Picosecond Optical Pulse Generation Research Articles

Generation of Picosecond Pulses by Lasers with Distributed Feedback at a Wavelength of 1064 nm

The mode of generation of picosecond optical pulses in the spectral range near 1064 nm by semiconductor lasers with distributed feedback and active region based on an InGaAs/GaAs quantum well has been studied. In the gain-modulation mode, the width of laser pulses decreases from 150 to 35 ps as the temperature increases from 5 to 50°C. It was demonstrated that there is a temperature range in which the pulse width is at a minimum, 35 ps, at a full spectrum width at half-maximum of 70 pm. The laser was mounted in a hermetically sealed butterfly case, which enabled a temperature tuning of the wavelength within 3 nm in the generation mode of pulses with width less than 45 ps. The peak output power was 0.4 W at the outlet of a single-mode fiber, with the polarization preserved.

Picosecond Optical Pulse Generation by Nonlinear Mirror Mode-Locking: A Review

Background/Objectives: This article provides comprehensive review on nonlinear mirror mode-locked laser which is compact, efficient, simplest and stable source of picosecond optical pulse and is of immense research interest. Methods/ Analysis: Starting with the basics of nonlinear mirror mode-locking technique, a chronological development of the subject is presented. Issues with the efficiency and stability of the nonlinear mode-locking are addressed in both theoretical and experimental perspective. Different schemes of nonlinear mirror mode-locking, reported till date, are illustrated and compared in reference to the obtained pulse durations, power scaling, self starting and self sustained efficient modelocking. Findings: Nonlinear mirror, comprising a second harmonic generating crystal and a dichroic output coupler, can mode-lock a laser due to its behaviour analogous to fast saturable absorber. Efficiency of the laser is increased with the diode pumping; however nonlinear mirror is observed prone to passive Q-switching instability. Simultaneously Q-switched and mode-locked operation gives a simple way of increasing the peak power but is of no use because of rapid fluctuations of pulse amplitude and repetition rate. Incorporation of an accousto-optic Q-switch in the laser cavity helps run the laser in actively Q-switched and passively mode-locked regime which provides enormous stability of the Q-switched and modelocked pulse envelops and the enhanced peak power becomes useful. Pure contentious wave mode-locking is obtained by incorporation of additional intensity dependent loss mechanism by way of introducing third harmonic generation in the laser cavity and it gives an inverse saturable nonlinear loss modulation. Inverse saturable nonlinear mirror produces efficient, self sustained and stable contentious wave mode-locked picosecond optical pulse train. Application /Improvement: Nonlinear mirror mode-locked lasers have wide application in micromachining, optical frequency conversion, pumping optical parametric oscillators etc. Propositions are made for getting improved nonlinear mirror mode-locking to get bandwidth limited pulse width.

Laser diode structures with a saturable absorber for high-energy picosecond optical pulse generation by combined gain-and Q-switching

The performance of gain-switched Fabry–Perot asymmetric-waveguide semiconductor lasers with a large equivalent spot size and an intracavity saturable absorber was investigated experimentally and theoretically. The laser with a short (∼20 μm) absorber emitted high-energy afterpulse-free optical pulses in a broad range of injection current pulse amplitudes; optical pulses with a peak power of about 35 W and a duration of about 80 ps at half maximum were achieved with a current pulse with an amplitude of just 8 A and a duration of 1.5 ns. Good quality pulsations were observed in a broad range of elevated temperatures. The introduction of a substantially longer absorber section leads to strong spectral broadening of the output without a significant improvement to pulse energy and peak power.

Widely Continuous Tunable ps Pulse Train Generation Based on SOA Nonlinear Dynamics

We propose a simple setup based on nonlinear dynamics in a semiconductor optical amplifier (SOA) and solitonic compression for the generation of stable and tunable repetition rate picosecond (ps) optical pulses. A quantum-well SOA is used to amplify electrical-optic-modulated rectangular optical signal, during which the nonlinear amplification process induces front-edge distortion. Due to the non-zero linewidth enhancement factor, the front-edge distortion can be isolated by the optical filtration of the chirped frequency component, which eventually becomes Gaussian-like pulse train of tens of ps FWHM pulsewidth. Following a stage of solitonic compression and a stage of pedestal suppression, we are able to obtain a train of 1-ps high-quality pulses for which the root mean square timing jitter is $C$ -band.

