Damage-free single-mode transmission of deep-UV light in hollow-core PCF

Three stage HCF fabrication technique for high yield, broadband UV-visible fibers

Hollow-core optical fibers can offer broadband, single mode guidance in the UV-visible-NIR wavelength range, with the potential for low-loss, solarization-free operation, making them desirable and potentially disruptive for a wide range of applications. To achieve this requires the fabrication of fibers with <300nm anti-resonant membranes, which is technically challenging. Here we investigate the underlying fluid dynamics of the fiber fabrication process and demonstrate a new three-stage fabrication approach, capable of delivering long (∼350m) lengths of fiber with the desired thin-membranes.

Ultra-high sensitive refractive index sensor based on D-shaped photonic crystal fiber with graphene-coated Ag-grating

In this paper, an ultra-high sensitive plasmonic sensor is theoretically proposed for refractive index based on D-shaped photonic crystal fiber (PCF) with graphene-coated Ag-grating in mid-infrared region. Surface plasmon polariton at the metal/dielectric interface can be effectively excited by the fundamental guiding mode, leading to the surrounding medium-dependent loss spectrum. This metallic-grating PCF sensor exhibits a maximum sensitivity of 18612 nm/RIU with a detection resolution of 4.16 × 10^-6 RIU in the index range from 1.33 to 1.395. Dependences of loss spectrum on the PCF parameters (air hole diameter and lattice constant) and the grating structure (grating thickness, period and width) are systematically analyzed. Moreover, the influence of the material parameters on the sensor performance is also investigated in term of graphene-layer number and the thickness of Ag layer. The compact design not only has great potentials in the applications of liquid detection, but also offers a guidance in the engineering of the metallic-grating fiber sensor.

Stack, seal, evacuate, draw: a method for drawing hollow-core fiber stacks under positive and negative pressure

The two-stage stack and draw technique is an established method for fabricating microstructured fibers, including hollow-core fibers. A stack of glass elements of around a meter in length and centimeters in outer diameter forms the first stage preform, which is drawn into millimeter scale canes. The second stage preform is one of the canes, which is drawn, under active pressure, into microscopic fiber. Separately controlled pressure lines are connected to different holes or sets of holes in the cane to control the microstructure of the fiber being drawn, often relying on glues or other sealants to isolate the differently-pressured regions. We show that the selective fusion and collapse of the elements of the stack, before it is drawn to cane or fiber, allows the stack to be drawn directly under differential pressure without introducing a sealant. Three applications illustrate the advantages of this approach. First, we draw antiresonant hollow-core fiber directly from the stack without making a cane, allowing a significantly longer length of fiber to be drawn. Second, we fabricate canes under pressure, such that they are structurally more similar to the final fiber. Finally, we use the method to fabricate new types of microstructured resonators with a non-circular cross-section.

Enhancement of UV-visible transmission characteristics in wet-etched hollow core anti-resonant fibers

We report on the feasibility of short-wavelength transmission window modification in anti-resonant hollow core fibers using post-processing by hydrofluoric (HF) acid etching. Direct drawing of stacked anti-resonant hollow core fibers with sub-micron thin cladding capillary membranes is technologically challenging, but so far this has been the only proven method of assuring over an octave-spanning transmission windows across the visible and UV wavelengths. In this study we revealed that low HF concentration allows us to reduce the thickness of the cladding capillary membranes from the initial 760 nm down to 180 nm in a controlled process. The glass etching rates have been established for different HF concentrations within a range non-destructive to the anti-resonant cladding structure. Etching resulted in spectral blue-shifting and broadening of anti-resonant transmission windows in all tested fiber samples with lengths between 15 cm and 75 cm. Spectrally continuous transmission, extending from around 200 nm to 650 nm was recorded in 75 cm long fibers with cladding membranes etched down to thickness of 180 nm. The experiment allowed us to verify the applicability and feasibility of controlling a silica fiber post-processing technique, aimed at broadening of anti-resonant transmission windows in hollow core fibers. A practical application of the processed fiber samples is demonstrated with their simple butt-coupling to light-emitting diodes centered at various ultraviolet wavelengths between 265 nm and 365 nm.

Ultra-low-vibration closed-cycle cryogenic surface-electrode ion trap apparatus

We describe the design, commissioning, and operation of an ultra-low-vibration closed-cycle cryogenic ion trap apparatus. One hundred lines for low-frequency signals and eight microwave/radio frequency coaxial feed-lines offer the possibility of implementing a small-scale ion-trap quantum processor or simulator. With all supply cables attached, more than 1.3 W of cooling power at 5 K is still available for absorbing energy from electrical pulses introduced to control ions. The trap itself is isolated from vibrations induced by the cold head using a helium exchange gas interface. The performance of the vibration isolation system has been characterized using a Michelson interferometer, finding residual vibration amplitudes on the order of 10 nm rms. Trapping of ⁹Be⁺ ions has been demonstrated using a combination of laser ablation and photoionization.

