Effective Pulse Compression Research Articles

Chirped self-similar optical solitons with cubic–quintic–septic–nonic form of self-phase modulation

This study investigates the dynamics of ultrashort light pulses in an inhomogeneous optical medium exhibiting all orders of nonlinearity up to the ninth order. The research focuses on exploring the existence and properties of self-similar solitons while varying cubic, quintic, septic, and nonic nonlinearities, group velocity dispersion, and loss or gain. It is found that the transmission system supports the existence of novel types of self-similar bright and dark pulses in the presence of various physical processes. Importantly, these self-similar localized waves exhibit a linear chirp, a crucial factor for achieving effective pulse amplification or compression. Based on the chirp property, the dynamical behaviors of these self-similar waveforms are discussed in a periodically distributed amplification system. The findings highlight that the shape and dynamics of these chirped self-similar pulses can be precisely controlled by selecting appropriate profiles for gain or loss, nonlinearity, and dispersion. Additionally, the research numerically discusses the interaction dynamics between two and three adjacent solitons.

Picosecond synchronously pumped diamond Raman laser

With diamond crystals as Raman media, picosecond synchronously pumped solid-state Raman laser is theoretically studied in detail for the first time. High efficient working point and effective pulse compression working point are investigated. For both 532 nm and 1064 nm pumping, high Raman conversion efficiency can be achieved for negative cavity length detuning (∆x) and diamond crystal length of 5 mm. The higher efficiency can be obtained with longer Raman crystal, longer pumping pulse width and higher pumping power. For 532 nm pumping, effective pulse width compression can be realized for ∆x = 0 nearby and diamond crystal length of 10 mm. Shorter pulse width and higher peak power of 1st Stokes laser can be achieved with longer Raman crystal, shorter pumping pulse width and higher pumping power. The findings can contribute to the design and optimization of picosecond synchronously pumped diamond Raman lasers.

An efficient ultra-short pulse compressor based on a triangular corrugated photonic crystal

In this letter, ultra-fast pulse compression capacity of a triangular corrugated photonic crystal (PhC) was investigated through the finite difference time domain method. The group velocity dispersion of the devised structure was dramatically improved compared to the conventional 1-D PhCs. Calculated dispersion relation of the allowed modes indicates that the geometrical parameters of the proposed photonic architecture can be arranged such that the central wavelength of the incoming pulse lies at the band-edge of the transmission spectrum. The presented design was successfully employed as a pulse dispersion compensator, and the compression factors up to 353 were documented. In addition, the necessity of the optimum condition for the achievement of an effective pulse compression mechanism was discussed.

A New Dynamic Complex Baseband Pulse Compression Method for Chirp-Coded Excitation in Medical Ultrasound Imaging.

Chirp-coded excitation can increase the signal-to-noise ratio (SNR) without degrading the axial resolution. Effective pulse compression (PC) is important to maintain the axial resolution and can be achieved with radio frequency (RF) and complex baseband (CBB) data (i.e., and , respectively). can further reduce the computational complexity compared to ; however, suffers from a degraded SNR due to tissue attenuation. In this paper, we propose a new dynamic CBB PC method ( that can improve the SNR while compensating for tissue attenuation. The compression filter coefficients in the method are generated by dynamically changing the demodulation frequencies along with the depth. For PC, the obtained coefficients are independently applied to the in-phase and quadrature components of the CBB data. To evaluate the performance of the proposed method, simulation, phantom, and in vivo studies were conducted, and all three studies showed improved SNR, i.e., maximally 3.87, 7.41, and 5.75 dB, respectively. In addition, the measured peak range sidelobe level of the proposed method yielded lower values than the and , and it also derived a suitable target location, i.e., a <0.07-mm target location error, while maintaining the axial resolution. In an in vivo abdominal experiment, the method depicted brighter and clearer features in the hyperechoic region because highly correlated signals were produced by compensating for tissue attenuation. These results demonstrated that the proposed method can improve the SNR of chirp-coded excitation while preserving the axial resolution and the target location and reducing the computational complexity.

Effective pulse compression in dispersion decreasing and nonlinearity increasing fibers

We numerically demonstrate effective pulse compression in photonic crystal fibers with linearly decreasing dispersion and linearly increasing nonlinearity. The proposed fiber design can achieve nearly chirp-free and pedestal-free pulse compression and provides a feasible and a much simpler design in practice.

