Optical Nanofiber Research Articles

Optically Induced Sieve Effect for Nanoparticles near a Nanofiber Taper

We demonstrate size-selective optical trapping and transport for nanoparticles near an optical nanofiber taper. Using a two-wavelength counterpropagating mode configuration, we show that 100-nm-diameter and 150-nm-diameter gold nanospheres (GNSs) are trapped by the evanescent field in the taper region at different optical powers. Conversely, when one nanoparticle species is trapped the other may be transported, leading to a sievelike effect. Our results show that sophisticated optical manipulation can be achieved in a passive configuration by taking advantage of mode behavior in nanophotonic devices.

Light-induced rotation of dielectric microparticles around an optical nanofiber: publisher’s note

This publisher’s note reports a correction to the funding section of Optica 7, 59 (2020)OPTIC82334-253610.1364/OPTICA.374441.

Unraveling Two-Photon Entanglement via the Squeezing Spectrum of Light Traveling through Nanofiber-Coupled Atoms.

We observe that a weak guided light field transmitted through an ensemble of atoms coupled to an optical nanofiber exhibits quadrature squeezing. From the measured squeezing spectrum we gain direct access to the phase and amplitude of the energy-time entangled part of the two-photon wave function which arises from the strongly correlated transport of photons through the ensemble. For small atomic ensembles we observe a spectrum close to the line shape of the atomic transition, while sidebands are observed for sufficiently large ensembles, in agreement with our theoretical predictions. Furthermore, we vary the detuning of the probe light with respect to the atomic resonance and infer the phase of the entangled two-photon wave function. From the amplitude and the phase of the spectrum, we reconstruct the real and imaginary part of the time-domain wave function. Our characterization of the entangled two-photon component constitutes a diagnostic tool for quantum optics devices.

A Versatile Quantum Simulator for Coupled Oscillators Using a 1D Chain of Atoms Trapped near an Optical Nanofiber

The transversely confined propagating light modes of a nanophotonic optical waveguide or nanofiber can effectively mediate infinite-range forces. We show that for a linear chain of particles trapped within the waveguide’s evanescent field, transverse illumination with a suitable set of laser frequencies should allow the implementation of a coupled-oscillator quantum simulator with time-dependent and widely controllable all-to-all interactions. Using the example of the energy spectrum of oscillators with simulated Coulomb interactions, we show that different effective coupling geometries can be emulated with high precision by proper choice of laser illumination conditions. Similarly, basic quantum gates can be selectively implemented between arbitrarily chosen pairs of oscillators in the energy as well as in the coherent-state basis. Key properties of the system dynamics and states can be monitored continuously by analysis of the out-coupled fiber fields.

Probing Surface-Bound Atoms with Quantum Nanophotonics.

Quantum control of atoms at ultrashort distances from surfaces would open a new paradigm in quantum optics and offer a novel tool for the investigation of near-surface physics. Here, we investigate the motional states of atoms that are bound weakly to the surface of a hot optical nanofiber. We theoretically demonstrate that with optimized mechanical properties of the nanofiber these states are quantized despite phonon-induced decoherence. We further show that it is possible to influence their properties with additional nanofiber-guided light fields and suggest heterodyne fluorescence spectroscopy to probe the spectrum of the quantized atomic motion. Extending the optical control of atoms to smaller atom-surface separations could create opportunities for quantum communication and instigate the convergence of surface physics, quantum optics, and the physics of cold atoms.

Studying joint spectral intensity of spontaneous four-wave mixing in optical nanofibers

Joint spectral intensity of the biphoton field generated via spontaneous four-wave mixing in an optical nanofiber was studied both experimentally and theoretically. The measured two-photon frequency distribution agrees well with the theoretically expected one that is calculated taking into account the spatially inhomogeneous profile of the taper. It is shown that measuring joint spectral intensity of the biphoton field makes it possible to determine the nanofiber radius with high accuracy.

Tunable pulse advancement and delay by frequency-chirped stimulated Raman gain with optical nanofiber.

We demonstrate a novel method to optically tune the pulse advancement and delay based on stimulated Raman gain in hydrogen. With a frequency-chirped pump, the generated signal pulse is selectively amplified at the leading or trailing edge of the pump pulse, depending on whether the frequency difference between the pump and the signal beam is blue or red detuned from the Raman transition, which results in advancement or delay of the signal peak. Different from the method of slow/fast light, where advancement and delay are accompanied with power loss and gain, respectively, for a single resonance, both the advancement and delay are realized in the gain region for the method here. With a piece of 48-mm-long optical nanofiber in hydrogen, the time-shift for a signal peak ranging from 3.7 to -3.7 ns is achieved in a Raman-generated pulse with width of ∼12n s.

Optical transport of sub-micron lipid vesicles along a nanofiber.

