Er-doped Fiber Laser Research Articles

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.

Polarization sensitive ReS2-GaSe nanosheets for Er&Yb co-doped fiber laser

We report a mixed polarization sensitive ReS2-GaSe saturable absorber (SA) for Er-doped mode-locked fiber lasers. The SA shows an obviously polarization sensitive transmission to the 1.55 μm polarized lasers. The mixed SA shows a modulation depth of 5.5%. The narrowest pulse width of 7.1 ps was obtained in Er & Yb co-doped fiber mode-locking laser at 1550 nm. The single pulse energy is up to 1.6 nJ with the repetition rate of 10.34 MHz.

Observation of 550 MHz passively harmonic mode-locked pulses at L-band in an Er-doped fiber laser using carbon nanotubes film**Project supported by the National Natural Science Foundation of China (Grant No. 61605107), Young Eastern Scholar Program at Shanghai Institutions of Higher Learning, China (Grant No. QD2015027), the “Young 1000 Talent Plan” Program of China, the Open Program of the State Key

We demonstrate a passively harmonic mode-locked (PHML) fiber laser operating at the L-band using carbon nanotubes polyvinyl alcohol (CNTs-PVA) film. Under suitable pump power and an appropriate setting of the polarization controller (PC), the 54th harmonic pulses at the L-band are generated with the side mode suppression ratio (SMSR) better than 44 dB and a repetition frequency of 503.37 MHz. Further increasing the pump power leads to a higher frequency of 550 MHz with compromised stability of 38.5 dB SMSR. To the best of our knowledge, this is the first demonstration on the generation of L-band PHML pulses from an Er-doped fiber laser based on CNTs.

212-kHz-linewidth, transform-limited pulses from a single-frequency Q-switched fiber laser based on a few-layer Bi2Se3saturable absorber

Conventional Q-switched fiber lasers operating at multi-longitudinal-mode oscillation usually suffer from self-mode-locking-induced temporal instability, relatively strong noise, and low coherence. Here, we address the challenge through demonstrating, for the first time, to the best of our knowledge, a single-longitudinal-mode (SLM) Er-doped fiber (EDF) laser passively Q-switched by a few-layer Bi2Se3 saturable absorber (SA). The Bi2Se3 SA prepared by the liquid-phase exfoliation method shows a modulation depth of ∼5% and saturation optical intensity of 1.8 MW/cm2. A section of 1-m unpumped EDF together with a 0.06-nm-bandwidth fiber Bragg grating is used as an ultra-narrow autotracking filter to realize SLM oscillation. Stable SLM Q-switching operation at 1.55 μm is successfully achieved with the spectral linewidth as narrow as 212 kHz and the pulse duration of 2.54 μs, manifesting near-transform-limited pulses with a time-bandwidth product of 0.53. In particular, we found that the SLM Q-switching possesses the higher signal-to-noise ratios of 62 dB (optical) and 48 dB (radio frequency), exhibiting its advantages of low noise and high stability. Such an SLM Q-switched fiber laser could gain great interest for some applications in coherent detection, coherent optical communications, and high-sensitivity optical sensing.

Relative Intensity Noise of Hybrid Mode-Locked Bound Soliton Fiber Laser: Theory and Experiment

Relative intensity noises (RIN) of mode-locked lasers are properties which are crucial for applications. In the literature, there have been plenty of theoretical/experimental studies on the RIN noises of passive/active single-pulse mode-locked lasers. Since some mode-locked lasers can also be operated under the bound-pulse mode-locking state, it is thus very interesting to further examine the RIN properties under bound-pulse mode-locking, and to verify if there are possibilities for RIN noise reduction as predicted by some previous theoretical works. The conventional analytical formula based on the soliton perturbation theory can no longer be applied due to the pulse shape complexity for the bound-pulse mode-locking cases. New theoretical tools for modelling general mode-locked lasers are eagerly awaited. In the present work, the RIN noises of an environmentally stable 10 GHz hybrid mode-locked Er-doped fiber laser capable of bound-soliton generation are experimentally investigated, and a novel theoretical method based on the linearized backpropagation approach is theoretically developed for calculating the RIN noise spectra of general mode-locked lasers. Both the theoretical and experimental results demonstrate that the RIN noise of the bound-soliton state can be lower than that of the single-soliton state by following the laser power scaling tendency.

