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The longitudinal relaxation time (T 1 ) of noble gas nuclear spins is a critical parameter for evaluating the performance of an atomic comagnetometer, significantly influencing the signal-to-noise ratio of the system. Traditional measurement techniques, such as the free induction decay method combined with the spin growth technique (FIDSG), are time-consuming for gases with extended T 1 durations, such as 21 Ne, and are prone to substantial environmental variability. Here, we propose the transverse low-frequency square-wave magnetic field modulation (LSMM) method for the rapid measurement of T 1 . The experiment indicates that the LSMM significantly condenses the measurement time to 19.2% of the original, thereby diminishing the robustness demands of the system. Although a minor discrepancy of up to 3 min (or 1.3%) exists between LSMM and FIDSG results, the LSMM method provides strong support for calibrating the performance of comagnetometer cells and conducting various nuclear spin polarization experiments, thereby improving efficiency and reducing energy loss.

We report an all-solid-state near-infrared single-frequency (single longitudinal mode, SLM) Pr 3+ :LiYF4 (Pr:YLF) laser with the spectral linewidth at the sub-picometer level. The SLM lasers with center wavelengths of 868 and 907 nm are realized in Pr:YLF crystal for the first time to the best of our knowledge. The maximum output powers of SLM lasers at 868 and 907 nm are 102  and 213mW, corresponding to the narrowest spectral linewidths of 82 MHz (0.21 pm) and 94 MHz (0.26 pm), respectively. At the maximum output power, the beam quality factors in the x and y directions are measured as 1.25 and 1.16 at 868 nm and 1.21 and 1.13 at 907 nm, respectively. The output power stabilities of the 868 and 907 nm SLM lasers are calculated as 1.39% and 0.87%, respectively. The successful realization of 868 and 907 nm all-solid-state SLM lasers makes up for the gap that the Pr:YLF SLM lasers developed in the past are focused on the visible region, enriches the types of near-infrared (NIR) SLM lasers, and can provide practical applications in biomedicine, cold atom physics, and optical atom manipulation.

Fringe projection profilometry (FPP) faces significant challenges regarding calibration difficulty and stitching error accumulation when operating across scenes ranging from tens to hundreds of meters. This Letter presents a calibration-free 3D measurement method by integrating a binocular vision of a FPP scanner with a wide field-of-view (FoV) vision that constructs global benchmarks to unify local 3D scanning and global 3D stitching, which is adaptable to arbitrarily large-scale scenes. A posterior global optimization model is then established to determine the reconstruction parameters and stitching poses simultaneously at each scanning node with adaptively distributed benchmarks. Consequently, the integrated vision measurement system not only eliminates the large-scale pre-calibration and stitching error accumulation but also overcomes system structural instability during moving measurement. With the proposed method, we achieved 3D measurements with an accuracy of 0.25 mm and a density of 0.5 mm for over 50-m-long scenes.

We report a high-performance wavelength-switchable near-infrared Pr 3+ :LiYF 4 (Pr:YLF) laser by InGaN laser diode (LD) pumping. The 895, 922, and 924 nm lasers with low emission cross sections in the Pr:YLF crystal have been successfully realized using a birefringent filter Lyot as well as designing and optimizing optical thin films and the laser resonant cavity. The maximum output powers of the 895, 922, and 924 nm lasers are 2.01, 1.92, and 1.95 W, respectively. As far as we know, these are the highest power for Pr:YLF lasers at 895, 922, and 924 nm so far. The beam quality M x 2 and M y 2 factors are measured to be 1.85 and 1.71 at 895 nm, 1.94 and 1.67 at 922 nm, and 1.76 and 1.60 at 924 nm, respectively. The laser output power fluctuates within ±3%. In addition, the transmittance of the Lyot is theoretically calculated to achieve laser wavelength switching. The successful realization of the wavelength-switchable watt-level continuous wave near-infrared Pr:YLF laser can provide many practical applications in biomedicine and other fields.

