All-fiber Cavity Research Articles

Conventional soliton and noise-like pulse emissions at 1.98μm utilizing tungsten trioxide as mode-locker

In this paper, we experimentally demonstrate the dual pulse emissions of conventional soliton (CS) and noise-like pulse (NLP) in thulium-holmium co-doped fiber laser using tungsten trioxide saturable absorber (WO3-SA). The CS pulse delivered 2[Formula: see text]ps width, centered at 1982.8[Formula: see text]nm. Increasing the pump power and alteration of polarization states switched the CS to the NLP regime with 1990.0[Formula: see text]nm central wavelength, 17.2[Formula: see text]nm spectral bandwidth, and 396[Formula: see text]fs spike width riding on top of a wide picosecond pulse pedestal in the time domain. This work suggests the capability of WO3-SA as a pulse initiator for future dual-source ultrashort pulses based on an all-fiber laser cavity design.

High-energy noise-like pulsing in a thulium/holmium co-doped fiber laser with watt-level average output power

A Thulium/Holmium co-doped fiber laser with high-energy noise-like rectangular pulses at the central wavelength of 1985 nm is experimentally demonstrated. The experimental setup is based on a 298-m long nonlinear optical loop mirror. By varying the pump power from 3 to 10 W, the noise-like rectangular pulse width can be tuned from 2.8 to 15.2 ns, respectively, and under a maximum pump power of 10 W, 1.45 W of average output power is obtained. The pulse repetition rate is 671 kHz. Consequently, highly energetic optical pulses with 2.16 µJ pulse energy and an estimated peak power of 142 W are achieved. To the best of our knowledge, these pulses, which are generated directly from the laser cavity, possess the highest average output power and pulse energy for noise-like pulse emission in the near 2 µm wavelength region. The proposed laser source has the most straightforward all-fiber cavity design that has been proposed for generating high-energy noise-like rectangular pulses, and as such has potential applications in scientific research and as a pump source for mid-infrared supercontinuum generation.

5.3 W/265 μJ Mid-IR All-Fiber Er3+:ZBLAN Gain-Switched Laser Based on Dielectric Fiber Mirror and Fiber-Tip Protection

We report a 2.8 μm all-fiber high-power and high-energy gain-switched Er3+:ZBLAN laser based on dielectric fiber mirror and fiber-tip protection. The fiber pigtail mirror, specifically designed for dichroic operation (i.e., anti-reflection at 976 nm pump wavelength and high-reflection around 2.8 μm laser wavelength), shows high damage density of >10 MW/cm2. An anti-reflection protective film is coated on the input tip of Er3+:ZBLAN fiber and an AlF3 endcap is spliced to the output tip of Er3+:ZBLAN fiber for mitigating the fiber-tip photodegradation and high-power catastrophic failure at 2.8 μm. The compact all-fiber cavity is formed by efficiently connecting the Er3+:ZBLAN fiber with dielectric fiber mirror using the standard FC/PC fiber adaptor. When the 976 nm pump operates in pulsed regime, the all-fiber mid-infrared gain-switched laser can be attained with two states of single-pulse and pulse-burst output. The extracted maximum pulse energy is 4.8 μJ in the single-pulse state, and the shortest pulse width is 426 ns. The pulse-burst mode can generate a maximum average power of 5.291 W and burst energy of 264.55 μJ. This work may offer a promising way to realize the low-cost, all-fiber, high-power and high-energy gain-switched laser at MIR wavelengths.

Exploring the potential of a bismuth-erbium-vanadium co-doped optical fiber as a stable Q-switcher in the 1550 nm region

This paper experimentally demonstrates the ability of a bismuth-erbium-vanadium co-doped optical fiber as a saturable absorber (BEV-FSA) to generate stable Q-switched pulses in the 1550 nm region. The laser cavity delivered passively Q-switched pulses exploiting an erbium-ytterbium co-doped double-clad fiber (DC-EYDF) as the laser gain medium while maintaining an all-fiber cavity configuration. The output parameters of the laser such as output power, repetition rate, pulse duration, and pulse energy have been studied in detail with the variation of pump power. The output spectrum centered at 1550.86 nm throughout the experiment. The system produced stable pulses with a minimum pulse width of 1.83 µs with a pulse energy≈0.4µJ at the highest pump power of 2.31 W. The highest achievable repetition rate was 47.5 kHz with an of SNR≈53dB.