Q-switched and mode-locked Er-doped fiber laser using PtSe2 as a saturable absorber

We report a passively Q-switched and mode-locked erbium-doped fiber laser (EDFL) based on PtSe2, a new two-dimensional material, as a saturable absorber (SA). Self-started Q-switching at 1560 nm in the EDFL was achieved at a threshold pump power of 65 mW, and at the maximum pump power of 450 mW, the maximum single Q-switched pulse energy is 143.2 nJ. Due to the polarization-dependent characteristics of the PtSe2-based SA, the laser can be switched from the Q-switched state to the mode-locked state by adjusting the polarization state. A mode-locked pulse train with a repetition rate of 23.3 MHz and a pulse width of 1.02 ps can be generated when the pump power increases to about 80 mW, and the stable mode-locked state is maintained until the pump power reaches its maximum 450 mW. The maximum single mode-locked pulse energy is 0.53 nJ. This is the first time to our knowledge that successful generation of stable Q-switched and mode-locked pulses in an Er-doped fiber laser has been obtained by using PtSe2 as a saturable absorber.

Nonlinear absorption properties of indium selenide and its application for demonstrating pulsed Er-doped fiber laser

Two-dimensional materials are now receiving continuously increasing attention due to their exceptional optical properties. Recently, it has been proved that indium selenide (InSe) is also an excellent photoelectric material, with wide applications in the field of photodetecters and so on. In our work, layered InSe was prepared through the liquid-phase exfoliation method, and the nonlinear saturable absorption properties of InSe were also experimentally investigated. In addition, InSe-polyvinyl alcohol film was successfully prepared and employed as an saturable absorber for demonstrating an Er-doped passive Q-switched mode-locked fiber laser for the first time. The largest Q-switched pulse energy was as high as 112.97 nJ and the narrowest mode-locked pulse duration was 2.96 ns at a repetition rate of 1.74 MHz. Our results fully indicate that InSe also has excellent nonlinear absorption properties in comparison with other commonly used 2D materials. Thus, the applications of InSe can be deeply investigated to promote the development of ultra-fast optics in the near future.

Chaos-Control and Locking in a Dual-Ring Er-Doped Fiber Laser by Adjusting Loss

Chaos-Control and Locking in a Dual-Ring Er-Doped Fiber Laser by Adjusting Loss

Decaying evolution dynamics of double-pulse mode-locking

Taking advantage of the dispersive Fourier transformation technique, the decaying evolution processes of double-pulse mode-locking in a single-walled carbon-nanotube-based Er-doped fiber laser are observed in detail for the first time to our knowledge. The decaying dynamics of the double-pulse mode-locking state is analyzed in the spectral and temporal domains. We reveal that the two pulses in one cluster disappear either simultaneously or one by one during the decaying processes of double-pulse mode-locking states. In addition, the spectral evolution patterns of the special double-pulse states (i.e., bound states) are extremely distinct at different decline rates of the pump power.

Tunable multi-wavelength Er-doped fiber laser based on a fiber taper

We demonstrate a multi-wavelength Er-doped fiber laser at room temperature by using a fiber taper as an optical comb filter. A taper filter fabricated with a flame brushing technique has a filter period of 1.9 nm and modulation depth of 9.7 dB. Four-wave-mixing induced by a 400 m SMF-28e fiber was employed to suppress the mode-competition. Stable cw laser with 11 lasing lines was obtained with a wavelength spacing of 1.9 nm by appropriately setting the pump strength and laser polarization state. The multi-wavelength fiber laser could be precisely tuned through carefully stretching the fiber taper.

High-energy solitons generation with a nonlinear multimode interference-based saturable absorber

We demonstrate a mode-locked all-fiber Er-doped fiber laser using the structure of a step-index multimode fiber and a graded index fiber as a new saturable absorber (SA) based on nonlinear multimode interference. By bending the SA to a certain state, stable soliton pulses are obtained at a pump threshold of 65 mW. The oscillator generates soliton pulses at 1598 nm with a spectral bandwidth of 3.4 nm, 960 fs duration and a fundamental repetition rate of 9.789 MHz. The output power of 24 mW is achieved at the maximum pump power of 700 mW, corresponding to a single pulse energy of 2.44 nJ. To the best of our knowledge, this is the first time anyone has achieved the highest single pulse energy in a fiber laser with the SA at 1.5 µm to date. Moreover, the impact of diverse mode field diameters of graded index fiber on mode-locking behavior will also be discussed.

