Mode-locked Ytterbium-doped Fiber Research Articles

Generation of high fidelity 62-fs, 7-nJ pulses at 1035 nm from a net normal-dispersion Yb-fiber laser with anomalous dispersion higher-order-mode fiber

Fiber oscillators operating in the normal dispersion regime allow generating high energy output pulses. The best stability of such oscillators is observed when the intracavity dispersion is close to zero. Intracavity dispersion compensation in such oscillators can be achieved using a higher-order mode fiber, which substantially reduces the higher order dispersion compared to all-normal dispersion oscillators or oscillators using intracavity gratings for dispersion compensation. Using this approach, we are able to obtain relatively high energy pulses, with high fidelity. Our modeling based on an analytic approach for oscillators operating in the normal dispersion regime predicts that at intermediate pulse energies an almost flat chirp can be obtained at the oscillator output enabling good pulse compression with a grating compressor close to Fourier limited duration. Here, we present a mode-locked ytterbium-doped fiber oscillator with a higher-order mode fiber operating in the net normal-dispersion regime, delivering 7.2 nJ pulses that can be dechirped down to 62 fs using a simple grating compressor.

Efficient mid-infrared single-photon frequency upconversion detection with ultra-low background counts

We demonstrate an efficient mid-infrared single-photon detection system with ultra-low background counts based on the frequency upconversion detection technique. The signal photons of 3.39 μm came from a He–Ne laser and the pump beam was provided by a mode-locked ytterbium-doped fiber laser. Taking into account the pulsed pumping and continuous-wave signaling scheme, the peak conversion efficiency of 64% was achieved at an average pump power of 28.3 mW. The corresponding detection efficiency was inferred to be 6.1% with ultra-low background counts of 400 s−1.

Generation of sub-7-cycle optical pulses from a mode-locked ytterbium-doped single-mode fiber oscillator pumped by polarization-combined 915 nm laser diodes

We report on a passively mode-locked ytterbium-doped fiber oscillator pumped by polarization-combined diodes emitting at a wavelength of 915 nm instead of 976 nm. Stable mode-locked operation based on nonlinear polarization evolution generated a broad spectrum of 140 nm, spanning from 950 to 1090 nm. The output power was 16.3 mW at a repetition rate of 93.1 MHz. External compression using a pair of transmission gratings resulted in pulse durations as short as 21.6 fs, which is equivalent to 6.6 cycle optical pulses at a wavelength of around 1000 nm.

Tunable all-fiber dissipative-soliton laser with a multimode interference filter

We report on a tunable all-fiber dissipative-soliton laser with a multimode interference filter that consists of a multimode fiber spliced between two single-mode fibers. By carefully selecting the fiber parameters, a filter with a central wavelength at 1032 nm and a bandwidth of 7.6 nm is constructed and used for spectral filtering in an all-normal-dispersion mode-locked ytterbium-doped fiber laser based on nonlinear polarization evolution. The laser delivers 31 mW of average output power with positively chirped 7 ps pulses. The repetition rate of the pulses is 15.3 MHz, and pulse energy is 2.1 nJ. Tunable dissipative-soliton over 12 nm is achieved by applying tension to the single-mode-multimode-single-mode filter.

Fourier-Limited 19-ps Yb-Fiber Seeder Stabilized by Spectral Filtering and Tunable Between 1015 and 1085 nm

We report a passively mode-locked picosecond ytterbium-doped fiber laser operating in the normal dispersion regime, tunable over 70 nm around 1.05 μm. Mode-locking operation is achieved through a free-space coupled semiconductor saturable absorber. An external grating in Littrow configuration is used for both tuning and mode-locked stabilization through spectral filtering. Pulse duration of 19 ps with pulse repetition rates below 20 MHz is obtained with a maximum average output power of 1.5 mW.

Dissipative soliton in actively mode-locked fiber laser

A dissipative soliton in an all-normal-dispersion actively mode-locked ytterbium-doped fiber laser is reported for the first time. Pulses with 10-ps duration and edge-to-edge bandwidth of 9 nm are generated, and then extra-cavity compressed down to 560 fs due to the large chirp. Widely wavelength tuning between 1031 and 1080 nm is achieved by adjusting the driving frequency only. Our simulation shows that the proposed laser operates in the dissipative soliton shaping regime.

Stretched-pulse mode-locking synchronously triggered by a femtosecond master laser at sub-megahertz repetition rate

A stretched-pulse mode-locked ytterbium-doped fiber laser was passively synchronized to a femtosecond Ti:sapphire laser at a low repetition rate of 240 kHz through large cross absorption modulation along additional 1-m-long erbium-doped fiber. The synchronous fiber laser with an ultra-long fiber cavity could produce not only nanosecond flat-top pulses with tunable pulse duration but also Gaussian-shape stretched pulses with its minimum pulse duration of ∼450 ps as confirmed by cross-correlation measurement. When operating in the stretched pulse regime, the sub-nanosecond fiber laser could be synchronously triggered by the master injection with the cavity-length mismatch tolerance up to ∼7.8 cm and timing jitter less than 400 fs, confirming that the stretched-pulse mode-locking of the ultra-long slave fiber laser could be robustly controlled by cross absorption modulation effects in the erbium-doped fiber with appropriate femtosecond master injection.

