Picosecond Optical Pulses Research Articles

Integrated thin-film lithium niobate electro-optic frequency comb for picosecond optical pulse train generation

In recent years, high-performance thin-film lithium niobate (TFLN) electro-optic (EO) modulators boost the fast development of highly integrated, low loss, and large comb spacing EO frequency combs. Furthermore, ultra-short optical pulse trains (USOPTs) can be generated by the temporal domain compression of the optical frequency comb, which play an essential role in photonic sampling analog-to-digital conversion. Here, we demonstrate a flat and broadband EO frequency comb based on a packaged TFLN chip including a monolithic integrated intensity modulator, a phase modulator, and edge couplers. The 25 comb lines with a power fluctuation less than 3 dB are presented successfully. Moreover, we obtain a 10 GHz repetition rate USOPT, the pulse width of which is compressed to 2.67 ps. Our device may find its applications in the fields of ultrafast measurement, wavelength-division-multiplexing optical communication, or high-precision photonic sampling.

Accurate modeling of ultrafast nonlinear pulse propagation in multimode gain fiber

The nonlinear propagation of picosecond or femtosecond optical pulses in multimode fiber amplifiers underlies a variety of intriguing physical phenomena as well as the potential for scaling sources of ultrashort pulses to higher powers. However, existing theoretical models of ultrashort-pulse amplification do not include some critical processes, and, as a result, they fail to capture basic features of experiments. We introduce a numerical model that combines steady-state rate equations with the unidirectional pulse propagation equation, incorporating dispersion, Kerr and Raman nonlinearities, and gain/loss-spectral effects in a mode-resolved treatment that is computationally efficient. This model allows investigation of spatiotemporal processes that are strongly affected by gain dynamics. Its capabilities are illustrated through examinations of amplification in few-mode gain fiber, multimode nonlinear amplification, and beam cleaning in a multimode fiber amplifier.

High-Contrast Frontend for Petawatt-Scale Lasers Using an Optically Synchronized Picosecond Optical Parametric Chirped Pulse Amplification

We present a new scheme of picosecond optical parametric chirped pulse amplification (OPCPA) in which a Fourier-transform-limit 5.0 ps pulse is optically sheared from a single-longitudinal-mode 1064 nm CW laser. The pulse is amplified and frequency-doubled as the pump in order to maintain the pump narrow bandwidth and picosecond duration simultaneously, which is very important to ensure the high temporal contrast for an OPCPA amplifier. Combined with the cross-polarized wave generation (XPW), a compound frontend for the high-power femtosecond laser system that delivers a 1 Hz chirped pulse train is established. The experiments provide an output pulse energy of 17.1 mJ, a spectrum bandwidth 71 nm (FWHM), and a pulse duration 16.4 fs. The pulse contrast reaches 1:10−12 several picoseconds before the peak of the main pulse, which is the best value of the available measuring instruments.

Complete characterization of picosecond optical pulses by the offset frequency intensity modulation.

We present a method for characterizing the intensity waveform, spectrum, frequency chirp, and spectral phase of picosecond pulses at a moderate repetition rate of ∼100 MHz. The proposed method exploits the intensity modulation at ∼10 GHz, which is slightly offset from the integer multiple of the repetition rate of the pulses. The modulated pulses are split into two, and one is measured by an optical spectrum analyzer, whose output is detected by a lock-in amplifier, while the other is directly detected by a photodiode and its output is used as a reference signal of the lock-in amplifier. In the experiment, we demonstrate the measurement of picosecond Ti:sapphire laser pulses to investigate frequency chirp induced by self-phase modulation. We anticipate that the proposed method will be useful for the characterization of various types of picosecond pulses.

Graphene oxide-based waveguides for enhanced self-phase modulation

The enhanced self-phase modulation (SPM) in silicon nitride (Si3N4) and silicon (Si) waveguides integrated with graphene oxide (GO) films is experimentally demonstrated. By using both picosecond and femtosecond optical pulses, we observe significant spectral broadening in the waveguides due to the high Kerr nonlinearity of GO films. The maximum broadening factors of up to ~3.4 and ~4.3 are achieved in GO-coated Si3N4 waveguides and GO-coated Si waveguides, respectively. The spectral broadening for femtosecond pulses is more significant than the picosecond pulses, which can be attributed to their relatively high peak power. These results show the strong potential of GO films for improving the Kerr nonlinearity of photonic devices.

Optical charge injection and coherent control of a quantum-dot spin-qubit emitting at telecom wavelengths

Solid-state quantum emitters with manipulable spin-qubits are promising platforms for quantum communication applications. Although such light-matter interfaces could be realized in many systems only a few allow for light emission in the telecom bands necessary for long-distance quantum networks. Here, we propose and implement an optically active solid-state spin-qubit based on a hole confined in a single InAs/GaAs quantum dot grown on an InGaAs metamorphic buffer layer emitting photons in the C-band. We lift the hole spin-degeneracy using an external magnetic field and demonstrate hole injection, initialization, read-out and complete coherent control using picosecond optical pulses. These results showcase a solid-state spin-qubit platform compatible with preexisting optical fiber networks.

