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Two-dimensional layered materials and low-loss, high-quality on-chip functional devices formed by optical waveguides have received widespread attention in the field of integrated photonics. In this work, we demonstrate an electro-optic modulator based on Mach-Zehnder interference (MZI) for the first time, which is integrated with MoS2. The ionic liquid is directly cover the surface of the MoS2-SiN waveguide device to form a capacitor structure Due to the outstanding electro-refractive and electro-absorption properties of MoS2, the phase modulation efficiency obtained by adjusting the voltage on the long and short arms is 445 pm/V, the maximum phase change is 1.14π, the half-wave voltage length product VπL is 0.11 V·cm, and the maximum effective refractive index offset is 2.93 × 10−3 RIU. Notably, we can achieve a wavelength shift of 1780 nm and an electro-optic response bandwidth exceeding 8.5 GHz at voltage saturation. The proposed electro-optic modulator is expected to be applied to low-loss, high-performance large-scale photonic integrated systems.

Demonstration fusion reactor (DEMO) will aim to fulfill the tritium self-sufficiency in fuel recycling and generate economical fusion energy in the future. The tritium breeding blanket is one of the key components inside the vacuum vessel of a fusion reactor. Achieving tritium self-sufficiency is one of the most important goals, which involves whether fusion reactors can achieve fuel cycle and sustained stable operation. Furthermore, the tritium release efficiency is also an important factor affecting the operation of DEMO, which is intimately related to the temperature field inside the breeding blanket. Consequently, the research is focused on the thermal principles of thermal hydraulics in the breeding blanket for the tritium generation process. In this work, a preliminary study considering the blanket structure and the cooling conditions based on a PWR water-cooled blanket was carried out. A neutronics model was established using the Monte Carlo N Particle Transport Code (MCNP) and the nuclear heat distribution in the blanket was analyzed. The nuclear heat is used as the preprocessing data for thermal calculation. The ANSYS code is used to perform the finite element technique analysis on the coolant parameters related to the temperature field, such as the inlet velocity, pipe diameter, pipe spacing, and so on. The breeding blanket met the temperature requirements while also possessing ideal tritium release performance. This work will be beneficial to the DEMO blanket design activities and as a useful reference in the future.

The high-temperature performance of a sapphire fiber Bragg grating (FBG) has been characterized by a commercial single-mode interrogator. By using the mode field matching fusion splicing method, we proposed before, high-order modes in the reflection spectrum of the sapphire FBG could be suppressed and a quasi-single-mode reflection spectrum could be obtained from a single-mode fiber-based demodulation system. A 48-h isothermal annealing at 900 °C and two temperature calibration processes, one up to 800 °C and another up to 1200 °C, were carried out successively. There was no obvious reflectivity decay or wavelength drift during the 900 °C annealing process, and no hysteresis during the two temperature calibration processes. The precisions of the sapphire FBG were ±0.25 °C in the 800 °C calibration process, while increased to ±5 °C in the 1200 °C calibration process.

Spatiotemporal mode-locking (STML) in fiber lasers has attracted significant attention due to its wide scientific and industrial applications, and achieved great progress in the near-infrared wavelength range. Here, we demonstrate both theoretically and experimentally a mid-infrared (MIR) STML laser based on a step-index multimode Er:ZBLAN fiber. The laser adopts a short linear cavity mode-locked by a large-relaxation-time saturable absorber, and generates stable 78.6 ps pulses at 2.79 μm with a repetition rate of 79.8 MHz. Through adjustment of the coupling condition, a wide variety of STML states are observed. Numerical simulations show that the modal dispersion is counteracted by the spatial filtering effect alone. This work provides a simple scheme for MIR fiber lasers to achieve STML, and helps to understand the underlying nonlinear dynamics.

Instead of utilizing commercial detectors and a detection scheme based on 2-D layer semiconductors or surface plasmon enhancement effect, we have developed a novel terahertz (THz) detector consisting of an array of microgrooves. This device combines the exceptional performance of materials with the localized surface plasmon (LSP) effect in a sub-wavelength structure electromagnetic-induced well detector. At room temperature, our device achieves a detectivity ( ${D}^{\ast }$ ) of ${6.3} \times {10}^{{8}}$ cm Hz $^{\text {1/2}}$ pW $^{-{1}}$ and a responsivity (Rv) of ${3.31} \times {10}^{{5}}$ V $\text{W}^{-{1}}$ at 0.1 THz, with a $20 \mu \text{m}$ line spacing array. Furthermore, the effective detection area of our device is $6.5\times2$ mm, making it much more suitable for practical applications. These high-performance THz wave photodetectors open up possibilities for the effective detection of THz waves, which have wide-ranging applications in areas such as high-capacity communications, THz radar, biological diagnosis, and THz detection.

