Harmonic Mode-locked Fiber Laser Research Articles

2.5 GHz harmonic mode locking from a femtosecond Yb-doped fiber laser with high fundamental repetition rate.

We experimentally demonstrated a high repetition rate harmonic mode-locked fiber laser with a high signal-to-noise ratio (SNR) and super mode suppression ratio. A novel approach using a laser with a high fundamental repetition rate and low harmonic order was presented. 2.5 GHz harmonic mode-locking from an Yb-doped fiber laser was realized with a short cavity length corresponding to a 167 MHz fundamental repetition rate. The laser operated at anomalous net dispersion regime and generated soliton-like pulses at 1050 nm. At the harmonic order of 15th, the laser had a stable output of 773 fs at 2.5 GHz with the average power of 48 mW under a subwatt pump power of 406 mW, and the time jitter was 2 ps. A high RF SNR over 70 dB was measured. A super mode suppression ratio was confirmed larger than 60 dB. This is, to the best of our knowledge, the highest SNR and super mode suppression ratio achieved in harmonic mode-locked fiber lasers with an over 2 GHz repetition rate.

Experimental demonstration of harmonic mode-locking in Sb2Se3-based thulium-doped fiber laser

Studies have shown that Sb2Se3 had the potential to be used as an optical switch or a mode-locker. However, the actual performance of its optical switch capability in fiber lasers has not been proved yet. In this paper, we experimentally demonstrate the nonlinear optical modulation characteristics and optical switch capabilities of Sb2Se3 with a harmonic mode-locked thulium-doped fiber laser (TDFL). The nonlinear modulation depth and saturation power of Sb2Se3-based SA at 1930 nm are 9.3% and 4.08 kW, respectively. The fundamentally mode-locked pulses operate at the central wavelength of 1961.35 nm have the 3-dB bandwidth of 4.57 nm, repetition rate of 22.36 MHz and pulse width of 890 fs. The 2th to 31th harmonic mode locking (HML) are observed, corresponding to the pulse repetition rates ranging from 44.7 to 693 MHz. To the best of our knowledge, this is the highest operating frequency that has ever been demonstrated in a Sb2Se3-based fiber laser. The experimental results indicate that Sb2Se3 could be a promising candidate for generating ultrashort pulses with high repetition rates.

Nonlinearity managed passively harmonic mode-locked Er-doped fiber laser based on carbon nanotube film.

We examine the implication of intracavity nonlinearity for harmonic mode locking (HML) by exploiting highly nonlinear fiber in a carbon nanotube film mode-locked Er-doped fiber laser. It is found that the reasonably large nonlinearity is of benefit to increase the extent of harmonic order while the excessive nonlinearity leads to some peculiar multi-pulse patterns such as noise-like pulse and soliton rain. Via appropriate nonlinearity management, nearly 4 GHz repetition rate pulses at the 91st harmonic with 936 fs pulse duration are delivered under the pump power of 280 mW. The pulse stability is evidenced by the super-mode suppression ratio of 35.6 dB. To the best of our knowledge, it is the highest repetition rate yet reported for a passively HML fiber laser based on a film-type physical saturable absorber. Furthermore, the laser exhibits steep pumping efficiency slope of ${\gt}{19}\;{\rm MHz/mW}$, which is also a record among all of the passively HML fiber lasers.

Stabilization of a Harmonic Mode-Locking by Shifting the Carrier Frequency

Harmonically mode-locked soliton fiber lasers have been intensively investigated in recent years due to their wide range of applications. Drawback of these lasers is relatively large timing jitter which is significantly higher than the timing jitter in lasers operating at fundamental frequency. We report the stabilizing frequency shift effect in harmonic mode-locking ring soliton fiber laser that is studied theoretically and numerically. It is known that a harmonic mode-locking regime in a fiber laser occurs due to interpulse repulsion, which leads to a uniform distribution of pulses in the cavity. We demonstrate that the frequency shift contributes to an increase in the hardness of interpulse interactions and can led to stabilization of the periodic arrangement of pulses. The experiment carried out confirms the theoretical predictions and the results of numerical simulation.

