Gaussian Optical Pulse Research Articles

Phase-change material-assisted all-optical temporal differentiator.

This paper proposes a novel microring resonator (MRR)-based all-optical tuning temporal differentiator (DIFF). Specifically, the DIFF uses nonvolatile phase-change material Ge2Sb2Te5 (GST) to achieve low energy consumption and high-speed optical control of the state of the MRR, avoiding the traditional electro-optic (EO) and thermo-optic (TO) tuning designs. By changing the crystallinity of GST to changing the coupling regimes of the MRR, a broad range for the differentiation order α, i.e., 0.47-1.64 can be realized. The intensity response and phase response of the GST-assisted MRR, and normalized intensity in the output of the temporal DIFFs for Gaussian optical pulses have been obtained by simulation. Furthermore, input pulse width and detuning influence on the differentiation order and output deviation are discussed. Finally, our structure can effectively reduce the chip area and power consumption compared with the traditional EO and TO tuning designs.

The Physics Research of Optical Information Effect at Low Loss in Nonlinear Optical Fiber Transmission

Both nonlinear effects and dispersion are important factors that affect the transmission of optical pulses in optical fibres. In the anomalous dispersion region, the mutual balance of dispersion and nonlinear effects can achieve optical soliton transmission. Starting from the nonlinear Schrodinger equation of the optical pulse, under the condition of ignoring the dispersion, the nonlinear phase shift and frequency chirp of the Gaussian optical pulse under the nonlinear effect of self-phase modulation (SPM) are derived and simulated; the numerical simulation of the SPM the spectrum of Gaussian optical pulses with different maximum phase shifts without chirp and with positive chirp. The study found that the fusion loss of the fibre obtained by this algorithm is less than 0.11dB than that of the traditional single-mode fibre, and the additional bending loss caused by the wavelength range of 1460nm to 1625nm after winding 100 times on a 60mm cylinder is less than 0.02dB/km.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ ЭНЕРГЕТИЧЕСКИХ СПЕКТРОВ, ФОРМИРУЮЩИХСЯ ПРИ УСКОРЕНИИ ЭЛЕКТРОНОВ РЕЛЯТИВИСТСКИ ИНТЕНСИВНЫМИ ГАУССОВСКИМИ И ЛАГЕРРОВСКИМИ ЛАЗЕРНЫМИ ИМПУЛЬСАМИ

A mathematical model is constructed that describes the propagation of laser pulses in vacuum, taking into account the corrections due to their finite duration. On its basis, using Newton relativistic equations with the corresponding Lorentz force, the energy spectra of an ensemble of electrons are simulated by relativistically intense laser radiation. The characteristics of these spectra are studied for the cases of Gaussian and Laguerre optical pulses. Electronic spectra in the fixed angular ranges are localized around the relativistic maxima in the case of Gaussian pulses, but are substantially non-monoenergetic in the case of Laguerre pulses.

An anamorphic time-lens-based optical cryptosystem for protection of time-varying signals

The similarity between in-plane directions of spatial optics and overlapped time ranges of temporal optics is introduced as a new rule of the space–time duality. Applying this rule, an optical dual random phase encoding (DRPE) cryptosystem in the temporal anamorphic fractional Fourier transform (TAFrFT) domain is proposed for physical-level protection of time-varying signals. The structure of a TAFrFT system is an anamorphic time lens (ATL) sandwiched by two identical dispersion elements. The additional key provided by a TAFrFT system is only related to phase profile of the involved ATL, leading to a dispersion-independent manner of key updating as well as an enlarged key space (KS) in comparison with the conventional temporal FrFT and Fresnel transform system. This manner of key updating has potential as a one-time key strategy to evade the intrinsic linearity and symmetry weakness of DRPE-like temporal cryptosystems, due to the updating speed being comparable to the frame rate of plaintext signals. As the temporal counterpart of a spatial optical device composed of cylindrical lenses along different directions, an ATL is designed as an equal-spaced array of time lenses with unipolar phase, constant extension, and varying phase height. Implemented by an arbitrary waveform generator (AWG)-driven electro-optic phase modulator (EOPM), the time interval of adjacent time lenses, extension of each time lens, and the standard phase height are optimally designed as functions of the AWG bandwidth B M and the EOPM damage phase threshold . By numerical simulations, a 16-slot input optical Gaussian pulse sequence with half pulse width of 10 ps and frame length of 2000 ps is encrypted with a KS near provided by ATLs at parameters GHz and radians under the state of the art, enough for resistance to brute-force attacks.

