Peak Pump Power Research Articles

Experimental Demonstration of High-Efficiency Harmonic Generation in Photonic Moiré Superlattice Microcavities.

Integrated photonic microcavities have demonstrated powerful enhancement of nonlinear effects, but they face a challenge in achieving critical coupling for sufficient use of incident pump power. In this work, we first experimentally demonstrate that highly efficient third-harmonic generation (THG) and detectable second-harmonic generation (SHG) can be produced from high-Q photonic moiré superlattice microcavities, where a critical coupling condition can be achieved via selecting a magic angle. Furthermore, at the magic angle of 13.17°, critical coupling is satisfied, resulting in a normalized THG conversion efficiency of 136%/W2 at a relatively low peak pump power of 6.8 MW/cm2, which is 3 orders of magnitude higher than the best results reported previously. Our work shows the power of photonic moiré superlattices in enhancing nonlinear optical performances through flexible and feasible engineering resonant modes, which can be applied in integrated frequency conversion and generation of quantum light sources.

Giant enhancement of third harmonic generation via guided mode resonances in notched silicon waveguides

We report a giant enhancement of the third harmonic generation (THG) at 343 nm by periodically notched silicon waveguide arrays supporting guided mode resonances (GMRs) at 1030 nm. Maximum efficiency of the third harmonic generation η = 7.71 × 10−5 is achieved with a peak pump power density of 5.31 GW/cm2. The enhancement factor of the THG from the GMR metasurface reaches up to 1.3 × 107 compared to a flat silicon film with the same thickness. This observation demonstrates a promising approach to design high-efficiency nonlinear optical metasurfaces.

Investigations of a 1018 nm gain-switched Yb-doped fiber oscillator.

In this paper, we investigate a 1018nm gain-switched ytterbium-doped fiber oscillator at a low repetition rate in terms of theory and experiment. Theoretically, a numerical model applicable to a 1018nm gain-switched ytterbium-doped fiber laser was established. The influence of the pump peak power and active fiber lengths on the 1018nm gain-switched ytterbium-doped fiber laser was numerically simulated. Experimentally, a compact 1018nm all-fiber-structured pulsed laser oscillator is constructed, in which a pulse width of 110ns and a single-pulse energy of 0.1mJ were obtained. Moreover, the experimental results are in agreement with the numerical simulation ones. To the best of our knowledge, this is the first time that gain-switching technology has been applied to 1018nm fiber lasers to generate nanosecond pulsed lasers. The model and experimental results can provide a reference for the engineering design of the same type of low repetition rate fiber lasers below the kilohertz level.

A π-polarized 1084 nm laser with pump pulse modulation based on Nd:MgO:LiNbO3 crystal

A π-polarized （π-pol） 1084 nm laser based on Nd:MgO:LiNbO3 crystal under modulation pulsed pumping mode was demonstrated. The anisotropic Nd:MgO:LiNbO3 slab crystal was end-pumped by a pulsed laser diode (LD) with a different duty cycle for experiments. The dual-wavelength fundamental laser emission range was effectively controlled within a certain pump peak power interval, and the unmatched polarized fundamental laser is completely suppressed when the duty cycle is 20 % and below. At a repetition frequency of 5 Hz and pulse width of 40 ms, the π-pol 1084 nm fundamental laser with a maximum average output power of 1.396 W in the whole pump range was obtained, and the single pulse energy was 279.2 mJ.

Raman amplification at 2.2 μm in silicon core fibers with prospects for extended mid-infrared source generation

Raman scattering provides a convenient mechanism to generate or amplify light at wavelengths where gain is not otherwise available. When combined with recent advancements in high-power fiber lasers that operate at wavelengths ~2 μm, great opportunities exist for Raman systems that extend operation further into the mid-infrared regime for applications such as gas sensing, spectroscopy, and biomedical analyses. Here, a thulium-doped fiber laser is used to demonstrate Raman emission and amplification from a highly nonlinear silicon core fiber (SCF) platform at wavelengths beyond 2 μm. The SCF has been tapered to obtain a micrometer-sized core diameter (~1.6 μm) over a length of 6 cm, with losses as low as 0.2 dB cm−1. A maximum on-off peak gain of 30.4 dB was obtained using 10 W of peak pump power at 1.99 μm, with simulations indicating that the gain could be increased to up to ~50 dB by extending the SCF length. Simulations also show that by exploiting the large Raman gain and extended mid-infrared transparency of the SCF, cascaded Raman processes could yield tunable systems with practical output powers across the 2–5 μm range.

