Optics letters最新文献

We propose a scheme to generate nonreciprocal entanglement and one-way steering between two distant ferrimagnetic microspheres in waveguide electromagnonics, where the magnon modes of two yttrium iron garnet (YIG) spheres are simultaneously coupled to each other through coherent and dissipative interactions. By matching the coherent interaction with its corresponding dissipative counterpart, unidirectional coupling between two magnon modes can be realized, and then in the presence of significant Kerr nonlinearities, we can obtain strong entanglement and one-way steering. Depending on the direction of the microwave propagation, the long-distance entanglement and steering can be generated nonreciprocally. Our work presents a novel, to the best of our knowledge, approach for generating nonreciprocal quantum correlations, which may find potential applications in chiral quantum networking.

The harmonic generation in an indium tin oxide (ITO) thin film induced by a ω₀ + 2ω₀ two-color field (ω₀ is the frequency of a fundamental laser field) is investigated based on the numerical solution of the full-wave Maxwell-paradigmatic-Kerr equations. By changing the topological charge number and the amplitude ratio of the ω₀ and 2ω₀ field components, different photon combination pathways in support of each harmonic generation are distinguished, which are manifested as characteristic tempo-spatial field distributions, doughnut-shaped intensity distributions with different diameters, and spiral phase diagrams with different topological charge numbers. The results here provide a new, to the best of our knowledge characterization method to distinguish the photon combination pathways for each order harmonic generation.

We propose a continuously tunable low-loss phase shifter based on weak-dispersion spoof surface plasmon polariton (SSPP) waveguide. Unlike traditional designs of SSPP devices that rely on the strong-dispersion property, we address the high insertion loss issue by leveraging the weak-dispersion region of SSPP. A detailed study reveals the relation between the waveguide length, phase shift, and insertion loss of SSPP. Based on the weak-dispersion SSPP structure, we design an active SSPP unit by integrating a varactor to tune the phase continuously. Experimental results show that continuous phase shifts up to 258° are achieved with an insertion loss less than 0.016 dB per degree at the designed frequency of 8.5 GHz. Compared to the traditional phase shifters, the proposed design exhibits significant performance.

A novel, to the best of our knowledge, frequency offset estimation (FOE) scheme is proposed and demonstrated for coherent digital subcarrier multiplexing (DSCM) systems, where frequency offset (FO) leads to severe filtering damage of subcarriers due to bandwidth limitations. The scheme exploits the symmetry of the signal spectrum, which naturally arises from the transmitter's frequency response and introduces frequency skewness as a cost function to search for FO. To achieve fast FOE, the false position (FP) method is employed to iteratively compute frequency shifts. Experimental results show that within 80% of the cumulative distribution function (CDF), the proposed scheme (with an FFT size of 2048) achieves FOE in just three iterations. In the 4-subcarrier system, the maximum error is less than 250 MHz, while in the 6- and 8-subcarrier systems, the maximum error is less than 80 MHz. In a 6-subcarrier system, the proposed scheme exhibits stable performance under different FO values and received optical power (ROP), even under severe filtering conditions where existing schemes tend to degrade or fail. Therefore, the proposed scheme provides a robust FOE solution for coherent digital subcarrier multiplexing systems with strong filtering impairments.

The combined pulse laser (CPL) based on long-pulsed lasers has been proven to be an effective way of improving laser processing efficiency by combining their processing advantages. In this Letter, a CPL with a 500 mJ millisecond pulse and a 150 mJ nanosecond pulse is utilized to study the interaction process between laser and silicon. Based on high-speed images of plasma distribution and laser supported detonation wave (LSDW), as well as the height characteristics of ablation morphology, the energy coupling of plasma with variable delay time is analyzed. The irradiation of the material by millisecond pulse within the delay time enhances the strong coupling process between nanosecond pulse and the target.

