Fiber Saturable Absorber Research Articles

Holmium based nanoseconds pulsed fibre laser generation in the 2-micron region

We demonstrate and compare nanoseconds pulse induced by a Holmium oxide PVA film (HOPF, 50 μm thick) and a Holmium-doped fibre (HDF, 8 cm long) saturable absorber (SA) in a Thulium doped-fibre laser (TDFL) cavity. The HOPF SA produced a nanoseconds pulse operating at 1960 nm wavelength, with a pulse width of 57 ns. On the other hand, the HDF SA produced a pulsed laser operating at 1963 nm wavelength, with a pulse width of 53 ns. The HDF SA established a slightly better maximum pulse energy of 0.87 nJ as compared to the HOPF SA with only 0.62 nJ.

L-band Q-switched fiber laser with gallium/thulium-doped silica fiber saturable absorber

An L-band Q-switched fiber laser was demonstrated using gallium/thulium-doped silica fiber saturable absorber. At 10 cm in length, the saturable absorber generated Q-switched fiber laser at a pump power threshold of 39.6 mW and a central wavelength of 1601.93 nm. Beyond 53.3 mW, a spectrum with a central wavelength at 1602.00 nm was generated. On the other hand, the pulse repetition rate was obtained from 3.44 to 7.47 kHz whereas the pulse width reduces from 100.2 to 58.6 µs for pump power ranges from 39.6 to 53.3 mW. Within this range, the pulse energy is attained between 0.2600 and 0.2843 µJ, at a laser power slope efficiency of 6.94%. The constantly operated Q-switched fiber laser over 50 min observation time at 53.3 mW pump power ensures the feasibility of this pulse laser source as a practical device.

Titanium dioxide fiber saturable absorber for Q-switched fiber laser generation in the 1-micrometer region.

A passively Q-switched ytterbium-doped fiber laser (YDFL) operating at 1062nm was demonstrated by using a segment of 20cm titanium dioxide-doped fiber saturable absorber (TiO2DF SA). The Q-switched YDFL emerged stably with tunable repetition rates ranging from 32kHz to 53kHz as the pump power rose from 109mW to 233mW. Within this range of pump power, a maximum output power of 10.1mW, maximum peak power of 75mW, and maximum pulse energy of 191nJ were obtained. The narrowest pulse width of 2.55μs was attained at the maximum pump power of 233mW, while the signal-to-noise ratio of the fundamental frequency was 47dB. This demonstration reveals that the proposed TiO2DF SA is feasible for constructing a flexible and reliably stable Q-switched pulsed fiber laser in the 1-micrometer region.

Generation of pulse-width controllable dissipative solitons and bound solitons by using an all fiber saturable absorber.

A passively mode-locked fiber laser with controllable pulse width is demonstrated by use of an all-fiber saturable absorber based on a hybrid no-core fiber (NCF)-graded index multimode fiber (GIMF) structure incorporated into an Er-doped fiber ring cavity. Such a hybrid NCF-GIMF structure has a tunable intracavity filtering effect. As a result, the mode-locking operation is achieved with controllable pulse width and spectral bandwidth in the normal dispersion regime by only stretching the fiber device. Soliton pulses with the pulse width of 7.7-23ps are generated, and bound solitons with variable widths are also experimentally demonstrated. The results obtained reveal the versatility and flexibility of the NCF-GIMF structured device in controlling the pulse dynamics for different experimental requirements.

Passively Q-switched Erbium doped fiber laser by incorporating a segment of Thulium doped fiber saturable absorber

We propose a segment of 11 cm long Thulium-doped fiber (TDF) as a passive saturable absorber (SA) in generating a stable Q-switched Erbium-doped fiber laser (EDFL). The obtained pulsed laser has a central wavelength of 1560 nm and emerges stably within a repetition rate range of 54.1-106.7 kHz over a pump power range of 35-136 mW. At the maximum pump power of 136 mW, the EDFL produces a maximum output power of 14.3 mW, a maximum pulse energy of 134.7 nJ and a maximum peak power of 41 mW as well as the narrowest pulse width of 3.28 µs. The fundamental frequency of the pulsed laser has a signal to noise ratio (SNR) of approximately 63 dB. The proposed laser would have a good prospect for material processing and medicine.