High-power Nd:YLF four-level lasers with 68% slope efficiency.

Three laser resonators are demonstrated emitting at 1053nm and pumped at 797nm by volume Bragg grating-equipped diodes, achieving the highest reported efficiencies for Nd:YLF in a four-level system, to the best of our knowledge. A peak output power of 880W is achieved by pumping the crystal with a diode stack of 1.4kW of peak pump power.

Broadband optical wavelength conversion through four-wave mixing in W3-type AlGaAs photonic crystal waveguides

We realized a wide-band wavelength conversion method through four-wave mixing in W3-type AlGaAs photonic crystal waveguides. AlGaAs exhibits a large third-order nonlinearity. Furthermore, because of its large bandgap, two-photon absorption can be avoided in the 1550 nm range. A four-wave mixing efficiency of −7 dB was obtained for a pump peak power of 7 W. Furthermore, by utilizing the two even guided bands of the W3-type photonic crystal waveguide, a conversion bandwidth greater than 38 nm was achieved with a conversion efficiency of −22 dB.

Supercontinuum and frequency comb generations in the slot SiC waveguide with four zero-dispersion wavelengths

In this paper, a slot SiC waveguide with four zero-dispersion wavelengths (ZDWs) is proposed for the supercontinuum (SC) and frequency comb generations. The four ZDWs are located at 1089, 1656, 2222, and 3113 nm, respectively. The effects of the pump wavelength, peak power, pulse width, and waveguide length on the SC generation are discussed when the waveguide is pumped near the first ZDW and the third ZDW in the anomalous dispersion region, respectively. While pumping at 1300 and 2450 nm, a near-infrared SC covering from 873 to 2444 nm and a mid-infrared SC extending from 1349 to 4727 nm with good coherences are obtained, respectively. By utilizing a 50-pulses pump source at a repetition rate of 1 GHz, we also investigate the SC-based frequency comb generation.

Enhanced supercontinuum generation and dispersive wave emission in a silicon nitride waveguide pumped at 1550 nm telecom wavelength

We have numerically demonstrated that supercontinuum (SC) generation and dispersive wave (DW) emission in a silicon nitride waveguide can be actively controlled harnessing the weak continuous wave (CW) trigger scenario. The detailed simulation results suggest that the SC bandwidth, the temporal coherence, and the conversion of DWs are significantly enhanced after applying the CW trigger at the selected frequencies. These results are analyzed through the pump depletion occurring in the nonlinear propagation process. By tuning the CW trigger power, the CW power requirement for this approach is proved to be as low as 1 0 − 5 of the pump peak power. These numerical investigations provide valuable insight into obtaining the on-chip enhanced SC and DWs with an active control method.

1.14 kW peak power mid-infrared Er:YAG planar waveguide MOPA laser.

We report on a quasi-continuous Er:YAG planar waveguide laser operated at 2.94 µm based on the major oscillator power amplification configuration. With the total pump peak power of 32.01 kW, a maximum output peak power of 1.14 kW was obtained at the seed injection peak power of 184.4 W operated at 400µs, 40 Hz. Furthermore, the numerical simulation results indicate that better performance of the laser could be obtained with the higher injected seed laser power. To the best of our knowledge, this is the first experimental demonstration of 2.94 µm planar waveguide laser with an Er doped host material.

Quarter acoustic period pulse compression using stimulated Brillouin scattering in PF-5060.

The pulse duration of the near quarter-acoustic period (τa) is demonstrated in transient stimulated Brillouin scattering (SBS) pulse compression by the suppressing Stokes trailing-edge broadening at high intensities. A theoretical analysis reveals that the difficulty in attaining the transient compression limit is caused by the broadening of the Stokes trailing edge owing to insufficient pump depletion, and this undesirable phenomenon can be significantly suppressed by a high SBS gain coefficient. An average pulse duration of ∼1.05 τa was experimentally achieved in transient compression with a high-energy efficiency of over 30%. Benefiting from energy back conversion, compression below the transient SBS limit (< τa) also occurred when the pump peak power was increased to 150 MW.

Low pump power coherent supercontinuum generation in heavy metal oxide solid-core photonic crystal fibers infiltrated with carbon tetrachloride covering 930-2500 nm.

