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Showing papers on "Chirp published in 2010"


Journal ArticleDOI
TL;DR: In this paper, a supercontinuum (SC) generation in all-normal dispersion photonic crystal fiber under high energy femtosecond pumping is numerically investigated, and it is shown that coherent octave spanning SC spectra with flatness of better than ± 1 dB can be achieved over the entire bandwidth.
Abstract: Supercontinuum (SC) generation in all-normal dispersion photonic crystal fiber under high energy femtosecond pumping is numerically investigated. It is shown that coherent octave spanning SC spectra with flatness of better than ±1 dB can be achieved over the entire bandwidth. A single pulse is maintained in the time domain, which may be externally compressed to the sub-10 fs regime even by simple linear chirp elimination. The single optical cycle limit is approached for full phase compensation, leading to peak power spectral densities of multiple kilowatts/nanometer. The generated SC is therefore ideal for applications which require high broadband spectral power densities as well as a defined pulse profile in the time domain. The properties of the generated SC are shown to be independent of the input pulse duration.

267 citations


Journal ArticleDOI
Toshiya Mitomo1, N. Ono1, Hiroaki Hoshino1, Yoshiaki Yoshihara1, Osamu Watanabe1, Ichiro Seto1 
TL;DR: In this paper, the first 77 GHz frequency modulated continuous wave (FMCW) radar transceiver IC with an accurate FMCW chirp signal generator using a 90 nm CMOS process is presented.
Abstract: The first 77 GHz frequency modulated continuous wave (FMCW) radar transceiver IC with an accurate FMCW chirp signal generator using a 90 nm CMOS process is presented. To realize accurate FMCW radar system in CMOS, a PLL synthesizer based FMCW generator with chirp smoothing technique that is able to output linear FMCW frequency chirp using a nonlinear reference chirp signal supplied from a low spec/cost digital-oriented frequency reference is applied. The fabricated IC consists of an LNA, a down-conversion mixer with an output buffer, a driver amplifier, a power amplifier with power combiner, an LO distributer and an FMCW synthesizer. The measured FMCW signal from the proposed FMCW generator achieves 93 kHz frequency error (nonlinearity) at the 77 GHz chip signal. Radar performance of the IC has less than 1% ranging error from 1 m to 8 m distance from the measurement in a laboratory. These results show the transceiver achieves a fundamental function for radar applications with 520 mW power consumptions.

251 citations


Journal ArticleDOI
TL;DR: Parabolic amplifier similaritons are observed inside a normal-dispersion laser and exhibit large (20 times) spectral breathing, and the pulse chirp is less than the group-velocity dispersion of the cavity.
Abstract: Parabolic amplifier similaritons are observed inside a normal-dispersion laser. The self-similar pulse is a local nonlinear attractor in the gain segment of the oscillator. The evolution in the laser exhibits large (20 times) spectral breathing, and the pulse chirp is less than the group-velocity dispersion of the cavity. All of these features are consistent with numerical simulations. The amplifier similariton evolution also yields practical features such as parabolic output pulses with high energies, and the shortest pulses to date from a normal-dispersion laser.

202 citations


Journal ArticleDOI
TL;DR: A spectroscopic method of molecular detection based on dispersion measurements using a frequency-chirped laser source that relies on heterodyne beatnote frequency measurements and shows high immunity to variations in the optical power received by the photodetector.
Abstract: A spectroscopic method of molecular detection based on dispersion measurements using a frequency-chirped laser source is presented. An infrared quantum cascade laser emitting around 1912 cm(-1) is used as a tunable spectroscopic source to measure dispersion that occurs in the vicinity of molecular ro-vibrational transitions. The sample under study is a mixture of nitric oxide in dry nitrogen. Two experimental configurations based on a coherent detection scheme are investigated and discussed. The theoretical models, which describe the observed spectral signals, are developed and verified experimentally. The method is particularly relevant to optical sensing based on mid-infrared quantum cascade lasers as the high chirp rates available with those sources can significantly enhance the magnitude of the measured dispersion signals. The method relies on heterodyne beatnote frequency measurements and shows high immunity to variations in the optical power received by the photodetector.

