Showing papers on "Chirp published in 1984"
TL;DR: In this article, the results of a theoretical analysis of the self-phase modulation in a single-mode fiber are presented for the achievable compression and compressed pulse quality as functions of fiber length and input pulse intensity.
Abstract: The use of self-phase modulation in a single-mode fiber to chirp an optical pulse, which is then compressed with a grating-pair compressor, has been shown to be a practical technique for the production of optical pulses at least as short as 30 fsec. We report the results of a theoretical analysis of this process. Numerical results are presented for the achievable compression and compressed pulse quality as functions of fiber length and input pulse intensity. These results are given in normalized units such that they can be scaled to describe a wide variety of experimental situations and can be used to determine the optimum fiber length and compressor parameters for any given input pulse. Specific numerical examples are presented that suggest that the technique will generally be useful for input pulses shorter than about 100 psec. For energies of a few nanojoules per pulse, the compressed pulse widths will typically be in the femtosecond regime.
561 citations
TL;DR: In this paper, the inherent connection between frequency deviations and the optical power wave-form of a directly modulated semiconductor laser was derived, providing for the first time a quantitative assessment of inherent optical fiber dispersion penalties.
Abstract: Relations are derived concerning the inherent connection between frequency deviations and the optical power wave-form of a directly modulated semiconductor laser, providing for the first time a quantitative assessment of inherent optical fibre dispersion penalties of directly modulated lasers. The relations also indicate that control of chirp involves only the control of the intensity modulation characteristics and proper current drive of semiconductor lasers. Experimental measurement of FM and IM characteristics of a 1.55 μm DFB laser support the results.
349 citations
TL;DR: In this article, the authors evaluated the contribution of a few components of a mode-locked dye laser cavity to the dispersion of pulses of about 100 fs or shorter and found that the dispersive contributions should influence the mode-locking behavior for pulses of up to 100 fs.
Abstract: The contribution to dispersion of a few components of a mode-locked dye laser cavity has been evaluated. The chirp produced by the self-phase modulation within the saturable absorber has also been evaluated and compared with that resulting from the dispersive components. Cavity mirrors and blocks of transparent materials (glass or quartz) of a length exceeding 1 mm give the largest dispersion. The effect of self-phase modulation, at least for high saturation of the absorber, seems to play a comparable role. The dispersive contributions should influence the mode-locking behavior for pulses of about 100 fs or shorter.
87 citations
TL;DR: In this article, the reduction of frequency chirping and dynamic spectral linewidth in high-speed directly modulated semiconductor lasers, by external injection from a CW single-mode laser, was reported.
Abstract: We report the reduction of frequency chirping and dynamic spectral linewidth in high-speed directly modulated semiconductor lasers, by external injection from a CW single-mode laser. Reduction by more than a factor of 2 in chirped line-width was obtained in a GaAlAs laser modulated with a 1 GHz, 100 Ps current pulses.
67 citations
Patent•
03 Jul 1984
TL;DR: In this paper, a laser radar system employing a linear FM chirp laser followed by post detection pulse compression by a surface acoustic wave (SAW) device is described. Butler et al. used a high pressure CO 2 laser with an intracavity electro-optic modulator of CdTe.
Abstract: A laser radar system employing a linear FM chirp laser followed by post detection pulse compression by a surface acoustic wave (SAW) device. The system includes an FM chirp modulator that provides the needed tuning range and linearity for pulse compression. This modulation is accomplished by using a high-pressure CO 2 laser with an intracavity electro-optic modulator of CdTe. The frequency of the transmitter laser is accurately controlled through the application of high linearity, high frequency, sawtooth voltages to the two plates of the CdTe crystal, with the voltage waveform applied to one plate being out of phase with that applied to the other crystal plate. With the performance the system offers, absolute radar ranges can be measured to 0.22 m and velocities to 0.37 m/sec.
60 citations
TL;DR: In this article, a small current step in the leading edge of the drive pulse was proposed to reduce the carrier density oscillations and frequency chirping of single frequency semiconductor lasers. But the performance of the modified current pulse was limited.
Abstract: Carrier density oscillations and frequency chirping of pulse code modulated single frequency semiconductor lasers are shown to be greatly reduced by use of a small current step in the leading edge of the drive pulse. For a 100 km single mode fibre link the dispersion power penalty at 1.55 ?m resulting from dynamic line broadening is predicted to be reduced from 3.7 to 1.0 dB by use of the modified current pulse.
