The limits on the numerical aperture and diameter of optical elements restrict the propagation distance of a Bessel beam, resulting in finite depth of focus. In this paper, a method is proposed to elongate the focal depth by splicing a Bessel beam with a circular Airy beam, which is respectively excited by left- and right-circularly polarized light with a birefringent dielectric metasurface. Simulation shows that the focal depth of the spliced Bessel beam at the wavelength of 532 nm is 2.56 times that of the original. The lateral resolution satisfies the Rayleigh criterion, and the focal spot remains consistent. This scheme not only breaks the transmission distance limit of a Bessel beam but also provides an alternative way to extend the beam focal depth. This can be applied in micromachining and microscopic imaging.

The structure of double gain arms is the typical arrangement for Mamyshev oscillators (MOs), which is complex and costly compared with common mode-locking cavities. To pursue a simpler structure, single gain-arm MOs attract researchers. Realizing a single gain-arm structure in erbium (Er)-doped MOs encounters difficulties due to the intrinsic dispersion properties of silica fiber at 1.55 μm. Here, by utilizing a broadband band-pass filter in the cavity structure, we numerically and experimentally demonstrate an all-fiber Er-doped MO with a single gain arm. This single gain-arm Er-doped MO has a low mode-locking threshold and delivers a maximum output power of ∼16.68 mW corresponding to a pulse energy of ∼2.27 nJ. The mode-locking pulses with a repetition rate of ∼7.36 MHz have a pulse duration of ∼113  fs. We believe our work opens a way to achieve a single gain-arm Er-doped MO, which is attractive for practical applications.

Phosphors with emission in the second near-infrared (NIR) bio-window (1000 nm-1700 nm) have promising applications in bio-imaging, food quality analysis, and nondestructive examination. However, developing an efficient NIR phosphor in this emission range is a significant challenge. Herein, we report a perovskite-like LiMgSbO:Ni phosphor, which exhibits a broadband NIR emission peaking at 1380 nm and a full width at half maximum (FWHM) of 281 nm under near-ultraviolet 395 nm excitation. The optimized sample, LiMgSbO:0.015Ni, demonstrates a rarely high internal quantum efficiency (IQE = 87.1%). Furthermore, multifunctional applications of the fabricated device were realized, demonstrating the excellent practicability of this material.

In this Letter, we report mode-locking operation of a red-diode-pumped Er/Dy codoped fluoride fiber laser at >3 μm, for what we believe is the first time, by employing an InAs/GaSb Type-II superlattice semiconductor saturable absorber mirror. At the free-running wavelength of 3447.9 nm, picosecond pulses with a repetition rate of 17.03 MHz and a temporal width of 4.2 ps have been achieved, yielding a maximum energy of 10.2 nJ with a corresponding peak power of 2.3 kW. Attributable to the wideband feature stemming from the combination effect of Er (F→I) and Dy (H →H) transitions, the wavelength of picosecond pulses can be tuned from 3046.9 to 3644.8 nm, where the ∼600 nm span is the widest level of mid-infrared (MIR) mode-locked fluoride fiber lasers, to the best of our knowledge. These results provide the new opportunity for wideband picosecond pulse generation in the MIR.

Due to their potential as excellent dual-comb light sources, the dynamics of dual-color solitons within a single cavity have garnered widespread attention. In this work, we constructed a single-cavity ytterbium-doped passively mode-locked fiber laser (MLFL). By utilizing the birefringent filtering effect, dual-color solitons were successfully generated, and both collision and oscillatory dynamics of the dual-color solitons were observed. Using time-stretched dispersive Fourier transform (DFT), we revealed the details of these two distinct dynamical behaviors. We verified through numerical simulations that by adjusting the modulation depth and bandwidth of the filtering effect, it is possible to switch between the two distinct soliton dynamics behaviors. We believe that our research will contribute to the development of single-cavity dual-comb light sources and the exploration of nonlinear dynamics.

