We report on laser performances obtained in Q-switch mode operation from buried depressed-cladding waveguides of circular shape (100 mu m diameter) that were inscribed in Nd:YAG and Nd:YVO4 media by direct writing wit...
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We report on laser performances obtained in Q-switch mode operation from buried depressed-cladding waveguides of circular shape (100 mu m diameter) that were inscribed in Nd:YAG and Nd:YVO4 media by direct writing with a femtosecond laser beam. The Q-switch operation was realized with a Cr4+:YAG saturable absorber, aiming to obtain laser pulses of moderate (few mu J) energy at high (tens to hundreds kHz) repetition rate. An average power of 0.52 W at 1.06 mu m consisting of a train of pulses of 7.79 mu J energy at 67 kHz repetition rate, was obtained from a waveguide realized in a 4.8 mm long, 1.1-at % Nd:YAG ceramics;the pulse peak power reached 1.95 kW. A similar waveguide that was inscribed in a 3.4 mm long, 1.0-at % Nd:YVO4 crystal yielded laser pulses with 9.4 mu J energy at 83 kHz repetition rate (at 0.77 W average power) and 1.36 kW peak power. The laser performances obtained in continuous-wave operation were discussed for each waveguide used in the experiments. Thus, a continuous-wave output power of 1.45 W was obtained from the circular buried depressed-cladding waveguide inscribed in the 1.1-at %, 4.8 mm long Nd:YAG;the overall optical-to-optical efficiency, with respect to the absorbed pump power, was 0.21. The waveguide inscribed in the 1.0-at %, 3.4 mm long Nd:YVO4 crystal yielded 1.85 W power at 0.26 overall optical efficiency. This work shows the possibility to build compact laser systems with average-to-high peak power pulses based on waveguides realized by a femtosecond (fs) laser beam direct writing technique and that are pumped by a fiber-coupled diode laser.
We investigate the occurrence of acoustic topological edge states in a 2D phononic elastic waveguide due to a phenomenon that is the acoustic analog of the quantum valley Hall effect. We show that a topological transi...
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We investigate the occurrence of acoustic topological edge states in a 2D phononic elastic waveguide due to a phenomenon that is the acoustic analog of the quantum valley Hall effect. We show that a topological transition takes place between two lattices having broken space-inversion symmetry due to the application of a tunable strain field. This condition leads to the formation of gapless edge states at the domain walls, as further illustrated by the analysis of the bulk-edge correspondence and of the associated topological invariants. Interestingly, topological edge states can also be triggered at the boundary of a single domain, when boundary conditions are properly selected. We also show that the static modulation of the strain field allows us to tune the response of the material between the different supported edge states. Although time-reversal symmetry is still intact in this material system, the edge states are topologically protected when intervalley mixing is either weak or negligible. This characteristic enables selective valley injection, which is achieved via synchronized source strategy.
Eu-doped 70SiO(2)-23HfO(2)-7ZnO ( mol%) glass-ceramic waveguides have been fabricated by sol-gel method as a function of heat-treatment temperatures for on-chip blue-light emitting source applications. Structural evol...
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Eu-doped 70SiO(2)-23HfO(2)-7ZnO ( mol%) glass-ceramic waveguides have been fabricated by sol-gel method as a function of heat-treatment temperatures for on-chip blue-light emitting source applications. Structural evolution of spherical ZnO and spherical as well as rod-like HfO2 nanocrystalline structures have been observed with heat-treatments at different temperatures. Initially, in the as-prepared samples at 900 degrees C, both, Eu2+ as well as Eu3+ ions are found to be present in the ternary matrix. With controlled heat-treatments of up to 1000 degrees C for 2 h, local environment of Eu-ions become more crystalline in nature and the reduction of Eu3+ to Eu2+ takes place in such ZnO/HfO2 crystalline environments. In these ternary glass-ceramic waveguides, heat-treated at higher temperatures, the blue-light emission characteristic, which is the signature of 4f(6)5d -> 4f(7) energy level transition of Eu2+ ions is found to be greatly enhanced. The as-prepared glass-ceramic waveguides exhibit a propagation loss of 0.4 +/- 0.2 dB cm(-1) at 632.8 nm. Though the propagation losses increase with the growth of nanocrystals, the added functionalities achieved in the optimally heat-treated Eu-doped 70SiO(2)-23HfO(2)-7ZnO (mol%) waveguides, make them a viable functional optical material for the fabrication of on-chip blue-light emitting sources for integrated optic applications.
