Tungsten tri-oxide (WO3) film absorber for generating Q-switched pulses in erbium laser

ABSTRACT

This paper reports a new type of passive saturable absorber (SA) made of transition metal oxide (TMO) embedded in polyvinyl alcohol (PVA). The Tungsten trioxide (WO₃)-PVA SA is placed in an erbium-doped fibre laser cavity to produce Q-switched pulses operating at 1562.82?nm. The pulse laser starts to manifest at the threshold pump power of 40?mW and continues to exist until the maximum pump power of 195?mW. Within that pump power range, its pulse energy, repetition rate and pulse width vary from 98 to 142.85?nJ, 29.86 to 56.7?kHz and 5.032 to 1.85?µs, respectively. The pulse train is stable with a signal to noise ratio of 70?dB. This is the first demonstration of a Q-switched laser using such a SA.     

Passive mode-locking in erbium-doped fibre laser based on BN-GO saturable absorber

A C-band mode-locked fibre laser incorporating a boron nitride-doped graphene oxide (BN-GO)-based saturable absorber (SA) is proposed and demonstrated. The SA is fabricated by depositing multiple layers of synthesized BN-GO nanoparticles onto the polished surface of a side-polished fibre, which is then inserted into an erbium-doped fibre laser cavity to generate the desired pulsed output. The strong nonlinear optical response and light absorption of the BN-GO nanoparticles induces the generation of a highly stable mode-locked pulse at 1567.32?nm with visible Kelly’s sidebands. The pulses have a measured repetition rate of 13.56?MHz and a pulse width of 1.18?ps at the maximum pump power of 280.5?mW. The pulses have a frequency signal-to-noise ratio of ～53?dB, indicating a highly stable output. The proposed laser would find significant telecommunications applications, particularly for dense wavelength division multiplexing systems.     

Mode-locked soliton erbium-doped fiber laser using a single-walled carbon nanotubes embedded in polyethylene oxide thin film saturable absorber

We demonstrate a simple, compact, and low cost mode-locked erbium-doped fiber laser (EDFL) using a single-walled carbon nanotubes (SWCNTs) embedded in polyethylene oxide (PEO) thin film as a passive saturable absorber (SA). The film with a thickness of 50?μm was fabricated using a prepared homogeneous SWCNT solution with 0.1% loading percentage, which was mixed with a diluted PEO solution and casted onto a glass Petri dish to form a thin film by evaporation technique. The film is sandwiched between two fiber connectors to construct a SA, which is then integrated in an EDFL cavity to generate a self-started stable soliton pulses operating at 1558?nm. The soliton pulse starts to lase at pump power threshold of 17.6?mW with a repetition rate of 50?MHz, pulse width of 0.67?ps, average output power of 0.158?mW, pulse energy of 3.16?pJ, and peak power of 4.43?W.     

MEH-PPV organic material as saturable absorber for Q-switching and mode-locking applications

ABSTRACT

Q-switched and mode-locked pulse generation in Erbium-doped fiber lasers (EDFLs) are demonstrated using Poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) organic semiconductor material as a saturable absorber (SA) for the first time. The MEH-PPV was prepared in the form of a thin film having a modulation depth of 12% and saturation intensity of 40?MW/cm². The SA was placed in a laser cavity to produce a stable Q-switched operating at 1564.0?nm. The maximum repetition rate of 78.62?kHz, minimum pulse width of 3.54?µs and maximum pulse energy of 59.45?nJ were attained at 125.2?mW pump power. On the other hand, by incorporating an additional 100?m long single mode fiber, the mode locked EDFL self-started as the pump power was raised above 125.2?mW. The soliton pulse was obtained due to the enhancement of the nonlinearity in the cavity. The mode-locked laser operated at 1568.5?nm with a fixed repetition rate of 1.859?MHz and pulse width of 2.97?ps.     

Pure antimony film as saturable absorber for Q-switched erbium-doped fiber laser

This paper reports on the use of Antimony (Sb) polymer film to generate stable Q-switching pulses in Erbium-doped fiber laser (EDFL) cavity. The SA is fabricated by coating a thin layer of Sb on a polyvinyl alcohol (PVA) film through physical vapour deposition (PVD) process. A 1 × 1 mm area of the film SA is cut and integrated into between two fiber ferrules inside the laser cavity for intra-cavity loss modulation. Self-starting and stable Q-switched pulses are obtained within a pump power range from 60 to 142 mW. Within this range, the repetition rate increases from 70.82 to 98.04 kHz, while pulse width decreases from 7.42 to 5.36 μs. The fundamental frequency signal-to-noise ratio of the pulse signal is 74 dB, which indicates the excellent stability of the pulses. The maximum output power and pulse energy are 8.45 mW and 86.19 nJ, respectively. Our demonstration shows that Sb film SA capable of generating stable pulses train operating at 1.55-micron region.     