Solving the multimode issue of sapphire fiber is of great significance for improving the performance and extending the application fields of sapphire fiber-based high-temperature sensors. Here, a mode field matching fusion splicing method between sapphire fiber and single-mode fiber was reported to obtain a quasi-single mode reflection spectrum from sapphire fiber Bragg grating (SFBG). By optimizing the splicing parameters, an overlapped double conical (ODC) splicing structure between sapphire fiber and single-mode fiber could be formed. The mode field matching between sapphire fiber and single-mode fiber could be well achieved by this structure, realizing the suppression of high-order modes in the reflection spectrum. A quasi-single mode reflection spectrum from SFBG was obtained based on this method with a full-width at half-maximum of 0.3 nm and a signal-to-noise ratio (SNR) of 8 dB. Further improvement has been made on this fusion splicing method by using pretapered single-mode fiber, and the SNR reached 14 dB. In addition, we combined our SFBG sensor with a commercial single-mode interrogator and achieved real-time temperature monitoring up to 1160 °C.

We have theoretically investigated the polarization-dependent ultrashort pulse amplification in erbium-doped fluoride fibers. The numerical model is based on the coupled generalized nonlinear Schrödinger equations and the rate equations. It is found that the Raman effect can be weakened by converting the seed polarization from linear to circular. Compared with the linearly polarized seed pulses, amplification of the circularly polarized seed pulses can generate Raman solitons with a larger pulse energy of the same central wavelength, although more pump power is needed. Furthermore, the amplification dynamics when no pulse splitting occurs have also been investigated. We demonstrate that amplification of the circularly polarized seed pulses allows the main pulse to accumulate more energy while maintaining a single-pulse profile. It is predicted that sub-two-cycle laser pulses at 2.8 μm with megawatt peak power and hundreds of nanojoules pulse energy can be directly generated from the erbium-doped fluoride fiber amplifiers. The investigations conducted in this article can provide guidelines for the design of Raman-soliton-based tunable fiber laser systems and high-power few-cycle fiber laser systems.

Infrared camouflage is an effective technique to avoid many kinds of target detection by detectors in the infrared band. For a high-temperature environment, thermal management of selective emission is crucial to dissipate heat in the mid-infrared non-atmospheric window (5–8 μm). However, it still remains challenges for balancing infrared camouflage and thermal management. Here, we experimentally demonstrate a multilayer film structure (MFS) for infrared camouflage with thermal management. Combining the ideal emission spectrum and genetic algorithm (GA), the inverse-design MFS containing 7 layers of five materials (SiO2, Ge, ZnS, Pt and Au) has been designed. Based on the hierarchical metamaterial, the optimized MFS has high performance of infrared camouflage to against the lidar detection in the near-infrared band. The experimental results reveal the high compatible efficiency among thermal camouflage (ε3–5μm= 0.21, ε8–14μm= 0.16), laser stealth (ε1.06μm= 0.64, ε1.55μm= 0.90, ε10.6μm= 0.76) and thermal management (ε5–8μm= 0.54). Therefore, the proposed MFSs are attractive as basic building block of selective emitter, for the application of advanced photonics such as radiative cooling, infrared camouflage, and thermal emission.

We demonstrated all-fiber mid-infrared enhanced supercontinuum generation in an Erbium-doped ZBLAN fiber amplifier. A 2 μm low repetition rate noise like-pulse mode-locked fiber laser was adopted as the pulse seed for the system. After amplified in a Thulium-doped fiber amplifier, the noise like-pulse generated a supercontinuum covering the range from ∼2 μm to ∼3.8 μm in a piece of InF3 fiber. Then, the supercontinuum was injected into an Erbium-doped ZBLAN fiber amplifier as the seed for the next stage in-amplifier mid-infrared enhanced supercontinuum generation. A novel silica-fluoride fiber pump combiner was designed and fabricated to couple the 976 nm LD pump laser into the Erbium-doped ZBLAN fiber. The supercontinuum laser source realized mid-infrared enhancement and power boosting beyond 2.7 μm in the Erbium-doped ZBLAN fiber amplifier. A ∼1.4 W mid-infrared enhanced SC with long wavelength edge of ∼4200 nm and 97% power beyond 2.7 μm was obtained. This simple and compact all-fiber supercontinuum laser source has a great potential application in the 3–5 μm molecular fingerprint region.