Hollow-Core Fiber Technology: The Rising of “Gas Photonics”

Since their inception, about 20 years ago, hollow-core photonic crystal fiber and its gas-filled form are now establishing themselves both as a platform in advancing our knowledge on how light is confined and guided in microstructured dielectric optical waveguides, and a remarkable enabler in a large and diverse range of fields. The latter spans from nonlinear and coherent optics, atom optics and laser metrology, quantum information to high optical field physics and plasma physics. Here, we give a historical account of the major seminal works, we review the physics principles underlying the different optical guidance mechanisms that have emerged and how they have been used as design tools to set the current state-of-the-art in the transmission performance of such fibers. In a second part of this review, we give a nonexhaustive, yet representative, list of the different applications where gas-filled hollow-core photonic crystal fiber played a transformative role, and how the achieved results are leading to the emergence of a new field, which could be coined “Gas photonics”. We particularly stress on the synergetic interplay between glass, gas, and light in founding this new fiber science and technology.

Understanding Dispersion of Revolver-Type Anti-Resonant Hollow Core Fibers

Here, we analyze the dispersion behavior of revolver-type anti-resonant hollow core fibers, revealing that the chromatic dispersion of this type of fiber geometry is dominated by the resonances of the glass annuluses, whereas the actual arrangement of the anti-resonant microstructure has a minor impact. Based on these findings, we show that the dispersion behavior of the fundamental core mode can be approximated by that of a tube-type fiber, allowing us to derive analytic expressions for phase index, group-velocity dispersion and zero-dispersion wavelength. The resulting equations and simulations reveal that the emergence of zero group velocity dispersion in anti-resonant fibers is fundamentally associated with the adjacent annulus resonance which can be adjusted mainly via the glass thickness of the anti-resonant elements. Due to their generality and the straightforward applicability, our findings will find application in all fields addressing controlling and engineering of pulse dispersion in anti-resonant hollow core fibers.

Four-wave mixing in Ar-filled hollow core bandgap photonic crystal fiber

To study the four-wave mixing (FWM) effect and wavelength conversion in a hollow core bandgap photonic crystal fiber filled with Ar, we conducted an experiment using a femtosecond laser with the pulse width of 120 fs, a repetition rate of 76 MHz, and tunable central wavelength from 760 to 980 nm. It is observed that new spectra are generated in both sides of the pump at a special wavelength, which can exactly satisfy the phase matching conditions of FWM. Combining experimental results with theoretical analysis, we find that the experimental phenomenon is mainly caused by FWM, and some other nonlinear phase effects, such as self-phase modulation, stimulated Raman scattering, and the soliton effect, have also occurred in this nonlinear process.

Single-mode solarization-free hollow-core fiber for ultraviolet pulse delivery

In this paper, we report anti-resonant silica hollow-core fibers (AR-HCFs) for solarization-free ultraviolet (UV) pulse transmission. The new fibers reported have lower attenuation than any previous HCFs for this spectral range. We report a single fiber that guides over a part of the UV-C and the whole of the UV-A spectral regions in adjacent transmission bands. A second AR-HCF is used for delivery of 17 nanosecond laser pulses at 266 nm at 30 kHz repetition rate. The fiber maintained a constant transmission, free of silica fluorescence and solarization-induced fiber degradation while delivering 0.46 μJ pulses for a period of over one hour. By direct comparison, we demonstrate that the single-mode AR-HCF significantly outperforms commercially-available high-OH and solarization-resistant silica multimode fibers for pulsed light delivery in this spectral range.

Nanotherapy of cancer by photoelectrons emitted from the surface of nanoparticles exposed to nonionizing ultraviolet radiation

AIM

We introduce a new method for selectively destroying cancer cell organelles by electrons emitted from the surface of intracellularly localized nanoparticles exposed to the nonionizing ultraviolet (UV) radiation.

METHODS

We propose to target cancerous intracellular organelles by nanoparticles and expose them to UV radiation with energy density safe for healthy tissue.

RESULTS

We simulate the number of photoelectrons produced by the nanoparticles made of various metals and radii, calculate their kinetic energy and compare it to the threshold energy for producing biological damage.

