GHz Repetition Frequency Research Articles

171st-order harmonic soliton erbium-doped fiber laser based on 2H-MoTe2 saturable absorber

We have demonstrated a high order harmonic mode-locked erbium-doped fiber laser by utilizing 2H-MoTe2 film as a saturable absorber (SA). The SA is synthesized by depositing 2H-MoTe2 film on a D-shaped fiber. The nonlinear optical properties of the 2H-MoTe2 SA are characterized, showing a modulation depth of 14.7% and a saturation intensity of 3 GW cm−2. Through optimizing the pump power and intra-cavity polarization state, a 171st-order harmonic soliton at 0.9 GHz repetition frequency with a pulse width of 1.06 ps was obtained. The fundamentally mode-locked pulse train had a pulse width of 1.03 ps and a repetition rate of 5.33 MHz. To the best of our knowledge, the 171st-order harmonic soliton is the highest operating repetition frequency that has ever been demonstrated in a 2H-MoTe2 SA mode locked fiber laser. The results indicate the potential of 2H-MoTe2 SA at high repetition rates regimes, which could benefit for future possible application.

High-power, gigahertz repetition frequency self-mode-locked Ho:GdVO4 laser resonantly pumped by a Tm-doped fiber laser.

A self-mode-locked Ho:GdVO4 laser with the GHz pulse repetition frequency oscillation near 2.06 µm was demonstrated for the first time to our knowledge. The output performances of the self-mode-locked Ho:GdVO4 laser were investigated for a few output coupler transmittances at the pulse repetition frequency of 1.89 GHz. At the incident pump power of 8.12 W, the maximum average output power was as high as 2.28 W, corresponding to the slope efficiency and optical-to-optical efficiency of 36.3% and 28.1%, respectively. This is the maximum average output for the 2 µm self-mode-locked solid-state laser with a GHz pulse repetition frequency. This work provides a new way for generating an efficient and a high-power ultrafast pulse laser with a GHz repetition frequency in the 2 µm wave band.

Continuous GHz femtosecond laser interacting with aluminum film: Simulation and experiment

GHz femtosecond laser has attracted more research interest due to the so-called high-efficiency cold ablation effect. In this study, behavior of continuous GHz (cGHz), i.e., GHz repetition frequency femtosecond laser with no burst mode, interacting with aluminum (Al) film has been investigated numerically and experimentally. For this purpose, an axisymmetric two-temperature model was used, accounting for the thermodynamical evolution of Al film. Laser irradiating Al film experiments were also carried out simultaneously. The calculated temperature field evolution was in good agreement with the observed experimental results. Effects of laser fluence and scanning speed on morphology, area, height, and volume of the residual Al film were then sequentially studied. Interestingly to see, for this cGHz femtosecond laser source, melting and re-solidification lead to the material removal under low laser fluence, say, ≤0.0337 J/cm2 in this study. For the whole Al film, with laser fluence increasing, the outmost lattice evaporation and beneath lattice melting occur together, both responsible for material removal and morphology variation. Finally, a potentially beneficial GHz femtosecond laser mode for high-quality microfabrication is proposed.

A 1.25-GHz multi-amplitude modulator driver in 0.18 μm SiGe BiCOMOS technology for high speed quantum key distribution.

Quantum key distribution (QKD) research has yielded highly fruitful results and is currently undergoing an industrialization transformation. In QKD systems, electro-optic modulators are typically employed to prepare the required quantum states. While various QKD systems operating at GHz repetition frequency have demonstrated exceptional performance, they predominantly rely on instruments or printed circuit boards to fulfill the driving circuit function of the electro-optic modulator. Consequently, these systems tend to be complex with low integration levels. To address this challenge, we have introduced a modulator driver integrated circuit in 0.18 µm SiGe BiCMOS technology. The circuit can generate multiple-level driving signals with a clock frequency of 1.25GHz and a rising edge of ∼50ps. Each voltage amplitude can be independently adjusted, ensuring the precise preparation of quantum states. The measured signal-to-noise ratio was more than 17 dB, resulting in a low quantum bit error rate of 0.24% in our polarization-encoding system. This work will contribute to the advancement of QKD system integration and promote the industrialization process in this field.