Enhanced manipulation and analysis of bio-particles using light confined in nano-scale dielectric structures has proceeded apace in the last several years. Small mode volumes, along with the lack of a need for bulky optical elements give advantages in sensitivity and scalability relative to conventional optical manipulation. However, manipulation of lipid vesicles (liposomes) remains difficult, particularly in the sub-micron diameter regime. Here we demonstrate the optical trapping and transport of sub-micron diameter liposomes along an optical nanofiber using the nanofiber mode's evanescent field. We find that nanofiber diameters below a nominal diffraction limit give optimal results. Our results pave the way for integrated optical transport and analysis of liposome-like bio-particles, as well as their coupling to nano-optical resonators.

Storage and retrieval of ultraslow soliton at optical nanofiber interface via electromagnetically induced transparency.

We theoretically investigate the optical memory in a nanofiber system via electromagnetically induced transparency (EIT) in a nonlinear region. Because of the tight transverse confinement, the light-atom interaction is significantly enhanced and thus, the EIT effect is enhanced. The inhomogeneous mode field distribution contributes spatially to the EIT dispersion. We develop a systematic analysis method to study the nonlinearity of the system and prove that the optical soliton is available in the system and can be stored and retrieved with high efficiency and stability. We also study a strategy to optimize the soliton optical memory. The results obtained in this study are promising for practical applications of all-optical information processing.

Design and implementation of a tunable composite photonic crystal cavity on an optical nanofiber

We report a novel approach to the design and implementation of a tunable cavity on an optical nanofiber (ONF). The key point is to create a composite photonic crystal cavity (CPCC), by combining an ONF and a chirped period defect mode grating. Using numerical simulations we design the CPCC with low scattering loss while tuning the cavity resonance wavelength of \pm10 nm around the designed wavelength. We experimentally demonstrate the tunability of the CPCC, showing good agreement with the simulation results. Our results lay the foundation for a versatile platform for ONF cavity-quantum-electrodynamics with narrow bandwidth quantum emitters.

Manipulation of Laser-cooled Atoms Using an Optical Nanofiber

Manipulation of Laser-cooled Atoms Using an Optical Nanofiber

Spin selection in single-frequency two-photon excitation of alkali-metal atoms

We report on an experimental test of the spin selection rule for two-photon transitions in atoms. In particular, we demonstrate that the $5S_{1/2}\to 6S_{1/2}$ transition rate in a rubidium gas follows a quadratic dependency on the helicity parameter linked to the polarization of the excitation light. For excitation via a single Gaussian beam or two counterpropagating beams in a hot vapor cell, the transition rate scales as the squared degree of linear polarization. The rate reaches zero when the light is circularly polarized. In contrast, when the excitation is realized via an evanescent field near an optical nanofiber, the two-photon transition cannot be completely extinguished (theoretically, not lower than 13\% of the maximum rate, under our experimental conditions) by only varying the polarization of the fiber-guided light. Our findings lead to a deeper understanding of the physics of multiphoton processes in atoms in strongly nonparaxial light.

Imaging and Localizing Individual Atoms Interfaced with a Nanophotonic Waveguide.

Single particle-resolved fluorescence imaging is an enabling technology in cold-atom physics. However, so far, this technique has not been available for nanophotonic atom-light interfaces. Here, we image single atoms that are trapped and optically interfaced using an optical nanofiber. Near-resonant light is scattered off the atoms and imaged while counteracting heating mechanisms via degenerate Raman cooling. We detect trapped atoms within 150ms and record image sequences of given atoms. Building on our technique, we perform two experiments which are conditioned on the number and position of the nanofiber-trapped atoms. We measure the transmission of nanofiber-guided resonant light and verify its exponential scaling in the few-atom limit, in accordance with Beer-Lambert's law. Moreover, depending on the interatomic distance, we observe interference of the fields that two simultaneously trapped atoms emit into the nanofiber. The demonstrated technique enables postselection and possible feedback schemes and thereby opens the road toward a new generation of experiments in quantum nanophotonics.

Highly Photostable Perovskite Nanocubes: Toward Integrated Single Photon Sources Based on Tapered Nanofibers

The interest in perovskite nanocrystals (NCs) such as CsPbBr$_3$ for quantum applications is rapidly raising, as it has been demonstrated that they can behave as very efficient single photon emitters. The main problem to tackle in this context is their photo-stability under optical excitation. In this article, we present a full analysis of the optical and quantum properties of highly efficient perovskite nanocubes synthesized with an established method, which is used for the first time to produce quantum emitters, and is shown to ensure an increased photostability. These emitters exhibit reduced blinking together with a strong photon antibunching. Remarkably these features are hardly affected by the increase of the excitation intensity well above the emission saturation levels. Finally, we achieve for the first time the coupling of a single perovskite nanocube with a tapered optical nanofiber in order to aim for a compact integrated single photon source for future applications.