Ytterbium doped fiber saturable absorber for a stable passively Q-switched fiber laser in the 1-micron region

In this paper, we experimentally demonstrate a stable passively Q-switched fiber laser in the 1-micron regime by incorporating a segment of Ytterbium-doped fiber (YDF, 12 cm) as a saturable absorber (SA) in a ring cavity scheme. The fiber SA exhibits a linear absorption of about 2.44 dB at the Q-switched oscillating regime (1068 nm). The Q-switched pulses started to self-occur as the pump power elevated to its threshold of 151 mW and steadily existed up to the maximum pump power of 233 mW. At the maximum pump power, we obtained a maximum repetition rate of 74.2 kHz, a maximum output power of 3.7 mW, a maximum pulse energy of 49 nJ and a pulse width as short as 1.97 µs. Our results denote that a segment of YDF is possible of generating a reliable Q-switched fiber laser in the 1-micron regime, revealing its potential as another fiber SA candidate.

All-fiber passively Q-switched erbium fiber laser implementing erbium-ytterbium-thulium co-doped saturable absorber fiber

We demonstrate a passive Q-switched fiber laser using an erbium-ytterbium-thulium (Er-Yb-Tm) doped fiber. The length of the Er-Yb-Tm co-doped fiber is varied from 0.4 m to 1.4 m to study the effect of this passive gain medium for pulse laser performance. The proposed laser operates in the pulse operation regime within a certain range of pump powers, which is dependent on the length of the Er-Yb-Tm co-doped fiber. A longer fiber employed in the laser cavity results in a higher laser pump power threshold, but a wider pump power range of pulse laser operation. The experimental outcome shows that a 1.0 m Er-Yb-Tm co-doped fiber offers the best performance in this work with a Q-switched pump power threshold of 45.1 mW, the widest pulse energy output range of 0.0439 μJ from 0.0167 μJ to 0.0606 μJ, with the supplementary advantage of 120.7 mW Q-switched laser operating range. This fiber gain medium analysis contributes to the generation of short pulse laser source without employing any chemical materials and complex laser setup.

Ultrafast soliton and stretched-pulse switchable mode-locked fiber laser with hybrid structure of multimode fiber based saturable absorber

We demonstrate an all-fiber mode locked laser based on hybrid structure of multimode fiber saturable absorber (SA) that can realize both conventional soliton and stretched-pulse states. Stable 16.44 MHz conventional soliton pulses are achieved by injecting 80 mW threshold pump power. By increasing the incident pump power to 420 mW, the laser evolves from soliton operation into stretched-pulse mode locking state. 310 fs stretched-pulse are obtained with the same repetition rate as the soliton pulses. The center wavelength and its 3 dB spectrum bandwidth are 1603 nm and 14.2 nm, respectively. For the first time, we experimentally confirm transition between conventional soliton and stretched-pulse in 1.5 μm mode-locked fiber laser by introducing multimode optical fiber SA. Moreover, the maximum single pulse energy of nearly 1 nJ is achieved. Such all-fiber mode-locked lasers based on hybrid structure of multimode fiber are attractive for practical applications without damage and the limitation of life time.

Wavelength tuning of a passively Q-switched Er-doped fiber laser based on a Tm–Ho codoped fiber saturable absorber

With a piece of Tm–Ho codoped fiber as the saturable absorber, stable passive Q-switching of an Er-doped fiber laser can be attained in a wide wavelength range. A theoretical model concerning this passively Q-switched laser system with wavelength tuning is established. Output characteristics of this laser system are discussed and compared both experimentally and numerically. Analysis shows that, for saturable absorber-based passive Q-switching, a relatively higher coupling ratio and a longer wavelength not only help to expand the pump range and the repetition rate range of the laser system, but also indicate higher output energy and Q-switching efficiency.

Passively Q-switched fibre laser utilizing erbium-doped fibre saturable absorber for operation in C-band region

ABSTRACTIn this paper, a stable and robust all-fibre passively Q-switched erbium-doped fibre laser (EDFL) emitting at 1558 nm is described. The proposed laser utilizes an 11 cm long erbium-doped fibre as saturable absorber (SA). The fibre SA features a linear optical absorption of about 13 dB in the Q-switched EDFL operating regime. By elevating the input pump power from the threshold of 60 mW to the maximum available power of 142 mW, a pulse train with a maximum repetition rate of 86 kHz, minimum pulse width of 3.39 µs, maximum average output power of 10.5 mW, maximum pulse energy of 122 nJ and maximum peak power of 36 mW are obtained. The signal to noise ratio (SNR) of the spectrum is measured to be around 70 dB. This fibre SA is simple, reliable, compact and alignment free. Thus it is suitable for making a portable pulse laser source.

Q-switched ytterbium-doped fiber laser via a thulium-doped fiber saturable absorber.

