Increasing capacity and fidelity remains a primary challenge in underwater optical communication. An innovative and robust underwater optical communication system is proposed combining polygonal vortex beams with an improved Re-MobileViT recognition network. This system uses octal and quaternary coding schemes to encode and decode grayscale images, thereby enabling multidimensional encoding information transmission. The single-beam scheme achieves eight distinguishable modes, while the coaxial combination scheme expands the codebook to 16 modes. An underwater turbid medium was simulated using milk to evaluate the transmission performance of polygonal vortex beam encoding. Images are transmitted by applying both orbital angular momentum and geometric dimensions for encoding and decoding, allowing the improved Re-MobileViT network to achieve high-precision recognition and improving the system’s robustness against interference. Experimental results demonstrate that the system maintains a transmission accuracy of over 99%, even under high turbidity.
To address the challenge of high cost and scarcity of inorganic and organic synthetic dyes, we extracted Rubiadin dye from the mahogany wood (Swietenia macrophylla) using solvent extraction methods with four distinct media: aqueous, alkaline, acidic, and hydro-alcoholic, as well as the maceration method. FTIR, UV-Vis, LSV, and I-V measurements are performed to identify functional groups, analyze dye spectra, assess photocatalytic activity, and characterize photovoltaic properties. The dye structure is Rubiadin (1,3-dihydroxy-2-methyl anthraquinone). The dye from the alkaline method shows the broadest absorption range. The hydro-alcoholic extract exhibits the highest dye loading on TiO2 due to a higher content of hydroxyl and carbonyl groups. One and two peaks were observed at the positive bias for dyes extracted using the hydro-alcoholic and aqueous methods, suggesting photo-oxidation. A sharp reduction peak at negative bias for the maceration method indicates more efficient electron injection into TiO2, supported by the highest J(sc) and V-oc in the photovoltaic data. The maceration-based dye-extraction method provides better photovoltaic performance in complete DSSC cells.
A Mach-Zehnder Modulator (MZM) based on high-efficiency Thin-Film Lithium Niobate (TFLN) modulator with enhanced modulator characteristics is proposed to achieve slow-light dispersion engineering in the proposed device. The validation of robust baseline is attained using RWG1000 waveguides. The optimized 2 mu m electrode gap yields voltage-length product (V pi L) of 2.78 V center dot cm in a push-pull configuration. Optimization of sidewall width corrugations to engineer the group velocity near the Brillouin zone edge is performed. The proposed device demonstrates group velocity enhancement factor of 2. In addition, the engineered device shows the lowest value of V pi L of 1.59 V center dot cm . The compact and reduced V pi L of proposed device pave the way of energy-efficient and high-speed on-chip photonic devices.
Flexible optical limiting materials that combine high transparency, environmental stability, and strong nonlinear optical responses are highly desirable for laser protection applications. In this work, three composite films based on vanadium oxides with different valence states, namely VO2/PMMA, V2O3/PMMA, and V2O5/PMMA, were fabricated by a solution-casting method using PMMA as the polymer matrix. The morphology, phase composition, valence states, and interfacial interactions of the powders and composite films were systematically characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The results show that the three vanadium oxides retain their characteristic structural features in the PMMA matrix. Nanosecond open-aperture Z-scan measurements at 532 and 1,064nm reveal pronounced wavelength- and composition-dependent nonlinear optical responses. At 532nm, all three composite films exhibit valley-shaped transmission attenuation and optical limiting behavior, among which V2O3/PMMA shows the strongest response and the lowest optical limiting threshold of 128.28mJ/cm(2), outperforming VO2/PMMA and V2O5/PMMA. At 1,064nm, VO2/PMMA and V2O3/PMMA still display strong attenuation-type responses, whereas V2O5/PMMA exhibits a peak-shaped response characteristic of saturable absorption. These results demonstrate that the nonlinear optical behavior of VOx/PMMA films can be effectively tuned by the vanadium valence state, providing useful guidance for the design of flexible materials for optical limiting and saturable absorption applications.