We propose a novel nodeless conjoined-tube hollow-core fiber (CT-HCF) with elliptical arcs as negative curvature boundaries to limit the leakage of transmitted light. The cladding nodes are effectively eliminated by the attachment of arcs to the outermost dielectric tube. Numerical simulations performed using the full-vector finite element method show that a significant reduction in fiber loss over a wide bandwidth can be obtained. The confinement losses for the proposed fiber are two orders of magnitude lower than those obtained for a typical CT-HCF. The total loss, including confinement loss and surface scattering loss, is also investigated. The proposed fiber shows a loss of less than 0.1 dB/km for a bandwidth of 450 nm, with a minimum loss of 6.58·10−5 dB/m at 1.45 μm. Moreover, the proposed fiber exhibits good single-mode performance, with the higher-order mode extinction ratio reaching a maximum value of 39341 at 1.7 μm.

High-performance terahertz wave detectors at room temperature are still urgently required for a wide range of applications. The available technologies, however, are plagued by low sensitivity, narrow spectral bandwidth, complicated structure, and high noise equivalent power (NEP). Here, we have demonstrated a Weyl semimetal surface plasmon-enhanced high-performance terahertz wave detectors which are based on microdisk array deposited WTe2nanofilm epitaxially grown on GaN substrate for room temperature operation. With the microdisk array combined the WTe2layer, strong terahertz wave surface plasmon polaritons can be generated at the WTe2–air interfaces, which results in significant improvement in detecting performance. For the 40 μm diameter microdisk array, a detectivity (D*) of 5.52 × 1012cm Hz1/2pW−1at 0.1 THz is achieved at room temperature. In addition, the responsivity (RA) of 8.78 A W−1is also obtained. Such high-performance millimeter and terahertz wave photodetectors are useful for wide applications such as high capacity communications, walk-through security, biological diagnosis, spectroscopy, and remote sensing.

It is particularly appealing for efficient active terahertz (THz) modulators using photonic structures to enhance light–matter interaction. Here, an optical controlled THz modulator is proposed that combines lead sulfide (PbS) quantum dots with subwavelength metallic split-ring resonators (SRRs) for providing field enhancement. The modulation depth reaches 60.3%, which is approximately 3 times larger than the PbS quantum dots film without SRRs (as reference) in the frequency range of 0.1–1.1 THz. Such significant enhanced THz modulation is mainly due to the local THz field enhancement caused by the SRRs, which is consistent with the simulation result.

We demonstrate a wavelength-tunable, sub-200?fs, and watt-level thulium-doped ultrafast fiber oscillator with a fundamental frequency repetition rate of 509.7?MHz. The wavelength can be tuned between 1918.5?nm and 2031?nm by adjusting the intra-cavity waveplates. When the wavelength is tuned to below 2000?nm, the average output power exceeds 1?W. The oscillator provides a maximum average power of 1.314?W (corresponding to a pulse energy of 2.58?nJ) and a highest peak power of 12.5?kW at 1940?nm. Such a high-power, tunable 2-µm mode-locked fiber laser is an ideal light source candidate for a variety of applications, such as frequency metrology, molecular spectroscopy, and ultrafast pump-probe spectroscopy.

Gradient-based optimization combined with the adjoint method has been demonstrated to be an efficient way to design a nano-structure with a vast number of degrees of freedom. However, most inverse-designed photonic devices are applied as linear photonic devices. Here, we demonstrate the nonlinear optical response in inverse-designed integrated splitters fabricated on a SiN platform. The splitting ratio is tunable under different incident powers. The thermo-optical effect can be used as an effective approach for adjusting the nonlinear optical response threshold and modulation depth of the device. These promising results indicate the great potential of inverse-designed photonic devices in nonlinear optics and optical communications.