We present the first Kerr-lens mode-locked solid-state laser based on ytterbium-doped monoclinic magnesium monotungstate as an active medium. The diode-pumped Yb:MgWO laser delivers soliton pulses as short as 32 fs at 1079 nm with a pulse repetition rate of ∼68 MHz via soft-aperture Kerr-lens mode-locking. To the best of our knowledge, these are the shortest pulses ever achieved from any ytterbium-doped tungstate crystals.

The generation of high-performance pulses in the 2 μm wavelength range has been widely considered. A Mamyshev oscillator featuring cascaded spectral broadening and offset spectral filtering is an excellent platform for generating high-energy femtosecond pulses. In order to make up for the shortcomings of complex structure and unsuitability for practical use, in this Letter, we present an experimental investigation of an all-fiber thulium-doped Mamyshev oscillator that enables self-starting operation and generates high-performance pulses. The oscillator emits pulses with energy of up to 7.5 nJ, which can be compressed to 350 fs. Furthermore, we investigate the nonlinear dynamics of the multi-pulse state, such as soliton molecules and high-order harmonic mode-locking. The oscillator generates 130th order harmonic mode-locking that corresponds to the repetition rate of 588 MHz, and the signal-to-noise ratio exceeds 60 dB.

We introduce a method that synergistically combines the distinct phase noise profiles of a dielectric resonator oscillator (DRO) and bichromatic Brillouin laser oscillator (BBLO), for high spectral purity microwave generation. Typically, free-running DROs exhibit high-phase noise at low-frequency offsets but ultra-low-phase noise at high offsets. In contrast, BBLOs based on photonic devices demonstrate very low-phase noise at low offsets, yet they experience increased phase noise at higher offsets due to photodetector shot noise. By locking the DRO to a frequency-matching BBLO, our experiment combines the merits of both oscillators and generates X-band microwave with exceptional phase noise across the entire frequency offset range, reaching -93 dBc/Hz at 100 Hz offset and -171 dBc/Hz at 10 MHz offset.

A spiral phase filter can perform a radial Hilbert transform (RHT) and is useful in isotropic edge enhancement. For selective edge enhancement, the inclusion of anisotropy warrants the filter to be replaced. In this Letter, we introduce for the first time, to our knowledge, a novel and versatile filter that can be tuned between isotropic/anisotropic edge detection and contrast enhancement protocols. To achieve this, we use a : a special kind of spin-orbit beam that is a superposition of spin and orbital angular momentum states of light. We devised a 4 imaging setup in microscope configuration to encode the object Fourier spectrum into inhomogeneous polarization distribution. The novelty and advantages of the proposed method lie in selecting the spatial frequency content through polarization transformations in the image reconstruction path, just before the detector, without altering the Fourier plane parameters. Considering a scalar-to-vector diffraction approach and invoking the polarization degree of freedom of light, the edge enhancement capabilities of a lemon-star polarization dipole and a monopole (star or lemon) are shown through experiment results.

Bromide-chloride mixed perovskites have garnered significant attention as a direct and efficient material for achieving pure-blue emission. However, the complex problem of halide migration in mixed halide perovskites presents a significant obstacle to achieving stable electroluminescence (EL) spectra. Here, we investigate the mechanism of partially replacing the B-site Pb with the non-toxic Sr to achieve pure-blue emission based on first principles. The ion mobility activation energy of Sr is 1.23 eV, which is an order of magnitude greater than that of halogens. Meanwhile, the incorporation of Sr triples the activation energy for halogen migration. Furthermore, the halide defect formation energy increases from 4.75 eV to 5.62 eV, thereby reducing ion migration channels. Transient absorption spectroscopy demonstrates that suppressing the ion mobility pathway and enhancing ion mobility activation energy promotes the perovskite film to exhibit excellent spectral stability under laser pumping. Our work provides insights for the development of highly stable and eco-friendly perovskite devices.

