Pulsed Pump Regime Research Articles

Kerr optical frequency comb generation using whispering-gallery-mode resonators in the pulsed-pump regime

Kerr comb generation is usually based on the nonlinear dynamics of the intracavity field in a whispering-gallery-mode resonator pumped by a continuous-wave laser. However, using a pulsed instead of a continuous-wave pump opens an alternative research avenue from both the theoretical and experimental viewpoints, as it permits us to tailor the spectral properties of ultrashort pulse trains with a single passive nonlinear element. In this article we study the dynamics of Kerr optical frequency combs when the whispering-gallery-mode resonator is pumped by a synchronous pulse train. We propose a model that is based on an extension of the Lugiato-Lefever equation, which accounts for both the pulsed nature of the pump and the mismatch between the free-spectral range of the resonator and the repetition rate of the pulse train. We lay a particular emphasis on the effect of pump-cavity desynchronization on the spectral shape of the output combs. The numerical simulations are successfully compared with experimental measurements where the optical pulses are generated via time-lens soliton compression, and the resonator is a millimeter-size magnesium fluoride resonator with a billion quality factor at the pump wavelength.

Continuous-wave laser diodes based on epitaxially integrated InGaAs/AlGaAs/GaAs heterostructures

We report the results of the development and investigation of the main characteristics of integrated laser emitters for the spectral range from 1040 to 1080 nm. These devices are fabricated using epitaxially integrated InGaAs/AlGaAs/GaAs heterostructures with one or two emitting regions, and measurements are performed in pulsed, quasi-continuous, and continuous-wave pump regimes. It is found that along with the obvious advantage of integrated emitters − an increase in the output optical power, they also have a significant limitation, which consists in increasing the amount of released heat. Despite this, it is shown that such integrated double laser diodes operate efficiently in the continuous-wave generation regime (P max ∼ 6 W), demonstrating a 1.7-fold increase in the differential quantum efficiency as compared to single laser diodes.

Si-rich Si nitride waveguides for optical transmissions and toward wavelength conversion around 2 μm.

We show that subwavelength Si-rich nitride waveguides efficiently sustain high-speed transmissions at 2 μm. We report the transmission of a 10 Gbit/s signal over 3.5 cm with negligible power penalty. Parametric conversion in the pulsed pump regime is also demonstrated using the same waveguide structure with an efficiency as high as -18 dB.

Silicon Waveguides for High-Speed Optical Transmissions and Parametric Conversion Around 2 $~\mu$ m

We show that single-mode Si waveguides efficiently sustain high-speed transmissions at 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$~\mu$ </tex-math></inline-formula> m. We report the transmission of a 10-Gb/s signal over 7 cm with a power penalty below 1 dB. Parametric conversion in the continuous-wave regime is also demonstrated using the same waveguide structure with a conversion window over 70 nm and an efficiency as high as −25 dB that can be further increased in the pulsed pump regime.

Design of atomic clock cavity based on a loop-gap geometry and modified boundary conditions

In this study, we investigate a concept that can be used to improve the magnetic field homogeneity in a microwave cavity applied in a novel, high-performance atomic frequency standard. We show that by modifying the boundary conditions in the case of a loop-gap geometry, a good improvement of the field homogeneity can be obtained. Such a design demonstrates high potential to improve the frequency stability; it is compact and hence suitable for a future generation of compact, high-precision frequency standards based on vapor cells and a pulsed optical pumping (POP) regime (POP atomic clocks).

Compact nanosecond laser system for the ignition of aeronautic combustion engines

We have studied and developed a compact nanosecond laser system dedicated to the ignition of aeronautic combustion engines. This system is based on a nanosecond microchip laser delivering 6 μJ nanosecond pulses, which are amplified in two successive stages. The first stage is based on an Ytterbium doped fiber amplifier (YDFA) working in a quasi-continuous-wave (QCW) regime. Pumped at 1 kHz repetition rate, it delivers TEM00 and linearly polarized nanosecond pulses centered at 1064 nm with energies up to 350 μJ. These results are in very good agreement with the model we specially designed for a pulsed QCW pump regime. The second amplification stage is based on a compact Nd:YAG double-pass amplifier pumped by a 400 W peak power QCW diode centered at λ = 808 nm and coupled to a 800 μm core multimode fiber. At 10 Hz repetition rate, this system amplifies the pulse delivered by the YDFA up to 11 mJ while preserving its beam profile, polarization ratio, and pulse duration. Finally, we demonstrate that this compact nanosecond system can ignite an experimental combustion chamber.

Third-order spontaneous parametric down-conversion in a ring microcavity

The theory of third-order spontaneous parametric down-conversion (TOSPDC) in a ring waveguide microcavity is developed. Analytical expressions for the rate of photon triplet emission are presented for both the monochromatic-pump and pulsed-pump regimes. In the latter case, rising exponential pulses are considered as optimal ones for the cavity excitation. It is demonstrated by numerical simulations that a silicon-nitride based ring microcavity can be a promising system for developing narrowband sources of photon triplets based on TOSPDC.

Peculiarities of the single and repetitive pulse threshold pump power for stimulated Brillouin scattering in long optical fibres

It is shown that in the undepleted pulsed pump regime of stimulated Brillouin scattering (SBS) the duration of a Stokes pulse in long optical fibres increases by the doubled time of flight for a pump pulse through a fibre. A consequence of this is up to three times difference between the SBS threshold power in a single pump pulse regime when the instant power or energy of the scattered radiation is measured. A distinguishing peculiarity of a repetitive pump pulse regime is a stepwise reduction of the threshold power with the decrease of an interpulse interval when the interval equals the doubled time of flight for a pump pulse through a fibre.