Praseodymium (Pr) lasers have achieved outstanding pico- and sub-picosecond pulsations covering the near-infrared (NIR) and visible spectral range in recent years. However, it has been a stagnant task for more than two decades to leapfrog into the sub-100 femtosecond (fs) regime as the Pr gain bandwidths are too narrow for their major transition lines. Although the wide tunability at the NIR bands in the Pr:YLF crystals has been explored, the spectral tails in these transitions suffer severely from weak gains for mode locking, combined with the intricate dispersion control to achieve transform-limit formation. In this work, we target the Pr:YLF's 895-nm line with a specially designed edge-pass filter to balance the gain bandwidth and transitional strength. By deploying a symmetric dispersion scheme and tuning with the soft actor-critic artificial intelligence (AI) algorithm, we have achieved the pulse duration down to sub-100-fs in a Pr laser for the first time. This work also enriches the AI-assisted methodology for ultrafast solid-state laser realizations.

Diffractive lenses are popular in large optical systems owing to their lightweight and multifunctional design. However, they are difficult to calibrate accurately due to the cross talk between the first-order diffraction and the background light. Here, a quadriwave lateral shearing interferometry (QWLSI) with spherical wave illumination was proposed to absolutely measure the focusing properties of diffractive lenses by means of the reference background light, in which the corresponding theoretical modeling was first derived, and then the single-shot experiment on a 210 mm-diameter beam was carried out. The results showed that the measurement error of the focal length was 0.59 % , and the consistency error was 0.008 % .

Optical metasurfaces have shown great potential for revolutionizing wave plates by enabling compact footprints and diversified functionalities. However, most metasurface wave plates (meta-WPs) are typically passive, featuring defined responses after fabrication, whereas dynamic meta-WPs have so far often been limited to ON and OFF states. Here, we design a dynamic dual-functional meta-WP based on judiciously designed low-loss Sb 2 Se 3 meta-molecules at the telecom wavelength of 1.55 µm which enables reconfigurable linear-to-circular and linear-to-linear polarization conversion for orthogonal linear polarizations when Sb 2 Se 3 transits between amorphous and crystalline states. In addition, a comprehensive electro-thermal simulation is carried out to verify the phase change process for realistic implementation. The designed dynamic dual-functional wave plate may open new avenues for developing integrated adaptive photonics with dynamic and multiplexed functionalities.

To date, lasing in the visible to near-infrared wavelengths has been studied for praseodymium-doped fluoride fibers with the upper energy level of 3 P 0 . In this Letter, a fiber laser operating at 1015 nm has been realized for the first time, to the best of our knowledge, which confirms a new mechanism where 1 D 2 can be the upper energy level. A maximum output power of 241 mW, with a slope efficiency of 30%, was achieved by using a 150-cm-long active fiber pumped at a maximum pump power of 823 mW. Furthermore, the broad emission spectra of Pr 3+ -doped fibers in the near-infrared band have been exploited as new, to the best of our knowledge, spectral sources.

We demonstrate a free-space optical communication link with an optical transmitter that harvests naturally occurring Planck radiation from a warm body and modulates the emitted intensity. The transmitter exploits an electro-thermo-optic effect in a multilayer graphene device that electrically controls the surface emissivity of the device resulting in control of the intensity of the emitted Planck radiation. We design an amplitude-modulated optical communication scheme and provide a link budget for communications data rate and range based on our experimental electro-optic characterization of the transmitter. Finally, we present an experimental demonstration achieving error-free communications at 100 bits per second over laboratory scales.

Ultrafast lasers in the true-green spectrum, which are scarce due to the "green gap" in semiconductor materials, are in high demand for the surging field of biomedical photonics. One ideal candidate for efficient green lasing is Ho:ZBLAN fiber, as ZBLAN-hosted fibers have already reached picosecond dissipative soliton resonance (DSR) in the yellow. When attempting to push the DSR mode locking further into the green, traditional manual cavity tuning is faced with extreme difficulty, as the emission regime for these fiber lasers is so deeply concealed. Breakthroughs in artificial intelligence (AI), however, provide the opportunity to fulfill the task in a fully automated manner. This work, inspired by the emerging twin delayed deep deterministic policy gradient (TD3) algorithm, represents the first application, to the best of our knowledge, of the TD3 AI algorithm to generate picosecond emissions at the unprecedented true-green wavelength of ∼545 nm. The study thus extends the ongoing AI technique further into the ultrafast photonics region.

