Er-doped Fiber Laser Research Articles

Chromium oxide film for Q-switched and mode-locked pulse generation.

Chromium oxide (Cr2O3) is a promising material used in the applications such as photoelectrochemical devices, photocatalysis, magnetic random access memory, and gas sensors. But, its nonlinear optical characteristics and applications in ultrafast optics have not been studied yet. This study prepares a microfiber decorated with a Cr2O3 film via magnetron sputtering deposition and examines its nonlinear optical characteristics. The modulation depth and saturation intensity of this device are determined as 12.52% and 0.0176 MW/cm2. Meanwhile, the Cr2O3-microfiber is applied as a saturable absorber in an Er-doped fiber laser, and stable Q-switching and mode-locking laser pulses are successfully generated. In the Q-switched working state, the highest output power and shortest pulse width are measured as 12.8 mW and 1.385 µs, respectively. The pulse duration of this mode-locked fiber laser is as short as 334 fs, and its signal-to-noise ratio is 65 dB. As far as we know, this is the first illustration of using Cr2O3 in ultrafast photonics. The results confirm that Cr2O3 is a promising saturable absorber material and significantly extend the scope of saturable absorber materials for innovative fiber laser technologies.

Self-injection locking of a low-noise erbium-doped random fiber laser by a random fiber grating ring.

We demonstrate a self-injection locking (SIL) in an Er-doped random fiber laser by a high quality factor (high-Q) random fiber grating ring (RFGR) resonator, which enables a single-mode narrow-linewidth lasing with ultra-low intensity and frequency noise. The RFGR resonator includes a fiber ring with a random fiber grating to provide random feedback modes and noise suppression filters with self-adjusted peak frequency adaptable to small perturbations allowing single longitudinal mode over 7000 s with frequency jitter below 3.0 kHz. Single-mode operation is accomplished by carefully controlling phase delays and mode coupling of resonant modes between main ring and RFGR with a side-mode suppression ratio of 70 dB and narrow linewidth of 1.23 kHz. The relative intensity noise is -140 dB/Hz above 100 kHz and the frequency noise is 1 Hz/Hz1/2 above 10 kHz.

Dissipative pure-quartic soliton resonance in an Er-doped fiber laser

Dissipative pure-quartic soliton (DPQS) that arises from the balance of positive fourth-order dispersion (FOD), nonlinearity, gain and loss has been proposed to generate high-energy pulse. Herein, we numerically investigate the generation of dissipative pure-quartic soliton resonance (DPQSR) in an Er-doped mode-locked fiber laser with all positive FOD. Our findings indicate that the formation of DPQSR depends on the reverse saturable absorption (RSA) effect of real saturable absorber. Then, the impacts of pump power, RSA coefficient and positive FOD in generating DPQSR pulse are investigated. With the increase of pulse energy, the asymmetrical temporal profile of DPQS transforms into a rectangular one. This work can be utilized to comprehend the dissipative pure-quartic soliton resonance as well as the development of an all positive FOD Er-doped fiber laser. In addition, it lays the way for the development of highly stable, high-energy pulsed lasers.

Generation of dissipative soliton resonance and soliton rain in passively mode-locked fiber laser based on GeTe saturable absorber

We report the generation of dissipative soliton resonance and soliton rain in an Er-doped fiber laser based on GeTe as saturable absorber. When the pump power is 60 mW, the fiber laser achieved the stable dissipative soliton resonance mode-locked operation. The pulse width of the trapezoidal envelope pulses increases from 21 to 35.5 ns with the increase of the pump power, while keeping the pulse profile and intensity invariable. By properly adjusting the polarization controller, a stable soliton rain pulse is obtained at the pump power of 70.4 mW. With the increase of pump power, its average output power increased from 0.52 to 1.56 mW, and its corresponding fundamental repetition rate, central wavelength and 3-dB bandwidth is 3.21 MHz, 1562.6 nm and 2.74 nm, respectively. The experimental results demonstrate that GeTe nanosheets could be developed as an effective saturable absorber for ultrashort pulse fiber lasers.