Numerical Investigation of the Temporal Contrast in ps-OPCPA with Compact Double BBO Arrangement

The picosecond optical parametric chirped pulse amplifier (ps-OPCPA) with double BBO arrangement can support the ultrabroad spectrum even under a relatively long pump pulse duration (∼100 ps). In this work, five-wave-coupled equations taking into consideration different phase matching conditions between the parametric superfluorescence (PSF) and the signal are proposed to investigate the temporal contrast in ps-OPCPA schemes. Both the temporal contrast and the amplified spectrum are numerically analyzed in double BBO arrangements with four phase matching conditions. Numerical results show that the high temporal contrast and ultrabroad spectrum can be simultaneously realized by choosing the proper phase matching geometry in a double BBO arrangement. The numerical investigation here relaxes the requirement of very short pump pulses in ps-OPCPA, which can provide beneficial guidance for the design and construction of ps-OPCPA.

Генерация пикосекундных импульсов волоконным лазером с полупроводниковым оптическим усилителем в спектральном диапазоне 1.06 μm

Picosecond optical pulses generation in a ring fiber laser with a semiconductor optical amplifier was investigated. Optical spectrum width is minimal at a fundamental resonant repetition frequency of 45 MHz, corresponding to a fiber resonator length of 4.5 m. As the frequency increases, the spectral width increases by an order of magnitude while the pulse duration decreases to 18 ps, and the power increases to 0.5 W. The power of picosecond optical pulses at the output of the semiconductor amplifier is 7 times higher than in the CW mode due to the carrier accumulation effect that occurs with short pump pulses.

Picosecond pulses generation by fiber laser with semiconductor optical amplifier in 1.06 μm spectral range

Picosecond optical pulses generation in a ring fiber laser with a semiconductor optical amplifier was investigated. Optical spectrum width is minimal at a fundamental resonant repetition frequency of 45 MHz, corresponding to a fiber resonator length of 4.5 m. As the frequency increases, the spectral width increases by an order of magnitude while the pulse duration decreases to 18 ps, and the power increases to 0.5 W. The power of picosecond optical pulses at the output of the semiconductor amplifier is 7 times higher than in the CW mode due to the carrier accumulation effect that occurs with short pump pulses. Keywords: Semiconductor optical amplifier, Fiber ring laser, Gain-Switching.

Enhanced self-phase modulation in silicon nitride waveguides integrated with 2D graphene oxide films

We experimentally demonstrate enhanced self-phase modulation (SPM) in silicon nitride (Si3N4) waveguides integrated with 2D graphene oxide (GO) films. GO films are integrated onto Si3N4 waveguides using a solution-based, transfer-free coating method that enables precise control of the film thickness. Detailed SPM measurements are carried out using both picosecond and femtosecond optical pulses. Owing to the high Kerr nonlinearity of GO, the hybrid waveguides show significantly improved spectral broadening compared to the uncoated waveguide, achieving a broadening factor of up to ~3.4 for a device with 2 layers of GO. By fitting the experimental results with theory, we obtain an improvement in the waveguide nonlinear parameter by a factor of up to 18.4 and a Kerr coefficient (n2) of GO that is about 5 orders of magnitude higher than Si3N4. Finally, we provide a theoretical analysis for the influence of GO film length, coating position, and its saturable absorption on the SPM performance. These results verify the effectiveness of on-chip integrating 2D GO films to enhance the nonlinear optical performance of Si3N4 devices.

Unifying femtosecond and picosecond single-pulse magnetic switching in Gd-Fe-Co

Many questions are still open regarding the physical mechanisms behind the magnetic switching in GdFeCo alloys by single optical pulses. Phenomenological models suggest a femtosecond scale exchange relaxation between sublattice magnetization as the driving mechanism for switching. The recent observation of thermally induced switching in GdFeCo by using both several picosecond optical laser pulse as well as electric current pulses has questioned this previous understanding. This has raised the question of whether or not the same switching mechanics are acting at the femo- and picosecond scales. In this work, we aim at filling this gap in the understanding of the switching mechanisms behind thermal single-pulse switching. To that end, we have studied experimentally thermal single-pulse switching in GdFeCo alloys, for a wide range of system parameters, such as composition, laser power and pulse duration. We provide a quantitative description of the switching dynamics using atomistic spin dynamics methods with excellent agreement between the model and our experiments across a wide range of parameters and timescales, ranging from femtoseconds to picoseconds. Furthermore, we find distinct element-specific damping parameters as a key ingredient for switching with long picosecond pulses and argue, that switching with pulse durations as long as 15 picoseconds is possible due to a low damping constant of Gd. Our findings can be easily extended to speed up dynamics in other contexts where ferrimagnetic GdFeCo alloys have been already demonstrated to show fast and energy-efficient processes, e.g. domain-wall motion in a track and spin-orbit torque switching in spintronics devices.