We demonstrate a low-power, compact micro-ring phase shifter based on hybrid integration with atomically thin two-dimensional layered materials, and experimentally establish a low-loss silicon nitride platform. Using a wet transfer method, a large-area few-layer MoS_2 film is hybrid integrated with a micro-ring phase shifter, leading to a tuning efficiency of 5.8 pm V^−1 at a center wavelength of 1545.294?nm and a half-wave-voltage-length product as low as 0.09?V cm. Our device is designed to provide a hybrid-integration-based active phase modulation scheme for integrated optical communication networks with large-cross-section silicon nitride waveguides.

We report a compact, self-starting dispersion-managed mode-locked thulium-doped fiber oscillator that delivers 2.6 nJ pulses at 2 µm with a repetition rate of 250 MHz. The average output power and spectral bandwidth of the pulses reach impressive values of 648 mW and 103 nm, respectively. The generated pulses are near linearly chirped, capable of linearly compressing to 74 fs in a normal dispersion fiber after power attenuation. Using a nonlinear fiber compression scheme can even compress the pulses to 29 fs (4.3-cycle). The remaining pulse energy is 1.15 nJ, and the corresponding peak power is estimated as 39.4 kW. To the best of our knowledge, this is the first demonstration of nonlinearly compressing the pulse of a 2 µm fiber oscillator to the sub-5 cycle regime. Such a few-cycle fiber laser could be an ideal candidate source for short-wavelength mid-infrared frequency metrology and molecular spectroscopy applications.

The generation of square-wave pulses in a 1/1.5-µm dual-band mode-locked fiber laser is experimentally demonstrated. The laser is based upon a peculiar “figure-θ” architecture that exploits a single active fiber to realize dual-band operation. High-energy square-wave pulses are simultaneously generated in both the 1-µm and the 1.5-µm spectral band using the laser. The 1-µm pulse maintains wave-breaking-free operation during the increase of the pump power and finally achieves energy as high as 88.6 nJ, while the 1.5-µm pulse achieves energy up to 1.5 µJ before it ultimately collapses into second-order mode locking. To the best of our knowledge, this is the first report on the formation of square-wave pulses in dual-band mode-locked fiber lasers.

A Q-switched Er:ZBLAN fiber laser operating at 2.8 µm was realized by employing Sb as the saturable material. The Sb material was deposited on a gold mirror by the magnetron-sputtering deposition method to develop a saturable absorber mirror (SAM). By employing the Sb-SAM in an Er:ZBLAN fiber laser, stable Q-switching operation was achieved at central wavelength of 2799.7 nm with the repetition rates ranging from 33.3 to 58.8 kHz and the pulse duration ranging from 5.7 to 1.7 µs. The Sb-SAM still works stably under the maximum pump power of 5.6 W, with an output power of 59 mW corresponding to the pulse energy of 1.03 µJ. To our knowledge, this was the first demonstration of Sb-based saturable material in Er:ZBLAN fiber laser for mid-infrared Q-switched pulse generation operating in the 2.8 µm regime, indicating its potential applications in the mid-infrared waveband.

We demonstrate a compact, self-starting mode-locked thulium-doped fiber laser based on nonlinear polarization evolution (NPE), with a fundamental repetition rate of ∼344MHz and a pulse duration of ∼160fs. The generated pulses centered at ∼1975nm have a maximum output power of ∼560mW, corresponding to a pulse energy of ∼1.63nJ. To the best of our knowledge, the achieved repetition rate represents the highest value of fundamentally NPE mode-locked fiber lasers at ∼2µm, while the average output power is also higher than the previously reported 2 µm ultrafast single-mode fiber oscillators. The timing jitter in the integrated range [5 kHz, 10 MHz] and the integrated relative intensity noise in the range [10 Hz, 10 MHz] reach ∼35fs and ∼0.009%, respectively. Our high-performance laser is an ideal candidate for various applications, including mid-infrared frequency metrology and high-speed optical sampling.