We demonstrated a reliable and stable Q-switched ytterbium-doped fiber laser centered at 1069nm by employing a segment of 11cm thulium-doped fiber (TDF) as a saturable absorber (SA) in the ring cavity. The fiber SA has an optical absorption of 1.35dB at the Q-switched operating regime. As we increased the pump power from 109mW to the maximum available pump power of 206mW, a consistent Q-switched laser with output power ranging from 1.8 to 4.8mW was attained. The pulse width narrowed from 4.9 to 2.87μs, whereas the repetition rate increased from 40 to 60.2kHz. In addition, maximum pulse energy of 80.7nJ and a maximum peak power of 28.1mW were obtained at the maximum pump power. The signal to noise ratio (SNR) was around 47dB. Our experimental study shows that a segment of TDF can be used as a Q-switcher in the 1μm fiber laser cavity to facilitate a reliable and robust microsecond pulse generation.

All-fiber laser with simultaneous Tm3+ passive Q-switched and Ho3+ gain-switched operation

We experimentally demonstrate simultaneous Tm3+ passive Q-switched (PQS) and Ho3+ gain-switched laser operations at 1888.8 and 2021.2nm, respectively, in a single-cavity all-fiber laser. The PQS operation of the Tm3+ laser is based on the use of a high-concentration holmium-doped fiber as a fiber saturable absorber. Then the Tm3+ laser emission is used as a pulsed pump source to achieve Ho3+ gain-switched pulses. A high birefringence fiber optical loop mirror used as a spectral filter allows the tuning of both Tm3+ and Ho3+ laser emissions.

Highly stable mode-locked fiber laser with graphene oxide-coated side-polished D-shaped fiber saturable absorber

A highly stable mode-lock fiber laser with a thin film coating of graphene oxide (GO) nanoparticles on a D-shaped fiber is proposed and demonstrated. The GO-coated D-shaped fiber, which serves as the cavity's saturable absorber (SA), is fabricated by drop-casting GO nanoparticles on the smooth and consistently polished area of the D-shaped fiber made using a disk-polishing machine. Mode-locking is induced through the interaction of the evanescent field from the D-shaped fiber and GO nanoparticle layer. The cavity has a length of 12.5 m with a fundamental frequency of 16.5 MHz and operates in the anomalous dispersion regime. Stable soliton modelocking is obtained above a pump power of 76.6 mW, with a central lasing wavelength of 1555.7 nm and welldefined Kelly's sidebands. The generated pulses have a repetition rate of 16.5 MHz and pulse duration of 1.18 ps over a pump power range of 76.6 to 280.5 mW, with only minor fluctuations observed. A signal-to-noise ratio of 58.3 dB is computed, indicating a highly stable output. The proposed SA fabrication technique provides a simple, cost-effective, and consistent method of generating mode-locked pulses in fiber lasers. © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).

An 8 cm long holmium-doped fiber saturable absorber for Q-switched fiber laser generation at 2-µm region

Abstract We demonstrate a Q-switched all-fiber laser operating at 2-µm region by adding a piece of 8 cm long holmium doped fiber (HDF) as a fiber saturable absorber (SA) in Thulium doped fiber laser (TDFL) ring cavity. Doping of Ho ions into yttria-alumina silica glass was done through conventional Modified Chemical Vapor Deposition (MCVD) technique in conjunction with solution doping process. The fabricated HDF has a linear absorption of 3 dB with a core diameter and a numerical aperture of 10 µm and 0.18, respectively. A self-started Q-switching operation begins at 418 mW pump level and continually dominant until 564 mW pump level. As the pump power increases, stable pulse train presence from 30.61 kHz to 38.89 kHz while the pulse width reduces from 3.18 µs to 2.27 µs. Both maximum output power and maximum peak power are obtained at 5.05 mW and 57.2 mW, respectively, while the maximum pulse energy is calculated to be 129 nJ. The signal-to-noise ratio (SNR) of the fundamental frequency is 50 dB. Our work may contribute to the discovery of stable, robust, and economic SA for pulse fiber laser generation at 2-µm region.

Experimental Observation of Bright and Dark Solitons Mode-Locked with Zirconia-Based Erbium-Doped Fiber Laser

We demonstrate the generation of dark and bright solitons with our homemade zirconia-based erbium-doped fiber and graphene oxide (GO) saturable absorber in anomalous dispersion region. The GO is fabricated using an abridged Hummer’s method, which is combined with polyethylene oxide to produce a composite film. The film is sandwiched between two optical ferrules and embedded in the laser cavity to enhance its birefringence and nonlinearity. The self-starting bright soliton is easily generated at pump power of 78mW with the whole length cavity of 14.7 m. The laser produces the bright pulse train with repetition rate, pulse width, pulse energy and central wavelength being 13.9 MHz, 0.6 ps, 2.74 pJ and 1577.46 nm, respectively. Then, by adding the 10m of single mode fiber into the laser cavity, dark soliton pulse is produced. For the formation of dark pulse train, the measured repetition rate, pulse width, pulse energy and central wavelength are 8.3 MHz, 20 ns and 4.98 pJ and 1596.82 nm, respectively. Both pulses operate in the anomalous region

Conventional soliton or stretched pulse delivered by nanotube-mode-locked fiber laser.

