Mode-locked Fiber Laser Oscillator Research Articles

Nonlinear polarization rotation based 635-nm praseodymium doped mode-locked fiber laser

Abstract We demonstrated a mode-locked fiber laser oscillator using nonlinear polarization rotation as a saturable absorption system. The fiber laser generates mode-locked pulses by adjusting four waveplates. A single-clad Pr3+-doped single mode fluoride fiber with a 425-mW threshold pump power serves as the foundation for the ring cavity, which operates in the dissipative soliton resonance regime. The radio frequency signal-to-noise ratio of the pulses at 634.9 nm is 60 dB, maximum output power of 5.5 mW, and repetition rate of 34.5 MHz. These findings provide a foundation for the advancement of photonic applications in the visible spectrum.

High power chirped pulse Yb fiber amplifier seeded by mode-locked fiber laser oscillator with multimode interference based saturable absorber

In this research, we demonstrate a novel femtosecond fiber laser system which comprises of ytterbium (Yb) doped mode-locked fiber laser oscillator using nonlinear multimode interference (NL-MMI) based saturable absorber (SA) seeded into a chirped pulse fiber amplifier. The laser pulses from the oscillator centered at a wavelength of 1033.2 nm with a pulse duration of 2.4 ps. Correspondingly, the pulse energy is 120 pJ at the fundamental repetition rate of 21.35 MHz. By integrating the laser oscillator with the amplification system, an output average power of 11 W with compressed pulse duration of 340 fs and pulse energy of 0.51 μJ is achieved. The pulse possesses high stability with signal-to-noise ratio up to 58 dB. These characteristics evince that the fiber amplifier system seeded with NL-MMI based mode-locked laser oscillator results in a highly stable femtosecond laser.

Energy scaling of an erbium-doped mode-locked fiber laser oscillator

We investigate a promising approach to the energy scaling of mode-locked erbium fiber lasers. It consists in a special cavity design, comprised of a really long polarization maintaining (PM) part and a short non-PM part. Two separate fiber parts ensure the principle of space division for highly chirped dissipative soliton formation and NPE-based self-amplitude modulation effects. As a result, the pulse energy was increased up to 4 nJ with an estimated transform-limited pulse duration of 150 fs. It was also found that further energy scaling is limited by transition to a noise-like pulse generation regime. Numerical simulations revealed that this transition is associated with a contrast of the employed spectral filter and the amplifier noise level, which agrees well with the experiment.

Phase-locked and mode-locked multicore photonic crystal fiber laser with a saturable absorber.

Multicore photonic crystal fiber (MC-PCF) can scale the output power with the number of cores by spatial beam combining if the in-phase mode is selected. We demonstrated simultaneous realization of phase-locked and mode-locked laser using Yb-doped 7-core MC-PCF by a semiconductor saturable absorber placed in the near-field inside a resonator. High energy 333 nJ pulses were obtained directly from a mode-locked fiber laser oscillator at a 42.4 MHz repetition rate with an average power of 14.1 W at 24 W excitation. We observed the direct output pulse width of 52 ps assuming a sech2 profile. However, it might be noise-like pulses because of no variation when we performed pulse compression. Single-pulse operation was achieved by increasing the bandwidth of the intracavity filter. In this case, 137 nJ, 42.4 MHz pulses were generated with a 5.8 W average power and the compressed output pulse width was 8.6 ps.

Enhanced self-phase modulation effect: an effective method of generating high average and peak power femtosecond laser pulses

This work experimentally explores the important application of the enhanced self-phase modulation (SPM) effect for the generation of high average power and high peak power femtosecond laser pulses in an all-fiber mode-locked laser oscillator pumped by a single-mode laser diode. Depending on the utilization of a section of nonlinear spectral broadening fiber with a 4.2 µm mode field diameter (MFD) and the optimization of the polarization-maintaining (PM) fiber length in a polarization-based all-fiber Lyot filter, the oscillator delivers 350 mW of average power at a 46.2 MHz repetition rate, resulting in 7.5 nJ pulse energy. The laser produces SPM-broadened spectrum and the spectrum features symmetrical multi-peak distribution. The resulting compressed pulse duration and average power are 107 fs and 271 mW, respectively, which corresponds to 54.8 kW of peak power. Additionally, comparative experiments have also been performed by replacing the nonlinear spectral broadening fiber with equal-length standard fiber with 6.2 µm MFD and shortening the length of the 45° aligned PM fiber of the all-fiber polarization-based Lyot filter, respectively. The presented experimental scheme demonstrates a notable improvement in terms of average and peak power compared to conventional experimental methods. Simultaneously, the experimental scheme also shows that the enhanced SPM effect in a mode-locked fiber laser oscillator has important application value for minimizing pulse duration and lowering the mode-locking threshold.

Flexible double-cladding ytterbium fibre based 9 W mode-locked laser with 102 fs compressible pulse duration

We report on a high power mode-locked femtosecond fiber laser oscillator with flexible double-cladding (DC) ytterbium-doped fiber (Yb-fiber) as gain medium and a fused fiber combiner as a pump coupling scheme, based on the nonlinear polarization evolution effect in a ring cavity configuration with a dual-stage birefringent plate as the spectral filter. Laser pulses with a pulse energy as high as 122 nJ and compressible pulse duration as short as 102 fs at 1041 nm center wavelength could been obtained. The experimentally recorded power fluctuations were better than 0.42% RMS and 0.40% RMS in 3 h under 5 W and 9 W output power, respectively. The measured beam quality factors M2 were 1.3 in both the horizontal and perpendicular directions. To the best of our knowledge, this is the highest output power generated from a flexible DC Yb-fiber-based ultrashort pulse mode-locking fiber laser oscillator pumped with a fusion spliced combiner.

