Fundamental Mode Power Research Articles

Electronic excitation of high-order spoof surface plasmons on metallic grating at terahertz frequencies

High-order spoof surface plasmon (SSP) mode on corrugated metallic surfaces can find many interesting applications, such as in imaging, sensing, transmission and enhanced radiation source, etc. In this paper, an efficient excitation method of the high-order SSP mode by using an injected electron beam on the uniform rectangular metallic grating is proposed and investigated numerically. Based on the matched wave momentum between the SSP mode and the electron beam, both the fundamental and high-order SSP modes can be excited on the structure by using a single injected electron beam. Numerical simulation results indicate that the maximum electric field intensity of the generated high-order SSP mode is about two orders higher than that of the fundamental SSP mode. In addition, the peak power of the excited high-order SSP mode is almost two times that of the fundamental SSP mode power by the same energy electron beam, which demonstrates the obvious advantage of the high-order SSP electronic excitation approach compared to the previous fundamental SSP mode excitation on the structure. The central working frequency of high-order SSP power spectrum is about three times that of the fundamental SSP power spectrum. Moreover, the influences of the injected electron beam energy on the excited SSP power spectrum are analyzed specifically. It is shown that the generated SSP power spectrum demonstrates a blue shift with the decreased working voltage of the electron beam simultaneously, with its peak power increasing. However, the working bandwidth is narrowed with decreased beam voltage, which further reveals its working mechanism of presented electronic excitation of the SSP mode. The presented studies provide a new method to excite a high-order SSP mode on the metallic grating, which can find some potential applications in high-sensitivity sensing, deep sub-wavelength waveguide, and many others in terahertz spectra.

Flux Flattening Large Heavy Water Power Reactors with Accelerator-Driven Photoneutron Source

Flux flattening and power uprating of large heavy water power reactors (HWRs) are demonstrated as an application of an accelerator-driven photoneutron source (ADS) in the ADS-CANDU concept where an array of electron linear accelerators is configured around the periphery of a subcritical CANDU-6 core. The localized ADS generated through (e−,γ,n) reactions in the HWR lattice perturbs the reactor power distribution by increasing the power of low-power bundles and depressing the power at the core center relative to the fundamental mode power distribution. Gross power uprating is feasible when the system is near critical, but the ADS array consumes tens of megawatts electric exceeding the power gained by a factor of more than 2 for the conservative ADS performance specifications assumed in the analysis. Several important challenges of fixed-source Monte Carlo simulations of near-critical multiplying media are investigated including severe load imbalance issues with distributed-memory parallel computing architecture and correlated local tallies in nonanalog (implicit absorption) Monte Carlo radiation transport. All subcritical fixed-source simulations in the study readily exceed the default random number stride used in most production Monte Carlo codes, and the stride exceedance causes both bias in local tally results (bundle powers) and spatial autocorrelation of these errors/biases in the large core. A legacy stride exceedance is critically reviewed, and the conclusions and subsequent interpretations of those conclusions are rejected. Several classes of radiation transport Monte Carlo problems are likely to be susceptible to stride exceedance, and this issue needs to be promptly addressed by the Monte Carlo analyst and code developer communities.

Conical Double-Core Structure LPmn Mode Converter

In this work, a LPmn mode converter is proposed based on a tapered double-core structure. With opposite changes of the two cores in radius dimension, matching the effective refractive index between the fundamental mode (LP01) in one core and one desired high-order mode in the other core is obtained, and the fundamental mode power is gradually converted to the high-order mode. The simulation results show that the mode conversion of LP01 to any high-order mode of LP11, LP21, LP31, LP12, LP41, LP22, LP32, LP42 and LP23 modes can be obtained with a conversion efficiency of ∼99%, ∼96%, ∼92%, ∼93%, ∼82%, ∼92%, ∼84%, ∼85% and ∼81% at the working wavelength of 1550 nm, respectively, and also conversion bandwidth (>80% conversion efficiency) is 265, 125, 130, 130, 100, 35 and 30 nm, respectively. Compared to the previously reported works, the proposed mode converter structure is more universal to support any of higher-order mode conversions with wider bandwidth.