140 citations


Journal ArticleDOI
TL;DR: In this paper, a direct approach using ABR-latencies from normal-hearing subjects in response to octave-band chirps over a wide range of levels was proposed.
Abstract: A recent study evaluates auditory brainstem responses (ABRs) evoked by chirps of different durations (sweeping rates) [Elberling et al. (2010). J. Acoust. Soc. Am. 128, 215–223]. The study demonstrates that shorter chirps are most efficient at higher levels of stimulation whereas longer chirps are most efficient at lower levels. Mechanisms other than the traveling wave delay, in particular, upward spread of excitation and changes in cochlear-neural delay with level, are suggested to be responsible for these findings. As a consequence, delay models based on estimates of the traveling wave delay are insufficient for the design of chirp stimuli, and another delay model based on a direct approach is therefore proposed. The direct approach uses ABR-latencies from normal-hearing subjects in response to octave-band chirps over a wide range of levels. The octave-band chirps are constructed by decomposing a broad-band chirp, and constitute a subset of the chirp. The delay compensations of the proposed model are similar to those found in the previous experimental study, which thus verifies the results of the proposed model.

135 citations


Journal ArticleDOI
TL;DR: The stepped-frequency chirp signal (SFCS) is used to synthesize the ultrabroad bandwidth and reduce the requirement of sample rates and the simulations validate the theoretical formulation and robustness of the proposed m-D extraction method.
Abstract: The micro-Doppler (m-D) effect induced by the rotating parts or vibrations of the target provides a new approach for target recognition. To obtain high range resolution for the extraction of the fine m-D signatures of an inverse synthetic aperture radar target, the stepped-frequency chirp signal (SFCS) is used to synthesize the ultrabroad bandwidth and reduce the requirement of sample rates. In this paper, the m-D effect in SFCS is analyzed. The analytical expressions of the m-D signatures, which are extracted by an improved Hough transform method associated with time-frequency analysis, are deduced on the range-slow-time plane. The implementation of the algorithm is presented, particularly in those extreme cases of rotating (vibrating) frequencies and radii. The simulations validate the theoretical formulation and robustness of the proposed m-D extraction method.

111 citations


Journal ArticleDOI
TL;DR: In this paper, the authors numerically analyze the characteristics of silicon-based microring modulators consisting of a single-ring resonator and show that cavity dynamics significantly affect the modulation properties.
Abstract: We numerically analyze the characteristics of silicon-based microring modulators consisting of a single-ring resonator. Performance of the devices as digital intensity modulators is examined in terms of extinction ratio, pulsewidth, frequency chirp, spectral broadening, and signal quality. Three types of the modulators built in single-waveguide under-/overcoupling and dual-waveguide configurations are discussed. We show that cavity dynamics significantly affect the modulation properties. Data transmission performance over single-mode fibers is also presented. A silicon microring modulator with negative chirp could achieve 0.8 dB power penalty in 80-km fiber transmission without dispersion compensation.

105 citations


Journal ArticleDOI
TL;DR: In this paper, the authors introduced a general theoretical description of femtosecond pump-probe spectroscopy with chirped pulses whose joint spectral and temporal profile is expressed by Wigner spectrograms.
Abstract: This paper introduces a general theoretical description of femtosecond pump-probe spectroscopy with chirped pulses whose joint spectral and temporal profile is expressed by Wigner spectrograms. We demonstrate that the actual experimental time resolution intimately depends on the pulse-sample interaction and that the commonly used instrumental response function needs to be replaced by a sample-dependent effective response function. We also show that, using the proper configurations in excitation and/or detection, it is possible to overcome the temporal smearing of the measured dynamics due to chirp-induced pulse broadening and recover the temporal resolution that would be afforded by the transform-limited pulses. We verify these predictions with experiments using broadband chirped pump and probe pulses. Our results allow optimization of the temporal resolution in the common case when the chirp of the pump and/or probe pulse is not corrected and may be extended to a broad range of time-resolved experiments.

