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Ultrafast fiber lasers with a wide spectral range have huge demands for many applications. In this article, magnetron sputtering deposition (MSD) technique was utilized to prepare a new broadband microfiber based Sb thin film saturable absorber (SA), and ultrafast pulses in both 1.5 and 2 μm wavebands were generated with the integrated microfiber-based Sb thin film SA in erbium-doped fiber laser (EDFL) and thulium-doped fiber laser (TDFL), respectively. Pulse duration of 544 fs/972 fs and output power of 21.76 mW/36.1 mW centered at 1557 nm/1892 nm were respectively produced from stable mode-locked EDFL and TDFL. To the best our knowledge, this is the first time that ultrafast fiber lasers including both 1.5 μm and 2 μm wavebands were mode locked by a single microfiber-based Sb thin film SA.

A passively mode-locked thulium-doped fiber laser using a tungsten ditelluride saturable absorber ( W T e 2 - S A ) is demonstrated. High-power mode-locked pulses with an average output power of 108.1 mW were achieved by incorporating the W T e 2 - S A into a thulium-doped fiber oscillator. To the best of our knowledge, this is the highest average power obtained from a W T e 2 - S A -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 W T e 2 - S A could be an excellent candidate for a high-power fiber laser system.

In this letter, molybdenum ditelluride (MoTe2), a new member of the transition metal dichalcogenides family, has been characterized and fabricated as an optical modulator for the development of broadband wavelength tunable laser using a Tm3+-doped CaYAlO4 crystal as a laser gain medium. The maximum average output power reaches 0.75 W with the shortest pulse width of about $0.69~\mu \text{s}$ and repetition rate of 70.9 kHz, which leads to a pulse energy of about $10.58~\mu \text{J}$ and peak power of 15.3 W. Keeping the MoTe2 optical modulator inside the laser resonator and at the same time introducing an undoped YAG for wavelength tuning, wavelength tunable passively Q-switched laser operation with a wavelength range of about 112 nm has been demonstrated. This letter experimentally verifies the potential of the novel 2D material MoTe2 as an optical modulator. At the same time, this letter paves the way toward the realizations of simple and compact wavelength tunable pulsed laser sources based on broadband 2D materials saturable absorbers.

We have experimentally demonstrated both 1.82 μm and 1.84 μm Tm:YAP lasers at the operation mode of continuous-wave (CW) and mode-locking. These individual wavelength lasers are realized by using well-chosen output couplers. For the CW operation, a short Fabry-Perot cavity is employed. The maximum output power of the 1825 nm Tm:YAP laser is 7.04 W, and the corresponding slope efficiency is 59.3%. For 1844 nm Tm:YAP laser, the output power is 7.1 W. A commercial semiconductor saturable absorber mirror (SESAM) is used for realizing continuous-wave mode-locking (CWML) operation. The average output power of Tm:YAP laser at 1823.7 nm is 0.3 W, and the pulse duration is 126 ps. Further, stable CWML laser operating at 1844 nm is realized by inserting a 5 mm fused-quartz plate into the cavity with the Brewster angle. The average output power of 0.63 W is achieved, and the pulse duration is 156 ps.

We demonstrate a simple Fe3O4 nanoparticles (FONPs) based Q-switched fiber laser that is able to generate stable nanosecond pulses with single-wavelength or multiwavelength regimes. In the single-wavelength lasing scheme, the fiber laser generates 613-ns pulse with average output power of 41.2 mW, pulse energy of 321.3 nJ, and signal-noise-ratio of 54.4 dB. In the multiwavelength lasing scheme, stable pulse is achieved with 18-wavelength channels contained within the 3-dB bandwidth range. Our results prove that the FONPs can act as an effective Q-switch for high-energy pulse generation.

Vanadium Diselenide (VSe 2 ) has a high electrical conductivity owing to the electron delocalization of the vanadium lattice framework. Most of previous research has been focused on its electronic properties. The nonlinear optical properties of VSe 2 have not been investigated yet. Herein, we prepared few-layer VSe 2 nanoflakes by liquid phase exfoliation. Subsequently, we utilized Z-scan technique to study the nonlinear optical properties of few-layer VSe 2 nanoflakes. And we prepared VSe 2 based saturable absorbers (SA) and achieved passively mode-locked operation in Er-doped fiber laser. The results indicate that VSe 2 nanosheets own remarkable nonlinear optical properties and could be employed as ideal saturable absorption materials in pulsed fiber lasers.

