Phase-locked Arrays Research Articles

Propagation of general-type of phase-locked beam array in a turbulent atmosphere

The propagation of a general-type of phase-locked beam array in a turbulent atmosphere is studied, in which four practical issues, i.e., apertured, conformal, partially coherent, and flattened beam array is taken into consideration for accurate modeling of beam array in power beaming applications. The average intensity distribution in the receiving plane is deduced analytically based on extended Huygens–Fresnel principle. The influence of beam order, transverse coherence length, and truncation ratio is briefly discussed.

Propagation factors of laser array beams in turbulent atmosphere

The propagation factors of phased locked laser array beams of radial and rectangular symmetries in a turbulent atmosphere are investigated based on the extended Huygens–Fresnel integral and the Wigner distribution function. Analytical propagation formulae for the propagation factors are derived and numerical examples are illustrated. We find that unlike their propagation invariant properties in free space, the propagation factors of laser array beams increase when propagating in turbulent atmosphere, and are closely related to the parameters of initial beams and the atmosphere.

Phase-locked arrays of surface-emitting terahertz quantum-cascade lasers

We report the demonstration of phase-locked arrays of surface-emitting distributed-feedback (DFB) terahertz quantum-cascade lasers with single-mode operations. Carefully designed “phase sector” locks several surface-emitting DFB laser ridges in-phase, creating tighter beam-patterns along the phased-array direction with full width at half maximum (FWHM)≈10°. In addition, the phase sector can be individually biased to provide a mechanism of frequency tuning through gain-induced optical index change, without significantly affecting the output power levels. A tuning range of 1.5 GHz around 3.9 THz was achieved. This fine tunability could be utilized to frequency- or phase-lock the DFB array to an external reference.

Propagation of a phase-locked circular dark hollow beams array in a turbulent atmosphere

The propagation of phase-locked circular dark hollow beams array in a turbulent atmosphere is studied. An analytical expression for the average intensity distribution at the receiving plane is obtained based on the extended Huygens–Fresnel principle. The effects of turbulence, dark parameter and beam order of the beams array on the intensity pattern are studied and analyzed. It is found that the intensity pattern of the phase-locked circular dark hollow beams array will evolve from a multiple-spot-pattern into a Gaussian beam spot under the isotropic influence of the turbulence. The intensity pattern of beam array with a larger dark parameter and beam order evolves into the Gaussian-shape faster with increasing propagation distance.

Propagation of phase-locked truncated Gaussian beam array in turbulent atmosphere

Truncation manipulation is a simple but effective way to improve the intensity distribution properties of the phase-locked Gaussian beam array at the receiving plane. In this paper, the analytical expression for the propagation of the phase-locked truncated Gaussian beam array in a turbulent atmosphere is obtained based on the extended Huygens–Fresnel principle. Power in the diffraction-limited bucket is introduced as the beam quality factor to evaluate the influence of different truncation parameters. The dependence of optimal truncation ratio on the number of beamlets, the intensity of turbulence, propagation distance and laser wavelength is calculated and discussed. It is revealed that the optimal truncation ratio is larger for the laser array that contains more lasers, and the optimal truncation ratio will shift to a larger value with an increase in propagation distance and decrease in intensity of atmosphere turbulence. The optimal truncation ratio is independent of laser wavelength.

Enhancement of Perpendicular Anisotropy of Co/Cu Multilayer Nanowires by Phase Doping

A multisegment structure of Co/Cu nanowires with tunable perpendicular anisotropy, associated with phase transformation, was fabricated. The mixed crystal structure, formed by doping nano grains of the hcp phase into the fcc phase in the cobalt structure, markedly improves the perpendicular anisotropy. Cobalt nano grains with the hcp phase with a preferred orientation, which were transformed from (100) to (002), by doping fcc nano grain with high preferred (111) orientation and additionally the effective magnetocrystalline energy density of mixed structure was increased, the perpendicular magnetic anisotropy can be enhanced and tunable. The magnetoresistance ratios along the parallel and perpendicular axes of nanowires are 23.4% and 7.2% respectively. This novel approach promises to be of strong interest for subsequent fabrication of phase-locked arrays of spin transfer nano-oscillators with increased output power for microwave applications.