Wavelength tunable actively mode-locked Tm3+ doped fiber laser with GHz repetition rate

Using a phase modulator to synchronize the longitudinal modes in an all-fiber cavity, we demonstrate a wavelength tunable (1955–2045 nm) diode pumped actively mode-locked Thulium doped fiber laser with tunable repetition rate up to 10 GHz with the shortest measured pulse width of 42 ps and average output power of 5 mW. We have performed a detailed analysis of the stable mode-locking regimes, including the self mode-locking condition that challenges the harmonic mode-locked operation. We demonstrate a supermode suppression ratio of > 50 dB across the entire wavelength band of operation while maintaining a pulse width and timing jitter of < 50 ps and < 1 ps, respectively.

Noise-like pulses generation and its beam self-cleaning effect in an all-fiber multimode cavity with a figure-8 scheme

The beam profiles of multimode mode-locked fiber lasers are highly multimode, the speckled beam profiles limit their potential application. To improve the beam profiles of multimode mode-locked fiber lasers, we proposed an all-fiber figure-8 multimode cavity and experimentally demonstrated the generation of noise-like pulses (NLPs) and beam self-cleaning of NLPs in the cavity at 1.5 µm. The laser was mode locked by a nonlinear amplifying loop mirror, an Er/Yb co-doped fiber provided gain, and 50 m OM4 fiber introduced enough nonlinear phase shift difference. The scheme generated NLPs with 159 mW average power, 2.78 MHz repetition rate and 57.19 nJ pulse energy. The packet duration of the NLPs increased from 0.61 ns to 2.99 ns when the pump power was increased from 2 W to 9 W. Nonlinear beam self-cleaning with a near Gaussian beam profile output was achieved in the multimode fiber laser. The M2 was measured to be 2.41 at the pulse energy of 6.83 nJ. We also obtained spatiotemporal mode-locked pulses with 1.03 ps duration and speckled beam profiles. This is the first experimental demonstration of NLPs in multimode fiber lasers, and beam self-cleaning of NLPs was observed for the first time. The results enriched nonlinear dynamics in multimode fiber lasers.

Transient light shift register mechanism of bi-chromatic pulse generation

Primary methods for generating short pulses in lasers require intracavity elements or physical mechanisms for modulation or the saturable absorption of radiation. This often complicates laser design and limits capabilities, particularly beyond single-wavelength operation. We propose and explore a method for the synchronous generation of bicolor, high-repetition-rate pulses that combines stimulated emission from Yb rare-earth ions and Raman scattering in a shared all-fiber laser cavity, without employing saturable absorbers or modulators. The proposed mechanism for pulsed lasing is analogous to an optical shift register, with two pulse trains shifting relative to each other by one period after every round trip. This naturally solves the critical problem of compensating for the dispersion-induced differential delay of bi-chromatic pulses during an intracavity round trip. The shift register inherently enables stationary generation of bi-chromatic pulses with a common relatively high repetition rate that is inversely proportional to the differential delay. We have demonstrated the feasibility of the proposed technique through the stable generation of sub-nanosecond bi-chromatic (1066 and 1241 nm) pulses with a repetition rate exceeding 166 MHz. The proposed approach is rather general, and we anticipate that it can facilitate more affordable bi-chromatic pulse generation in a variety of laser systems.

Tunable optical nonlinearities and surface plasmon resonance in Fe3O4 nanoparticles-decorated Ti3C2 MXene composite for ultrafast fiber lasers

