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- ItemFast, Label-Free Tracking of Single Viruses and Weakly Scattering Nanoparticles in a Nanofluidic Optical Fiber(Washington, DC : Soc., 2015) Faez, Sanli; Lahini, Yoav; Weidlich, Stefan; Garmann, Rees F.; Wondraczek, Katrin; Zeisberger, Matthias; Schmidt, Markus A.; Orrit, Michel; Manoharan, Vinothan N.High-speed tracking of single particles is a gateway to understanding physical, chemical, and biological processes at the nanoscale. It is also a major experimental challenge, particularly for small, nanometer-scale particles. Although methods such as confocal or fluorescence microscopy offer both high spatial resolution and high signal-to-background ratios, the fluorescence emission lifetime limits the measurement speed, while photobleaching and thermal diffusion limit the duration of measurements. Here we present a tracking method based on elastic light scattering that enables long-duration measurements of nanoparticle dynamics at rates of thousands of frames per second. We contain the particles within a single-mode silica fiber having a subwavelength, nanofluidic channel and illuminate them using the fiber's strongly confined optical mode. The diffusing particles in this cylindrical geometry are continuously illuminated inside the collection focal plane. We show that the method can track unlabeled dielectric particles as small as 20 nm as well as individual cowpea chlorotic mottle virus (CCMV) virions-26 nm in size and 4.6 megadaltons in mass-at rates of over 3 kHz for durations of tens of seconds. Our setup is easily incorporated into common optical microscopes and extends their detection range to nanometer-scale particles and macromolecules. The ease-of-use and performance of this technique support its potential for widespread applications in medical diagnostics and micro total analysis systems.
- ItemAll-optical manipulation of photonic membranes(Washington, DC : Soc., 2021) Askari, Meisam; Kirkpatrick, Blair C.; Čižmár, Tomas; Di Falco, AndreaWe demonstrate the all-optical manipulation of polymeric membranes in microfluidic environments. The membranes are decorated with handles for their use in holographic optical tweezers systems. Our results show that due to their form factor the membranes present a substantial increase in their mechanical stability, respect to micrometric dielectric particles. This intrinsic superior stability is expected to improve profoundly a wide range of bio-photonic applications that rely on the optical manipulation of micrometric objects.
- ItemSide-view holographic endomicroscopy via a custom-terminated multimode fibre(Washington, DC : Soc., 2021) Silveira, Beatriz M.; Pikálek, Tomáš; Stibůrek, Miroslav; Ondráčková, Petra; Jákl, Petr; Leite, Ivo T.; Čižmár, TomášMicroendoscopes based on optical fibres have recently come to the fore as promising candidates allowing in-vivo observations of otherwise inaccessible biological structures in animal models. Despite being still in its infancy, imaging can now be performed at the tip of a single multimode fibre, by relying on powerful holographic methods for light control. Fibre based endoscopy is commonly performed en face, resulting in possible damage of the specimen owing to the direct contact between the distal end of the probe and target. On this ground, we designed an all-fibre probe with an engineered termination that reduces compression and damage to the tissue under investigation upon probe insertion. The geometry of the termination brings the field of view to a plane parallel to the fibre’s longitudinal direction, conveying the probe with off-axis imaging capabilities. We show that its focusing ability also benefits from a higher numerical aperture, resulting in imaging with increased spatial resolution. The effect of probe insertion was investigated inside a tissue phantom comprising fluorescent particles suspended in agarose gel, and a comparison was established between the novel side-view probe and the standard en face fibre probe. This new concept paves the way to significantly less invasive deep-tissue imaging.
- ItemThermal tuning of a fiber-integrated Fabry-Pérot cavity(Washington, DC : Soc., 2021) Singer, Clemens; Goetz, Alexander; Prasad, Adarsh S.; Becker, Martin; Rothhardt, Manfred; Skoff, Sarah M.Here, we present the thermal tuning capability of an alignment-free, fiber-integrated Fabry-Pérot cavity. The two mirrors are made of fiber Bragg gratings that can be individually temperature stabilized and tuned. We show the temperature tuning of the resonance wavelength of the cavity without any degradation of the finesse and the tuning of the individual stop bands of the fiber Bragg gratings. This not only permits for the cavity’s finesse to be optimized post-fabrication but also makes this cavity applicable as a narrowband filter with a FWHM spectral width of 0.07 ± 0.02 pm and a suppression of more than -15 dB that can be wavelength tuned. Further, in the field of quantum optics, where strong light-matter interactions are desirable, quantum emitters can be coupled to such a cavity and the cavity effect can be reversibly omitted and re-established. This is particularly useful when working with solid-state quantum emitters where such a reference measurement is often not possible once an emitter has been permanently deposited inside a cavity.
- ItemUltrafast intermodal third harmonic generation in a liquid core step-index fiber filled with C2Cl4: erratum(Washington, DC : Soc., 2021) Schaarschmidt, Kay; Kobelke, Jens; Nolte, Stefan; Meyer, Tobias; Schmidt, Markus A.We provide a correction due to an erroneous repetition rate of one of the laser systems (90 fs pulse duration) in our previously published paper [Opt. Express28, 25037 (2020)10.1364/OE.399771].