95 citations


Journal ArticleDOI
TL;DR: In this article, an approach to generate large time-bandwidth product (TBWP) microwave arbitrary waveforms based on optical pulse shaping using a single spatially discrete chirped fiber Bragg grating (SD-CFBG) is presented.
Abstract: We propose and experimentally demonstrate an approach to generating large time-bandwidth product (TBWP) microwave arbitrary waveforms based on optical pulse shaping using a single spatially discrete chirped fiber Bragg grating (SD-CFBG). The SD-CFBG functions to perform simultaneously spectral slicing, frequency-to-time mapping, and temporal shifting of the input optical pulse, which leads to the generation of an optical pulse burst with the individual pulses in the burst temporally spaced by the time delays determined by the SD-CFBG. With the help of a bandwidth-limited photodetector (PD), a smooth microwave waveform is obtained. The SD-CFBG is fabricated using a linearly chirped phase mask by axially shifting the photosensitive fiber to introduce a spatial spacing between two adjacent sub-gratings during the fabrication process. By properly designing the fiber shifting function, a large TBWP microwave arbitrary waveform with the desired frequency chirping or phase coding can be generated. An equation that relates the fiber shifting function and the microwave waveform frequency chirping is derived. The photonic generation of large TBWP microwave waveforms with a linear, nonlinear and stepped frequency chirping is experimentally demonstrated.

94 citations


Journal ArticleDOI
TL;DR: In this article, the authors report on the experimental observations for giant-chirped dissipative solitons emitted from a passively mode-locked fiber laser, which has ultra-large normal cavity dispersion.
Abstract: We report on the experimental observations for giant-chirped dissipative solitons emitted from a passively mode-locked fiber laser, which has ultra-large normal cavity dispersion. Two types of solitons coexist in the same cavity and evolve with different spectrum shapes, one of which is exhibited as a rectangular-spectrum profile and the other is as a bell-spectrum profile. Both are highly chirped due to the positively nonlinear effect together with strong normal dispersion. The maximal time-bandwidth product of solitons reported here can be as large as 236.3, which is far larger than 0.315 for the classical solitons. The dynamic evolution of solitons versus pump power is demonstrated. The experimental results suggest that the nonlinear polarization rotation and the gain filtering effect dominate the pulse-shaping alternately, which lead to the spectrum profile transforming. With further increasing the pump power, the proposed laser emits multiple pulses one by one, and the number of pulses can be up to five at the pump power of ~ 505 mW.

94 citations


Journal ArticleDOI
TL;DR: The first demonstration of a mode-locked parabolic pulse fiber laser, which can potentially be run at any wavelength using Raman gain is reported, using a new all-fiber ring similariton laser scheme.
Abstract: We report here the first demonstration of a mode-locked fiber laser delivering parabolic pulses (similaritons) at 1534 nm The use of a Raman-based gain medium potentially allows its implementation at any wavelength The 22nJ output similariton pulses have a true parabolic shape both in the time and spectral domains and a linear chirp Linear recompression close to Fourier limit is demonstrated allowing us to obtain 6 ps compressed pulses with a compression factor of 75

Journal ArticleDOI
TL;DR: By utilizing this novel technique, clear ISAR imaging can be achieved for maneuvering targets without an exhaustive search procedure for the motion parameters.
Abstract: A new inverse synthetic aperture radar (ISAR) imaging approach is presented for application in situations where the maneuverability of noncooperative target is not too severe and the Doppler variation of subechoes from scatterers can be approximated as a first-order polynomial. The proposed algorithm is referred to as the range centroid Doppler (RCD) ISAR imaging technique and is based on the stretch Keystone-Wigner transform (SKWT). The SKWT introduces a stretch weight factor containing a range of chirp rate into the autocorrelation function of each cross-range profile and uses a 1-D interpolation of the phase history which we call stretch keystone formatting. The processing simultaneously eliminates the effects of linear frequency migration for all signal components regardless of their unknown chirp rate in time-frequency plane, but not for the noise or for the cross terms. By utilizing this novel technique, clear ISAR imaging can be achieved for maneuvering targets without an exhaustive search procedure for the motion parameters. Performance comparison is carried out to evaluate the improvement of the RCD technique versus other methods such as the conventional range Doppler (RD) technique, the range instantaneous Doppler (RID) technique, and adaptive joint time-frequency (AJTF) technique. Examples provided demonstrate the effectiveness of the RCD technique with both simulated and experimental ISAR data.