In this work, the Ti3C2 MXene was modified with Fe3O4 nanoparticles to obtain a composite with in-plane optical anisotropy and surface plasmon properties. Based on a side-polished D-shaped fiber (DSF), this Fe3O4/Ti3C2 MXene (F/M) composite exhibits a tunable nonlinear optical (NLO) absorption response under 1.5 μm laser excitation with different polarization states. The modulation depths can be obtained from 0.9% to 12.1%. As an application, the ultrafast erbium-doped fiber laser (EDFL) with multiple pulsed laser operations was demonstrated using the F/M-DSF device as a saturable absorber (SA). Both stable Q-switching and mode-locking operations were demonstrated in the same all-fiber laser cavity, which generated pulsed laser with microsecond and sub-picosecond durations respectively. In addition, the bound state (BS) of solitons in harmonic mode-locked lasers with the pulse time interval of 3 ps and the highest order of 30th was also realized. This versatile and simple-structured all-fiber laser has great potential in various applications, such as optical communication. With the numerical simulations, the dynamic of F/M composite-based soliton mode-locking was also explored, illustrating the mechanism of soliton formation and propagation. This work not only expands the advanced applications of F/M composite in ultrafast photonics but also provides a new perspective for designing and optimizing its ultrafast modulating performance.

All-fiber low threshold tunable multimode Q-switched mode locked fiber laser using a few mode Er-doped fiber

We report an all-fiber low threshold (70 mW) multimode Q-switched mode-locked (QML) fiber laser at 1.5 m. Nonlinear polarization rotation and a few mode Er-doped fiber (FM-EDF) were both adopted to achieve a low threshold QML operation initially, and the later experimental results showed and verified that the FM-EDF was the key factor of the QML pulses generation. A multimode QML state at 70 mW pump power was obtained with an 18 μs Q-switched pulse width and a 7.41 kHz repetition rate. The repetition rate and pulse width of the mode-locked pulses within the Q-switched envelope were 16.9 MHz and ∼910 ps respectively. The multimode QML fiber laser can be turned from 1561.8 nm to 1575.1 nm owing to the multimode interference and the fiber birefringence filtering effect. The QML pulses with dual-wavelength and three-wavelength were also observed by manipulating the polarization controllers and increasing the pump power. The experimental results showed that multimode QML pulses can be achieved with a short FM-EDF at a lower pump power in an all-fiber multimode cavity. The generated low threshold and tunable QML multimode fiber laser has potential application in measuring and mode-division multiplexed system.

All-fiber cyan laser at 491.5 nm

We report, for the first time to our knowledge, a compact continuous-wave all-fiber cyan laser. The all-fiber cavity consists of a 443-nm fiber-pigtail laser diode as pump source, a 4.5-cm single-clad Pr3+-doped fluoride fiber, and two custom-built dielectric-coated fiber-pigtail mirrors in the visible spectral region. Downconversion cyan lasing at 491.5 nm is directly achieved, providing a maximum output power of 97.5 mW with a slope efficiency of 23.7% and a power fluctuation of less than 0.41%. Such a compact all-fiber cyan laser may be of great significance to expand the color reproduction range of laser displays, and has potential applications in fluorescence imaging, underwater communication, and detection.

All-PM Fiber Mamyshev Oscillator Delivers Hundred-Nanojoule and Multi-Watt Sub-100 fs Pulses

An all-fiber Mamyshev oscillator with a single amplification arm is experimentally demonstrated to achieve high-energy and high-average-power ultrafast pulse output, with the initiating of an external seed pulse. In the high-energy operation, a maximum single-pulse energy of 153 nJ is achieved at a repetition rate of 9.77 MHz. After compression with a pair of diffraction gratings, a measured pulse width of 73 fs with a record energy of 122.1 nJ and a peak power of 1.7 MW is obtained. In the high-average-power operation, up to 5th harmonic mode locking of the oscillator is realized via slightly adjusting the output coupling ratio and the cavity length. The achieved maximum output power is 3.4 W at a repetition rate of 44.08 MHz, while the corresponding pulse width is compressed to around ~100 fs. Meanwhile, the system is verified to be operated reliability in both high-energy and -average-power operation regimes through assessing its short- and long-term stabilities. To the best of our knowledge, these are the highest records in pulse energy and average power delivered from a single all-fiber ultrafast laser oscillator with picosecond/femtosecond pulse duration. It is believed that even higher-energy and -average-power ultrafast laser can be realized with the proposed laser scheme through further increasing the core diameter of the all-fiber cavity, providing promising sources for advanced fabrication, biomedical imaging, laser micromachining, and other practical applications, as well as an unprecedented platform for exploring undiscovered nonlinear dynamics.