The pumping mechanism based on the cross-phase modulation (XPM) effect can achieve a flat broadband supercontinuum (SC) output. In this paper, we demonstrate a novel, to the best of our knowledge, scheme for SC generation from a large mode area (LMA) erbium-ytterbium co-doped fiber (EYDF) amplifier based on this XPM effect by utilizing both the gain and dispersion characteristics of the EYDF, achieving a hundred-watt-level flat broadband SC output. The scheme consists of two pulsed lasers with a synchronized trigger signal and a LMA-EYDF amplifier. In order to enhance the XPM effect effectively, the central wavelengths of two pulsed lasers are selected as 1030 nm and 1535 nm according to the calculated group velocity curve of the passive fiber in the EYDF amplifier. The output powers of 1030 nm and 1535 nm pulses are scaled to 58 W and 131 W after the EYDF, where the dual-wavelength is first amplified and the output power is the highest level in the 1 µm/1.5 µm dual-wavelength lasers reported so far. After the dual-wavelength lasers undergo the nonlinear accumulation in the EYDF amplifier, the final SC with a spectrum spanning the 770 nm-2055 nm at -10 dB level excluding the residual pump peak is achieved and an output power of 104 W is obtained. This is the widest spectral bandwidth at -10 dB level and the highest output power in the reported SC generation from an EYDF amplifier. This work provides a common platform to generate a high-power flat broadband SC independent of fiber design, further promoting the development of LMA fiber-based SC sources.

Fiber lasers operating in the 900 nm wavelength band have garnered significant interest due to their extensive array of applications. However, their development is still hindered by various factors, with the output power currently being restricted to the hundred-watt level. Despite numerous proposed solutions, achieving higher power outputs in this wavelength band remains a challenge. In this Letter, we have pioneered a new approach that harnesses stimulated Raman scattering within a fiber nonlinear gain framework. We have engineered a high-brightness laser diode source by utilizing techniques such as spectral beam combining and polarization beam combining, which are then employed directly for pumping. Through meticulous optimization of the fiber laser system and by incorporating brightness enhancement strategies such as multimode fiber beam cleaning and resonant cavity spatial mode selection, we have achieved a record-breaking output power of 315 W with an outstanding beam quality factor of M = 2.45 for high-brightness fiber lasers at ∼950 nm.

We present a mode decomposition method for multicore fibers (MCFs) that is based on intensity measurements in the far-field. Mode decomposition of several homemade multicore fibers is demonstrated in the far-field with low residual errors. Accurate measurement of supermode compositions and of the electric fields among cores is crucial for many applications involving multicore fibers as well as their integration into multimode platforms.

This publisher's note contains a correction to Opt. Lett.50, 229 (2025)10.1364/OL.547590.

This Letter presents the first-ever, to the best of our knowledge, demonstration of a passive -switched mode-locked (QML) laser with wavelength self-sweeping. QML generation was observed in a figure-of-nine cavity Yb-doped fiber laser. A train of microsecond-long pulses was generated with each pulse consisting of a sequence of nanosecond-long pulses. The duration of the nanosecond-scale pulses was measured to be 3 ns, corresponding to the generation of ∼60 phase-locked longitudinal modes. At the same time, the spectral dynamics was self-induced wavelength sweeping with a sweeping range of up to 5 nm near 1075 nm. The results widen the understanding of the self-sweeping phenomenon and can be useful in applications requiring tunable pulsed radiation.

To address the challenges posed by chromatic dispersion (CD)-induced power fading and nonlinear signal distortions in double-sideband (DSB) intensity modulation and direct detection (IM/DD) transmission systems, a combination of a Volterra feed-forward equalizer (VFFE) and a Volterra decision-feedback equalizer (VDFE) is widely employed. However, the conventional VFFE-VDFE exhibits significant computational complexity, particularly for longer memory lengths. In this Letter, a low-complexity cluster-assisting look-up table-based VDFE (CLUT-VDFE) is proposed to effectively reduce the computational complexity associated with compensating for CD and nonlinear distortions. By utilizing CLUTs, all multiplication operations required for the implementation of the VDFE are completely eliminated. To validate the effectiveness of the proposed CLUT-VDFE, experiments on a C-band 100-Gb/s PAM-4 transmission system over a 60-km standard single-mode fiber (SSMF) are conducted. The experimental results show that the CLUT-VDFE not only achieves comparable equalization performance to the conventional VDFE but also effectively eliminates multiplication operations and significantly saves 48.8% real-valued additions.