47 citations
TL;DR: The phase modulation arising from multilayer dielectric laser mirrors of a fs-dye-ringlaser has been calculated and measured by the determination of an equivalent intracavity path length in glass as discussed by the authors.
39 citations
TL;DR: In this paper, the frequency chirp characteristics of single-longitudinal-mode semiconductor laser operating at 15 μm wavelength and subject to large signal amplitude modulation in the 50 to 800 MHz range were measured on cleaved-coupled-cavity (C3) and GRIN-rod external cavity lasers.
Abstract: We have measured the frequency chirp characteristics of single-longitudinal-mode semiconductor lasers operating at 15 μm wavelength and subject to large signal amplitude modulation in the 50 to 800 MHz range Measurements on cleaved-coupled-cavity (C3) and GRIN-rod external cavity lasers show that the wavelength chirp is large enough to cause a penalty in ultra-high-bit-rate long-haul optical-fibre systems
34 citations
TL;DR: In this paper, the power response and the dynamic frequency shift (chirp) of an external cavity semiconductor laser are analyzed using a set of generalized rate equations for a single longitudinal mode selected by the coupled cavity device.
Abstract: Modulation characteristics such as the power response and the dynamic frequency shift (chirp) of an external‐cavity semiconductor laser are analyzed using a set of generalized rate equations for a single longitudinal mode selected by the coupled‐cavity device. The general formalism is applied to the specific case where the external cavity consists of a rod of graded‐index material (GRINROD cavity). Particular attention is paid to the chirp reduction and its optimization in the presence of intercavity coupling. The results are in reasonable agreement with the recent experimental observations.
31 citations
TL;DR: In this article, the frequency chirp in gain-guided, weakly index-guided and strongly-index-guided InGaAsP laser sources was measured under direct-current modulation.
Abstract: We have measured the frequency chirp in gain‐guided, weakly index‐guided, and strongly index‐guided InGaAsP lasers under direct‐current modulation. The measured chirp width is largest for gain‐guided and smallest for weakly index‐guided ridge waveguide lasers. The chirp width for 1.5‐μm InGaAsP lasers is about a factor of 2 larger than that for 1.3‐μm InGaAsP lasers of the same structure. The frequency chirping results from a modulaton of the carrier density which modulates the effective refractive index of the guided mode. The frequency chirping can introduce a limitation on the performance of single‐frequency injection laser sources for high bit‐rate digital transmission in fiber communication systems at 1.55 μm.
30 citations
Patent•
18 May 1984
TL;DR: In this article, the authors used a TE/CO2 multi-atmosphere gain module with sodium chloride windows amplified and shortened the optical pulse during successive passes through the module.
Abstract: A plasma is induced in a transmissive medium, and causes a chirp to be impressed on an optical pulse. The chirped pulse when passed through a dispersing means is then compressed. Applications of this pulse compression technique include the generation of short pulses of infrared at high power levels. Picosecond pulses of 10 micron energy are generated by switching a 2 picosecond portion from the output of a multi-atmosphere laser oscillator, and amplifying the portion in a CO2 gain module operated at gain saturation to cause a plasma front to propagate with the portion being amplified. A blue chirp of the pulse results. The pulse is passed through a dispersive medium, and a substantial decrease in pulse width and increase in energy density occurs during successive passes of the pulse through the gain module. Pulses as short as 500 femtoseconds have been produced at power densities of the order of 1012 watts/cm2. A TE/CO2 oscillator is used as the source of pulses, which are switched by a dye laser and a pair of cadmium/telluride reflection switches and a silicon transmission switch, and a TE/CO2 multi-atmosphere gain module with sodium chloride windows amplified and shortens the pulse during successive passes through the module.
TL;DR: In this paper, it was shown that the detectability of the plasma line in incoherent scatter radar experiments on the ionospheric plasma can be increased by factors in the range of 10-100 by chirping the transmitter frequency at a rate matching the rate of change of plasma frequency with height.
Abstract: It is shown that the detectability of the plasma line in incoherent scatter radar experiments on the ionospheric plasma can be increased by factors in the range of 10–100 by chirping the transmitter frequency at a rate matching the rate of change of plasma frequency with height. The method is explained in detail, and some initial experiments carried out at the Arecibo Observatory are described. Plasma frequency versus height profiles with an accuracy better than one part in 10³ were established with 1-s integration time per point. An example of quasi-periodic oscillation of ionospheric electron density with a period of about 18 min is also shown. The chirped frequency observations will greatly facilitate plasma line studies of photoelectrons, allow for studies of small-amplitude wavelike density perturbations, provide electron density profiles with high time resolution and unprecedented accuracy, make it possible to measure electron temperature independently of ion temperature, and probably allow for observations of vertical currents.
