Fiber Saturable Absorber Research Articles

Multi-Wavelength Passively Q-Switched Fiber Laser Based on Erbium-Doped Fiber Saturable Absorber and Analysis of Gain Saturable Absorption Characteristics

Multi-Wavelength Passively Q-Switched Fiber Laser Based on Erbium-Doped Fiber Saturable Absorber and Analysis of Gain Saturable Absorption Characteristics

All-fiber passively Q-switched Tm-doped laser with a mode field area mismatched Tm-doped saturable absorber.

We demonstrate a high peak power, all-fiber passively Q-switched Tm-doped laser operating at 1940 nm for applications in soft tissue ablation. High peak power and passive Q-switching were achieved via a clad pumped gain fiber and a smaller core Tm-doped fiber saturable absorber respectively. Clad pumping was achieved via two 30 W diodes operating at 793 nm. At 50.7 W of pump power, laser pulses with 140 ns FWHM duration and average power of 14.5 W were obtained at a repetition rate of 328 kHz which corresponded to a pulse energy of ~44 µJ and a peak power of ~316 W. The laser had a narrow 0.14 nm linewidth at the maximum output power. The laser was used to cut chicken breast as well as ovine cortical and subcortical brain tissues and average ablation efficiencies of 29, 40 and 42% were obtained, respectively. Cutting speeds of 10 mm/s for ovine brain tissue and 5 mm/s for chicken breast were achieved. Further resection experiments were performed with the target tissue placed under a thin layer of water. A resected volume with length, width and depth of 5 mm, 2.5 mm, and 2.8 mm were obtained, corresponding to a resection rate of ~0.58 mm3/s. To our best knowledge, this is the first report of an all-fiber clad-pumped passively Q-switched Tm-doped fiber laser with a core mismatched saturable absorber being used for tissue ablation experiments.

Generation of Bright–Dark Pulse Pairs in the Er-Doped Mode-Locked Fiber Laser Based on Doped Fiber Saturable Absorber

This study reports new types of passive mode-locked Er-doped fiber laser (EDFL) based on a segment of doped fiber saturable absorber (DFSA) with Tm/Ho-doped fiber (THDF), Yb-doped fiber (YDF), and Er-doped fiber (EDF). By employing THDF-SA, a bright pulse sequence with a fundamental repetition rate of 17.86 MHz was obtained. In addition, various mode-locked output states, including dark pulses, dark–bright pulse pairs, bright–dark pulse pairs, and second-harmonic pulses, were obtained through polarization modulation and gain modulation, and the orthogonality of dark–bright pulses in both polarization directions was verified. Furthermore, using EDF-SA and YDF-SA, dark pulses and dark–bright pulses were obtained. A comparison of the three experiments revealed that THDF-SA effectively reduces the mode-locked threshold and improves the average output power. Compared with bright pulses, dark pulses offer several advantages such as resisting noise, increasing propagation speed, and suppressing nonlinear scattering (such as pulse-intrinsic Raman scattering); thus, the EDFL can find broad application in long-distance transmission, precision measurement, and other fields.

Demonstration of a 700 W × 2 ports single-stage all-fiber nanosecond amplifier seeded by a multi-cavity passively Q-switched laser.

We demonstrate a single-stage all-fiber nanosecond amplifier with a total average power of greater than 1.4 kW by employing what we believe to be a novel multi-cavity passively Q-switched fiber laser as the seed laser. The multi-cavity seed laser adopts a piece of Yb-doped fiber (YDF) as saturable absorber (SA), and it includes two external cavities resonating at 1030 nm and an internal cavity working at 1064 nm, respectively. Using such a scheme, a stable dual-channel laser output with a total average power of >35 W, a pulse width of 45 ns, and an optical conversion efficiency of 72% operating at 1064 nm is achieved. By power scaling the multi-cavity seed laser, a dual-channel single-stage nanosecond amplifier is obtained with a single-port average power of exceeding 700 W and a pulse energy of about 7.3 mJ. To the best of our knowledge, this work is the highest average power and optical conversion efficiency for passively Q-switched all-fiber laser employing SA fiber, and the highest average power for a single-stage all-fiber nanosecond amplifier.