Recently, the active controlled broadband terahertz (THz) emitter from semiconductor crystal has attracted considerable attention due to its field intensity tuning properties, which makes it a promising candidate for wide applications in THz photonics. A broadband THz wave radiation intensity by applying electric field control in an n-type semiconductor tin selenide (SnSe2) crystal had been reported. In addition, due to the weak phonon absorption of the material in the THz band, the resulting THz spectral range is up to 3.5 THz. With an applied voltage of −5 V, the actively modulated depth of THz intensity is up to 123%. Our work directly demonstrates that when the excited laser photon energy exceeds the material bandgap, photon drag effect would be the main mechanism of THz wave radiation rather than nonlinear effects. Owing to simple structure and high modulation depth, electrically controlled THz radiation, the SnSe2 crystal has great applications in generation and modulation devices in THz region.

We demonstrate a compact all-fiber-optic vector magnetometer based on Mach-Zehnder interferometer by utilizing nano-magnetic fluid filled double-clad photonic crystal fiber (DC-PCF). The magnetic fluid (MF) serving as sensing elements is injected into the micro-channel-arrays of DC-PCF. The magnetometer is constructed by splicing a section of MF-filled DC-PCF between two standard single mode fibers forming a high stable all-fiber structure without any additional sealed capillary. The vector magnetometer has the capability of simultaneous measurement of magnetic field intensity and orientation by monitoring a specific dip wavelength shift or transmission loss of Mach-Zehnder interference spectrum. The magnetometer with response sensitivities of 114.5 pm/mT, 1.79 dB/mT (X-axis) and 41.9 pm/mT, 0.52 dB/mT (Y-axis) at two particular orthogonal magnetic field orientations was fabricated and investigated.

Single crystalline titanium dioxide thin film in the rutile phase (r-TiO2) is exfoliated from bulk material using a He+-implantation method, and is bonded onto SiO2 substrate to form a heterostructure using Cu-Sn bonding technology. The exfoliated r-TiO2 thin film was examined to be in good quality, and the exfoliation mechanism of ion-implanted r-TiO2 was analyzed. The obtained r-TiO2 thin film heterostructure with high refractive index contrast has a potential application in the fabrication of high-Q optical microcavities in visible wavelengths, which is useful in integrated photonic devices.

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 compact in-fiber integrated microresonator based on a silica microsphere and microstructure fiber. Whispering-gallery-modes (WGMs) are effectively excited through evanescent field coupling between the silica microsphere and one of the input tube waveguides of negative curvature fiber. The WGM spectrum with the Q-factor of ∼2.56 × 103 and the extinction ratio of ∼15.2 dB is achieved. The transmission spectra evolution for 5 h reveals the long-term stability of WGM excitation. The experimental results indicate that the in-fiber integrated resonator has the advantages of high stability, high integration, robustness, alignment-free assembly structure, and low cost, motivating potential applications in the lab-in-fiber platform.

A passively mode-locked thulium-doped fiber (TDF) laser was realized by employing chemical vapor deposited few-layer molybdenum ditelluride (MoTe2) as a saturable absorber (SA). The few-layer MoTe2 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.

We demonstrated a novel ultracompact fiber-optic micro-Michelson interferometer (MMI) for high temperature sensing. In the MMI structure, a 45° angled reflector is polished at the tip of a single mode fiber using a fiber-lensing machine. This reflector divides the fiber core into two parts and splits the inputting light into two beams producing Michelson interference fringe. The experimental results indicate that the proposed sensor has average temperature sensitivity of 13.32 pm/°C as the temperature increases from 19 °C to 950 °C. With the all-glass assembly-free-based structure, the sensor has a capability of surviving in the high temperature harsh environment.