All-normal dispersion supercontinuum (ANDi SC) generation in a lead-bismuth-gallate glass solid-core photonic crystal fiber (PCF) with cladding air-holes infiltrated with carbon tetrachloride (CCl4) is experimentally investigated and numerically verified. The liquid infiltration results in additional degrees of freedom that are complimentary to conventional dispersion engineering techniques and that allow the design of soft-glass ANDi fibers with an exceptionally flat near-zero dispersion profile. The unique combination of high nonlinearity and low normal dispersion enables the generation of a coherent, low-noise SC covering 0.93-2.5 µm requiring only 12.5 kW of pump peak power delivered by a standard ultrafast erbium-fiber laser with 100 MHz pulse repetition rate (PRR). This is a much lower peak power level than has been previously required for the generation of ANDi SC with bandwidths exceeding one octave in silica- or soft-glass fibers. Our results show that liquid-composite fibers are a promising pathway for scaling the PRR of ANDi SC sources by making the concept accessible to pump lasers with hundreds of megahertz of gigahertz PRR that have limited peak power per pulse but are often required in applications such as high-speed nonlinear imaging, optical communications, or frequency metrology. Furthermore, due to the overlap of the SC with the major gain bands of many rare-earth fiber amplifiers, our source could serve as a coherent seed for low-noise ultrafast lasers operating in the short-wave infrared spectral region.

Role of energy transfer in concentrated Dy3+-doped fibers

Using high power quasi-cw pulse pumping, we show that energy transfer upconversion (ETU) processes in highly doped Dy3+ double clad ZBLAN fibers creates a pathway for significant excitation loss that clamps the gain. For a 4 mol.% Dy3+-doped fiber, we establish that the pump absorption is non-saturable up to a maximum launched (peak) pump power of 100 W. We propose that this arises from a co-operative three-ion ETU process. Additionally, the high power pulsed pumping of Tm3+, Dy3+-co-doped fiber produces laser relaxation spikes that appear after the pump pulse, suggesting that ETU dominates all other process during pumping.

4-Bit All-Optical Serial-to-Parallel Converter With Sub-dB/cm Delay Lines Based on Rib Waveguides

This paper extends our previous work on the microring resonator-type serial-to-parallel conversion scheme aimed for all-optical label processing on the silicon photonic platform. In the previously proposed scheme, the architecture of the delay lines was silicon wires. This resulted in considerable propagation loss, confining multibit operation of serial-to-parallel conversion to a label packet of 2 bits. However, during a practical application, propagation loss at the delay lines has to be improved to support label packets comprising of a greater number of bits. The purpose of this article is twofold. First, we confirm that propagation loss can be lowered to sub-dB/cm values by introducing rib waveguides via simulations and experiment. Second, we demonstrate multibit serial-to-parallel conversion on a 4-bit label “1101” by utilizing a cascaded microring resonator device of which the straight sections of the delay lines are of rib waveguide architecture. In order to focus on free-carrier dispersion effect of silicon during operation, we left out a temporal delay between the pump pulses and probe bits to be extracted. As a result, serial-to-parallel conversion was viable even at peak pump power levels as low as ∼100 mW. We hereby verify that the proposed serial-to-parallel conversion scheme incorporated with rib waveguide delay lines is a realistic solution in realizing a photonics-based solution to all-optical label processing.

Growth, spectroscopic properties and 1060 nm laser operation of Nd:GdPO4 crystal

A Nd:GdPO4 single crystal with dimensions of 31 × 13 × 10 mm3 was grown by the top-seeded solution method. Polarized absorption and fluorescence spectra of the crystal were measured at room temperature and analyzed based on the Judd-Ofelt theory. The effects of the energy transfer and energy migration processes on the fluorescence lifetime of the 4F3/2 multiplet of Nd3+ were discussed, as well as the concentration-dependent fluorescence quenching effect was also investigated. End-pumped by a quasi-continuous-wave 790 nm laser diode, a 1060 nm laser with a maximum output peak power of 1.12 W and a slope efficiency of 21.9% was obtained in a Nd:GdPO4 crystal at an absorbed pump peak power of 5.39 W.

