Raman Lasing and Transverse Mode Selection in a Multimode Graded-Index Fiber with a Thin-Film Mirror on Its End Face.

Multimode fibers are attractive for high-power lasers if transverse modes are efficiently controlled. Here, a dielectric thin-film mirror (R~20%) is micro-fabricated on the central area of the end face of a 1 km multimode 100/140 µm graded-index fiber and tested as the output mirror of a Raman laser with highly multimode (M2~34) 940 nm diode pumping. In the cavity with highly reflective input FBG, Raman lasing of the Stokes wave at 976 nm starts at the threshold pump power of ~80 W. Mode-selective properties of mirrors with various diameters were tested experimentally and compared with calculations in COMSOL, with the optimum diameter found to be around 12 µm. The measured Raman laser output beam at 976 nm has a quality factor of M2~2 near the threshold, which confirms a rather good selection of the fundamental transverse mode. The power scaling capabilities, together with a more detailed characterization of the output beam's spatial profile, spectrum, and their stability, are performed. An approximately 35 W output power with an approximately 60% slope efficiency and a narrow spectrum has been demonstrated at the expense of a slight worsening of beam quality to M2~3 without any sign of mirror degradation at the achieved intensity of >30 MW/cm2. Further power scaling of such lasers as well as the application of the proposed technique in high-power fiber lasers are discussed.

Mechanism Analysis of Rock Vitrification by Strip Laser Scanning.

The process of casing the wellbore in oil and gas drilling consumes a significant amount of time and economic resources. High-energy laser rock fracturing, as an efficient and cost-effective new approach, holds the potential to create a glass-like casing by irradiating the rocks as an alternative to traditional casing. The mechanism behind the vitrification of rocks using laser irradiation, a key factor in achieving glassified casings, remains to be studied. This paper, based on experiments involving scanning sandstone with a line laser, investigates the mechanism of rock vitrification using numerical simulations and X-ray diffractometers. The results demonstrate that the sandstone surface is transformed into glass after laser scanning, with multiple scans and the application of high-speed airflow helping to reduce the formation of bubbles and other phenomena. Furthermore, the speed of laser scanning showed a negative correlation with the laser ablation depth, glass thickness, temperature diffusion rate, and temperature gradient. Based on these findings, a groundbreaking method is proposed for creating high-quality glass by moving the laser to scan the rocks multiple times, offering insights for research into laser-manufactured wellbore casings. Furthermore, this approach holds promising prospects for enhancing and embellishing the exterior of structures and for in situ environmental modifications on planetary surfaces and beyond.

Steady-state versus burst lasing techniques for thulium fiber laser.

OBJECTIVE: To evaluate the stone ablation rate and direct thermal damage from thulium fiber laser (TFL) lithotripsy using continuous (C) and burst (B) lasing techniques on an in vitro ureteral model. METHODS: The TFL Drive (Coloplast, Humlebaek, Denmark) was used in an in vitro saline-submerged ureteral model. Ten participants, including five junior and five experienced urologists, conducted the experimental setup with 7 different settings comparing two lasing techniques: steady-state lasing (0.5 J/10 Hz = 5W for 300 s and 0.5 J/20 Hz = 10W for 150 s) and burst, intermittent 5 s on/off lasing (0.5 J/20 Hz, 0.5 J/30 Hz, 0.5 J/60 Hz, 0.1 J/200 Hz, and 0.05 J/400 Hz) with a target cumulative energy of 1500 J using cubic 125 mm3 phantom BegoStonesTM. Ureteral damage was graded 1-3 based on the severity of burns and holes observed on the surface of the ureteral model. RESULTS: The were no significant differences in stone ablation mass neither between C and B lasing techniques, nor between expertise levels. At C lasing technique had only mild ureteral lesions with no significant differences between expertise levels (p: 0.97) or laser settings (p: 0.71). At B lasing technique, different types of thermal lesions were found with no expertise (p: 0.11) or setting (p: 0.83) differences. However, B laser setting had higher grade direct thermal lesions than C (p: 0.048). CONCLUSION: Regarding efficacy, C and B lasing techniques achieve comparable stone ablation rates. Safety-wise, B lasing mode showed higher grade of direct thermal lesions. These results should be further investigated to verify which of the lasing mode is the safest in vivo. Until then and unless proven otherwise, a C mode with low frequency should be recommended to avoid ureteral wall lesions.