A position determination method for low-coherence interference fringe in optical fiber sensing is proposed. This method can be used to measure displacement or length. An amplitude ratio curve is created from spatially modulated interference fringes. There is a one-to-one correspondence relationship between the peaks of the amplitude ratio curve and the extremes of the low-coherence interference fringe. The peak positions of the amplitude ratio curve only rely on the Fabry-Pérot (F-P) cavity length. In addition, the peaks of the amplitude ratio curve are very sharp, which can be easily identified. In the calculation of the amplitude ratio curve, the low-coherence interference fringe is spatially modulated by Pockels effects. The impacts of the modulated voltage on the sensing precision are analytically and numerically discussed. Compared with the envelop detection method, the position determination precision of low-coherence interference fringe is enhanced about 30 times by creating an amplitude ratio curve. This method can be widely employed in the sensing of all kinds of parameters that can be converted to displacement or length.

A high precision demodulation method in frequency domain is proposed for a polarized low-coherence interferometer with location-dependent birefringence dispersion. By minimizing the frequency nonlinearity caused by dispersion effects, the proposed method avoids the jump errors of traditional frequency domain analysis method and exactly retrieve the absolute phase at multiselected-wavenumber point simultaneously, which makes it superior in accuracy, stability, and measurement range. We carried out experiments with an optical fiber Fabry–Perot pressure sensing system to verify the effectiveness of the proposed method. The experiment result showed that the measured error was less than 0.049 kPa and the measurement range was widened to 285 kPa, which could be wider with suited experimental equipment and is no limit in theory.

We establish an optical path difference (OPD) distribution model in a spatial scanned polarized low-coherence interferometry (LCI) considering the nonperpendicular incidence of light to explore the spatial frequency drift. Simulation shows that the OPD is no longer linearly distributed on a charged coupled device (CCD) and that the spatial frequency drifts approximately linearly as low coherent interference fringe (LCIF) shifts. A compensation process for spatial frequency domain analysis (SFDA)-based algorithm is proposed to avoid interference-order misidentification and consequent jump error. We verified our analysis and effectiveness of the proposed algorithm with an optical fiber Fabry-Pérot pressure sensing experiment. The measured spatial frequency drift agreed well with simulation results, and the interference-order misidentification was eliminated.

Two-dimensional materials have become the focus of research for their photoelectric properties, and are employed as saturable absorption materials. Currently, the challenge is how to further improve the modulation depth of saturable absorbers (SAs) based on two-dimensional materials. In this paper, three kinds of WSe2 films with different thicknesses are prepared using the chemical vapor deposition method. The nonlinear optical responses of the WSe2 films including the nonlinear saturable absorption and nonlinear refractive index are characterized by the double-balanced detection method and Z-scan experiments. Different modulation depths are successfully obtained by controlling the thickness of the WSe2 films. We further incorporate them into an all-fiber laser to generate mode-locked pulses. The mode-locked fiber lasers with a pulse duration of 185 fs, 205.7 fs and 230.3 fs are demonstrated when the thickness of the WSe2 films is measured to be 1.5 nm, 5.7 nm and 11 nm, respectively. This work provides new prospects for WSe2 in ultrafast photonic device applications.

We prepared ReS 2 nanosheets by liquid-phase exfoliation and fabricated ReS 2 saturable absorbers with all-fiber integrated structure. Their nonlinear optical properties were investigated systematically. The results demonstrate that ReS 2 nanosheets owns excellent nonlinear saturable absorption properties.

We demonstrated a fiber-optic sensor using spheroidal-cavity-overlapped fiber Bragg grating (FBG) for simultaneous temperature and strain sensing. The spheroidal cavity is fabricated through splicing two sections of the photon-sensitive fiber together and located in the center of the FBG to act as a Fabry-Pérot interferometer (FPI). Experimental results demonstrate that the temperature sensitivity of the FPI part of the sensor is 0.67 pm/°C at the range of -70 °C-20 °C, and its strain sensitivity is 3.76 pm/με at the range of 0-500 με, while those of the FBG part are 8.40 pm/°C and 1.40 pm/με, respectively. The sensitivity difference ensures good simultaneous measurement performance.