We demonstrate for the first time, to the best of our knowledge, the fabrication of a high-quality fiber Bragg grating (FBG) in ZBLAN fiber by using an efficient femtosecond laser point-by-point technology. Two types of FBG, e.g., high coupling coefficient and narrow bandwidth grating, are successfully obtained. The coupling coefficient is strongly dependent on the grating order and pulse energy. A second-order FBG with an ultrahigh coupling coefficient of 325 m -1 and reflectivity of 97.8% is inscribed in the ZBLAN fiber. A pair of FBGs with a narrow FWHM of 0.30 and 0.09 nm are also demonstrated.

High-power red lasers (mainly at 639 and 670 nm) based on Pr 3+ :YLF crystals have been presented in many works. However, the spectral resources of Pr 3+ :YLF in the red region have not been fully developed to obtain lasers due to their relatively low emission cross sections and the irrepressible strong emission at ∼639 nm. In this work, we propose a scheme to further develop the spectral resources of Pr 3+ :YLF in the red region and improve the red laser powers based on this crystal. The laser wavelengths are obtained from 634.5 to 674.7 nm (continuous tunings are achieved at some wavebands). To the best of our knowledge, the output powers obtained at 638.7, 644.6, 670.1, and 674.7 nm (2.88 W, 1.87 W, 3.55 W, and 1.73 W, respectively) are the highest to date. Furthermore, lasing originating from the 3 P 2 energy level of Pr 3+ :YLF (∼653 nm) is realized for the first time.

Ultrafast yellow lasers are in high demand in recent biomedical and medical applications; however, direct emission of mode-locked pulses in yellow at the high-power level still presents a huge technical challenge to date. By integrating the nonlinear polarization rotation (NPR) scheme into a Dy:ZBLAN fiber laser, dissipative soliton resonance pulses at ∼575 nm are demonstrated for the first time, to the best of our knowledge. The average output power reaches ∼240 mW at maximum, which is an improvement of almost two orders of magnitude over those reported from the latest mode-locked visible fiber lasers. The laser scheme combines a piece of large-core Dy:ZBLAN gain fiber and free-space NPR components designated at the yellow bandwidth. The maximal pulse energy is 2.4 nJ at the repetition rate of ∼100 MHz and the minimal pulse duration is 83 ps. The achieved wavelength of 575 nm is the shortest ever reached from a fiber-based mode-locked laser to date.

Localized tilted fiber Bragg gratings (TFBGs) with low insertion loss are reported. A series of second-order TFBGs with tilt angles of 0°, 7°, 14°, and 21° was inscribed line by line directly in a single-mode fiber. For the 7° TFBG, the Bragg resonance was 2.4 dB at 1550 nm, and the maximum cladding-mode resonance reached 24.6 dB with an insertion loss of 0.8 dB, the same level as that for TFBGs fabricated by the phase-mask method. The range in cladding-mode resonance for the TFBGs obtained was wider than 170 nm with an intensity exceeding 20 dB. Combined with microscope images, the formation of these localized TFBGs and their spectral performance are discussed. The effect of an inscription offset along the $y$-axis direction was further investigated. With increasing offset, the intensity of the cladding-mode resonance dropped rapidly. The refractive index response sensitivity of the 7° TFBG was measured at 507.54 nm/RIU.

Dynamic self-assembly of micropillars has found wide applications in targeted trapping, micro-crystallization and plasmonic sensing. Yet the efficient fabrication of micropillars array with high flexibility still remains a grand challenge. In this Letter, holographic femtosecond laser multi-foci beams (fs-MFBs) based on a spatial light modulator (SLM) is adopted to efficiently create micropillars array with controllable geometry and spatial distribution by predesigning the computer-generated holograms (CGHs). Based on these micropillars array, diverse hierarchical assemblies are formed under the evaporation-induced capillary force. Moreover, taking advantage of the excellent flexibility and controllability of fs-MFBs, on-demand one-bead-to-one-trap of targeted microspheres at arbitrary position is demonstrated with unprecedentedly high capture efficiency, unfolding their potential applications in the fields of microfluidics and biomedical engineering.

This Letter reports an approach to single-shot three-dimensional (3D) imaging that is combining structured illumination and light-field imaging. The sinusoidal distribution of the radiance in the structured-light field can be processed and transformed to compute the angular variance of the local radiance difference. The angular variance across the depth range exhibits a single-peak distribution trend that can be used to obtain the unambiguous depth. The phase computation that generally requires the acquisition of multi-frame phase-shifting images is no longer mandatory, thus enabling single-shot structured-light-field 3D imaging. The proposed approach was experimentally demonstrated through a dynamic scene.