Fiber optical parametric oscillator made of soft glass

Fiber optical parametric oscillators (FOPOs) are compact optical sources of coherent and broadly tunable light compatible with operation in unconventional spectral bands. Highly nonlinear silica fibers have enabled the development of FOPOs in the telecommunication wavelength band, but the strong material absorption of silica glass at wavelengths >2 µm limits its applicability in the mid-infrared (MIR) spectral range. In this work, we overcome this issue and report a FOPO designed entirely out of soft glass fiber. For this purpose, we combine an As2Se3 single-mode fiber coupler, an As2Se3 parametric gain medium, and a low-loss ZBLAN delay fiber to build the first all-fiber laser cavity made of soft glass. Two proof-of-concept FOPOs are presented, one driven by pure parametric gain leading to wavelength-tunable Stokes emission within the range 2.088-2.139 µm, and the other driven by Raman-assisted parametric gain leading to Stokes emission within the range 2.023-2.048 µm. This demonstration is a promising first step toward the development of fully fiberized MIR light sources.

Nanostructured Large Mode Area Fiber for Laser Applications

We developed a passive silica based large mode area fiber with the nanostructured core with a diameter of 30 m devoted to fiber Bragg grating inscription for application in an all-fiber laser cavity. The fiber is perfectly matched to the commercial active fiber with NA=0.06 and core/cladding diameters 30/250 m. Measured modal characteristics and bending loss of the fiber confirm single-mode operation for bending diameter of 8 cm with bending losses as low as 0.15 dB/m. Although the nanostructured fiber core is low germanium doped, we fabricated high reflectivity (98.5%) UV induced fiber Bragg grating (FBG) and verified its performance in fiber laser setup. The laser cavity formed with highly reflective FBG inscribed in the fiber and Fresnel reflection on the free end of active fiber results in lasing efficiency of 65.5%. The flexibility of the nanostructuring approach gives prospects for the development of free-form large mode area fibers for passive fiber components and matched with any type of active fibers.

Ultrashort pulse generation in All-fiber Erbium-doped fiber cavity with thulium doped fiber saturable absorber

Generation of ultrashort pulses in an all-fiber Erbium-doped fiber laser (EDFL) cavity with doped fiber saturable absorber (DFSA) is demonstrated for the first time. The doped fiber saturable absorber is fabricated by a single-mode 12 cm-long thulium-doped fiber (TDF). The optical characteristic of TDF indicates a saturable absorption of 3.6 %, which indicates it’s capability to function as a mode-locker. Continuous wave, mode-locked and combined-mode operations are observed sequentially with the increase of pump power. The mode-locked erbium-doped fiber laser operates at 1568.2 nm with a pulse width of 2.27 ps. A mode-locked pulse train with a constant repetition rate of 0.99 MHz is obtained as the pump power increased from 96 mW to 178 mW. At the pump power of 178 mW, the maximum peak power and pulse energy are calculated as 1.75 kW and 3.93 nJ, respectively. The obtained pulse train is very robust with a signal-to-noise ratio (SNR) of 63 dB. The experimental results attest that utilizing doped fiber saturable absorber can achieve ultrashort pulses and possess the potentially increasable power of mode-locked operation in all-fiber lasers.

High energy switchable pulsed High-order Mode beams in a mode-locking Raman all-fiber laser with high efficiency.

High energy pulsed High-order Mode (HOM) beams has great potential in materials processing and particle acceleration. We experimentally demonstrate a high energy mode-locking Raman all-fiber laser with switchable HOM state. A home-made fiber mode-selective coupler (MSC) is used as the mode converter with a wide bandwidth of 60 nm. By combining advantages of MSC and stimulated Raman scattering, 1.1 μJ pulsed HOM beams directly emitting from the all-fiber cavity can be achieved. After controlling the category and phase delay of vector modal superposition, different pulsed HOM beams including cylindrical vector beams (CVBs) (radial and angular) and optical vortex beams (OVBs) are reasonably obtained with high purity (all over 95%), as well as arbitrary switching. Furtherly, the slope efficiency of HOM beams in the mode-locking and continuous wave operations are as much as 20.3% and 31.8%, respectively. It may provide an effective way to achieve high energy pulsed HOM beams.