Large-area and highly crystalline transition metal dichalcogenides (TMDs) films possess superior saturable absorption compared to the TMDs nanosheet counterparts, which make them more suitable as excellent saturable absorbers (SA) for ultrafast laser technology. Thus far, the nonlinear optical properties of large-scale WSe2 and its applications in ultrafast photonics have not yet been fully investigated. In this work, the saturable absorption of chemical vapor deposition (CVD) grown WSe2 films with large-scale and high quality are studied and the use of WSe2 films as a broadband SA for passively mode-locked fiber lasers at both 1.5 and 2 μm ranges is demonstrated. To enhance the light-material interaction, large-area WSe2 film is tightly transferred onto the side wall of a microfiber to form a hybrid structure, which realizes strong evanescent wave interaction between light and WSe2 film. The integrated microfiber-WSe2 device shows a large modulation depth of 54.5%. Using the large-area WSe2 as a mode-locker,stable soliton mode-locked pulse generation is achieved and the pulse durations of 477 fs (at 1.5 μm) and 1.18 ps (at 2.0 μm) are demonstrated, which suggests that the large-area and highly crystalline WSe2 films afford an excellent broadband SA for ultrafast photonic applications.

Nanoferrofluid is emerging as promising nanomaterials for the critical element of magneto-optical fiber devices. Herein, we demonstrate the mechanism of anisotropic nanochain-clusters formation and motion of nanoferrofluid around an optical fiber with the variation of magnetic field intensity and its direction. Based on anisotropic distribution of nanochain-clusters, we design a new nanoferrofluid-based vector magnetometer with simultaneous measurement of magnetic field intensity and direction. The sensing mechanism is based on the tunable ERI modulation of asymmetric cladding modes in fiber, modulated by magnetic field dependent nanochain-clusters. The all-fiber vector magnetometer with direction detection error of ±1.5°, and intensity sensitivity of 222.0pm/mT was fabricated and investigated.

We demonstrate the HfSe2 saturable absorber (SA) for the generation of ultrafast pulse laser. The HfSe2 SA device is fabricated by integrating HfSe2 nanosheets (NSs) with a microfiber. The material and optical characteristics of HfSe2 NSs show their high quality. The nonlinear optical absorption of HfSe2 SA is measured with a modulation depth of 5.8%. Stable soliton mode-locked laser based on HfSe2 SA is realized at the central wavelength of 1561.43 nm with pulse duration of 297 fs and the maximum pulse energy of 2.68 nJ. Our soliton fiber laser has a maximum output power of 48.5 mW with a high slope efficiency of 12.8%, which indicate that HfSe2 is a good candidate of SA for high efficient ultrashort pulses generation.

Two-dimensional layered materials have been widely utilized as nonlinear absorption materials to transfer continue-wave into pulse trains in fiber laser systems. Here, we prepare robust GaSe/GeSe composites with high power bearing capacity as saturable absorbers (SAs) and then investigate their nonlinear optical properties via broadband Z-scan measurement at 800 nm and 1550 nm, respectively. The modulation depths of GaSe/GeSe based SAs are measured to be 11.97% and 7.69% at 1550 nm. After incorporating the GaSe/GeSe SAs into an Erbium-doped fiber laser cavity, passively Q-switched pulse trains could be obtained with repetition rates changing from 83.58 to 136.78 kHz (70.41 to 161.65 kHz). The maximum output power and pulse energy are 52.1 mW/370.67 nJ (GaSe) and 21.6 mW/133.74 nJ (GeSe) under the maximum pump power of 600 mW. The results indicate that GaSe and GeSe possess outstanding thermal stability and could be employed as remarkable saturable absorption materials for high-energy pulses generation.

We demonstrated a simple and batch-producible fiber-optic sensor based on hybrid Fabry-Perot (FP) configuration for simultaneous pressure and temperature sensing. The proposed sensor head chips are batch fabricated by double-sided anodic bonding of a through-holes-array-structured glass wafer and two silicon wafers. The silicon-glass-silicon sandwich bonding structure constructs two serially connected low-finesse FP cavities naturally. The first cavity (FP 1 ) is a silicon cavity and utilizes the refractive indices temperature dependence of silicon to achieve temperature sensing. The second cavity (FP 2 ) is a vacuum cavity and employs a thin silicon diaphragm as a pressure sensing element. The reflection spectra exhibit hybrid interference fringes with different frequencies produced by silicon and vacuum cavity, and the temperature and pressure are simultaneously measured. Experiment results demonstrate that the pressure sensitivity of FP 2 is 12.82 nm/kPa with a high linear pressure response over the range of 10-250 kPa, and the temperature sensitivity of FP 1 is 142.02 nm/°C under the range of -20 °C-70 °C.