Propagation of partially coherent partially phase-locked laser array in turbulent atmosphere

The mechanism for beam quality degradation in recently developed phase locking of high power solid state lasers, which is caused mainly by partially coherent property of element beam and partially phase locking of the laser array, is analyzed in detail. Analytical expression for propagation of partially coherent partially phase-locked laser array in turbulent atmosphere is obtained based on extended Huygens–Fresnel principle. The effect of coherence width, phase error and intensity of turbulence on the beam quality in the target-plane is studied in detail. The tolerance on phase error for laser array with different coherence property is analyzed. It is concluded that the laser array with better coherence is more sensitive to turbulence, and phase control can improve beam quality in the receiving plane only in the case when the element beam has good beam quality and propagates in weak turbulence.

13μm-wavelength phase-locked VCSEL arrays incorporating patterned tunnel junction

We report the fabrication and the performance of phase-locked VCSEL arrays emitting near 1310 nm wavelength. The arrays were fabricated using double wafer fusion by patterning a tunnel junction layer, which serves to define the individual single mode array elements. Phase-locking in both one-dimensional and two-dimensional array configurations was confirmed by means of far field and spectral measurements as well as theoretical modeling. CW output powers of more than 12 mW were achieved.

All-fiber 50 W coherently combined passive laser array

We experimentally demonstrate 50 W of spontaneously phase-locked two-laser array in an all-fiber and all-passive configuration using large-mode-area (LMA) polarization-maintaining fiber laser cavities and an LMA fiber coupler. We show that both laser cavity length difference and fiber nonlinearity play an important role in achieving efficient and stable coherent beam combining. In addition, we compare the difference in coherent combining efficiency by using fibers with different mode-field diameters and discuss the underlying phase-locking mechanism and its power scalability.

A Beam-Steering and -Switching Antenna Array Using a Coupled Phase-Locked Loop Array

We present the analysis and experimental results of a beam-steering and -switching antenna array using coupled oscillators and phase-locked loops. With the use of a type-II coupled phase-locked loop array and an external reference signal, the antenna array can steer its beam by a single control voltage, reduce the beam-pointing error arising from the phase errors of the oscillator array, and hold its output frequency stably at the reference signal frequency in operation. Using a double-pole double-throw switch and a difference amplifier at the center element of the antenna array, one can switch the array radiation pattern between the sum pattern and the difference pattern. Moreover, the beam-scanning range is extended to plusmn 90deg by properly using frequency prescalers in the phase-locked loops. The radiation characteristics of a three-element antenna array are measured to verify the array performance.

Phase-Locked Array Laser Diodes (LDs) by Using $1\times N$ Active Multimode-Interferometer (MMI)

1timesN active multimode-interferometer (MMI) laser diodes (LDs), with integrated phase-match region, are demonstrated as phase-locked array LDs. In general, the phase of output ports of MMI divider is not the same for all N ports. This phase-mismatch leads to enormous excess loss inside the 1timesN active MMI-LD cavity, which results in very low quantum efficiency or even no lasing. Therefore, we integrate the phase-match region, which can lead to regular lasing, without any enormous excess loss. The implemented 1times3 active MMI-LDs showed lasing with no enormous degradation of quantum-efficiency. Additionally, significant output power increase of 200 mW was observed, compared to the regular single stripe LDs fabricated simultaneously, with the phase-locked condition.

Adaptive Array of Phase-Locked Fiber Collimators: Analysis and Experimental Demonstration

We discuss development and integration of a coherent fiber array system composed of densely packed fiber collimators with built-in capabilities for adaptive wavefront phase piston and tilt control at each fiber collimator. In this system, multi-channel fiber-integrated phase shifters are used for phase locking of seven fiber collimators and the precompensation of laboratory-generated turbulence-induced phase aberrations. Controllable x and y displacements of the fiber tips in the fiber collimator array provide additional adaptive compensation of the tip and tilt phase aberration components. An additional control system is utilized for equalization of the intensity of each of the fiber collimator beams. All three control systems are based on the stochastic parallel gradient descent optimization technique. The paper presents the first experimental results of adaptive dynamic phase distortion compensation with an adaptive phase-locked fiber collimator array system.

