Photonic Band Gap Cavity Research Articles

RF behavior of a second harmonic photonic band gap cavity gyrotron oscillator

RF behavior of a second harmonic photonic band gap cavity gyrotron oscillator

Exploration of a PBG-based cavity structure for a multiple-beam extended interaction klystron

The feasibility of a photonic band-gap (PBG)-based interaction structure was analytically explored for a multiple-beam extended interaction klystron amplifier. This configuration accrues the advantages of the multiple-defect PBG-based extended interaction structure and multiple-beam operation. The mode configurations were analysed through 3D electromagnetic simulation and the applicability of the photonic band-gap cavity was studied for the multiple-beam operation of an extended interaction klystron amplifier. A typical six-defect cavity operating at around 83 GHz was designed for electron–wave interaction at 2π mode with 6 electron beams each carrying 300 mA current at the accelerating potential of 16.5 kV. A particle-in-cell simulation shows that an output power of ∼2 kW is possible with electronic efficiency of around 6.7%. A frequency-scaled-down interaction structure at Ku-band was fabricated and cold measurements were carried out to ascertain the feasibility. The measured values of the frequency for various modes, loaded quality factor and 3 dB bandwidth were found to be within 0.36%, 5.3% and 4.07%, respectively, against those from the simulation.

Scaling Theory of Wave Confinement in Classical and Quantum Periodic Systems.

Functional defects in periodic media confine waves-acoustic, electromagnetic, electronic, spin, etc.-in various dimensions, depending on the structure of the defect. While defects are usually modeled by a superlattice with a typical band-structure representation of energy levels, determining the confinement associated with a given band is highly nontrivial and no analytical method is known to date. Therefore, we propose a rigorous method to classify the dimensionality of wave confinement. Starting from the confinement energy and the mode volume, we use finite-size scaling to find that ratios of these quantities raised to certain powers yield the confinement dimensionality of each band. Our classification has negligible additional computational costs compared to a band structure calculation and is valid for any type of wave, both quantum and classical, and in any dimension. In the quantum regime, we illustrate our method on electronic confinement in 2D hexagonal boron nitride (BN) with a nitrogen vacancy, in agreement with previous results. In the classical case, we study a three-dimensional photonic band gap cavity superlattice, where we identify novel acceptorlike behavior. We briefly discuss the generalization to quasiperiodic lattices.

Fiber Optofluidic Microlasers: Structures, Characteristics, and Applications

AbstractHerein, recent progress in fiber optofluidic lasers and their applications in biochemical detection are reviewed. The unique properties of optical fibers are introduced for the development of optofluidic microlasers, including high quality factor, small mode volume, high aspect ratio, high reproducibility, and low cost. Optical fiber microresonators based on Fabry–Pérot cavity, microring resonator or photonic bandgap cavity are highlighted to provide optical feedback for optofluidic lasing. For applications, the capability of fiber optofluidic lasers is emphasized to perform biochemical analysis with ultrahigh sensitivity, fast response, high throughput, and disposable optical biodetection. The challenges and prospects for fiber optofluidic lasers are also discussed.

Optimization of multibeam klystron double gap cavities loaded by metal rods

AbstractIn this paper, the results of numerical investigation of a metal photonic band gap cavity are presented. The investigated resonator is dual‐gap and is considered as an intermediate for the K‐band multibeam klystron. A working mode is a 2n mode with a frequency of 24.15 GHz. Electrodynamic characteristics of the cavity (characteristic impendance, beam coupling factor, relative electronic conductivity, Q‐factor) were calculated and the conditions for achieving the maximum effciency are found. Based on the obtained data, the required number of gaps in the output cavity was estimated, as well as the power and efficiency of the multibeam klystron with this type of cavities, depending on the microperveance of the electron beam.