A Comparison of the First 60 Enucleation Cases Using a Thulium Fiber Laser without a Mentor to a Transurethral Resection of the Prostate (TURP) and Open Prostatectomy, and the Learning Curve.

Background and Objectives: In the surgical treatment of benign prostatic hyperplasia (BPH), laser enucleation of the prostate is recommended as an alternative to transurethral resection (TURP) and open prostatectomy (OP). The thulium fiber laser, with its superficial penetration depth, can offer a rapid learning process by causing less heat injury and capsule damage. This study compares the first 60 cases of an endourologist performing thulium fiber enucleation of the prostate (ThuFLEP) without a mentor to the results of OP and TURP performed by experienced surgeons. It also identifies the case number at which the operation time for ThuFLEP starts to plateau. Materials and Methods: Between 1 November 2021 and 1 November 2023, the initial 60 ThuFLEP cases of an endourologist with no prior enucleation experience were compared with TURP and OP operations performed by experienced surgeons. Since the first 60 ThuFLEP cases involved 80-120 cc prostates, TURP and OP operations within this size range performed during the same period were included in the study. The groups were assessed for age, preoperative and postoperative prostate volume, PSA levels, the IPSS, the IPSS Quality of Life (QoL), and maximum urinary flow (Qmax). The 60 consecutive ThuFLEP cases were divided into three groups of 20 (Groups 1, 2, and 3) and compared for operation time, IPSS, and Qmax. Results: The operation time for TURP was shorter than for ThuFLEP and OP (p < 0.001). There was no significant difference between ThuFLEP and OP in postoperative Qmax and IPSS, while TURP had lower values than the other two methods. For ThuFLEP, the operation time was longer in the first 20 cases but plateaued in groups 2 and 3 (p < 0.001). Postoperative Qmax and IPSS values showed no significant differences among the three ThuFLEP groups (p > 0.05). Conclusions: For large prostates, ThuFLEP provides better postoperative results than TURP and offers shorter catheterization and hospital stay times than OP. Its short learning curve makes it a preferable method for treating BPH compared to other laser techniques.

Comparison of holmium:yttrium-aluminium-garnet (YAG), thulium fiber laser, and pulsed thulium:YAG lasers on soft tissue: an ex vivo study.

OBJECTIVES: To assess laser-tissue interactions through ablation, coagulation, and carbonisation characteristics in a non-perfused porcine kidney model between three pulsed lasers: holmium (Ho): yttrium-aluminium-garnet (YAG), thulium fiber laser (TFL), and pulsed thulium (p-Tm):YAG. MATERIALS AND METHODS: A 150-W Ho:YAG, a 60-W TFL, and a 100-W p-Tm:YAG lasers were compared. The laser settings that can be set identically between the three lasers and be clinically relevant for prostate laser enucleation were identified and used on fresh, unfrozen porcine kidneys. Laser incisions were performed using stripped laser fibers of 365 and 550 µm, set at distances of 0 and 1 mm from the tissue surface at a constant speed of 2 mm/s. Histological analysis evaluated shape, depth, width of the incision, axial coagulation depth, and presence of carbonisation. RESULTS: Incision depths, widths, and coagulation zones were greater with Ho:YAG and p-Tm:YAG lasers than TFL. Although no carbonisation was found with the Ho:YAG and p-Tm:YAG lasers, it was common with TFL, especially at high frequencies. The shapes of the incisions and coagulation zones were more regular and homogeneous with the p-Tm:YAG laser and TFL than with Ho:YAG laser. Regardless of the laser used, short pulse durations resulted in deeper incisions than long pulse durations. Concerning the distance, we found that to be effective, TFL had to be used in contact with the tissue. Finally, 365-µm fibers resulted in deeper incisions, while 550-µm fibers led to wider incisions and larger coagulation zones. CONCLUSION: Histological analysis revealed greater tissue penetration with the p-Tm:YAG laser compared to the TFL, while remaining less than with Ho:YAG. Its coagulation properties seem interesting insofar as it provides homogeneous coagulation without carbonisation, while incisions remained uniform without tissue laceration. Thus, the p-Tm:YAG laser appears to be an effective alternative to Ho:YAG and TFL lasers in prostate surgery.