TL;DR: In this paper, it was shown that the phase modulation originates from saturation and phase memory in off-resonance interaction and the full cavity round-trip equation has been established and solved for steady-state pulses under different conditions.
Abstract: Starting from the complete set of Maxwell's equations and density matrix equations for the atomic systems, the change of amplitude and phase of light pulses in passing through absorbing and amplifying samples has been calculated by using certain approximations. It is shown that the phase modulation originates from saturation and phase memory in off-resonance interaction. The use of the simple rate-equation approximations.is only justified if saturation dominates. The full cavity round-trip equation has been established and solved for steady-state pulses under different conditions. For the case of pulses being outside resonance with the media we take into account a linear optical element for intracavity chirp compensation in order to describe the regime, where in experiment the shortest pulses have been found.
TL;DR: In this paper, the authors used a conventional and a cleaved-coupled-cavity (C3) laser obtained from the same wafer and found that the chirp for a C3 laser is typically reduced by a factor of 2.
Abstract: Chirping in coupled‐cavity lasers is studied experimentally and theoretically. Using a conventional and a cleaved‐coupled‐cavity (C3) laser obtained from the same wafer, we find that the chirp for a C3 laser is typically reduced by a factor of 2. A simple rate equation model is presented to account for reduced chirping. Mode selectivity arising from the cavity coupling is incorporated through wavelength‐dependent cavity‐loss variations.
01 Mar 1984
TL;DR: Real-time acousto-optic SAR processors are described and experimentally demonstrated in one of the architectures and in a different implementation, the imaging is preformed by interfering the light beams diffracted from two separate acoustic devices, one modulated the radar signal and the second by the reference chirp waveform.
Abstract: Real-time acousto-optic SAR processors are described and experimentally demonstrated SAR imaging is performed in one of the architectures by applying the signal to an acousto-optic device and correlating it with chirp signals recorded on an optical transparency by time integration on a CCD detector In a different implementation, the imaging is preformed by interfering the light beams diffracted from two separate acousto-optic devices, one modulated the radar signal and the second by the reference chirp waveform
TL;DR: In this paper, a closed solution for the stationary amplitude and phase of the pulses from a cw dye laser in the colliding pulse mode-locking regime is given for a single-pulse regime.
Abstract: Taking account of the different frequencies of the amplifier and absorber transitions and also of the pulse centre, equations are established and a closed solution is given for the stationary amplitude and phase of the pulses from a cw dye laser in the colliding pulse mode-locking regime. The results concerning the frequency range of a stable single pulse regime, the pulse duration and the sweep of the instantaneous carrier frequency of the pulse (chirp) give a good description of experimental data and permit an estimation of the conditions for extracavity and intracavity chirp compensation. The advantages of colliding pulse mode-locking are shown to arise from the enhanced pulse energy in the absorber due to the pulse timing, as well as from the coherent interaction of the counterpropagating pulses.
TL;DR: In this paper, the temporal coherence properties of picosecond pulses from GaAlAs semiconductor lasers have been studied by measuring first and second-order autocorrelation functions with a Michelson interferometer.
Abstract: The temporal coherence properties of picosecond pulses from GaAlAs semiconductor lasers have been studied by measuring first- and second-order autocorrelation functions with a Michelson interferometer. The time-bandwidth product and chirp have been evaluated for several different laser structures and frequency stabilization schemes. Time-bandwidth products from 1.2 for a CSP laser to 3.6 for a TJS laser were obtained with operating conditions representative of high-speed communication systems. Computer simulations based on the rate equations have been used to model the temporal coherence during the pulse and they show good agreement with our measurements. The results show that it is important to select the appropriate laser structure and stabilization scheme in applications where the temporal coherence is significant for system performance.
TL;DR: A class of bandlimited reference signals that have N discrete frequency components of equal magnitude is defined and it is shown that the system performance is primarily determined by the aperture weighting function and is much less dependent on the specific signal waveform.
