Transform-limited Pulse Train Research Articles

1 GHz fundamental repetition rate thulium-doped all-polarization maintaining modelocked fiber laser

Abstract In this work, we present a passively modelocked all-fiber laser that fully retains polarization with a fundamental repetition rate of 1 GHz. The whole cavity consists of a 106-mm-long highly-Tm-doped polarization-maintaining fiber with a dichroic mirror on one end and a semiconductor saturable absorber mirror on the other. We experimentally characterized the output of this laser, which emits a train of transform-limited light pulses with a temporal width of 520 fs at the central optical wavelength of 1.96 μm. The high stability of this laser was also experimentally verified. Together with this, a detailed theoretical model was developed, confirming the experimental results.

Mode-Locked Topological Insulator Laser Utilizing Synthetic Dimensions

We propose a system that exploits the fundamental features of topological photonics and synthetic dimensions to force many semiconductor laser resonators to synchronize, mutually lock, and under suitable modulation emit a train of transform-limited mode-locked pulses. These lasers exploit the Floquet topological edge states in a 1D array of ring resonators, which corresponds to a 2D topological system with one spatial dimension and one synthetic frequency dimension. We show that the lasing state of the multi-element laser system possesses the distinct characteristics of spatial topological edge states while exhibiting topologically protected transport. The topological synthetic-space edge mode imposes a constant-phase difference between the multi-frequency modes on the edges, and together with modulation of the individual elements forces the ensemble of resonators to mode-lock and emit short pulses, robust to disorder in the multi-resonator system. Our results offer a proof-of-concept mechanism to actively mode-lock a laser diode array of many lasing elements, which is otherwise extremely difficult due to the presence of many spatial modes of the array. The topological synthetic-space concepts proposed here offer an avenue to overcome this major technological challenge, and open new opportunities in laser physics.

Continuous repetition rate tuning from 960 MHz to 1.72 GHz of a sub-300 femtosecond mode-locked semiconductor disk laser

Dataset supports: Chen Sverre, T. et al (2018). Continuous repetition rate tuning from 960 MHz to 1.72 GHz of a sub-300 femtosecond mode-locked semiconductor disk laser. Applied Physics Letters, 113(16), [161106].Vertical External Cavity Surface Emitting semiconductor Lasers rely on Semiconductor Saturable Absorbing Mirrors for mode-locking, allowing laser cavities to be designed far from stability limits. We have harnessed this feature to study repetition rate tunability. The cavity element separations were determined by a coded cavity design protocol based on cavity round trip matrix calculations. We produced a sub-300-fs near transform-limited pulse train with a repetition rate of 0.96 MHz - 1.72 GHz, at 1035 nm and average power of 50 mW.

47-fs Kerr-lens mode-locked Cr:ZnSe laser with high spectral purity.

We report on a room-temperature Kerr-lens mode-locked Cr:ZnSe femtosecond laser operating at around 2.4 μm emission wavelength. Self-starting nearly transform-limited pulse trains with a minimum duration of 47 fs, corresponding to six optical cycles, and average output power of 0.25 W are obtained with repetition frequencies in the range from 140 to 300 MHz. The femtosecond pulse train is characterized by high-spectral purity and low time jitter.

Synchronized 4 × 12 GHz hybrid harmonically mode-locked semiconductor laser based on AWG.

We report a monolithically integrated synchronized four wavelength channel mode-locked semiconductor laser chip based on arrayed waveguide grating and fabricated in the InP material system. Device fabrication was completed in a multiproject wafer foundry run on the Joint European Platform for Photonic Integration of Components and Circuits. The integrated photonic chip demonstrated 5th harmonic electrical hybrid mode-locking operation with four 400 GHz spacing wavelength channels and synchronized to a 12.7 GHz RF clock, for nearly transform-limited optical pulse trains from a single output waveguide. A low timing jitter of 0.349 ps, and RF frequency locking range of ~50 MHz were also achieved.