Fiber-type difference frequency generation infrared optical frequency comb based on the femtosecond pulses generated by a mode-locked fiber laser

Optical frequency comb (OFC) is a new type of high-quality laser source. The visible and near-infrared OFCs have become mature, and it has been widely used in optical frequency metrology, time/frequency transfer, precision laser spectroscopy and other fields. Since the mid and far-infrared spectral regions contain a large number of baseband absorption lines for molecules and the absorption intensities are several orders of magnitude higher than those in the visible and near-infrared spectral region, one has made great efforts to develop the mid and far-infrared OFCs in recent years. Although a variety of approaches to achieving infrared OFCs directly have been proposed, the method of difference frequency generation (DFG) infrared OFC based on the optical rectification technique is still more efficient. DFG infrared OFCs with widely tuning ability have been demonstrated based on fiber lasers so far. However, how to obtain the broadband spectrum for a DFG infrared OFC with widely tuning ability still needs to be solved. In this paper we report a fiber-type DFG infrared OFC by using the femtosecond pulses from a mode-locked erbium-doped fiber laser as the fundamental light. Based on the self-developed mode-locked fiber laser oscillator with repetition rate locked, the two-color fundamental pulse trains with the central wavelengths of 1.5 and 2.0 m are respectively achieved after the chirped pulse fiber amplification and all-fiber supercontinuum (SC) generation techniques have been utilized. With a time-domain synchronous detection system based on the intensity autocorrelation principle, the accurate synchronization with the fundamental two-color pulses is obtained by optimizing the OFS compensated fiber length and adjusting a tunable optical delay line. Finally, by using the optical rectification technique, a fiber-type DFG infrared OFC is successfully generated with the help of a suitable designed GaSe nonlinear crystal. Our experimental results also show that the spectral location of the DFG infrared OFC can be tuned by controlling the spectral shape of the SC combined with the adjustment of the phase-matching for the nonlinear crystal. The measured tuning range of the DFG infrared OFC is from 6 to 10 m, and the maximum spectral width is 1.3 m. This fiber-type DFG infrared OFC may play an important role in the molecular spectroscopy, the atmospheric environmental monitoring, and other fields.

Carbon Nanotube Mode-Locked Thulium Fiber Laser With 200 nm Tuning Range

We demonstrated a mode-locked thulium/holmium (Tm/Ho) fiber laser continuously tunable across 200 nm (from 1860 nm to 2060 nm), which to the best of our knowledge represents the widest tuning range ever achieved for a passively mode-locked fiber laser oscillator. The combined use of a broadband carbon nanotube (CNT) saturable absorber and a diffraction grating mirror ensures ultra-broad tuning range, superb stability and repeatability, and makes the demonstrated laser a highly practical source for spectroscopy, imaging and optical communications. The laser emits <5 ps pulses with an optical spectral bandwidth of ∼3 nm across the full tuning range. Our results indicate that carbon nanotubes can be an excellent saturable absorber for achieving gain-bandwidth-limited tunable operation for 2 μm thulium fiber lasers.

All-normal dispersion passively mode-locked Yb-doped fiber laser with Bi 2 Te 3 absorber

An all-normal dispersion passively mode-locked Yb-doped fiber laser with a Bi2Te3 absorber is presented. The modulation depth of this kind of saturable absorber was measured to be 8.4%. By incorporating a Bi2Te3/PVA film into a Yb-doped fiber laser oscillator, a mode-locked fiber laser oscillator was achieved. The repetition rate and the central wavelength are 25.6 MHz and 1052.7 nm, respectively. The 3-dB spectral width is 0.45 nm and the pulse duration is 417 ps. The results indicate that topological insulator Bi2Te3 possesses the potential for ultrafast fiber laser application.

Sub-50-fs pulse generation from thulium-doped ZBLAN fiber laser oscillator

An ultrafast, passively mode-locked fiber laser oscillator has been realized using thulium-doped ZBLAN fibers. Very low dispersion of ZBLAN glass fibers enabled generation of pulses with broad spectra extending from 1730 nm to 2050 nm. Pulses are obtained with the average power of 13 mW at the repetition rate of 67.5 MHz when the pump power is 140 mW. The output pulses are compressed with a pair of SF10 prisms and their durations are measured with SHG FROG, from which we obtained the pulse duration as short as 45 fs.

Mode-Locked Tm–Ho-Codoped Fiber Laser at 2.06 $\mu$m

A mode-locked Tm-Ho-codoped fiber laser is reported, which is the first demonstration of a mode-locked fiber laser oscillator at the wavelength beyond 2 μm . The laser was built with a piece of newly developed Tm-Ho-codoped dc silicate fiber and a Sb-based semiconductor saturable absorber mirror (SESAM). When cladding pumped with a laser diode at 0.8 μm, the fiber laser generates mode-locked solitons at 2.06 μm with a pulse energy of 0.41 nJ and pulse duration of 1.1 ps.

Generation and detection of broadband coherent terahertz radiation using 17-fs ultrashort pulse fiber laser

We describe the generation and detection of broadband terahertz radiation using an all-fiber laser. Optical pulses from a mode-locked fiber laser oscillator are compressed using nonlinear and dispersion effects induced in optical fibers, and 17-fs optical pulses with 170-kW peak power are generated at the wavelength region around 1.5 microm. By injecting these pulses into an organic crystal DAST (4-N, N-dimethylamino-4'-N"-methyl-stilbazolium tosylate), broadband terahertz field is radiated at 0.1-25 THz. The frequency region exceeding 20 THz is achieved with a fiber laser for the first time.