Optical Pulse Amplification Research Articles

Controlled compression, amplification and frequency up-conversion of optical pulses by media with time-dependent refractive index.

Control over the time dependence of the refractive index of a material allows one to modify and manipulate the properties of light propagating through it. While metamaterials provide a promising avenue in this context, another route has been extensively explored by the ultrafast community - the so-called molecular modulators. Indeed, impulsively-aligned diatomic molecules provide a unique medium, where periodic rotational revivals induced by a pump pulse persist for tens of picoseconds, offering an excellent opportunity for the controlled modification of the refractive index and, therefore, of femtosecond laser pulses propagating through these media. Here we present an analytical theory which describes this process and stumble across a novel mechanism revealing exponential transformations of the probe pulse - its compression, amplification and frequency up-conversion. In particular, our analytical results predict the generation of amplified ultrashort (about 20fs) ultraviolet pulses centered around 550nm, starting with near infrared input pulses centered on 1μm of about 30fs duration, under very realistic experimental conditions.

Cleaning up of high-energy ultrashort pulses with saturable absorbers

Pulse energy transferred from the peak to wings is inevitable in the process of ultrashort optical pulse amplification due to the accumulation of high nonlinearity, which degrades the temporal pulse quality. The energy-related saturable absorbers are applied to remove the wings of high-energy pulses without causing a severe loss of the peak in this research. A cascaded-saturable-absorbers system is proposed, and the effects of the cascaded order, low-intensity loss coefficient, saturable fluence, relaxation time and input fluence distribution on the pulse wings are numerically investigated, respectively. The obtained results can provide a general guidance of design for high-energy ultrashort pulse cleaning.

Low coherence laser pulse amplification theory for rare earth ions doped glass medium.

A new theory for the low coherence laser amplification in rare ions doped glass has been proposed. Based on one-dimensional continuous energy level assumption and independent response assumption, the theory can describe the amplification of low coherence laser pulses with any time scale and any bandwidth. By the new theory, McCumber formula can be obtained, and a complete low coherence optical pulse amplification model in neodymium glass is established. Computation shows that at high fluences, inhomogeneous broadening will severely limit energy extraction of narrowband high coherence laser, therefore the extraction of broadband low coherence laser will exceed that of narrowband high coherence laser. In addition, the portion of long-wave of the output spectrum is slightly larger than that predicted by the homogeneous model. The new theory could be beneficial for the studies of low coherence pulse amplification in rare earth doped medium and other laser mediums.

Generalized self-similar propagation and amplification of optical pulses in nonlinear media with high-order normal dispersion

We investigate theoretically and numerically the self-similar propagation of optical pulses in the presence of gain, positive Kerr nonlinearity, and positive (i.e., normal) dispersion of even order $m$. Starting from a modified nonlinear Schr\"odinger equation, separating the evolution of amplitude and phase, we find that the resulting equations simplify considerably in the asymptotic limit. Exact solutions to the resulting equations indicate that the temporal intensity profile follows a $1\ensuremath{-}{T}^{m/(m\ensuremath{-}1)}$ function with an $m$-dependent scaling relation, with a ${T}^{1/(m\ensuremath{-}1)}$ chirp, where $T$ is the pulse's local time. These correspond to a triangle and a step function, respectively, as $m\ensuremath{\rightarrow}\ensuremath{\infty}$. These results are borne out by numerical simulations, although we do observe indications of nonasymptotic behavior.

Characterization of partially deuterated KDP crystals using two-wavelength phase-matching angles

Partially deuterated potassium dihydrogen phosphate (DKDP) allows for the optical parametric chirped-pulse amplification of high-energy broadband optical pulses to generate ultrashort, high-peak-power pulses. Modeling and experimental optimization of the noncollinear interaction geometry require the combination of a model for the deuteration-dependent optical indices and knowledge of the deuteration level of the DKDP crystal being used. We study and demonstrate a novel experimental technique that determines the deuteration level of a DKDP crystal consistent with a specific index model, based on the phase-matching angles measured at two wavelengths. Simulations and experiments show that the simple two-wavelength technique allows for consistent results with three different index models, and in particular, for the characterization of four crystals with deuteration levels ranging from 70% to 98%.

Analysis of pulse amplification characteristics in vertical cavity semiconductor optical amplifiers

Based on the transfer matrix method (TMM), a comprehensive dynamic numerical model describing the optical pulse amplification in vertical cavity semiconductor optical amplifiers (VCSOAs) is established, which treats the whole VCSOA as one multilayer dielectric structure, including the two Distributed Bragg Reflectors (DBRs) and the middle active region. In this model, the spatial dependence of the carriers and optical field in the longitudinal direction and the discontinuity of refractive index distribution in the resonant cavity are accounted for. Moreover, in this study the influence of the two photon absorption (TWP) is also taken into consideration. By employing this model, we investigate the signal distortion and the pulse energy gain characteristic in single pulse amplification of VCSOAs operated in reflection mode in detail. The numerical results show that the pulse distortion can be mitigated in a satisfactory manner via reducing the period of top DBR. It further shows that the energy gain during the pulse amplification can be increased by enhancing the pump power; larger saturation input pulse energy (SIPE) could be obtained by either lowering the period of top DBR or reducing the pump power; for the input pulse with duration ranging from several to tens of picoseconds, the energy gain characteristics of VCSOA is pulsewidth independent.