Nonlinear optical (NLO) materials play a vital role in the field of optical communication. Among these, V-shaped fluorenone molecules are of particular importance in the development of all-carbon polymers, as their self-assembled supramolecular structures exhibit excellent NLO properties. In this study, density functional theory (DFT) was employed to investigate the structures, molecular orbitals, absorption spectra, and NLO responses of DPFO monomers, dimers, and trimers. The results showed that as self-assembly progressed and the number of molecular layers increased, the band gap energy (E-gap) gradually decreased. Concurrently, with increasing aggregation, the absorption peaks showed redshift, accompanied by enhanced absorption intensity. Moreover, the polarizability (alpha tot), first hyperpolarizability (beta(tot)), and second hyperpolarizability (gamma(tot)) of the V-shaped fluorenone molecules increased significantly with the degree of aggregation. Specifically, the trimer exhibited values as high as 1411.9, 702.5, and 1,988,797a.u. for alpha(tot), beta(tot), and gamma(tot), respectively. These findings demonstrated that enhancing the degree of aggregation was an effective strategy for boosting the NLO response. This work provided a theoretical foundation for further experimental research on the self-assembly behavior and NLO properties of V-shaped fluorenone molecules.
The heterojunction engineering can provide an effective platform for optimizing and synthesizing the properties of nanomaterials. Herein, the TiS2 powder was synthesized via the solid-phase sintering method and the TiS2/graphene (TiS2/G) heterostructure film with enhanced saturable absorption was developed by using the liquid-phase exfoliation and the layer-by-layer spin-coating techniques. Measurement results at 2.8 mu m revealed that it exhibited a modulation depth of similar to 5.7%, an obvious enhancement compared to the similar to 4.2% of pure TiS2 film, meanwhile, the saturation intensity was similar to 0.12 MW/cm(2), markedly lower than similar to 0.17 MW/cm(2) of solo TiS2 device. With this SAM, a robust passively Q-switched Er:YAP bulk laser operating at similar to 2.8 mu m was demonstrated. The maximal signal-to-noise ratio of the stable pulse sequence reached 35dB at an absorbed pump power of 6.1 W, with a repetition rate of 177.3 kHz, a pulse width of 232 ns and an average output power of 0.42 W. This functional TiS2/Graphene heterostructure film can provide an available optical modulator for a robust passively Q-switched laser operation in the mid-infrared band.
Suppressing molecular alignment dephasing is of significant practical value for applications involving nonrigid rotors. In this work, we propose a strategy that employs a train of time-delayed, phase-modulated laser pulses to achieve the elimination of alignment dephasing over an extended temporal window. Our findings demonstrate that for molecules with short rotational periods, such as CO or N 2 used in this study, dephasing can be completely eliminated for at least a dozen revival periods, thereby restoring alignment approaching the rigid-rotor limit. For molecules exhibiting longer revival periods, however, the effectiveness of this approach is somewhat diminished. While complete dephasing elimination is not achieved in such cases, the method remains sufficiently effective for most practical applications. We also qualitatively analyze the underlying reasons for the reduced performance in molecules with longer rotational periods.
In this work, systematic experimental research was conducted on the erbium-doped fiber lasers based on the nonlinear polarization rotation technology, achieving various types of soliton pulse lasers and discussing their output laser performance. Based on the NPR technology, a highly stable traditional soliton passive mode-locked fiber laser with a pulse width of 482fs was achieved. The bound-state soliton phenomenon was achieved by adjusting the polarization state of the laser cavity. The modulation period of the spectrum was 1.80nm, and the corresponding interval between adjacent two pulses within the bound-state soliton was 4.2ps. Through cavity design, the net dispersion value of the laser resonator cavity was adjusted to be close to zero dispersion, thereby generating an output of stretched soliton mode-locked pulses, with a full width at half-maximum of optical spectral exceeding 45.14nm. Based on the experimental device of stretched pulse soliton, by adding dispersion compensation fibers to adjust the net dispersion of the resonator to positive dispersion, dissipative soliton pulse laser output was achieved, with a full width half maximum spectral as high as 29.66nm, and the 3-dB spectral range covering about 1540-1570nm. These results highlight the multifunctionality of the 1.5 mu m fiber laser in controlling soliton pulse patterns, compactness and stability. We further conducted numerical simulations to verify these experimental results. This work will enrich the research on nonlinear photonics and pulse dynamics and provide valuable insights for the development of ultrafast fiber lasers. It holds significant value in promoting the advancement of ultrafast fiber lasers and the broader field of pulse nonlinear polarization dynamics.