In this Letter, we present a binocular chiral metalens (BCM) device designed for four-dimensional (4D) imaging, which integrates both three-dimensional spatial perception and polarization detection. The BCM consists of two identical monocular metalenses that spatially separate left- and right-handed circularly polarized (LCP and RCP) light. When integrated with a commercial camera, the metalenses enable simultaneous measurement of the depth and polarization information. Numerical simulations and experimental results demonstrate that the BCM can achieve a circular polarization extinction ratio (CPER) of 29.2 dB and an average 3D reconstruction error of 4.09%. The proposed system paves a pathway for multi-dimensional imaging, with significant potential in applications in security, surveillance, and future advancements in more complex imaging tasks across other electromagnetic bands, including terahertz and infrared regimes.

We report the first demonstration of an ultra-wide tunable MIR optical parametric amplifier (OPA) based on a new nonlinear crystal, BaHgGeSe (BHGSe). Pumped by a picosecond (ps) 1.064 µm laser, the OPA achieves an unprecedented idler tuning range of 3-14 µm, with pulse energies of 176 µJ at 7.3 µm and 143 µJ at 11.8 µm, and pump to idler conversion efficiency of 2.15 and 1.74%, respectively. The results indicate that the new BHGSe crystal can be an excellent candidate for ultra-wide tuning MIR radiation generation under 1.064 µm laser pumping.

We propose what we believe to be a novel interconnection technique between single-mode fiber (SMF) and nested anti-resonant node-less fiber (NANF), using a coreless fiber (CLF) melted micro-ball lens for mode field matching. The ball lens is fabricated by melting a section of the CLF, while the remaining portion provides an air gap for beam expansion and collimation. Theoretical analysis indicates that this structure exhibits significant dimensional tolerance, enabling efficient mode field matching for NANF with varying mode field diameters (MFDs). Experimental results validate the large fabrication tolerance of interconnection, with coupling loss fluctuations within 0.2 dB across a diffraction length variation of approximately 78 µm. The fabricated SMF-NANF-SMF sample achieves an insertion loss of less than 0.24 dB per interconnection and a return loss below -36 dB attributed to the anti-reflection coating applied to the ball lens. Furthermore, higher-order mode excitation is suppressed to below -45 dB, indicating good mode purity. This interconnection method offers a reliable and versatile solution for NANF-to-SMF integration across various applications.

Dielectric metasurfaces are a promising platform for implementing lasers and sensors. This paper proposes a metasurface operated on a trapped mode that strongly responds to gain-loss perturbations. The metasurface under study is made of dielectric disk-shaped resonators regularly arranged on a thick substrate and covered by a superstrate. The perturbations are caused by the inhomogeneity of the doping of the superstrate or semiconductor disks. The randomized Weierstrass function describes the dielectric properties of an inhomogeneous substance. The presence of inhomogeneity in the constitutive material leads to the appearance of radiative losses, which in turn results in the trapped mode excitation in the metasurface. Thus, the resonance quality factor can be considered as a measure of the inhomogeneity in the doped material.

The Aubry-André-Harper (AAH) model with imaginary periodic or quasiperiodic modulations could regulate the local properties of the system. In this work, we apply the non-Hermitian AAH potential field to the photonic system induced by gain and loss. It is found that the potential field with different parameters will cause the system to exhibit different local properties and induce different localized edge states under the open boundary conditions. Moreover, we investigated the influence of non-Hermitian AAH potential parameters on the edge states of the Haldane model under periodic boundary conditions. It is shown that two-dimensional magnetic photonic crystals can undergo topological transitions and switchable edge states by tuning the potential field parameters. This offers a versatile method for controlling optical flow in photonic platforms.