Optics letters最新文献

Stimulated Brillouin scattering (SBS) provides a robust and versatile foundation for the development of mode-locked lasers, microwave signal generators, and optical gyroscopes across diverse optical platforms. Nonetheless, the relatively low efficacy of Brillouin interactions in traditional silicon photonic waveguides presents a barrier to the advances of silicon-based Brillouin laser technology. The emergence of hybrid photonic-phononic waveguides has brought to light the robust and adaptable nature of Brillouin interactions in silicon, marking a significant advancement. Here we numerically calculated the SBS gain in the valley Hall photonic-phononic topological insulator (VH-PTI), which confines the phonons in the optical waveguide to achieve light transmission under large-angle bending. Our results show that the SBS gain at 9.101 GHz is G_b/Q_m = 14.94 W^-1·m^-1, enhanced by 1.4 times compared to the highest reported value so far. In addition, we realized arbitrary location decoupling on the chip, introducing a topological state into SBS devices. This work provides a way to implement VH-PTI into silicon photonic circuits for Brillouin laser applications.

Achieving stable output and control of higher-order laser arrays has long been a challenge in the development of a passively Q-switched fiber laser. In this Letter, we reported a notable peak power of 14.9 kW alongside an average output power of 0.91 W in a passively Q-switched fiber laser. Particularly noteworthy is the observed evolution of laser modes into high-order laser arrays, extending to dimensions of up to 7 × 7 with increasing pump power. This advancement in generating high peak power laser arrays in the Q-switched states holds significant promise for applications, including optical communication and nanomicroscopic imaging.

Narrowband tunable filters play a key role in advancing the capabilities of multispectral and hyperspectral imaging (HSI and MSI) systems. Yet, some challenges limit their effectiveness including low optical throughput, slow response time, and limited tunability range. In this Letter, the common path Sagnac setup was employed to obtain a fast and polarization-independent narrowband tunable filter using liquid crystal (LC) wave plates at both the folded and fan Solc configurations. The filter provides full tunability over the visible range for multiple orders of transmission peaks. The setup allows the collection of both the S- and the P-polarization components with a total throughput twice that of the polarization-dependent Solc filter. The enhanced throughput enables using a larger number of LC retarders at relatively thin thicknesses, thus obtaining a shorter response time. The Sagnac common path configuration helps in miniaturization and minimizes the effects of LC thickness variations.

Chaotic optical communication has recently garnered considerable research interest for providing physical layer security. In this work, we propose and demonstrate a secure space-division-multiplexing (SDM) system based on multi-channel chaos random en/decryption with remotely synchronized Fabry-Perot (FP) lasers. By a random combination of multi-longitudinal modes from the FP lasers, multi-channel low-correlated chaotic signals can be produced and then utilized for encrypting the confidential data, which effectively provides multiple possibilities of optical encryption from a single chaotic laser source. As a proof-of-principle demonstration in a multi-core fiber-based SDM system, 28 Gb/s/core on-off keying (OOK) and 64 Gb/s/core quadrature phase-shift keying (QPSK) signals are successfully encrypted and securely transmitted over a 10 km seven-core fiber. The demonstrated scheme may provide a new way for a physical-layer secure SDM system with enhanced capacity and security.

Polarization-insensitive, thermo-optic (TO), silicon photonic phase shifters using vertical slot waveguides are proposed. For such slot waveguides that support slot modes only for transverse-electric (TE) polarized modes, the TO coefficients of the fundamental TE and transverse-magnetic (TM) polarized modes (i.e., TE₀ and TM₀, respectively) can be easily engineered to be the same by designing the widths of the slot and the total waveguide. In the experiments, the TO coefficients of the TE₀ and TM₀ modes for various slot waveguides are characterized by measuring the electrical switching powers of dual-polarization MZI optical switches using the slot waveguides as the TO phase shifters. A small switching power difference of <0.3% between the two polarization modes is observed for the switch using the slot waveguide engineered to act as a polarization-insensitive phase shifter. The performance of the developed optical switch is also experimentally characterized to prove the potential of the proposed phase shifters to realize polarization-independent switches.