用于光纤激光器阵列锁相的光纤环特性研究

用于光纤激光器阵列锁相的光纤环特性研究

Simulation study of effect of magnetic field over I-V characteristic of intrinsic stacked Josephson junctions

Josephson junction (JJ) is natural high frequency source tuneable up to terahertz. However the line width of single JJ is large and maximum power is small. The line width can be narrowed and power can be increased by using phase locked arrays of many nearly identical JJs. The single crystal and c-axis oriented CuO based high temperature superconductors (HTS) are natural stacks of JJs with the CuO2layer of 0.3 nm acting as superconducting electrodes and the Bi2O3 or Tl2O3 or Y2O3 or (Ba, Ca)O layers of approximately 1.0 nm acting as insulating barrier (intrinsic Josephson effect). The I-V characteristic of the intrinsic stacked Josephson junctions (ISJJ) as a function of magnetic field are simulated. ISJJ has been modelled as one dimensional series array of JJ. Each JJ of the series is considered as resistively shunted junction model in which the effect of capacitance, inductance and a current source producing white noise are included. The critical current of the ISJJ as function of magnetic field shows Fraunhoffer like pattern. The simulated results have been compared with the Tl2212 mesas experimental results. It has been found that the simulated results are in good agreement with the experimental one.

Mutual injection-locking of two individual double-clad fibre lasers

Phase-locking and coherent beam combination of two individual double-clad fibre lasers by a novel extra-cavity mutual injection-locking method are proposed and experimentally demonstrated. Steady interference stripes with high contrast ratio (about 0.5) are observed. The output power of the phase-locked array exceeds 11 W and the power-combining efficiency is about 80%. No power-restriction optical components are utilised in the phase-locking experiment and the output power can be further up-scaled.

Coherent addition of high power laser diode array with a V-shape external Talbot cavity

We designed a V-shape external Talbot cavity for a broad-area laser diode array and demonstrated coherent laser beam combining at high power with narrow spectral linewidth. The V-shape external Talbot cavity provides good mode-discrimination and does not require a spatial filter. A multi-lobe far-field profile generated by a low filling-factor phase-locked array is confirmed by our numerical simulation.

Mode selection and phase locking of sidelobe-emitting semiconductor laser arrays via reflection coupling from an external narrow-bandwidth grating

A phase locked array design, utilizing direct reflection feedback between adjacent cavities by an external grating, is analyzed and proposed. The narrow grating reflection bandwidth causes longitudinal mode selection, while the array geometry causes transverse wavenumber selection through the coupling strength. As a result, only one among the free running cavity eigenmodes can couple effectively into a phase locked collective eigenmode. The coupled array mode is experiencing the high reflectivity of the grating and surpasses the low gain of the free running modes, that experience only a much lower reflectivity from the cavity edge antireflective coating. These results suggest that in-phase locking and single mode operation can be achieved simultaneously through the use of an external narrow-bandwidth grating.

Diffractive-optics-based beam combination of a phase-locked fiber laser array

A diffractive optical element (DOE) is used as a beam combiner for an actively phase-locked array of fiber lasers. Use of a DOE eliminates the far-field sidelobes and the accompanying loss of beam quality typically observed in tiled coherent laser arrays. Using this technique, we demonstrated coherent combination of five fiber lasers with 91% efficiency and M2=1.04. Combination efficiency and phase locking is robust even with large amplitude and phase fluctuations on the input laser array elements. Calculations and power handling measurements suggest that this approach can scale to both high channel counts and high powers.

Analysis of the phase-locked laser diode array with an external cavity

The nonlinear equations describing the steady state of the laser diode array (LDA) positioned inside an external cavity have been given. The relation between the photon density and the carrier density in the steady state has been reviewed. The characteristics of the steady state when the LDA operates in the in-phase mode and out-phase mode have been studied.

Template-Grown NiFe/Cu/NiFe Nanowires for Spin Transfer Devices

We have developed a new reliable method combining template synthesis and nanolithography-based contacting technique to elaborate current perpendicular-to-plane giant magnetoresistance spin valve nanowires, which are very promising for the exploration of electrical spin transfer phenomena. The method allows the electrical connection of one single nanowire in a large assembly of wires embedded in anodic porous alumina supported on Si substrate with diameters and periodicities to be controllable to a large extent. Both magnetic excitations and switching phenomena driven by a spin-polarized current were clearly demonstrated in our electrodeposited NiFe/Cu/ NiFe trilayer nanowires. This novel approach promises to be of strong interest for subsequent fabrication of phase-locked arrays of spin transfer nano-oscillators with increased output power for microwave applications.