holes burnt in a diffraction limited spot, with the prospects for multihole-depth or multilevel encoding to increase the number of bits stored per spectral hole. Using thermoelectrically cooled temperatures down to 175 K, a larger number of holes is also demonstrated. The technique presented is predicted to allow for optical data densities approaching terabits/cm2 by exploiting the unique properties of these inorganic phosphors. Refereed/Peer-reviewed

Refereed/Peer-reviewed Whispering gallery modes (WGMs) in micro-resonators are of interest due to their high Q-factors. Ultra-thin fiber tapers are widely deployed to couple light into micro-resonators but achieving stable and practical coupling for out-of-lab use remains challenging. Here, a new WGM coupling scheme using an exposed-core silica fiber (ECF) is proposed, which overcomes the challenge of using fragile fiber tapers. Microspheres are deposited onto the exposed channel for excitation via the evanescent field of the fiber's guided modes. The outer jacket of the ECF partially encapsulates the microspheres, protecting them from external physical disturbance. By varying the mode launching conditions in this few-mode ECF, in combination with a Fano resonance effect, we demonstrate a high degree of tunability in the reflection spectrum. Furthermore, we show multi-particle WGM excitation, which could be controlled to occur either simultaneously or separately through controlling the ECF mode launching conditions. This work can bring value towards applications such as optical switches and modulators, multiplexed/distributed biosensing, and multi-point lasing, integrated in a single optical fiber device that avoids fiber post-processing.

This paper describes the design and characterization of miniaturized optofluidic devices for sensing based on integrating collimating optical fibers with custom microfluidic chips. The use of collimating graded-index fiber (GIF) tips allows for effective fiber-channel-fiber interfaces to be realized when compared with using highly-divergent standard single-mode fiber (SMF). The reduction in both beam divergence and insertion losses for the GIF configuration compared with SMF was characterized for a 10.0 mm channel. Absorption spectroscopy was demonstrated on chip for the measurement of red color dye (Ponceau 4R), and the detection of thiocyanate in water and artificial human saliva. The proposed optofluidic setup allows for absorption spectroscopy measurements to be performed with only 200 mu L of solution which is an order of magnitude smaller than for standard cuvettes but provides a comparable sensitivity. The approach could be integrated into a lab-on-a-chip system that is compact and does not require free-space optics to perform absorption spectroscopy. Refereed/Peer-reviewed

There is great interest in the use of highly-efficient all-inorganic halide perovskites CsnPbBr2+n for optoelectronic applications. There however remains considerable debate as to the origins of the green luminescence in the zero-dimensional phase of the perovskite Cs4PbBr6, with theories suggesting it originates either from defects in the Cs4PbBr6 lattice or CsPbBr3 impurities/inclusions. The confusion has arisen due to the two phases being miscible and typically co-existing. Moreover, low impurity levels of CsPbBr3 in Cs4PbBr6 are difficult to detect by XRD measurements, yet have much stronger photoluminescence than bulk CsPbBr3 that exhibits quenching, further contributing to the confusion as to the origins of the green photoluminescence. With the rise of significant debate and misconceptions, we provide conclusive evidence that the green emission from Cs4PbBr6 is indeed due to nanocrystalline CsPbBr3 impurities. This is demonstrated by undertaking cathodoluminescence and EDX measurements on samples prepared mechanochemically by ball-milling. Cathodoluminescence imaging clearly shows the presence of small crystals embedded in/or between larger crystallites of Cs4PbBr6 and they emit around 520 nm. EDX shows that the smaller crystal inclusions have a Pb : Br ratio that is approximately 2 times higher, confirming the CsPbBr3 phase, which has the expected size-dependent shift to shorter wavelengths (about 528 to 515 nm). These studies make significant inroads into understanding these lead halide perovskites for their use in a variety of optoelectronic and photovoltaic applications.