High-performance passively Q-switched fiber laser based on CuFeO2/SiO2 as saturable absorber

In this paper, we report the optical properties and applications of the CuFeO2 (CFO)/SiO2 novel saturable absorber (SA) by the sol–gel method. The measured results show that our SA’s modulation depth, unsaturated loss and damage threshold are 10.9%, 10.1% and 5121 mJ/cm 2, respectively. High-quality passively Q-switched fiber laser output at 1.5μm was successfully achieved using CFO/SiO2 SA. Due to the high damage threshold and low insertion loss of the SA, the maximum output power of the laser are 59.6 mW, the optical conversion efficiency is 6.4%, much higher than other reports, corresponding to an output pulse’ peak power and single pulse energy of up to 723.98 mW and 307.7 nJ, and the signal-to-noise ratio of 74 dB indicating its stability. The results indicate that the CFO/SiO2 SA prepared by the sol–gel method provides a new opportunity to develop high-performance SA and high-power passive Q-switched fiber lasers.

Observation of Optical Spectrum Dynamics and Longitudinal-Mode Feature in a Single- Frequency Self-Sweeping Fiber Laser

In this study, we constructed and realized a single-frequency self-sweeping fiber laser that can perform both reverse and normal sweeping. The laser can convert sweeping directions using different lengths of fiber saturable absorber (FSA). The maximum sweeping ranges for normal and reverse sweeping are 5.072 and 3.457 nm, respectively, and are optimized results based on a unidirectional ring cavity. We summarized the optical spectra and pulse dynamics of both normal and reverse sweeping, and we also observed the longitudinal-mode feature of the fiber laser, revealing a phenomenon in which the interval of frequency change is twice the spacing of longitudinal-mode. Furthermore, the reflected spectra of FSA at different lengths and wavelengths were calculated to explain the sweeping direction and longitudinal mode features.

Switchable single/dual-wavelength Q-switched all-fiber laser utilizing thulium-doped fiber saturable absorber

Switchable single/dual-wavelength Q-switched all-fiber laser utilizing thulium-doped fiber saturable absorber

Sub-kHz linewidth 1.6-µm single-frequency fiber laser based on a heavily erbium-doped silica fiber.

We present a single-frequency erbium-doped fiber laser operated at 1608.8 nm using a homemade, heavily erbium-doped silica fiber as gain medium. The laser configuration is based on a ring cavity, which is combined with a fiber saturable absorber to achieve single-frequency operation. The measured laser linewidth is less than 447 Hz and the optical signal-to-noise ratio exceeds 70 dB. The laser exhibits an excellent stability, without any instance of mode-hopping during 1-hour observing. The fluctuations in both wavelength and power were measured to be 0.002 nm and less than 0.09 dB in a 45-minutes period. The laser produces over 14 mW of output power with a slope efficiency of 5.3%, which, to the best of our knowledge, is currently the highest power directly obtained from a single-frequency cavity based on an erbium-doped silica fiber above 1.6 µm.

Black Phosphorus Coated D-Shape Fiber as a Mode-Locker for Picosecond Soliton Pulse Generation

We demonstrate the production of a picosecond pulse from an Erbium laser cavity using black phosphorous (BP) on side-polished fiber saturable absorber (SA) as a mode-locker. The surface of the fiber was removed utilizing a polishing wheel, and then BP was mechanically deposited onto it to develop an excellent evanescent field on the polished surface area. The SA device was used in a 56 m long Erbium-doped fiber laser (EDFL) ring cavity to generate soliton mode-locked pulses with a center wavelength of 1556.2 nm and a 3 dB spectral bandwidth of 2.2 nm. Stable 3.48 MHz soliton pulses with pulse width as short as 1.17 ps were achievable by setting the pump power within 92 mW to 145 mW. The highest pulse energy and peak power obtainable were 5.4 nJ and 4.7 kW, respectively. The results show that BP deposited onto side-polished fiber can be used as an SA in an EDFL cavity. Its easy construction makes it suitable for producing a portable mode-locked laser source.