Deep-red semiconductor monolithic mode-locked lasers

A deep-red semiconductor monolithic mode-locked laser is demonstrated. Multi-section laser diodes based on an AlGaAs multi-quantum-well structure were passively mode-locked, enabling the generation of picosecond optical pulses at 752 nm, at pulse repetition rates of 19.37 GHz. An investigation of the dependence of the pulse duration as a function of reverse bias revealed a predominantly exponential decay trend of the pulse duration, varying from 10.5 ps down to 3.5 ps, which can be associated with the concomitant reduction of absorption recovery time with increasing applied field. A 30-MHz-tunability of the pulse repetition rate with bias conditions is also reported. The demonstration of such a compact, efficient and versatile ultrafast laser in this spectral region paves the way for its deployment in a wide range of applications such as biomedical microscopy, pulsed terahertz generation as well as microwave and millimeter-wave generation, with further impact on sensing, imaging and optical communications.

PICOSECOND OPTICAL PULSE GENERATION USING CASCADED MACH-ZEHNDER ELECTRO-OPTIC LIGHT INTENSITY MODULATORS

In this paper, the author proposes a technique for the generation of picosecond optical pulses using cascaded Mach-Zehnder electrooptic light intensity modulators. Each individual Mach-Zehnder modulator is driven by the same microwave signal. By providing proper dc bias to the modulators, the repetition frequency of the generated optical pulse can be made equal to twice the frequency of the applied microwave drive signal. By tuning the microwave drive frequency, the repetition frequency of the generated optical pulse can be varied. The normalized optical pulse intensity and pulse width of the generated pulse have been calculated. The variation of the pulse width with different system parameters is also presented. Typical pulse width of 2.52 picosecond can be achieved using a cascade of four modulators driven by 60 GHz mm-wave signal.

7-ps optical pulse generation from a 1064-nm gain-switched laser diode and its application for two-photon microscopy

In this study, we investigated the picosecond optical pulse generation from a 1064-nm distributed feedback laser diode under strong gain switching. The spectrum of the generated optical pulses was manipulated in two different ways: (i) by extracting the short-wavelength components of the optical pulse spectrum and (ii) by compensating for spectral chirping in the extracted mid-spectral region. Both of these methods shortened the optical pulse duration to approximately 7 ps. These optical pulses were amplified to over 20-kW peak power for two-photon microscopy. We obtained clear two-photon images of neurons in a fixed brain slice of H-line mouse expressing enhanced yellow fluorescent protein. Furthermore, a successful experiment was also confirmed for in vivo deep region H-line mouse brain neuron imaging.

Microchip Laser-Based Optoelectronic System for Kilovolt Picosecond Electromagnetic Pulse Generation

An optoelectronic electromagnetic generator was developed for the creation and shaping of picosecond pulses. The system integrated a homemade compact picosecond source. The infrared pulse-source switches optoelectronic components mounted on a microstrip line generator. The technology is based on a microchip laser that delivers subnanosecond pulses, whose duration is shortened in a standard optical fiber before amplification in a 3D multipass amplifier. This technique permits the generation of picosecond optical pulses with several tens of microjoules and kilohertz repetition rates. Rectangular electrical picosecond pulses with kilovolt positive and negative amplitudes are obtained with particular shapes and bipolar electrical pulses.

High peak-power picosecond pulse generation at 126 µm using a quantum-dot-based external-cavity mode-locked laser and tapered optical amplifier

In this paper, we present the generation of high peak-power picosecond optical pulses in the 1.26 μm spectral band from a repetition-rate-tunable quantum-dot external-cavity passively mode-locked laser (QD-ECMLL), amplified by a tapered quantum-dot semiconductor optical amplifier (QD-SOA). The laser emission wavelength was controlled through a chirped volume Bragg grating which was used as an external cavity output coupler. An average power of 208.2 mW, pulse energy of 321 pJ, and peak power of 30.3 W were achieved. Preliminary nonlinear imaging investigations indicate that this system is promising as a high peak-power pulsed light source for nonlinear bio-imaging applications across the 1.0 μm - 1.3 μm spectral range.