Mode analysis of spherical probe of fiber sensor for smart grids

Fiber sense technologies of vibration, ultrasonic, and partial discharge are the core technologies for building smart grids. Single-mode fiber probes are key components of the above fiber sensors. The evolution of optical wave modes in fiber probes directly affects performance of fiber sensor. A simulation model for single-mode fiber spherical probe is established, and the modes of the spherical probe are simulated and analyzed in detail, and the evolution law of the optical wave mode in spherical probe is explored. The simulation results show that the longitudinal non-uniform spherical probe structure excites high-order modes. The fundamental mode power is gradually reduced, and the high-order mode power increases continuously. The main mode coupling in a single-mode fiber spherical probe is a strong coupling between the first and second-order cladding modes. At the top of the single-mode fiber spherical probe, with the decrease of the core layer radius, the high-order guided mode gradually transforms into the radiation mode, and the number of transmitted guided modes decreases gradually.

VCSEL mode and polarization control by an elliptic dielectric mode filter.

In this paper, we demonstrate the effectiveness of polarization mode control in vertical-cavity surface-emitting lasers (VCSELs) with integrated elliptic dielectric mode filters. The single-mode single-polarization laser operation is obtained by an irregularly shaped oval dielectric mode filter, aimed at cost-effective mass production. The orthogonal polarization suppression ratio was measured to be 16.7 dB, and the side-mode suppression ratio exceeded 30 dB. A single fundamental mode power of 0.55 mW was achieved at a bias current of 4 mA. We compared the spectra and near-field intensities of the dielectric mode filter VCSEL with a reference device. The comparison clearly indicates the effectiveness of our dielectric mode filter in controlling the transverse- and polarization-mode properties of VCSELs.

Bi-Doped Optical Fibers and Fiber Lasers

The current state of the art in infrared Bi-doped fiber laser research is reviewed. The relevant fiber glass compositions and fiber technologies are introduced. Lasers operating on transitions ranging from 1.15 to 1.55 μm occurring in the bismuth active centers and their energy level schemes are discussed on the basis of the spectroscopic properties of these centers. Continuous-wave fundamental-mode power levels ranging from a few mW near 1.55 μm up to 16 W near 1.16 μm and 22 W near 1.46 μm have been demonstrated in recent years.

Photonic crystal fiber for fundamental mode operation of multicore fiber lasers and amplifiers

A mode-selection method based on a single-mode photonic crystal fiber (PCF) in the multicore fiber (MCF) lasers is presented. The designed PCF has a central core region formed by a missing air-hole, and three air-hole rings. With an appropriate choice of the design parameters of the PCF, the power coupling between the fundamental mode (FM) of the PCF and the fundamental MCF mode can be much higher than those between the FM and the other supermodes. As a result, the fundamental MCF mode has the maximum power reflection coefficient on the right-hand side of the MCF laser cavity, and dominates the output laser power. Since the maximum power of the fundamental MCF mode will lead to the desired laser beam profile, higher the fraction of the fundamental MCF mode power contained in the total output power contributes to higher beam quality. The numerical simulations show that the effectiveness of the fundamental MCF mode-selection is higher in the MCF lasers with the PCF as a mode-selection component than in the MCF lasers based on the free-space Talbot cavity method. Additionally, for the MCF amplifiers, an approach is presented to decrease the sensitivity of the amplifier performance to the variation of Gaussian beam waist utilizing the coupling between the Gaussian beam and the FM of the PCF. The numerical results show that this method can effectively increase the design flexibility for a broad range of the Gaussian beam waist.

