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ABSTRACT: We realized the repetition rate multiplication in a phase-modulated soliton fiber laser with the rational harmonic mode-locking method. A modified pulse phase-locking method is used to stabilize the fiber laser at 10-GHz repetition rate with the rational harmonic order up to five (limited by the component performance). The laser showed an excellent stabilization performance in a long-term bit-error-rate test
IEEE Photonics Technology Letters 04/2007; · 2.19 Impact Factor
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ABSTRACT: Second-harmonic generation (SHG) of 40-GHz picosecond optical pulses with different pulsewidths, pulse energies, and central wavelengths in a MgO-doped periodically poled lithium niobate (PPLN) waveguide is studied experimentally and theoretically. In the experiments, the picosecond pulses are generated from a 40-GHz mode-locked fiber laser and two tunable filters, with which the lasing wavelength can be tuned from 1530 to 1570 nm, and the pulsewidth can be tuned from 2 to 7 ps. The second-harmonic (SH) pulses are generated when the picosecond pump pulses pass through the MgO-doped PPLN waveguide. Dependences of SHG on pump pulsewidth, average pump power, and pump central wavelength are then investigated systematically. Meanwhile, dynamic behaviors of both pump and SH pulses in propagation are simulated numerically. Based on the temporal and spectral characteristics of SHG, a quantitative and systematic analysis on SHG efficiencies in terms of both pulse energy and spectral peak is presented. The simulation results are in good agreement with the measured data.
Journal of Lightwave Technology 11/2006; 24(10):3698-3708. · 2.78 Impact Factor
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ABSTRACT: The effect of Brillouin slow light on distributed Brillouin fiber sensors (DBFSs) is studied. We demonstrate Brillouin slow light for a 1.2 ns pulse with peak powers (PS) from 3.3 to 56.2 mW on depletion of the pump power (PP) ranging from 1.3 to 83.2 mW in conventional optical fibers (SMF-28). Experiments show that, when pump power depletion is not negligible, for a given PP the Brillouin gain and delay time of a pulse decrease when PS increases in a long (> or =10 km) sensing fiber. The optimum pump beam depletion resulting from strong interaction of the pump and the probe in the fiber provides accurate temperature and strain information at a high spatial resolution. Our study reveals that at low PP the spatial resolution error caused by the pulse delay for a DBFS with centimeter spatial resolution is less than 5% of the pulse length.
Optics Letters 10/2006; 31(18):2698-700. · 3.40 Impact Factor
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ABSTRACT: The wavelength conversion of picosecond optical pulses based on the cascaded second-harmonic generation-difference-frequency generation process in a MgO-doped periodically poled lithium niobate waveguide is studied both experimentally and theoretically. In the experiments, the picosecond pulses are generated from a 40 GHz mode-locked fiber laser and two tunable filters, with which the lasing wavelength can be tuned from 1530 to 1570 nm, and the pulse width can be tuned from 2 to 7 ps. New-frequency pulses, i.e., converted pulses, are generated when the picosecond pulse train and a cw wave interact in the waveguide. The conversion characteristics are systematically investigated when the pulsed and cw waves are alternatively taken as the pump at the quasi-phase-matching wavelength of the device. In particular, the conversion dependences on input pulse width, average power, and pump wavelength are examined quantitatively. Based on the temporal and spectral characteristics of wavelength conversion, a comprehensive analysis on conversion efficiency is presented. The simulation results are in good agreement with the measured data.
Applied Optics 08/2006; 45(21):5391-403. · 1.41 Impact Factor
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ABSTRACT: What we believe to be a new and simple approach was developed for stabilizing a harmonic mode-locked fiber laser at 40 GHz. It uses a computer to tune the modulation frequency in a 100 kHz band near 40 GHz to follow variations in the length of the optical cavity. A second approach was also developed to compare with the new approach and to draw conclusions on its performance. Results for the pulse characteristics, side-mode suppression ratio, and timing jitter show that both approaches provide an efficient way of stabilizing a harmonic FM mode-locked fiber laser.