It is generally accepted that the bound states in the continuum (BICs) are usually realized in a one-dimensional system by the TM-polarized light incident at Brewster's angle. However, the optimal BICs can be achieved only under specific incident light and at a specific polarization incident angle, which poses challenges to its experimental implementation. Serving this purpose, we design a system composed of an anisotropic material (AM) embedded in one-dimensional photonic crystals (1D-PhCs), demonstrating that both TE and TM waves can realize BICs. Moreover, the existence of BICs does not hinge on the specific angle of the incident light. In contrast to the traditional methods of creation system symmetry to achieve symmetry-protected BICs (SP-BICs), we use the 1D-PhC to confine the TE or TM wave in different frequencies first as a form of cavity (localized) mode and rotating the optical axis of AM at a specific angle to realize the field mismatch. Besides, our system can realize Friedrich-Wintgen BICs (FW-BICs) because of the destructive interference of the radiative waves in other specific angles, which can be detected as some Fano resonance collapsing points in reflection spectra. Our results provide more flexible conditions for the realization of BICs under the TE-polarized light, making the implementation of switch Q-factor easier.

Gallium nitride (GaN) materials have high absorption coefficient and wide bandgap. In this work, an excellent ohmic contact electrode with low specific contact resistivity of 5.9 × 10^-6 Ω·cm² is prepared on semi-insulating GaN material grown by MOCVD. Moreover, the high-responsivity lateral GaN photoconductive semiconductor switch (PCSS) is developed on a GaN film with a thickness of only 2.5 microns at a laser trigger having a wavelength of 355 nm. For the GaN PCSS with an electrode gap of 3 mm, when the input voltage is 10 kV and the laser energy is 2 mJ, the output peak current reaches 137.6 A and the responsivity is up to 5 × 10^-4 A/W. The results of experiment and simulation could prove that the silicon ion implantation improves the ohmic contact quality of the device, regulates the electric field distribution during on-state, and reduces the peak electric field.

We propose a source entropy controlled enumerative sphere shaping (EC-ESS) scheme to address inflexible source entropy control in sphere shaping. The proposed scheme employs a model-driven interval search algorithm to establish the relationship between the source entropy of one-dimensional and two-dimensional symbols. Data analysis indicates that within various ranges of source entropy, the number of achievable source entropies for EC-ESS surpasses that of optimum ESS (OESS). The experimental results indicate that EC-ESS provides considerable OSNR gains compared to the reference schemes, with gains of 0.04 dB, 0.27 dB, and 0.52 dB compared to OESS, BL-DM, and CCDM, respectively.

We propose and demonstrate a wavelength-division multiplexing (WDM)-based degenerate architecture for array photonic analog to digital converters (ADCs), which can be applied in phased array and multiple input multiple output (MIMO) systems. This architecture is capable of optical sampling and demultiplexing simultaneously with excellent synchronization and consistency. In the experiment, the four-channel array photonic ADCs is realized with a 20 GSa/s sampling rate for each channel. The synchronization accuracy among channels is below 0.2 ps. The frequency response uniformity in the operating frequency range of 20 GHz is also characterized. The effective number of bits is ∼6.5 bits within 20 GHz. Furthermore, we successfully apply the array photonic ADCs in wideband digital beamforming of multiple linear frequency modulated signals at 8-10 GHz.

Monolayer graphene, with a gapless conical electronic band structure, demonstrates scale invariance, showing universal linear optical responses. The impacts of this feature on nonlinear optical responses remain unclear. Our work reveals that the gate-tunable difference-frequency four-wave mixing (DFM) responses in monolayer graphene are significantly influenced by the energy ratios between excitation photons. This effect arises from scale invariance, rather than their absolute energies. Through theoretical analysis, we show that these energy ratios critically impact the DFM response relative to the chemical potential by tailoring the sequence, magnitude, and phase of resonant channels involved. Our findings deepen the understanding of the gate-tuning behavior in the nonlinear optical responses from materials featuring Dirac cones, paving the way for innovative nonlinear photonic applications.