Highly-stable optical injection wavelength locking of Er-doped random fiber lasers

A highly-stable and effective Er-doped random fiber laser (RFL) is proposed and experimentally demonstrated based on external optical injection locking technology. By adjusting the optical injected wavelength, the lasing wavelength can be selected precisely and emitted separately within the spectral bandwidth of 1555.5 nm to 1563.5 nm. The wavelength and output power fluctuation are less than 0.004% and 2.9%, respectively, indicating that optical injection locking of the RFL is quite stable over a long time. The optical injection locking technology is used in the half-open cavity incoherent RFL systems based on the random distributed Rayleigh scattering scheme, which provides an effective method to control or select the wavelength emission with high stability in a RFL.

Tunable and switchable single-/dual-wavelength Er-doped hybrid mode-locked fiber laser by dual-PMFs Lyot filter

Tunable and switchable single-/dual-wavelength Er-doped hybrid mode-locked fiber laser by dual-PMFs Lyot filter

CrPS4 Nanoflakes as Stable Direct-Band-Gap 2D Materials for Ultrafast Pulse Laser Applications

Two-dimensional (2D) materials have attracted considerable attention due to their potential for generating ultrafast pulsed lasers. Unfortunately, the poor stability of most layered 2D materials under air exposure leads to increased fabrication costs; this has limited their development for practical applications. In this paper, we describe the successful preparation of a novel, air-stable, and broadband saturable absorber (SA), the metal thiophosphate CrPS4, using a simple and cost-effective liquid exfoliation method. The van der Waals crystal structure of CrPS4 consists of chains of CrS6 units interconnected by phosphorus. In this study, we calculated the electronic band structures of CrPS4, revealing a direct band gap. The nonlinear saturable absorption properties, which were investigated using the P-scan technique at 1550 nm, revealed that CrPS4-SA had a modulation depth of 12.2% and a saturation intensity of 463 MW/cm2. Integration of the CrPS4-SA into Yb-doped fiber and Er-doped fiber laser cavities led to mode-locking for the first time, resulting in the shortest pulse durations of 298 ps and 500 fs at 1 and 1.5 µm, respectively. These results indicate that CrPS4 has great potential for broadband ultrafast photonic applications and could be developed into an excellent candidate for SA devices, providing new directions in the search for stable SA materials and for their design.

Nonlinear photoresponse of PdSe2 nanosheets for soliton operations in passive mode-locked Er-doped fiber lasers

In this study, we investigated the nonlinear absorption properties of palladium diselenide (PdSe2). We employed PdSe2 with a saturable intensity of 23.40 MW/cm2 and a modulation depth of 7.39 % as a saturable absorber (SA), which was successfully exploited to attain a stable mode-locked pulse within an Er-doped fiber laser (EDFL). Centered at 1557 nm, the EDFL produced stable pulses when the pulse width was 1.31 ps and the fundamental frequency rate was 12.56 MHz. Single, double, and triple pulses were observed by changing the polarization state of the EDFL. The third, fourth, sixth, tenth and eleventh harmonic mode-locked pulses were obtained by adjusting the pump power as well as the polarization state of the laser cavity. This proved that PdSe2 was an outstanding SA in the research of ultrafast optical modulators due to its excellent ultra-fast modulation properties.

Generation of bright-dark solitons in an Er-doped fiber laser employing InSb as a saturable absorber.

