Pump Power Range Research Articles

Mode-locked soliton pulse generation using copper phthalocyanine absorber in long erbium-doped fibre laser cavity

We present the development of a mode-locked erbium-doped fibre laser (EDFL) utilizing Copper Phthalocyanine (CuPc) as a saturable absorber (SA). CuPc exhibits unique optical properties, including its high nonlinear optical response and rapid recovery time. To seamlessly integrate CuPc into the laser cavity, we employed a simple embedding technique within a polymer film. The SA demonstrates a modulation depth of 3.1% and a saturation intensity of 17 MW/cm2. Operating within a pump power range of 90.6 to 122.9 mW, the laser achieves mode-locked operation, producing a soliton pulse train with a fundamental frequency of 1.82 MHz and a pulse width of 6.4 ps at a wavelength of 1561.5 nm. It attains a maximum output power of 13.97 mW and a pulse energy of 7.67 nJ. These results underscore CuPc's potential as a promising material for generating mode-locked pulses, suggesting new avenues in ultrafast laser development for diverse applications.

Cerium oxide for L-band Q-switched pulse laser generation

Cerium oxide (CeO2), a rare earth metal oxide belonging to the lanthanide group is a mature engineered nanoparticle that has been developed for various industry applications. The nanoparticle features defects in its lattice structure, which is highly advantageous for bandgap tuning, and is acclaimed for its least cytotoxicity among other metal oxides. In this work, CeO2 is employed as a saturable absorber (CeO2-SA) in the generation of an L-band Q-switched erbium-doped fiber laser. Q-switching was attained at 33.33 mW pump power threshold with a central wavelength of 1600.512 nm. Within 33.33 mW to 153.20 mW pump power range, the Q-switched laser obtained pulse repetition rates between 11.00 to 34.48 kHz, and pulse widths between 39.0 to 12.0 µs, with a high maximum pulse energy of 410 nJ. The Q-switched fiber laser remained stable over a 45-minute observation time at 153.20 mW pump power. The room temperature and direct mechanical deposition fabrication technique of the CeO2-SA in this work demonstrates the extreme simplicity and low cost of the device, which would reduce the overall cost and facilitate a wider technology adoption of pulse laser systems.

A novel tuning range search method for single soliton state micro-comb generation

Abstract Mode-locked single-soliton state micro-comb (SSC) can be achieved in a miniaturized highly compact platform by pumping the micro-resonator with a single-frequency continuous wave laser. However, a significant challenge lies in effectively exploring the tuning range of pump power, spanning over hundreds of mW, as well as the detuning range and tuning speed in the range of hundreds of MHz and the order of MHz/s to GHz/s respectively. Here, we delve into a simulation model, considering thermal effects to ensure that the simulation accurately reflects the power drop and thermal detuning observed in the experimental process. Our simulation model, featuring precision scanning and iterative parameter demonstrations, has proven instrumental in accurately exploring the optimal tuning range for the existence of SSC to a few MHz. This provides a foundation for controlled and predictable SSC generation experiments.

Polyacrylonitrile enabled soliton mode-locked fiber laser

Exploring novel saturable absorber (SA) materials with superior performance to enable mode-locking operation remains a forefront in ultrafast laser research. In this study, we unveil the potential of polyacrylonitrile (PAN) based SA for ultrafast fiber laser applications. By probing the nonlinear absorption characteristics of PAN SA within the telecommunication band using the balanced twin-detector method, we reveal its substantial modulation depth of 10.7 %. Incorporating PAN SA into the Erbium-doped fiber laser (EDFL) cavity facilitated stable mode-locking operation. The resultant EDFL system produces a conventional soliton pulse train centered at 1568.4 nm wavelength, with mode-locking sustained over a pump power range from 87.2 to 254.1 mW. Moreover, the laser exhibits a pulse duration of 3.64 ps and achieves a maximum pulse energy of 2.04 nJ. These results highlight the efficacy of PAN-based SA, demonstrating properties comparable to established 2D SAs. The implications of this research are pivotal in advancing the application of novel organic polymers in ultrafast lasers.