A generation of 2 μm Q-switched thulium-doped fibre laser based on anatase titanium(IV) oxide film saturable absorber

We demonstrate a Q-switched thulium-doped fibre laser operating at approximately 1935 nm wavelength using anatase titanium(IV) oxide (TiO₂) embedded in polyvinyl alcohol as the passive newly saturable absorber (SA). The film has absorption loss of 3.5 dB and modulation depth of 33%. It is sandwiched between two fibre ferrules in a ring laser cavity to produce self-started pulse train with a repetition rate that is tuned from 30.12 to 36.96 kHz as the 1552-nm pump power is increased from 289 to 485 mW. At maximum pump power, the laser produced a Q-switching pulse train with pulse duration, output power, pulse energy and peak power of 1.91 μs, 11 mW, 0.3 μJ and 146 mW, respectively. These results show that the TiO₂ is a new potential SA material for pulsed laser applications.     

Wideband tunable Q-switched fiber laser using graphene as a saturable absorber

An ultra-wide wavelength tuning range, which covers three different band regions consisting of the S-, C-, and L-bands, is proposed and demonstrated for a graphene-based Q-switched erbium-doped fiber laser using a tunable bandpass filter as the wavelength tuning and filtering mechanism. A 3?m length of erbium-doped fiber is used as the gain medium in a ring laser cavity configuration, with absorption coefficients of between 11 and 13 dB?m^?1 at 980?nm and about 18?dB?m^?1 at 1550?nm. The tuning range of the Q-switching pulses covers a wide wavelength range of 58?nm, which spans from 1512.5?nm to 1570.5?nm. In addition, the lasing and Q-switching thresholds are considerably low, with respective values of ～11.0?mW and ～18.4?mW. A repetition rate of 55.3?kHz is obtained at the maximum pump power of 100.4?mW, together with pulse width and pulse energy of 1.6?μs and 25.8?nJ, respectively.     

Triple-wavelength passively Q-switched ytterbium-doped fibre laser using zinc oxide nanoparticles film as a saturable absorber

We report on the generation of a triple-wavelength passively Q-switched ytterbium-doped fibre laser using a saturable absorber (SA) based on zinc oxide nanoparticles (ZnO NPs) film. The SA was fabricated by embedding ZnO NPs powder into a polyvinyl alcohol as a host polymer. By properly adjusting the pump power and the polarization state, single-, dual- and triple-wavelength Q-switching are stably generated without additional components (such as optical filter, or fibre grating). For the triple wavelength operation, the fibre laser generates a maximum pulse repetition of 87.9 kHz with the shortest pulse duration of 2.7 μs. To the best of authors’ knowledge, it’s the first demonstration of triple-wavelength passively Q-switching fibre laser using ZnO NPs as a SA. Our results suggest that ZnO is a promising SA for multi-wavelength laser operation.     

Generation of soliton and bound soliton pulses in mode-locked erbium-doped fiber laser using graphene film as saturable absorber

We report an observation of soliton and bound-state soliton in passive mode-locked fibre laser employing graphene film as a passive saturable absorber (SA). The SA was fabricated from the graphene flakes, which were obtained from electrochemical exfoliation process. The graphene flakes was mixed with polyethylene oxide solution to form a polymer composite, which was then dried at room temperature to produce a film. The film was then integrated in a laser cavity by attaching it to the end of a fibre ferrule with the aid of index matching gel. The fibre laser generated soliton pulses with a 20.7 MHz repetition rate, 0.88 ps pulse width, 0.0158 mW average output power, 0.175 pJ pulse energy and 18.72 W peak power at the wavelength of 1564 nm. A bound soliton with pulse duration of ~1.04 ps was also obtained at the pump power of 110.85 mW by carefully adjusting the polarization of the oscillating laser. The formation of bound soliton is due to the direct pulse to pulse interaction. The results show that the proposed graphene-based SA offers a simple and cost efficient approach of generating soliton and bound soliton in mode-locked EDFL set-up.     