Is Bigger Better? Comparison of 150 µm and 200 µm Thulium Fiber for In Situ Lower-Pole Lithotripsy.

Introduction: The thulium fiber laser (TFL) generates a focused beam, which can be transmitted to laser fibers with small core diameters and may facilitate in situ lower-pole lithotripsy. This study compares lithotripsy performance of the 150 and 200 µm TFL in a lower pole benchtop kidney model. Materials and Methods: Using a 3D model printed from an actual kidney, in situ laser lithotripsy was performed on 1 cm lower-pole BegoStones (calcium oxalate monohydrate consistency) using four different settings (all 20W) and two fiber sizes (150 and 200 µm). Procedure time, laser time, total pulse energy, and fiber stripping were compared between the two fibers using an ANOVA or independent t-test. Results: The 150 µm fiber at 0.2 J × 100 Hz had the shortest lasing and procedure time (17.3 and 18.5 minutes) and lowest total pulse energy (20.75 kJ) compared with other study arms (p < 0.001). Overall procedure time, lasing time, and total pulse energy were significantly different between the 8 settings (p < 0.001 for all). At higher frequency (100 and 200 Hz), lasing time was significantly faster compared with 20 and 50 Hz (19.9 vs 27.3 minutes; p < 0.001). Furthermore, the average total procedure time was shorter with 150 µm compared with 200 µm regardless of settings (23.2 vs 29.8 minutes; p < 0.001). Conclusion: The 150 µm fiber results in shorter procedure and lasing time at lower total energy levels during lower-pole in situ lithotripsy. Overall, the fastest setting was 0.2 J and 100 Hz with the 150 µm fiber. Smaller laser fibers can potentially allow more efficient in situ laser lithotripsy with better irrigation and visibility at higher deflection angles.

The Advancement of Waterjet-Guided Laser Cutting System for Enhanced Surface Quality in AISI 1020 Steel Sheets.

This study investigates the effects of a water-guided laser on the cutting performance of AISI 1020 steel sheets of various thicknesses by comparing the results with respect to a conventional laser. For this purpose, a novel nozzle design has been devised enabling the delivery of laser beams to the workpiece conventionally as well as through water guidance. Diverging from prior literature, a fiber laser is used with a high wavelength and a laser power output of 1 kW. Experiments are conducted on steel sheets with thicknesses ranging from 1.5 mm to 3 mm using three different cutting speeds and laser power levels. Analysis focuses on assessing surface roughness, burr formation and heat effects on the cut surfaces for both conventional and waterjet-guided cutting. Surface roughness is evaluated by using a 3D profilometer and cut surfaces are examined through SEM imaging. The results showed that the waterjet-guided laser system greatly reduced surface roughness and minimized problems associated with traditional laser cutting such as kerf, dross adherence and thermal damage. The study revealed that cutting speed had a greater effect on surface roughness reduction than laser power, with the most noticeable differences occurring in thinner sheets. Furthermore, the investigation suggests that the waterjet-guided laser cutting system demonstrates superior performance relative to conventional methods, particularly in surface quality.

A 3.2 kW Single Stage Narrow Linewidth Fiber Amplifier Emitting at 1050 nm.

In this paper, we have demonstrated a narrow linewidth high power fiber laser emitting at a short wavelength of ~1050 nm. The fiber laser is based on a structure of master oscillator power amplification (MOPA) with an optimized fiber Bragg-grating-based laser cavity as the seed. Both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) effects have been effectively suppressed by using a long passive fiber between the seed and the amplifier. Based on the fiber amplifier, we have ultimately boosted the narrow linewidth laser from ~40 W to 3.2 kW with a slope efficiency of 85.1% and a 3-dB linewidth of ~0.1 nm. The SRS suppression ratio of the laser is ~29.7 dB at maximum power. Due to our fiber mode control strategies, the beam quality always stays near-diffraction-limited while amplifying, and the measured M2 factor is ~1.4 at the maximum power. Further increase in output power is limited by the SBS effect.