Sub-megahertz compact self-pulsed Raman laser

Broadband self-pulsed Raman laser operating at sub-megahertz (sub-MHz) has been widely used in optical sensing, high-spectral-resolution lidar, frequency-division multiplexing, and optical communication. However, it is a big challenge for achieving stable self-pulsed Raman laser oscillation in a wide pump power range. Here, we construct a compact Yb:YAG/YVO4 Raman laser for generating broadband self-pulsed laser operating at high repetition rate. The effects of cavity length (LC) and Raman crystal length (LR) on the performance of self-pulsed Raman laser have been investigated. By utilizing a 1.5 mm-thick YVO4 crystal as a Raman crystal, the repetition rate increases dramatically from 62 to 280 kHz when the LC decreases from 10 to 4 mm. Meanwhile, the pulse width of 0.66 μs and peak power of 1.1 W are achieved for the self-pulsed Raman laser with LC = 4 mm. For the 4 mm-long Raman laser cavity constructed with a 2 mm-thick YVO4 crystal, the pump power range enable for self-pulsed Raman laser oscillation extends from 1.8 to 3.9 W, the repetition rate has been further increased from 258 to 467 kHz. While the peak power and pulse width are 0.6 W and 0.98 μs, respectively. The Yb:YAG/YVO4 self-pulsed Raman laser oscillates in broadband multi-longitudinal-mode, the spectral bandwidth is 27.4 nm covering from 1051.1 to 1078.5 nm. Utilization of a tilted 2 mm-thick YVO4 crystal as output coupler to construct compact Yb:YAG/YVO4 self-pulsed Raman laser dramatically expands the pump power range for generating high repetition rate self-pulsed Raman laser. Sub-MHz self-pulsed Raman lasers with a wide spectral bandwidth have potential applications in materials processing, quantum information processing, and optical communications.

Mode-locked erbium-doped fiber laser based on Cr2GaC saturable absorber

We successfully generated short pulse in an erbium-doped fiber laser (EDFL) cavity utilizing a new saturable absorber (SA) based on chromium gallium carbide (Cr2GaC). The SA film was prepared by implanting the Cr2GaC compound into a polyvinyl alcohol (PVA) matrix. Upon integration into the laser’s cavity, we achieved a stable mode-locked laser centered at 1558.24 nm. This stability was maintained within a pump power range of 53.7–95.2 mW. Operating at a fixed repetition rate of 1.82, matching the cavity length, the laser consistently delivered pulses with a duration of 3.04 picoseconds. At its peak performance with a pump power of 95.2 mW, the laser exhibited an average power output of 6.81 mW, a peak power of 1.08 W, and a pulse envelope energy of 3.74 nJ. A noteworthy aspect of our study is the exceptional stability demonstrated by the laser. This stability is evidenced by a signal-to-noise ratio of 71.7 dB for the fundamental frequency. Importantly, this research represents a significant milestone as it marks the first instance of achieving soliton pulses in a laser cavity utilizing Cr2GaC as a SA.

High-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser operating at 1.7 µm

We report on a high-power and narrow-linewidth nanosecond pulsed intracavity crystalline Raman laser at 1.7 µm. Driven by an acousto-optically Q-switched 1314 nm two-crystal Nd:YLF laser, the highly efficient cascaded YVO4 Raman laser at 1715nm was obtained within the well-designed L-shaped resonator. Thanks to the absence of spatial hole burning in the stimulated Raman scattering process, significant spectral purification of second-Stokes radiation was observed by incorporating a fused silica etalon in the high-Q fundamental cavity. Under the repetition rate of 4 kHz, the highest average output power for single longitudinal mode operation was up to 2.2 W with the aid of precision vibration isolation and precision temperature controlling, corresponding to the pulse duration of ∼2.8 ns and the spectral linewidth of ∼330 MHz. Further increasing the launched pump power, the second-Stokes laser tended toward be always multimode, and the maximum average output power amounted to 4.8 W with the peak power of ∼0.8 MW and the spectral linewidth of ∼0.08 nm. The second-Stokes emission was near diffraction limited with M2 < 1.4 across the whole pump power range.

