Amplitude Of Pulse Train Research Articles

Mode locking in a tapered two-section quantum dot laser: design and experiment.

In this Letter, the pulse generation and pulse train stability of a tapered two-section InAs/InGaAs quantum dot laser emitting at 1250nm are numerically predicted and experimentally verified. Simulations based on a multi-section delayed differential equation model are used to properly design a laser source able to generate stable mode-locked pulses at a 15GHz repetition rate with picosecond width and output power larger than 1W, and to identify the device stability regions depending on the bias conditions. Possible instabilities are associated with the existence of a leading or trailing edge net gain window outside the optical pulse. Experimentally, we confirm the existence of different stability regions where instabilities manifest in broadband or multi-periodic pulse train amplitude modulations. Our results confirm the correctness to the design and may be helpful in achieving high-power pulses while avoiding detrimental pulse train instabilities, both being important for time-critical applications.

Design of High Voltage and High Frequency Pulse Generator Using DC Choke

Pulsed Electric Field (PEF) processing has demonstrated a high potential for various applications ranging from extraction of valuable components from different biological objects to water treatment. Therefore, high voltage and high frequency pulse generator design is essential in order to fulfill the requirement of a PEF processing system. A high voltage and high frequency pulse generator using DC choke is proposed in this works as solution to increase the pulse train amplitude. The DC choke was verified using function generator to identify its operating frequency and voltage. Results showed that the operating frequency of the DC choke was between 24 kHz to 35 kHz and that it was able to retain the pulse shape of the input pulse train. These results show the ability of the DC choke as a potential solution to increase the pulse amplitude of a pulse train while retaining its shape and duty cycle by cascading it with other power topologies to produce high voltage and high frequency pulse generator for various applications.

Time and frequency observation of pulse amplitude equalization of harmonic mode‐locked fiber laser

AbstractIn this article, we achieve the output observation in time and frequency domain of a rational harmonic mode‐locked fiber laser (RHMLFL). The pulse amplitude of pulse train is equalized by operating at nonlinear modulation transfer function region of active modulator in RHMLFL. Without adding any other additional predistortion components, amplitude equalized short pulses up to the fourth order rational harmonic mode‐locking are successfully demonstrated for 7.5, 10, and 15 GHz. One can extend such a method for various mode‐locked lasers even with much higher repetition rates. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 957–961, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23256

Eighth-order rational harmonic mode-locked fiber laser with amplitude-equalized output operating at 80?Gbits?s

We report the generation of an 80 Gbit/s pulse train by an eighth-order rational harmonic mode-locking technique. Equalized pulse-train amplitude is achieved by proper adjustment of the dc bias point and the 10 GHz modulation strength applied to the cavity-loss modulator. A numerical model is developed to simulate the properties of the generated 80 Gbit/s pulse train. The simulated results are well supported by the experimental measurements.

Generation of a superstable Lorentzian pulse train with a high repetition frequency based on a Fabry–Perot resonator integrated with an electro-optic phase modulator

A simple technique for converting a continuous-wave laser beam into a stable Lorentzian pulse train with a high repetition frequency is demonstrated experimentally. We generated transform-limited pulses of up to 40 GHz, which were composed of higher-order sidebands produced by a Fabry-Perot resonator integrated with an electro-optic phase modulator (EOM). The rf power supplied to the EOM determines the pulse width in the pulse train. This approach enables the pulse width to be continuously tuned from 2.1 to 7.0 ps at the same repetition frequency without any wavelength shift. Furthermore, we experimentally evaluated the stability of the pulse train's amplitude and obtained stable bit-error-free operation at 9.95 GHz.

Pulse shortening and spectral broadening by periodic pulse-train amplitude modulation in a self-mode-locked Ti:sapphire laser

Pulse shortening from 22 to 18 fs and spectral-broadening from 41 to 108 nm were observed in a self-mode-locked Ti:sapphire laser when the pulse train showed amplitude modulation with a period ranging from 150 to 400 ns. The mechanism of pulse-train amplitude modulation is attributed to the high-order transverse modes in the laser cavity.

Slow amplitude modulation in the pulse train of a self-mode-locked Ti:sapphire laser

Periodic pulse-train amplitude modulations have been observed in a Kerr-lens self-mode-locked Ti:sapphire laser when the size of an intracavity slit is reduced below its optimal value for stable mode locking. These transient processes are dominated by 100-500 kHz periodic pulse-energy modulations and are inherent to the Kerr-lens mode-locking mechanism based on the intensity dependent transverse-beam profile of the laser and the long gain relaxation lifetime (3.2 ps) of the Ti:sapphire rod. We observe that when the slit width is decreased from 2 mm to 1.4 mm the modulation period increases from 2 ps to 10 mu s and amplitude modulation deepens to almost 100%. An explanation similar to repetitive self-Q-switching and undamped relaxation oscillation is presented, which is consistent with the experimental results. A large low-frequency timing jitter on the order of submicroseconds, associated with the periodic pulse-train modulations, is also observed. The timing jitter is analyzed by incorporating the pulse energy modulation into the phase variation through the Kerr effect and consistent results are obtained. We have determined the cavity parameters to control these detrimental processes for stable mode-locked output. The observation of the amplitude modulation further confirms the Kerr-lens self-focusing model of self-mode locking in Ti:sapphire lasers. >

A compact subnanosecond high power Nd:YAG laser system

In this paper, a high power Nd:YAG laser system is described, which consists of an actively-passively mode-locked Nd:YAG laser oscillator with variable subnanosecond pulsewidths (200 ps to 1 ns), a Pockels-cell shutter and a coaxial four-pass Nd:YAG amplifier. With the oscillator operating in the colliding pulse regime, and a BDN dye film as the saturable absorber, and an acousto-optic modulator as the active modelocker, we have achieved a shot-to-shot stability of the pulse-train amplitude < ±4%. For a 0.1 mJ, 200 ps laser pulse, we obtained four-pass amplification of 7 × 102 with a pump energy of 106 J.

Shuttle pulse measurement of the reflectance of mirrors deposited on fiber ends

The effective reflectance of multilayer high reflectance mirrors applied to fiber ends is determined by a shuttle pulse method. Light from a pulsed laser diode at 1.53-μm wavelength is injected into a fiber with mirrors at both ends, and the emergent pulse train amplitude decrement is used to obtain the reflectance.