Comparison of the effects of Ho: YAG laser virtual Basket™ pulse modulation and Thulium fiber laser on kidney tissue - an ex vivo experimental study.

Through an ex vivo experimental study, we aimed to compare the effects of the Ho: YAG laser Virtual Basket (VB™) modulation and a Thulium fiber laser (TFL) on kidney tissue in different environments and using laser configurations. The 100 W Ho: YAG (Cyber Ho, Quanta System, Italy) and 60 W TFL (Fiber Dust, Quanta System, Italy) laser devices were used. The following laser settings were selected: power in the range of 10-60 W, frequency of 20-40 Hz, and energy of 0.5-1-1.5 J. A medium pulse duration of 600 µsec was used for VB™, while short (spdTFL; 50 µsec) and long (lpdTFL; 15,000 µsec) were used for TFL. The tissue's incision depth (ID), vaporization area (VA), coagulation area (CA), total laser area (TLA = VA + CA), surface section (SS), and lateral effect (LE) were measured. In total, 108 experiments were conducted. No statistically significant difference in mean VA, TLA, ID, LE, or SS was observed between VB™, spdTFL, and lpdTFL in the low-power output group in saline (p > 0.05). However, the mean CA was statistically significantly higher for VB™ (p = 0.005). In saline and high-power output group, the mean VA, CA, TLA, LE, and ID were higher when using lpdTFL than other pulse durations (p = 0.001, p = 0.001, p = 0.001, p = 0.006, and p = 0.001, respectively). Similar to lpdTFL, VB™ may provide controlled dissection and incision as well as haemostasis. At different laser settings, the individual effects of laser properties (such as pulse length, energy and frequency) on tissue may be more significant.

Treatment of Urolithiasis with Thulium Fiber Laser in Fragmentation Mode Using Optimized Pulse Sequences.

Objectives: The super-pulsed thulium fiber laser (SP TFL) is a new alternative to high-power holmium laser for intracorporeal lithotripsy. The SP TFL has shown advantages in dusting regimes, but benefits in fragmentation regimes are less understood. The second-generation SP TFL introduces an advanced fragmentation pulse (AFP) sequence to maximize SP TFL's efficiency in fragmentation. This study evaluates safety and efficacy of the SP TFL fragmentation mode in ureteroscopy (URS) and mini percutaneous nephrolithotomy (mini-PCNL). Materials and Methods: The study was conducted in two phases. Safety of a new AFP was compared ex vivo to standard SP TFL fragmentation settings by measuring the dimensions of wounds created in porcine kidney after laser exposure for 0.5, 1.0, and 2.0 s. The resulting wounds were evaluated histologically using nitro blue tetrazolium chloride (NBTC) stain. In the clinical phase, the second-generation SP TFL was used to fragment and extract ureteral and renal stones in 40 patients using ureteroscopic and percutaneous approaches. The stone size, volume, density, laser-on-time, and total energy were recorded for each patient. In addition, the chemical composition, ablation rate, and ablation efficiency were assessed for each stone treatment. Results: The ex vivo mucosa damage profiles caused by AFP were similar to those caused by regular pulses. In clinical phase, the median volume and density for ureteral stones were 0.4 cm3 and 1029 Hounsfield units (HU), for renal stones 1.3 cm3 and 1113 HU, respectively. Different stone types were crushed into fragments suitable for extraction. The mean AFP energy was 3 J and the average power for ureteral stones was 10.5 W, whereas for renal stones it was 28.5 J and 31 W, respectively. The overall complication rate was low in both groups. Conclusion: ST PFL with AFP capability facilitates effective fragmentation of ureteral and renal stones of any composition during URS and mini-PCNL with minimal complication rates.

Fiber Laser Writing of Highly Sensitive Nickel Nanoparticle-Incorporated Graphene Strain Sensors.