Ultra-precise time tuning and central frequency shift of optical pulses via small weak values

Ultra-precise time tuning and the central frequency shift of optical pulses via a weak measurement scheme were fully analyzed. A new defined weak value contains the information about the influence of the central frequency of the optical pulse, which cannot be arbitrarily ignored in the task of ultra-precise time tuning and shifting the central frequency of optical pulses. Interestingly, it is shown that a small weak value is more suitable than an abnormally large weak value in this type of task, which is completely different from that in weak value amplification techniques. Whether a Gaussian optical pulse or a general complex Gaussian optical pulse, ultra-small time tuning and shifting of the central frequency below the precise resolution of the controlling time and frequency of the apparatus can be achieved using this method.

Spatiotemporal multiplexing based on hexagonal multicore optical fibres

Based on a genetic algorithm, we have solved the problem of finding the parameters of optical Gaussian pulses which make their efficient nonlinear combining possible in one of the peripheral cores of a 7-core hexagonal fibre. Two approaches based on individual selection of peak powers and field phases of the pulses launched into the fibre are considered. The found regimes of Gaussian pulse combining open up new possibilities for the development of devices for controlling optical radiation.

Demonstration of an [formula omitted]-Gb/s optical time-division multiplexing system

An 8×25-Gb/s optical time-division multiplexing (OTDM) system is demonstrated experimentally. The optical pulse source is based on optical frequency comb (OFC) generation and pulse shaping, which can generate nearly chirp-free 25-GHz 1.6-ps optical Gaussian pulse. The eightfold optical time-division demultiplexer consists of a single-driven dual-parallel Mach–Zehnder modulator (DPMZM) and a Mamyshev reshaper. Error-free demultiplexing of 8×25-Gb/s back-to-back (B2B) signal with a power penalty of 4.1 dB to 4.4 dB at a bit error rate (BER) of 10−9 is achieved to confirm the performance of the proposed system.

Numerical simulations of dispersion effects in chirped Gaussian and soliton pulses

A finite-difference method is used to solve the nonlinear Schrodinger equation. A not frequently used numerical method is developed by replacing the time end space derivate by central-difference replacements. Results from solving the nonlinear Schrodinger equation by using the numerical method called method of lines are used to simulate the propagation of Gaussian pulses in optical fibers. Gaussian input pulse was used for the analysis of dispersion effects. For the simulation was chosen the nonlinear Schrodinger equation modified for dispersion mode. Based on the changes of the chirp parameter have been achieved final shapes of transmitted Gaussian pulses. The main objective was to demonstrate the impact of the broadening factor of the pulse and also to clarify the correlation between the change in phase and frequency chirp. The main goal of this paper is to describe and simulate effects of dispersion by using short Gaussian and hyperbolic secant optical pulses. The effect of dispersion caused frequency shift which can be compensated by effect of self-phase modulation. Frequency chirp caused by the dispersion effects can be compensated by generating opposite frequency chirp with SPM effect. This compensation can lead to fundamental soliton pulse shape generation. Temporal solitons are attractive for optical communications because they are able to maintain their width even in presence of fiber dispersion. Only a fundamental soliton maintains its shape and remains chirp-free during propagation inside optical fibers.

Generation of Millimeter-Wave Ultra-Wideband Pulses Free of Strong Local Oscillation and Background

A novel scheme of generating millimeter-wave (MMW) ultra-wideband (UWB) pulses free of strong local oscillation (LO) and background is proposed and demonstrated. The frequency of the optical Gaussian pulses is first up-converted by a Mach–Zehnder modulator, which is biased at its minimum transmission point to achieve carrier suppression modulation. Then, the up-converted Gaussian pulses are equally split into two parts with a relative time delay. At last, the two parts are injected into the two arms of a balanced photodetector (BPD) respectively. After the BPD, the low-frequency components are effectively suppressed and MMW-UWB pulses free of background and strong LO are generated. The polarity of generated MMW-UWB can be converted by adjusting the relative time delay between the two parts. In the experiment, a pair of polarity-reversed background-free UWB pulses centered at 25 GHz is successfully generated. The 10-dB bandwidth of the MMW-UWB spectra is 4.14 and 4.05 GHz, respectively.

Multicolor optical Nyquist pulse generation based on self-phase modulation without line-by-line control

Multicolor optical Nyquist pulse generation based on self-phase modulation without line-by-line control is proposed and experimental demonstrated. By 1.4-ps nearly chirp-free optical Gaussian pulse pumping of a high nonlinearity fiber, a 25-GHz spacing, flat-topped supercontinuum (SC) over 17.8nm within 3.6dB power variation at a modest pump power of 21.8dBm is performed. As the phase of the central 90 tones is almost linear to the wavelength after dispersion compensation, spatial light modulator placed after SC for precise line-by-line control both of amplitude and phase can be replaced by conventional optical band-pass filter (OBPF). With an array of quasi-rectangular OBPFs, nearly transform-limited optical Nyquist pulses with a duty cycle of 5.5% on 4 wavelengths are achieved simultaneously.