In this paper, an indium antimonide (InSb) saturable absorber (SA) was successfully fabricated. The saturable absorption properties of the InSb SA were studied, and they show a modulation depth and a saturable intensity of 5.17% and 9.23M W/c m 2, respectively. By employing the InSb SA and building the ring cavity laser structure, the bright-dark soliton operations were successfully obtained by increasing the pump power to 100.4mW and adjusting the polarization controller. As the pump power increased from 100.4 to 180.3mW, the average output power increased from 4.69 to 9.42mW, the corresponding fundamental repetition rate was 2.85MHz, and the signal-to-noise ratio was 68dB. The experimental results show that InSb with excellent saturable absorption characteristics can be used as a SA to obtain pulse lasers. Therefore, InSb has important potential in fiber laser generation, further applications in optoelectronics, laser distance ranging, and optical fiber communication, and it can be widely developed.

Polarization maintaining harmonically mode-locked fiber laser with suppressed supermode noise due to continuous wave injection

We report on experimental studies of a SESAM mode-locked Er-doped fiber laser completely spliced from polarization-maintaining fiber components. With the fiber mode spot properly aligned to the SESAM, the laser operates harmonic mode-locking (HML) available in a whole range of pump powers up to ∼355mW with the supermode suppression level (SSL) less than 25 dB. Importantly, the HML laser generates the pulses in a linear polarization state and enables the pulse repetition rate (PRR) up to ∼1145 MHz. In our experiments we show that an optical injection of an external continuous wave (CW) into the laser cavity improves the stability of the laser operation in HML regime resulting in an increase of the SSL by 20–30 dB. Besides, the CW injection is able to expand the range of pump powers available with HML laser providing an increase of the maximal laser PRR up to ∼2195 MHz. Importantly, the implemented optical injection does not affect high purity of the laser polarization state. The presented numerical simulations enable qualitative explanations of the effects observed experimentally.

MoxTa(1-x)Se2 as saturable absorber for ultrafast photonics

Two-dimension ternary transition metal dichalcogenides have drawn great interests from both the fields of nanotechnology and materials science, due to their extraordinary physical performance, and great potential applications in nanodevice. Here, the applications of MoxTa(1-x)Se2 nanosheets in ultrafast photonics are discussed. The MoxTa(1-x)Se2 nanosheets are prepared by liquid phase exfoliation method. A MoxTa(1-x)Se2-based saturable absorber is fabricated by depositing these nanosheets onto the side surface of d-shaped fiber, which is inserted into a Er-doped fiber laser cavity. By adjusting polarization state and pump power, both harmonic mode-locking and large energy mode-locking operations are realized, respectively. In the former state, a 56th harmonic mode-locking is obtained, which corresponds to a repetition rate of 312.5 MHz. For the later state, the maximum average output power of 12.24 mW and single pulse energy of 2.19 nJ are obtained when the pump power is 500mW. The results demonstrate that MoxTa(1-x)Se2 can be widely used in ultrafast photonics and nonlinear optics.

Dynamics of frequency detuning in a hybrid Er-doped mode-locked fiber laser

Frequency detuning of mode-locked fiber lasers displays many remarkable nonlinear dynamical behaviors. Here we report for the first time the evolution of pulses from mode-locking through period pulsation to Q -switched mode-locking for three fundamental cases. Our experiments are performed in a hybrid actively and passively amplitude-modulated all-fiber polarization-maintaining mode-locked fiber laser, where the amplitude modulation frequency artificially deviates from the fundamental frequency of the cavity. We design and numerically simulate the laser with coupled Ginzburg–Landau equations. The experimentally observed dynamics of the mode detuning process is discussed with the assistance of the fitted model and numerical simulations, showing the generalizability of the optical mode detuning variation process. Our work provides fundamental insights for understanding perturbations in nonlinear optical resonant cavities and expands the ideas for studying chaotic path theory in hybrid mode-locked fiber lasers.

Periodic transition between two evolving soliton pulsation states in an Yb-doped fiber laser.

