Waveguide Diameter Research Articles

Investigation of hollow cylindrical metal terahertz waveguides suitable for cryogenic environments.

The field of terahertz (THz) waveguides continues to grow rapidly, with many being tailored to suit the specific demands of a particular final application. Here, we explore waveguides capable of enabling efficient and accurate power delivery within cryogenic environments (< 4 K). The performance of extruded hollow cylindrical metal waveguides made of un-annealed and annealed copper, as well as stainless steel, have been investigated for bore diameters between 1.75 - 4.6 mm, and at frequencies of 2.0, 2.85 and 3.4 THz, provided by a suitable selection of THz quantum cascade lasers. The annealed copper resulted in the lowest transmission losses, < 3 dB/m for a 4.6 mm diameter waveguide, along with 90° bending losses as low as ~2 dB for a bend radius of 15.9 mm. The observed trends in losses were subsequently analyzed and related to measured inner surface roughness parameters. These results provide a foundation for the development of a wide array of demanding low-temperature THz applications, and enabling the study of fundamental physics.

Er3+Active Yb3+Ce3+Co-Doped Fluorozirconate Guided-Wave Chip Lasers

We report efficient 1.55-μm laser operation in a waveguide chip laser femtosecond-laser inscribed in bulk fluorozirconate glass. The ternary doped glass is composed of erbium as the active laser ion, ytterbium sensitizer, and cerium to enhance the branching ratio from the pump to the erbium upper laser state. We have achieved slope efficiencies up to 25%, with a low 100-mW threshold. To meet diverse application requirements, we also report the wide tunability of 1507-1593 nm, and large single-transverse-mode Gaussian beam-output from the 55 μm diameter waveguides.

Power scaling from buried depressed-cladding waveguides realized in Nd:YVO4 by femtosecond-laser beam writing

We report on output power performances obtained by diode-laser pumping of buried cladding-waveguides that were inscribed with a femtosecond-laser beam writing technique in several Nd:YVO4 media. Continuous-wave output power of 3.4W at 1.06µm for an absorbed pump power at 808nm of 10.3W was obtained from a circular waveguide of 100-μm diameter that was realized in a 6.9-mm long, 0.5-at% Nd:YVO4 crystal; the slope efficiency with respect to the absorbed pump power was 0.36. The pump at 880nm, directly into the 4F3/2 emitting level, was used to improve the waveguide output characteristics. With an absorbed pump power of 9.8W at 880nm, the same waveguide yielded 4.4W at 1.06µm, whereas for emission at 1.34µm the output power reached 1.7W; the slope efficiency improved to 0.47 for laser emission at 1.06µm and reached 0.24 for operation at 1.34µm. Results recorded from similar waveguides that were inscribed in 0.7-at% Nd:YVO4 and 1.0-at% Nd:YVO4 crystals are presented.

Phase-matching of the HE11 and HE13 modes of highly doped GeO2–SiO2 fiber waveguides at 1596 nm and 532 nm, respectively, for triple-photon generation

We theoretically investigate a phase-matching (PM) between the HE11 and HE13 modes at wavelengths 1596 and 532 nm, respectively, of a real germania-silica fiber waveguide, whose preform was made by MCVD technology. For several measured refractive index profiles of the fiber preform, the corresponding waveguide diameters, providing homogeneous PM, both with modal dispersion and power characteristics, are calculated. The PM parameters obtained for the real fiber are compared to that calculated for a standard step-index fiber model.

Investigation of Ultrasonic Guided Waves Interacting With Piezoelectric Transducers

Ultrasonic guided waves (UGW) can be used to inspect and monitor a structure from a single test location. Piezoelectric transducers are commonly dry-coupled with force to the surface of the waveguide in order to excite UGWs. These UGWs propagating within the waveguide will interact and reflect from known features, thus possible damage could be detected. In this paper, the interaction of UGWs with piezoelectric transducers is reported and investigated. A Finite Element Analysis (FEA) approach has been used to conduct a parametric study in order to quantify the effect of the waveguide diameter on the guided wave response. Laboratory experiments are carried out to measure the effect of the force on the dry-coupled piezoelectric transducers and the corresponding guided wave response, including reflections and mode conversions. A test rig is used to apply and measure the force on the piezoelectric transducers. For verification, a 3D Laser Doppler Vibrometry (3D-LDV) scan is performed on the waveguide in order to quantitatively identify the modes of interest. The conclusions reached this paper, particularly with respect to the quantification of the wave mode properties, lead to useful recommendations which may contribute to field inspection scenarios.