Molybdenum tungsten disulphide (MoWS2) as a saturable absorber for a passively Q-switched thulium/holmium-codoped fibre laser

In this work, a passively Q-switched Thulium/Holmium-doped fibre laser (THDFL) using a molybdenum tungsten disulphide (MoWS₂) saturable absorber (SA) is proposed and demonstrated. The MoWS₂ nanosheets are prepared by hydrothermal exfoliation and then suspended in a polyvinyl alcohol (PVA) thin film host. Q-switching of the THDFL at a maximum 1550 nm pump power of 445.2 mW gives a maximum repetition rate and minimum pulse width of 36.3 kHz and 2.8 µs with a corresponding pulse energy of 86.4 nJ and peak power of 31.1 mW. The MoWS₂ based Q-switched THDFL's output has a very high signal-to-noise value of ～62.2 dB which strongly indicates that the laser is working in a stable operation. To the best of our knowledge, this is the first demonstration of MoWS₂ as a passive SA in a THDFL for operation in the 2.0 µm region. The proposed laser would have significant medical and sensing applications, particularly at the biologically active 2.0–2.1 µm regions.     

Passively Q-switched erbium-doped fibre laser using cobalt oxide nanocubes as a saturable absorber

We demonstrate a Q-switched Erbium-doped fibre laser (EDFL) utilizing cobalt oxide (Co₃O₄) nanocubes film based saturable absorber (SA) as a passive Q-switcher. Co₃O₄ nanocubes are embedded into a polyethylene oxide film to produce a high nonlinear optical response, which is useful for SA application. It has saturation intensity and modulation depth of 3 MW/cm² and 0.35%, respectively. The proposed laser cavity successfully generates a stable pulse train where the pulse repetition rate is tunable from 29.8 to 70.92 kHz and the pulse-width reduces from 10.9 to 5.02 μs as the 980 nm pump power increases. This result indicates that the Co₃O₄ is excellent for constructing an SA that can be used in producing a passively Q-switched fibre laser operating at a low pump intensity. To the best of our knowledge, this is the first demonstration of Co₃O₄ film based fibre laser.     

Tunable passively Q-switched thulium doped fluoride fibre (TDFF) laser using reduced graphene oxide-silver (rGO-Ag) as saturable absorber

A tunable, passively Q-switched thulium doped fluoride fibre (TDFF) laser using a reduced-graphene oxide-silver (rGO-Ag) thin film as a saturable absorber (SA) for S band operation is proposed and its efficacy demonstrated. Over a pump power range of 91.4?mW up to 158.6?mW, passively generated Q-switched pulses are observed with repetition rates from 20 to 34.5?kHz and pulse widths from 3.1 to 7.1?µs. The highest pulse energy observed is 101.2?nJ with a signal to noise ratio of ～42?dB. The proposed laser has a tuning range ～52?nm from 1458 to 1510?nm with a tunable bandpass filter (TBPF) introduced into the cavity.     

Q-switched thulium-doped fiber laser operating at 1940 nm region using a pencil-core as saturable absorber

Q-switched thulium-doped fiber laser (TDFL) is demonstrated using pencil-core flakes as a saturable absorber (SA) for the first time. The SA was fabricated by exfoliating pencil-core flakes on adhesive tape surface, then repeatedly folded over the tape until the flakes homogenously deposited on the tape. A small piece of the tape is sandwiched between two ferrules and incorporated in TDFL cavity to realize a stable Q-switching pulse train. By increasing the 1552-nm pump power from 389 to 431 mW, the repetition rate of the TDFL increases from 14.95 to 34.60 kHz while the pulse width decreases from 6.70 to 4.69 μs. The maximum pulse energy of 46.05 nJ is generated with repetition rate and pulse width of 21.25 kHz and 6.27 μs, respectively. To the best our knowledge, this is a first demonstration SA from mundane object as alternative to commercial bulk graphite for Q-switched fiber laser.     

Nickel oxide nanoparticles thin film saturable absorber for 1-micron pulsed all-fibre lasers operation

A passive Q-switched and mode-locked ytterbium-doped fibre laser (YDFL) pulse generation using a nickel oxide thin film as a saturable absorber is reported. The nickel oxide nanoparticle thin film was fabricated by a simple processing technique, and it has a modulation depth of 39% and saturation intensity of 0.04 MW/cm². The saturable absorber was constructed by inserting a small piece of the film between two fibre ferrules. Then it was integrated in a YDFL cavity. The Q-switching operation started at a threshold pump power of 117.73 mW with an initial wavelength of 1073.5 nm. When the pump power was raised from 117.73 to 133 mW, the repetition rate grew from 9.5 to 15.8 kHz. The pulses had a maximum pulse energy of 478 nJ. Furthermore, a stable self-started mode-locked pulse was also succesfully generated at the threshold pump power of 97.3 mW. The central wavelength and repetition rate of the laser were 1037.72 nm and 23 MHz, respectively. The maximum pulse energy of 0.56 nJ and a peak power of 26.4 W were recorded at a pump power of 137.5 mW.     