Journal ArticleDOI
TL;DR: A passive optical resonator is used to enhance the power of a pulsed 78 MHz repetition rate Yb laser providing 200 fs pulses and limitations relating to the achievable time-averaged and peak power are found, which are distinguished by varying the duration of the input pulses.
Abstract: A passive optical resonator is used to enhance the power of a pulsed 78MHz repetition rate Yb laser providing 200fs pulses. We find limitations relating to the achievable time-averaged and peak power, which we distinguish by varying the duration of the input pulses. An intracavity average power of 18kW is generated with close to Fourier-limited pulses of 10W average power. Beyond this power level, intensity-related effects lead to resonator instabilities, which can be removed by chirping the seed laser pulses. By extending the pulse duration in this way to 2ps, we could obtain 72kW of intracavity circulating power with 50W of input power.

Journal ArticleDOI
TL;DR: The chirp managed laser (CML) as mentioned in this paper is an alternative transmitter technology that allows a directly modulated laser (DML) to be used in high-performance applications with a smaller size, lower power consumption, less device complexity, and lower cost.
Abstract: The chirp managed laser (CML) is an alternative transmitter technology that allows a directly modulated laser (DML) to be used in high-performance applications with a smaller size, lower power consumption, less device complexity, and lower cost. The CML comprises a DML and an isolated, passive optical filter. A key feature of the CML is its large tolerance to fiber dispersion, reaching over 360 km transmission at 10 Gb/s in standard single-mode fiber without dispersion compensation. The combination of adiabatic chirp from the laser and filter edge response produces high extinction ratio pulses with nearly uniform phase, abrupt phase shifts at bit transitions, and a correlation between the 1 bits; 1 bits separated by odd number of 0 bits are out of phase. This results in destructive intersymbol interference after fiber transmission. Other applications of CML are generation of advanced modulation formats, such as return-to-zero (RZ) alternate mark inversion, and RZ differential phase-shift keying. Tunable CML using DFB array, and sampled grating deterministic bit rate (DBR) technologies for 10 Gb/s metro applications have now been demonstrated. A four-element DBR array CML has also been demonstrated for 100 Gb/s metro applications. This paper reviews the principle of operation of CML and its various applications, as well as recent advances in CML-based devices.

Journal ArticleDOI
TL;DR: An analysis of a very broadband and linear (<1 ppm) chirped ladar system based on active chirp linearization as to their effect on the dynamic range, precision, and accuracy.
Abstract: As the bandwidth and linearity of frequency modulated continuous wave chirp ladar increase, the resulting range resolution, precisions, and accuracy are improved correspondingly. An analysis of a very broadband (several THz) and linear (<1 ppm) chirped ladar system based on active chirp linearization is presented. Residual chirp nonlinearity and material dispersion are analyzed as to their effect on the dynamic range, precision, and accuracy of the system. Measurement precision and accuracy approaching the part per billion level is predicted.

Journal ArticleDOI
TL;DR: By means of the similarity transformation connecting with the solvable stationary cubic-quintic nonlinear Schrodinger equation (CQNLSE), the authors construct explicit chirped and chirp-free self-similar cnoidal wave and solitary wave solutions of the generalized CQNL SE with spatially inhomogeneous group velocity dispersion (GVD) and amplification or attenuation.

Journal ArticleDOI
TL;DR: It is shown that the pulse broadening of the QD-MLL is caused by linear chirp for all values of current and voltage investigated here, resulting in a significantly increased overall mode-locking range of 101 MHz.
Abstract: A complete characterization of pulse shape and phase of a 1.3 µm, monolithic-two-section, quantum-dot mode-locked laser (QD-MLL) at a repetition rate of 40 GHz is presented, based on frequency resolved optical gating. We show that the pulse broadening of the QD-MLL is caused by linear chirp for all values of current and voltage investigated here. The chirp increases with the current at the gain section, whereas larger bias at the absorber section leads to less chirp and therefore to shorter pulses. Pulse broadening is observed at very high bias, likely due to the quantum confined stark effect. Passive- and hybrid-QD-MLL pulses are directly compared. Improved pulse intensity profiles are found for hybrid mode locking. Via linear chirp compensation pulse widths down to 700 fs can be achieved independent of current and bias, resulting in a significantly increased overall mode-locking range of 101 MHz. The suitability of QD-MLL chirp compensated pulse combs for optical communication up to 160 Gbit/s using optical-time-division multiplexing are demonstrated by eye diagrams and autocorrelation measurements.