A Multifrequency Notch Filter for Millimeter Wave Plasma Diagnostics based on Photonic Bandgaps in Corrugated Circular Waveguides

Sensitive millimeter wave diagnostics need often to be protected against unwanted radiation like, for example, stray radiation from high power Electron Cyclotron Heating applied in nuclear fusion plasmas. A notch filter based on a waveguide Bragg reflector (photonic band-gap) may provide several stop bands of defined width within up to two standard waveguide frequency bands. A Bragg reflector that reflects an incident fundamental TE11 into a TM1n mode close to cutoff is combined with two waveguide tapers to fundamental waveguide diameter. Here the fundamental TE11 mode is the only propagating mode at both ends of the reflector. The incident TE11 mode couples through the taper and is converted to the high order TM1n mode by the Bragg structure at the specific Bragg resonances. The TM1n mode is trapped in the oversized waveguide section by the tapers. Once reflected at the input taper it will be converted back into the TE11 mode which then can pass through the taper. Therefore at higher order Bragg resonances, the filter acts as a reflector for the incoming TE11 mode. Outside of the Bragg resonances the TE11 mode can propagate through the oversized waveguide structure with only very small Ohmic attenuation compared to propagating in a fundamental waveguide. Coupling to other modes is negligible in the non-resonant case due to the small corrugation amplitude (typically 0.05·λ0, where λ0 is the free space wavelength). A Bragg reflector for 105 and 140 GHz was optimized by mode matching (scattering matrix) simulations and manufactured by SWISSto12 SA, where the required mechanical accuracy of ± 5 μm could be achieved by stacking stainless steel rings, manufactured by micro-machining, in a high precision guiding pipe. The two smooth-wall tapers were fabricated by electroforming. Several measurements were performed using vector network analyzers from Agilent (E8362B), ABmm (MVNA 8-350) and Rohde&Schwarz (ZVA24) together with frequency multipliers. The stop bands around 105 GHz (- 55dB) and 140 GHz (-60dB) correspond to the TE11-TM12 and TE11-TM13 Bragg resonances. Experiments are in good agreement with theory.

Reversible positioning of single molecules inside zero-mode waveguides.

We have developed a hybrid nanopore/zero-mode waveguide device for single-molecule fluorescence and DNA sequencing applications. The device is a freestanding solid-state membrane with sub-5 nm nanopores that reversibly delivers individual biomolecules to the base of 70 nm diameter waveguides for interrogation. Rapid and reversible molecular loading is achieved by controlling the voltage across the device. Using this device we demonstrate protein and DNA loading with efficiency that is orders of magnitude higher than diffusion-based molecular loading.

Single dipole evanescently coupled to a multimode waveguide.

We consider a single dipole evanescently coupled to a cylindrical multimode waveguide. The emission rate into the waveguide is calculated as a function of the waveguide diameter and the dipole orientations, and the result is confirmed by finite-difference-time-domain simulations. We show that as the guide radius increases, the coupling to a given mode decreases but new decay channels to higher order modes open up to increase the density of states. This study gives insight for designing waveguide-based single photon sources that exploit superposition of transverse modes.

Waveguide-integrated single-crystalline GaP resonators on diamond.

Large-scale entanglement of nitrogen-vacancy (NV) centers in diamond will require integration of NV centers with optical networks. Toward this goal, we present the fabrication of single-crystalline gallium phosphide (GaP) resonator-waveguide coupled structures on diamond. We demonstrate coupling between 1 μm diameter GaP disk resonators and waveguides with a loaded Q factor of 3,800, and evaluate their potential for efficient photon collection if integrated with single photon emitters. This work opens a path toward scalable NV entanglement in the hybrid GaP/diamond platform, with the potential to integrate on-chip photon collection, switching, and detection for applications in quantum information processing.