A passively mode-locked thulium-doped fiber laser using a tungsten ditelluride saturable absorber (${{\rm WTe}_2}\mbox{-}{\rm SA}$WTe_2-SA) is demonstrated. High-power mode-locked pulses with an average output power of 108.1 mW were achieved by incorporating the ${{\rm WTe}_2}\mbox{-}{\rm SA}$WTe_2-SA into a thulium-doped fiber oscillator. To the best of our knowledge, this is the highest average power obtained from a ${{\rm WTe}_2}\mbox{-}{\rm SA}$WTe_2-SA-based fiber laser. We further amplified the output power to 5.60 W with an all-fiber thulium-doped double-cladding fiber amplifier. Our result indicates that ${{\rm WTe}_2}\mbox{-}{\rm SA}$WTe_2-SA could be an excellent candidate for a high-power fiber laser system.

A high-power and high-efficiency diode-end-pumped Tm:YLF laser at 1.83 μm is demonstrated for the first time, to our best knowledge. To make the laser operate at 1.83 μm, a simple way of controlling the transmittance of the output coupler is used, and the criteria of the transmittance of the output coupler at the emission peaks of Tm:YLF are theoretically analyzed, which are verified by experimental results. Based on the theoretical analysis, laser oscillation at only 1.83 μm is realized. Maximum output power at 1833 nm is 8.5 W with corresponding slope efficiency of 53.4% regarding absorbed pump power. In addition, tunability of this laser from 1827 nm to 1837 nm is obtained. Laser beam quality at 1833 nm is measured to be 1.4 at maximum output power. The achieved laser performance represents considerable improvement compared to any other bulk laser emitting around 1.83 μm.

Mid-infrared laser materials with low phonon energy have significant applications. However, the development of available glass systems for high-power laser gain medium have posed a great challenge. Therefore, we investigated the 2.7 μm spectroscopic properties of Er3+/Yb3+-codoped oxyfluoride glass containing gallium, which were prepared by typically melting and quenching methods. The 2.7 μm luminescence properties of the Er3+/Yb3+-codoped oxyfluoride glass containing gallium were recorded by a 980 nm laser diode. The Judd–Ofelt parameters, decay curves, emission cross section, energy transfer efficiency and quantum efficiency were calculated. The maximum emission cross section of YbFGa-0.5 is 1.63 × 10−20 cm2by 980 nm excitation. The energy transfer efficiency is calculated to be 77.8% for the YbFGa-0.5 glass around 2700 nm. The quantum efficiency at 1530 nm is 65.6%. The result reveals that the best doping concentration ratio of Er3+:Yb3+ions is 1:0.5, and suggests an effective energy transfer from Yb3+to Er3+ions.

We propose a dynamic scheme to realize mode-switchable generation of LP_11a/b modes and ±1-order orbital angular momentum (OAM) modes simultaneously, which are induced by an acoustically induced fiber grating driven by radio frequency modulation. LP_11a/b mode degeneration in a few-mode fiber is induced by the geometric irregularity of optical fibers. A dual-wavelength resonance of mode coupling from LP_01 to LP_11a/b modes is found based on the combined effects of optical and acoustic birefringence. Within the configuration of continuous-wave intra-cavity laser output, we experimentally demonstrate a fast-switchable generation of LP_11a/b modes and optical vortex beams with ±1-order OAM at a switching speed up to 4.3 kHz. This approach has potential applications in mode-division multiplexing, particle manipulation, stimulated emission depletion microscopy, and quantum information science.

We demonstrate a high-peak-power femtosecond fiber laser system based on single-mode holmium (Ho)-doped fibers. 833 fs, 27.7 MHz pulses at 2083.4 nm generated in a passively mode-locked Ho fiber laser are amplified and compressed to near transform-limited 172 fs, 7.2 nJ pulses with 24.3 kW peak power. We achieve this performance level by using the soliton effect and high-order soliton compression. To the best of our knowledge, this is the first demonstration of sub-200 fs pulses, with peak power exceeding 10 kW from a Ho-doped single-mode fiber laser system without using bulk optics compressors.

With the magnetron-sputtering deposition method, α phase indium selenide (α-In_2Se_3) was developed into a saturable absorber (SA) with wideband saturable absorption property at 800, 1560, and 1930 nm. After inserting the α-In_2Se_3 SA into erbium-doped fiber laser (EDFL) and thulium-doped fiber laser (TDFL) systems, we can easily obtain stable soliton pulse trains. The pulse duration/pulse energy/slope efficiency for EDFL and TDFL were 276 fs/2.03 nJ/15.8% and 1.02 ps/7.1 nJ/23.5%, respectively. These results showed that the MSD-grown α-In_2Se_3 could be regarded as high efficiency material to be applied in ultrafast photonics.