Gigahertz femtosecond laser-by a novel asymmetric one-dimensional photonic crystal saturable absorber device with defect layer

Abstract High repetition frequency (HRF) ultrashort pulse fiber laser has been widely used in laser cold processing. The technical solutions such as short cavity length fiber laser have been proposed to achieve HRF ultrashort pulse output recently. However, the application of material-based saturable absorbers in this field has been astricted due to the low modulation depth, low damage resistance threshold, and high saturation fluence. Here, we designed a one-dimensional asymmetric photonic crystal with defect layer (1D-APCDL) as a novel saturable absorber, where the defect layer is Bi1.6Sb0.4Te3 with high modulation depth. The harmonic pulse with 3.82 GHz repetition frequency is achieved at the wavelength of 1562 nm, which is the highest repetition frequency of the topological insulator-based ring fiber laser so far to the best of our knowledge. The research provides a new saturable absorber solution, and provides a new idea for the application of material-based nonlinear optical chip in high-repetition frequency ultrashort pulse fiber lasers.

Numerical Investigation and Design of Electrically-Pumped Self-Pulsing Fano Laser Based on III-V/Silicon Integration

A self-pulsing III-V/silicon laser is designed based on the Fano resonance between a bus-waveguide and a micro-ring resonator, partially covered by the graphene as a nonlinear saturable absorption component. The Fano reflector etched on the straight waveguide is used as one of the cavity mirrors in the coupling region to work with the graphene induced loss and nonlinearity to achieve pulsed lasing in GHz repetition frequency. The detailed lasing characteristics are studied numerically by using the rate equation and finite-difference time-domain (FDTD) simulations. The results show that the CMOS compatible hybrid laser can generate picosecond pulses with repetition rate at 1~3.12 GHz, which increases linearly with the injection current.

Compact green Ti:sapphire astro-comb with a 43 GHz repetition frequency

A compact green astro-comb with a 43 GHz repetition rate is developed based on a Ti:sapphire optical frequency comb (OFC) and a mode-selecting cavity. The OFC’s large repetition rate of 1.6 GHz eases the requirements for the mode-selecting cavity. Unnecessary frequency modes of the OFC are suppressed down to 5 × 10 − 4 at 535–550 nm using a single mode-selecting cavity with 70 MHz linewidth. The radial velocity precision σ ∼ 1.4 m / s is achieved at the high dispersion echelle spectrograph for the Okayama 188 cm telescope of the National Astronomical Observatory of Japan using our astro-comb. With further improvements of the mode-selecting cavity and removal of fiber modal noises, our system will provide a simple, compact, and precise astro-comb setup in the visible wavelength region.

A real-time three-dimensional coherent ladar demonstration: System structure, imaging processing, and experiment result

A new real-time, high-precision three-dimensional (3D) laser radar with a coherent system is presented. A self-designed arbitrary waveform generator (AWG), an electro-optic modulator, and an optical filter are proposed to generation a linear frequency modulated continuous waveform (FMCW) with a bandwidth of 2.4 GHz and pulse repetition frequency (PRF) of 100kHz. The heterodyne coherent detection and Micro-Electro-Mechanical System (MEMS) scanner are implemented with high sensitivity and fast 3D imaging. At the same time, multi-phase FFT algorithm is proposed to realize the frequency calculation with real-time. In this paper, we present the system structure, signal processing, and the experimental results in detail. The system achieves static 3D target and dynamic target imaging verification, and the experiment result validates the performance of system for real-time 3D imaging. It acquires 3D imaging at 40 frames per second (fps), which can satisfy the demand of high imaging speed requirements for special situation.