Applied Optics 07/2006; 45(16):3826-30. · 1.41 Impact Factor
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ABSTRACT: The repetition rate multiplication was observed in a phase-modulated mode-locking fiber laser when the modulation frequency was detuned by a fraction of the fundamental frequency. This phenomenon is quite similar to the rational harmonic mode-locking in amplitude modulated lasers, which almost everybody believed could not exist when applying phase modulation. The harmonics of the amplified driving signal is the reason behind this phenomenon. Because most RF amplifiers cannot avoid generating high-order harmonics of the amplifying signal, the "rational harmonic mode-locking" can be obtained in most phase-modulation fiber lasers when the driving signal is amplified, even in some cases when using linear amplifiers
IEEE Photonics Technology Letters 07/2006; · 2.19 Impact Factor
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ABSTRACT: We demonstrate a method for generating ultrashort pulses from a phase-modulated optical signal by using a dispersion-imbalanced nonlinear loop mirror instead of the traditional linear dispersion medium. The extinction ratio of the pulses is greatly improved at the same time. By controlling the bandwidth of the phase-modulated signal and the dispersion map of the dispersion-imbalanced nonlinear loop mirror, we can control the pulse width from several picoseconds to hundreds of femtoseconds.
Optics Letters 05/2006; 31(8):1032-4. · 3.40 Impact Factor
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ABSTRACT: The influence of Brillouin slow light on distributed Brillouin fiber sensors is studied. Wedemonstrate Brillouin slow light for a 1.2 ns pulse with peak power from 3.3 to 56.2 mW at thedepletion of the pump power from 1.3 mW to 83.2 mW in conventional optical fibers (SMF-28). Ourexperimental results show that when the depletion of the pump power is not negligible (pump andprobe powers are comparable, which is the optimized distributed Brillouin fiber sensor regime), for agiven pump power the Brillouin gain and delay time of a pulse decrease when the pulse peak powerincreases in a long length ($geq$10 km) sensing fiber. The strong depletion of the pump beam resultingfrom the strong interaction between pump and probe in the fiber provides accurate local temperatureand strain information at high spatial resolution. Our study reveals that for a nanosecond pulse at lowpump power, the spatial resolution error caused by pulse delay for a distributed Brillouin fiber sensorwith centimeter spatial resolution is less than 5% of the pulse length, which is within experimentaluncertainty.
Optical Fiber Sensors; 01/2006
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ABSTRACT: We demonstrate a simple scheme to multiply the repetition rate in an actively mode-locking fiber laser by using a phase modulated optical fiber loop mirror (PMOLM). The PMOLM can convert phase modulation to amplitude modulation at double the modulation frequency. In principle, it is easy to double the repetition rate. However, the PMOLM also induces residual chirp which can disable this method in some cases. Numerical simulation shows that the best results can be obtained when the intracavity dispersion is negative and the modulation frequency is an odd harmonic of half of the cavity fundamental frequency. This agrees with the experimental results, in which an 80-GHz 1.74-ps transform limited pulse was obtained. By using rational harmonic modulation which requires detuning the modulation frequency and adjusting the modulation index, the repetition rate can be increased by three or four times.
IEEE Journal of Quantum Electronics 11/2005; · 1.88 Impact Factor
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ABSTRACT: We demonstrated a simple method to realize repetition-rate-doubling in a frequency modulation (FM) mode-locking fiber laser. The mode-locking of the laser is based on converting FM modulation to amplitude modulation by using a phase-modulated optical fiber loop mirror, which is formed by a phase modulator and an additional coupler only. With 40-GHz modulation, we obtained 80-GHz 1.74-ps transform-limited pulse train in the experiments.
IEEE Photonics Technology Letters 03/2005; · 2.19 Impact Factor
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ABSTRACT: A 40-GHz frequency modulation oscillation fiber laser is demonstrated and the continuous-wave (CW) output is used for generating a high repetition rate short pulse train by external cavity chirp compensation. A 1.37-ps transform-limited pulse is obtained from its chirped, 488.1-GHz width CW output.
IEEE Photonics Technology Letters 08/2004; · 2.19 Impact Factor
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ABSTRACT: The intracavity phase-modulated laser can work in two distinct stages: 1) phase mode-locking when the applied modulation frequency is equal to the cavity’s fundamental frequency or one of its harmonics, and 2) the FM laser oscillation at a moderate detuned modulation frequency. In this paper, we experimentally studied the noise buildup process in the transition from FM laser oscillation to phase mode-locking in a phase-modulated laser. We found that the relaxation oscillation frequency varies with the modulation frequency detuning and the relaxation oscillation will occur twice in the transition region. Between these two relaxation oscillations, the supermode noise can be significantly enhanced, which is evidence of excess noise in laser systems. All of these results can be explained by the theory of Floquet modes in a phase-modulated laser cavity.
Phys. Rev. A. 74(3).
