External transient impact loads widely exist in the service environment of various engineering structures,and urgent engineering and military application requirements call for research on the theory and method of impa...
详细信息
External transient impact loads widely exist in the service environment of various engineering structures,and urgent engineering and military application requirements call for research on the theory and method of impact *** manuscript proposes a method to identify the impact *** employing the dispersive property of wave propagation through the waveguides,a dispersion-based average power spectral density(PSD)curve for quantitative representation of the dispersion is established,and its evolution law is investigated to apply the identification of impact *** critical parameters of the average PSD curve are obtained by analyzing the response of the structure from the perspective of *** effectiveness of this method is verified through the development of the triple-successive-impact split Hopkinson bar and the triple-successive-impact *** the method proposed in this manuscript,a kind of impact identification under multiple impact loads,which is not convenient to measure directly by the sensor,is realized,especially in the case of highly transient external impact.
Non-Hermitian photonic wave modulators utilizing exceptional points (EPs) was previously proposed as a potential approach to realize high-performance and compact optical modulators. However, their practical implementa...
详细信息
Non-Hermitian photonic wave modulators utilizing exceptional points (EPs) was previously proposed as a potential approach to realize high-performance and compact optical modulators. However, their practical implementation has been restricted by their substantial footprint size limit due to stringent adiabatic conditions near EPs. Here, we demonstrate a principle for efficient wave modulation through optimized parametric trajectories around an EP. By employing rapid encirclement or parametric jump over the EP, we achieve an extinction ratio of 43 dB within a total device length of 15 coupling-length unit. Importantly, we show that adiabatic processes around the EP in the initial stage of the entire evolution can be replaced by an instantaneous parametric jump without compromising the switching performance in stark contrast to the conventional wisdom from the standard adiabaticity.
In this article, we present the design of a wideband orthomode transducer (OMT) that aims for the frequency band 210-373 GHz. The OMT employs a modified B empty set ifot layout and is optimized to fit into the tight s...
详细信息
In this article, we present the design of a wideband orthomode transducer (OMT) that aims for the frequency band 210-373 GHz. The OMT employs a modified B empty set ifot layout and is optimized to fit into the tight spatial constraints, e.g., of the ALMA cartridge. The OMT layout harmonizes the receiver cartridge components for both polarizations by allowing the use of the same configuration and components in both polarization chains because of the OMT outputs' colinear positioning. The OMT features a built-in novel broadband 90 degrees waveguide twist, which minimizes the insertion RF loss by removing the H-split waveguide while eases receiver component integration with the 2SB mixers in the ALMA cartridge. The manufactured OMT was characterized by direct measurements with a VNA employing frequency extension modules. The waveguide adapters were used accommodating the OMT waveguide ports having dimensions 760 x 760 mu m for the input port and 380 x 760 mu m for the output ports to the VNA extension modules. The OMT demonstrated the cross pol better than -25 dB across 95% of the frequency band, the output reflections better than 15 dB, and the RF insertion loss better than 0.8 dB.
Chirp modulation can generate a relatively flat electro-optic frequency comb (EO comb) and offers the advantage of frequency reconfigurability, demonstrating significant potential in high-precision sensing and absorpt...
详细信息
Chirp modulation can generate a relatively flat electro-optic frequency comb (EO comb) and offers the advantage of frequency reconfigurability, demonstrating significant potential in high-precision sensing and absorption spectroscopy measurements. However, nonresonant devices such as waveguides are susceptible to limitations in modulation efficiency and bandwidth during electro-optic modulation. In this paper, by utilizing chirp modulation resonance mode, we have realized an EO comb based on a lithium niobate resonator with small tooth spacing and high flatness. Theoretically, the chirp modulation of phase is achieved by modulating the dispersion coupling term in the resonant mode transmission equation. Compared with conventional waveguide-based EO combs, the resonant mode chirp modulation is capable of generating a multistage flat comb, and thus the bandwidth of the comb is significantly expanded. In the experiment, with a repetition rate as low as 20 kHz and a bias voltage of 1 V, the comb bandwidth extended to over 150 MHz, where the number of 3 dB flat comb teeth for a single stage exceeds 2,000. Finally, we evaluated the measurement capability of the frequency comb at different temperatures by utilizing the transmission spectrum of the germanium-doped silica waveguide cavity as the absorption spectrum, measuring a temperature sensitivity of 1505.00 MHz/K and a temperature instability of 1.13 mK/Hz1/2.
This study is focused on the fabrication and characterization of various dual waveguides through femtosecond (fs) laser irradiation of GeO2-based glass samples. The objective of the present work is to develop diverse ...
