Picosecond Pulse Generation Research Articles

High Repetition Rate Fiber Laser Coupled to a Linear Cavity Generating Picosecond Pulses

An experimental investigation is presented for obtaining picosecond (ps) pulses at a repetition rate of 11 GHz using a fiber laser coupled to an external cavity. Without applying active mode locking and without a nonlinear element in the coupled cavity, pulses of about 15 ps with an average power of 20 mW have been generated using a (cw) diode pump laser. The pulse duration decreases with increasing repetition rate.

Generation of time-aligned picosecond pulses on wavelength-division-multiplexed beams in a nonlinear fiber

A fundamentally different way to generate time-aligned data pulses on wavelength-division-multiplexed (WDM) beams in a single-mode fiber is found. A large-amplitude pulse called a shepherd pulse is launched on one of the copropagating beams (shepherd pulse is defined as a pulse that can affect other copropagating pulses in a WDM format while maintaining its own propagation behavior). Initially at the launching plane no other pulse exists on any of the other copropagating wavelength-division-multiplexed beams. Due to the nonlinear cross-phase modulation effect, time-aligned pulses are generated on all other beams after a given fiber length. Both theoretical and experimental results are presented.

Electrical wavelength tunable and multiwavelength actively mode-locked fiber ring laser

Electrical single- and dual-wavelength tuning and three-wavelength operation of an actively mode-locked fiber ring laser generating picosecond pulses were demonstrated by using a cavity with large dispersion. A continuous tuning range up to ∼37 nm of single-wavelength picosecond pulses at ∼1 GHz was achieved by only changing the modulation frequency. Continuous wavelength tuning of dual-wavelength (18.5 nm spacing) 3 GHz picosecond pulses was also demonstrated with a tuning range up to ∼17 nm. The tuning ranges were mainly limited by the gain bandwidth of the Er-doped fiber. Simultaneous generation of three-wavelength picosecond pulses at ∼2 GHz was also demonstrated by further increasing the cavity dispersion.

High-repetition-rate picosecond pulse generation at 15 µm by intracavity laser frequency modulation

We propose and experimentally demonstrate generation of transform-limited pulse trains at a 2.5-GHz repetition rate from a frequency-modulated erbium-ytterbium bulk glass laser by using an intracavity lithium niobate phase modulator and an external fiber Bragg grating filter. Light pulses with durations tunable from 40 to 80 ps and 0.2-mW fiber-coupled average power at 1535 nm have been obtained.

Improving the accuracy of a time lens

A method for improving the accuracy of temporal imaging with an imperfect time lens is proposed. Signal distortion arising from complicated dispersion of the delay lines can be reduced considerably by appropriate choice of the phase-modulation function including the second harmonic of the basic modulation frequency and a specific phase shift of the modulation with respect to the main signal. The method is of particular interest for picosecond and femtosecond optical pulse generation.

Multiwavelength 10-GHz picosecond pulse generation from a single-stripe semiconductor diode laser

A single-stripe GaAs-AlGaAs semiconductor optical amplifier (SOA) has been used to generate four tunable wavelength-division multiplexed (WDM) channels simultaneously, each transmitting 12-ps pulses at 2.5 GHz, for an aggregate pulse rate of 10 GHz. Wavelength tuning over 18 nm has been demonstrated with channel spacing ranging from 0.8 to 2.1 nm. A potential spectral correlation across the multiwavelength spectrum has been studied in both experiment and simulation methods. These results show the potential for utilizing single stripe laser diodes as multiwavelength sources in WDM-TDM network.

Ultralow timing jitter picosecond pulse generation from electrically gain-switched oxidized vertical-cavity surface-emitting lasers

Ultralow timing jitter picosecond optical pulses are generated by electrically gain switching oxide-confined vertical-cavity surface-emitting lasers (VCSELs) at repetition rates of up to 10.0 GHz. Timing jitter as low as 1.2 ps is measured, which is at least four times lower than that measured for implanted VCSELs. The ultralow timing jitter is attributed to the high level of spontaneous coupling in the oxide-confined VCSEL due to multimode operation resulting from the index guiding properties of the oxide layer.