Publisher's Note: “Picosecond optical pulse generation from self-pulsating bisectional GaN-based blue-violet laser diodes” [Appl. Phys. Lett. 94, 161103 (2009)

Publisher's Note: “Picosecond optical pulse generation from self-pulsating bisectional GaN-based blue-violet laser diodes” [Appl. Phys. Lett. 94, 161103 (2009)

Picosecond optical pulse generation from self-pulsating bisectional GaN-based blue-violet laser diodes

Self-pulsations of 407 nm emitting GaN-based blue-violet laser diodes with bisectional (BS) electrodes were demonstrated by applying a reverse bias (VSA) to the subelectrode of the saturable absorber (SA) section. By increasing the injected current to the main electrode of the gain section with a reverse bias of VSA=−12 V, the optical pulses shortened to 30 ps. The optical peak output power was as high as 2.4 W with a pulse width of 30 ps and a repetition frequency of 0.9 GHz. This is so far the shortest pulse width from a self-pulsating BS GaN-based laser diode achieved by applying a reverse bias to the SA section.

Timing Jitter Tolerant All-Optical TDM Demultiplexing Using a Saw-Tooth Pulse Shaper

We experimentally demonstrate the generation of picosecond saw-tooth optical pulses, which are shaped using a fiber Bragg grating to provide timing jitter tolerant optical time-division multiplexing data demultiplexing in a scheme based on cross-phase modulation in an optical fiber, with subsequent offset filtering. A power improvement of more than 5 dB is obtained compared to demultiplexing with more conventional shapes, such as Gaussian, with a similar pulsewidth.

40-GHz picosecond-pulse second-harmonic generation in an MgO-doped PPLN waveguide

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

A method of tunable high repetition-rate picosecond optical pulse generation using injection locking of laser diodes

A method of tunable, high repetition-rate optical pulse generation by using optical injection locking of semiconductor lasers has been described in this paper. This method utilizes the superposition of five coherent optical carriers obtained from the spectrum of optical phase modulation, which results in a sharp optical pulse. Theoretical calculations indicate that a pulse width of 1 ps and a repetition rate of 200 GHz can be achieved for a modulator drive frequency of 40 GHz.

Picosecond pulse generation by internal gain switching in laser diodes

A laser diode structure realizing internal gain switching is suggested for high-power picosecond optical pulse generation. A thin wideband barrier layer is incorporated in the active region of this structure, in order to provide additional control of the carrier distribution and the gain dynamics. The dynamic laser output response to the nanosecond pumping current pulses is modeled and analyzed. The pulse generation mechanism is studied and the possibility to generate optical pulses with power density of 0.416 W/μm2 is demonstrated. This result compares well with that provided by the best modern picosecond laser diodes operating in Q-switching mode.

Laser diode structure for the generation of high-power picosecond optical pulses

A laser diode structure is designed and tested that permits the generation of high-power (∼100 W) picosecond-range optical pulses. Direct current pumping is used with a current pulse duration of a few nanoseconds and a current amplitude of ∼105 A/cm2. The main distinguishing feature of the structure is separation of the electron injector (p–n junction) from the active region by a potential barrier. The optical gain in the active region is controlled by the transverse electric field, which is determined by the magnitude of the current at each instant. The design allows emission wavelength control by means of band gap engineering.

Ultraviolet picosecond optical pulse generation from a mode-locked InGaN laser diode

Ultraviolet optical pulses were generated by actively mode locking an external cavity InGaN laser at a wavelength of 409 nm with a temporal pulse duration of 30 ps. The average power was 2 mW and the time–bandwidth product was 1.2. Dynamic detuning plays a major role in pulse development.

Repetition rate, using a mode-locked hybrid distributed Bragg reflector (ML-HDBR) laser source

In the present paper we report the realization of a mode-locked hybrid distributed Bragg reflector (HDBR) laser for picosecond optical pulse generation at 10-GHz repetition rate, 12.7-ps 2-mW optical pulses, with 400-MHz locking bandwidth have been obtained by using a saturated (95% of peak reflectivity) Gaussian Bragg grating. Linear phase gratings have shown even better results in terms of stability and output power (7 mW), whereas so far 15 ps of pulsewidth has been achieved, mainly limited by the spectral bandwidth of the grating. Key features of this realization are the intrinsic simplicity and the compactness of the laser source.

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.

Q-switching in single-heterojunction lasers and generation of ultrahigh-power picosecond optical pulses

Q-switching has been obtained for single-heterojunction lasers. The ultrafast saturable absorber in the laser cavity is created by implantation of high-energy heavy ions. The peak power generated by the lasers in a 150 μm stripe width is 380 W with a pulse length of 40 ps.