Strong photon-photon interactions are a required ingredient for deterministic two-photon optical quantum logic gates. Multiphoton transitions in dense atomic vapors have been shown to be a promising avenue for produci...
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Strong photon-photon interactions are a required ingredient for deterministic two-photon optical quantum logic gates. Multiphoton transitions in dense atomic vapors have been shown to be a promising avenue for producing such interactions. The strength of a multiphoton interaction can be enhanced by conducting the interaction in highly confined geometries such as small-cross-section optical waveguides. We demonstrate, both experimentally and theoretically, that the strength of such interactions scale only with the optical mode diameter, d, not d2 as might be initially expected. This weakening of the interaction arises from atomic motion inside the waveguides. We create an interaction between two optical signals, at 780 and 776 nm, using the 5S1/2→5D5/2 two-photon transition in rubidium vapor within a range of hollow-core fibers with different core sizes. The interaction strength is characterized by observing the absorption and phase shift induced on the 780-nm beam, which is in close agreement with theoretical modeling that accounts for the atomic motion inside the fibers. These observations demonstrate that transit-time effects upon multiphoton transitions are of key importance when engineering photon-photon interactions within small-cross-section waveguides that might otherwise be thought to lead to enhanced optical nonlinearity through increased intensities.
Extending the data transfer rates through dense interconnections at inter- and intraboard levels is a well-established technique especially in consumer electronics at the expense of more cross talk, electromagnetic in...
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Extending the data transfer rates through dense interconnections at inter- and intraboard levels is a well-established technique especially in consumer electronics at the expense of more cross talk, electromagnetic interference (EMI), and power dissipation. Optical transmission using optical fibre is practically immune to the aforementioned factors. Among the manufacturing methods, UV laser ablation using an excimer laser has been repeatedly demonstrated as a suitable technique to fabricate multimode polymer waveguides. However, the main challenge is to precisely control and predict the topology of the waveguides without the need for extensive characterisation which is both time consuming and costly. In this paper, the authors present experimental results of investigation to relate the fluence, scanning speed, number of shots, and passes at varying pulse repetition rate with the depth of ablation of an acrylate-based photopolymer. The depth of ablation essentially affects total internal reflection and insertion loss, and these must be kept at minimum for a successful optical interconnection on printed circuit boards. The results are then used to predict depth of ablation for this material by means of adaptive neurofuzzy inference system (ANFIS) modelling. The predicted results, with a correlation of 0.9993, show good agreement with the experimental values. This finding will be useful in better predictions along with resource optimisation and ultimately helps in reducing cost of polymer waveguide fabrication.
We experimentally studied the tunability and robustness of unidirectional waveguides comprising gyro-magnetic rods in a straight-line chain. By changing the constitution parameters of the chain, we achieve the tuning ...
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We experimentally studied the tunability and robustness of unidirectional waveguides comprising gyro-magnetic rods in a straight-line chain. By changing the constitution parameters of the chain, we achieve the tuning of one-way transmission (OWT) characteristics, the center frequency and the bandwidth. Smaller period a of the chain causes wider OWT bandwidth and lower center frequency, while the larger normalized radius R = r/a results in the wider band and higher center frequency. The bandwidth tuning by a is narrower than that by R. The experimental results are in good agreement with theoretical ones. Further, the transmission measurement of the magnetic chain with sharp turns verifies the robustness of one-way transmission of the magnetic chain. The flexibility of chain structure may have many applications in the non-reciprocal devices such as tunable isolators or tunable filters.
One-way edge states at the surface of photonic topological insulators are of significant interest for communications and nonlinear and quantum optics. Moreover, when reciprocity is broken in a photonic topological ins...