Soliton mode-locked pulse generation with Polyaniline saturable absorber

We demonstrate the successful mode-locking of an Erbium-doped fiber laser (EDFL) utilizing a Polyaniline (PANI) saturable absorber (SA), resulting in the production of picosecond pulses at a frequency of 1.8 MHz within an elongated ring cavity. The SA is engineered by embedding PANI into Polyvinyl Alcohol (PVA). This conducting polymer-based SA exhibits favorable optical nonlinear properties, boasting a modulation depth of 2.3 %, a saturation intensity of 7.8 MW/cm2, and a non-saturable loss of 5.6 %. The laser system generates a conventional soliton pulse train at a central wavelength of 1572.62 nm. The mode-locking operation is sustained within a pump power range from 139.4 to 254.12 mW. The laser also achieves a pulse duration of 3.0 ps and a maximum pulse energy of 0.4 nJ. These findings underscore the effectiveness of the proposed PANI-based SAs, which exhibit comparable properties to currently utilized 2D SAs. The successful mode-locking operation and the promising optical characteristics of the PANI-based SA provide a solid foundation for their potential applications in the realm of ultrafast photonics.

Passively Q-Switched 1.5- μm Erbium-Doped All-Fibre Laser with Silver Saturable Absorber

This research examines the operation of a passively Q-switched erbium-doped all-fibre laser (EDFL) using a silver (Ag) based saturable absorber (SA) by comparing the output characteristics of the Q-switched laser with those of continuous wave all-fibre lasers. A study was done on how the laser's Q-factor is modified and affects the rate at which pulses are repeated, as well as their output power, width, and energy. The results showed that high-energy Q-switched pulses were successfully generated at the essential 1.5 µm wavelength within the pump power range of 83.6 mW to 171.7 mW, with repetition rates ranging from 33.46 kHz to 77.96 kHz. The EDFL generated a pulse with a width of 4.033 µs and an energy of 2.82 nJ at a pump power of 171.7 mW. The results indicate that Ag may potentially be a good SA for pulse production in the 1.5 µm wavelength area as well as for use in a wide range of applications.

Liquid-cooled heat sink design methodology with technical and commercial viability considerations: Case study of a partially 3-D printed prototype

A two-step methodology is proposed for the design and optimization of liquid-cooled heat sinks, where manufacturing costs are included as a commercial viability assessment metric. First, manifold modifications were made to reduce pressure losses in the baseline design. Second, a full-factorial parametric computational fluid dynamics (CFD) study fed an artificial neural network (ANN) model for further optimization. The aforementioned methodology was applied to the optimization of liquid-cooled heat sinks for CPU cooling. The baseline design consisted of a 3-D printed resin plenum mounted on a metallic heat spreader with parallel fin channels. The plenum delivers a slot jet along the center of the heat sink into a central passage that bifurcates the fin channels. An improved plenum design with ∼11% lower pressure losses than the baseline model was generated after the first optimization step. The designs generated in the parametric CFD study achieved average thermal resistances as low as 0.01 K/W for a theoretical pumping power range of 50–350 mW. A representative design from this study was manufactured and experimentally tested to assess the simulation approach, providing reasonable agreement with the numerical results. Consecutively, the ANN allowed for a higher resolution sampling of the design space, where optimal configurations were found in terms of an overall thermo-hydraulic performance parameter and an additional metric accounting for manufacturing costs. The methodology reported herein caters to heat sink designers seeking commercialization of their prototypes as the contrast between technical performance and manufacturing costs is addressed. Additionally, the mathematical tools utilized allow for cost-effective topology optimizations.

Generation of Q-switched and mode-locked pulses in erbium-doped fiber ring laser using saturable absorption of Ti2SnC

MAX phase materials have garnered significant attention due to their corrosion resistance, impressive antioxidation and high electrical and optical conductivity. One such material, Titanium Tin Carbide (Ti2SnC), has demonstrated notable nonlinear optical properties. The saturable absorption of Ti2SnC, embedded into a polyvinyl (PVA) film, was measured to assess its potential. The Ti2SnC -PVA film exhibited a calculated modulation depth of 7.8%. In the context of practical applications, the Ti2SnC-PVA film was employed as a saturable absorber (SA) in an Erbium-doped fiber laser (EDFL) cavity. This configuration enabled the generation of stable Q-switched and mode-locked pulse trains. Q-switched operation occurred in a pump power range of 51.67 mW–83.83 mW, reaching a peak pulse energy of 110.94 nJ. Transitioning to mode-locking operation, the laser cavity demonstrated efficiency in the pump power range of 105.27 mW–196.39 mW. At a pump power of 196.39 mW, the fiber laser cavity achieved its highest pulse energy of 5.42 nJ, characterized by a pulse width of 2.32 ps and a pulse repetition rate of 1.825 MHz. These results highlight the promising potential of Ti2SnC-PVA thin film as a cutting-edge material for applications in pulsed laser systems. The material's excellent nonlinear optical properties make it a compelling candidate for advancing the field of pulsed laser technology.

