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• We firstly propose a cascaded Kerr beam self-cleaning scheme that combines multiple MMFs to further improve multimode beam quality. • Radial offset between fiber 1 and fiber 2 of the cascaded multimode fiber system should be as small as possible for cascaded beam self-cleaning. • Our results also suggest that an increased number of HOMs with negligible energy along with a higher number of cascaded fibers contribute to superior multimode beam quality. Spatial beam self-cleaning has shown a nonlinear improvement in beam quality in multimode fibers (MMFs), proving its value in high-power fiber lasers and nonlinear biomedical imaging. In this Letter, we propose a novel cascaded Kerr beam self-cleaning scheme that combines multiple MMFs to further improve beam quality. Through this scheme, the initially speckled beam gradually evolves into a well-defined bell-shaped, primarily dominated by the fundamental mode, after undergoing two or three cascaded self-cleaning processes. Simulation results also suggest that an increased number of high-order modes (HOMs) with negligible energy along with a higher number of cascaded fibers contribute to superior beam quality. This phenomenon is attributed to the new excited HOMs acting as attractor and facilitating an energy cascade towards the fundamental mode. [ABSTRACT FROM AUTHOR]

Highlights • Our fiber curvature sensor has merits of inline compact, low cost and sensitive. • Highly sensitivity −15.33 dB/m−1 in the range 3.63–4.69 m−1 is experimentally demonstrated. • Low cross sensitivity 0.018 m−1/°C implies it is insensitive to environmental temperature change. Abstract An inline fiber structure formed by a silica tube spliced between single-mode fibers has been developed and tested for curvature measurement based on anti-resonant reflecting waveguide. A Fabry-Perot resonator with leaky modes of guided light in the silica tube is formed based on anti-resonant effect in the resonant wavelengths, which results in lossy dips in the transmission spectrum. Since the transmission power of the resonant dips is sensitive to structure bending, an inline curvature sensor can be realized. Experimental results reveal a high sensitivity up to −15.33 dB/m−1 in the wide curvature range of 3.63–4.69 m−1. The proposed sensor also demonstrates a low temperature sensitivity 0.27 dB/°C implying a small temperature cross sensitivity 0.018 m−1/°C. Our sensor has its merits of compact, low cost and high sensitivity. [ABSTRACT FROM AUTHOR]

We theoretically investigate the correlated electron dynamics in strong-field nonsequential double ionization (NSDI) of Ar by the parallel two-color pulses consisting of 800- and 400-nm laser fields with the semiclassical ensemble model. Our calculations show that the momentum distributions of Ar 2+ in the direction parallel to the polarization of laser field exhibit the single- or double-hump structure, depending on the relative phase of the two-color fields. Back analysis of the NSDI trajectories reveals that recollision of returning electron is well confined in a time window of several attoseconds, and the position of which can be controlled with attosecond precision by changing the relative phase of the two-color fields. Thus, the recollision energy is accurately controlled with the two-color fields. As a consequence, the time delay between the double ionization and recollision changes with the relative phase, resulting in the relative-phase-dependent ion momentum distributions. More interestingly, the different peaks of ion momentum spectra result from the NSDI events with different time delays between double ionization and recollision. Thus, the corresponding correlated electron dynamics for different peaks in the ion momentum distributions can be directly determined in the two-color fields. [ABSTRACT FROM AUTHOR]

We investigate the topological interface modes of surface plasmon polaritons in a multilayer system composed of graphene waveguide arrays. The topological interface modes emerge when two topologically distinct graphene multilayer arrays are connected. In such multilayer system, the non-trivial topological interface modes and trivial modes coexist. By tuning the configuration of the graphene multilayer arrays, the associated non-trivial interface modes present robust against structural disorder. The total number of topological modes is related to that of graphene layers in a unit cell of the graphene multilayer array. The results provide a new paradigm for topologically protected plasmonics in the graphene multilayer arrays. The study suggests a promising approach to realize light transport and optical switching on a deep-subwavelength scale. [ABSTRACT FROM AUTHOR]