Multi-wavelength Q-switched Erbium-doped fiber laser with photonic crystal fiber and multi-walled carbon nanotubes

A simple multi-wavelength passively Q-switched Erbium-doped fiber laser (EDFL) is demonstrated using low-cost multi-walled carbon nanotubes (MWCNTs)-based saturable absorber, which is prepared using polyvinyl alcohol as a host polymer. The multi-wavelength operation is achieved based on non-linear polarization rotation effect by incorporating 50?m long photonic crystal fiber in the ring cavity. The EDFL produces a stable multi-wavelength comb spectrum for more than 14 lines with a fixed spacing of 0.48?nm. The laser also demonstrates a stable pulse train with the repetition rate increasing from 14.9 to 25.4?kHz as the pump power increases from the threshold power of 69.0?mW to the maximum pump power of 133.8?mW. The minimum pulse width of 4.4?μs was obtained at the maximum pump power of 133.8?mW while the highest energy of 0.74 nJ was obtained at the pump power of 69.0?mW.     

Wavelength-switchable C-band erbium-doped fibre laser incorporating all-fibre Fabry–Perot interferometer fabricated by chemical etching

A switchable and stable triple-wavelength, ring-cavity, erbium-doped fibre laser incorporating an all-fibre Fabry–Perot interferometer (FPI) is designed and experimentally demonstrated. In the proposed fibre laser, the all-fibre FPI is fabricated using the chemical etching method and is used to generate the filter effect. The laser threshold is 88 mW. Switchable single-wavelength lasing at 1529.9, 1545.1 and 1560.2 nm can be realized with a power fluctuation less than 0.64 dB under 20 min of scanning time at room temperature. In addition, the wavelength-switchable dual-wavelength lasers can be tuned by changing the polarization state in the experiment, and the maximum power fluctuations for the 1545.1 and 1560.2 nm lasers are less than 1.19 and 1.57 dB at 26 °C, respectively. Furthermore, a triple-wavelength laser is obtained by adjusting the polarization controller. The results demonstrate that switchable single-, dual-, or triple-wavelength lasers can be generated through the proposed fibre laser.     

Mode-locked thulium doped fibre laser with copper thin film saturable absorber

We demonstrate the generation of mode-locked Thulium-Doped Fibre Laser by employing a newly developed saturable absorber (SA) based on copper (Cu) thin film. The SA was prepared by depositing nano-sized particles of Cu onto the surface of polyvinyl alcohol (PVA) film through the E-Beam evaporation process. A stable mode-locking pulse train operating at 1951?nm was successfully generated by introducing the Cu PVA SA into a laser cavity. The laser generated a pulse train at the fundamental frequency of 8.5?MHz with a calculated minimum pulse width of 14.8?ps. This demonstration proves that the Cu PVA based SA is suitable for generating mode-locked fibre laser at 2?µm region.     

Wide-band,passively Q-switched Yb- and Tm-doped fibre laser using WSSe saturable absorber

A wide-band, passively Q-switched fibre lasers based on ytterbium- and thulium-doped fibre gain medium are proposed and demonstrated. The lasers employ a transition metal dichalcogenide, tungsten sulphoselenide as a saturable absorber (SA) which is prepared by mechanical exfoliation technique. By integrating the SA in the laser cavities, self-starting Q-switched at 1038 and 1982?nm are obtained. The generated pulses exhibit a microsecond pulse duration with few kilohertz repetition rate. The proposed SA has high potential as a new material to cater to the needs of various scientific, industrial and biomedical applications.     

Tenth-order rational-harmonic frequency multiplication and detuning of optical pulse injection-locked erbium-doped fiber laser

The jitter and frequency-detuning dynamics of a 10-GHz rational-harmonic frequency-multiplied pulse train generated from an erbium-doped fiber laser (EDFL) is studied. The EDFL is self-feedback seeded and optically injection locked by a gain-switched laser diode (GSLD) with a pulse width and an average power of 17.6 ps and 0.2 mW, respectively, at a repetition frequency of 1 GHz. The repetition frequency of the optical pulse train can be tenth-order multiplied by a slight detuning of the repetition frequency of the GSLD to match the rational-harmonic injection-locked condition of the EDFL. As the repetition frequency is multiplied from 1 to 10 GHz, the peak power, the pulse width, and the frequency-detuning bandwidth of the injection-locked EDFL pulses decrease from 1.2 to 0.3 W, from 40 to 21 ps, and from 40 to 9 kHz, respectively. The timing jitter of the injection-locked EDFL repeated at 1 GHz remains unchanged (< 0.5 ps) within the detuning bandwidth, which inevitably increases to 1.2 ps after tenth-order multiplication.