Complex Multi-Pulse Interactions in Harmonic Mode-Locked Fiber Laser Based on Acousto-Optic Effect

Complex Multi-Pulse Interactions in Harmonic Mode-Locked Fiber Laser Based on Acousto-Optic Effect

SnS nanosheets for harmonic pulses generation in near infrared region

Two-dimensional materials have attracted increasing attention because of their excellent mechanical, thermodynamic, magnetic, electrical and optical properties. Here, a new two-dimensional material of tin sulfide (SnS) is experimentally prepared. It is layered like black phosphorus and owns distinct optoelectronic properties, but eliminates the disadvantage of instability. The nonlinear saturable absorption characteristics of the SnS nanosheets is investigated at 1563.3 nm by the double-balanced detection method. The obtained modulation depth and saturation intensity are 5.4% and 66.3 MW/cm2, respectively. A passively harmonic mode-locked erbium-doped fiber laser based on the SnS saturable absorber (SA) has been demonstrated. The results show that mode-locking with fundamental frequency of 5.47 MHz is realized at pump power of 28.38 mW. With the increase of pump power, the laser can operate from fundamental frequency to high-order harmonic mode-locking. The maximum repetition rate of 412.73 MHz has been obtained, which is equivalent to the 76th harmonic mode-locking. This work reveals that SnS nanosheets is a novel and efficient SA with high damage threshold, which will find potential applications in optical communication, photoelectric detection, laser medicine, etc.

Microfiber-assisted gigahertz harmonic mode-locking in ultrafast fiber laser.

Optoacoustic interaction can be strongly enhanced in tiny core fibers, and it holds significant potential for stable harmonic mode-locking at gigahertz (GHz) and higher repetition rate. In this Letter, we propose and demonstrate a microfiber-assisted GHz harmonic mode-locking fiber laser, which is achieved by the enhanced optomechanical coupling between cavity modes in microfiber with the waist length of ∼16cm and the waist diameter of ∼1.56µm. The repetition rates can be stably locked at 2.3828 GHz and predominately locked at 1.7852 GHz, corresponding to the frequencies of radial R01 and torsional-radial TR21 acoustic modes, respectively. Our results provide novel insight into the design of a high-repetition-rate laser source and the application of microfibers in the optomechanical field.

Intracavity birefringence-controlled GHz-tuning range passively harmonic mode-locked fiber laser based on NPR.

We experimentally demonstrate a harmonic-order controllable L-band Er-doped passively mode-locked fiber laser based on nonlinear polarization rotation (NPR). Distinct from all previous reports, we find that the intracavity birefringence is able to control the harmonic order of a passively mode-locked fiber laser. Experimentally, under a constant pump power of 704 mW, the harmonic order can be tuned from 113th to 39th monotonically by adjusting the polarization controller orientation only. The corresponding repetition rate changes from 2.21 to 0.77 GHz simultaneously. Remarkably, the super-mode suppression ratio of each harmonic order we observed is higher than 29 dB with a maximum of 36.5 dB. Simulated transmission spectra of NPR prove that the changed transmission plays an important role in controlling the harmonic order.

Highly stable MXene (V2CTx)-based harmonic pulse generation

Abstract MXene as a novel two-dimensional (2D) material exhibits a lot of advantages in nonlinear optics. However, the common MXene, Ti3C2Tx and Ti2CTx nanosheets, easily suffer from degradation under ambient conditions, greatly limiting their practical applications. Here, we demonstrated one of MXene compounds, V2CTx, which has a strong modulation depth (nearly 50%), can serve as an excellent saturable absorber (SA) in passively mode-locked (PML) fiber lasers. More importantly, 206th harmonic order has been successfully generated in Er-doped mode-locked fiber laser, exhibiting maximum repetition rate of 1.01 GHz and pulse duration of 940 fs, which to the best of our knowledge, is the highest harmonic mode-locked fiber laser from the MXene SA so far. In addition, the high harmonic order mode-locked operation can maintain at least 24 h without any noticeable change, suggesting MXene V2CTx nanosheets have excellent stability in this mode-locked fiber laser. It is anticipated that the present work can pave the way to new design for MXene-based heterostructures for high-performance harmonic mode-locked lasers.

