Pump Light Power Research Articles

Investigation of All-Optical Tunable Notch Filter Based on Sum-Frequency Generation in a PPLN Waveguide

We propose and simulate an all-optical tunable notch filter based on a sum-frequency generation process in a periodically poled lithium niobate (PPLN) waveguide. The central wavelength of the filter can be tuned by adjusting the wavelength of input pump light. The maximum signal suppression at the central wavelength can be also changed by varying the power of input pump light. A maximum signal depletion of up to 34.4 dB is achieved when the central wavelength is tuned at 1545 nm. The simulation results show that this nonlinear optical filter owns a wide tuning range and steady 3-dB bandwidth on different signal power and wavelength values under low input pump power.

All-optical tuning of a nonlinear silicon microring assisted microwave photonic filter: theory and experiment.

We propose and demonstrate an all-optical tuning mechanism to tune the response of a microwave photonic filter (MPF) based on a nonlinear silicon microring resonator (MRR). The tuning mechanism relies on the optical nonlinearities induced resonant wavelength shift in the silicon MRR, leading to the change of frequency difference between the optical carrier frequency and resonant frequency of the silicon MRR. A detailed theoretical model is established to describe the operation of the proposed all-optical tunable MPF. Two cases are studied in the experiment, i.e. the optical carrier frequency is located at the left or right side of the MRR resonant frequency. Both forward and backward pumping configurations in each case are demonstrated. Using the fabricated silicon MRR and exploiting light to control light, the central frequency of the notch MPF can be flexibly tuned by adjusting the pump light power. Moreover, the presented all-optical tuning mechanism might also facilitate interesting applications such as microwave switching and microwave modulation.

Effect of the pump depletion on the quasi-phase-matching for [formula omitted] nonlinearities

In this study, an analytical solution is proposed to solve the general problems of three-wave mixing with pump depletion. The so-called quasi-phase-matching (QPM) for χ(2) nonlinearities, including sum frequency generation (SFG), second harmonic generation (SHG) and difference frequency generation (DFG), is amended when the depletion of the pumping light power is considered. The optimum domain width and the corresponding conversion efficiency are discussed. The optimum domain widths deviate from the coherence length lc=π/Δk, but the deviation is so small that it can be ignored according to the actual situation. The applicable scope of undepleted pump approximation (UPA) is estimated by a proposed relative tolerance. Analysis indicates that the relative tolerance showing the difference of conversion efficiency between the UPA and the exact solution is solely determined by the conversion efficiency. Based on the relative tolerance curves for SFG, SHG, and DFG, two models are developed: one can be used to describe the SFG and SHG processes, whereas the other can be used for the DFG process. These findings can be used to provide direct guidance for practical application, and can also make the estimation of practical samples more convenient.

Ultrafast tunable chirped phase-change metamaterial with a low power.

We numerically demonstrate an all-optical tunable dual-band double negative (DNG) index chirped metamaterial (MM) in the mid-infrared (M-IR) region. This MM possesses an ultrafast and significant tunability under low pump light power, realized by combining phase change material (PCM). It has a configuration of elliptical nanohole array (ENA) penetrating through metal/PCM/metal (Au-Ge(2)Sb(2)Te(5)-Au) films. Here, we consider the case when the chirp is introduced by displacing the positions of the ENA along the short axis of the elliptical apertures inside the primitive cell, which can achieve multiple internal surface-plasmon polariton (SPP) modes at the inner metal-dielectric interfaces of the structure and thus providing a dual-band negative index with simultaneous negative permittivity and permeability. The influence of amorphous and crystalline states of Ge(2)Sb(2)Te(5) on the effective optical parameters of the structure is analyzed. Switching between these states provides a large wavelength shift of the structure's effective optical parameters. A photothermal model is used to study the temporal variation of the temperature of the Ge(2)Sb(2)Te(5) layer to show a potential to switch the phase of Ge(2)Sb(2)Te(5) by optical heating. Generation of the tunable dual-band DNG index presents clear advantages as it possesses a fast tuning time of 0.4 ns, a low pump light intensity of 7.3μW/μm(2), and a large tunable wavelength range of 978 nm. We expect that our design may have potential applications in actively tunable multi-band nanodevices.

Mode conversion based on forward stimulated Brillouin scattering in a hybrid phononic-photonic waveguide.