Abstract: Both the spatial and the temporal spectra of reference signals used in interferometric spectrum analyzers affect the system performance. We define a class of bandlimited reference signals that have N discrete frequency components of equal magnitude. We show that the system performance is primarily determined by the aperture weighting function and is much less dependent on the specific signal waveform. The aperture weighting function can be used to match the spectral shape to the photodetector size, which then optimizes the dynamic range. Further, since the spatial aperture weighting is converted to an equivalent temporal weighting, this function can also be used to control spurious temporal modulation products. The analysis is extended to include results for periodic chirp signals such as those produced by VCO or SAW devices and shows that the results are not affected by using a reduced duty cycle. We also find that the effect of using finite as opposed to point photodetectors is to introduce an additional factor to the aperture weighting function. Control of both the spatial and temporal modulation products introduced by the periodic reference is necessary to achieve the expected dynamic range.
TL;DR: In this paper, a theoretical and experimental investigation of laser-induced frequency chirping in an e-beam controlled CO 2 laser is presented. The frequency increased as the cube of time at a rate proportional to the laser output power.
TL;DR: In this article, the spectral properties of a DFB laser under high-speed direct modulation were studied with an emphasis on the spectral analysis, and the possibility of reducing the frequency chirping by device parameter optimization was predicted on the basis of the experimental results obtained.
Abstract: Characteristics of a DFB laser under high-speed direct modulation are studied with an emphasis on the spectral analysis. A stable single-longitudinal-mode oscillation was confirmed up to 8.4 GHz direct modulation. The possibility of reducing the frequency chirping by device parameter optimisation is predicted on the basis of the experimental results obtained.
19 Jun 1984
TL;DR: In this paper, an optical pulse can be compressed by passing it through a singlemode fiber to induce a frequency chirp (as a result of self-phase modulation) followed by compression by a grating pair.
Abstract: An optical pulse can be compressed by passing it through a single-mode fiber to induce a frequency chirp (as a result of self-phase modulation) followed by compression by a grating pair. This technique has produced pulses as short as 30 fsec (Ref. 1) and high compressions in single and two-stage configurations.2 The technique is potentially useful over a wide range of input pulse parameters, but the magnitude of the compression and the quality of the compressed pulse are sensitive functions of the width, peak power, and wavelength of the input pulse as well as depending critically on the fiber length and the separation between the gratings.
TL;DR: In this article, the effect of laser chirp on optical systems was assessed and the results were in good agreement with simple modelling, which predicts no penalty for this system. But further tests are needed to determine whether this behaviour is typical.
Abstract: Initial assessment of the effect of laser “chirp” on optical systems is described. Measurements of the wavelength shift and its effect on the received pulse after 4 km and 80 km of dispersive fibre are presented. The results are in good agreement with simple modelling, which predicts no penalty for this system Further tests are needed to determine whether this behaviour is typical.
TL;DR: A mathematical model of this detection scheme which is used to extract the instantaneous time-dependent laser wavelength λ(t) from the measured data is presented.
Abstract: Picosecond pulses from semiconductor lasers are chirped (have time-dependent wavelengths) due to the effect of free carriers on the refractive index of the laser material. For optically pumped ultrashort-cavity semiconductor film lasers, the chirp is large (>1 nm/psec) and nonlinear in time because of the very high carrier concentration (> 1020 carriers/cm3) present during the operation of the laser. Experimentally, the chirp of film lasers is measured by optical upconversion sampling of the laser pulse followed by spectral filtering. This paper presents a mathematical model of this detection scheme which is used to extract the instantaneous time-dependent laser wavelength λ(t) from the measured data. Coefficients for the linear and quadratic terms of a power-series expansion of λ(t) are obtained for two InGaAsP film lasers. These parameters are used to compute time-averaged pulse spectra, which are compared with measured spectra. A formula is presented for the compression of chirped pulses in dispersive optical media which is used for comparison with experimental pulse compression results obtained by passing the film laser pulse through a short dispersive optical fiber. Finally, the time-dependent wavelength is related to the instantaneous carrier concentration in semiconductor material.
Patent•
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10 Feb 1984
TL;DR: In this article, the power consumption can be reduced by turning off the sweep current of a deflecting coil, returning the electronic beam to the central position of a CRT and making the consumption current except the sweep time into zero even at the off-center sweeping, after the sweep of a radar image or an electronic azimuth line.