Superior Performances of Q-Switched and Mode-Locked Erbium-doped Fiber Laser using Black Titanium Dioxide Thin-film Saturable Absorbers

This work reports on the improved Q-switched and mode-locked performances of black titanium dioxide (BTiO2-x) nanoparticles embedded in thin-film composite material as a saturable absorber compared to TiO2 in an erbium-doped fiber laser. The thin-film saturable absorbers were prepared by mixing the nanoparticles with polyvinyl alcohol (PVA) as a host. BTiO2-x has a better nonlinear absorption coefficient, β of -12.46 x 10-7 m/W compared to -7.15x 10-7 m/W for TIO2 determined using z-scan measurement. The laser performance was evaluated in the 85.21 mW – 126.48 mW pump power range. Upon inserting TiO2 and BTiO2-x SA in a laser cavity, the peaks of the output spectrum shifted from 1566.62 nm to 1563.24 nm and 1565.75 nm, respectively. Regarding Q-switched performances, BTiO2-x SA generates a shorter pulse width of 16.00 µs than TiO2 SA. The slope efficiency of the TiO2 SA was 11.72 %, which is higher than the slope efficiency of the BTiO2-x SA. The maximum average and peak power generated by the BTiO2-x SA were 55.67 % and 54.83 % higher than the TiO2 SA. As for mode-locked outputs, BTiO2-x SA can generate pulsed laser at a low threshold power of 62.29 mW compared to TiO2 SA. Furthermore, BTiO2-x SA produced a shorter pulse width of 5.04 ps, whereas TiO2 is 9.20 ps. This study demonstrates that BTiO2-x SA has the potential to produce ultrashort pulse width using the mode-locked technique.

Domain-wall dark pulse generation with SMF-GIMF-SMF structure as artificial saturable absorber

We experimentally demonstrated the generation of domain-wall dark pulse in an Erbium-doped fiber laser using the combination of a 10 cm graded index multimode fiber sandwiched by single mode fibers as artificial saturable absorber. The interaction of phase difference in grade index multimode fiber allowed the stable dual-wavelength oscillation in the cavity. The dual-wavelength centered at 1567.2 nm and 1569.4 nm produces the topological defect in temporal domain and achieved a dark pulse formation with repetition rate of 21.5 MHz. The highest average pulse energy is calculated as 769.6 pJ with pulse width of 5 ns. Throughout the operating pump power range, the average pulse energy and output power increase linearly, with R2 of 0.9999 and achieved the laser efficiency of 9.33%. From the measurement in frequency domain, the signal-to-noise ratio is measured as 49 dB. As compared to reported DW dark pulse works, the proposed structure only required a short length of multimode fiber, which allowed the domain-wall dark pulse to achieve higher pulse repetition rate. The venture of domain wall dark pulse is potentially to pave the foundation toward sustainable industrial growth.

Spatio-temporal study of single and multi-wavelength quasi-continuous-wave generation regimes in an all-normal dispersion ring cavity

In this paper, we report a comprehensive experimental study of quasi-continuous-wave operation in an all-normal-dispersion ring cavity laser with nonlinear polarization rotation based saturable absorber action. Using the temporal mapping technique, we analyze in real time spiking dynamics, characterized by the existence of ephemeral spikes that continually emerge and decay amidst the background radiation. In particular, the effects of the pumping level and its direction of variation on the laser emission dynamics were analyzed. The overall behavior, in particular the well-defined pattern of spike evolution between their emergence until their vanishing, is found to be qualitatively invariant over a broad range of pump power, from 70 mW to 550 mW, albeit the values of spiking parameters vary widely over this range. The spiking phenomenon appears from low pumping powers, just above the laser threshold. A phenomenon of hysteresis was also discovered, as some emission parameters, in particular the optical spectrum, depend on whether pump power is being raised or decreased. 2D autocorrelation analysis also proved insightful, showing that each spike appears at random, having no connection with other spikes. Finally, high pump power settings and birefringence adjustments enabled the discovery of more complex spiking dynamics where emission at various wavelengths occur, some of the lines presenting additional slow dynamics at the millisecond scale. These results indicate that deterministic complexity is, together with stochasticity, an essential ingredient to take into account for a better understanding of the operational modes in fiber lasers far from the pulsed regime.