We propose a nanotube-mode-locked erbium-doped fiber laser that can deliver conventional solitons (CSs) or stretched pulses (SPs) based on a D-shaped fiber saturable absorber where evanescent-field interaction works. The net cavity dispersion of the laser is slightly negative. In our experiment, by optimizing the polarization controller in the cavity, CS and SP can be obtained at the central wavelengths of 1530.6nm and 1530.3nm due to carbon nanotubes and the spectral filtering effect induced by nonlinear polarization rotation. Although the acquired CS and SP nearly have the same central wavelengths, they show distinct optical spectra, 3-dB bandwidths. The proposed fiber laser is attractive for practical applications.

Regenerated fiber Bragg grating for fiber laser sensing at high temperatures

Thermally regenerated low-reflectivity fiber Bragg gratings (RFBGs), as one mirror of a resonant cavity, have been introduced as linear-cavity fiber lasers combining with fiber saturable absorbers. The output of lasing presents an optical signal-to-noise ratio of 50 dB and temperature sensitivity coefficient of 15.36 pm/°C for the heating process and 15.46 pm/°C for the cooling process. The lasing wavelength variation and power fluctuation at 700°C are less than 0.02 nm and 0.21 dB, respectively. The RFBG-based fiber laser sensing has displayed good linearity for both the temperature rising and cooling processes, and favorable stability at high temperatures.

A Novel Nanotube-Based Fiber Laser for Ultrashort Pulse Generation and Fast Measurements

We propose a nanotube-based erbium-doped fiber laser that can deliver conventional soliton (CS) and stretched pulse (SP) based on D-shaped fiber saturable absorber (DF-SA) where evanescent-field interaction works. The novel Nanotube-based Fiber Laser can generate SP or CS by tuning pump power and polarization controller (PC) properly. The net cavity dispersion of laser is slightly negative. In our experiment, by optimizing the PC in the cavity, CS and SP can be obtained at the central wavelengths of 1530.6 nm and 1530.3 nm due to on carbon nanotubes and the spectral filtering effect induced by nonlinear polarization rotation. Although the acquired CS and SP nearly have the same central wavelengths, they show distinct optical spectra, 3-dB bandwidths. The proposed fiber laser with switchable CS and SP is attractive for ultrashort pulse generation and fast measurements in practical applications.

All-fibre Q-switching YDFL operation with bismuth-doped fibre as saturable absorber

We demonstrate the generation of a passively Q-switched ytterbium-doped fibre laser (YDFL) using a bismuth-doped fibre (BDF) as a solid-state fibre saturable absorber (FSA) in a ring cavity. The BDF used has a wide and low absorption band of 5 dB/m at the 1.0 μm region due to the ion transition of that occurs around the region. When introduced into a YDFL laser cavity, a stable Q-switched pulse operation was observed and the pulse repetition rate was proportional to the input pump power. It was limited to 72.99 kHz by the maximum power that the laser diode could supply. Meanwhile, the pulse width decreased from 12.22 to 4.85 μs as the pump power was increased from 215.6 to 475.6 mW. The finding suggests that BDF could be used as a potential SA for the development of robust, compact, efficient and low cost Q-switched fibre lasers operating at 1 micron region.

Development of a 2 μm Tm-doped fiber laser for hyperspectral absorption spectroscopy applications

The hyperspectral absorption spectroscopy is attracting more and more attention as this technique enables continuous wavelength sweep over a whole absorption band, rather than one or several discrete absorption lines. Owing to the H2O possesses much stronger and more abundant absorption lines in the 2μm region, this work develop a widely tunable, narrow linewidth Tm-doped fiber laser around 1.87μm for the application of combustion diagnostics. The laser wavelength tuning range is designed from 1850 nm to 1890 nm to overlap the strong absorption band of H2O, and the laser linewidth is further narrowed to 0.04 nm by a fiber saturable absorber. With this laser system, demonstration experiments are implemented for the continuous detection of H2O absorption lines. Detailed absorption peaks of H2O from 1866 nm to 1879 nm are detected and well-resolved. The measured absorption spectrum agree well with the theoretical computation derived from HITRAN2012 database quantitatively, verifying this laser system ready for hyperspectral absorption applications.