Abstract: PURPOSE:To decrease power consumption by turning off the sweep current of a deflecting coil, returning the electronic beam to the central position of a CRT and making the consumption current except the sweep time into zero even at the off-center sweeping, after the sweep of a radar image or an electronic azimuth line is completed. CONSTITUTION:When a constant delaying time passes from the generating time of a trigger signal, the radar sweep signal for the X shaft and Y shaft is supplied to adding amplifiers 5A and 5B by a sweep gate signal, and the sweep of the radar and the azimuth line with an optional off-center position as a sweep starting point is started by an adding output with a bias voltage for the off-center. The sweep signal for the X shaft and Y shaft is also simultaneously supplied to a sweep signal generating circuit 22, and the circuit 22 outputs a sweep completing signal to a timing control circuit 24. The circuit 24 stops the output of the sweep gate signal, changes over switches 18a-20b to the ground side, and the supply is stopped from when the sweep of the bias signal for the off-center for the amplifiers 5A and 5B is completed until the next trigger occurs, and the deflecting electric current does not flow at deflecting coils 7A and 7B, and the power consumption is saved.
TL;DR: In this paper, the distortion of modulus and phase of the slowly varying envelope of ultrashort laser pulses in passing through absorbing samples has been calculated, and a frequency chirp has been detected.
Patent•
21 Dec 1984
TL;DR: By driving a semiconductor laser with a current pulse having an optimized shape, the relaxation oscillations of the laser are greatly suppressed, leading to significantly reduced frequency chirping and improved side mode suppression.
Abstract: By driving a semiconductor laser with a current pulse having an optimized shape, the relaxation oscillations of the laser are greatly suppressed This leads to significantly reduced frequency chirping and improved side mode suppression The pulse broadening normally produced by 100 km of single-mode fiber can be completely compensated by driving the laser with the optimized current pulse This invention can be applied to any type of single frequency laser including DFB, C 3 , and the like
Patent•
24 Jul 1984
TL;DR: In this paper, a method and apparatus for generating a sweep signal, the frequency of which is accurately known at all times during the sweep cycle, is described. But this method requires a phase-locked loop and the resulting error correction voltages are stored.
Abstract: A method and apparatus for generating a sweep signal, the frequency of which is accurately known at all times during the sweep cycle. The beginning and ending frequencies are fixed by a phase-locked loop and the resulting error correction voltages are stored. During the sweep, these error voltages determine the offset and slope of the D.C. voltage ramp signal which governs the frequency of the sweep oscillator.
TL;DR: An incoherent optical method for computing two-dimensional complex-valued Fourier transforms is described, based on implementing the two- dimensional chirp-z algorithm with incoherent Optical convolutions and indirect representation of complex- valued functions.
Abstract: An incoherent optical method for computing two-dimensional complex-valued Fourier transforms is described. It is based on implementing the two-dimensional chirp-z algorithm with incoherent optical convolutions and indirect representation of complex-valued functions.
01 Jan 1984
TL;DR: In this paper, the authors report the design, fabrication and assessment of a spectrum analyser in which the input is an SCT and the output is an array of transducers positioned along the locus traced out by the focus as the frequency changes.
Abstract: It has been shown that the Slanted Chirped Transducer (scp) launches surface wave8 (SAW) upon Y-cut lithium niobate that focus to a point and that the position of the focus is frequency dependent [I]. This paper reports the design, fabrication and assessment of a spectrum analyser in which the input is an SCP and the Output is an array of transducers positioned along the locus traced out by the focus as the frequency changes. Particular attention had been si6 to reducing the acoustic cross-tallc ( side-lobe levels) between channels employing techniques such a8 (i) weighting of the acoustic beam using the diffractive properties of the fingers, (ii) improving the focusing action by selecting a substrate orientation such that anisotropy compensated for the aberration p resent in the isotropic properties of an SCT and (iii) introducing frequency selectivity in the output transducer array. Experimental performance will be presented and compared with other spectrum analysers.
TL;DR: In this paper, the authors present experimental evidence for a chirp of about 1014 Hz/s in the cavity resonance during the pulse build-up time of a TEA CO2 laser.
Abstract: We present experimental evidence obtained by a laser heterodyne technique for a chirp of about 1014 Hz/s in the cavity resonance during the pulse build-up time of a TEA CO2 laser The frequency sweep arises from the refractive-index contribution of the time-dependent electron density in the exciting discharge plasma The phenomenon provides a mechanism, previously unexplained, for the extended and asymmetric mode selection zone in injection experiments