In this paper, we present the dynamics of supercontinuum (SC) generation in an asymmetric semiconductor quantum well (SQW) system employing modulated nonlinearity and dispersion under an electromagnetically induced transparency (EIT) window. Specifically, we utilize a weak probe pulse in the system, which is modulated by a strong control field, exploiting the phenomenon of EIT. Adjusting the control field parameters, we obtain large nonlinearities of the order gamma = 2.02 & times; 10(5 )W(-1)m(-1) and 4.04 & times; 10(4 )W(-1)m(-1) at probe wavelengths lambda(p) = 5.105 mu m and 5.051 mu m, respectively. The corresponding dispersion values are D = 1.903 & times; 10(2) ps.nm(-1)m(-1) (for anomalous dispersion) and - 0.382 & times; 10(2) ps.nm(-1)m(-1) (for normal dispersion), respectively. We investigate the generation of a supercontinuum in the system separately for both the dispersion regimes by using a narrow-band Gaussian pulse. In the regime of anomalous dispersion, the broadening of the SC is mainly governed by the nonlinear processes like the self-phase modulation (SPM), the dispersive wave emission and the soliton self-frequency shift. These nonlinearities manifest into a highly modulated spectral profile with a span of around four octaves ( similar to 3-11.5 mu m). However, in the domain of normal dispersion, the SC is dominated by SPM, extending asymmetrically to the higher wavelength side owing to the third-order dispersion. This results in the formation of a smooth and practically flat spectrum, but with a reduced bandwidth of around 3 mu m. Our study highlights the versatility of EIT-assisted nonlinear optical control in SQW systems and refers to their possible use in the development of broadband light sources for spectroscopy, optical communications and the development of integrated photonic devices.
Theoretical investigation of an optical fiber having sine, raised sine, hyperbolic tangent, and Gaussian taper profile-based surface plasmon resonance sensor is presented. The reflectivity is calculated by transfer matrix method at left quarter, central, and the right quarter taper positions for each taper profile. The sensor performance parameter sensitivity, full width half maximum, amplitude dip, signal to noise ratio, and figure of merit are systematically analyzed and compared for each taper profile. The sine taper profile attained maximum sensitivity 16.9 mu m/RIU with 2.47 signal-to-noise ratio at the middle of the taper section. The optimal sensor performance is also achieved for a sine taper profile with FOM values of 37.2 (1/RIU) at 0.3 taper ratio. At last, it is concluded that geometrical perturbations significantly modify the field confinement at each taper position and enhance the figure of merit compared to conventional optical fiber.
In this paper, we theoretically investigate second-harmonic generation driven by random structured pump beams with engineered two-dimensional spatial coherence distributions. Taking a multi-Gaussian correlated Schell-model beam as a representative example, we derive the analytical cross-spectral density of the generated second-harmonic field and analyze its focusing characteristics. The results show that the pump's spatial coherence structure is transferred to the frequency-doubled field through nonlinear interaction, resulting in pronounced intensity self-shaping. The flat-top shaping effect is significantly enhanced by increasing the beam order, decreasing the coherence width, and extending the nonlinear crystal length, demonstrating that coherence-structured nonlinear interaction governs the redistribution of second-harmonic intensity. These findings provide new insight into coherence engineering in nonlinear frequency conversion.
This study investigates the performance of a passively Q-switched (PQS) erbium-doped fiber laser (EDFL) incorporating copper (Cu) and copper oxide (CuO) material as a saturable absorber (SA). The structural and surface properties of the Cu and CuO-SA were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Energy dispersive X-ray spectroscopy (EDS), along with elemental mapping, was utilized to ensure the elemental composition, and Raman spectroscopy was used to investigate the structural properties of CuO material. The modulation depth of the Cu and CuO-SA was systematically investigated using a twin-detector method and was found to be 15.08% for CuO-SA and 8.25% for Cu-SA. The integration of Cu-SA material inside a laser cavity generated a stable pulse operation with a minimum pulse width of 2.4 mu s, a maximum repetition rate of 116kHz, and an average output power of 2.87mW. In contrast, the EDFL based on CuO-SA yielded a minimum pulse width of 1.93 mu s, a repetition rate of 129.9kHz, and an output power of 4.58mW, underscoring the superior efficacy of CuO as an SA material. The long-term stability of Cu/CuO-SA-based EDFL was measured by continuously monitoring the pulse width for a period of 4h. Finally, the band structure and optical characteristics of CuO were thoroughly examined by DFT computations that confirmed the CuO-SA's potential as an efficient SA in EDFL. These findings demonstrate that CuO-based SA significantly outperform Cu-based counterparts, establishing CuO as an efficient material for enhancing the performance of PQS-EDFL, making it a promising candidate for fiber laser applications.