In recent years, mechanochemistry has experienced a massive resurgence allowing for solvent-free preparation of many important materials with minimal energy requirements. This paper provides a review of the mechanochemical preparation of nanocrystalline metal halides for applications as inorganic phosphor materials. The review puts strong emphasis on our recent work on optical and X-ray storage phosphors such as the matlockite BaFCl:Sm3+. In addition, previously unpublished results are presented including the effect on the samarium oxidation state when using ball-milling, as well as results on other rare earth-doped matlockites. We outline how mechanochemical methods can be applied to synthesise, without the need for solvents and high temperatures, a wide range of halides ranging from the most important commercial X-ray storage phosphor BaFBr:Eu2+ to lead perovskites of the formula APbX3 with A = Cs+, CH3NH3+, etc., and X = F, Cl, Br, I or a mixture thereof. We also demonstrate that a wide variety of solid solutions of the general formula $$ {\text{M}}_{x}^{1} {\text{M}}_{1 - x}^{2} {\text{FX}}_{y}^{1} {\text{X}}_{1 - y}^{2} $$ (with M1 and M2 = Ba, Sr, Ca; X1, X2 = Cl, Br, I) that can be suitable hosts for luminescent activator ions, can be prepared by mechanochemical methods. Importantly, for prolonged grinding times with a high-energy ball-mill, crystallites on the nanoscale can be obtained as can be confirmed by Rietveld refinements of powder XRD patterns and electron microscopy.

We propose a two-dimensional distributed sensing scheme using few-mode exposed-core fibre and optical frequency domain reflectometry. This scheme aims to measure the size and position of particles using the evanescent field of different guided modes. © 2020 The Author(s)

The increase in Internet data demand has resulted in the development of novel optical fibers. Ultrafast laser inscription is a powerful tool to create 3D waveguide circuits that can interface with these new fiber types. Refereed/Peer-reviewed

To meet future data traffic demand, the telecommunications industry is developing optical fiber network architectures that exploit space division multiplexing (SDM). Femtosecond laser written photonics is a promising platform for SDM end-of-fiber components. Refereed/Peer-reviewed

Fiber-optic Fabry-Perot interferometers developed using collimating graded-index fiber tips are shown to allow for dramatic improvements in fringe visibility of up to 10-fold for long pathlength, small FSR, cavities

There is great interest in the use of highly-efficient all-inorganic halide perovskites CsnPbBr2+n for optoelectronic applications. There however remains considerable debate as to the origins of the green luminescence in the zero-dimensional phase of the perovskite Cs4PbBr6, with theories suggesting it originates either from defects in the Cs4PbBr6 lattice or CsPbBr3 impurities/inclusions. The confusion has arisen due to the two phases being miscible and typically co-existing. Moreover, low impurity levels of CsPbBr3 in Cs4PbBr6 are difficult to detect by XRD measurements, yet have much stronger photoluminescence than bulk CsPbBr3 that exhibits quenching, further contributing to the confusion as to the origins of the green photoluminescence. With the rise of significant debate and misconceptions, we provide conclusive evidence that the green emission from Cs4PbBr6 is indeed due to nanocrystalline CsPbBr3 impurities. This is demonstrated by undertaking cathodoluminescence and EDX measurements on samples prepared mechanochemically by ball-milling. Cathodoluminescence imaging clearly shows the presence of small crystals embedded in/or between larger crystallites of Cs4PbBr6 and they emit around 520 nm. EDX shows that the smaller crystal inclusions have a Pb : Br ratio that is approximately 2 times higher, confirming the CsPbBr3 phase, which has the expected size-dependent shift to shorter wavelengths (about 528 to 515 nm). These studies make significant inroads into understanding these lead halide perovskites for their use in a variety of optoelectronic and photovoltaic applications.

An analysis is provided of fiber-optic Fabry–Perot interferometers designed and fabricated using collimating graded-index fiber (GIF) tips as an alternative to typical highly divergent standard single-mode fibers (SMFs). The collimated beam from the GIF tips allows for significantly longer etalons to be fabricated due to the increased collection efficiency when used either in reflection or transmission mode. We extend previous results, showing that GIF tips using coreless fiber segments can allow for up to four-fold increase in fringe visibility (FV) at 1550 nm compared with standard SMF Fabry–Perot etalons of the same length. The collimating GIF tips help lessen the FV vs cavity length trade-off typically observed in fiber-optic Fabry–Perot systems. We also explore the effects on FV improvement when using capillaries to align the fibres. This paper also provides easily accessible design guidelines and considerations for fabricating GIF based devices at 1550 nm.