Modal frequency degeneracy in thermally loaded optical resonators

We observe power coupling from the fundamental mode to frequency-degenerate higher-order spatial modes in optical resonators illuminated with a 30 W laser. Thermally-induced modal frequency degeneracy facilitates power transfer from the fundamental mode to higher-order modes, reduces power coupling into the cavity, and triggers power fluctuations. Modeling thermoelastic deformation of a mirror's surface shows predicted modal frequency degeneracy to be in reasonable agreement with experimental observations. Predictions for the Laser Interferometer Gravitational-wave Observatory (LIGO) show that the circulating fundamental-mode power necessary for gravitational-wave detection is compromised at coating absorptions of 3.8 and 0.44 ppm for Enhanced and Advanced LIGO Fabry-Pérot cavities, respectively.

Design of wide-emitter single-mode laser diodes

An accurate laser simulator is developed to investigate the influences of various device parameters on modal discrimination and beam quality to optimize the brightness of semiconductor lasers. Previous work using the Prony method is extended, both by using a more robust laser simulator to solve for the optical fields and by extending the Prony method to operating conditions above threshold. The semiconductor laser model is used to investigate the effects of various device parameters on the characteristics of a gain-guided 980-nm Al-free stripe geometry laser. The device parameters investigated are the device geometry, the thickness and doping level of the waveguiding layer and the front facet reflectivity. Together with practical and economic considerations, the device parameters of a wide emitter gain-guided laser are optimized. The optimized gain-guided laser is predicted to operate in the fundamental mode up to 1.15 W. At this maximum fundamental mode power, the slow axis beam divergence at 1/e/sup 2/ points is 5.4/spl deg/, the beam quality factor M/sup 2/ is 1.62, the astigmatism is 27 /spl mu/m, and the brightness is 61 MW/cm/sup 2/sr.

Proton implanted singlemode holey vertical-cavity surface-emitting lasers

Wedge-shaped holes have been fabricated in the top mirror of proton implant confined vertical-cavity surface-emitting lasers. The index confinement and selective loss introduced by these patterns improved the performance by both increasing the singlemode power and reducing the threshold current of the lasers. A maximum single fundamental mode power of 3.5 mW with a simultaneous reduction of lasing threshold compared to an unmodified laser was observed. Multimode operation was suppressed over the entire laser operating range.

Relationship between thermally induced lensing and output power for a high‐power laser‐diode side‐pumped solid‐state laser

AbstractThe variable focal length of thermal lensing in grains of a thermally loaded Nd:YAG crystal rod have been calculated and compared with the measurements of our system. By use of the space‐dependent rate equations, the analytical expression of the output power on the pump power, which consists of the factors of threshold volume and the focal length of thermal lensing, is presented. We investigate the threshold pump power, and the relationships between the output power and the pumping power under different lengths of thermal lensing. Experimental results concerning the output power of fundamental mode and the pump power, which are related to the thermal lensing and agreeable to the theoretical analysis are given. Finally, the optimized experimental output power of our laser system is obtained. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 361–365, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20305

An improved multimode horn for Gaussian mode generation at millimeter and submillimeter wavelengths

An improvement on the dual-mode horn for Gaussian mode generation has been developed. Previous designs have used a sudden transition or linear taper to generate the required TE/sub 11/ and TM/sub 11/ mode mixture. In the improved design presented here, an optimized nonlinear taper is used to generate multimodes, which have a fundamental Gaussian mode power fraction of 99% that exceeds that of the corrugated horn (98%). The bandwidth and return loss are both improved over other dual-mode horn designs.

Multiple Diodes Quasi-Optical Oscillater

This paper presents quasi-optics techniques, millimeter techniques and a global optimization method etc techniques. It is a structure of quasi-optics power combiner, that includes a spherical reflection, that the radius of the curvature is R and another one is a hybrid reflector that is called input reflector. The space of the both reflectors is LL. The monolithic source-array is made up of 25 Gunn diodes that are mounted of parallel brass bars that have low thermal resistance. And the bars are fixed on the inner plane surface of the hybrid reflector. The hybrid reflector made up of a plane and a spherical, that the radius of the curvature are R. It is designed that higher fundamental mode power, larger fractional power of fundamental mode power and more combining efficiency of the quasi-optics power combiner.