A passively mode-locked thulium-doped fiber (TDF) laser was realized by employing chemical vapor deposited few-layer molybdenum ditelluride (MoTe_2) as a saturable absorber (SA). The few-layer MoTe_2 film was transferred onto the waist of a microfiber and then incorporated into a TDF laser with a typical all-fiber ring cavity configuration. Stable soliton pulses emitting at 1930.22 nm were obtained with a 3 dB bandwidth of 4.45 nm, a pulse duration of 952 fs, and an average power of 36.7 mW.

Ultrafast pulse generation was demonstrated in a thulium-doped fiber laser mode-locked by magnetron-sputtering deposited WTe_2 with a modulation depth, a nonsaturable loss, and a saturable intensity of 31%, 34.3%, and 7.6??MW/cm^2, respectively. Stable soliton pulses could be obtained at a 1915.5 nm central wavelength with a pulse duration of 1.25 ps, an average output power of 39.9 mW, and a signal-to-noise ratio of 95 dB. To the best of our knowledge, this was the first demonstration of WTe_2-based saturable absorbers in fiber lasers at a 2 μm regime.

In this Letter, high-quality WS_2 film and MoS_2 film were vertically stacked on the tip of a single-mode fiber in turns to form heterostructure (WS_2-MoS_2-WS_2)-based saturable absorbers with all-fiber integrated features. Their nonlinear saturable absorption properties were remarkable, such as a large modulation depth (∼16.99%) and a small saturable intensity (6.23  MW·cm^−2). Stable pulses at 1.55 μm with duration as short as 296 fs and average power as high as 25 mW were obtained in an erbium-doped fiber laser system. The results demonstrate that the proposed heterostructures own remarkable nonlinear optical properties and offer a platform for adjusting nonlinear optical properties by stacking different transition-metal dichalcogenides or modifying the thickness of each layer, paving the way for engineering functional ultrafast photonics devices with desirable properties.

AbstractHigh-power femtosecond mid-infrared (MIR) lasers are of vast importance to both fundamental research and applications. We report a high-power femtosecond master oscillator power amplifier laser system consisting of a single-mode Er:ZBLAN fiber mode-locked oscillator and pre-amplifier followed by a large-mode-area Er:ZBLAN fiber main amplifier. The main amplifier is actively cooled and bidirectionally pumped at 976 nm, generating a slope efficiency of 26.9%. Pulses of 8.12 W, 148 fs at 2.8 μm with a repetition rate of 69.65 MHz are achieved. To the best of our knowledge, this is the highest average power ever achieved from a femtosecond MIR laser source. Such a compact ultrafast laser system is promising for a wide range of applications, such as medical surgery and material processing.

We demonstrate a compact, all-fiber-integrated laser system that delivers Raman solitons with a duration of ∼100  fs and pulse energy of up to 13.3 nJ, continuously wavelength tunable from 1.98 to 2.29 µm via Raman-induced soliton self-frequency shift (SSFS) in a thulium-doped fiber amplifier. We realize a >90% efficiency of Raman conversion, the highest reported value from SSFS-based sources, to the best of our knowledge. This enables us to achieve >10  nJ soliton energy from a 2.16 to 2.29 µm range, the highest energy demonstrated above 2.22 µm from an SSFS-assisted, all-fiber tunable single-soliton-pulse source, to the best of our knowledge. Our simple and compact all-fiber tunable laser could serve as an efficient ∼2  µm femtosecond source for a wide range of mid-infrared applications.

In order to optimize the operational safety and reliability of the upper launcher for the CFETR ECRH system, a design of the launcher for NTM control based on the remote steering concept is currently being carried out for comparison with the front steering equivalent. This paper presents the layout design and analysis of the quasi-optical system in the remote steering launcher. A 3D visual quasi-optical design tool has been developed for the quasi-optical system, which can parameterize modeling, perform general astigmatic beam calculation and show the accurate beam propagation path in the upper port. Three identical sets of quasi-optical modules are arranged in the launcher, and each one consists of two fixed double-curvature focusing mirrors, which focus and reflect the steering beams (−12°–12°) from two square corrugated waveguides. The beam characteristics at the resonance layer are described, and the average beam radius is < 100 mm. The peak head loads on the surfaces of the two fixed mirrors are 1.63 MW/m2and 1.52 MW/m2. The position and size of the beam channel in the blanket are obtained, and the opening apertures on the launcher-facing and plasma-facing sides of the blanket module are 0.54 m2and 0.4 m2, respectively.