Recent Advances in InAs Quantum Dot Lasers Grown on On‐Axis (001) Silicon by Molecular Beam Epitaxy

Recent advances in InAs quantum dot (QD) lasers epitaxially grown on on-axis (001) silicon are reported. Fabry-Perot QD lasers show a CW threshold current of 4.8 mA at 20 °C, extrapolated laser lifetimes more than 10 million hours when aged at 35 °C, NRZ direct modulation up to 12 Gbps, and low linewidth enhancement factor of ≈0.1. Ultra-small microring QD lasers reveal a CW threshold of 0.5 mA and single-section mode-locked QD lasers demonstrate 490 fs ultra-short pulses at a 31 GHz repetition frequency. Possible ways to grow QD lasers on Si without misfit dislocations in active region are considered in order to further enhance reliability of QD Si lasers at high aging temperature and aging current density.

Inverse synthetic aperture LADAR demonstration: system structure, imaging processing, and experiment result.

A long-distance inverse synthetic aperture LADAR (ISAL) imaging experiment outdoors over 1km for cooperative targets is demonstrated, which gets a two-dimensional high-resolution image with resolution exceeding 2.5cm. The system utilizes an electro-optic in-phase and quadrature modulator to output a linear frequency-modulated continuous waveform (LFMCW) with a bandwidth of 6GHz and pulse repetition frequency (PRF) of 16.7KHz. For the problem of the coherence of the laser, the effects of the coherent processing interval (CPI) and time delay of the local oscillator (LO) on the coherence are discussed. The fiber delay line is set and the CPI is reduced to lower the requirement of the frequency stability of the laser source. The images are formed by two-dimensional Fourier transform and joint time-frequency transform methods, respectively. In this paper, we present the system structure, imaging processing, and the experiment result in detail. The experiment result validates the performance of our system for ISAL imaging.

High dynamic range single channel sampling of wideband RF signals using ultra‐fast nanoscale photoconductive switching

This Letter reports on new experimental high dynamic range sub-sampling performances obtained from nanoscale microwave photoconductive switches operating under a 0.8 µm wavelength pulsed illumination. Experimental results have been performed on different samples benefiting of a low temperature grown Gallium Arsenide absorbing layer on GaAs substrate, coplanar microwave electrode profile optimisation, and the use of an ultra-low noise jitter optical source delivering optical pulses of 1 to10 ps pulse width at a 2 GHz repetition frequency at 0.8 µm optical wavelength. Thanks to carrier lifetime tunability achievement from 1 to 20 ps, in association with a carrier mobility of 3900 cm²/V.s, experimental demonstrations of 54 and 45 dB signal-to-noise ratio microwave signal sampling for signals at 5,76 and 20 GHz frequency bandwidth respectively confirms submicron devices functionality as a new class of single channel photonic analogue to digital converters.

Impact of Coulomb Scattering on the Ultrafast Gain Recovery in InGaAs Quantum Dots

The application of quantum dot (QD) semiconductor optical amplifiers (SOAs) in above 100-Gbit Ethernet networks demands an ultrafast gain recovery on time scales similar to that of the input pulse approximately 100 GHz repetition frequency. Microscopic scattering processes have to act at shortest possible time scales and mechanisms speeding up the Coulomb scattering have to be explored, controlled, and exploited. We present a microscopic description of the gain recovery by coupled polarization- and population dynamics in a thermal nonequilibrium situation going beyond rate-equation models and discuss the limitations of Coulomb scattering between 0D and 2D-confined quantum states. An experiment is designed which demonstrates the control of gain recovery for THz pulse trains in InGaAs QD-based SOAs under powerful electrical injection.

A passively mode-locked fiber laser at 1.54 μm with a fundamental repetition frequency reaching 2 GHz

We demonstrate a fundamentally mode-locked fiber laser with a repetition frequency in excess of 2 GHz at a central wavelength of 1.535 mum. Co-doped ytterbium-erbium fiber provides the gain medium for the laser, affording high gain per unit length, while a semiconductor saturable absorber mirror (SAM) provides the pulse shaping mechanism in a standing wave cavity. Results are shown confirming cw mode-locking for 1 GHz and 2 GHz repetition frequency systems. The response of the frequency comb output to pump power variations is shown to follow a single pole response. The timing jitter of a 540MHz repetition-rate laser has been suppressed to below 100 fs through phase-lead compensated feedback to the pump power. Alternatively, a single comb line of a 850MHz repetition-rate laser has been phase-locked to a narrow linewidth cw laser with an in-loop phase jitter of 0.06 rad(2). The laser design is compatible with low-noise oscillator applications.