Optical detection of nano-particle characteristics using coupling to a nano-waveguide

Recently, much research concerning the combination of nano-scale waveguides with nano-crystals and other nano-particles has been reported because of possible applications in the field of quantum information and communication. The most useful and convenient method to verify the nature of such systems is optical detection. However, due to the diffraction limit, optical identification of characteristics such as particle type, particle position, etc., is difficult or impossible. However, if such particles are placed on a waveguide, the coupling of scattered light to the waveguide-guided modes can reveal the information about the particles. Here we consider how illumination with light of arbitrary polarization can reveal the difference between isotropic and non-isotropic nano-particles placed on the surface of an optical nanofiber. Specifically, we measure the polarization response function of gold nano-rods (GNRs) on an optical nanofiber surface and show that it is qualitatively different to that for gold nano-spheres (GNSs). This experimental technique provides a simple new tool for the optical characterization of hybrid nano-optical devices.

OPTICAL NANOFIBER AS A SMART DETECTOR OF MYCOTOXINS IN BLOOD

The objective of this study is to use the optical fiber, an emerging device due to their biocompatibility, photo-sensitivity, as a biosensor which can detect the mycotoxin produced by the Aspergillus sp. found in food and feed product of animals. First, we have treated the Red Blood Corpuscles (RBCs) of human blood with different concentration of Aflatoxin B1 and Aflatoxin G1 (AflB1 and AflG1respectively) and after certain time slot, we have studied the changes of the RBC and its protein by Circular Dichorism spectroscopy (CD)and, Fluorescent Spectroscopy. From these Spectroscopic data, it has been found that there was a change in the structure of the Haemoglobin (Hb), supported by theReactive Oxygen Species (ROS), which gives the apoptotic dimension of the RBC. These experiments followed by the preparation of the nanoprobe by etching optical nanofibre with Hydrofluoric Acid (HF) upto certain extent. The prepared nanoprobe was then used to detect theAflB1and AflG1treated RBC.The outcome of the experiments it has been found that the optical nanofiber can detect a small variation of pH of the solution.

Nanofiber based displacement sensor

We report on the realization of a displacement sensor based on an optical nanofiber. A single gold nano-sphere is deposited on top of a nanofiber and the system is placed within a standing wave which serves as a position ruler. Scattered light collected within the guided mode of the fiber gives a direct measure of the nanofiber displacement. We calibrated our device and found a sensitivity up to 1.2~nm/$\sqrt{\text{Hz}}$. A mechanical model based on the Mie scattering theory is then used to evaluate the optically induced force on the nanofiber by an external laser. With our sensing system, we demonstrate that an external force of 1~pN applied at the nanofiber waist can be detected.

Spontaneous emission and energy shifts of a Rydberg rubidium atom close to an optical nanofiber

In this paper, we report on numerical calculations of the spontaneous emission rates and Lamb shifts of a $^{87}\text{Rb}$ atom in a Rydberg-excited state $\left(n\leq30\right)$ located close to a silica optical nanofiber. We investigate how these quantities depend on the fiber's radius, the distance of the atom to the fiber, the direction of the atomic angular momentum polarization as well as the different atomic quantum numbers. We also study the contribution of quadrupolar transitions, which may be substantial for highly polarizable Rydberg states. Our calculations are performed in the macroscopic quantum electrodynamics formalism, based on the dyadic Green's function method. This allows us to take dispersive and absorptive characteristics of silica into account; this is of major importance since Rydberg atoms emit along many different transitions whose frequencies cover a wide range of the electromagnetic spectrum. Our work is an important initial step towards building a Rydberg atom-nanofiber interface for quantum optics and quantum information purposes.

Occurrence control of charged exciton for a single CdSe quantum dot at cryogenic temperatures on an optical nanofiber

We discuss photo-luminescence characteristics of CdSe core/shell quantum dots at cryogenic temperatures using a hybrid system of a single quantum dot and an optical nanofiber. The key point is to control the emission species of quantum dot to charged excitons, known as trions, which have superior characteristics to neutral excitons. We investigate the photocharging behavior for the quantum dots by varying the wavelength and intensity of irradiating laser light, and establish a method to create a permanently charged situation which lasts as long as the cryogenic temperature is maintained. The present photocharging method may open a new route to applying the CdSe quantum dots in quantum photonics, and the hybrid system of photocharged quantum-dot and optical nanofiber may readily be applicable to a fiber-in-line single-photon generator.

Efficient fiber in-line single photon source based on colloidal single quantum dots on an optical nanofiber

We demonstrate a fiber in-line single photon source based on a hybrid system of colloidal single quantum dots deposited on an optical nanofiber and cooled down to cryogenic temperature (3.7 K). We show that a charged state (trion) of the single quantum dot exhibits a photo-stable emission of single photons with high quantum efficiency, narrow linewidth (3 meV FWHM) and fast decay time ($10.0\pm0.5$ ns). The single photons are efficiently coupled to the guided modes of the nanofiber and eventually to a single mode optical fiber. The brightness (efficiency) of the single photon source is estimated to be $16\pm2\%$ with a maximum photon count rate of $1.6\pm0.2$ MHz and a high single photon purity ($g^2(0)=0.11\pm0.02$). The device can be easily integrated to the fiber networks paving the way for potential applications in quantum networks.