The hasty progression in telecommunication industry on the route to the sixth generation (6G) introduces stringent necessities for durable photonic fronthaul communication networks. In this study, a photonic 100-Gbps centered passive optical network (100G-PON) transmission approach is presented for 6G fronthaul that leverages millimeter wave. A progressive digital procedure Dual-Polarization 16-Quadrature Amplitude Modulation (DP-16-QAM) is used to strengthen 6G fronthaul performance twice under dense collision whereas, heterodyne technique is employed via signal synthesis to generate 160GHz. The outcomes are observed in an optical band analyzer to validate the sub-THz spectrum, error vector magnitude (EVM), Q-factor and diminish the phase error rate for X-Y polarizer.
Spectral broadening in multi-pass cells (MPC) enables post-compression of high-energy femtosecond pulses, while structured optical pulses carrying orbital angular momentum are additionally limited by spatiotemporal coupling during nonlinear propagation. Here, we investigate the nonlinear evolution and compression of Laguerre-Gaussian pulses in an MPC under different initial amplitude and phase perturbations using a unified propagation model. We show that spectral uniformity and compression quality are weakly affected by transverse amplitude modulation but are strongly degraded by initial nonlinear phase distortions. The compression limit is governed not by the nonlinear phase magnitude itself, but predominantly by frequency-dependent wavefront distortions quantified by the spatiotemporal Strehl ratio. These results establish clear physical criteria for high-fidelity post-compression of structured ultrafast pulses.
A passively Q-switched single-frequency orange-yellow pulsed laser at 593nm is demonstrated using an LD-pumped Nd:YVO4 crystal to generate simultaneous dual-fundamental waves at 1064nm and 1342nm. A Ti3C2Tx film (modulation depth 7.24%) serves as the saturable absorber. Intracavity photon densities are balanced at a 1:1 ratio via a Brewster window, while a Fabry-Perot etalon enforces single longitudinal mode operation. Sum-frequency generation in an LBO crystal produces 593nm pulses. At a pump power of 5.8W, the laser delivers an average power of 50.8mW at 525.6kHz, with 36ns pulse width and 6.55MHz Lorentzian optical linewidth. Over 4h, power instability and RMS noise remain below +/- 0.41% and 0.32%, respectively. The combination of Brewster window polarization control, F-P etalon mode selection, and Ti3C2Tx film Q-switching provides a feasible route to stable, low-noise single-frequency orange-yellow pulsed emission.
This work innovatively designs an all-dielectric metasurface fabricated using 3D printing technology with alumina as the substrate material. This metasurface successfully generates vectorial nondiffracting Bessel beams at a specific frequency of 0.1THz. Initially, through comprehensive simulation analysis of the interaction between the metasurface and the incident beam, it was discovered that the metasurface can precisely manipulate the properties of the transmitted beam based on the polarization state of the incident beam. Specifically, when illuminated by a left-handed circularly polarized (LCP) Gaussian beam, the transmitted beam manifests as a radially polarized Bessel beam. Conversely, under right-handed circularly polarized (RCP) Gaussian beam illumination, the transmitted light transforms into an azimuthally polarized Bessel beam. Building upon the theoretical simulations and considering experimental constraints, further experimental validation was conducted using linearly polarized light, confirming the effectiveness and feasibility of the proposed design. Experimental results demonstrate that the presented all-dielectric alumina metasurface, fabricated via 3D printing, successfully achieves the generation of vector nondiffracting Bessel beams. On one hand, the combination of alumina material and 3D printing technology significantly reduces manufacturing costs, laying a foundation for large scale application. On the other hand, leveraging the high precision of 3D printing ensures the accurate fabrication of the metasurface structure, thereby guaranteeing the high quality and stability of the generated vector beams. This work provides a novel approach for the efficient generation of Bessel beams and is expected to have profound implications in the field of terahertz technology.