Passively mode-locked composite erbium fiber laser with a pulse repetition rate of 150 MHz

We demonstrate a short cavity passively mode-locked composite erbium-doped fiber laser with saturable absorber based on aerosol-synthesized single-walled carbon nanotubes. Optical pulses had a duration of 973 fs while an average output power – 6 mW. Using a shortened laser cavity, a stable soliton generation with a pulse repetition rate of 150 MHz at the output of the all-fiber linear cavity was obtained.

Pulsed fiber laser oscillator at 1.7 µm by stimulated Raman scattering in H2-filled hollow-core photonic crystal fibers.

We have reported a pulsed fiber gas Raman laser oscillator at 1.7 µm based on an all-fiber resonant cavity, which is made by splicing solid-core fibers with a 50-meter-long hydrogen-filled hollow-core photonic crystal fiber and further introducing homemade fiber Bragg gratings at the Raman wavelength. Pumping by a homemade pulsed 1540 nm fiber amplifier, a 1693 nm Stokes wave is obtained by pure rotational stimulated Raman scattering of H2. The maximum optical-to-optical efficiency inside the hollow-core fiber is about 54% with the repetition frequency of 6 MHz, giving an average Raman power of 1.5 W, and the Raman threshold of peak power is as low as 3.6 W, which is more than 10 times lower than that of the single-pass structure. The relationship between pulse characteristics and Raman threshold is systematically studied, and the Raman threshold can be reduced dramatically when the repetition frequency of pulses is consistent with the resonant frequency of the cavity. This work provides good guidance for achieving low-threshold pulsed all-fiber gas Raman lasers, which is significant for development and application.

All-Fiber Gas Raman Laser by D2-Filled Hollow-Core Photonic Crystal Fibers

We report here an all-fiber structure tunable gas Raman laser based on deuterium-filled hollow-core photonic crystal fibers (HC-PCFs). An all-fiber gas cavity is fabricated by fusion splicing a 49 m high-pressure deuterium-filled HC-PCF with two solid-core single-mode fibers at both ends. When pumped with a pulsed fiber amplifier seeded by a tunable laser diode at 1.5 μm, Raman lasers ranging from 1643 nm to 1656 nm are generated. The maximum output power is ~1.2 W with a Raman conversion efficiency of ~45.6% inside the cavity. This work offers an alternative choice for all-fiber lasers operating at 1.6–1.7 μm band.

All-Fiber Gas Cavity Based on Anti-Resonant Hollow-Core Fibers Fabricated by Splicing with End Caps

In recent years, fiber gas lasers have obtained a rapid development, however, efficient and stable pump coupling is a key limitation for their applications in the future. Here, we report an all-fiber gas cavity based on anti-resonant hollow-core fibers which have the beneficial properties of adjustable broad transmission bands and potential low transmission attenuation, especially in the mid-infrared. This kind of all-fiber gas cavity is fabricated by directly splicing with end caps at both ends for the first time. The high-power laser transmission characteristics were studied, and the experimental results show that the all-fiber gas cavities have a very stable performance. The maximum input laser power at 1080 nm is about 260 W, and the output power is 203 W, giving a total transmission efficiency of 78.1%. This work opens a new opportunity for the development of high-power all-fiber structured fiber gas lasers.

Hydrogen Molecules Rotational Stimulated Raman Scattering in All-Fiber Cavity Based on Hollow-Core Photonic Crystal Fibers

Here, we report the rotational stimulated Raman scattering (SRS) of hydrogen molecules in an all-fiber cavity based on hollow-core photonic crystal fibers (HC-PCFs). The gas cavity consists of a 49 m long HC-PCF filled with 18 bar high-pressure hydrogen and two sections of fusion spliced solid-core fibers on both ends. When pumped by a homemade 1064 nm pulsed fiber amplifier, only rotational SRS occurs in the gas cavity due to the transmission spectral characteristics of the used HC-PCF, and 1135 nm Stokes wave is obtained (Raman frequency shift of 587 cm−1). By changing the pulse width and repetition frequency of the pump source, the output characteristics are explored. In addition, a theoretical model is established for comparison with the experimental results. This work is helpful for the application of gas Raman laser based on the HC-PCFs.