In this Letter, a reconfigurable holographic polymer dispersed liquid crystal (HPDLC) grating template is presented that is obtained by removing the liquid crystal from a formed HPDLC grating. The diffraction characteristics of the HPDLC grating template are studied theoretically and experimentally. Compared to the typical HPDLC grating, the HPDLC grating template possesses higher diffraction efficiency with lower polarization dependency. The diffraction efficiency of the HPDLC grating template can be dynamically reconfigured by refilling organic solution with a different refractive index. Moreover, a waveguide display system based on the HPDLC grating template is constructed. The merits of the ease of fabrication, high diffraction efficiency, low polarization dependency, and reconfigurable characteristics shown by the HPDLC grating template will benefit the waveguide display to obtain higher light efficiency and better exit pupil expansion.

Modern interferometers such as LIGO have achieved sensitivities limited by quantum noise, comprising radiation pressure and shot noise. To mitigate this noise, a static system is employed that minimizes the quantum noise within the measurement band. However, since gravitational wave inspiral signals are a single frequency changing over time, only noise at the chirp frequency needs to be minimized. Here we demonstrate a proof-of-principle experiment of dynamically tracking a target signal using an optical spring, resulting in an increased signal-to-noise ratio (SNR). By injecting white noise to simulate excess shot noise, we found the SNR increased by up to a factor of 40 via dynamical tracking when compared to a static configuration.

This work presents the generation of an Airy beam by a leaky-wave structure (LWS) designed from a substrate-integrated waveguide (SIW) with dimension-varying slots. The Airy beam is radiated by judiciously designing the length of the slots to modulate the phase distribution. Compared to Airy beams generated by phased array antennas or metasurfaces, no complex feeding network associated with phase shifters and no space-wave illumination is required, thus allowing one to reach a low-profile structure. The features of the generated Airy beam are verified by experimental measurements performed on the LWS operating in the microwave domain. The parabolic path as well as the self-accelerating mainlobe of the Airy beam is validated in a frequency band spanning from 7.5 GHz to 8 GHz. The proposed low-profile Airy beam generator can be readily applied to wireless near-field communications for applications related to wireless power transfer, radio frequency identification, and the Internet of Things.

In this Letter, we propose a highly secure OFDM scheme based on multi-level masking and performance-enhanced key-accompanying transmission. Our scheme exploits a four-dimensional hyperchaotic model and uses subcarriers and symbols to scramble the signal, thereby achieving chaotic encryption and enhancing system security. The dual-mode index technique is employed to conceal the key within the encrypted signal, enabling cooperative transmission of both the key and the signal. We conducted experiments that successfully transmitted a 28 Gb/s dual-mode QPSK (DM-QPSK) signal and a 42 Gb/s dual-mode 8QAM (DM-8QAM) signal over a 2-km stretch of 7-core fiber. The results demonstrated that our proposed key-accompanying transmission scheme did not compromise the system's transmission performance. Moreover, the key space of this scheme is as large as 10¹³⁵, effectively ensuring system security. Under the received optical power corresponding to the bit error rate of 3.8 × 10^-3, the minimum number of key repetitions in DM-8QAM that makes the key bit error rate zero is less than 9 times. This demonstrates that our proposed scheme effectively enhances the transmission performance of the key, achieving high-quality joint transmission of both the key and the signal.

Here we experimentally demonstrate the dynamics of Bloch-Zener oscillations (BZOs) in a synthetic temporal lattice formed by the optical pulses in coupled fiber loops. By periodically modulating the phases imposed to the optical pulses in linear driven lattices, a two-band Floquet system with tunable bandgaps is realized, and the related BZOs that occurred in this system are displayed. On this basis, by manipulating the phase difference and coupling angle of the synthetic lattice, the widths of 0-gap and π-gap are tuned feasibly so that a wide variety of the interplays between Bloch oscillations and Landau-Zener tunneling (LZT) are exhibited. As an application, the temporal Mach-Zehnder interferometer utilizing BZOs is realized, where the output patterns could be modulated by the coupling rate of the synthetic lattice. This work lays the foundation for exploring BZO physics with synthetic dimensions, which may find applications in temporal pulse controlling and optical signal processing.