Deterministic synthesis of mechanical NOON states in ultrastrong optomechanics

We propose a protocol for the deterministic preparation of entangled NOON mechanical states. The system is constituted by two identical, optically coupled optomechanical systems. The protocol consists of two steps. In the first, one of the two optical resonators is excited by a resonant external $\ensuremath{\pi}$-like Gaussian optical pulse. When the optical excitation coherently partly transfers to the second cavity, the second step starts. It consists of sending simultaneously two additional $\ensuremath{\pi}$-like Gaussian optical pulses, one at each optical resonator, with specific frequencies. In the optomechanical ultrastrong coupling regime, when the coupling strength becomes a significant fraction of the mechanical frequency, we show that NOON mechanical states with quite high Fock states can be deterministically obtained. The operating range of this protocol is carefully analyzed. Calculations have been carried out taking into account the presence of decoherence, thermal noise, and imperfect cooling.

Long-term nonlinear propagation and damped oscillation behaviors of Gaussian and super-Gaussian pulses in optical fibers

The long-term nonlinear propagation of Gaussian and super-Gaussian optical pulses in the anomalous dispersion regions of optical fibers are investigated numerically in terms of the pulse shapes and spectra evolution. The results show that, both the pulse shapes and spectra exhibit interesting damped oscillation behavior with decreasing oscillation amplitude for very long distance. In particular, the spectra profiles exhibit interesting arrow shaped evolution. Variations of the pulse widths, maximal normalized amplitudes, and maximal spectral amplitudes with the propagation distance, are also presented. We find that, for the higher-order super-Gaussian pulses, their pulse widths and maximal normalized amplitudes have larger values of oscillation periods and initial oscillation amplitudes. However, the higher-order super-Gaussian pulses have larger values of average pulse widths but smaller values of average maximal normalized amplitudes. In frequency domain, the higher-order super-Gaussian pulses have larger values of average maximal spectral amplitudes.

Microring-based reconfigurable optical pulse shaper

Based on the amplitude and phase-shift characteristics of microring (MR) resonator, a novel reconfigurable optical pulse shaping approach is proposed. By adjusting the variable attenuators to set the proper relative weights, a transform-limited Gaussian input optical pulse can be shaped into flat-top waveform or triangular waveform flexibly. In contrast to the conventional pulse shaping method, only positive real relative weights are used in the proposed pulse shaper, which not only facilitates the reconfigurable adjustment, but also is robust to the wavelength detuning and temporal duration variations of the input pulse.

Tunable microwave generation method based on birefringence photonic crystal fiber

A new method is proposed to generate tunable microwave by using single-light source and birefringence photonic crystal fiber (PCF), which is based on the interaction and the coupling between the two polarizations of the initial Gaussian optical pulse in PCF. A full vector finite element is used to design a high birefringence PCF. The expressions of the microwave are derived by couple-mode theory. The proof of concept device consists of a light source, a birefringence PCF, a polarizer controller and a photodetector. The frequency of the generated pulses can be controlled by adjusting the parameters of the optical fiber system. The simulation results demonstrate the system can generate the frequency of microwave are 8.03–37.67GHz and 26.82–125.5GHz from two kinds of PCFs, respectively. The system is elastic, stable, brief and highly efficient.

Nonlinear pulse shaping-assisted ultrashort optical pulse generation

An ultrashort optical pulse generator based on nonlinear pulse shaping is proposed and demonstrated. With a spatial light modulator placed prior to a high nonlinearity fiber, \((\mu +\lambda )\)-evolution strategy is introduced to dynamically adjust the transfer function of spatial light modulator both in phase and in amplitude. Nearly chirp-free 2.2-ps optical Gaussian pulse and 0.73-ps optical Nyquist pulse with a repetition rate of 25 GHz are both achieved in simulation. The scheme also has a certain tolerance to phase quantization error of the spatial light modulator and power fluctuation.