Design and PIC Simulation Studies of Millimeter-Wave-Tunable Gyrotron Using Metal PBG Cavity as its RF Interaction Circuit

In this article, a millimeter-wave gyrotron using a metal photonic band gap (PBG) cavity as its RF interaction circuit is studied for its tunability. A PBG cavity operating in a TE7,2-like mode is designed and analyzed for its mode selective property at ~260 GHz. Particle-in-cell (PIC) simulation of the PBG gyrotron predicted a continuous wave (CW) RF output of ~121 W in the desired TE7,2-like mode with an axial mode number, $q = 1$ . Furthermore, the tunability of a PBG gyrotron is studied by varying the magnetic field, which, in turn, varies with the axial mode number of the desired operating mode. A broad continuous tunable bandwidth of ~1.5 GHz is obtained for more than ~1.5 W of the output power. The designed PBG cavity is thermally analyzed to study the structural deformation of metal rods and its effect on the performance of the tunable gyrotron.

Integration of Semiconducting Carbon Nanotubes Within a Silicon Photonic Molecule

Integration of nanomaterials within optical nanocavities provides a unique potential for flexible control of light emitters properties by photonic band gap engineering and cavity Purcell effects. Here, we propose a one-dimensional heterostructure nanocavity exhibiting both non-coupled and coupled cavity modes, i.e. simultaneously acting as a single cavity and as a photonic molecule. The main cavity resonances are engineered to yield a wide spectral separation and for the first time to match the emission wavelengths of two different kinds of semiconducting single wall carbon nanotubes (s-SWNTs). By probing the photoluminescence (PL) from s-SWNTs coupled with the nano cavity modes, coupling of the s-SWNTs PL simultaneously into the several cavity modes is demonstrated. For modes governed by the photonic molecule behavior, the wavelength splitting of the two coupled modes is dominated by the cavity barrier width. The excitation of the bonding (B) and anti-bonding (AB) cavity modes then yields PL resonant enhancement that can be tuned by the pumping position and polarization filter. These results demonstrate the potential of the proposed multimode photonic molecule to tailor light-nanomaterial interactions on chip, paving the way for the development of tunable hybrid photonic circuits relying on nanoemitters in cavities for light generation purposes.

Three-dimensional photonic band gap cavity with finite support: Enhanced energy density and optical absorption

We study numerically the transport and storage of light in a 3D photonic band gap crystal doped by a single embedded resonant cavity. The crystal has finite support since it is surrounded by vacuum, as in experiments. Therefore, we employ the finite element method to model the diamond-like inverse woodpile crystal that consists of two orthogonal arrays of pores in a high-index dielectric such as silicon and that has experimentally been realized by CMOS-compatible methods. A point defect that functions as the resonant cavity is formed in the proximal region of two selected orthogonal pores with a radius smaller than the ones in the bulk of the crystal. We present a field-field cross-correlation method to identify resonances in the finite-support crystal with defect states that appear in the 3D photonic band gap of the infinite crystal. Out of 5 observed angle-independent cavity resonances, one is s-polarized and 4 are p-polarized for light incident in the X or Z directions. It is remarkable that quality factors up to Q = 1000 appear in such thin structures (3 unit cells). We find that the optical energy density is remarkably enhanced at the cavity resonances by up to 2400x the incident energy density in vacuum or up to 1200x the energy density of the equivalent effective medium. We find that an inverse woodpile photonic band gap cavity with a suitably adapted lattice parameter reveals substantial absorption in the visible range. Below the 3D photonic band gap, Fano resonances arise due to interference between the discrete fundamental cavity mode and the continuum light scattered by the photonic crystal. We argue that the five eigenstates of our 3D photonic band gap cavity have quadrupolar symmetry, in analogy to d-like orbitals of transition metals. We conclude that inverse woodpile cavities offer interesting perspectives for applications in optical sensing and photovoltaics.