Journal ArticleDOI
TL;DR: An amplification medium for optical parametric chirped-pulse amplification that allows for ultrabroadband gain in a collinear configuration based on aperiodic quasi-phase-matching using a QPM grating design with a linear chirp of its associated spatial frequencies is presented.
Abstract: We present an amplification medium for optical parametric chirped-pulse amplification that allows for ultrabroadband gain in a collinear configuration. Our approach is based on aperiodic quasi-phase-matching (QPM). For the first demonstration of this method in a mid-IR optical parametric chirped-pulse amplifier, we chose a QPM grating design with a linear chirp of its associated spatial frequencies. The resulting 7.4-mm-long, aperiodically poled Mg:LiNbO(3) amplification crystal has a chirp rate of kappa'=-250 cm(-2) and provides gain over the 800 nm bandwidth centered at 3.4 microm. We were able to generate pulses as short as 75 fs and the pulse energy at the output of the optical parametric amplifier before compression was 1.5 microJ. Low thermal load on the amplification medium allows for operation at a high repetition rate, 100 kHz in our case, and high average power limited only by the available pump power.

Journal ArticleDOI
TL;DR: The feasibility of high-SNR continuous wave depth-resolved photoacoustics with frequency-swept (chirp) modulation pattern has been demonstrated and utilization of chirped modulation waveforms achieves dramatic SNR increase of the periodic signals and preserves axial resolution comparable to the time-domain method.
Abstract: Sensitivity analysis of photoacoustic measurements is conducted using estimates of the signal-to-noise ratio (SNR) achieved under two different modes of optical excitation. The standard pulsed time-domain photoacoustic imaging is compared to the frequency-domain counterpart with a modulated optical source. The feasibility of high-SNR continuous wave depth-resolved photoacoustics with frequency-swept (chirp) modulation pattern has been demonstrated. Utilization of chirped modulation waveforms achieves dramatic SNR increase of the periodic signals and preserves axial resolution comparable to the time-domain method. Estimates of the signal-to-noise ratio were obtained using typical parameters of piezoelectric transducers and optical properties of tissue.

Journal ArticleDOI
TL;DR: Two novel bandwidth efficient pump-dithering Stimulated Brillouin Scattering suppression techniques are introduced that employ a frequency-hopped chirp and an RF noise source to impart phase modulation on the pumps of a two pump Fiber Optical Parametric Amplifier (FOPA).
Abstract: Two novel bandwidth efficient pump-dithering Stimulated Brillouin Scattering (SBS) suppression techniques are introduced. The techniques employ a frequency-hopped chirp and an RF noise source to impart phase modulation on the pumps of a two pump Fiber Optical Parametric Amplifier (FOPA). The effectiveness of the introduced techniques is confirmed by measurements of the SBS threshold increase and the associated improvements relative to the current state of the art. Additionally, the effect on the idler signal integrity is presented as measured following amplification from a two pump FOPA employing both techniques. The measured 0.8 dB penalty with pumps dithered by an RF noise source, after accruing 160ps/nm of dispersion with 38 dB conversion gain in a two-pump FOPA is the lowest reported to date.

Journal ArticleDOI
TL;DR: A compact all-fiber high-energy fiber laser that consists of a laser oscillator and a compression section that produces pulses with high energy and large chirp and dechirps the chirped pulses.
Abstract: We report a compact all-fiber high-energy fiber laser that consists of a laser oscillator and a compression section. The laser oscillator generates the pulses with high energy and large chirp. The compression section is made of a piece of standard single-mode fiber that dechirps the chirped pulses. The compact all-fiber fiber laser produces pulses with 8 nJ of the pulse energy and 290 fs of the pulse duration.

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate state-of-the-art slow light in silicon-on-insulator photonic crystal coupled waveguide, which allows slow light pulse transmission and its tunable delay by means of structural chirping.
Abstract: In this paper, we demonstrate state-of-the-art slow light in silicon-on-insulator photonic crystal coupled waveguide, which allows slow light pulse transmission and its tunable delay by means of structural chirping. The key idea of this study is the application of a folded chirping profile to the structure, instead of the conventional monotonous chirping. It suppresses unwanted spectral oscillation caused by structural disordering and expands the tuning range. By postprocessing an airhole-diameter-chirped device, we show that 0.9-ps-wide slow light pulses are delayed for 72 ps, corresponding to a buffering capacity of 80 bits. In a separate, unchirped device, we demonstrate a tunable delay by applying thermally induced index chirping. Here, a maximum tuning range of 103 ps and a tunable capacity of 22 bits are obtained.