Femtosecond Soliton Pulse Generation Using Evanescent Field Interaction Through Tungsten Disulfide (WS <sub>2</sub>) Film

We investigated nonlinear optical characteristics of Tungsten disulfide (WS2) films and experimentally demonstrated their high potential for application as nonlinear saturable absorbers in passively mode-locked fiber lasers. Side polished fiber (SPF) was fabricated and WS2 film was overlaid to provide an efficient evanescent field interaction. The WS2 film was prepared using two methods: liquid phase exfoliation to form few-layer nano-sheets, and chemical vapor deposition (CVD) to grow uniform multilayer WS2 on a SiO2 substrate. Two SPF saturable absorbers were prepared by either spin coating WS2 solution or lifting off the multilayer CVD WS2 on SPF. An all-fiber ring cavity was built and the WS2 film overlaid on SPF was employed as a mode locker along with Er-doped fiber as a gain medium. Using the spin-coated WS2 SPF, stable soliton-like pulses were generated with a spectral width of 5.6 nm and 467 fs pulse duration. The fiber laser cavity containing CVD WS2 SPF generated a transform-limited soliton pulse train with a spectral width of 8.23 nm and a pulse duration of 332 fs. Our study confirmed a high potential of WS2 film as a novel 2-D nonlinear optical material for laser applications.

Energy-Efficient Optical Pulse Multiplication and Shaping Based on a Triply Sampled Filter Utilizing a Fiber Bragg Grating

An efficient method for simultaneous optical pulse multiplication and shaping is first proposed that is based on a triply sampled spectral filter utilizing a fiber Bragg grating. The proposed method enables efficient generation of an optical pulse train with a large multiplication factor and an arbitrary intensity profile. As examples, pulse trains with a repetition rate of 225 GHz and either a flat-top or triangular pulse waveform are numerically demonstrated, generated from a 1-GHz transform-limited Gaussian pulse train.

Mode locking at terahertz frequencies using a distributed Bragg reflector laser with a sampled grating

We present a highly reproducible method of producing terahertz (THz) optical pulses using a class of mode-locked AlGaInAs/InP laser operating in the 1.55 μm wavelength range. The device uses a sample grating distributed Bragg reflector to provide strong frequency selectivity at the mode-locked frequency while the distributed reflectors relax the fabrication tolerances and ensure the cavity can self adjust to being an integral number of mode-locked periods in length. The measured devices provide nearly transform-limited pulse trains at 640 GHz or 1.28 THz with a high degree of controllability and operate with consistent performance over a wide range of drive conditions. Being low cost and compact sources of THz radiation, these lasers will open up many applications, including systems for high-speed optical communication and THz imaging.

Passive mode locking of an in-band-pumped Ho:YLiF_4 laser at 206 μm

We demonstrate the passive mode-locking operation of an in-band-pumped Ho:YLiF(4) laser at 2.06 μm using a semiconductor saturable absorber mirror based on InGaAsSb quantum wells. A transform-limited pulse train with minimum duration of 1.1 ps and average power of 0.58 W has been obtained at a repetition frequency of 122 MHz. A maximum output power of 1.7 W has been generated with a corresponding pulse duration of 1.9 ps.

Mode locking of an erbium-doped fiber laser with intra-cavity polarization modulation

Erbium-doped fiber lasers are normally actively mode-locked through amplitude modulation or phase modulation. In this paper, we demonstrate that the laser can also be mode-locked by employing polarization modulation with a polarization-dependent cavity loss. We obtain a nearly transform-limited mode-locked pulse train at 10 GHz repetition rate with timing jitter as low as 164 fs. The timing jitter is only limited by the timing jitter of the driving signal.

High-repetition-rate pulse generation using dual-mode self-injection locking in a Fabry-Perot laser diode

A novel and simple method is presented to generate a tunable high-repetition-rate pulse train based on dual-mode self-injection locking of a Fabry-Perot laser diode (FP-LD). Two fiber Bragg gratings (FBGs) are used in the experiment as feedback components. The two self-injection-locked modes evolve into a high-power, high-repetition-rate pulse train through the interplay between self-phase modulation and anomalous dispersion in a highly nonlinear fiber. A 139.6-GHz transform-limited pulse train with a peak power of 120 mW is generated. The pulsewidth is 1.7 ps, and the time-bandwidth product is 0.31. The repetition rate can be tuned by tuning the Bragg wavelengths of one of the two or both FBGs to coincide with other FP-LD modes. The output pulse is stable.

CW and femtosecond operation of a diode-pumped Yb:BaY_2F_8 laser

We report for the first time on laser action of a diode-pumped Yb:BaY(2)F(8) crystal. Both CW and femtosecond operations have been demonstrated at room-temperature conditions. A maximum output power of 0.56 W, a slope efficiency of 34%, and a tunability range from 1013 to 1067 nm have been obtained in CW regime. Transform-limited pulse trains with a minimum duration of 275 fs, an average power of 40 mW, and a repetition rate of 83 MHz have been achieved in a passive mode-locked regime using a semiconductor saturable absorber mirror.