Unlocking new dimensions in wearable sensor technology, this research highlights ultrasensitive stretchable strain sensors fabricated with the customized laser-induced graphene (LIG) decorated with uniformly distributed nickel nanoparticles with a fiber laser writing process. The nickel nanoparticle-incorporated LIG (Ni-NPs@LIG) strain sensors fabricated by a simple all-laser-based method utilize a commercial fiber laser. The Ni-NPs@LIG sensors showcase an impressive gauge factor, reaching up to 248 for strain values below 5%, demonstrating a sensitivity increase of up to 430% compared to the pure LIG sensors. Moreover, these sensors offer adjustable strain sensitivity based on laser fluence. The key advancement of this study lies in the direct laser writing of highly porous nickel-graphene nanostructures with adjustable properties, making them applicable across a broad range of applications. As an application demonstration, the strain sensors were employed to assess the small deformation of a pouch battery or track the large deformation of a balloon surface.

Ag/MXene as Saturable Absorber for Tm:Ho Co-Doped Q-Switched Fiber Laser.

Q-switched fiber lasers have become reliable light sources for generating high-energy pulses, which can be passively modulated by saturable absorbers with excellent nonlinear optical properties. The composite combining Ag and MXene exhibits a broadband nonlinear response and high modulation depth, making it a promising candidate for saturable absorbers in pulsed lasers. Herein, we demonstrate a Q-switched Tm:Ho co-doped fiber laser centered at 2 µm, where the Ag/MXene composite serves as a saturable absorber to generate pulses. The typical spectrum, pulse train, and radio frequency spectrum of Q-switched pulses were observed, in which the 60 dB signal-to-noise ratio was higher than that of 2 µm Q-switched fiber lasers based on other materials, demonstrating the stability of the output pulses. Additionally, the long-term stability of the laser was evaluated over 2 h, where the well-maintained central wavelength and output power also indicated the robustness of the Q-switched laser. Furthermore, the influence of the pump power on the parameters of Q-switched pulses was also investigated, which is conducive to control the output characteristics of lasers. Specifically, the pulse width of the Q-switched pulse decreased, while the repetition rate, output power, and single pulse energy all increased with the increase in pump power. These experimental results demonstrate the ability of Ag/MXene as a saturable absorber and show its potential for generating high-performance pulses in ultrafast lasers.

Thulium Fiber Versus Holmium:Yttrium-aluminum-garnet Laser for Endoscopic Enucleation of the Prostate: A Systematic Review and Meta-analysis.

BACKGROUND AND OBJECTIVE: Thulium fiber laser (TFL) emerged as a competitor of holmium:yttrium-aluminum-garnet (Ho:YAG) laser for anatomic enucleation of the prostate (AEEP) in men with lower urinary tract symptoms (LUTS) related to benign prostatic obstruction (BPO). The aim was to compare the surgical outcomes of Ho:YAG and TFL for AEEP. METHODS: A literature search was conducted to identify reports published from inception until January 2024. The Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed to identify eligible studies. The coprimary outcomes were the postoperative International Prostate Symptom Score (IPSS), IPSS-Quality of Life (IPSS-QoL), and peak urinary flow (Qmax). KEY FINDINGS AND LIMITATIONS: Five studies met our inclusion criteria, and data from 1287 and 1555 patients who underwent AEEP with Ho:YAG (holmium laser enucleation of the prostate [HoLEP]) and TFL (thulium fiber laser enucleation of the prostate [ThuFLEP]), respectively, were reviewed. ThuFLEP was associated with a better IPSS at 3 mo even if the difference was not clinically significant (mean difference [MD] 0.59, 95% confidence interval [CI]: 0.29-0.88; p < 0.001). No difference was found for IPSS at 6-12 mo (p = 0.9), and IPSS-QoL at 3 mo (p = 0.9) and 6-12 mo (p = 0.2). HoLEP was associated with a better Qmax at 3 mo (MD 1.41 ml/s, 95% CI: 0.51-2.30; p = 0.002) and ThuFLEP at 6-12 mo (MD -2.61 ml/s, 95% CI: -4.68 to 0.59; p = 0.01), but the differences were not clinically significant. No difference was found in the major (p = 0.3) and overall (p = 0.3) complication rates. HoLEP was associated with shorter enucleation (MD -11.86, 95% CI: -22.36 to 1.36; p = 0.03) but not total operative time (p = 0.5). CONCLUSIONS AND CLINICAL IMPLICATIONS: The present review provides the most updated evidence on the impact of Ho:YAG and TFL in AEEP, demonstrating that these two energy sources are effective in relieving bothersome LUTS in men with BPO. PATIENT SUMMARY: Thulium fiber laser is a new energy source that can be used safely for performing endoscopic enucleation of the prostate in men with bothersome symptoms associated with benign prostatic enlargement.