Low-repetition-rate, high-energy, twin-pulse, passively mode locked Y_b ^3+-doped fiber laser

We report an all-normal-dispersion, low-repetition-rate, high-energy, twin-pulse, passively mode locked ytterbium-doped fiber laser. The mode-locking mechanism of the laser is based on nonlinear polarization evolution and strong pulse shaping with a cascade long-period fiber grating bandpass filtering in a highly chirped pulse. The laser generates a highly stable twin-pulse group with 248 ps and 296 ps duration simultaneously and maximum pulse energy of 26.8 nJ-each pulse at a 2.5445 MHz repetition rate. Energy quantization is observed, which demonstrates the nonparabolic nature of these pulses. The laser can also work in third-harmonic mode locking with 17.8 nJ energy (at a repetition rate of 7.65 MHz and pulse width of 780 ps).

High energy giant chirped passively mode-locked Yb3+-doped fiber laser with nanoseconds to picoseconds pulses

We report an all normal dispersion low repetition rate high energy passive mode-locked ytterbium-doped fiber laser with output pulses duration ranging from nanoseconds to picoseconds. The mode-locking mechanism of the laser is based on nonlinear polarization evolution and strong pulses shaping with a cascade long-period fiber grating bandpass filtering in highly chirped pulses. The laser generates highly stable pulses duration from 2.62 ns to 315 ps with a maximum pulse energy of 49.5 nJ and 2.5435 MHz repetition rate.

Passive Harmonically Mode-Locked Yb$^{3 +}$-Doped Fiber Laser Free From Anomalous Dispersion

We report on an all normal dispersion harmonically mode-locked ytterbium-doped femtosecond fiber laser. The mode-locking mechanism of the laser is based on nonlinear polarization evolution with strong pulse shaping. Bandpass filtering is achieved with a cascaded long-period fiber grating, forming highly chirped pulses. The laser generates stable 2.5-ps duration pulses at a repetition rate of 125.39 MHz that could be dechirped externally to 310 fs with a maximum pulse energy of 0.36 nJ.

Fiber optical parametric oscillator for sub-50 fs pulse generation: optimization of fiber length

We demonstrate generation of 48fs pulses with linear chirp using a short (27mm) fiber optical parametric oscillator (FOPO), which is synchronously pumped by a mode-locked ytterbium-doped fiber laser. We also study the pulse quality for both the short- and long-wavelength operation where the fiber length inside of the oscillator varies from 17 to 61mm. The optimal pulse duration is observed only in the short-wavelength operation. Furthermore, we model the FOPO system as a single-pass parametric amplifier including dispersive pulse broadening and walk-off between the pump and output. The optimal condition arises from the minimization of the walk-off and dispersion. When walk-off is large, the parametric amplification process is most efficient over some reduced effective fiber length, leading to an upper limit in the amount of the observed pulse broadening.

All-fiber mode-locked nanosecond laser employing intracavity chirped fiber gratings

We demonstrate that nanosecond pulses are generated directly from an all-fiber mode-locked ytterbium-doped fiber laser. A pair of Chirped Fiber Gratings (CFGs) with different sign of dispersion is employed for intracavity dispersion management. Self-starting stabilized mode-locking operation is achieved by nonlinear polarization evolution (NPE). The 1.27 ns pulses are obtained after one CFG with large positive dispersion. The pulse energy is up to 15 nJ at a repetition rate of 3.48 MHz.

Pulse dynamics in a passively mode-locked chirped-pulse fiber laser

We report experimental and numerical results on the new pulse dynamics in a passively mode-locked ytterbium-doped fiber laser operating in the chirped-pulse regime. Due to the negligible nonlinearity of added highly-positive GVD segment in the purely-normal-dispersion regime, highly-positive chirped pulses can be formed through weak intra-cavity temporal and spectral breathing. Numerical simulations reveal intra-cavity pulse evolution with local temporal stretching phenomena and pulse shaping properties.

Sub-100 fs pulses from a low repetition rate Yb-doped fiber laser

We report on a passively mode-locked ytterbium-doped fiber laser with a repetition rate of 1.8 MHz. The laser was hybridly mode-locked via nonlinear polarization evolution and a semiconductor saturable absorber mirror. It generated chirped 3.8 ps long pulses with a pulse energy of 1.0 nJ which could be dechirped to a pulse duration of 93 fs.

Generation of 28-fs pulses from a mode-locked ytterbium fiber oscillator

An ultrashort-pulse, mode-locked ytterbium-doped fiber laser has been developed. The group-delay dispersion was compensated with a grating pair inside the cavity. A broad spectrum from 1000-nm to 1120-nm was obtained without intracavity compensation of third-order dispersion. A 0.7-nJ pulse as short as 28.3 fs was obtained with a repetition rate of 80 MHz. To our knowledge, this is the shortest pulse reported from an Yb fiber laser oscillator.

Dynamics of parabolic pulses in an ultrafast fiber laser

We report experimental and numerical results on the dynamics and propagation of parabolic pulses in a passively mode-locked ytterbium-doped fiber laser. Experimental data and numerical simulations are shown to match. Particular importance is attached to the pulse-shaping process in the different sections of the resonator. The paramount role of the gain fiber and saturable absorber in the laser is explicated.

Experimental and theoretical study of the passively mode-locked ytterbium-doped double-clad fiber laser

We consider a Yb-doped double-clad fiber laser in a unidirectional ring cavity containing a polarizer placed between two half-wave plates. Depending on the orientation of the phase plates, the laser operates in continuous, Q-switch, mode-lock, or unstable self-pulsing regime. An experimental study of the stability of the mode-locking regime is realized versus the orientation of the half-wave plates. A model for the stability of self-mode-locking and cw operation is developed starting from two-coupled nonlinear Schr\odinger equations in a gain medium. The model is reduced to a master equation in which the coefficients are explicitly dependent on the orientation angles of the phase plates. Analytical solutions are given together with their stability versus the angles.