Tunable dual-wavelength picosecond pulse generation using multiple-optical-path self-seeding approach

A simple system is developed to generate tunable dual-wavelength optical pulses by self-injection seeding of a laser diode. The wavelengths are selected by controlling two light paths incident on a single diffraction grating. The spectral separation has been tuned from 1.8 to 16.1 nm while maintaining an output side-mode-suppression-ratio (SMSR) over 21 dB. This multiple-optical-path self-seeding approach is simple and efficient, thus providing an attractive alternative to generate tunable multiwavelength pulses.

Nearly transform-limited 1.4 µm picosecondpulse generation by supercontinuum and pulse amplification in Tm-doped optical amplifier

Transform-limited 10 GHz picosecond pulse generation is experimentally demonstrated in the 1.4 /spl mu/m wavelength region by amplifying supercontinuum pulses in a Tm-doped optical amplifier. Through bit error rate measurements, power penalties of <1.5 dB are found in the range 1450-1470 nm.

Generation of tunable picosecond pulses by synchronouspumping of a periodically poled lithium niobate optical parametric oscillator

A tunable quasi phase-matched optical parametric oscillator synchronously pumped at 1.047 µm is reported. The signal was tuned from 1.33 to 1.45 µm, corresponding to a calculated idler tuning range of 2.67 – 4.86 µm. Average signal powers of up to 100 mW and pulse durations of 3.2 ps were obtained.

Picosecond domain electromagnetic pulse measurements in an exposure facility: An error compensation routine using deconvolution techniques

This article presents a two-step deconvolution routine to compensate for the measurement distortions of transient electrical fields in the picosecond domain in an electromagnetic pulse exposure facility. Because of the low-pass nature of connection cables and the limited bandwidth of a transient digitizer (Tektronix SCD 5000), the measured signal is a distorted output of D-dot (dD/dt, where D is the electric displacement) sensors. An empirical transfer function of the cable-digitizer system was evaluated using a reference impulse generated by a picosecond pulse generator. The reference impulse was injected into the connection cable at the D-dot sensor end and measured with the SCD 5000 while the cable was kept in the same position as for making D-dot measurements to ensure an in-position compensation. Two types of asymptotic conical dipole (ACD) D-dot sensors were utilized as the electrical field sensing devices: an axial model ACD-1(A) and a radial model ACD-1(R). Due to its right-angle structures, the ACD-1(R) gives a different output from that of ACD-1(A) to the same pulse, especially to the fast leading edge. The right-angle bends in ACD-1(R) cause reflections of a sensed signal in the sensor. To correct the errors due to the reflections, the impulse response of the ACD-1(R) D-dot sensor was proposed as a summation of the δ function and the parameters were determined with a pulse measurement using the ACD-1(A) D-dot sensor and an optimization procedure with the Levenberg–Marguardt algorithm. With this routine the measurement accuracy for the electrical pulse in picosecond domain has been improved significantly.

Generation of picosecond pulses with the wavelength 1.54 μm by two-stage compression in stimulated scattering of nanosecond Nd3+ : YAG laser pulses

Cascaded compression of 8 ns pulses from an Nd3+ : YAG laser by stimulated Brillouin scattering in CCl4 and then by backward stimulated Raman scattering in methane at a high pressure was used to generate Stokes (λ=1.54μm) pulses of 20 ps duration and ∼ 6 mJ energy at a repetition frequency of 0.5 Hz. A detailed study was made of backward stimulated Raman scattering in high-pressure methane used to compress pulses of 500 ps duration with the λ=1.064 μm wavelength.

Evolution of the time characteristics and the dynamics of picosecond lasing under the conditions of self-interaction and passive negative feedback

An investigation was made of the conditions for optimisation of passive negative feedback with GaAs plates acting as feedback elements in picosecond pulse generation. A long (1μs) train of pulses (τ=13 ps) was generated in an Nd : YAG laser. A study was made of the influence of self-defocusing of picosecond pulses in the course of two-photon absorption in GaAs on the evolution of the time and energy parameters of the laser radiation.