详细信息
This study is focused on the fabrication and characterization of various dual waveguides through femtosecond (fs) laser irradiation of GeO2-based glass samples. The objective of the present work is to develop diverse waveguide configurations, namely straight, S-bend and Y-shaped waveguides within GeO2-PbO glasses embedded with silver nanoparticles, utilizing a double-guide platform, for photonic applications such as resonant rings and beam splitters. Enhanced guidance was observed with a larger radius of curvature (80 mm) among the two distinct S-bend waveguides produced. The maximum relative propagation loss was recorded for the S-bend waveguide with a 40 mm radius, while the minimum loss was noted for the Y-shaped waveguide. In the latter configuration, with an opening angle of 5 degrees and a separation of 300 mu m between the two arms, an output power ratio of 50.5/49.5 between the left and right arms indicated promising potential for beam splitter applications. During the study, the quality factor (M-2) of the proposed architectures was measured and the 80 mm S-bend configuration presented the best symmetry between the x and y axes;in the case of the Y configuration the similarity between the M-2 values in both axes, for the first and second arms, indicates comparable light guidance.
A travelling wave resonant ring has been developed at Bhabha Atomic Research Centre (BARC) to test 325 MHz radio frequency (RF) power couplers for accelerator cavities. It mainly consists of half height rectangular wa...
详细信息
A travelling wave resonant ring has been developed at Bhabha Atomic Research Centre (BARC) to test 325 MHz radio frequency (RF) power couplers for accelerator cavities. It mainly consists of half height rectangular waveguide components. The ring has been tested for output power of 30 kW with gain of 14.4 dB. Presently, RF characterization and high power testing has been completed without RF couplers. The design, RF simulations and characterization of the entire ring, along with the high power test results, are presented in this paper.
We show that twisted single-ring hollow-core fibers can exhibit strong helical dichroism, i.e., a different transmission depending on the orbital angular momentum of the launched light. Experimentally, we observe loss...
详细信息
We show that twisted single-ring hollow-core fibers can exhibit strong helical dichroism, i.e., a different transmission depending on the orbital angular momentum of the launched light. Experimentally, we observe loss differences of at least 40 dB/m over a broad spectral range (>60 THz). We investigate the effect via analytical and numerical studies and show that considerably higher differential loss can be achieved over a broader spectral range (>180 THz). Our observation provides new routes for controlling the polarization state, extends previous studies of circularly dichroic waveguides, and has many potential applications, such as the realization of new polarizing elements in previously inaccessible spectral regions, chiral sensing, broadband generation of vortex beams, and optical communication.
Efficient light coupling into the fiber waveguides is important in numerous applications, while the low in-coupling coefficients of commercially available step-index fibers significantly narrow their application domai...
详细信息
Efficient light coupling into the fiber waveguides is important in numerous applications, while the low in-coupling coefficients of commercially available step-index fibers significantly narrow their application domains. It is recently introduced that well-defined periodic nanostructures, such as annulus gratings, allow to substantially boost in-coupling coefficients. In this study, the genetic algorithm is applied for the optimization of trapezoidal polymer gratings. The experimental data showcase multiply enhanced light coupling at preselected incident angles with respect to a bare fiber. As a breakthrough result, the development of an axial-asymmetric four-sector grating, reaching the percentage level of light coupling efficiency in a broad angular range from 0 degrees$<^>{\circ }$ to 70 degrees$<^>{\circ }$ that outperforms axial-symmetric gratings by about order of magnitude. Further, the high average light coupling efficiency is verified in the finite angular intervals at multiple wavelengths of 650, 1000, and 1550 nm. This solution highlights the enhancement of algorithm-designed structures axially-asymmetric systems for fiber-based highly efficient light collections, that will further benefit extensive applications such as wide-field endoscopies.
Terahertz (THz) fiber that provides high-speed connections is one of the most essential components in THz communication systems. The emerging space-division-multiplexing technology is expected to increase the transmis...
详细信息
Terahertz (THz) fiber that provides high-speed connections is one of the most essential components in THz communication systems. The emerging space-division-multiplexing technology is expected to increase the transmission capacity of THz communications. A promising candidate to achieve that is integrating multiple channels in a compact THz multi-core fiber system. Here, we propose and experimentally demonstrate a THz subwavelength rectangular dielectric dual-core fiber structure, where two identical cores can be densely integrated, thanks to the polarization-maintaining feature of the rectangular fiber. Different configurations of the fiber structure, including the placements, core-spacings, and polarization states of two fiber cores, are comprehensively investigated to improve the channel isolation. Numerical simulations show that the fractional power in core of fiber mode has a dominant effect on inter-core coupling performance. Moreover, we design the core size (1 mm x 0.5 mm) slightly less than the WR5.1 waveguide (1.295 mm x 0.6475 mm) so that the fiber can be conveniently connected with the WR5.1 flange port with mode excitation efficiencies up to 62.8%. A cost-efficient dielectric 3D printing technique is employed for rapid fabrications of dual-core fibers as well as corresponding polymer flange structures that offer solid integration between the fiber samples and the WR5.1 port. Experimental measurements of dual-core fibers demonstrate that a 4-mm core-spacing (less than three times of the operation wavelengths over a frequency range of 0.17-0.21 THz) is sufficient to support robust dual-channel propagation with channel isolation values more than 15 dB, which are consistent with the theoretical and numerical results. This work provides a densely integrated dual-core fiber system with low fabrication cost and practical connection to WR5.1 flange, holding exciting potentials for high-capacity THz space-division-multiplexing communication systems.
暂无评论