Nobel Prize in Physics awarded to Arthur Ashkin, Gérard Mourou, and Donna Strickland for laser physics techniques (optical tweezers and chirp pulse amplification)

<i>Nobel Prize in Physics awarded to Arthur Ashkin, Gérard Mourou, and Donna Strickland for laser physics techniques (optical tweezers and chirp pulse amplification)</i>

Demonstration of Input-to-Output Gain and Temporal Noise Mitigation in a Talbot Amplifier

We experimentally demonstrate intensity amplification of repetitive picosecond optical pulses with an input-to-output gain up to 5.5 dB using a passive Talbot amplifier. Through the dispersion-induced temporal Talbot effect, the amplifier uses electro-optic phase modulation and a low-loss dispersive medium to exploit and coherently redistribute the energy of the original pulse train into fewer, replica, amplified pulses. In addition, we show how our passive amplifier mitigates the pulse train timing-jitter and pulse-to-pulse intensity fluctuations above a specific cutoff frequency.

Programmable passive Talbot optical waveform amplifier

We introduce and experimentally demonstrate a new design for passive Talbot amplification of repetitive optical waveforms, in which the gain factor can be electrically reconfigurable. The amplifier setup is composed of an electro-optic phase modulator followed by an optical dispersive medium. In contrast to conventional Talbot amplification, here we achieve different amplification factors by using combinations of fixed dispersion and programmable temporal phase modulation. To validate the new design, we experimentally show tunable, passive amplification of picosecond optical pulses with gain factors from m = 2 to 30 using a fixed dispersive line (a linearly chirped fiber Bragg grating).

Comparison of different fiber amplifiers in Yb-doped fiber femtosecond optical frequency combs

Recently, Yb-doped fiber femtosecond optical frequency combs (Yb-FOFCs) have obtained high repetition rates and high power outputs, and the wavelengths can cover the visible region by using a photonic crystal fiber to broaden the spectrum. In this paper, f0 (carrier-envelope offset frequency) with a signal-to-noise ratio (SNR) of 40dB is generated in an Yb-FOFC by adopting a scheme which includes the three processes of amplifying, broadening the spectrum and detecting f0, and optimizing the system parameters. The effects of two types of amplifiers which employ direct optical pulse amplification and self-similar amplification, respectively, on the output parameters of the amplifiers, minimal output power of the octave spectrum meeting f0 detection requirements, and the SNR of f0 are compared and analyzed in detail.

Fiber-Optical Parametric Amplification of Sub-Picosecond Pulses for High-Speed Optical Communications

This article reviews recent results of amplification of short optical pulses using fiber-optical parametric amplifiers. This includes chirped-pulse amplification of 400 fs pulses, error-free amplification of a 640-Gbit/s optical time-division multiplexed signal with less than a 1-dB power penalty, and all-optical phase-preserving amplitude regeneration of a 640-Gbit/s return-to-zero differential phase-shift keying optical time-division multiplexed signal.

Picosecond pulse amplification up to a peak power of 42 W by a quantum-dot tapered optical amplifier and a mode-locked laser emitting at 1.26µm.

We experimentally study the generation and amplification of stable picosecond-short optical pulses by a master oscillator power-amplifier configuration consisting of a monolithic quantum-dot-based gain-guided tapered laser and amplifier emitting at 1.26 µm without pulse compression, external cavity, gain- or Q-switched operation. We report a peak power of 42 W and a figure-of-merit for second-order nonlinear imaging of 38.5 W2 at a repetition rate of 16 GHz and an associated pulse width of 1.37 ps.

Pattern effect reduction scheme for high-speed all-optical amplification system

A method for high-bit-rate optical pulse amplification without a pattern effect (PE) phenomenon is numerically analyzed and presented. In the proposed new scheme, the input signals are applied to a series of 1×2 optical switches and semiconductor optical amplifiers (SOAs). Based on the input signal bit rate and the desired PE reduction rate, it is shown that the number of these devices can be easily optimized. For reducing the SOA nonlinearities on the output signal, a high-birefringent fiber loop mirror is used as an optical Gaussian filter. The achieved results depict that symmetry and the time-bandwidth product of the output signal obtained by this filter are significantly improved. The simulations are performed for high bit-rate signals (>50 Gbps); therefore, in the SOA model, all relevant nonlinear effects that occur in the subpicosecond regimes are taken into account.