A microstrip photonic crystal bandgap device with a switchable negative epsilon plasma element

AbstractWe present a microstrip photonic bandgap (PBG) device with a switchable plasma element integrated into the patterned ground plane. A pulsed laser plasma is generated in one of the PBG cavity structures creating a medium having an effective negative permittivity in the 8–10 GHz frequency range due to the high plasma density ne = 1017 cm−3. The PBG structure consists of a linear array of seven cavities along the length of the microstrip manufactured by removing cylindrical portions of copper in the ground plane. The plasma is produced in the central cavity of the PBG array and recombines over times of several microseconds allowing for the characterization of the microstrip transmission over a range of plasma density. The results confirm a switchable transmission due to plasma interactions with the electromagnetic field within the PBG structure.

A tunable microwave plasma photonic crystal filter

The integration of gaseous plasma elements into a microwave photonic crystal band gap cavity structure allows for active tuning of the device. An alumina rod array microwave photonic crystal waveguide resonator is simulated and characterized through finite difference time domain methods. A gaseous plasma element is integrated into the cavity structure and the effect of plasma density on the transmission properties of the structure is investigated. We show, through both simulations and experiments, that the permittivity of the plasma can be adjusted to shift the peak resonance to allow for both switching and tunability of transmission. The experimentally measured peak shifts in transmission are compared to those simulated and the electron density of the gaseous plasma element is calculated and compared to values determined from the measured discharge current density.

Effects of electron beam parameters and velocity spread on radio frequency output of a photonic band gap cavity gyrotron oscillator

In this paper, the effects of electron beam parameters and velocity spread on the RF behavior of a metallic photonic band gap (PBG) cavity gyrotron operating at 35 GHz with TE041–like mode have been theoretically demonstrated. PBG cavity is used here to achieve a single mode operation of the overmoded cavity. The nonlinear time-dependent multimode analysis has been used to observe the beam-wave interaction behavior of the PBG cavity gyrotron, and a commercially available PIC code “CST Particle Studio” has been reconfigured to obtain 3D simulation results in order to validate the analytical values. The output power for this typical PBG gyrotron has been obtained ∼108 kW with ∼15.5% efficiency in a well confined TE041–like mode, while all other competing modes have significantly low values of power output. The output power and efficiency of a gyrotron depend highly on the electron beam parameters and velocity spread. The influence of several electron beam parameters, e.g., beam voltage, beam current, beam velocity pitch factor, and DC magnetic field, on the PBG gyrotron operations has been investigated. This study would be helpful in optimising the electron beam parameters and estimating accurate RF output power of the high frequency PBG cavity based gyrotron oscillators.

Design of a three-dimensional photonic band gap cavity in a diamondlike inverse woodpile photonic crystal

We theoretically investigate the design of cavities in a three-dimensional (3D) inverse woodpile photonic crystal. This class of cubic diamondlike crystals has a very broad photonic band gap and consists of two perpendicular arrays of pores with a rectangular structure. The point defect that acts as a cavity is centered on the intersection of two intersecting perpendicular pores with a radius that differs from the ones in the bulk of the crystal. We have performed supercell band structure calculations with up to $5\ifmmode\times\else\texttimes\fi{}5\ifmmode\times\else\texttimes\fi{}5$ unit cells. We find that up to five isolated and dispersionless bands appear within the 3D photonic band gap. For each isolated band, the electric-field energy is localized in a volume centered on the point defect, hence the point defect acts as a 3D photonic band gap cavity. The mode volume of the cavities resonances is as small as 0.8 ${\ensuremath{\lambda}}^{3}$ (resonance wavelength cubed), indicating a strong confinement of the light. By varying the radius of the defect pores we found that only donorlike resonances appear for smaller defect radius, whereas no acceptorlike resonances appear for greater defect radius. From a 3D plot of the distribution of the electric-field energy density we conclude that peaks of energy are found in sharp edges situated at the point defect, similar to how electrons collect at such features. This is different from what is observed for cavities in noninverted woodpile structures. Since inverse woodpile crystals can be fabricated from silicon by CMOS-compatible means, we project that single cavities and even cavity arrays can be realized, for wavelength ranges compatible with telecommunication windows in the near infrared.