Design consideration and performance of high-power and high-brightness InGaAs-InGaAsP-AlGaAs quantum-well diode lasers (/spl lambda/=0.98 /spl mu/m)

We conduct a theoretical analysis of the design, fabrication, and performance measurement of high-power and high-brightness strained quantum-well lasers emitting at 0.98 /spl mu/m. The material system of interest consists of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. Some key parameters of the laser structure are theoretically analyzed, and their effects on the laser performance are discussed. The laser material is grown by metal-organic chemical vapor deposition and demonstrates high quality with low-threshold current density, high internal quantum efficiency, and extremely low internal loss. High-performance broad-area multimode and ridge-waveguide single-mode laser devices are fabricated. For 100-/spl mu/m-wide stripe lasers having a cavity length of 800 /spl mu/m, a high slope efficiency of 1.08 W-A, a low vertical beam divergence of 34/spl deg/, a high output power of over 4.45 W, and a very high characteristic temperature coefficient of 250 K were achieved. Lifetime tests performed at 1.2-1.3 W (12-13 mW//spl mu/m) demonstrates reliable performance. For 4-/spl mu/m-wide ridge waveguide single-mode laser devices, a maximum output power of 394 mW and fundamental mode power up to 200 mW with slope efficiency of 0.91 mW//spl mu/m are obtained.

Observation of power drop and low threshold due to beam waist shrinkage around critical configurations in an end-pumped Nd:YVO 4 laser

Under pumping spot size less than that of the cavity mode, we observed a decrease of the fundamental mode power in an end-pumped solid-state laser when the cavity length was adjusted approaching certain critical resonator configurations where the transverse modes are degenerate. In the proximity of these configurations, we found, for the first time to our knowledge, that the laser exhibits a relatively low threshold pump power together with an unexpected far-field beam profile and shrinking beam waist.

Directional achromatic heterodyne fiber laser Doppler anemometer

The application of diode-pumped double-clad Nd:glass fiber lasers with high fundamental mode power for laser Doppler anemometry (LDA) will be presented. An acousto-optic modulator (AOM) is used as a diffractive beam splitter, so that the LDA calibration constant is wavelength independent, i.e., achromatic. Hence, broadband emitting powerful fiber lasers can also be employed. The directional discrimination of the LDA velocity measurement was achieved using the heterodyne technique with the frequency shift of the AOM element.

Mmw source CAD in quasi-optical resonator

This paper presents a quasi-optical resonator that design methode basic on IBM PC computer (CAD). There is an exellent method to calculate global optima of the fundamental mode power, fractional power of the fundamental mode and combining efficiency etc. It also presents a process of CAD of microcomputer.

Global optimization method in millimeter wave combiner

This paper describes an algorithm which can determine the global optima of the power combiner of solid-state millimeter wave resonator. The global optimization mehtod can determine a neighborhood of the global optima of an objective function and an estimation of the global optima. In this paper the objective function as follow: In the quasi-optical resonator, the objective function are the fundamental mode power, the fractional power of fundamental mode and the combining dfficiecy were done the objective functiona respectively, to calculate the global optima respectively.

Rapid communication Novel high-power laser Doppler anemometer using a diode-pumped fiber laser

We present for the first time the application of a diode-pumped double-clad fiber laser in laser Doppler anemometry. The use of fiber lasers with a fundamental transverse mode power of multiple Watts enables the realization of powerful laser Doppler anemometers with a high portability.

A global optimization method for quasi-optics power combiner

This paper describes an algorithm which can determine a neighborhood of the global optimum of an objective function and an estimate of the global optimum. This method wasemployed to determine global optimum of the fundamental mode power, the fractional power of the fundamental mode and the combining efficiency. Given this information, a local optimization procedure can be employed to local the global optimum.