Ultra-Narrow-Bandwidth Single-Frequency Self-Sweeping Ytterbium-Doped Fiber Laser

The sterling merits of single-frequency self-sweeping fiber laser in linewidth, compact design, wavelength and pulse dynamics make it a promising tool for laser measurement. In this letter, we proposed an ultra-narrow-bandwidth ytterbium-doped self-sweeping fiber laser by using a reflector including collimator and mirror. The self-sweeping state was achieved by a 2 m long fiber saturable absorber, and was confirmed by the unique pulse intensity. The central wavelength of laser located at 1065.382 nm along with a self-sweeping range within 2 pm. The radio frequency spectrum observed the relaxation oscillation and beat frequency signals. Especially, the nonlinear saturable absorption feature was confirmed by fitting the intervals of beat frequency signals. The behaviors of relaxation oscillation peaks were summarized and fitted by the empirical formula. This work provides a new self-sweeping laser tool with a narrow bandwidth and can be applied in laser ranging and tunable microwave signal generation.

Triple-wavelength mode-locked laser based on a Cr2Si2Te6 saturable absorber

In this work, a Cr2Si2Te6-based tapered fiber saturable absorber with a modulation depth of 4.7 % and a saturable intensity of 28.67 MW/cm2 was fabricated by liquid-phase exfoliation. A triple-wavelength erbium-doped mode-locked fiber laser with a Sagnac loop structure was successfully generated. Its output wavelengths were 1560.2, 1561.3, and 1562.8 nm. The basic repetition rate was 0.97 MHz, corresponding to a signal-to-noise ratio of 49 dB. This is the first demonstration of a triple-wavelength mode-locked fiber laser focusing on a two-dimensional ferromagnetic insulator Cr2Si2Te6. This experiment shows that this triple-wavelength mode-locked fiber laser has excellent performance.

Titanium dioxide fiber saturable absorber for Q-switched fiber laser generation in the 1-micrometer region: publisher's note.

This publisher's note serves to correct an error in Appl. Opt. 58, 3495 (2019)APOPAI0003-693510.1364/AO.58.003495.

Ti3AlC2 coated D-shaped fiber saturable absorber for Q-switched pulse generation

Ti3AlC2 coated D-shaped fiber saturable absorber for Q-switched pulse generation

Single-frequency Tm-doped fiber laser with 215 mW at 2.05 µm based on a Tm/Ho-codoped fiber saturable absorber.

We demonstrate an efficient single-frequency Tm-doped fiber laser at 2050 nm. A ring cavity scheme is employed to boost the net gain at the wavelength. A piece of Tm/Ho-codoped fiber with an absorption coefficient at 2050 nm higher than that of a Tm-doped fiber is used to establish the dynamic Bragg grating for enhancing the frequency selection capability. A single-frequency output of 215 mW is obtained under 2 W of 1570-nm pump power, with the slope efficiency being 22%. To the best of our knowledge, this is the highest single-frequency all-fiber laser oscillator output power above 2 µm.

Generation of stable Q-switched pulses at 1566 nm by using a segment of erbium-doped fiber as saturable absorber

In this manuscript, the performance of a passively Q-switched fiber laser has been presented, where a segment of un-pumped erbium-doped fiber (EDF) is used as the saturable absorber (SA). We have taken an erbium and ytterbium (Er/Yb) co-doped double cladding fiber as the gain media for efficient pump absorption and checked the potential of the laser by changing the length of the in-house fabricated erbium-doped fiber saturable absorber (EFSA). For a fixed length of EFSA, variation of important system parameters such as output power, repetition rate, pulse width, etc, with the change of the pump power has also been reported. The laser has delivered pulses of a minimum duration of 1.35 µs with maximum energy of 2.8 µJ. The repetition rate varies in the range from 24.8 kHz to 47 kHz with alteration of the length of the SA. The central wavelength of the output spectra is 1566 nm.