Synergistic effect of picosecond optical and nanosecond electrical pulses on dielectric breakdown in aqueous solutions

The combined effect of short (picosecond) optical and (nanosecond) electrical pulses on dielectric breakdown is investigated both theoretically and experimentally. It was demonstrated that nanosecond electrical pulses (nsEPs), being applied simultaneously with picosecond optical pulses, reduce the threshold for optical breakdown. Experimental results are discussed with respect to an extended model for opto-electrical-induced breakdown. The newly unveiled effect is expected to play a significant role in spatially confined electroporation and further advances in laser-ablation-based processes while also allowing for measurements of ambipolar diffusion constants.

A self-referenced in-situ arrival time monitor for X-ray free-electron lasers.

We present a novel, highly versatile, and self-referenced arrival time monitor for measuring the femtosecond time delay between a hard X-ray pulse from a free-electron laser and an optical laser pulse, measured directly on the same sample used for pump-probe experiments. Two chirped and picosecond long optical supercontinuum pulses traverse the sample with a mutually fixed time delay of 970 fs, while a femtosecond X-ray pulse arrives at an instant in between both pulses. Behind the sample the supercontinuum pulses are temporally overlapped to yield near-perfect destructive interference in the absence of the X-ray pulse. Stimulation of the sample with an X-ray pulse delivers non-zero contributions at certain optical wavelengths, which serve as a measure of the relative arrival time of the X-ray pulse with an accuracy of better than 25 fs. We find an excellent agreement of our monitor with the existing timing diagnostics at the SACLA XFEL with a Pearson correlation value of 0.98. We demonstrate a high sensitivity to measure X-ray pulses with pulse energies as low as 30 upmu J. Using a free-flowing liquid jet as interaction sample ensures the full replacement of the sample volume for each X-ray/optical event, thus enabling its utility even at MHz repetition rate XFEL sources.

Nanotwist of aluminum with irradiation of a single optical vortex pulse

A nanoscale twisting of aluminum (Al) is demonstrated by irradiation with a single picosecond optical vortex pulse with relatively low energy near the ablation threshold, due to the orbital angular momentum (OAM) transfer effects. The twisting needle is easily transformed into a microscale non-twisting needle by only the deposition of several overlaid optical vortex pulses. Irradiation with a picosecond/nanosecond optical vortex pulse with a millijoule level pulse energy also enabled the fabrication of a microscale non-twisting needle. Such nano/microstructuring of Al provides a new physical insight for the interaction between OAM and materials, and it also offers an entirely new nano/microfabrication technique towards ultraviolet plasmonic devices.

Numerical Analysis of Supercontinuum Generated Microstructured Optical Fiber with all Normal Chromatic Dispersion

A micro-structured photonic crystal fiber (M-PCF) with all normal chromatic dispersion has been proposed for supercontinuum spectrum generation which is applicable in optical transmission and optical coherence tomography applications. Calculations of its different properties using finite difference method have shown that the proposed M-PCF has a high nonlinear coefficients at 1.06 μm, 1.30 μm and 1.55 μm wavelength with flattened chromatic dispersion, low confinement losses and broad supercontinuum spectrum. Moreover, it has been shown that the proposed design obtain high power and short fiber length at 1.06 μm, 1.30 and 1.55 μm center wavelengths by propagating sech2 picosecond optical pulses with 1.0 ps pulse width at a full width at half maximum.

Indium Tin Oxide optical access for magnetic tunnel junctions in hybrid spintronic–photonic circuits

The all-optical magnetization reversal of magnetic layers, by picosecond optical pulses, is of particular interest as it shows the potential for energy-efficient and fast magnetic tunnel junction (MTJ) elements. This approach requires memory elements that are optically and electronically accessible, for optical writing and electronic read-out. In this paper, we propose the integration of indium tin oxide (ITO) as a transparent conducting electrode for magnetic tunnel junctions in integrated spintronic–photonic circuits. To provide light with sufficient energy to the MTJ free layer and allow electrical read-out of the MTJ state, we successfully integrated indium tin oxide as a top transparent electrode. The study shows that ITO film deposition by physical vapor deposition with conditions such as high source power and low O2 flow achieves smooth and conductive thin films. Increase in grain size was associated with low resistivity. Deposition of 150 nm ITO at 300 W, O2 flow of 1 sccm and 8.10−3 mbar vacuum pressure results in 4.8 × 10−4 Ω.cm resistivity and up to 80% transmittance at 800 nm wavelength. The patterning of ITO using CH4/H2 chemistry in a reactive ion etch process was investigated showing almost vertical sidewalls for diameters down to 50 nm. The ITO based process flow was compared to a standard magnetic tunnel junctions fabrication process flow based on Ta hard mask. Electrical measurements validate that the proposed process based on ITO results in properties equivalent to the standard process. We also show electrical results of magnetic tunnel junctions having all-optical switching top electrode fabricated with ITO for optical access. The developed ITO process flow shows very promising initial results and provides a way to fabricate these new devices to integrate all-optical switching magnetic tunnel junctions with electronic and photonic elements.