Cladding waveguides realized in Nd:YAG ceramic by direct femtosecond-laser writing with a helical movement technique

Circular cladding waveguides were realized in a 5.0-mm long, 1.1-at.% Nd:YAG ceramic by direct femtosecond-laser writing using a scheme in which the laser medium is moved on a helical trajectory along its axis and parallel to the writing direction. Laser emission was obtained under the pump with a fiber-coupled diode laser. A 100-μm diameter waveguide delivered laser pulses at 1.06 μm with 3.4-mJ energy for the pump with pulses of 13.1-mJ energy, at 0.30 slope efficiency; laser pulses at 1.3 μm with 1.2-mJ energy were obtained from the same device. Comparison with a waveguide of the same dimension that was inscribed by the classical translation method of the laser medium is made. Efficient integrated lasers based on cladding waveguides that are pumped by fiber-coupled diode lasers could be realized by this writing method.

Laser emission from diode-pumped Nd:YAG ceramic waveguide lasers realized by direct femtosecond-laser writing technique

We report on realization of buried waveguides in Nd:YAG ceramic media by direct femtosecond-laser writing technique and investigate the waveguides laser emission characteristics under the pump with fiber-coupled diode lasers. Laser pulses at 1.06 μm with energy of 2.8 mJ for the pump with pulses of 13.1-mJ energy and continuous-wave output power of 0.49 W with overall optical efficiency of 0.13 were obtained from a 100-μm diameter circular cladding waveguide realized in a 0.7-at.% Nd:YAG ceramic. A circular waveguide of 50-μm diameter yielded laser pulses at 1.3 μm with 1.2-mJ energy.

A Novel Adjustable Plasmonic Filter Realization by Split Mode Ring Resonators

A novel nanoscale plasmonic filter consisting of two coupled metal-insulator-metal (MIM) waveguides is introduced. The new structure functionality is verified by numerical simulations in different configurations of the filter. The impedance variation characteristic named as split mode ring resonancy is achieved by partially narrowing or expanding the waveguide diameter. The main parameters of the filter are evaluated by using the parameters of an implemented type of ring resonator. Moreover, modal analysis for Surface Plasmon Polariton (SPP) propagation is performed while changing the main spatial parameters of the device.

Study of the loss of the H 11 mode in a modified circular waveguide in a wide frequency range

The specific attenuation coefficient of the hybrid HE 11 mode in a modified circular waveguide is calculated using a method developed earlier. Calculations are performed in a wide frequency range for a number of waveguide diameters. Combinations of the parameters of modified waveguides providing a substantial decrease in the specific attenuation as compared to that in an empty waveguide are determined.

Fabrication of nanoscale zero-mode waveguides using microlithography for single molecule sensing

We present a novel approach to the fabrication of zero-mode waveguides (ZMWs) using inexpensive processing techniques. Our method is capable of rapid fabrication of circular nanoapertures with diameters ranging from 70 nm to 2 μm, allowing us to perform a detailed characterization of the dependence of the fluorescence emission on the waveguide diameter. We also validated the use of the fabricated ZMWs by detecting single molecule binding events with a signal-to-noise ratio of ten.

Spontaneous emission control of single quantum dots in bottom-up nanowire waveguides

Nanowire waveguides with controlled shape are promising for engineering the collection efficiency of quantum light sources. We investigate the exciton lifetime in individual InAsP quantum dots, perfectly positioned on-axis of InP nanowire waveguides. We demonstrate control over the quantum dot spontaneous emission by varying the nanowire diameter in e-beam patterned arrays, which modifies the coupling efficiency of the emitter to the fundamental waveguide mode. The spontaneous emission rate is inhibited by a factor of 12 in thin nanowires compared to nanowires with optimized waveguide diameter. From the measured inhibition factor, we determine a high radiative yield exceeding 92% in bottom-up grown nanowires.

Study of the photosensitivity of GeS binary glasses to 800nm femtosecond pulses

We present the first study of the photosensitivity of GeS binary glasses in response to irradiation to femtosecond pulses at 800 nm. A maximum positive refractive index change of 3.5x10(-3) is demonstrated with the possibility to control the waveguide diameter from ~8 to ~50 µm by adjusting the input pulse energy. It is also demonstrated that under different exposure conditions, a maximum negative index change of -7.5x10(-3) can be reached. The present results clearly illustrate the potential of this family of glasses for the fabrication of mid-infrared waveguides.