We propose a direct and nondestructive self-referenced residual pressure measurement method for MEMS chip of fiber-optic pressure sensor. In the proposed method, two multimode fibers are placed at the center and the edge position of the sealed cavity. With scanning external pressure, two groups of cavity lengths data are obtained by using polarization low-coherence interference demodulator. The intersection point of their linear fitting curves indicates that the diaphragm is in flat condition and residual pressure is determined by the external pressure at this point. We successfully demonstrated the effectiveness of the residual pressure measurement method with measure error 0.049 kPa.

Despite extensive applications ranging from optoelectronic devices to flexible devices, two-dimensional layered materials used as ultrafast optical modulation materials have suffered from limited operation wavebands due to their intrinsic bandgap. Here, we investigate the nonlinear optical (NLO) response of group IIIA/IVA monochalcogenides XTe (X = Ga and Ge), which exhibit a remarkable saturable absorption response at a broadband wavelength. By using a liquid phase exfoliation technique, we prepare XTe nanosheets with few-layer thickness in a deionized water solvent and investigate their NLO responses at 800 nm, 1.5 µm, and 2 µm, respectively. Both GaTe and GeTe nanosheets exhibit ultrafast saturable absorption at 800 nm with 32.4 μJ (48.4 µJ) incident intensity. After preparing microfiber-based nanosheet optical modulators, their saturable absorptions are measured at 1.5 µm and 2 µm. The GaTe-SA possesses a little bit higher modulation depth (42.3% at 1.5 µm/30.7% at 2 µm) than the GeTe-SA (30.5% at 1.5 µm/8.3% at 2 µm) at two wavelengths. The lifetime of GaTe and GeTe nanosheets is measured to be 2.8 ps and 3.3 ps, respectively. In addition, we further examine their saturable absorption via incorporating them into an erbium- and a thulium-doped fiber laser system and obtain stably passively mode-locked pulse trains, respectively. The distinct NLO properties indicate a large potential of XTe nanosheets in the development of an ultrafast optical mode locker with a wideband operation wavelength.

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have attracted significant interest in various optoelectronic applications due to their excellent nonlinear optical properties. One of the most important applications of TMDs is to be employed as an extraordinary optical modulation material (e.g., the saturable absorber (SA)) in ultrafast photonics. The main challenge arises while embedding TMDs into fiber laser systems to generate ultrafast pulse trains and thus constraints their practical applications. Herein, few-layered WS2 with a large-area was directly transferred on the facet of the pigtail and acted as a SA for erbium-doped fiber laser (EDFL) systems. In our study, WS2 SA exhibited remarkable nonlinear optical properties (e.g., modulation depth of 15.1% and saturable intensity of 157.6 MW cm(-2)) and was used for ultrafast pulse generation. The soliton pulses with remarkable performances (e.g., ultrashort pulse duration of 1.49 ps, high stability of 71.8 dB, and large pulse average output power of 62.5 mW) could be obtained in a telecommunication band. To the best of our knowledge, the average output power of the mode-locked pulse trains is the highest by employing TMD materials in fiber laser systems. These results indicate that atomically large-area WS2 could be used as excellent optical modulation materials in ultrafast photonics.

Temperature is an important monitoring parameter for applications in aviation industry. We have developed a series of optical fiber temperature sensors to fulfil the different requirements based on interference, including the pressure-based optical fiber temperature sensor with the capability of being integrated with optical fiber MEMS pressure sensor, micro-interferometer-based optical fiber medium temperature sensor with no special assembly process needed, and sapphire-solid-cavity-based high temperature sensor. The sensors all have compact structure and show good performance, which make them to possess a promising application prospect.