Dynamic Chirp Control and Pulse Compression for Attosecond High-Order Harmonic Emission

We propose a scheme to compensate dynamically the intrinsic chirp of the attosecond harmonic pulses. By adding a weak second harmonic laser field to the driving laser field, the chirp compensation can be varied from the negative to the positive continuously by simply adjusting the relative time delay between the two-color pulses. Using this technique, the compensation of the negative chirp in harmonic emission is demonstrated experimentally for the first time and the nearly transform-limited attosecond pulse trains are obtained.

Diode-pumped Yb^3+:KYF_4 femtosecond laser

Passive mode locking of a diode-pumped Yb(3+):KYF(4) laser is demonstrated using a semiconductor saturable absorber mirror. A high-stability, transform-limited pulse train with a repetition rate of 57 MHz is generated. Solitonlike pulses with maximum average output power of 250 mW, minimum pulse duration of 170 fs, and rms time jitter of 360 fs were obtained.

80-GHz pulse generation from a repetition-rate-doubled FM mode-locking fiber laser

We demonstrated a simple method to realize repetition-rate-doubling in a frequency modulation (FM) mode-locking fiber laser. The mode-locking of the laser is based on converting FM modulation to amplitude modulation by using a phase-modulated optical fiber loop mirror, which is formed by a phase modulator and an additional coupler only. With 40-GHz modulation, we obtained 80-GHz 1.74-ps transform-limited pulse train in the experiments.

Single- and dual-wavelength pulse train generation in frequency-modulated Er–Yb lasers up to [formula omitted

In this paper we present recent results obtained on the generation of ultra-high repetition rate optical pulse trains at 1.5 μm in asynchronously frequency-modulated Er–Yb : glass lasers. Nearly transform-limited pulse trains at either single or dual carrier wavelength with repetition rates up to ∼20 GHz are generated by means of an external fiber Bragg grating. These pulse trains are of great potential interest for soliton-based optical transmission systems.

Generation of a 160-GHz transform-limited pedestal-free pulse train through multiwave mixing compression of a dual-frequency beat signal

We report the experimental generation of a 160-GHz picosecond pulse train at 1550 nm, using multiple four-wave mixing temporal compression of an initial dual-frequency beat signal in the anomalous-dispersion regime of a nonzero dispersion-shifted fiber. Complete intensity and phase characterizations of the pulse train were carried out by means of a frequency-resolved optical gating technique, showing that 1.27-ps transform-limited pedestal-free Gaussian pulses were generated.

Generation of a 64-GHz, 33-ps transform-limited pulse train from a fiber laser employing higher-order frequency-modulated mode locking

We demonstrate the generation of optical pulses at a repetition rate of 64 GHz directly from a frequency-modulated (FM) mode-locked fiber laser. This is achieved by phase modulation at 16 GHz and by initiating of higher-order FM mode locking by use of an intracavity Fabry-Perot filter with a free spectral range of 64 GHz. This process yielded transform-limited pulses with a width of 3.3 ps. We investigated the operating characteristics of the laser and compared them with the characteristics that were predicted theoretically.

Dynamic analysis of mode-locked sampled-grating distributed Bragg reflector laser diodes

A mode-locked sampled-grating distributed-Bragg-reflector (SGDBR) laser diode for generating a train of light pulses at terahertz repetition rates is proposed with a numerical analysis based on a time-domain large-signal model. The device consists of three parts: the saturable absorber section which serves as a mode-locker, the gain section as an amplifier, and the SGDBR as a spectrum filter. It is predicted that spectrum filtering of the SGDBR along with passive mode locking due to the saturable absorber is effective in generating a train of transform-limited mode-locked pulses at a high repetition rate.

5-GHz repetition-rate dual-wavelength pulse-train generation from an intracavity frequency-modulated Er–Yb:glass laser

We report the experimental demonstration of nearly transform-limited dual-wavelength pulse trains at a 5-GHz repetition rate that were generated by spectral filtering of an intracavity 2.5-GHz frequency-modulated Er-Yb bulk-glass laser operating at the 1533-nm wavelength. Highly stable dual-wavelength pulse trains with approximately 165-GHz frequency separation, approximately 48-ps pulse duration, and approximately 1-mW average single-mode fiber-coupled power were obtained.