Effects of PEMFC cooling channel insulation coating on heat transfer and electrical discharge characteristics of nanofluid coolants

Nanofluids have high thermal conductivity and electrical conductivity, and there is a problem of electrical discharge when used as a coolant in proton exchange membrane fuel cell (PEMFC). In this study, the compact Al2O3 insulating coating was prepared by supersonic plasma spray processing technology and evenly coated in the cooling channel. The electrical discharge effect and heat transfer enhancement ability of three coolants, namely deionized water, Al2O3 nanofluid and graphene nanofluid, were studied when applied in the electrically active atmosphere of PEMFC. The results show that, the graphene nanofluid has the best heat transfer performance before insulation coating integration, but the dispersion of solid nanoparticles in the base fluid leads to a higher pressure drop, with an increase of 6.7%. When the voltage is 200 V, the leakage current of Al2O3 nanofluid and graphene nanofluid is up to 16 mA and 33 mA respectively. After insulation coating integration, the index of uniform temperature (IUT) and maximum temperature of graphene nanofluids further decrease, while the pressure drop increases by 7.0%. The leakage current of all three coolants at different voltages and Re numbers decrease to 0, indicating a significant improvement in the insulation performance of PEMFC cooling channel. In addition, dimensionless evaluation parameter ε for the applicability of heat transfer fluids were proposed from the perspectives of work and energy. Within the pump power range of 0.0065 W ∼ 0.0325 W, the ε of graphene nanofluids with insulating coating is always lower than Al2O3 nanofluid. At the pump power of 0.014 W, the ε of graphene nanofluids with insulating coating is 0.76, which has the best coolant applicability when applied in the electrically active atmosphere of PEMFC.

Novel design and numerical investigation of a windward bend flow field for proton exchange membrane fuel cell

3D flow field design usually improves the performance of proton exchange membrane fuel cell (PEMFC) with the penalty of a dramatically increasing pressure drop. To surmount this issue, a novel windward bend flow field that exhibits superior mass transfer performance under a constant pumping power is proposed in this study. The performance of PEMFC with windward bend flow field is numerically compared with two canonical 3D flow fields, namely 3D wave flow field and cutting cylindrical baffles flow field. Results demonstrated that compared with two canonical 3D flow fields, windward bend flow field gets a better water management capability. The optimal distance, tilt angle and direction for the windward bend structure embedded in channel are 2.0 mm, 15° (at the direction of the front section of the windward bend structure tilts towards membrane electrode assembly). Furthermore, the average enhancement rate of the maximum power density of PEMFC with optimal windward bend flow field is 7.6 % and 12.4 % compared with cutting cylindrical baffles flow field and 3D wave flow field owing to the larger Sherwood number of optimal windward bend flow field under the specified pumping power range.

Performance improvement of dual-GSA-wavelength pumped heavily-doped 3 μm Er:YSGG laser by using wing-pumping method

The dual-GSA-wavelength pumping combined with wing-pumping method has been successfully used to improve the output performance of a 30 at.% Er:YSGG laser at 3 μm. According to the GSA spectrum of 4I15/2→4I9/2 transition at 0.8 μm, two pump wavelengths of 785 and 798 nm are used to verify the effectiveness of dual-GSA-wavelength pumping, with 798 nm overlapping an absorption peak, while 785 nm deviating from the absorption peak of Er:YSGG crystal. With regard to the 798/976 nm dual-wavelength pumping, the output power fails to maintain a continuous growth trend with the dual-wavelength pump power in comparison with the single-wavelength pumping at 976 nm. This indicates the influence of thermal effects on the heavily erbium-doped material is more severe, resulting in a significant reduction in the available pump power range. When the 785 nm with weak absorption is used for dual-wavelength pumping, the output power achieves a nearly linear increase within a larger range of dual-wavelength pump power. The achievable maximum output power is 662 mW for the 785/976 nm dual-wavelength pumping, respectively increased by 13.2 % and 64.7 % compared to the achievable maximum output power obtained in 976 nm single-wavelength and 798/976 nm dual-wavelength pumping. It is also found that the introduction of 785 nm pump light would lower the threshold for achieving dual-wavelength laser output for the Er:YSGG laser. The dual-GSA-wavelength pumping combined with wing-pumping method provide an effective solution for improving the performance of heavily erbium-doped lasers at 3 μm.