Optimal parameter settings of thulium fiber laser for ureteral stone lithotripsy: a comparative study in two different testing environments.

This study aims to identify optimal parameters for using Thulium fiber lasers (TFL) in ureteral stone lithotripsy to ensure laser safety and maximize efficacy. Our goal is to improve the outcomes of single-use semi-rigid ureteroscopy for treating stones located in the proximal ureter. A clinically relevant thermal testing device was designed to investigate heating effects during TFL stone fragmentation. The device was utilized to identify safe power thresholds for TFL at various irrigation rates. Three other devices were used to assess varying pulse energy effects on stone fragmentation efficiency, dusting, retropulsion, and depth of tissue vaporization. Comparative experiments in fresh porcine renal units were performed to validate the efficacy and safety of optimal TFL parameters for semi-rigid ureteroscopy in proximal ureteral stone procedures. Our study found that the improved device generated a higher thermal effect. Furthermore, the safe power threshold for laser lithotripsy increased as the irrigation rate was raised. At an irrigation rate of 40 ml/min, it is safe to use an average power of less than 30 watts. Although increasing pulse energy has a progressively lower effect on fragmentation and dust removal efficiency, it did lead to a linear increase in stone displacement and tissue vaporization depth. Thermal testing showed 20 W (53.87 ± 2.67 °C) indicating potential urothelial damage. In our study of laser lithotripsy for proximal ureteral stones, the group treated with 0.3 J pulses had several advantages compared to the 0.8 J group: Fewer large fragments (> 4 mm): 0 vs. 1.67 fragments (1-2.25), p = 0.002, a lower number of collateral tissue injuries: 0.50 (0-1.25) vs. 2.67 (2-4), p = 0.011, and lower stone retropulsion grading: 0.83 (0.75-1) vs. 1.67 (1-2), p = 0.046. There was no significant difference in operating time between the groups (443.33 ± 78.30 s vs. 463.17 ± 75.15 s, p = 0.664). These findings suggest that TFL irradiation generates a greater thermal effect compared to non-irradiated stones. Furthermore, the thermal effect during laser lithotripsy is influenced by both power and irrigation flow rate. Our study suggests that using a power below 15 W with an irrigation flow rate of 20 ml/min is safe. Moreover, a pulse energy of 0.3 J appears to be optimal for achieving the best overall stone fragmentation effect.

Coherent beam combining of two all-PM thulium-doped fiber chirped pulse amplifiers.

In this paper, we report a coherent beam combining (CBC) system that involves two thulium-doped all-polarization maintaining (PM) fiber chirped pulse amplifiers. Through phase-locking the two channels via a fiber stretcher by using the stochastic parallel gradient descent (SPGD) algorithm, a maximum average power of 265 W is obtained, with a CBC efficiency of 81% and a residual phase error of λ/17. After de-chirping by a pair of diffraction gratings, the duration of the combined laser pulse is compressed to 690 fs. Taking into account the compression efficiency of 90% and the main peak energy proportion of 91%, the corresponding peak power is calculated to be 4 MW. The laser noise characteristics before and after CBC are examined, and the results indicate that the CBC would degrade the low frequency relative intensity noise (RIN), of which the integration is 1.74% in [100 Hz, 2 MHz] at the maximum combined output power. In addition, the effects of the nonlinear spectrum broadening during chirped pulse amplification on the CBC efficiency are also investigated, showing that a higher extent of pulse stretching is effective in alleviating the spectrum broadening and realizing a higher output power with decent combining efficiency.

Efficient single-pixel imaging based on a compact fiber laser array and untrained neural network.