Layered iron pyrite for ultrafast photonics application

Abstract Two-dimensional (2D) transition metal dichalcogenide materials have attracted much attention in recent years due to their excellent electro-optical properties. FeS2, the ideal composition of iron pyrite, is a 2D transition metal dichalcogenide which has been potentially used in the electronic, optical, and chemical fields. On the other hand, the narrow band gap of FeS2 (≈0.96 eV) makes it very suitable and promising for the ultrafast application in near-infrared regimes. However, the potential application of FeS2 in laser technology has not been explored till now. Ultrashort pulse lasers have great applications in industry and science because of its stability, ease of operation, and portability. Passively mode-locked fiber lasers using 2D materials (such as MoS2, CuS2, and WS2) as saturable absorber are intensively investigated. Here, layered FeS2 has been characterized systematically. It is successfully applied in ultrafast photonics and plays a key component in the passively mode-locked laser for the first time. The single pulse can be obtained with 1.7-ps pulse duration, 1.89-nm spectral width, and fundamental repetition of 6.4 MHz at 1563 nm central wavelength. Through controlling the pump power, the evolution of the pulse train can be observed, which can be transformed from single pulse to bound states. Also, the harmonic mode-locked fiber laser is observed with the pump power high enough.

Sub-nanosecond multiple-wavelength harmonic mode-locked Tm-Ho co-doped fiber laser

We demonstrate an all-fiber sub-nanosecond passively mode-locked Tm-Ho co-doped fiber laser. With 1.1-km single-mode fiber (SMF) inserted into the cavity, the laser system can generate 183.4-kHz and 720-ps pulses based on a GaAs saturable absorber (SA). The output spectrum is presented with three wavelengths, which are at 1858.5, 1861.3, and 1864.2 nm, respectively. In addition, with the adjustment of the polarization controller and pump power, the multiple-pulse operation, such as the harmonic mode-locking operation, can also be observed. Higher order of harmonic mode locking is promising but limited by the damage threshold of the SA.

2.4 GHz L-Band Passively Harmonic Mode Locked Er-Doped Fiber Laser Based on Carbon Nanotubes Film

We experimentally demonstrate a passively harmonic mode locked (PHML) Er-doped fiber laser with pump power efficiency up to 17 MHz/mW operating at L-band based on single walled carbon nanotubes polyvinyl alcohol (SWCNTs-PVA) film. Under 233 mW pump power, the stable pulse train at 1594.97 nm with 40.5 dB side mode suppression ratio (SMSR) and 742 fs pulse duration is obtained at a repetition rate of 1.923 GHz, corresponding to 170th harmonic of the fundamental frequency. Under optimized intracavity conditions, the pulses frequency is able to scale up to 2.415 GHz with a high level of 40 dB SMSR, which to the best of our knowledge, is the highest value yet reported from a L-band PHML fiber laser incorporating SWCNTs as saturable absorber (SA). Such high repetition rate and stable fiber laser operating at L band may be desirable for various applications.

L-Band GHz Femtosecond Passively Harmonic Mode-Locked Er-Doped Fiber Laser Based on Nonlinear Polarization Rotation

Via using an L -band optimized in-fiber polarizing grating device, a GHz L -band femtosecond passively harmonic mode-locked Er-doped fiber laser based on nonlinear polarization rotation is first demonstrated. In total, 4.22 GHz pulses with the duration of 810 fs and super-mode suppression ratio (SMSR) of 32 dB are obtained under the pump power of 712 mW corresponding to 215th harmonic order. The central wavelength of 4.22 GHz pulses is 1581.7 nm with 10.1 nm 3 dB bandwidth. Furthermore, under this fixed pump power, higher harmonic orders can also be attained by rotating the polarization controllers properly. The highest repetition rate we obtained is 7.41 GHz with the SMSR of 20.7 dB.