Monolithic multisegment mode-locked DBR laser for wavelength tunable picosecond pulse generation

Monolithic active/passive mode-locked DBR laser for 4/spl times/10 Gb/s optical time division multiplexing (OTDM) application at 1.55 /spl mu/m are realized by low-cost 2"-technology. The devices show excellent performance at STM-64 frequency: they deliver nearly time-bandwidth limited (<0.4) and wavelength tunable (4.3-nm range) optical return-to-zero (RZ) pulses of down to 8-ps pulsewidth.

Dual-wavelength picosecond pulse generation usinga single grating and a Michelson interferometer in a self-injection seedingscheme

A single grating combined with a Michelson interferometer is used to generate dual-wavelength picosecond pulses by self-injection seeding of a laser diode. The wavelengths and their spacing can be readily tuned by adjusting the grating and the mirrors in the interferometer. The system is simple, robust, and is of low cost.

Picosecond intracavity optical parametric oscillator

We present a novel technique to generate picosecond pulses at 1.57 microm with kilohertz repetition rates, using an intracavity optical parametric oscillator. With this device we were able to generate up to 120-mW average power at a repetition rate of 2.5 kHz.

Highly efficient generation of tunable picosecond pulses in an LiF:F2- laser crystal

An investigation was made of a synchronously pumped pulsed LiF:F2- crystal laser. The pump radiation was provided by a neodymium phosphate glass laser operating under passive mode-locking conditions and generating pulses of 7 ps duration. The LiF:F2- laser generated 2 ps pulses tunable in the 1.10–1.22 μm range and the efficiency of the conversion process was 35%. Under the conditions of quasi-cw nanosecond pumping and active mode locking the LiF:F2- laser generated pulses of duration of the order of 400 ps.

Influence of carrier transport/capture and gain flattening in picosecond pulse generation of InGaAs microcavity lasers

We have fabricated and studied the dynamics of In0.16Ga0.84As λ-cavity lasers focusing on the influence of carrier transport/capture and gain flattening by using optical resonant pumping and off-resonant pumping. With the off-resonant pumping, shoulders in the lasing pulse shape were observed, while no shoulder appeared with the on-resonant pumping. From rate equation analysis and time-resolved photoluminescence measurement, it was concluded that the shoulders result from carrier transport/capture effects. Saturation of the inverse rise time was observed at high pump levels. This results from gain flattening due to the steplike density of states of 2D carriers. The pulse width obtained from the laser was as narrow as 7.7 ps.

Simulation of gain-switched picosecond pulse generation from quantum well lasers

Circuit models for gain-switched quantum well laser diodes are developed and simulated using the circuit analysis program SPICE2. Effects of cavity length and number of wells on the output pulse shape are analysed. Picosecond pulses of 7 and 2 ps full-width at half-maximum (FWHM) are observed, corresponding to second and third quantized level transitions, respectively. A remarkable reduction in the output pulse width observed for the third quantized level transition, demonstrates the significance of higher sub-band transitions for ultrashort pulse generation.

Visible picosecond pulse generation in a frequency doubled optical parametric oscillator based on LiB 3O 5

We report the attainment of transform-limited pulses across the entire tuning range of a high-repetition-rate, synchronously-pumped picosecond optical parametric oscillator (SPOPO) based on LiB 3O 5, by the inclusion of dispersion compensation in the positive dispersive regime of the crystal. This system which is synchronously pumped by 1.1 ps pump pulses from a self-mode-locked Ti:sapphire laser at 81 MHz, generated transform-limited signal pulses with durations of 1–1.2 ps and idler pulses with durations of 2–2.2 ps over the continuous wavelength range of 1.16–2.26 μm at average powers of 580 mW. By external frequency doubling output signal pulses from the SPOPO in noncritically phase-matched, temperature-tuned LiB 3O 5, we have produced transform-limited picosecond pulses in the visible range from 584 to 771 nm at average powers of up to 68 mW. Second harmonic pulses with durations between 840 and 880 fs have been obtained for signal durations of 1–1.2 ps.