In this Letter, we demonstrate a laser fabrication strategy that uses the long focal depth femtosecond axilens laser beam to manufacture the high-aspect-ratio (HAR) micropillars and atomic force microscopy (AFM) probes by one-step exposure. The long depth of focus is generated by modulating laser beam focused at different positions. By adjusting the exposure height, the morphology of HAR micropillars can be tuned flexibly, and the micropillar with an ultra-high aspect ratio (diameter of 1.5 µm, height of 102 µm, ${\rm AR}={70}$AR=70) can be fabricated within 10 ms which is a great challenge for other processing methods to obtain such a HAR microstructure in such a short time. In addition, the HAR micropillar is fabricated onto a cantilever to form the AFM probe. The homemade probe shows fine imaging quality. This method greatly improves the processing efficiency while ensuring the fabrication resolution which provides a powerful method for processing HAR microstructures.

This Letter presents a simple temperature-insensitive optical tilt sensor based on a single eccentric-core fiber Bragg grating (ECFBG). By partly inserting an ECFBG into a ceramic ferrule, the reflection spectrum of the ECFBG splits into two peaks as a result of the applied tilt angle. The magnitude and direction of inclination in one dimension can be determined by monitoring the wavelength separation between both peaks, which is inherently insensitive to temperature. The proposed tilt sensor has a good linear response within a wide dynamic range of ±45°, with a sensitivity of 0.012 nm/°, with a resolution of 0.83°, and with an accuracy of 0.41°. Being free from any inherent mechanical joint/friction, along with the advantages of a compact structure, good repeatability, and low cost, the proposed sensor is highly suitable for practical engineering applications.

We report on direct generation of an orthogonally polarized dual-wavelength vortex laser, for the first time to our knowledge, by means of a diode-pumped V-shaped Pr:YLF laser platform. A method of misaligning the folded mirror is proposed to realize the simultaneous orthogonally polarized dual-wavelength laser, while a method of orthogonally rotating the laser gain medium is proposed to generate an intracavity vortex beam (LG 01 mode). With the two methods, in continuous-wave (CW) mode, we have achieved simultaneous lasing of an orthogonally polarized dual-wavelength vortex laser at 604 and 607 nm with maximum output power of 237.7 mW. Moreover, based on this operation, a simultaneous orthogonally polarized dual-wavelength passively Q-switched vortex laser is also realized by inserting a Co:ASL crystal into the laser resonator as a saturable absorber. This work provides the simplest way for direct generation of an orthogonally polarized dual-wavelength vortex laser for potential applications.

In this Letter, the femtosecond laser holographic two-photon polymerization (HTPP) method is adopted to rapidly realize a unique lab-in-a-needle (LIN) device by manufacturing microtube arrays inside a needle. The HTPP method is to modulate a Gaussian beam into a ring Bessel beam by a spatial light modulator (SLM) loaded with a Bessel hologram, and can fabricate microtube arrays with controllable inside diameter (1-10 μm) and designable patterns on such complex three-dimensional (3D) substrates by optimizing experimental parameters. A single LIN device can be processed by this method in about 4 min, which is not possible with traditional micronano technology and is much faster than the traditional two-photon polymerization method (at least several hours). To further demonstrate the functionality of this LIN device, a particle separation experiment is carried out. For the purpose of achieving greater functionality and integration of the on-chip system, this HTPP method provides a powerful processing method for integrating 3D functional microstructures on 3D nonplanar substrates.

We report, to the best of our knowledge, the first demonstration of a wavelength-tunable and highly efficient Dy 3+ -doped fiber laser operating in the yellow spectral region. A 2-m-long Dy 3+ :ZBLAN fiber pumped by a 447-nm GaN laser diode provides a strong down-conversion gain around 575 nm. A fiber end-facet mirror and a visible reflective grating in the Littrow configuration construct the resonant cavity and introduce the wavelength tunability. A stable yellow laser with a <0.05-nm narrow linewidth is achieved and continuously tuned from 568.7 nm to 581.9 nm, covering more than half of the yellow spectral range. The slope efficiency is as high as 34.9%, and the maximum output power is 142 mW at 576.44 nm, which is 13 times higher than previously reported. It is, to the best of our knowledge, the highest power and conversion efficiency of a yellow-light Dy 3+ -doped fiber laser with wavelength tunability.