We propose a scheme for on-chip all optical mode conversion based on forward stimulated Brillouin scattering in a hybrid phononic-photonic waveguide. To describe the mode conversion the theoretical model of the FSBS is established by taking into account the radiation pressure and the electrostriction force simultaneously. The numerical simulation is carried out for the mode conversion from the fundamental mode E11x to the higher-order mode E21x. The results indicate that the mode conversion efficiency is affected by the waveguide length and the input pump light power, and the highest efficiency can reach upto 88% by considering the influence of optical and acoustic absorption losses in the hybrid waveguide. Additionally, the conversion bandwidth with approximate 12.5 THz can be achieved in 1550nm communication band. This mode converter on-chip is a promising device in the integrated optical systems, which can effectively increase the capacity of silicon data busses for on-chip optical interconnections.

Research on multiannular channel liquid cooling method for thin disk laser

For the nonuniform distribution of pump and temperature in the large-aperture, high-power, thin-disk laser medium, a cooling method of multiannular channel liquid cooling was proposed and examined both experimentally and theoretically. The temperature distribution in the gain medium becomes uniform utilizing the method of multiannular channel liquid cooling, which is proved by a numerical model using Ansys software. In the modeling, the distribution of temperature in the medium varies with the changes of the flow rate and temperature of the coolant in each annular channel. An excellent uniform temperature distribution could be obtained in the gain medium with arbitrary power and profile of pump light by setting a tailored parameter of the coolant in each annular channel. The highest temperature difference in the gain medium with multiannular channel liquid cooling reduces about 88% compared with evenly cooling. Also, the thermal effect has been suppressed; the experimental result is consistent with numerical modeling. This method could be a new idea for designing the thin-disk laser’s cooling system.

Enhanced violet Cherenkov radiation generation in GeO2-doped photonic crystal fiber

We demonstrate the generation of highly efficient Cherenkov radiation (CR) in the fundamental mode of a GeO2-doped two zero dispersion wavelengths photonic crystal fiber (PCF). Using a high power femtosecond Yb-doped PCF laser emitting 100 fs pulses as the pump source, CR with an efficiency of >40 % and a bandwidth of 38 nm is obtained in the visible-wavelength range when the average power of pump light is 1.27 W. It is that injecting the pump light in deep anomalous dispersion regime contributes to such an efficient spectrally isolated CR. The mechanism during the forming of CR is discussed and the experimental results are in good agreement with the calculation.

Effect of the pump depletion itself on the quasi-phase-matching for second-harmonic generation

The so-called quasi-phase-matching (QPM) for second-harmonic generation (SHG) considering depletion of the pumping light power is amended. The conversion efficiency of SHG and the optimum domain width are discussed. The applicable scope of undepleted pump approximation (UPA) is estimated and a relative tolerance showing the difference in the SHG between the UPA and the pump depletion is solely determined by the SHG conversion efficiency. A model is fitted using the relevant data, and the results reveal that the conversion efficiency of SHG can be conveniently and easily assessed under the given conditions of pump intensity, the nonlinear media and the number of domains. The optimum domain widths deviate from the coherence length lc = π/Δk. The deviation increases with the pump intensity, but there is little impact on SHG due to system variations in crystal length.

Theoretical analysis and experiment performance of slow-light based on stimulated Brillouin scattering (SBS)

Slow light technology will play a key role in future all-optical communication. The slow-light technology based on stimulated Brillouin scattering has become a research highlight because of its additional advantages, such as compatibility of the devices with existing telecommunication systems, room-temperature operation, and tunable at arbitrary wavelengths. According to the propagation of a cw pulse through a Brillouin fiber amplifier, whose frequency is near the Stokes resonance, via three-wave coupling equations, both pump depletion and fiber losses taken into consideration, the principle of how slow-light effect based on stimulated Brillouin scattering produced and the mathematical expression of time delay are strictly deduced. A delay of 8 ns is obtained when the input Stokes pulse is 200ns and the SBS (stimulated Brillouin scattering) gain G is ~18 in our designed experiment of SBS slow-light system. Then the extent of transformation from pump waves to Stokes waves is measured using MATLAB numerical simulation according to the experiment dates, based on the relation between output pump light power and input pump light power and also the relation between output Stokes light power and input pump light power. And the relation between the input light power and propagation distance is discussed as well. Finally the relation between slow light pulse delay and SBS gain is also obtained.