We report a novel method for detecting ionizing radiation by employing the phenomenon of upconversion luminescence. Nanocrystalline SrFCl:Yb 3+ /Er 3+ was prepared by ball-milling and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The photoluminescence properties of nanocrystalline SrFCl:Yb 3+ , SrFCl:Er 3+ and SrFCl:Yb 3+ /Er 3+ before and after X-irradiation were investigated. The results demonstrate that both Yb 3+ and Er 3+ ions in the SrFCl host are reduced to their divalent state upon X-ray exposure. Under 980 nm infrared excitation, SrFCl:Yb 3+ /Er 3+ nanocrystals displayed efficient upconversion luminescence. The upconversion luminescence intensity gradually decreased with increasing X-irradiation in a double exponential fashion with rate constants of k 1 = 0.08 Gy -1 and k 2 = 0.01 Gy -1 . In comparison with other X-ray storage phosphors, the present system shows a much higher stability of stored information since it is not subject to photobleaching in the read-out process. This is the first report on detecting ionizing radiation by upconversion luminescence, with the potential for improved read-out performance over traditional storage phosphors. Possible applications of the present phosphor include bioimaging and in vivo cell-level X-ray dose monitoring. Refereed/Peer-reviewed

We investigate crosstalk fluctuations between cores and modes in a few-mode-MCF, observing almost 20dB power fluctuations for CW signals. We then measure increased crosstalk penalty for LP 11 modes compared to the more confined LP 01 modes.

Optical microresonators have emerged over the last decades as the state of the art for biochemical sensing applications with several approaches having been demonstrated for single molecule, ion and nanoparticle detection. This has been achieved by taking advantage of the circulating light inside the microresonators, also known as whispering gallery modes (WGMs), which enable probing of the environment surrounding the resonator after each round trip. Despite the tremendous sensing performances, such approaches have not yet made their way to any commercial applications and are still largely secluded to research labs due to their inherent complexity and operating cost, requiring a phase-matched fiber taper or prism to couple the probing light into the resonator in addition to highly sophisticated equipment. Fluorescent microresonators, containing a gain medium such as organic dyes, quantum dots or inorganic nanocrystals, on the other hand, might alleviate the aforementioned limitations. Upon remote illumination with the appropriate light source, a WGM modulated fluorescence spectrum is generated, which can also be remotely collected. Besides their simplicity of operation, fluorescent microresonators are inherently easier to fabricate with multiple examples of dye doped polymer microspheres or fluorescent coated microcapillaries existing which can be prepared in batch, not requiring any of the advanced microfabrication facilities required for toroids or individually fabricated microspheres. Here, the emerging sensing applications for fluorescent microresonators will be discussed, from standard assays to real life protein detection and quantification in human serum. The limitations of these resonators, and especially their limited quality factors and detection limits will also be discussed as well as the avenues for improving their sensing performance and the addition of specific functionalities that exploit the unique nature of active resonators. Finally, we will explore the alternative sensing applications such as in-vivo sensing, only permitted by the remote excitation/collection scheme of these devices, and we will present a different approach for sensing exploiting the distinctive light emitting capability of these devices. Refereed/Peer-reviewed

Space-division multiplexing (SDM) in few-mode multi-core fibers (FM-MCF) allows the transmission of multi-petabit/s data-rates over a single optical fiber. Recently, transmission of more than 1.2 Pbit/s was demonstrated in a FM-MCF with a cladding diameter of 160 μm, compatible with the standard coating diameter of 250 μm [1]. When increasing the core density in FM-MCF or the transmission distance, inter-core crosstalk can limit the achievable data rates. Inter-core crosstalk is strongly wavelength-dependent and higher-order modes in FM-MCF are expected to show a larger crosstalk penalty compared to the fundamental mode, as their mode fields extend farther into the cladding [2]. In this paper, we present an experimental investigation of the crosstalk-induced Q-factor degradation of 16-Quadrature amplitude modulation (16-QAM) signals, transmitted over a four-core three-mode fiber Refereed/Peer-reviewed

Amongst significant debate we provide conclusive proof showing that the green luminescence from Cs4PbBr6 perovskites is in fact due to nanocrystalline CsPbBr3 impurities. This is verified with cathodoluminescence imaging and EDX measurements.

Fluorescence images approaching sub-micron resolution are formed in thin nanocrystalline phosphor films. The images are created with UV exposure of the films under chrome-coated quartz masks. The UV light locally changes the valence state of the samarium ions in the nanocrystalline phosphors to activate fluorescence properties. The red fluorescence images are then read-out with blue-violet light. With an imaging resolution approaching the diffraction limit, this technology has potential for anti-counterfeiting labelling or optical data storage applications Refereed/Peer-reviewed

Microcapillaries are inherently fluidic sensing platforms that can, under appropriate conditions, support lasing. We propose and demonstrate a lasing microcapillary sensor based on "star" and "triangle" interferences arising from reflection and refraction at the inner and outer microcapillary walls. These interferences lead to distinct modal trajectories that sample the channel medium inside the microcavity structure. Both star and triangle resonances are therefore sensitive to the nature of the channel medium, yielding theoretical and experimental sensitivities significantly exceeding those found for sensors based on conventional whispering-gallery modes. Additional enhancement can be achieved because the two main resonance families shift in an opposite sense, yielding a differential sensitivity that can reach several thousand nanometers per refractive index "unit." These devices represent a robust, yet easily fabricated optical sensor and capillary-based lasing system for microfluidic sensing. Refereed/Peer-reviewed

We demonstrate the potential of few-mode-fibers for all-optical signal processing by converting and receiving three wavelength-multiplexed 30-GBaud QPSK channels from 1533 nm wavelength launched into the LP11a mode to approximately 1549 nm received in the LP01 mode of a 4.7 km FMF.