Increased Susceptibility of Arterial Tissue to Wire Perforation With the Application of High-Frequency Mechanical Vibrations

High-frequency mechanical vibrations (20-50 kHz), delivered via small diameter flexible wire waveguides represent a minimally invasive technology for the treatment of chronic total occlusions and in other tissue ablation applications. Tissue disruption is reported to be caused by repetitive mechanical contact and cavitation. This work focuses on the effects of vibrating wire waveguides in contact with arterial tissue. An apparatus with clinically relevant parameters was used, characterized as operating at 22.5 kHz and delivering amplitudes of vibration of 17.8-34.3 μm (acoustic intensity, I(SATA): 1.03-3.83 W/cm(2)) via 1.0-mm diameter waveguides. Inertial cavitation (in water at 37 °C) was determined to occur above amplitudes of vibration greater than 31.4 μm (I(SATA) = 3.21 W/cm(2)). The energized waveguides were advanced through tissue samples (porcine aorta) and the force profiles were measured for a range of acoustic intensities. The results show that the tissue perforation initiation force, perforation initiation energy, and total energy required to perforate the tissue reduces with increasing acoustic intensity. No significant reduction in perforation force or energy was observed in the inertial cavitation region. Multistage perforation was evident through the force profile and histological examination of the tissue samples post wire waveguide perforation.

The Effect of Bends on the Long-Range Microwave Inspection of Thermally Insulated Pipelines for the Detection of Water

The detection of corrosion under insulation is an ongoing challenge in the oil and gas industry. An early warning of areas of pipe at risk of corrosion can be obtained by screening along the length of the pipeline to inspect the insulation layer for the presence of water, as water is a necessary precursor to corrosion. In a recent paper [Jones et al. in J. Nondestruct. Eval. 2011] we have shown that long-range detection of water volumes can be achieved with microwave signals, using the structure of the clad and insulated pipeline as a coaxial waveguide, with water volumes presenting an impedance contrast and producing reflections of the incident microwave signal. To achieve long-range inspection of complex pipe networks it is essential that the selected guided wave signal can transmit through structural features such as bends and supports whilst retaining a sufficient signal-to-noise ratio. This paper therefore presents a study on the effects of bends on the propagation of the fundamental Transverse Electromagnetic (TEM) mode. First, numerical simulations are used to study the amplitude of the TEM mode transmitted through a bend, as a function of bend radius and angle. It is found that for typical industrial bends with a bend angle of 90∘ and bend radii between three and five times the pipe diameter, the transmission coefficient varies between 96% and 93%, respectively. As the bend angle varies from 0 to 180∘ the transmission coefficient oscillates with maxima around 0, 90 and 180∘ and minima at around 45 and 130∘. Moreover, the amplitude of the oscillation decreases as the bend radius increases. Then, experimental results on a 12′′ diameter waveguide with a length of 7 m are used to validate the simulated results and are found to be in excellent agreement.

Optimization studies of the ITER low field side reflectometer

Microwave reflectometry will be used on ITER to measure the electron density profile, density fluctuations due to MHD/turbulence, edge localized mode (ELM) density transients, and as an L-H transition monitor. The ITER low field side reflectometer system will measure both core and edge quantities using multiple antenna arrays spanning frequency ranges of 15-155 GHz for the O-mode system and 55-220 GHz for the X-mode system. Optimization studies using the GENRAY ray-tracing code have been done for edge and core measurements. The reflectometer launchers will utilize the HE11 mode launched from circular corrugated waveguide. The launched beams are assumed to be Gaussian with a beam waist diameter of 0.643 times the waveguide diameter. Optimum launcher size and placement are investigated by computing the antenna coupling between launchers, assuming the launched and received beams have a Gaussian beam pattern.

탄성 도파봉에서 고주파수 파동의 전파 특성

The paper presents a theoretical analysis on the propagation characteristics of the high-frequency wave in an elastic waveguide whose diameter is less than or similar to the wavelength. The theoretical results were verified by comparing them with the numerical results obtained by the boundary-element method. The ratio of the waveguide diameter to the wavelength affects the number of the existing wavenumber, and thus it affects the propagation characteristics. In the media with attenuation, the trend is similar to that in the media without attenuation except the decreasing amplitude.