Pulsed and continuous-wave laser operation of TGT-grown Nd,Y-codoped :SrF2 single crystal

In this letter we present laser properties of temperature gradient technique (TGT) grown Nd,Y : SrF2 crystals with Nd3+ concentrations of 0.4, 0.65 and 0.8 at% and Y3+ concentration of 10 at%. The noncoated crystal samples, 3.1 or 5 mm long, were pumped by the 796 nm laser diode matching the Nd,Y : SrF2 absorption peak. In the pulsed pumping regime (pulse-duration 2 ms, frequency 10 Hz), maximum average output power of 75 mW (corresponding to peak power of 3.75 W) was obtained with slope efficiency as high as 51% and optical-to-optical efficiency of 42% with respect to the absorbed pump power. The output beam spatial profile was nearly Gaussian in both axes, oscillations started at the wavelength of 1057 nm. At higher pumping levels, the second emission line at 1051 nm appears corresponding to our fluorescence measurements. Wavelength tuning using a birefringent filter from 1048 to 1070 nm is probably given by the crystal-field splitting of the 4F3/2 manifold in Nd3+. True-continuous-wave laser operation was also successfully obtained at lower pumping levels with maximum output power of 380 mW and slope efficiency of 28% at the wavelength of 1057 nm.

High efficiency coupling of photon pairs in practice

Multi-photon and quantum communication experiments such as loophole-free Bell tests and device independent quantum key distribution require entangled photon sources which display high coupling efficiency. In this paper we put forward a simple quantum theoretical model which allows the experimenter to design a source with high pair coupling efficiency. In particular we apply this approach to a situation where high coupling has not been previously obtained: we demonstrate a symmetric coupling efficiency of more than 80% in a highly frequency non-degenerate configuration. Furthermore, we demonstrate this technique in a broad range of configurations, i.e. in continuous wave and pulsed pump regimes, and for different nonlinear crystals.

Recent developments in high power near-infrared supercontinuum generation based on photonic crystal fiber

High power supercontinuum generation has witnessed rapid developments during the past few years. The mechanism and the latest achievements in high power supercontinuum generation are reviewed both for the continuous wave pump regime and the pulsed pump regime. The challenges in scaling the average power of supercontinuum generation are analyzed. Some of our works on high power supercontinuum generation are summarized, and perspectives for the future development are discussed.

All-fiber 177.6 W supercontinuum source

Supercontinuum has wide and important applications in a range of fields, so it is one of the hot research spots in recent years. In this paper the mechanism and the latest achievements in high power supercontinuum generation under continuous wave laser pump and pulsed laser pump regimes during the past several years are reviewed. The challenges and the problems that need to overcome in scaling the average output power of supercontinuum generation are analyzed. An all-fiber supercontinuum source constructed at the national university of defense technology is demonstrated with 177.6 W average output power which overcomes the problems of low splicing loss, facet damage of the output fiber, the heat treatment and the effective control of the nonlinear effects through the optimization of the whole system. To the best of the author's knowledge, the 177.6 W average output power is the highest value in ever reported ones.

Analysis of acceptable spectral windows of quadratic cascaded nonlinear processes in a periodically poled lithium niobate waveguide

We report a systematic and comparative study of the acceptance bandwidths of two cascaded quadratic nonlinear processes in periodically poled lithium niobate waveguides, namely cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) and cascaded sum-frequency generation and difference-frequency generation (cSFG/DFG). We first theoretically and experimentally study the acceptance bandwidths of both the individual second-harmonic generation (SHG) and sum-frequency generation (SFG) processes in the continuous wave (CW) and pulsed-pump regimes. Our results show that the SHG bandwidth is approximately half that of the SFG process in the CW regime, whereas the SHG acceptance bandwidth can approach the CW SFG bandwidth limit when pulsed-pump is used. As a consequence we conclude that the tuning bandwidths of both cascaded processes should be similar in the pulsed pump regime once the pump pulse bandwidths approach that of SFG (i.e. the cSHG/DFG bandwidth is not limited by the CW SHG bandwidth). We confirm that this is the case experimentally.

Electronic (population) lensing versus thermal lensing in Yb:YAG and Nd:YAG laser rods and disks

A comparative study of electronic lenses (caused by population change of ground and excited states having different polarizabilities) and thermal lenses induced in Yb:YAG and Nd:YAG rods and disks under lasing and nonlasing conditions is carried out. The transient electronic lens can predominate over the thermal one in the pulsed-pump regime, whereas the stationary thermal lens may be predominant at CW broad pumping. The electronic lens effect is stronger in Yb:YAG than in Nd:YAG crystal.

Studying the characteristics of pulse-pumped semiconductor 1060-nm lasers based on asymmetric heterostructures with ultrathick waveguides

High-power semiconductor lasers based on asymmetric quantum-dimensional separate confinement InGaAs/GaAs heterostructures with ultrathick waveguides were fabricated by means of metalorganic hydride vapor phase epitaxy technology. The laser characteristics were studied in a pulsed pumping regime, in which the emission was excited by current pulses of 100 ns duration at a repetition frequency of 10 kHz and an amplitude of up to 200 A. The passage to a pulsed lasing regime allowed the active region heating to be reduced and the output power to be increased to 145 W for a laser diode with a 100-μm exit aperture. The results obtained for the pulsed lasing regime show that saturation of the output power-current characteristic observed in the continuous-wave regime is fully determined by overheating of the active region of a semiconductor laser.

Observation of the amplification of spin-wave envelope solitons in ferromagnetic films by parallel magnetic pumping

The propagation of envelope solitons of microwave-frequency spin waves in a spatially periodic field oriented parallel to the magnetic pump has been investigated experimentally. In a pulsed pumping regime with amplitude much greater than the threshold for parametric excitation of spin systems, amplification of spin-wave envelope solitons exceeding their natural damping was obtained.