Q-switched pulse generation by stimulated Brillouin scattering assisted four-wave mixing effect in erbium–bismuth co-doped multi-elements silica glass based optical fiber laser

We demonstrate Q-switched pulse generation at the 1562.5 nm region by using a 70 cm long erbium–bismuth co-doped alumina–germania–hafnium–yttria silica glass-based fiber as a gain medium in a simple ring resonator configured without saturable absorber and optical isolator devices. The Q-switching was obtained based on a stimulated Brillouin scattering assisted four-wave mixing effect in the gain medium, which induced the intensity modulation mechanism. The laser produced a multi-wavelength output comb centered at 1562.6 nm with a peak-to-peak spacing of about 0.09 nm due to nonlinear effects. Stable Q-switched operation of a hafnia–bismuth–erbium co-doped fiber laser was obtained at a pump power range of 129–319 mW with the repetition rate varying from 45.9 kHz to 89.3 kHz and the pulse width ranging from 8.8 µs to 3.58 µs. A maximum pulse energy of 26.9 nJ at an average output power of 2.4 dBm was achieved. This demonstrates a new passive technique based on a highly nonlinear gain medium for realizing Q-switched all-fiber laser sources.

Self-induced Q-switched fiber laser using tantalum aluminum carbide as a passive modulator

A self-induced Q-switched erbium-doped fiber laser operating at 1563 nm was achieved by integrating a passive modulator based on tantalum aluminum carbide (Ta2AlC) MAX phase film embedded into polyynyl alcohol. The modulator, serving as a saturable absorber (SA), established a modulation depth of 9% and a saturation intensity of 0.3 MW cm−2. Upon integration of the film SA, a stable Q-switched fiber laser was obtained, generating pulses with a minimum width of 7.6 µs at a repetition rate of 45.1 kHz, within a pump power range of 24.9–59.7 mW. The corresponding maximum average output power, maximum pulse energy, and highest peak power were determined at 1.6 mW, 36.2 nJ, and 4.7 mW, respectively. The RF fundamental spectrum exhibited a good signal-to-noise ratio of 61 dB, indicating excellent pulse signal quality. This demonstration of Ta2AlC MAX phase film Q-switched laser may open promising possibilities for scientific applications such as material processing.

Enhanced Q-switched pulse generation at 1.5 µm in erbium-doped fiber laser using Thin-Film Dititanium Tin Carbide as a saturable absorber

In this study, we demonstrate the utilization of a saturable absorber (SA) based on the Thin-Film Dititanium Tin Carbide (Ti2SnC), a novel MAX phase material, in a Q-switched erbium-doped fiber laser (EDFL) operating at 1.5 µm. The Ti2SnC was effectively integrated with an EDFL cavity to modulate cavity loss and facilitate Q-switching. The resultant SA was produced through a synergistic combination of Ti2SnC and polyvinyl alcohol (PVA), forming a thin film. The Q-switched operation exhibited high stability, achieving an impressive signal-to-noise ratio (SNR) of 65.41 dB. The laser operated within a pump power range of 67.75 mW to 115.99 mW, correlating to a laser diode current of 130–220 mA. This resulted in output power ranging from 2.33 to 6.65 mW, exhibiting a slope efficiency of 1.57%. The Q-switched laser generated pulses at a wavelength of 1531.25 nm, with the repetition rate varying from 64.18 kHz to 105.9 kHz. This corresponded to a pulse width between 5.68 and 3.00 µs. The maximum pulse energy obtained in our study was 62.80 nJ. Additionally, the 3 dB spectral bandwidth was measured to be 1.3 nm. These experimental results highlight the potential of Ti2SnC, as a cost-effective, efficient, and practical option for saturable absorbers in Q-switched fiber lasers, thereby paving the way for further developments in photonic applications.