In order to optimize the operational safety and reliability of the upper launcher for the CFETR ECRH system, a design of the launcher based on the remote steering concept is currently being carried out for comparison with the front steering equivalent. This paper presents the remote steering system's conceptual design and simulation analysis. A Square Corrugated Waveguide (SCW) of 65 × 65 mm has been designed with an optimized length of 9.35 m. By changing the relative length of the waveguide, the transmission efficiency of the SCW is optimized within the range of steering angles ±12°. Different error factors are investigated in detail, and corresponding acceptable error ranges are provided. Considering these error factors and ignoring ohmic losses and thermal effects, the relative transmission efficiency of the SCW is estimated to be >98 % within the steering angle range. A matching steering unit for the SCW is designed, which consists of an ellipsoidal focusing mirror and a steerable flat mirror. The detailed design of the steerable mirror motion trajectory is presented. Also, the influence of the possible beam incident errors caused by the steering unit on the transmission efficiency is analyzed in detail.

A simple and compact fiber bending sensor based on the Mach-Zehnder interferometer was proposed. A photonic crystal fiber (PCF) with a length of 10 mm was spliced by collapsing air holes with two conventional single mode fibers to consist of an all fiber bending sensor. The sensitivity of 0.53 nm/m−1was obtained at 1586 nm for the curvature range from 0 to 8.514 m−1. The temperature sensitivity was very low. The measurement error due to the temperature effect was about 8.68×10−3m−1/°c, and the temperature effect in the curvature measurement could be ignored. This device can avoid the cross sensitivity of the temperature in the curvature measurement.

We present three operation regimes with an L-band erbium-doped fiber laser passively mode-locked by a graphene oxide saturable absorber (GOSA) that is fabricated by using a wet chemical method. One is a stable state of single soliton emission with pulse duration of 426 fs, which is the shortest pulse duration ever achieved with an L-band design by employing GOSA as the mode-locker. The other two operation regimes include bound-state soliton and dual-wavelength nanosecond pulse generation, which are demonstrated for the first time by using the GOSA mode-locker. Our results further indicate the practical potential of GOSA in ultrafast fiber lasers for achieving various mode-locking regimes.

A long period fiber grating (LPFG) fabricated upon the all-solid photonic bandgap fiber by CO2laser irradiation was investigated, and its resonance wavelength was at 1335.76 nm with a modulation depth of 15 dB and a 3-dB bandwidth of 2.6 nm. We studied its strain, temperature, and index sensor characteristics, the strain sensitivity of 0.992 pm/μɛ was obtained by using linear fit, and the relationship between the refractive index and wavelength obeyed the distribution of quadratic function. Also, we demonstrated its temperature response was relatively insensitive (21.51 pm/°).

We experimentally observed three types of pulses generated in an erbium-doped fiber laser by incorporating a homemade graphene saturable absorber (GSA). The generated pulses from the laser oscillator include dual-wavelength dark pulses, fundamentally step-like pulses, and non-soliton second-harmonic pulses. These operation regimes are first reported by using graphene as the saturable absorber. Our results will further indicate that the GSA can function well for obtaining various ultrafast pulse phenomena, highlighting the practical potential of graphene in ultrafast photonics technologies.

Cylindrical vector beams (CVBs), with non-uniform state of polarizations, have become an indispensable tool in many areas of science and technology. However, little research has explored high power CVBs at the femtosecond regime. In this paper, we report on the generation of high quality CVBs with high peak power and femtosecond pulse duration in a fiber chirped-pulse amplification laser system. The radially (azimuthally) polarized vector beam has been obtained with a pulse duration of 440 fs (430 fs) and a maximum average output power of 20.36 W (20.12 W). The maximum output pulse energy is ∼20 μJ at a repetition rate of 1 MHz, corresponding to a high peak power of ∼46 MW. The comparison between simulated intensity profiles and measured experimental results suggests that the generated CVBs have a remarkable intensity distribution. The proposed configuration of our laser system provides a promising solution for high quality CVBs generation with the characteristics of high peak power, ultrashort pulse duration, and high mode purity.