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One-way edge states at the surface of photonic topological insulators are of significant interest for communications and nonlinear and quantum optics. Moreover, when reciprocity is broken in a photonic topological insulator, these states provide protection against disorder, which is of particular importance for slow-light applications. Achieving such a one-way edge state, however, requires the construction of a two-dimensional structure. Here, we show how unidiriectional Floquet bands can arise in purely one-dimensional, adiabatically modulated dynamic systems, in contrast with the higher dimensionality needed in topological insulators. We also show that, using realistic experimental parameters, the concept can be implemented using both a coupled-resonator optical waveguide and a photonic-crystal waveguide. Furthermore, we illustrate the associated protection against disorder and find it to be of a different nature when compared to Floquet topological insulators.
In this work, we experimentally demonstrate the phenomenon of nonlinearity-activated intermodal tunneling in a periodic elastic metamaterial waveguide with internal resonators and we show how this effect can be exploi...
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In this work, we experimentally demonstrate the phenomenon of nonlinearity-activated intermodal tunneling in a periodic elastic metamaterial waveguide with internal resonators and we show how this effect can be exploited to achieve conspicuous energy localization and trapping. The architecture of the waveguide is deliberately designed to promote tunneling from flexurally dominated to axially dominated modes, in order to accentuate the functional complementarity that can be harnessed during tunneling. 3D laser vibrometry at different scales of spatial refinement is employed to capture global and local in-plane features of the wavefield. The measured response naturally yields an experimental reconstruction of the band diagram of the waveguide and reveals unequivocally the spectral signature of the high-frequency modes that are activated by tunneling. Finally, a detailed scan of selected cells highlights a strong and persistent axial activation of the resonators, which displays subwavelength deformation features that are unattainable, for the axial mode, by exciting at the same frequency in a linear regime. This result demonstrates the viability of tuning strategies based on nonlinearity and paves the way for the design of metastructures with enhanced energy-trapping and harvesting capabilities.
Light transport through a multimode optical waveguide undergoes changes when subjected to bending deformations. We show that optical waveguides with a perfectly parabolic refractive index profile are almost immune to ...
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Light transport through a multimode optical waveguide undergoes changes when subjected to bending deformations. We show that optical waveguides with a perfectly parabolic refractive index profile are almost immune to bending, conserving the structure of propagation-invariant modes. Moreover, we show that changes to the transmission matrix of parabolic-index fibers due to bending can be expressed with only two free parameters, regardless of how complex a particular deformation is. We provide detailed analysis of experimentally measured transmission matrices of a commercially available graded-index fiber as well as a gradient-index rod lens featuring a very faithful parabolic refractive index profile. Although parabolic-index fibers with a sufficiently precise refractive index profile are not within our reach, we show that imaging performance with standard commercially available graded-index fibers is significantly less influenced by bending deformations than step-index types under the same conditions. Our work thus predicts that the availability of ultraprecise parabolic-index fibers will make endoscopic applications with flexible probes feasible and free from extremely elaborate computational challenges.
The exploration of the binary valley degree of freedom in topological photonic systems has inspired many intriguing optical phenomena such as the photonic Hall effect, robust delay lines, and perfect out-coupling refr...
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The exploration of the binary valley degree of freedom in topological photonic systems has inspired many intriguing optical phenomena such as the photonic Hall effect, robust delay lines, and perfect out-coupling refraction. In this work, we experimentally demonstrate the tunability of electromagnetic flow in a valley photonic crystal waveguide. By continuously controlling the phase differences of a microwave monopolar antenna array, the flow of electromagnetic waves can split into different directions according to the chirality of the phase vortex, and the splitting ratio varies from 0.9 to 0.1. Topological valley transport of edge states is also observed at the photonic domain wall. Tunable edge state dispersion, i.e., from gapless valley-dependent modes to gapped flat bands, is found at the photonic boundary between a valley photonic crystal waveguide and a perfect electric conductor, leading to the tunable frequency bandwidth of high transmission. Our work paves the way to the controllable and dynamic modulation of electromagnetic flow in topological photonic systems.
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