A novel radial beam smoothing scheme based on optical Kerr effect

Laser-beam illumination uniformity is a key issue in inertial confinement fusion facilities. In order to fulfill the requirement of improving illumination uniformity, a radial smoothing (RS) scheme is proposed. For smoothing the focal-spot pattern on a short time scale compared with the hydrodynamic response time of the target, the optical Kerr effect with extremely response time is taken into consideration. The basic principle of RS based on optical Kerr effect is that by using the interaction between optical Kerr medium and periodic Gaussian pulses to modulate a periodic spherical phase, to modulate periodic sphericel phase added at the wavefront of laser transmission wave, change the focal-spot size of the laser beam in far field, and further induce the fast radial redistribution of the speckles inside the focal spot in far field, and further induce the fast radial redistribution of the speckles inside the focal spot in far field. This fast radial redistribution of the speckles smoothes the intensity modulation of the focal spot on the target and eventually achieves the beam smoothing in the radial direction. The application of RS in the beamline is detailed. The optical Kerr medium is inserted in the front-end of the bemline, before the laser beam is injected into the main amplifier. The periodic Gaussian pulse for pumping the optical Kerr medium is obtained by the pulse stacking system based on fibers. The pulse width of stacked Gaussian pulse and the time delay between Gaussian pulses are set to be on a picosecond time scale or subpicosecond time scale. The induced refractive index of the optical Kerr medium by the pump laser fits spherical distribution with periodic variation, and results in the radial distribution of the speckles in focal plane. By establishing the theoretical model of the radial beam smoothing scheme implemented with continuous phase plate (CPP), the focusing characteristics of laser beam with RS and CPP are discussed in detail. The influences of the selection of optical Kerr medium and the characteristics of the radial redistribution on the radial smoothing effect are simulated and analyzed. Results indicate that the RS based on optical Kerr effect could efficiently achieve the periodic radial redistribution of the speckles on focal plane, and therefore improves the illumination uniformity in the radial direction while eliminating the stripe pattern presented in far field by one-dimensional smoothing spectral dispersion (SSD). The smoothing performance of RS is different from that of the conventional SSD due to its radial smoothing direction. Moreover, the combined application of RS with continuous phase plate could achieve a better smoothing level with a shorter time. The utilization of radial smoothing scheme in high power laser system may significantly improve the laser-beam irradiation with little influence on the performance of the beamline.

Optical Gaussian pulse source based on spectrum slicing and frequency chirp compression

An external-modulated optical Gaussian pulse generator based on optical filtering and chirp compression is proposed. The scheme works in linear regime using two phase modulators which does not require nonlinear compression and bias control. Theoretical and numerical analysis is first performed to elaborate the working principle and optimize the working condition of the pulse source. Using the analysis as a guideline, nearly chirp-free 25-GHz 3-ps Gaussian pulses are experimentally achieved over C band. The pulse source is further applied in 100-Gbit/s optical time-division multiplexing (OTDM) transmission system and the power penalty for 100-km transmission at a bit error rate (BER) of 10−9 is 0.6-dB, which demonstrates that the pulse generator is a simple, robust and practical pulse source for OTDM applications.

Optical wave breaking and soliton trains generation due to cross-phase modulation in an optical fiber with quintic nonlinearity

Based on the extended coupled nonlinear Schrödinger equations in an optical fiber with quintic nonlinearity (QN), the approximate analytical frequency chirps and the critical distances for the cross-phase modulation induced optical wave breaking (OWB) are discussed for the initial Gaussian optical pulses. Evolutions of the frequency chirps, shapes and spectra of pulses are numerically calculated in the normal dispersion regime. It is shown that, the approximate analytical frequency chirps accords well with the numerical ones at the initial evolution stages of the pulses. And the calculated approximate critical OWB distances accord well with the numerical ones only for the traditional OWB. In addition, for the positive QN and the negative one but with small absolute values, the traditional OWB can be observed. While for the negative QN with large absolute values, non-traditional OWB may occur. Namely, soliton pulse trains may develop during the pulse propagation.

On-Chip Tunable Second-Order Differential-Equation Solver Based on a Silicon Photonic Mode-Split Microresonator

We propose and experimentally demonstrate an on-chip all-optical differential-equation solver capable of solving second-order ordinary differential equations (ODEs) characterizing continuous-time linear time-invariant systems. The photonic device is implemented by a self-coupled microresonator on a silicon-on-insulator platform with mutual coupling between the cavity modes. Owing to the mutual mode coupling within the same resonant cavity, the resonance wavelengths induced by different cavity modes are self-aligned, thus avoiding precise wavelength alignment and unequal thermal wavelength drifts as in the case of cascaded resonators. By changing the mutual mode coupling strength, the proposed device can be used to solve second-order ODEs with tunable coefficients. System demonstration using the fabricated device is carried out for 10-Gb/s optical Gaussian and super-Gaussian input pulses. The experimental results are in good agreement with theoretical predictions of the solutions, which verify the feasibility of the fabricated device as a tunable second-order photonic ODE solver.

25-GHz dual-wavelength pedestal-free pulse source based on single-driven dual-parallel Mach-Zehnder modulator and Mamyshev reshaper

A dual-wavelength optical Gaussian pulse generation scheme based on a single-driven dual-parallel Mach-Zehnder modulator with subsequent Mamyshev reshaping is proposed. Experimental results show that nearly chirp-free Gaussian pulses with a full width at half maximum of 2.7-ps and a repetition rate of 25-GHz on 2 wavelengths are achieved simultaneously. By changing the central wavelengths of the continuous wave light and the optical bandpass filter, nearly transform-limited optical Gaussian pulses are obtained over the C-band. The pulse source is further employed in a 100-Gbit/s on–off keying optical time division multiplexing transmission system. Error-free bit error rate performance is also achieved, which confirms the high pulse quality.