Development and performance evaluation of an improved complex valued radar pulse compressor

Pulse compression is an important and burning issue in radar signal processing. In the recent past, many adaptive and neural network based methods have been proposed to achieve effective pulse compression performance for real coded transmitted waveforms. Even though the radar signal is complex, it is mostly processed as real-valued in-phase and quadrature components. Hence it is desirable that for processing complex radar signal for pulse compression both the structure as well as the learning algorithm associated with it need to be complex in nature. Accordingly in this paper a novel adaptive method is proposed by employing a complex valued fully connected cascaded (CFCC) neural network. For training this network, a new complex Levenberg–Marquardt (CLM) algorithm is derived and used for imparting effective training of its weights. The new CLM based CFCC (CFCC-CLM) model offers superior convergence performance with the least residual mean squared error during training phase compared to those provided by the multilayer perceptron (MLP) trained with complex domain backpropagation (CDBP) and CLM based methods. Further the comparison of peak signal-to-sidelobe ratio (PSR) under noisy and Doppler shift conditions of the proposed method exhibits best performance compared to those offered by the MLP-CDBP, MLP-CLM and the matched filter (MF) based methods.

Chirped optical pulse compression using a silicon photonic crystal waveguide

We present an integrated pulse compression method for chirped optical pulses based on silicon photonic crystal (PhC) line-defect waveguides. The PhC waveguide structure and dimensions, including the radius of the hole and the thickness of the slab, are carefully designed for effective pulse compression in a short waveguide. In the optimized PhC waveguide, the pulse is effectively compressed and a compression factor, which is defined as the ratio of the output pulse width with respect to the input pulse width, as small as 0.096 is achieved. Analysis shows that the compression effect depends on the initial chirp, the peak power, and the width of the input pulse. In order to realize the best compression, the PhC waveguide length should be carefully chosen to balance the initial chirp, dispersion and nonlinearity of the waveguide.

OPTIMIZATION OF FEMTOSECOND PULSE COMPRESSION BY PULSE ASYMMETRY MANAGEMENT

We present results of numerical studies of the phase compensation in the pulse compression process via the shaping of asymmetric pulses at the system input. In this case, an effective pulse compression is achieved, with a ratio corresponding to the pulse spectral broadening in fiber. This opportunity is caused by the fact that self-phase modulation in fiber results in a phase given by the pulse shape.

A compact double-pass Raman backscattering amplifier/compressor

The enhancement of stimulated Raman backscattering (SRBS) amplification was demonstrated by introducing a plasma density gradient along the pump and the seed interaction path and by a novel double-pass design. The energy transfer efficiency was significantly improved to a level of 6.4%. The seed pulse was amplified by a factor of more than 20 000 from the input in a 2mm long plasma, which also exceeded the intensity of the pump pulse by 2 orders of magnitude. This was accompanied by very effective pulse compression, from 500fsto90fs in the first pass measurements and in the second pass down to approximately 50fs, as it is indicated by the energy-pulse duration relation. Further improvements to the energy transfer efficiency and the SRBS performance by extending the region of resonance is also discussed where a uniform ∼4mm long plasma channel for SRBS was generated by using two subsequent laser pulses in an ethane gas jet.

Parametric oscillation and compression in KTP crystals

We report effective pulse compression under conditions of giant-pulse generation in a synchronously pumped parametric oscillator pumped by the second-harmonic radiation of an actively-passively mode-locked Nd;YAG laser with passive negative feedback. A minimum pulse duration of 0.39 ps is achieved. The output radiation can be tuned from 0.614 to 4.16 microm.

Range-time-sidelobe reduction technique for FM-derived polyphase PC codes

A simple, easy to implement technique is presented that can significantly reduce the range-time-sidelobes of a class of polyphase pulse compression codes. This technique reduces the highest sidelobes to only one code element magnitude independent of effective pulse compression ratio. The codes considered are polyphase codes that are derived from the step-approximation-to-linear-frequency-modulation and linear-frequency-modulation waveforms such as the P1, P3, P4, and the Frank codes. The characteristics of these codes that make this possible are explained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effective sum frequency pulse compression in nonlinear crystals

Sum frequency (SF) generation in the case of strong energy exchange and group velocity mismatch may lead to very effective SF pulse compression. The conditions needed for effective compression of SF pulses are found. It is possible to produce SF pulses the duration of which is sufficiently smaller than the initial duration of the pump pulses and almost the total energy of the pump pulses is converted into the SF wave. By this technique the 3 ps pump pulses (λ=1.06 μm) can be converted into a ≈3 cm KDP crystal to a 200 fs SF pulse (λ=0.53 μm) if the intensity of the pump pulses is ≈3 GW/cm 2.

Generation of chirped pulses in optical fibers suitable for an effective pulse compression

Simple formulae describing the generation of linearly frequency swept pulses in optical fibers and their subsequent compression are derived. The appropriate initial value problem is approximatively solved using partially the inverse scattering method and conservation laws for the nonlinear Schrödinger equation.