45 GHz self-pulsation with narrow linewidth in quantum dot Fabry-Perot semiconductor lasers at 1.5 µm

Self-pulsation at 45 GHz repetition frequency has been demonstrated in 1.5 µm monolithic single-section quantum dot Fabry-Perot semiconductor lasers without saturable absorber. The mode-beating exhibits a narrow linewidth below 100 kHz, demonstrating high phase correlation between these modes. Such modelocked lasers open ways to low timing-jitter components for clock recovery or millimetre-wave generation in wireless transmission applications.

Red picosecond pulses generated by frequency doubling a Raman amplified widely tunable 1.3 µm fiber ring laser

We generated 0.66 microm picosecond pulses by second-harmonic generation of the Raman amplified output of a 1.3 microm actively mode-locked fiber ring laser in a periodically poled potassium titanyl phosphate (PPKTP) waveguide. The ring laser produced 9 ps pulses at a 20 GHz repetition frequency, was tunable over 1284-1330 nm, and was based on a semiconductor optical amplifier and a Mach-Zehnder amplitude modulator. The Raman amplifier served both to amplify the ring laser and to compress the pulses as solitons. The spectral flexibility of the amplifiers and the modulator should enable similar configurations to be made at other wavelengths and facilitate efficient frequency doubling in waveguides to other visible wavelengths.

All-optical actively modelocked fibre ring laser based on cross-gain modulation in SOA

A novel actively modelocked fibre ring laser based on cross-gain modulation in a semiconductor optical amplifier (SOA) employed as both the gain medium and modelocking element has been demonstrated. Stable uniform pulse trains with pulse-widths about 21 ps at 5 GHz repetition frequency were obtained. The entire laser was operated in the optical domain with a large tuning range that could probably span the whole gain region of the gain medium employed.

Characterization of a Rydberg atom-based streak camera operating in synchroscan mode

A streak camera that operates in synchroscan mode has been developed with a spectral response throughout the infrared. A gas-phase sample of Rydberg atoms is used as a photocathode. This compact device possesses 5 ps time resolution and can be used with a total infrared energy of about 1 nJ, or 10 −7 of the total macropulse energy of the FELIX free electron laser. This combination of characteristics makes it not only an attractive device for use in a variety of infrared experiments, but also a powerful tool for the study of photo-induced electron emission in atomic systems. As an example, a Rydberg-atom based electron gun which produces about 20 pulses of electrons at a 70 GHz repetition frequency has been characterized using this synchroscan streak camera.

High-repetition frequency pulse generation at 102GHzusing modelocked lasers integrated withelectroabsorption modulators

The authors demonstrate active modelocking at a 102 GHz repetition frequency using a modelocked laser integrated with an electroabsorption modulator. Pulse generation at 2.4 ps is performed by half frequency (51 GHz) modulation. A low timing jitter of 0.33 ps is measured using a mixing technique.

Active mode locking at 50 GHz repetition frequency by half-frequency modulation of monolithic semiconductor lasers integrated with electroabsorption modulators

Active mode locking achieved at a 50 GHz repetition frequency by modulation at half (25 GHz) the cavity resonance frequency using a monolithic mode-locked InGaAsP laser integrated with an electroabsorption modulator is described. A pulse width of around 3 ps and a high suppression ratio of more than 33 dB of the intensity modulation at the driving frequency are obtained.

Control of spiky emission from a two-component heterojunction laser

A machine experiment was used to analyze the operating regimes of a two-component heterojunction laser in the range of unstable states under hard switching-on conditions. The dependences of the characteristics of a process on the currents in the isolated parts of the laser were determined. Calculations and experiments revealed a region of self-modulation bistability. The application of an external synchronizing signal resulted in generation of exactly periodic continuous trains of spikes of about 100 psec duration and 0.1–1.2 GHz repetition frequency. The promising nature of the use of such trains in determination of the pass band of fast-response photodetectors was demonstrated.