High-order harmonic mode-locked Yb-doped fiber laser based on a SnSe2 saturable absorber

In this paper, tin diselenide (SnSe2) was successfully prepared with liquid phase exfoliation method and embedded into polyvinyl alcohol (PVA) as a saturable absorber (SA) for obtaining harmonic mode-locked Yb-doped fiber laser generations. Based on the fundamental frequency of 333 kHz, four kinds of high-order harmonic mode-locking (HML) with frequencies of 400, 460, 520 and 550 MHz were achieved, corresponding to 1200th, 1380th, 1560th and 1650th order harmonics, with maximum signal to noise ratios (SNRs: 40.55, 37.72, 36.42 and 34.18 dB) and maximum 3 dB spectrum widths (0.2043, 0.3448, 0.216 and 0.3033 nm) as well as minimum pulse widths (759.9, 567.7, 717.3 and 561.4 ps), respectively. This was the first demonstration focusing on the application of SnSe2 in high-order harmonic mode-locked Yb-doped fiber lasers and our results fully proved that SnSe2 had excellent performance in designing high frequency ultra-fast fiber lasers.

Passive harmonic mode-locked ytterbium-doped fiber laser with chirped pulse amplification

A passive harmonic mode-locked ytterbium-doped fiber laser with all-normal dispersion has been demonstrated. The mode-locking mechanism of the laser is based on the interaction between semiconductor saturable absorber mirror and nonlinear polarization rotation. The repetition rate of the laser is adjustable from 7.91 MHz to 31.65 MHz. Via the chirped pulse amplification, the 1 ps mode-locked pulse at the fundamental repetition rate of 7.91 MHz is compressed to 720 fs with single pulse energy of 12.6 nJ.

Bound states of solitons in a harmonic graphene-mode-locked fiber laser

We report bound states of solitons from a harmonic mode-locked fiber laser based on a solution-processed graphene saturable absorber. Stable soliton pairs, 26.2 ps apart, are generated with 720 fs duration. By simply increasing the pump power, the laser can also generate harmonic mode-locking with harmonics up to the 26th order (409.6 MHz repetition rate). This is a simple, low-cost, all-fiber, versatile multifunction ultrafast laser that could be used for many applications.

3 GHz passively harmonic mode-locked Er-doped fiber laser by evanescent field-based nano-sheets topological insulator.

In this paper, we report on the experimental observation of harmonic mode locking (HML) fiber laser based on evanescent field of tapered fiber using topological insulator (TI) Bi2Te3 saturable absorber (SA). The optical deposition method was adopted to fabricate the tapered fiber-based TISA. By significant nonlinear optical property of the tapered fiber TISA and high nonlinear fiber (HNLF), the fiber laser could operate at the pulse repetition of 3.125 GHz under 976 nm pump power of 148 mW, the pulse width of 1.754 ps, and the output power of 6.4 mW. Our results demonstrate that the tapered fiber TI device and HNLF can act as both high nonlinear optical component and SA in fiber lasers, and could also have better performance to achieve ultrashort pulses with ultrahigh repetition.

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.

Passively harmonic mode-locked erbium-doped fiber laser at a 580 MHz repetition rate based on carbon nanotubes film

We propose and demonstrate a passively harmonic mode-locked erbium-doped fiber laser (EDFL) using carbon nanotubes polyvinyl alcohol (CNTs-PVA) film. The laser allows generation of the pulses with a repetition rate of 580 MHz, which corresponds to the 22nd harmonics of a 26.3 MHz fundamental repetition rate under 323 mW pump power. A particularly noteworthy feature of the pulses is the super-mode suppression ratio (SMSR), which is over 40 dB, indicating a stable operation.

Passively harmonic mode-locked erbium-doped fiber laser at a 580 MHz repetition rate based on carbon nanotubes film

Passively harmonic mode-locked erbium-doped fiber laser at a 580 MHz repetition rate based on carbon nanotubes film