This paper presents an efficient scheme for single-pixel imaging (SPI) utilizing a phase-controlled fiber laser array and an untrained deep neural network. The fiber lasers are arranged in a compact hexagonal structure and coherently combined to generate illuminating light fields. Through the utilization of high-speed electro-optic modulators in each individual fiber laser module, the randomly modulated fiber laser array enables rapid speckle projection onto the object of interest. Furthermore, the untrained deep neural network is incorporated into the image reconstructing process to enhance the quality of the reconstructed images. Through simulations and experiments, we validate the feasibility of the proposed method and successfully achieve high-quality SPI utilizing the coherent fiber laser array at a sampling ratio of 1.6%. Given its potential for high emitting power and rapid modulation, the SPI scheme based on the fiber laser array holds promise for broad applications in remote sensing and other applicable fields.

A Single-Longitudinal-Mode S + C Band Wavelength-Tunable Fiber Laser.

An external cavity wavelength-fiber ring laser (ECWTFL) based on a semiconductor optical amplifier and a combined wavelength scanning filter in the Littrow configuration is proposed and experimentally demonstrated. With the benefit of the combination of an external cavity wavelength filter and a Lyot filter, the laser achieves a single-mode narrow linewidth output with a linewidth of 1.75 kHz. The wavelength tuning range reaches 133 nm, covering the entire S + C band. The proposed ECWTFL is used for demodulation of a fiber EFPI sensor; the result shows that the proposed ECWTFL has the ability to demodulate the small cavity-length FPI sensor.

Cascaded All-Fiber Gas Raman Laser Oscillator in Deuterium-Filled Hollow-Core Photonic Crystal Fibers.

Hollow-core photonic crystal fibers (HC-PCFs) provide an ideal transmission medium and experimental platform for laser-matter interaction. Here, we report a cascaded all-fiber gas Raman laser based on deuterium (D2)-filled HC-PCFs. D2 is sealed into a gas cavity formed by a 49 m-long HC-PCF and solid-core fibers, and two homemade fiber Bragg gratings (FBGs) with the Raman and pump wavelength, respectively, are further introduced. When pumped by a pulsed fiber amplifier at 1540 nm, the pure rotational stimulated Raman scattering of D2 occurs inside the cavity. The first-order Raman laser at 1645 nm can be obtained, realizing a maximum power of ~0.8 W. An all-fiber cascaded gas Raman laser oscillator is achieved by adding another 1645 nm high-reflectivity FBG at the output end of the cavity, reducing the peak power of the cascaded Raman threshold by 11.4%. The maximum cascaded Raman power of ~0.5 W is obtained when the pump source is at its maximum, and the corresponding conversion efficiency inside the cavity is 21.4%, which is 1.8 times that of the previous configuration. Moreover, the characteristics of the second-order Raman lasers at 1695 nm and 1730 nm are also studied thoroughly. This work provides a significant method for realizing all-fiber cascaded gas Raman lasers, which is beneficial for expanding the output wavelength of fiber gas lasers with a good stability and compactivity.

Switchable Single- to Multiwavelength Conventional Soliton and Bound-State Soliton Generated from a NbTe2 Saturable Absorber-Based Passive Mode-Locked Erbium-Doped Fiber Laser.

As a member of transition metal dichalcogenides (TMDs), NbTe2 has a work function of 5.32 eV and a band gap of 0 eV at the Fermi level, which enables it to possess broadband absorption characteristics and has huge potential in optoelectronic devices. In this work, a combination of liquid phase exfoliation (LPE) and optical deposition methods (ODMs) were used to fabricate a NbTe2 saturable absorber (SA). Based on the NbTe2 SA, a ring passive mode-locked erbium-doped fiber laser (PML-EDFL) was constructed by adding NbTe2 SA into the laser cavity. A switchable single- to multiwavelength (dual/triple/quadruple) conventional soliton (CS) and a bound-state soliton (BS) were observed for the first time. The results reveal that NbTe2 SA has excellent saturable absorption characteristics (modulation depth of 2.6%, saturation intensity of 177.4 MW/cm2, and unsaturated loss of 63.8%) and can suppress mode competition and stabilize multiwavelength oscillation. This study expands the applications of NbTe2 nanosheets in ultrafast optoelectronics. The proposed switchable PML-EDFL has extensive applications in high-capacity all-optical communication, high-sensitivity optical fiber sensing, high-precision spectral measurements, and high-energy-efficiency photon neural networks.