Beam-wave interaction behavior of a 35 GHz metal PBG cavity gyrotron

The RF behavior of a 35 GHz photonic band gap (PBG) cavity gyrotron operating in TE041-like mode has been presented to demonstrate its single mode operation capability. In this PBG cavity gyrotron, the conventional tapered cylindrical cavity is replaced by a metal PBG cavity as its RF interaction structure. The beam-wave interaction behavior has been explored using time dependent multimode nonlinear analysis as well as through 3D PIC simulation. Metal PBG cavity is treated here similar to that of a conventional cylindrical cavity for the desired mode confinement. The applied DC magnetic field profile has been considered uniform along the PBG cavity length both in analysis as well as in simulation. Electrons energy and phase along the interaction length of the PBG cavity facilitates bunching mechanism as well as energy transfer phenomena from the electron beam to the RF field. The RF output power for the TE041-like design mode as well as nearby competing modes have been estimated and found above to 100 kW in TE041-like mode with ∼15% efficiency. Results obtained from the analysis and the PIC simulation are found in agreement within 8% variation, and also it supports the single mode operation, as the PBG cavity does not switch into other parasitic modes in considerably large range of varying DC magnetic field, contrary to the conventional cylindrical cavity interaction structure.

Raising gradient limitations in 2.1 GHz superconducting photonic band gap accelerator cavities

We report results from recent 2.1 GHz superconducting radio frequency (SRF) photonic band gap (PBG) resonator experiments at Los Alamos. Two 2.1 GHz PBG cells with elliptical rods were fabricated and tested at high power in a liquid helium bath at the temperatures of 4 K and below 2 K. The described SRF PBG cells were designed with a particular emphasis on changing the shape of the PBG rods to reduce peak surface magnetic fields and at the same time to preserve its effectiveness at damping higher-order-modes. The superconducting PBG cavities have great potential for damping long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. The cells performed in accordance with simulation's predictions and the maximum achieved accelerating gradient was 18.3 MV/m. This represents a 30% increase over gradients previously demonstrated in superconducting PBG cavities with round rods.

MULTIMODE ANALYSIS AND PIC SIMULATION OF A METAL PBG CAVITY GYROTRON OSCILLATOR

This paper is devoted to the study of beam-wave interaction behavior of a 35 GHz photonic band gap (PBG) cavity gyrotron operating in a higher order TE3,4,1 mode. For the present gyrotron, PBG cavity is used instead of conventional tapered cylindrical cavity due to its promising feature of the mode selectivity. In order to observe beam-wave interaction behavior, multimode theory has been used for the PBG cavity operating at the fundamental harmonic mode. Results obtained from the analysis have been validated using a commercially available 3D PIC code. The energy and phase variations of electrons demonstrate the bunching mechanism as well as energy transfer phenomena. RF power output obtained from the analysis as well as PIC simulation is compared and is found in close agreement within 12%. More than 45 kW of stable RF power output is achieved in TE3,4,1 mode with ∼ 17% efficiency. The existence of competing modes has been considerably reduced, and the single mode operation of PBG cavity gyrotron has been achieved.

Study on 220 GHz third harmonic photonic band gap cavity gyrotron oscillator

A design of 220 GHz third harmonic photonic band gap cavity gyrotron oscillator is proposed. Higher photonic crystal band gap is used to ensure the interaction between the high order electromagnetic mode (TE63-like) and the third harmonic electron cyclotron mode in gyrotron. The weak mode competition between TE63-like and TE92-like mode is studied by using a nonlinear theory, and the working conditions that ensure the start-up of the gyrotron to work in the third harmonic mode, as well as the nonlinear characteristics during the start-up process, are achieved. These results are in good agreement with the PIC (particle-in-cell) simulation. Our study shows that by using the photonic crystal as the high-frequency structure of gyrotron, high-order electromagnetic modes can interact with harmonic electron cyclotron modes efficiently.