Due to the fascinating features, pulsating solitons attract much attention in the field of nonlinear soliton dynamics and ultrafast lasers. So far, most of the investigations on pulsating soliton are conducted in Er-doped fiber lasers. In this work, we reported the periodic transition between two evolving pulsating soliton states in an Yb-doped fiber laser. By using the real-time measurement techniques, the spectral and temporal characteristics of this transition state were investigated. Two evolving soliton pulsation states have similar evolution process, i.e., from pulsating towards quasi-stable mode-locked states. However, the details of the two processes are different, such as the pulse energy levels, pulsating modulation depths, duration of quasi-stable mode-locked states. The transition between two evolving soliton pulsation states could be attributed to the interaction of the polarizer and the varying polarization states of the pulse inside the laser cavity. The experimental results will contribute to the further understanding of soliton pulsating dynamics in dissipative optical systems.

Ultra-short pulse burst laser around 1.98 µm obtained through an all-fiber nonlinear wavelength converter and Tm-doped fiber amplifier.

We report an all-fiber ultra-short pulse burst laser operating at around 1.98 µm that is obtained through a nonlinear wavelength converter and Tm-doped fiber amplifier. A mode-locked Er-doped fiber laser was first built and then amplified in subsequent amplifiers to an average power of 1.3 W. Ultra-short pulse burst output was achieved through a pulse multiplier and a fiber-pigtailed acousto-optic modulator. It was then injected into an all-fiber nonlinear wavelength converter constructed from P-doped fiber and Tm-doped fiber, obtaining an ultra-short pulse burst laser of 540 mW around 1.98 µm. Its average output power was then amplified to 4.33 W in a Tm-doped fiber amplifier with an intra-burst pulse repetition frequency of 0.9 GHz, a burst repetition frequency of 200 kHz, and a duty cycle of 2%, corresponding to about 200 pulses within each burst. This 1.98 µm pulse burst laser has enormous potential to be applied in bio-medical areas.

Nonlinear optical properties of carboxyl-functionalized graphene oxide for dissipative soliton resonance pulse generation

Here, we investigated the nonlinear optical (NLO) characteristics of carboxyl-functionalized graphene oxide (GO-COOH) in the near-infrared (NIR) region. The results revealed that GO-COOH samples exhibit strong saturable absorption at low pump levels and a gradual transition to reverse saturable absorption (RSA) with increasing pump power. Then the saturable absorber (SA) by depositing the GO-COOH on the side-polished fiber (SPF) was employed in Yb- and Er-doped fiber lasers. Stable ultrashort pulses operating in the dissipative soliton (DS) and conventional soliton (CS) regimes were obtained with pulse widths of 26.6 ps and 968 fs, respectively. Besides, the dissipative soliton resonance (DSR) phenomenon caused by the RSA of GO-COOH was also observed with increasing pump power. The high-stable DSR mode-locked pulses with the maximum pulse energy of 1.91 nJ and 0.74 nJ were obtained in YDFL and EDFL respectively. These results not only reveal the potentiality of GO-COOH in ultrafast photonics applications but also open a new avenue to explore high-pulse-energy laser sources based on two-dimensional materials.

Q-switched and noise-like mode-locked fiber laser based on ternary transition-metal carbide Nb2AlC saturable absorber

The saturable absorption of layered ternary transition-metal carbide (MAX) Nb2AlC is investigated in this work. Nb2AlC-based saturable absorber (SA) device is prepared and applied in an Er-doped fiber laser (EDFL). The EDFL can generate Q-switched and noise-like mode-locked pulses based on the excellent Nb2AlC SA. The EDFL operates in a Q-switched pulses mode state when the pump power is up to a threshold value of 50 mW. For the Q-switched pulse, the maximum single pulse energy is 66 nJ. The laser pulse generation mode switches to a noise-like mode-locked state when the pump power increases to 170 mW. The coherent spike duration is 2.8 ps and the corresponding maximum single pulse energy is 1.5 nJ at a pump power of 439 mW. A preliminary review of available literature indicates no reports of layered ternary carbide Nb2AlC as SA in an EDFL to generate switchable laser pulse modes. Results of this study suggest that ternary MAX Nb2AlC can be a remarkable nonlinear optical (NLO) device to explore switchable laser pulse generation modes and can encourage further studies on the ternary transition-metal carbides.