Wavelength converter using a highly Er-doped optical fiber ring laser

This work presents an all-fiber wavelength converter based on a highly Er-doped fiber laser, which has been experimentally demonstrated. Frequencies from several kilohertz up to tens of gigahertz have been investigated. Making use of the gain competition in the amplifying medium, the wavelength conversion can be carried out over not only one lasing wavelength, but over several. These analyses have also been carried out for more than one all-fiber ring structure, demonstrating the viability of this wavelength converter. To the best of our knowledge, this is the first time an Er-doped fiber wavelength converter has been validated.

Centimeter-scale Yb-free heavily Er-doped silica fiber laser.

The laser behavior of a centimeter-scale Er3+/Al3+ codoped silica fiber with core numerical aperture and core diameter of 0.15 and 8μm, respectively, is reported. The core glass was prepared by the sol-gel method combined with high-temperature sintering; it contained Er3+ ion concentration as high as 1.32×1020 ions/cm3 and an Al/Er mole ratio of 10. The high doping homogeneity of Er3+ ions in the fiber core was confirmed by an electron probe microanalyzer element scanning, long Er3+: I13/24 emission lifetime of 11.4ms, and low refractive index fluctuation of fiber core (±1×10-4). The signal gain of fibers with 4.6cm, 10cm, and 16cm lengths was tested in the 1500-1620nm range. A gain of 7dB is achieved at 1560nm in a 16-cm-long EDF under 230mW pump power. Aimed for CO2 sensor application, the laser behavior of Er/Al codoped fiber was tested at 1572nm. A slope efficiency of 12% and an output power of 15mW were achieved in a 10-cm-long fiber under 166mW absorbed pump power. The newly developed silica fiber is promising for use in high-repetition-rate lasers.

Octave Spanning Coherent Supercontinuum Comb Generation Based on Er-Doped Fiber Lasers and Their Characterization

Wideband, octave spanning, coherent supercontinuum (SC) with high flatness is very useful for many applications, but it has been difficult to achieve such ideal SC. In this paper, we investigated the octave spanning, coherent SC generation based on Er-doped ultrashort pulse fiber laser system. First, we developed a high power ultrashort pulse system using a single-wall carbon nanotube fiber laser and similariton amplifier. A 1.0–2.2 μ m octave-spanning coherent supercontinuum was successfully generated. Next, by use of a stabilized fiber laser comb system as the seed pulse, an octave spanning SC comb was demonstrated. An octave spanning, highly coherent comb with high flatness was generated with normally dispersive highly nonlinear fiber. The characteristics of the generated supercontinuum comb were examined via balanced heterodyne beat measurements with stable continuous-wave laser diodes. The SC comb was confirmed to have high coherence and low amplitude noise at the observed wavelengths. Finally, the SC generation in two kinds of highly nonlinear fibers with different dispersion properties and the characteristics of the generated comb were examined. The dependence on fiber length, wavelength, and dispersion properties were discussed.

WS2-Clad Microfiber Saturable Absorber for High-Energy Rectangular Pulse Fiber Laser

Tungsten disulfide (WS2), which possesses broadband nonlinear saturable absorption property, displays promising applications in passively mode-locked lasers. Recent research works have demonstrated that WS2 shows much higher thermal conductivity than other transition metal dichalcogenides, which can withstand higher optical intensity and exhibit a higher damage threshold. However, the WS2-based high-energy fiber lasers have not been extensively studied. Here, a WS2-clad microfiber (WCM) saturable absorber (SA) is exploited by an effective transferring approach, which is precisely accomplished under optical microscope. The evanescent field interaction scheme has ability to further raise the optical damage threshold, as well as take full advantage of the nonlinear effect of WS2. Based on the WCM SA, high-energy rectangular pulses are achieved in an Er-doped fiber laser whose pulse duration and energy almost increase linearly with the enhancement of pump power. The maximum energy of single pulse in the cavity can reach 810 nJ under pump power of 800 mW. The experimental results open up venues to create new high-energy laser systems with rich functionalities and novel physical effects.