A novel technique for the fabrication of a saturable absorber for fiber lasers: pulsed laser deposition

In the present work, for the first time, it is demonstrated that a zinc oxide (ZnO) thin film deposited directly on a fiber ferrule using a pulsed laser deposition (PLD) is a novel technique to prepare a saturable absorber (SA) for doped fiber lasers. The erbium-doped fiber laser based on this SA and erbium-doped fiber as a gain medium yields optical pulses with emission wavelength 1567.86 nm at a 3 dB spectral bandwidth of 1.24 nm at 42 mW. As the pump power is increased, the pulse duration decreases from 23.58 µs to 5.6 µs, and the pulse repetition rates increase from 10.79 kHz to 70.78 kHz. A maximum peak power, pulse energy and average output power of about 9.4 mW, 65.8 nJ, and 4.6 mW, respectively, have been achieved at a maximum pump power of 368 mW. The long-term stability and the damage threshold of the SA are also discussed. These findings suggest that the PLD technique is a promising technique to fabricate a cost-effective and stable SA for the fabrication of passively Q-switched fiber lasers.

Cerium oxide/polydimethylsiloxane composite tapered fiber saturable absorber for mode-locked pulsed erbium-doped fiber laser

This investigation demonstrates the nonlinear saturable absorption of cerium oxide (CeO2) nanoparticles; a lanthanide allotrope oxide material and its employment as a saturable absorber (SA) for the generation of stable mode-locked pulsed fiber laser. The CeO2 nanoparticles were simply prepared by sonicating its bulk solution and incorporating a polydimethylsiloxane (PDMS) polymer to form a thin film nanocomposite on tapered optical fiber for the fabrication of CeO2/PDMS-SA. The nonlinear intensity-dependent transmission characteristic of this material was confirmed with a modulation depth of 0.66% and saturation intensity of 77 MW/cm2. The SA was integrated into an erbium-doped fiber laser cavity, where mode-locking operation self-started at 35 mW pump power with stable soliton operation up to 250 mW in net anomalous dispersion regime. The pulse laser centered at 1561 nm wavelength with a constant repetition rate of 7.64 MHz, shortest pulse width of 800 fs, and highest signal to noise ratio of 54.2 dB. The highest pulse energy of 0.645 nJ and average power of 4.92 mW were measured at 250 mW pump power. Based on its simple preparation and stable pulse generation, this investigation suggests the viability of CeO2 nanoparticles as a new SA material for ultrashort pulse generation.

Cavity dynamics of a hybrid mode‐locked figure of eight fiber laser

AbstractMode‐locking is an increased focus area due to the augmented requirement of ultra‐short and high‐intensity optical pulses for varied applications. Tunable mode‐locked lasers capable of operating in the infrared range at high repetition frequency brought innovative opportunities for insensitive and accurate laser surgery. As one important application of optical pulse propagation in an optical fiber, we have discussed a dual‐ring hybrid mode‐locked fiber laser using modulator, and saturable absorber. The active mechanism, saturable absorber, and the nonlinear optical loop mirror result in an output with a peak power of 16 dBm, and 80 fs full‐width at half‐maximum with a high duty cycle. It occupies a small space and is easy to achieve miniaturization and intensification; the laser output can be adjusted by varying multiple parameters such as pump, input, doped fiber length, modulator (including modulation signal), saturable absorber, and other devices.

Generation of bound solitons in a mode- locked Tm-doped fiber laser based on a graded-index multimode fiber saturable absorber

In this work, we report on the experimental observations of bound solitons in a Tm-doped passively mode-locked fiber laser by using an all-fiber saturable absorber, structured by a stretched graded index multimode fiber. Stable out-of-phase soliton pairs are obtained, with a temporal separation of 4.36 ps between the two ∼1.88 ps pulses, while the central wavelength can be continuously tuned from 1959 nm to 1962 nm. Meanwhile, some different pulse separations from 16 ps to 18.02 ps of tightly bound soliton pairs have also been realized by cautiously adjusting the PC. The results are helpful for us to understand the nonlinear dynamics in fiber lasers and further explore high-capacity fiber communication.

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.