High efficiency, high repetition-rate Nd:YVO4 laser with TEM00 end-pumped by 887 nm

Thermal effect of laser crystal is a very important factor for solid lasers. The most of heat is generated from the quantum loss between pump light and lasing light. If a longer wavelength of pump light is adopted, quantum loss and quantum loss efficiency can be reduced and improved, respectively. In this paper, a Nd:YVO4 laser end-pumped by 887 nm LD is reported. Output power of 25 W is obtained from a single Nd:YVO4, when the crystal absorbs pump light power of 38 W. The corresponding opto-optic conversion efficiency is up to 65.7%. When 30.7 W pump light is absorbed in the crystal, 19.4 W TEM00 is obtained with M 2 x = 1.30, M 2 y = 1.26 and opto-optic conversion efficiency of 63.2%. The laser can work at the Q-switched mode. The uniform pulses are generated at high repetition of 100 kHz. And the conditions of pulse stability are analyzed in this paper.

Efficient green continuous-wave lasing of blue-diode-pumped solid-state lasers based on praseodymium-doped LiYF_4

We report highly efficient laser operation of praseodymium-doped LiYF(4) in the green spectral range. The influence of the crystal length and pump light focusing on the laser performance has been studied. The pump radiation was delivered by InGaN laser diodes. Optimizing the setup for a 2.9 mm long crystal with a doping concentration of 0.5% led to an electric to green laser power conversion efficiency as high as 7.4%. With 500 and 1000 mW of pump light power, output powers of 179 and 358 mW have been reached, respectively. With respect to absorbed power, slope efficiencies of up to approximately 60% have been achieved.

Generation and transmission simulation of 60 G millimeter-wave by using semiconductor optical amplifiers for radio-over-fiber systems

A novel method of the millimeter-wave (MMW) generation is proposed for Radio-over-fiber systems with low phase noise by using semiconductor optical amplifiers (SOAs). The simulation results show that the method is correct. When a pump light and a signal light are input into the SOA, the converted light induced by four-wave mixing (FWM) effect is generated. The optical MMW is generated between the signal light and converted light after filtering the pump light. The electrical MMW is obtained by beating the signal light and converted light via a photo-detector. The phase noise of the system is low because the phase difference between the signal light and converted light is stable for the FWM effect. The power of MMW is increased with the increase of the pump light power and the pump current of the SOA, is decreased with the increase of the polarization azimuths of the pump light.

Study of Nd3+-doped polarization maintaining fiber amplifier

The distribution of pump light and signal light power of Nd3+-doped fiber amplifier along the fiber is numerically simulated. The Nd3 +-doped polarization-maintaining fiber amplifier is experimentally studied, which is pumped by 808nm semiconductor laser. The enlargement factor of small-signal is 300（the gain is 25dB）, and the steady 5W amplificatory pulse is obtained by using the self-made Nd:YAG passive mode-locking laser as seed source. The 86142B-type spectrograph and TDS5104 oscillograph are employed to detect the output laser, and the output power is measured by power meter.

Experimental investigation into femtosecond fiber ring laser with passive mode locking

AbstractA passively mode‐locked Er3+‐doped fiber ring laser is experimentally investigated, with the emphasis on its practical design by considering the effects of ring cavity length, pumping light power, and optical amplification on the femtosecond optical pulses obtained. It is shown that the designed fiber ring laser can operate at the center wavelength of 1550 nm to produce a train of periodic optical pulses with full width at half maximum (FWHM) of 270 fs, repetition frequency of 20 MHz, and average output optical power of 146 μW. The resulting femtosecond optical pulses are then amplified by using three kinds of Er3+‐doped optical fibers with different lengths and Er3+‐doped concentrations, respectively, while employing the same pumping laser. In the experiments, both the FWHM of amplified optical pulses and the amplifier gain are measured under different conditions. The optimization of optical pulse width is also carried out in terms of pumping light power. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 63–67, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23985

Fiber-ring laser with tunable optical bistability

The structure of combining two segments of erbium-doped fiber (EDF) together—one EDF acting as an amplifier and the other as an absorber—has a special gain characteristic curve which has a maximum gain with an increase in the input signal power. This special gain characteristic curve can lead to an optical bistability (OB) phenomenon in a fiber-ring laser employing an EDF of this structure. By adjusting the pump light power injected into the second segment of the EDF, we can change the behavior of the absorber and can, therefore, control the range of the bistability region. A method is proposed to calculate the tunable optical bistability, and the calculation result is in accordance with our experiment.