Titanium Selenide Saturable Absorber Mirror for Passive Q-Switched Er-Doped Fiber Laser

Titanium selenide saturable absorber mirror (TiSe2-SAM) is fabricated by a combination of magnetron sputtering method and chemical vapor deposition method. With the optical circulator, the TiSe2-SAM is flexibly injected in the experimental cavity as the saturated absorber, and a steady Q-switched Er-doped fiber (EDF) laser is established. The modulation depth of TiSe2-SAM is measured to be 25.92%. Through appropriately adjusting the polarization states and changing the pump power, the shortest pulse duration and maximum output power of the passive Q-switched EDF laser are 1.126 μ s and 11.54 mW, respectively. The adjustable range of the repetition rate is 70–154 kHz, and the signal to noise ratio is greater than 62 dB. To our best knowledge, there is no report on Q-switched EDF lasers based on TiSe2 up to now, and our new attempt on TiSe2-based Q-switched EDF laser proves that TiSe2 as a powerful candidate is promising in ultrafast optical generation for the characteristics of high modulation depth and high stability.

Stretched graded-index multimode optical fiber as a saturable absorber for erbium-doped fiber laser mode locking.

A novel mode-locking method based on the nonlinear multimode interference in the stretched graded-index multimode optical fiber (GIMF) is proposed in this Letter. The simple device geometry, where the light is coupled in and out of the stretched GIMF via single-mode fibers, is demonstrated to exhibit the temporal intensity discrimination required for mode locking. The nonlinear saturable absorber (SA) characteristics of the device are controllable by simply adjusting the strength of the stretching applied. The modulation depth of the device, which consists of ∼23.5 cm GIMF, is tuned from 10.37% to 22.27%. Such a simple SA enables the wavelength-switchable mode-locking operation in a ring Er-doped fiber laser, and ultrafast pulses with a pulse width of 506fs at 1572.5nm and 416fs at 1591.4nm were generated. The versatility and simplicity of the SA device, together with the possibility of scaling the pulse energy, make it highly attractive in ultrafast photonics.

All-fiber mid-infrared source tunable from 6 to 9 μm based on difference frequency generation in OP-GaP crystal

We report the first fully fiberized difference frequency generation (DFG) source, delivering a broadly tunable idler in the 6 to 9 μm spectral range, using an orientation-patterned gallium phosphide (OP-GaP) crystals with different quasi-phase matching periods (QPM). The mid-infrared radiation (MIR) is obtained via mixing of the output of a graphene-based Er-doped fiber laser at 1.55 μm with coherent frequency-shifted solitons at 1.9 μm generated in a highly nonlinear fiber using the same seed. The presented setup is the first truly all-fiber, all-polarization maintaining, alignment-free DFG source reported so far. Its application to laser spectroscopy was demonstrated by the absorption spectrum measurement of ν4 band of methane in 7.5 - 8.3 µm spectral range. The system simplicity and compactness paves the way for applications in field-deployable optical frequency comb spectroscopy systems for gas sensing.

All-in-fiber amplification and compression of coherent frequency-shifted solitons tunable in the 1800–2000 nm range

We report an all-fiber, all-polarization maintaining (PM) source of widely tunable (1800–2000 nm) ultrashort pulses based on the amplification of coherent self-frequency-shifted solitons generated in a highly nonlinear fiber pumped with an Er-doped fiber laser. The system delivers sub-100 fs pulses with energies up to 8.6 nJ and is built entirely from PM optical fibers, without any free-space optics. The all-fiber alignment-free design significantly increases the suitability of such a source for field deployments.

Comparison on different repetition rate locking methods in Er-doped fiber laser

We demonstrate a systematic comparative research on the all-optical, mechanical and opto-mechanical repetition rate control methods in an Er-doped fiber laser. A piece of Yb-doped fiber, a piezoelectric transducer and an electronic polarization controller are simultaneously added in the laser cavity as different cavity length modulators. By measuring the cavity length tuning ranges, the output power fluctuations, the temporal and frequency repetition rate stability, we show that all-optical method introduces the minimal disturbances under current experimental condition.