Dynamic modeling of the birefringence effects induced in semiconductor optical amplifier for all-optical telecommunication systems

The semiconductor optical amplifiers (SOA) are all-optical multifunctional devices. The improvement of their performance will, therefore, be of great importance for modern optical telecommunication systems. We propose in this article to develop a dynamic model that enables us to simulate the dynamic behavior of SOA's birefringence effects. The determination of a numerical model is a multidisciplinary activity that needs engineering skills, optimization and physics. This numerical model enables to describe the propagation of a picosecond optical pulse passing through the SOA and takes into account its polarization and the phenomenon of energy coupling between the eigenmodes of SOA (TE mode and TM mode). In this paper, we will, first of all describe the numerical algorithm of our model, and then we will propose to make a dynamic characterization of the effect of the nonlinear polarization rotation in the SOA, which will allow us to study the all-optical logic gates as well as all the other digital components based on the nonlinear effect of birefringence in SOA.

Enhanced Kerr Nonlinearity and Nonlinear Figure of Merit in Silicon Nanowires Integrated with 2D Graphene Oxide Films.

Layered two-dimensional (2D) graphene oxide (GO) films are integrated with silicon-on-insulator (SOI) nanowire waveguides to experimentally demonstrate an enhanced Kerr nonlinearity, observed through self-phase modulation (SPM). The GO films are integrated with SOI nanowires using a large-area, transfer-free, layer-by-layer coating method that yields precise control of the film thickness. The film placement and coating length are controlled by opening windows in the silica cladding of the SOI nanowires. Owing to the strong mode overlap between the SOI nanowires and the highly nonlinear GO films, the Kerr nonlinearity of the hybrid waveguides is significantly enhanced. Detailed SPM measurements using picosecond optical pulses show significant spectral broadening enhancement for SOI nanowires coated with 2.2 mm long films of 1-3 layers of GO and 0.4 mm long films with 5-20 layers of GO. By fitting the experimental results with theory, the dependence of GO's Kerr nonlinearity on layer number and pulse energy is obtained, showing interesting physical insights and trends of the layered GO films from 2D monolayers to quasi bulk-like behavior. Finally, we show that by coating SOI nanowires with GO films, the effective nonlinear parameter of SOI nanowires is increased 16-fold, with the effective nonlinear figure of merit (FOM) increasing by about 20 times to FOM > 5. These results reveal the strong potential of using layered GO films to improve the Kerr nonlinear optical performance of silicon photonic devices.

High-speed infrared two-dimensional platinum diselenide photodetectors

Two-dimensional (2D) layered platinum diselenide (PtSe2) offers attractive optoelectronic properties including chemical stability in air, high electron mobility at room temperature, a non-zero thickness-dependent bandgap, and optical absorption that extends from visible to infrared wavelengths. We report the use of PtSe2 for high-speed photodetectors. In this work, we experimentally demonstrated that chemical-vapor-deposition-grown PtSe2 thin-film photodetectors can measure picosecond optical pulses. Finger-like electrodes are used to excite a plasmonic mode to enhance light absorption of the devices. The measured bandwidth of this device was ∼4.5 GHz. An improved bandwidth of about 17 GHz was achieved in an alternative electrode design which has smaller capacitance. The photodetector was stable, and maintained similar performance after several months' exposure to air. The PtSe2 is an attractive 2D material for high-speed optoelectronic devices and is a viable alternative to graphene and black phosphorus, potentially offering even better performance in certain applications because of its longer term stability and non-zero bandgap.

Microneedle structuring of Si(111) by irradiation with picosecond optical vortex pulses

We report on comparative studies of the optical vortex-induced structures of both Si(100) and Si(111) by irradiation with a single optical vortex picosecond pulse. Furthermore, we address the effects of the total angular momentum (TAM) on the optical vortex-induced microneedle. Si(111) allows for the faster growth of the microneedle, although this impacts the monocrystallization of the needle. The TAM then forces the melted silicon to spin axially, thereby yielding an efficient accumulation of melted silicon on the substrate for microneedle formation. These results provide new fundamental insights into the interactions between optical vortex fields and irradiated materials.