We demonstrate a compact all-fiber-optic vector magnetometer based on Mach-Zehnder interferometer by utilizing magnetic fluid filled double-clad photonic crystal fiber (DC-PCF). The magnetic fluid (MF) serving as crucial sensing elements is injected into the micro-channel-arrays of DC-PCF. The magnetometer is constructed by splicing a section of MF-filled DC-PCF between two standard single mode fibers forming a high stable all-fiber structure without any additional sealed capillary. The vector magnetometer has the capability of simultaneous measurement of magnetic field intensity and orientation by monitoring a specific dip wavelength shift or transmission loss of Mach-Zehnder interference spectrum. The magnetometer with response sensitivities of 114.5 pm/mT, 1.79 dB/mT (X-axis) and 41.9 pm/mT, 0.52 dB/mT (Y-axis) at two orthogonal magnetic field orientations was fabricated and investigated.

This paper reports on the supercontinuum generation in yttrium orthosilicate bulk crystal and 6-mm-long ion implanted planar waveguide. The waveguide is fabricated by 6 MeV oxygen ions implantation with fluence of 5 × 1014 ions/cm2 at room temperature. The yttrium orthosilicate bulk crystal and waveguide are pumped using a mode-locked Ti:Sapphire laser with a center wavelength of 800 nm. The generated broadest supercontinuum spans 720 nm (at −30 dB points) from 380 to 1100 nm in bulk crystal and 510 nm (at −30 dB points) from 490 to 1000 nm in ion implanted waveguide, respectively. Compared to the bulk crystal, the ion implanted waveguide requires almost three orders of magnitude lower pump power to achieve a similar level of broadening. The supercontinuum is generated in the normal dispersion regime and exhibits a relatively smooth spectral shape. Our research findings indicate that ion implantation is an efficient method to produce waveguide in yttrium orthosilicate crystal for low-threshold supercontinuum generation.

The pulse energy in the ultrafast soliton fiber laser oscillators is usually limited by the well-known wave-breaking phenomenon owing to the absence of a desirable real saturable absorber (SA) with high power tolerance and large modulation depth. Here, we report a type of microfiber-based MoTe2 SA fabricated by the magnetron-sputtering deposition (MSD) method. High-energy wave-breaking free soliton pulses were generated with pulse duration/pulse energy/average output power of 229 fs/2.14 nJ/57 mW in the 1.5 μm regime and 1.3 ps/13.8 nJ/212 mW in the 2 μm regime, respectively. To our knowledge, the generated soliton pulses at 1.5 μm had the shortest pulse duration and the highest output power among the reported erbium-doped fiber lasers mode locked by transition metal dichalcogenides. Moreover, this was the first demonstration of a MoTe2-based SA in fiber lasers in the 2 μm regime, and the pulse energy/output power are the highest in the reported thulium-doped fiber lasers mode locked by two-dimensional materials. Our results suggest that a microfiber-based MoTe2 SA could be used as an excellent photonic device for ultrafast pulse generation, and the MSD technique opens a promising route to produce a high-performance SA with high power tolerance and large modulation depth, which are beneficial for high-energy wave-breaking free pulse generation.

A simple and effective method for polarized low-coherence interference is proposed in this letter. Despite the need to extract the coherence envelope, it sets an appropriate threshold to retrieve valid peaks or troughs from various fluctuations. Subsequently, we can utilize any valid peak or trough for demodulation. Experiments were carried out to demonstrate the validity and exceptionally good performance of this method. Experimental results have shown that the proposed method can achieve higher accuracy and stability when compared with the envelope peak detection method.

We propose a novel fiber-optic Fabry–Perot interferometric (FFPI) temperature sensor based on differential pressure resulting from thermal expansion of sealed air. A thin silicon diaphragm is sandwiched between two micro-circular cavity-structured Pyrex plates to construct a FP and an air cavity. The thermal expansion of sealed air induces differential pressure variation between cavities and thus the deformation of thin diaphragm, which transfers temperature change into cavity length shift of FP interferometer. Theory analysis results indicate that the temperature-sensitivity can be designed flexibly by choosing the parameters of radius and thickness of silicon diaphragm, and the differential pressure between two cavities. Experimental results demonstrate that the temperature sensitivity of 6.07 nm/°C is achieved with the resolution of 0.10°C under the range of −50°C to 100°C, and the response time is around 1.3 s with temperature change from 28°C to 100°C.