Journal ArticleDOI
TL;DR: An experiment demonstrating the radarlike technique of "chirp and compress," where chirped biphotons are generated using a quasi-phase-matched nonlinear crystal where the phase-matched frequency varies linearly with position.
Abstract: We describe an experiment demonstrating the radarlike technique of "chirp and compress." Chirped biphotons are generated using a quasi-phase-matched nonlinear crystal where the phase-matched frequency varies linearly with position. Sum frequency generation is used to measure the amplitude of the biphoton wave function. As compared to a nonchirped crystal, compression and an increase in summing efficiency of a factor of 5 is observed.

Journal ArticleDOI
TL;DR: Output pulse energies of 20 nJ from an erbium-doped fiber oscillator that contains only positive dispersion fibers and is mode locked by use of nonlinear polarization evolution and stabilized with a birefringent filter are demonstrated.
Abstract: We demonstrate output pulse energies of 20nJ from an erbium-doped fiber oscillator that contains only positive dispersion fibers and is mode locked by use of nonlinear polarization evolution and stabilized with a birefringent filter. The fiber oscillator operates at a repetition rate of 3.5MHz with a central wavelength of 1550nm. The positively chirped output pulses have a duration of 53ps and are compressed to 750fs. The large positive chirp of the output pulses and the steep side edges of the pulse spectrum indicate dissipative soliton operation.

Journal ArticleDOI
TL;DR: In this article, a novel approach to achieving frequency sextupling using a polarization modulator and a wavelength-fixed optical notch filter is proposed and experimentally demonstrated, which can be used to generate high-spectral-purity subterahertz wave signals using relatively low-frequency electrical and optical devices.
Abstract: Optical frequency multiplication based on electrooptical modulation is an effective way to generate high-spectral-purity and frequency-tunable subterahertz waves. The previously demonstrated frequency-doubling and quadrupling techniques based on a Mach-Zehnder modulator have a low multiplication factor and suffer from bias drift problem and residual chirp. In this paper, a novel approach to achieving frequency sextupling using a polarization modulator and a wavelength-fixed optical notch filter is proposed and experimentally demonstrated. The method is free from bias drift problem and residual chirp, which can be used to generate high-spectral-purity subterahertz wave signals using relatively low-frequency electrical and optical devices. By using a narrow-bandwidth fiber Bragg grating as a wavelength-fixed optical notch filter, a high-spectral-purity microwave signal tunable from 18 to 27.6 GHz is generated when a microwave drive signal from 3 to 4.6 GHz is applied to the polarization modulator. The phase noise of the generated signal is measured as low as -107.57 dBc/Hz at a 10-kHz offset frequency. By replacing the narrow-bandwidth notch filter by an optical interleaver, a subterahertz wave tunable from 66 to 114 GHz is generated when the drive signal is tuned from 11 to 19 GHz. The distribution of the generated signal over optical fiber is investigated. The results show that the quality of the distributed subterahertz wave signal is maintained after transmission over a 40-km standard single-mode fiber.

Journal ArticleDOI
TL;DR: In this paper, a detailed theoretical and experimental study of the impact of amplified spontaneous emission (ASE) on self-phase modulation in semiconductor optical amplifiers (SOAs) is presented, including the ASE power and its effect on gain-saturation and gain-recovery.
Abstract: This paper presents a detailed theoretical and experimental study of the impact of amplified spontaneous emission (ASE) on self-phase modulation in semiconductor optical amplifiers (SOAs). A theoretical model of pulse propagation in SOAs is developed that includes the ASE power and its effect on gain-saturation and gain-recovery. We study the impact of ASE on the nonlinear phase shift, frequency chirp, spectrum, and shape of amplified picosecond pulses at a range of drive currents. We verify our predictions experimentally by launching gain-switched picosecond pulses with 3-mW peak power into a commercial SOA exhibiting 9-ps gain-recovery time at a current of 500 mA. Understanding the impact of ASE on SOAs is important for applications that employs SOAs for all-optical signal processing and as data-network amplifiers.