We use 368 PDM-256-QAM 24.5GBd signals and high-granularity FEC to achieve 1.2Pb/s throughput on a 3.37km few-mode multi-core fiber with 12 spatial channels and the lowest cladding diameter fiber (160 micrometer) to demonstrate Pb/s class transmission.

Mode-forming over multimode fiber without access to the remote end is needed for endoscopic imaging and beam steering. We use reflective spatial pilots and transmitter-side MIMO to form uncoupled spatial and polarization modes at the remote end Refereed/Peer-reviewed

We demonstrate 2400 km mode-multiplexed 16-QAM transmission over a low DMGD (27.1 ps/km) and low MDL (1.75 dB) 3-mode fiber link. The large effective-area 3-mode fiber is shown to outperform a standard single-mode fiber for distances up to 4500km. Refereed/Peer-reviewed

The exponential demand on the internet is producing a capacity crunch in legacy short haul communication networks based on multimode fibre, and is foreshadowed to do the same for long haul single mode fibre networks. Femtosecond lasers have been used to produce a range of compact lightwave circuits that are compatible with optical fibres. These include 3D lightwave chips that offer mode selectivity. Recent developments in plug-and-play devices produced by the fs laser direct-write technique have enabled the modes of few mode fibre (FMF) to be individually addressed with high fidelity (20dB mode extinction). 10G has also been demonstrated over 2 kms of conventional multimode fibre (OM1 and OM2) with fs laser written photonics. As a result, this platform can extend the service life of existing multimode fibre networks and enable next generation networks exploiting mode division multiplexing.

Whispering Gallery Mode (WGM) biosensors have been widely exploited over the past decade, owing to their unprecedented detection limits and label free capability. WGM based sensing mechanisms, such as resonance frequency shift, linewidth broadening, and splitting of the two counter-propagating WGMs, have been extensively researched and applied for bio-chemical sensing. However, the mode-splitting of the originally degenerate WGMs from different equatorial planes on a fluorescent microsphere has not been fully investigated. In this work, we break the symmetry of the surrounding environment outside the microsphere by partially embedding the sphere into a high-refractive-index medium (i.e. glue), to lift the degeneracy of the modes from different WGM planes. The split-modes from multiple planes of the fluorescent microsphere are indiscriminately collected. It is found that the effective quality factor Q of the WGMs increases non-conventionally as the Refractive Index (RI) of the probing liquid increases up to the point where it is equal to that of the glue. This presents a new methodology for quantifying changes in the probing environment based on the Q spoiling of the resonances as determined by the RI difference between the environment and that of the reference glue. Furthermore, we find that this sensing platform opens the door to simple self-referenced sensing techniques based on the analysis of the spectral positions of subsets of the split modes Refereed/Peer-reviewed

Lasing microresonators supporting Whispering Gallery Modes have now become contenders to more established label-free sensing techniques for biosensing applications. We review the progress made in this exciting field, discussing the intrinsic limitations and future prospects.

In this paper, a novel and efficient approach to digital optical data storage using rare-earth ion doped inorganic insulators is demonstrated. More specifically, the nanocrystalline alkaline earth halide BaFCl: Sm is shown to hold great potential for multilevel optical data storage. Proof-of-concept demonstrations show that these phosphors could be used for rewritable, multilevel optical data storage down to the physical dimensions of a single nanocrystal. Multilevel information storage is based on the highly-efficient and reversible conversion of Sm3+ to Sm2+ ions upon exposure to UV-C light. The stored information is efficiently read-out by employing the photoluminescence of the Sm2+ ions in the nanocrystals, with the signal strength being dependent on the UV-C intensity used during the write step. This serves as the mechanism for multilevel data storage in the individual nanocrystals. This data storage platform has the potential to be extended to 2D and 3D memory for storage densities that could approach tera- or even petabyte/cm(3) levels. Refereed/Peer-reviewed