This work reports the synthesis and characterization of two thermotropic liquid crystals (LCs) derived from Schiff bases of 4-bromophenylpyridyl (IeC8) and 2,4-dibromophenylpyridyl (ILC8), in combination with 4-octyloxybenzoic acid, with a focus on the influence of dibromo substitution on mesophase behavior and electro-optical properties. The compounds were synthesized and purified using established protocols. Phase transition temperatures were determined by differential scanning calorimetry (DSC), while mesophase textures were confirmed using polarized optical microscopy (POM), revealing nematic and smectic phases. Optical properties, including refractive indices, birefringence (Delta n), and optical band gap, were measured using an Abbe refractometer and a modified spectrophotometer. ILC8 consistently exhibited higher birefringence, indicating enhanced molecular ordering and rigidity due to dibromo substitution. Impedance spectroscopy revealed thermally activated charge dynamics, with abrupt changes in relaxation time (tau) and conductance (G) near phase transitions. ILC8 demonstrated moderate dielectric anisotropy (Delta epsilon approximate to 0.40), lower optical conductivity anisotropy, and greater activation energy (E-a approximate to 0.083eV), reflecting improved dipolar alignment and reduced optical losses. These results highlight the role of dibromo substitution in enhancing thermal stability, dielectric anisotropy, and birefringence, positioning ILC8 as a strong candidate for advanced electro-optic and display applications.
Optical Frequency Comb generation using channel waveguides has become a key enabler in integrated photonics. In this work, we report the numerical simulation of an Optical Frequency Comb generation in a 0.04m long Silicon Nitride waveguide with all-normal dispersion. The waveguide structure is optimized to support dual-frequency continuous-wave pumping near 1.55 mu m. A comb spanning 190nm with a 20dB bandwidth and approximately 25 lines is achieved, with a repetition rate of similar to 1 THz. To the best of our knowledge, this single-stage, compact channel waveguide design achieves a broadband frequency comb that outperforms previous studies. The proposed architecture holds significant potential for applications in optical atomic clocks, optical rulers, wavelength-division multiplexing, and precision metrology.
Nonlinear optical spectroscopy has been widely established as a powerful tool for probing interfaces with molecular specificity. However, for buried interfaces, the interfacial response is often obscured by strong bulk radiation when the adjoining media on both sides also exhibit nonlinear optical activity. Using sum-frequency generation (SFG) spectroscopy as an example, we demonstrate a general and experimentally simple strategy to suppress forward-generated bulk contributions from a second-order nonlinear crystal and isolate the buried interfacial response. The key idea is to tune the emission geometry near the Brewster condition at the exit interface, where the p-polarized Fresnel reflection sharply decreases, strongly attenuating the reflected forward-generated bulk field. The residual forward field then interferes destructively with the backward (BW)-generated field, providing additional suppression of the nonresonant bulk background. Experiments on an octadecyltrichlorosilane (OTS) monolayer at a quartz buried interface show that this Brewster-angle suppression reduces the bulk background by similar to two orders of magnitude and enables reliable retrieval of monolayer vibrational features in the C-H stretch region. Angle-dependent analysis further shows that the optimal signal-to-noise ratio (SNR) occurs slightly detuned from the bulk-intensity minimum, consistent with interference-based contrast. This approach enables high-fidelity in situ interrogation of buried interfaces across a broad range of systems and provides a general framework for quantitative analysis of interfaces embedded in complex environments.
We experimentally demonstrate dual- and triple-frequency pulses with controlled repetition frequency difference and signal-to-noise ratio in a carbon nanotube-based fiber laser. A short segment of multimode fiber is added to the resonant cavity to adjust the total cavity dispersion. Based on the principal modes in multimode fiber, the wavelength-multiplexing dual-frequency pulses are obtained with the repetition frequency difference variation from 32Hz to 1kHz. Linear and nonlinear mechanism enables tuned repetition frequency difference in this case. By carefully tailoring linear birefringence in multimode fiber, trip-frequency pulses are emitted. The tuning range for repetition frequency difference is 60Hz to 110Hz, and for signal-to-noise is 26.5dB in the two polarization-multiplexing pulses. This laser will provide a potential technical approach for applications such as versatile dual-comb ranging.