Ambiguity caused by a wrapped phase is an intrinsic problem in fringe projection-based 3D shape measurement. Among traditional methods for avoiding phase ambiguity, spatial phase unwrapping is sensitive to sensor noise and depth discontinuity, and temporal phase unwrapping requires additional encoding information that leads to an increase of image sequence acquisition time or a reduction of fringe contrast. Here, to the best of our knowledge, we report a novel method of absolute phase unwrapping based on light field imaging. In a recorded light field under structured illumination, i.e., a structured light field, a wrapped phase-encoded field can be retrieved and resampled in diverse image planes associated with several possible fringe orders in a measurement volume. Then, by leveraging phase consistency constraint in the resampled wrapped phase-encoded field, correct fringe orders can be determined to unwrap the wrapped phase without any additional encoding information. Experimental results demonstrated that the proposed method was suitable for accurate and robust absolute phase unwrapping.

This Letter reports a novel method to establish the metric relationship of depth value between object space and image space for unfocused plenoptic cameras. A three-dimensional (3D) measurement system was introduced to precisely construct benchmarks and matching features to compute the metric depths in the object space and the corresponding depth values in the image space for metric calibration. After metric calibration, precise measurement of the depth dimension was possible. Furthermore, with the aid of metric spatio-angular parameters determined via light field ray calibration, transverse dimensions were computed from the measured depth, realizing light field 3D measurement for unfocused plenoptic cameras. Finally, we experimentally performed accuracy analysis of the proposed method with depth measurement precision of 0.5 mm in a depth range of 300 mm, which illuminated potential applications of unfocused plenoptic cameras in the field of 3D measurement.

In this Letter, we present a light field regulation method to form a ring light field with controllable density distribution. This method is to compress the phase modulation depth of Bessel holograms superimposed with blazed gratings and tune the diffraction efficiency of the superimposed holograms by gray scale. The experimental light field generated by the superimposed holograms is consistent with the simulation results. By designing the phase modulation depth of the superimposed holograms with different parameters, ring light fields with suitable intensity distribution are obtained, and the fabrication of ring microstructure with uniform wall thickness is realized. Finally, as a special case of processing, dynamic holographic processing of high-aspect-ratio microtubes with variable diameter and uniform wall thickness is demonstrated.

In this Letter, we demonstrate the observation of colorful Airy beams and Airy imaging of letters, which we called Airy letters here, generated through the continuous cubic phase microplate (CCPP) elaborately fabricated by femtosecond laser two-photon processing. The fabricated CCPP with both micro size (60  μm×60  μm×1.1  μm) and continuous variation of phase shows a good agreement with the designed CCPP. Chromatic Airy beams and Airy letters "USTC" are experimentally generated via the CCPP illuminated by white light. In addition, superior properties of Airy letters are explored, demonstrating that the Airy letters inherit the nondiffraction, self-healing, and transverse acceleration characteristics of Airy beams. Our work paves the way toward integrated optics, light separation, optical imaging, and defective information recovery.

Tm:LuYO 3 ceramic is reported as an effective laser gain medium, for the first time to the best of our knowledge. For continuous-wave laser operation, a maximum output power of 1.55 W with a slope efficiency of 19.9% is achieved at 2050 nm. Passive Q-switching of the Tm:LuYO 3 ceramic is operated using a Cr:ZnSe saturable absorber. Single-wavelength Q-switching at 2047 nm is obtained with a maximum average output power of 0.54 W, a pulse width of 120.3 ns, a pulse energy of 20.5 μJ, and a pulse peak power of 170.6 W. Simultaneous dual-wavelength Q-switching at 1957 and 2047 nm is also attained with corresponding parameter values of 0.92 W, 151.6 ns, 30.2 μJ, and 199.1 W. These results indicate that Tm:LuYO 3 ceramic lasers could be a promising laser source operating in the eye-safe spectral region.