Experiments of all-optical switching due to cross-phase modulation in fiber grating coupler by lock-in amp. detection scheme

We report results of experiments examining cross-phase modulation effect on fiber grating coupler (FGC). All-optical switching are observed in both cases of high pump pulses emitted from high-power Nd:YAG laser and mode-locked EDF laser. Based on coherent detection using a lock-in amplifier, the red-shift of the Bragg wavelength for a FGC was estimated to be 0.04–0.06 nm/1.5–1.7 kW peak power of EDF pump light at 1.55 μm. To avoid mixture of pump pulse and signal light at 1.55 μm, we have also performed the experiment using high power Nd:YAG laser as a pump power. For a Nd:YAG laser, the red-shift of Bragg wavelength is estimated to be 0.06 nm at maximum pump power of 2.1 kW. A simple model for the proposed detection scheme is given and the resultant red-shift is analyzed numerically.

Second harmonic generations in aperiodic optical superlattices with finite width and in one-dimensional defective photonic crystals made of nonlinear optical materials

The characteristics of the second harmonic generations (SHGs) in homogeneous and inhomogeneous systems are investigated. We consider two kinds of structures: one is aperiodic optical superlattices (AOSs) with homogeneous linear susceptibility and the modulated second-order nonlinear susceptibility; the second is linear and nonlinear susceptibilities both the system with inhomogeneous. We derive a general solution of SHG for the AOS with finite lateral width and of SHG in considering the depletion of the pump light power. We carry out the design of AOSs by using simulation annealing (SA) algorithm and show that the constructed AOSs can implement multiple wavelength SHGs with identical effective nonlinear coefficient at the preassigned wavelengths of incident light. We observe great enhancement of SHGs in the one-dimensional photonic crystals (PCs) with defects consisting of multiple photonic quantum wells made of nonlinear material when the frequency of fundamental wave aims at one of the defect states. We also propose an effective design approach of aperiodically stacked layers of nonlinear material and air in terms of the SA method. The constructed structure can achieve multiple-wavelength SHGs at the preas-signed wavelengths.

Dielectric characteristic of photoinduced isomerization in azo-dye doped polymeric matrices

The dielectric permittivities and losses of poly(methyl methacrylate) doped with different concentrations of azo dye are investigated under the irradiation of 532nm light for the first time. The dielectric permittivities increase with the concentration of chromophores increasing, and the dielectric relaxation is mainly influenced by the doped azo-dye chromophores. Given the dye concentration, the dielectric permittivities depend on the pump power of 532nm light. With the increase of pumping light power, the low frequency dielectric losses increase while the high frequency dielectric losses decrease. The results are explained based on the photoinduced isomerization of chromophores and the interaction between the chromophores and polymer matrices.

Observation of carrier dynamics in CdO thin films by excitation with femtosecond laser pulse

Non-equilibrium dynamics of photoexcited carrier in cadmium oxide thin films were examined by the pump–probe transient optical transmission measurement technique using the second harmonics (400 nm) of femtosecond pulses as a pump light. Time-dependent blueshift of the absorption edge was clearly observed and it reached a maximum at ∼1 ps after the pumping. The magnitude of the blueshift increases with pump light power, which was well fitted to Burstein–Moss formula. The relaxation time of excited electrons from the bottom of the conduction band was obtained ∼350 ps and an effective mass for the electron carrier was estimated as ∼0.3 m e .

Observation of carrier dynamics in CdO thin films by excitation with femtosecond laser pulse

Non-equilibrium dynamics of photoexcited carrier in cadmium oxide thin films were examined by the pump–probe transient optical transmission measurement technique using the second harmonics (400 nm) of femtosecond pulses as a pump light. Time-dependent blueshift of the absorption edge was clearly observed and it reached a maximum at ∼1 ps after the pumping. The magnitude of the blueshift increases with pump light power, which was well fitted to Burstein–Moss formula. The relaxation time of excited electrons from the bottom of the conduction band was obtained ∼350 ps and an effective mass for the electron carrier was estimated as ∼0.3 m e.