We propose a dual-chirped optical parametric amplification (DC-OPA) scheme pumped by a broadband laser pulse. The pump pulse is spectrally broadened in a multi-plate system before amplifying the chirped seed in a BBO crystal. The system performance and phase-matching mechanism with different pump bandwidths are investigated thoroughly. It is found that the broadened pump bandwidth benefits the system most effectively when the pump and seed pulses are oppositely chirped. The idler bandwidth is nearly tripled in the broadband pumped system, supporting a transform-limited (TL) duration of 8.4 fs (∼1.3 cycles), meanwhile the energy bandwidth product of the idler is 72.6% higher. Furthermore, the idler wavelength is tunable between 1700 nm and 2050 nm, with sub-1.5-cycle TL duration and over 14% conversion efficiency. The proposed scheme provides a suitable approach for the generation of few-cycle pulses varying from near-infrared to mid-infrared regions. [ABSTRACT FROM AUTHOR]

• Low-cost fiber MI temperature sensor is formed by filling SCF with polymer-UV glue. • High sensitivity is obtained due to the great thermal properties of UV glue. • Our sensor shows advantages of robust, small size, and low cost. • The reflective tip structure enable for remote sensing in practical applications. A low-cost fiber tip temperature sensor is proposed and experimentally demonstrated. It is based on the Michelson interferometer (MI) structure which is partially filled with polymer-UV glue in the suspended core fiber (SCF). Due to the greater thermal properties of UV glue compared with the silica optical fiber, the length of the inner cavity in the MI structure is susceptible to temperature modulation, resulting in the interference wavelength drift. Experimental results show that the sensor achieves a sensitivity of −164 pm/°C in the temperature range of 25–60 °C, and the sensor offers good wavelength and power stability at room temperature. In addition, the sensor has advantages such as robust, small size, and low cost, especially the reflective tip structure is more suitable for remote sensing in practical applications. [ABSTRACT FROM AUTHOR]

• A highly-sensitive pressure sensor with sensitivity of 80.8 pm/kPa. • Low temperature cross sensitivity of 2.2 kPa/°C. • Experimental results in good agreement with the "Two-beam" interference model. • Simple fabrication technique without fiber machining, and possible for mass production. We propose and demonstrate a simple highly-sensitive gas pressure sensor based on harmonic Vernier effect. By fusion splicing two hollow silica capillaries, a cascaded Fabry-Perot (FP) cavity is formed. Without special photonics crystal fibers or laser machining involved, the fabrication process is greatly simplified. The interplay between the two interferometers consisting the FP cavity leads to optical Vernier effect. By properly adjusting the length of the silica capillaries harmonic of optical Vernier effect is observed and can be served as a sensitive probe for diagnosing gas pressure. Our results showed a sensitivity of 80.8 pm/kPa from 1 to 101 kPa with good linearity of 99.7%, and a low temperature cross sensitivity of 2.22 kPa/°C, a factor of three lower than that of the microstructure fiber-based gas pressure sensors. Combining both ease of fabrication and high sensitivity, this sensor can be a good candidate for mass production in fields of gas sensing and environmental safety monitoring. [ABSTRACT FROM AUTHOR]

• Optical fiber temperature sensor based on encapsulated S-taper fiber. • Different taper configurations and filling liquids are investigated. • Maximum sensitivity of −15.66 nm/°C in the range of 28–32 °C was experimentally achieved. • The multimode interference behavior in various external environments was calculated. • The "critical cladding mode" model explained the underline principle for wavelength shift and high sensitivity. We demonstrated a simple technique for a highly sensitive temperature sensor based on an "S"-shape fiber taper Mach-Zehnder interferometer (MZI) with no need of special fibers or micromachining technique using high power lasers. To enhance the sensitivity, an S-shape single mode fiber (SMF) taper was encapsulated in a capillary filled with high thermos-optic coefficient liquid. We experimentally investigated the tuning parameters for the sensor, such as the taper shape, the material of the capillary, and the role of the filling liquid. Our results show a maximum sensitivity of −15.66 nm/°C in a measurement range of 28–32 °C, and −11.88 nm/°C from 25.1 °C to 35 °C for isopropanol sealed in Teflon capillary. The multi-interference model simulation shows that a critical cladding mode is responsible for the high sensitivity. Simple configuration, ease of fabrication, robustness and low cost make it suitable for high sensitivity temperature sensing applications. [ABSTRACT FROM AUTHOR]