- ItemSupercontinuum generation in a carbon disulfide core microstructured optical fiber(Washington, DC : Soc., 2021) Junaid, Saher; Bierlich, Joerg; Hartung, Alexander; Meyer, Tobias; Chemnitz, Mario; Schmidt, Markus A.We demonstrate supercontinuum generation in a liquid-core microstructured optical fiber using carbon disulfide as the core material. The fiber provides a specific dispersion landscape with a zero-dispersion wavelength approaching the telecommunication domain where the corresponding capillary-type counterpart shows unsuitable dispersion properties for soliton fission. The experiments were conducted using two pump lasers with different pulse duration (30 fs and 90 fs) giving rise to different non-instantaneous contributions of carbon disulfide in each case. The presented results demonstrate an extraordinary high conversion efficiency from pump to soliton and to dispersive wave, overall defining a platform that enables studying the impact of non-instantaneous responses on ultrafast soliton dynamics and coherence using straightforward pump lasers and diagnostics.
- ItemNegative curvature hollow core fiber sensor for the measurement of strain and temperature(Washington, DC : Soc., 2021) Ferreira, Marta S.; Bierlich, Jörg; Kobelke, Jens; Pinto, João L.; Wondraczek, KatrinThree different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements.
- ItemSingle-shot interferometric measurement of pulse-to-pulse stability of absolute phase using a time-stretch technique(Washington, DC : Soc., 2021) Kudelin, Igor; Sugavanam, Srikanth; Chernysheva, MariaMeasurement of the absolute phase of ultrashort optical pulses in real-time is crucial for various applications, including frequency comb and high-field physics. Modern single-shot techniques, such as dispersive Fourier transform and time-lens, make it possible to investigate non-repetitive spectral dynamics of ultrashort pulses yet do not provide the information on absolute phase. In this work, we demonstrate a novel approach to characterise single-shot pulse-to-pulse stability of the absolute phase with the acquisition rate of 15 MHz. The acquisition rate, limited by the repetition rate of the used free-running mode-locked Erbium-doped fibre laser, substantially exceeds one of the traditional techniques. The method is based on the time-stretch technique. It exploits a simple all-fibre Mach-Zehnder interferometric setup with a remarkable resolution of ∼7.3 mrad. Using the proposed method, we observed phase oscillations in the output pulses governed by fluctuations in the pulse intensity due to Kerr-induced self-phase modulation at frequencies peaked at 4.6 kHz. As a proof-of-concept application of the demonstrated interferometric methodology, we evaluated phase behaviour during vibration exposure on the laser platform. The results propose a new view on the phase measurements that provide a novel avenue for numerous sensing applications with MHz data frequencies.
- ItemOrders of magnitude loss reduction in photonic bandgap fibers by engineering the core surround(Washington, DC : Soc., 2021) Upendar, S.; Ando, R.F.; Schmidt, M.A.; Weiss, T.We demonstrate how to reduce the loss in photonic bandgap fibers by orders of magnitude by varying the radius of the corner strands in the core surround. As a fundamental working principle we find that changing the corner strand radius can lead to backscattering of light into the fiber core. Selecting an optimal corner strand radius can thus reduce the loss of the fundamental core mode in a specific wavelength range by almost two orders of magnitude when compared to an unmodified cladding structure. Using the optimal corner radius for each transmission window, we observe the low-loss behavior for the first and second bandgaps, with the losses in the second bandgap being even lower than that of the first one. Our approach of reducing the confinement loss is conceptually applicable to all kinds of photonic bandgap fibers including hollow core and all-glass fibers as well as on-chip light cages. Therefore, our concept paves the way to low-loss light guidance in such systems with substantially reduced fabrication complexity.
- ItemTime-averaged image projection through a multimode fiber(Washington, DC : Soc., 2021) Boonzajer Flaes, Dirk; Štolzová, Hana; Čižmár, TomášMany disciplines, ranging from lithography to opto-genetics, require high-fidelity image projection. However, not all optical systems can display all types of images with equal ease. Therefore, the image projection quality is dependent on the type of image. In some circumstances, this can lead to a catastrophic loss of intensity or image quality. For complex optical systems, it may not be known in advance which types of images pose a problem. Here we show a new method called Time-Averaged image Projection (TAP), allowing us to mitigate these limitations by taking the entire image projection system into account despite its complexity and building the desired intensity distribution up from multiple illumination patterns. Using a complex optical setup, consisting of a wavefront shaper and a multimode optical fiber illuminated by coherent light, we succeeded to suppress any speckle-related background. Further, we can display independent images at multiple distances simultaneously, and alter the effective sharpness depth through the algorithm. Our results demonstrate that TAP can significantly enhance the image projection quality in multiple ways. We anticipate that our results will greatly complement any application in which the response to light irradiation is relatively slow (one microsecond with current technology) and where high-fidelity spatial distribution of optical power is required.