Ultrafast pulse generation was demonstrated in a thulium-doped fiber laser mode-locked by magnetron-sputtering deposited WTe2 with a modulation depth, a nonsaturable loss, and a saturable intensity of 31%, 34.3%, and 7.6 MW/cm2, 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 WTe2-based saturable absorbers in fiber lasers at a 2 μm regime.

Transition metal dichalcogenides (TMDs) have been successfully used as broadband optical modulator materials for pulsed fiber laser systems. However, the nonlinear optical absorptions of exfoliated TMDs are strongly limited by their nanoflakes morphology with uncontrollable lateral size and thickness. In this work, we provide an effective method to fully explore the nonlinear optical properties of MoSe2. Large-area and high quality lattice MoSe2 grown by chemical vapor deposition method was adopted as an optical modulator for the first time. The large-area MoSe2 shows excellent nonlinear optical absorption with a large modulation depth of 21.7% and small saturable intensity of 9.4 MW cm-2. After incorporating the MoSe2 optical modulator into fiber laser cavity as a saturable absorber, a highly stable Q-switching operation with single pulse energy of 224 nJ is achieved. The large-area MoSe2 possessing superior nonlinear optical properties compared to exfoliated nanoflakes affords possibility for the larger-area two-dimensional materials family as high performance optical devices.

In this Letter, high-quality WS2 film and MoS2 film were vertically stacked on the tip of a single-mode fiber in turns to form heterostructure (WS2-MoS2-WS2)-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.

The development of simple and sensitive sensors with the capability of simultaneously detecting magnetic field intensity and its direction in three-dimensional (3D) space is a technical imperative for magnetic field detection. In this paper, we first demonstrated the mechanism of anisotropic manipulation of ferromagnetism nanoparticles (FMNPs) in a non-continuous magnetic fluid film with the aid of varying magnetic fields. Second, based on the anisotropic distribution of the FMNPs around an optical fiber, we fabricated a vector magnetometer with a direction error of ±1.9° and an intensity sensitivity of 222.0 pm/mT, respectively. The sensing mechanism relies on the magnetism-controllable effective refractive index modification of asymmetric cladding modes in an in-line fiber-optic Mach-Zehnder interferometer. Compared to the previously reported intensity-based magnetometers, the as-fabricated magnetometer also provides an avenue to monitor the vector direction of the magnetic field in 3D space.

We present a high precision and fast speed demodulation method for a polarized low-coherence interferometer with location-dependent birefringence dispersion. Based on the characteristics of location-dependent birefringence dispersion and five-step phase-shifting technology, the method accurately retrieves the peak position of zero-fringe at the central wavelength, which avoids the fringe order ambiguity. The method processes data only in the spatial domain and reduces the computational load greatly. We successfully demonstrated the effectiveness of the proposed method in an optical fiber Fabry–Perot barometric pressure sensing experiment system. Measurement precision of 0.091 kPa was realized in the pressure range of 160 kPa, and computation time was improved by 10 times compared to the traditional phase-based method that requires Fourier transform operation.

We fabricated MEMS-based optical fiber pressure sensor with anodic bonding. The vacuum-sealed microcavity with a thin silicon diaphragm is used as sensing element and its deformation characteristics determine the pressure measurement performance. Considering residual gas inside Fabry-Perot cavity and the thermal properties of material, we established a sensor’s temperature response mathematical model based on ideal gas equation and elastic theory. Temperature experiment of this sensor was carried out under vacuum. This work will provide a guide of temperature compensation process for achieving high precision pressure measurement.