Design and analysis of metallic photonic band gap cavity for a Gyrotron

Design and analysis of a 35 GHz metal photonic band gap (PBG) resonant cavity operating in the TE041-like mode has been presented. The dispersion characteristics of a 2D metal PBG structure comprising of triangular array of rods has been obtained using FDTD method. Global band gap regions have been obtained to be used for the PBG cavity design. A mode map has been also generated to examine the occurrence of the possible modes in the PBG cavity. Electromagnetic simulation of the designed PBG cavity has been performed to study the operating modes and quality factors. Role of the number of metal rods layers around the defect in PBG structure has also been illustrated for confining the desired mode and deciding the diffractive quality factor. PBG cavity results have been compared with the analogous cylindrical cavity for the designed mode along with the possible nearby modes to examine the mode competition. It has been found that the mode competition has been successfully reduced in designed PBG cavity and nearly a single mode operation is achieved. It is hoped that present study would be useful for the application of the metal PBG structures in the Gyrotron devices to alleviate the mode competition problem while operating in the higher order modes.

First High Power Test Results for 2.1 GHz Superconducting Photonic Band Gap Accelerator Cavities

We report the results of the recent high power testing of superconducting radio frequency photonic band gap (PBG) accelerator cells. Tests of the two single-cell 2.1 GHz cavities were performed at both 4 and 2 K. An accelerating gradient of 15 MV/m and an unloaded quality factor Q(0) of 4×10(9) were achieved. It has been long realized that PBG structures have great potential in reducing long-range wakefields in accelerators. A PBG structure confines the fundamental TM(01)-like accelerating mode, but does not support higher order modes. Employing PBG cavities to filter out higher order modes in superconducting particle accelerators will allow suppression of dangerous beam instabilities caused by wakefields and thus operation at higher frequencies and significantly higher beam luminosities. This may lead towards a completely new generation of colliders for high energy physics and energy recovery linacs for the free-electron lasers.

Design of a second cyclotron harmonic gyrotron oscillator with photonic band-gap cavity

A photonic band-gap cavity (PBGC) gyrotron with a frequency of about 98 GHz is designed. Theoretical analyses and numerical calculations are made for the PBGC operating at fundamental and second cyclotron harmonic with a TE34 waveguide mode to demonstrate the beam–wave interaction. The results show that mode competition is successfully eliminated in the PBGC using mode selectivity and choosing the appropriate operating parameters. As a result, the second harmonic PBGC gyrotron operating at TE34 mode achieves a higher output efficiency than that of the fundamental. It is also demonstrated that, in the case of the chosen parameters for TE34 waveguide mode, the use of PBG structure in the second harmonic gyrotron brings about not only a lower operating B-field but also a weaker mode competition. The results show that the high-order electromagnetic mode can be developed to interact with the high cyclotron harmonic using the selectivity of the PBGC, which gives an encouraging outlook for the development of high-harmonic gyrotrons.

Self-consistent nonlinear theory of gyrotron oscillator with photonic-band-gap cavity

The effective radius of photonic-band-gap cavity (PBGC) is defined, the validity of using it to treat PBGC as a mode selective cylindrical metal cavity is demonstrated, the guiding role of it in the design of PBGC is revealed, and a self-consistent nonlinear theory is established for gyrotron oscillator with PBGC (PBG gyrotron) based on it. The results of theoretical analysis and numerical calculation show that the azimuthal polarized form (traveling wave or standing wave) of RF field has an obvious effect on the beam-wave interacting process and the device operating at second harmonic can achieve higher electron efficiency than that working at fundamental wave under TE-32 mode, which means PBG gyrotron is capable of operating at both high order electromagnetic mode and high order electronic cyclotron harmonic effectively owing to the excellent mode selective ability of PBGC. This gives a new clue to the research of gyrotron oscillator.