Colliding-pulse passive harmonic mode-locking in a femtosecond Yb-doped fiber laser with a semiconductor saturable absorber

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.

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.

Harmonically mode-locked Yb:CALGO laser oscillator

We present a passively mode-locked Yb:CALGO oscillator with harmonic repetition rate operation up to the third order. It is operated in the solitary regime with a fundamental roundtrip rate of 94 MHz and pulse durations between 200 fs and 600 fs. Harmonic operation was observed being stable for several days. The harmonic mode-locking regions are analyzed depending on intra-cavity dispersion. The transient pulsing dynamics converging to the stable harmonic modes is tracked and a theoretical model describing the pulse moving mechanisms is presented.

Passive harmonic hybrid mode-locked fiber laser with extremely broad spectrum

We demonstrate a harmonic mode-locking Erbium-doped fiber laser which is cooperatively mode-locked by nonlinear polarization evolution (NPE) and semiconductor saturable absorber mirror (SESAM). Via effective dispersion and nonlinearity optimization, 8th harmonic at a repetition rate of 666.7 MHz is obtained. The output pulses has a full spectrum width at half maximum (FWHM) of 181 nm and duration of 218 fs. The pulses are compressed to 91 fs by external chirp compensation. The average power of the direct output pulse at an available pump power of 1.5 W is 136 mW, which exhibits a single-pulse energy of 0.2 nJ. The cavity super-mode suppression is up to 60 dB and the signal-to-noise ratio of the 8th harmonic is over 75 dB.

Speckle-free femtosecond red-green-blue (RGB) source from a fiber laser driven spectrally efficient two zero dispersion wavelength fiber source

We report a novel ultrafast red-green-blue (RGB) laser source based on second harmonic generation from a two zero dispersion wavelength (TZDW) fiber continuum source. The TZDW fiber source consists of a custom-built Yb:fiber amplifier and a commercially available TZDW photonic crystal fiber (PCF) which enables low noise and efficient frequency conversion from the 1035 nm pump source to two spectrally localized pulses centered at 850 nm and 1260 nm with 39.6% and 33.7% power efficiencies. With angularly multiplexed simultaneous phase matching, we achieve mW average power of red, green and blue pulses at 630 nm, 517 nm and 426 nm from single pass second harmonic generation. With broad RGB bandwidths of 7.4 nm, 3.2 nm and 5.2 nm, the source is inherently speckle-free while maintaining an excellent color rendering capability with higher than 99.7% excitation purity of the RGB color primaries, leading to the coverage of 192% NTSC color gamut (CIE 1976). The reported source features a simple system geometry; its potential in power scaling is discussed with currently available technologies.

Toward higher-order passive harmonic mode-locking of a soliton fiber laser

We report >13 MHz/mW pump power efficiency in increasing the repetition rate of passive harmonic mode-locking by engineering the soliton pulse energy in Er fiber lasers incorporating carbon nanotube saturable absorber. Stable pulses with a ∼5 GHz repetition rate and 40 dB of super-mode suppression are demonstrated with only ∼400 mW pump power in a single-clad fiber laser.

Coexistence of unequal pulses in a normal dispersion fiber laser

We experimentally demonstrate unequal pulses delivered from an erbium-doped fiber (EDF) laser with net-normal dispersion. Two types of pulses with different durations, energies, and spectra coexist in the same ring cavity. The output spectrum exhibits a broadband base that corresponds to the main pulse and a small rectangular lump that corresponds to the additional satellite pulse. With the enhancement of pump power, the intensity of main pulse almost keeps unchanged while the satellite pulse nearly increases linearly. Based on experimental results, it is indicated that two different pulse shaping mechanisms coexist in laser cavity, where the nonlinear polarization rotation (NPR) and spectral filtering (SF) effect contribute to the formation of main pulse and satellite pulse, respectively.

Passive harmonic mode-locking of a soliton Yb fiber laser at repetition rates to 1.5 GHz

We report passive harmonic mode locking of a soliton Yb fiber laser at repetition rates continuously scalable up to 1.5 GHz. The laser generates transform-limited 500 fs pulses, with pulse energies of 30-100 pJ. At the 31st harmonic (1.3 GHz), the cavity supermodes are suppressed by 35 dB, and the pulse-to-pulse timing jitter is 6 ps.