Optical fiber sensor has great advantage for applications dealing with extreme environment. We developed a high precision optical pressure sensor for aviation industry. The optical pressure sensor is based on two-beam interference of microcavity and is fabricated with Micro-electromechanical systems (MEMS) and laser fusion technology. The cavity length variation resulting from external pressure is demodulated with spatial polarization low coherence interference unit and a high stable phase demodulation algorithm. The effect of light source output parameter is also investigated. We carried out research on optical fiber strain, temperature and acoustic vibration sensor for aerospace application. The optical fiber sensors for strain and temperature measurement are based on fiber Bragg grating(FBG).Both bare FBG and packaged FBG performances under cryogenic temperature and high vacuum are investigated. An eight-channel parallel FBG wavelength interrogator is developed. The optical fiber acoustic vibration sensor is based on two-beam interference of microcavity and use intensity demodulation method for high speed response. The mutiple-parameter and multiplepoint measurement instrument is successfully applied to status monitoring of water sublimator.

We present an effective method to compensate the spatial-frequency nonlinearity for polarized low-coherence interferometer with location-dependent dispersion element. Through the use of location-dependent dispersive characteristics, the method establishes the exact relationship between wave number and discrete Fourier transform (DFT) serial number. The jump errors in traditional absolute phase algorithm are also avoided with nonlinearity compensation. We carried out experiments with an optical fiber Fabry-Perot (F-P) pressure sensing system to verify the effectiveness. The demodulated error is less than 0.139kPa in the range of 170kPa when using our nonlinearity compensation process in the demodulation.

We propose a new wavelength-division-multiplexing method for extrinsic fiber Fabry–Perot interferometric (EFPI) sensing in a polarized low-coherence interferometer configuration. In the proposed method, multiple LED sources are used with different center wavelengths, and each LED is used by a specific sensing channel, and therefore the spatial frequency of the low-coherence interferogram of each channel can be separated. A bandpass filter is used to extract the low-coherence interferogram of each EFPI channel, and thus the cavity length of each EFPI channel can be identified through demultiplexing. We successfully demonstrate the simultaneous demodulation of EFPI sensors with same nominal cavity length while maintaining high measurement precision.

In this paper, we demonstrate a high-damage-resistant tungsten disulfide saturable absorber mirror (WSsub2/sub-SAM) fabricated by magnetron sputtering technique. The WSsub2/sub-SAM has an all-fiber-integrated configuration and high-damage-resistant merit because the WSsub2/sublayer is protected by gold film so as to avoid being oxidized and destroyed at high pump power. Employing the WSsub2/sub-SAM in an Erbium-doped fiber laser (EDFL) with linear cavity, the stable Q-switching operation is achieved at central wavelength of 1560 nm, with the repetition rates ranging from 29.5 kHz to 367.8 kHz and the pulse duration ranging from 1.269 μs to 154.9 ns. For the condition of the maximum pump power of 600 mW, the WSsub2/sub-SAM still works stably with an output power of 25.2 mW, pulse energy of 68.5 nJ, and signal-noise-ratio of 42 dB. The proposed WSsub2/sub-SAM configuration provides a promising solution for advanced pulsed fiber lasers with the characteristics of high damage resistance, high output energy, and wide tunable frequency.

A novel demodulation algorithm, comprising of a calibration algorithm and improved linear fitting phase-shift algorithm, is proposed for optical fiber sensing system based on low-coherence interference. The calibration algorithm is used to identify the fringe order. Traditional phase-shift algorithm is improved to get the linear fitting curve of the relative phase corresponding to zero-order fringe and the peak position is retrieved from its zero point. Comparing with Fourier based algorithms, the computation of proposed algorithm is small (approximately 25 times faster) while sustains high precision with 2nm maximum error of cavity length. Experiments were carried out to verify the performance.

A demodulation algorithm based on absolute phase recovery of a selected monochromatic frequency is proposed for optical fiber Fabry-Perot pressure sensing system. The algorithm uses Fourier transform to get the relative phase and intercept of the unwrapped phase-frequency linear fit curve to identify its interference-order, which are then used to recover the absolute phase. A simplified mathematical model of the polarized low-coherence interference fringes was established to illustrate the principle of the proposed algorithm. Phase unwrapping and the selection of monochromatic frequency were discussed in detail. Pressure measurement experiment was carried out to verify the effectiveness of the proposed algorithm. Results showed that the demodulation precision by our algorithm could reach up to 0.15kPa, which has been improved by 13 times comparing with phase slope based algorithm.