Self-phase modulation compensation in a regenerative amplifier using cascaded second-order nonlinearities

Self-phase modulation limits the amplification of short optical pulses because of spatial self-focusing and spectral broadening. Cascaded nonlinearities are theoretically and experimentally investigated for intracavity nonlinearity compensation in a neodymium-doped yttrium-lithium-fluoride (Nd:YLF) regenerative amplifier. Experimental results are in good agreement with simulations. Spectral broadening is significantly reduced, allowing for efficient amplification in a Nd:YLF power amplifier.

Wavelength conversion and parametric amplification of optical pulses via quasi-phase-matched four-wave mixing in long-period Bragg silicon waveguides.

We present a theoretical analysis supported by comprehensive numerical simulations of quasi-phase-matched four-wave mixing (FWM) of ultrashort optical pulses that propagate in weakly width-modulated silicon photonic nanowire gratings. Our study reveals that, by properly designing the optical waveguide such that the interacting pulses copropagate with the same group velocity, a conversion efficiency enhancement of more than 15 dB, as compared to a uniform waveguide, can readily be achieved. We also analyze the dependence of the conversion efficiency and FWM gain on the pulse width, time delay, walk-off parameter, and grating modulation depth.

Tunable stoichiometry of BCxNy thin films through multitarget pulsed laser deposition monitored viain situellipsometry

The supercontinuum (SC) generated by pumping in anomalous dispersion is sensitive to the input pulse fluctuations and pump laser’s shot noises and does not possess a single-pulse waveform, so the incident pulse becomes a noise-like train of spikes. A simple method of creating pulsed lasers with either pulse-maintaining ultrabroad SC or specially shaped pulse waveforms can be implemented using all-normal-dispersion microstructured optical fibers (ANDi-MOFs). An ANDi-MOF with a simple topology and dispersion profile maximum at 800 nm was designed using the effective index method. Its properties and suitability were characterized via numerical simulation of femtosecond parabolic pulse formation and generation of an octave-spanning pulse-maintaining SC using a generalized propagation equation. The designed ANDi-MOF is suitable for resolving both problems and allows some detuning of the pulse’s wavelength around 800 nm. However, a better choice for SC generation is pumping at or near the wavelength where the third-order dispersion becomes zero. This configuration benefits from the absence of pulse break-up under large pulse energies, which appears otherwise. The fiber can provide a low-cost method for developing supercontinuum sources and a solution to the problems of parabolic waveform formation to meet the needs of optical signal processing and pulse amplification and compression.

High-energy noncollinear optical parametric–chirped pulse amplification in LBO at 800 nm

The optical parametric-chirped pulse amplification (OPCPA) based on large-aperture nonlinear optical crystals is promising for implementation of an ultrahigh peak-power laser system of 10 PW and beyond. We demonstrated the highest energy broadband OPCPA at 800 nm, to the best of our knowledge, by using an 80 mm in diameter LiB(3)O(5)(LBO) amplifier, with an output energy of 28.68 J, a bandwidth of 80 nm (FWHM), and conversion efficiency of 25.38%. After compression, a peak power of 0.61 PW with 33.8 fs pulse duration is produced.

Unidirectional amplification and shaping of optical pulses by three-wave mixing with negative phonons

A possibility to greatly enhance frequency-conversion efficiency of stimulated Raman scattering is shown by making use of extraordinary properties of three-wave mixing of ordinary and backward waves. Such processes are commonly attributed to negative-index plasmonic metamaterials. This work demonstrates the possibility to replace such metamaterials that are very challenging to engineer by readily available crystals which support elastic waves with contra-directed phase and group velocities. The main goal of this work is to investigate specific properties of indicated nonlinear optical process in short pulse regime and to show that it enables elimination of fundamental detrimental effect of fast damping of optical phonons on the process concerned. Among the applications is the possibility of creation of a family of unique photonic devices such as unidirectional Raman amplifiers and femtosecond pulse shapers with greatly improved operational properties.

Amplification of ultra-short optical pulses in a two-pump fiber optical parametric chirped pulse amplifier

We demonstrate with realistic numerical simulations that fiber optical parametric chirped pulse amplification is able to amplify ultra-short optical pulses. Such amplifiers driven by two-pump waves can amplify pulse bandwidth twice as large as the one of a single pump configuration. We show that pulses as short as 50 fs can be directly amplified. In addition, we take benefit from the saturation regime to achieve spectral broadening which makes possible to reduce pulse duration down to 15 fs.

Self-similar modes of amplification and compression of electromagnetic pulses in their interaction with electron flows

Self-similar solutions describing the amplification and compression of ultrashort electromagnetic pulses in their interaction with quasi-stationary electron flows are constructed on the basis of analogy with the coherent amplification of short optical pulses by inverted laser media. It is shown that the effects of amplification of pulses with their simultaneous compression are universal and must be observed for different mechanisms of induced radiation, including the Cherenkov and cyclotron mechanisms.