Owing to the distinguishing properties of nondiffraction, self-healing, and transverse acceleration, Airy beams have attracted much attention in the past decade. To date, a simple approach for exquisitely fabricating cubic phase plates with both continuous variation of phase and micro size still remains challenging, which limits the generation of high-quality Airy beams for integrated micro-optics. Here, we report the elaborate design and fabrication of a continuous cubic phase microplate (CCPP) for generating high-quality Airy beams in micrometer scale. A CCPP with a precise size (60  μm×60  μm×1.1  μm) is fabricated by femtosecond laser direct writing, exhibiting a high optical efficiency (∼79%). The high-quality Airy beam generated via the CCPP demonstrates an unprecedentedly strong deflection (∼4.2  μm within a 90 μm propagation distance) as well as being diffraction-free. Our research on the design and fabrication of miniature Airy phase plates paves the way toward high-performance integrated optics, optical micromanipulation, and optical imaging.

Stimulated Brillouin scattering (SBS) in a microcavity is usually realized by employing a wavelength tunable external cavity diode laser (TECDL) as the pump source. In this Letter, we report the observation of SBS in a high Q microcavity based on a TECDL-free scheme. The microcavity is employed as a mode-reflecting mirror for constructing a fiber-ring laser and, simultaneously, pumped by the fiber-ring lasing with intrinsic resonance latching. Several regimes are observed in a microcavity with a diameter of ∼215  μm, such as single lasing pumped SBS and multiple regular lasing pumped SBSs (single or cascaded). The microwave signals from the beat notes of the composite output lasing are measured with full-width at half-maximum on the scale of kilohertz at ∼11 and ∼22  GHz, indicating the high coherence between the pump and the Brillouin lasing.

We experimentally demonstrated a compact single-wall carbon-nanotube (SWNT)-based deep-red passively Q-switched Pr 3+ -doped ZBLAN all-fiber laser operating at 716 nm. A free-standing SWNT/polyvinyl alcohol composite film embedded between a pair of fiber connectors was employed as a saturable absorber (SA). The deep-red Q-switched operation is attributed to the combination of implementing a pair of fiber end-facet mirrors to achieve the linear laser resonator and incorporating a SWNT-SA into the cavity as a Q-switcher. Stable short-pulse generation with a duration of 2.3 μs was realized. When gradually increasing the incident pump power, the pulse repetition rate can be linearly tuned from 32.6 to 86.5 kHz, corresponding to a maximum average output power of 1.5 mW and the highest single-pulse energy of 18.3 nJ. To the best of our knowledge, this is the first demonstration of SWNT-based SA for a Q-switched laser at a deep-red wavelength ∼716  nm.

Mode-locked pulses in the dissipative soliton resonance (DSR) regime enable extremely high pulse energy, but typically have the limited peak power of <100  W and a nanosecond-long pulse duration. In this Letter, we demonstrate high-peak-power, ultrashort DSR pulses in a compact Er:Yb co-doped double-clad fiber laser. The linear cavity is simply formed by two fiber loop mirrors (FLMs) using a 50/50 optical coupler (OC) and a 5/95 OC. The 5/95 FLM with a short loop length of 3 m is not only used as the output mirror, but also acts as a nonlinear optical loop mirror for initiating high-peak-power DSR. In particular, the mode-locked laser can deliver ∼100  ps DSR pulses with a maximum average power of 1.2 W and a peak power as high as ∼700  W. This is, to the best of our knowledge, the highest peak power of DSR pulses obtained in mode-locked fiber lasers.

We propose and experimentally demonstrate a simple scheme for generating optical frequency combs (OFCs) in a fiber-ring/microresonator laser system. The ultrahigh Q whispering gallery mode microresonator is employed both as a mode reflection mirror to generate erbium lasing and as a Kerr-nonlinearity initiator that introduces optical parametric oscillation signals to form OFCs. By controlling the coupling position between the fiber taper and microresonator, optimizing the fiber polarization, as well as the pump power from a 974 nm laser diode (LD), versatile OFCs can be tuned out from single-wavelength states. The OFCs have single, multiple, or combined free spectral ranges. In addition, a Raman-gain-assisted OFC is also observed with a bandwidth of ∼230  nm. This LD-pumped and multifunctional laser system could find applications in precision spectroscopy, biochemical sensing, and optical fiber communication systems.