Polarization dynamics, stability and tunability of a dual-comb polarization-multiplexing ring-cavity fiber laser

In this paper, we present a polarization-multiplexed system capable of generating two stable optical frequency combs with tunable frequency differences in the range from 100 to 250 Hz and an extinction ratio of 16.5 dBm. Also, the polarization dynamics of a dual-frequency comb generated from a single mode-locked Er-doped fiber laser are experimentally studied. The obtained results will extend the application to areas such as polarization spectroscopy and dual-comb-based polarimetry.

Quasi-2D Mn3Si2Te6 Nanosheet for Ultrafast Photonics.

The magnetic nanomaterial Mn3Si2Te6 is a promising option for spin-dependent electronic and magneto-optoelectronic devices. However, its application in nonlinear optics remains fanciful. Here, we demonstrate a pulsed Er-doped fiber laser (EDFL) based on a novel quasi-2D Mn3Si2Te6 saturable absorber (SA) with low pump power at 1.5 μm. The high-quality Mn3Si2Te6 crystals were synthesized by the self-flux method, and the ultrathin Mn3Si2Te6 nanoflakes were prepared by a simple mechanical exfoliation procedure. To the best of our knowledge, this is the first time laser pulses have been generated using quasi-2D Mn3Si2Te6. A stable pulsed laser at 1562 nm with a low threshold pump power of 60 mW was produced by integrating the Mn3Si2Te6 SA into an EDFL cavity. The maximum power of the output pulse is 783 μW. The repetition rate can vary from 24.16 to 44.44 kHz, with corresponding pulse durations of 5.64 to 3.41 µs. Our results indicate that the quasi-2D Mn3Si2Te6 is a promising material for application in ultrafast photonics.

Reverse saturable absorption in Ti3C2 MXene nanosheets for dissipative soliton resonance mode-locking operation in Er-doped fiber laser

In this paper, Ti3C2Tx MXene nanosheets were prepared using a low-power ultrasonic-assisted liquid phase exfoliation method. The Ti3C2Tx nanosheets based saturable absorber deposited on the tapered microfiber possessed the typical saturable absorption and reverse saturable absorption with the surface evanescent field. With a home-made femtosecond excitation source at 1550 nm, the modulation depth was determined as 4.8% with a saturation intensity of 18.7 MW/cm2. By inserting our as-prepared saturable absorber into an Erbium-doped fiber laser (EDFL), two types of mode-locked pulses operating in the stable conventional soliton (CS) and dissipative soliton resonance (DSR) regimes were realized at the fundamental repetition frequency of 7.39 MHz, respectively. The pulse width of the CS pulse was 1.185 ps with a central wavelength of 1560.6 nm. While the pulse width of the DSR pulses varied from 2.07 ns to a maximum of 8.13 ns with the increase of the pump power. Our work reveals the reverse saturable absorption effect of Ti3C2Tx could play a key role in the DSR pulse generation, which may benefit the application of the pulse modulation and optical communication with the two-dimensional materials.

Generation of widely tunable single- and dual-wavelength in a figure-eight mode-locked fiber laser

We report a single- and dual-wavelength tuning at the C + L band in a nonlinear amplifying loop mirror (NALM) mode-locked Er-doped all-fiber laser. The single-wavelength tuning range is 52 nm, and the dual-wavelength can vary from 1558 nm and 1581 nm to 1581 nm and 1606 nm, accompanied by a slight change in the spacing of the wavelengths. To our knowledge, this is the widest dual-wavelength tuning range achieved in an Er-doped mode-locked fiber laser. The optical spectrum of the dual wavelengths has no significant variation within 60 min, which indicates potential for applications such as dual-comb. Our work provides a compact and low-cost dual-wavelength all-fiber laser, which may facilitate the design and application of dual-wavelength sources.