Journal ArticleDOI
TL;DR: The Rayleigh backscattering is found to be a significant frequency noise source dependent on fiber length, chirping rate and the power imbalance of the interferometer arms and techniques are put forward to reduce this noise contribution.
Abstract: We report on a fiber-stabilized agile laser with ultra-low frequency noise. The frequency noise power spectral density is comparable to that of an ultra-stable cavity stabilized laser at Fourier frequencies higher than 30 Hz. When it is chirped at a constant rate of approximately 40 MHz/s, the max non-linearity frequency error is about 50 Hz peak-to-peak over more than 600 MHz tuning range. The Rayleigh backscattering is found to be a significant frequency noise source dependent on fiber length, chirping rate and the power imbalance of the interferometer arms. We analyze this effect both theoretically and experimentally and put forward techniques to reduce this noise contribution.

Journal ArticleDOI
TL;DR: The processing of wideband signals collected by a planar array and generated by a scene placed in both near-field and far-field conditions is enabled with a computational load that is one or two orders of magnitude lower than that of the traditional frequency-domain and time-domain beamforming implementations.
Abstract: A planar array of sensors is required to collect the signals coming from a 3-D scene to generate volumetric underwater acoustic images. The method most frequently used to process the acquired signals is a digital beamforming algorithm. In general, owing to the high number of sensors and beam signals, the computational load is prohibitive for real-time image generation. In the literature, a frequency-domain beamforming technique based on the chirp zeta transform (CZT), which is efficient and computationally advantageous, has been introduced for linear and planar arrays working in the far field. This paper proposes an extension of the CZT beamforming that has been specifically devised to cope with the requirements of volumetric sonar imaging. In particular, the processing of wideband signals collected by a planar array and generated by a scene placed in both near-field and far-field conditions is enabled with a computational load that is one or two orders of magnitude lower than that of the traditional frequency-domain and time-domain beamforming implementations. To attain this result, the Fresnel delay approximation, a useful definition of steering angles, and the setting up of multiple focal regions are adopted. In addition, a computationally convenient technique to generate cubic resolution cells is introduced.

Journal ArticleDOI
TL;DR: In this article, the authors analyzed chirped laser pulses with a subcycle structure, and investigated the effects of the chirp parameter on the momentum spectrum of the produced particles.
Abstract: The recent developments of high intensity ultrashort laser pulses have raised the hopes of observing Schwinger vacuum pair production which is one of the important nonperturbative phenomena in QED The quantitative analysis of realistic high intensity laser pulses is vital for understanding the effect of the field parameters on the momentum spectrum of the produced particles In this study, we analyze chirped laser pulses with a subcycle structure, and investigate the effects of the chirp parameter on the momentum spectrum of the produced particles The combined effect of the chirp and carrier phase of the laser pulse is also analyzed These effects are qualitatively explained by investigating the turning-point structure of the potential within the framework of the complex WKB scattering approach to pair production

Journal ArticleDOI
TL;DR: An all-optical UWB pulses generation and modulation scheme using cross phase modulation (XPM) effect of semiconductor optical amplifier (SOA) and DWDM-based multi-channel frequency discrimination is proposed and demonstrated, which has potential application in multiuser UWB-Over-Fiber communication systems.
Abstract: An all-optical UWB pulses generation and modulation scheme using cross phase modulation (XPM) effect of semiconductor optical amplifier (SOA) and DWDM-based multi-channel frequency discrimination is proposed and demonstrated, which has potential application in multiuser UWB-Over-Fiber communication systems. When a Gaussian pulse light and a wavelength-tunable CW probe light are together injected into the SOA, the probe light out from the SOA will have a temporal chirp due to SOA-XPM effect. When the chirped probe light is tuned to the slopes of single DWDM channel transmittance curve, the optical phase modulation to intensity modulation conversion is achieved at DWDM that serves as a multi-channel frequency discriminator, the inverted polarity Gaussian monocycle and doublet pulse is detected by a photodetector, respectively. If the probe lights are simultaneously aimed to different slopes of several DWDM channels, multi-channel or binary-phase-coded UWB signal generation can be acquired. Using proposed scheme, pulse amplitude modulation (PAM), pulse polarity modulation (PPM) and pulse shape modulation (PSM) to UWB pulses also can be conveniently realized.