We report the demonstration of a compact self-Q-switched green upconversion Er 3+ :ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF (ZBLAN) fiber laser operating at 543.4 nm. The all-fiber green laser simply consists of a 45 cm high-concentration Er 3+ :ZBLAN fiber, a 976 nm pump source, and a pair of fiber end-facet mirrors. Under the strong excitation of the 976 nm pump laser, green upconversion lasing at 543.4 nm is achieved from the compact Er 3+ :ZBLAN fiber laser. Interestingly, the green laser exhibits stable self-Q-switching operation. As the 976 nm pump power is increased, the pulse repetition rate linearly increases from 25.9 to 50.8 kHz and the pulse width narrows from 7.2 to 1.95 μs. The Q-switched green laser has a pump threshold of 118 mW and a maximum output power of 6.9 mW with a slope efficiency of 30%. This is, to the best of our knowledge, the shortest-wavelength operation of a self-started or passively Q-switched fiber laser.

We experimentally demonstrate an ultralow-threshold cascaded Brillouin microlaser for tunable microwave generation in a high-Q silica microsphere resonator. The threshold of the Brillouin microlaser is as low as 8 μW, which is close to the theoretical prediction. Moreover, the fifth-order Stokes line with a frequency shift up to 55 GHz is achieved with a coupled pump power of less than 0.6 mW. Benefiting from resonant wavelength shifts driven by thermal dynamics in the microsphere, we further realized tunable microwave signals with tuning ranges of 40 MHz at an 11 GHz band and 20 MHz at a 22 GHz band. To the best of our knowledge, it was the first attempt for tunable microwave source based on the whispering-gallery-mode Brillouin microlaser. Such a tunable microwave source from a cascaded Brillouin microlaser could find significant applications in aerospace, communication engineering, and metrology.

We present here the first broadband-tunable CW laser operation of a Pr(3+)-doped LiYF(4) crystal in the 900-nm spectral range after pumping with an optically pumped semiconductor laser at 479 nm. It is confirmed that the entire emission band can be assigned to the same set of thermalized emitting levels (I(6)1,P3(0,1)). It is also demonstrated that laser performance could be improved up to laser slope efficiencies of about 33% with threshold absorbed pump powers not exceeding 100 mW.

We report the generation of 2.06 W average-power and 232 nJ picosecond mode-locked pulses directly from an ultra-simple Yb-doped fiber laser. A section of Yb-doped double-clad fiber pumped by a 976 nm laser diode provides the large gain, and the linear cavity is simply formed by a 1064 nm highly reflective fiber Bragg grating and a fiber loop mirror (FLM) using a 5/95 optical coupler. The asymmetric FLM not only acts as the output mirror for providing ∼20% optical feedback, but also equivalently behaves as a nonlinear optical loop mirror (NOLM) to initiate the mode-locking operation in this cavity. Stable mode-locking is therefore achieved over a pump power of 3.76 W. The mode-locked pulses show the dissipative soliton resonance (DSR), which has the pulse duration of 695 ps to ∼1  ns, and the almost unchanged peak power of ∼200  W as increasing the pump power. In particular, this laser can emit 232 nJ high-energy DSR pulses with an average output power of >2  W. This is, to the best of our knowledge, the first demonstration of such an ultra-simple, mode-locked fiber laser that enables watt-level, high energy, picosecond DSR pulses.

A novel intermode beating mode-locking (IBML) technique combined with a cascaded Raman process is proposed to mode-lock an O-band two-cascaded Raman fiber laser. Using a 980-m-long phosphosilicate fiber pumped by a 1064 nm laser, the second-order Raman oscillation at 1319 nm is generated by the mixed-cascaded Raman shifts of P2O5 and SiO2. By precisely matching the intermode beating frequencies of the 1064 nm pump laser and the second-order Raman cavity frequency, harmonic mode-locking at 1319 nm is initiated. The dynamic process of the IBML operation in the cascaded Raman laser is experimentally investigated. The 131st-order harmonic mode-locking with a repetition rate of 27.247 MHz is very stable with the radio-frequency (RF) signal-to-noise ratio of >56  dB and the RF supermode-suppression ratio of >43  dB. The mode-locked pulses with the square profile are confirmed as the noise-like pulses by an autocorrelator. The IBML technique, in combination with the cascaded Raman process, could offer an exciting new prospect for obtaining simple, compact, and arbitrary-wavelength mode-locked laser sources.