Mid-infrared supercontinuum generation using low peak pump power in As38Se62 based chalcogenide photonic crystal fiber

A supercontinuum (SC) based chalcogenide As38Se62 PCF for broadband mid-infrared light source is numerically reported. For the computational studies, the design of the proposed structure is made up of three rings of air holes with circular and elliptical shapes. The proposed structure provides excellent nonlinear coefficient and dispersion optimization. For the analysis, the finite difference frequency domain (FDFD) method is employed. Due to the high nonlinear refractive index and optimizing design of As38Se62 chalcogenide glass, an effective mode area of 40.5972 μm2 is obtained. The dispersion characteristic of the proposed structure has a zero-dispersion wavelength at 3.89 μm. The nonlinear coefficient is 761 W-1km-1 at the wavelength of 4 μm. Dispersion is almost flat from 2 μm up to 10 μm. The supercontinuum spectrum calculated ranges from 2 μm to 9 μm. The presented structure is appropriate for medical imaging, optical coherence tomography and optical communications.

Application of Hollow-Core Photonic Crystal Fibers in Gas Raman Lasers Operating at 1.7 μm

A 1.7 μm pulsed laser plays an important role in bioimaging, gas detection, and so on. Fiber gas Raman lasers (FGRLs) based on hollow-core photonic crystal fibers (HC-PCFs) provide a novel and effective method for fiber lasers operating at 1.7 μm. Compared with traditional methods, FGRLs have more advantages in generating high-power 1.7 μm pulsed lasers. This paper reviews the studies of 1.7 μm FGRLs, briefly describes the principle and characteristics of HC-PCFs and gas-stimulated Raman scattering (SRS), and systematical characterizes 1.7 μm FGRLs in aspects of output spectral coverage, power-limiting factors, and a theoretical model. When the fiber length and pump power are constant, a relatively high gas pressure and appropriate pump peak power are the key to achieving high-power 1.7 μm Raman output. Furthermore, the development direction of 1.7 μm FGRLs is also explored.

Tellurium-oxide coated silicon-nitride hybrid waveguide for near-to-mid-IR supercontinuum generation: design and analysis

We report the design and numerical analysis of a tellurium-oxide coated silicon-nitride waveguide on a sapphire substrate for the generation of near-infrared to mid-infrared supercontinuum light. The hybrid waveguide structure is applicable for future on-chip photonic integrated circuits. We predict a supercontinuum spectrum that extends from 0.88 to 5.22 µm or 0.95 to 5.50 µm using a pump peak power of 10 kW at 1.55 µm (50 fs pulse-width) and 2 µm (200 fs pulse-width), respectively. To the best of our knowledge, this is the first analysis of the generation of supercontinuum light from hybrid tellurium-oxide coated silicon-nitride waveguide pumped in the normal dispersion region. Waveguides such as this could significantly expand the functionality of the future photonic integrated circuits.

Generation of supercontinuum and frequency comb in a nitrobenzene-core photonic crystal fiber with all-normal dispersion profile

In this paper, we design a nitrobenzene-core photonic crystal fiber (NC-PCF) with all-normal dispersion profile. The nonlinear coefficient of the designed NC-PCF at wavelength 1560 nm is as high as 1.43 W−1 m−1, which is 100 times larger than that of the traditional silica PCF. We investigate the influences of the pump center wavelength, pulse width, peak power, and fiber length on the supercontinuum (SC) generation. The highly coherent SC spanning from 1.0 to 2.3μm is generated when the pump pulses with the center wavelength of 1560 nm, peak power of 20 kW, and width of 120 fs are launched into the 3 cm long NC-PCF. Finally, the SC-based optical frequency comb is obtained by assuming a 50 pulse pump source at a repetition rate of 1 GHz.

Ring-shaped microstructured chalcogenide optical fiber for octave-spanning flat-top mid-infrared supercontinuum generation

Broadband flat-top mid-infrared supercontinuum (SC) generation in optical fibers is of great interest for many applications. Here, we designed a microstructured chalcogenide optical fiber composed of hexagonal rings. By optimizing the structure parameters, it is demonstrated that the fiber is characterized by an all-normal dispersion profile. Numerical simulation results show that the generated SC spectrum with intensity above − 3 d B ranges from 3450 nm to 8015 nm corresponding to more than one octave when the fiber is pumped with 150 fs pulses at 5 µm. By solving the generalized nonlinear Schrödinger equation, we investigated the influence of pump pulse parameters including pump wavelength, peak power, and pulse duration on the spectral broadening. The results turn out that the optimal pump wavelength is around 5 µm for obtaining SC spectra with sufficient flatness. High peak power and short duration enhance the spectral flatness and bandwidth. We also investigated SC generation in the optimized fiber pumped at 3 µm. The generated SC at − 6 d B level covers wavelength from 1970 to 4370 nm, corresponding to more than one octave.