CONCLUSION

Exposure of metal nanoparticles to UV radiation generates photoelectrons with kinetic energies up to 11 eV, which is high enough to produce single- to double-strand breaks in the DNA and damage the cancerous cell organelles.

Generation of a vacuum ultraviolet to visible Raman frequency comb in H2-filled kagomé photonic crystal fiber

We report on the generation of a purely vibrational Raman comb, extending from the vacuum ultraviolet (184 nm) to the visible (478 nm), in hydrogen-filled kagomé-style photonic crystal fiber pumped at 266 nm. Stimulated Raman scattering and molecular modulation processes are enhanced by higher Raman gain in the ultraviolet. Owing to the pressure-tunable normal dispersion landscape of the "fiber + gas" system in the ultraviolet, higher-order anti-Stokes bands are generated preferentially in higher-order fiber modes. The results pave the way toward tunable fiber-based sources of deep and vacuum ultraviolet light for applications in, e.g., spectroscopy and biomedicine.

Parallel Transport Quantum Logic Gates with Trapped Ions

We demonstrate single-qubit operations by transporting a beryllium ion with a controlled velocity through a stationary laser beam. We use these to perform coherent sequences of quantum operations, and to perform parallel quantum logic gates on two ions in different processing zones of a multiplexed ion trap chip using a single recycled laser beam. For the latter, we demonstrate individually addressed single-qubit gates by local control of the speed of each ion. The fidelities we observe are consistent with operations performed using standard methods involving static ions and pulsed laser fields. This work therefore provides a path to scalable ion trap quantum computing with reduced requirements on the optical control complexity.

Large mode area multi-trench fiber for UV and visible transmission

We experimentally demonstrate all-solid 10 and 20 μm core diameter multi-trench fibers for UV and visible wavelengths. Measurements ensure an effective single-mode operation over a wide range of bend radii, which is suitable for applications such as beam delivery. Both fibers were fabricated by the conventional modified chemical vapor deposition process, which is suitable for mass production. Moreover, all-solid fiber design ensures easy cleaving and splicing.

Low-loss single-mode guidance in large-core antiresonant hollow-core fibers

We present an approach how to combine large-mode field diameters with effective single-mode guidance in a hollow-core antiresonant optical fiber. We demonstrate experimentally and in simulations that single-mode guidance is achieved in a simplified hollow-core fiber design with a core diameter of 30 μm by shifting the effective indices of the first cladding modes close to those of higher order core modes. Our fiber shows low loss propagation and effective single-mode operation from the near infrared to deep ultraviolet wavelengths down to 270 nm on a loss level of approximately 3  dB/m.

Synchronous characterization of semiconductor microcavity laser beam

We report on a high-resolution double-channel imaging method used to synchronously map the intensity- and optical-frequency-distribution of a laser beam in the plane orthogonal to the propagation direction. The synchronous measurement allows us to show that the laser frequency is an inhomogeneous distribution below threshold, but that it becomes homogeneous across the fundamental Gaussian mode above threshold. The beam's tails deviations from the Gaussian shape, however, are accompanied by sizeable fluctuations in the laser wavelength, possibly deriving from manufacturing details and from the influence of spontaneous emission in the very low intensity wings. In addition to the synchronous spatial characterization, a temporal analysis at any given point in the beam cross section is carried out. Using this method, the beam homogeneity and spatial shape, energy density, energy center, and the defects-related spectrum can also be extracted from these high-resolution pictures.

Atomic mercury vapor inside a hollow-core photonic crystal fiber

We demonstrate high atomic mercury vapor pressure in a kagomé-style hollow-core photonic crystal fiber at room temperature. After a few days of exposure to mercury vapor the fiber is homogeneously filled and the optical depth achieved remains constant. With incoherent optical pumping from the ground state we achieve an optical depth of 114 at the 6(3)P(2) - 6(3)D(3) transition, corresponding to an atomic mercury number density of 6 × 10(10) cm(-3). The use of mercury vapor in quasi one-dimensional confinement may be advantageous compared to chemically more active alkali vapor, while offering strong optical nonlinearities in the ultraviolet region of the optical spectrum.

Single-mode optical fiber for high-power, low-loss UV transmission

We report large-mode-area solid-core photonic crystal fibers made from fused silica that resist ultraviolet (UV) solarization even at relatively high optical powers. Using a process of hydrogen loading and UV irradiation of the fibers, we demonstrate stable single-mode transmission over hundreds of hours for fiber output powers of 10 mW at 280 nm and 125 mW at 313 nm (limited only by the available laser power). Fiber attenuation ranges from 0.9 dB/m to 0.13 dB/m at these wavelengths, and is unaffected by bending for radii above 50 mm.