Photonic nanojet (PNJ) from liquid-filled hollow microcylinder (LFHM) under a liquid immersion condition is numerically investigated based on the finite element method and physically analyzed with ray optics. Simulation and analysis results show that, by simultaneously introducing the immersed liquid and filled liquid, the propagation beam is greatly flattened, and super-long PNJs with decay length more than 100 times the illumination wavelengths are obtained in the outer near-field region of the LFHM. With the variation of the refractive index contrast between the filled and immersed-liquids, the properties of the PNJs, such as the focal distance, decay length, full width at half-maximum, and maximum light intensity can be flexibly tuned.

A method based on thermal bistability for ultralow-threshold microlaser optimization is demonstrated. When sweeping the pump laser frequency across a pump resonance, the dynamic thermal bistability slows down the power variation. The resulting line shape modification enables a real-time monitoring of the laser characteristic. We demonstrate this method for a functionalized microsphere exhibiting a submicrowatt laser threshold. This approach is confirmed by comparing the results with a step-by-step recording in quasi-static thermal conditions.

We demonstrate a compact Q-switched dual-wavelength erbium-doped fiber (EDF) laser based on graphene as a saturable absorber (SA). By optically driven deposition of graphene on a fiber core, the SA is constructed and inserted into a diode-pumped EDF laser cavity. Also benefiting from the strong third-order optical nonlinearity of graphene to suppress the mode competition of EDF, a stable dual-wavelength Q-switching operation has been achieved using a two-reflection peak fiber Bragg grating as the external cavity mirror. The Q-switched EDF laser has a low pump threshold of 6.5 mW at 974 nm and a wide range of pulse-repetition rate from 3.3 to 65.9 kHz. The pulse duration and the pulse energy have been characterized. This is, to the best of our knowledge, the first demonstration of a graphene-based Q-switched laser.

We investigate heat generation in a Nd:YAG thin-disk laser composite with an undoped anti-amplified spontaneous emission (ASE) cap and a side ASE absorber under lasing and nonlasing conditions. The heat load unbalance in three different regions induces a large transverse temperature inhomogeneity under the nonlasing condition. The additional heat fraction generated by the concentration quenching is observed.

A cost-effective fiber optical parametric amplifier (FOPA) based on the laser intracavity pump technique has been proposed and demonstrated experimentally. The parametric process is realized by inserting a 1 km highly nonlinear dispersion-shifted fiber (HNL-DSF) into a fiber ring-laser cavity that consists of a high-power erbium-doped fiber (EDF) amplifier and two highly reflective fiber Bragg gratings. Compared with the conventional parametric pump schemes, the proposed pumping technique is free from a tunable semiconductor laser as the pump source and also the pump phase modulation. When the oscillating power of 530 mW in the EDF laser cavity is achieved to pump the HNL-DSF, a peak parametric gain of 27.5 dB and a net gain over 45 nm are obtained. Moreover, a widely tunable fiber-optic parametric oscillator is further developed using the FOPA as a gain medium.

A novel multiwavelength Raman fiber laser based on the mixed-cascaded Stokes effects of phosphosilicate fiber is proposed and demonstrated experimentally. By using stimulated Raman scattering of both P(2)O(5) and SiO(2) along 1 km phosphosilicate fiber pumped with a 1064 nm double-clad fiber laser, the mixed-cascaded Raman linear cavity is formed by a pair of fiber Bragg gratings at 1239 nm, a polarization-maintaining fiber (PMF) Sagnac loop filter, and a conventional optical loop mirror. Up to 15-wavelength stable oscillations around 1320 nm are obtained with a wavelength spacing of 0.44 nm and power nonuniformity of less than 4 dB. By changing the length of the PMF in the Sagnac loop filter from 10 to 5.5 m, the wavelength spacing is adjustable from 0.44 to 0.8 nm. The extinction ratio of the laser is more than 30 dB. Excellent stability is also observed with a peak power fluctuation of less than 0.8 dB in 1 h.

Ultrafast optical bistability was observed in a planar optical waveguide made with a 2,9,16,23-tetraoctadecanoylamido-substituted vanadyl phthalocyanine-doped polystyrene film. Input-output curves with hysteresis characteristics were measured with laser pulses of 60-ps pulse width at 532 nm. The switchup and switchdown times were less than 10 and 20 ps, respectively. The origin of the nonlinearity giving rise to optical bistability was predominantly electronic effects.