We report on a mid-infrared fiber laser that uses a single-walled carbon nanotube saturable absorber mirror to realize the mode-locking operation. The laser generates 3.5 µm ultra-short pulses from an erbium-doped fluoride fiber by utilizing a dual-wavelength pumping scheme. Stable mode-locking is achieved at the 3.5 µm band with a repetition rate of 25.2 MHz. The maximum average power acquired from the laser in the mode-locking regime is 25 mW. The experimental results indicate that the carbon nanotube is an effective saturable absorber for mode-locking in the mid-infrared spectral region.

In this paper, we drew a 500 m-long PCF taper directly on the industry drawing tower. The fiber taper has a uniform cross-section structure with OD from 170 m to 70 m, and demonstrates very good beam quality. The optical attenuation of PCF taper was measured. The optical attenuation is ~5 dB/km near 1200 nm, but the water absorption peak around 1400 nm and the attenuation beyond 1600 nm are still large. The zero dispersion wavelength (ZDW) was calculated to be ~1090 nm at the taper input end, and shifted to ~870 nm at the taper output end. The PCF taper was pumped with a picosecond laser source at wavelength of 1064 nm, and generated 200 mW output power of SC covering from ~450 nm to 1600 nm.

As one of the greatest inventions in the 20th century, ultrafast lasers have offered new opportunities in the areas of basic scientific research and industrial manufacturing. Optical modulators are of great importance in ultrafast lasers, which directly affect the output laser performances. Over the past decades, significant efforts have been made in the development of compact, controllable, repeatable, as well as integratable optical modulators (i.e., saturable absorbers). In this paper, we review the fundamentals of the most widely studied saturable absorbers, including semiconductor saturable absorber mirrors and low-dimensional nanomaterials. Then, different fabrication technologies for saturable absorbers and their ultrafast laser applications in a wide wavelength range are illustrated. Furthermore, challenges and perspectives for the future development of saturable absorbers are discussed and presented. The development of ultrafast lasers together with the continuous exploration of reliable saturable absorbers will open up new directions for the mass production of the next-generation optoelectronic devices.

We demonstrate a 2.8 ?m mid-infrared Er-doped ZBLAN mode-locked fiber laser by employing transition metal dichalcogenides (TMD) as a saturable absorber mirror (SAM) for the first time. The TMD-SAM with a large modulation depth of 24% was fabricated by transferring a chemical-vapor-deposited high-quality large-area few-layer WSe2on a gold-coated mirror. Stable mode-locked pulses of 21 ps were obtained with a repetition rate of 42.43 MHz and an average output power up to 360 mW.

A broadband continuum generation is reported in a novel multicore microstructured optical fiber (MOF) where irregular air holes are randomly distributed in cladding. By launching ultrashort light pulses from a Ti:sapphire laser into a 190-mm-long fiber of this type, we have observed a group of continua generated from different cores, each with distinct color. 20-dB bandwidth of the broadest continuum is 1260 nm with an average power of 143 mW. The result confirms that the multicore MOF can be fabricated, with different dispersion profiles tailored for specific supercontinuum (SC) generation towards practical applications.

An all-fiber Yb^(3+)-doped double-clad fiber laser using FBGs as cavity mirrors is investigated in this paper. Continuous-wave (CW) output power of 1.18 W with defined wavelength at 1.06 ?m and narrow line-width of less than 0.1 nm is obtained. The slope efficiency and the maximum optical-to-optical efficiency of laser output are 68% and 51%, respectively, with respect to absorbed pump power.

Supercontinuum generation (SC) of more than one octave spectrum spanning covering from 400 nm to 820 nm was achieved by pumping a piece of aluminum nitride (AIN) single crystal using a nanosecond 355 nm ultraviolet laser. The AlN with a thickness of ∼0.8??mm was grown by an optimized physical vapor transport technique and polished with solidification technology. Compared to previously reported ones, the achieved visible SC exhibited the broadest spectrum spanning from bulk materials pumped by a nanosecond pulse laser. The visible supercontinuum in AlN presents new opportunities for bulk material-based white light SC and may find more potential applications beyond typical applications in integrated semiconductive photoelectronic devices.