Showing papers on "Chirp published in 1995"
TL;DR: In this paper, the authors describe a compact, economic and versatile diode laser system based on commercial laser diodes, optically stabilized by means of feedback from a diffraction grating, which offers singlemode operation with a linewidth of a few 100 kHz, continuous scans over 25 GHz, high chirp rates (up to 9 GHz/ms) and FM-modulation up to the GHz range.
519 citations
TL;DR: In this paper, the authors demonstrate dispersion compensation at two different wavelengths with such a grating in a 240 km fiber link using a 10 Gbit/s externally modulated laser source.
Abstract: Chirped sampled fibre Bragg gratings have a dispersion that repeats itself periodically, and can thus be used for dispersion compensation over a broad bandwidth, or for multiple channels in WDM systems. The authors demonstrate dispersion compensation at two different wavelengths with such a grating in a 240 km fibre link using a 10 Gbit/s externally modulated laser source.
219 citations
TL;DR: In this paper, an approximate analytical evaluation technique of self-phase modulation (SPM) in cascaded optical amplifier systems is proposed, where the effect of SPM on optical pulse distortion is represented by the increase in the /spl alpha/parameter of the transmitter.
Abstract: We propose an approximate analytical evaluation technique of self-phase-modulation (SPM) in cascaded optical amplifier systems. The effect of SPM on optical pulse distortion is represented by the increase in the /spl alpha/-parameter of the transmitter. The waveform distortion is approximated by assuming that the pulse is transmitted over a dispersive fiber without nonlinearity. This technique greatly reduces the calculation time, and is especially useful in designing cascaded amplifier systems, evaluating theoretical maximum transmission distance. >
101 citations
TL;DR: This paper describes a new method that permits the compensation of the RDRCM effect using a nonstandard Fourier transform (FT) that is applied, in the two-dimensional Fourier domain, to the range signal spectrum and allows the Compensation of the azimuth frequency-dependent scaling factor due to theRDRCM.
Abstract: Precision synthetic aperture radar (SAR) data processing requires the compensation of the range-dependent range cell migration (RDRCM) phenomenon. This paper describes a new method that permits the compensation of the RDRCM effect using a nonstandard Fourier transform (FT). This operation is applied, in the two-dimensional Fourier domain, to the range signal spectrum and allows the compensation of the azimuth frequency-dependent scaling factor due to the RDRCM. The nonstandard FT is performed via a chirp z-transform that is carried out with one convolution operation and two phase multiplications. >
100 citations
TL;DR: In this article, the temporal chirp structure of white-light continuum pulses used in femtosecond time resolved absorption spectroscopy was measured based on the nonresonant optical Kerr effect.
Abstract: We have developed a convenient method of measuring the temporal chirp structure of white-light continuum pulses used in femtosecond time resolved absorption spectroscopy. This method, based on the nonresonant optical Kerr effect, is superior in many respects to the existing one that uses the sum or difference frequency generation by a nonlinear crystal.
98 citations
TL;DR: In this article, a comprehensive analysis of the propagation of short pulses in fiber nonlinear directional couplers is presented, in particular, the limitations as well as the merits of the variational approach to describe power and phase-controlled pulse switching are discussed.
Abstract: A comprehensive analysis of the propagation of short pulses in fiber nonlinear directional couplers is presented. In particular, the limitations as well as the merits of the variational approach to describe power- and phase-controlled pulse switching are discussed. Relying on beam propagation calculations a trial function that accounts for variable width, amplitude, phase, and chirp of the pulses is proposed. The corresponding Euler-Lagrangian equations for the pulse parameters are derived and solved. Concerning power-controlled switching an excellent agreement of the switching curve with beam propagation results is found. Moreover, even the evolution of the various pulse parameters is shown to be described reasonably by the analytical model used. Eventually, optimum criteria for efficient phase-controlled switching may be easily derived by using the model presented.
81 citations
TL;DR: In this paper, the authors demonstrated that virtually unlimited bandwidths can be decoupled effectively by using chirp pulses with linear frequency modulation for adiabatic inversion combined with phasecycles and supercycles similar to those used in composite pulse decoupling.
80 citations
TL;DR: In this paper, a detailed system evaluation with an optical preamplified PIN-receiver, reveals a negligible dispersion power penalty for transmission distances between 35 and 70 km.
Abstract: 10-Gb/s long-haul transmission on standard single-mode fibers at 1.55 /spl mu/m with intensity modulated, low-chirp MQW DFB lasers is investigated. Successful transmission is achieved by operating the laser at increased bias. Thus, the laser chirp acts favorably on the propagation after an initial distance of 30 km in the fiber. A detailed system evaluation with an optical preamplified PIN-receiver, reveals a negligible dispersion power penalty for transmission distances between 35 and 70 km. The power penalty, mainly caused by a lower extinction ratio, must be accepted. >
80 citations
30 Oct 1995
TL;DR: In this article, an adaptive short-time Fourier transform (STFT) with chirping windows was proposed for near-optimal time-frequency-based FM estimation.
Abstract: Instantaneous frequency estimation is important in many applications, including FM demodulation. Time-frequency-based methods have been widely studied for IF estimation, particularly for low SNR, where they prove to be the most effective methods. We propose a new adaptive short-time Fourier transform algorithm, with chirping windows which is tailored for near-optimal time-frequency-based IF estimation. Extensive performance evaluations with both synthetic and real data demonstrate modest (1-2 dB) improvements in the threshold SNR over the best fixed-window STFTs. The computational cost of the new method is about ten times that of a fixed-window STFT.
78 citations
Patent•
07 Jun 1995TL;DR: In this article, a direct digital-to-analog microwave frequency signal synthesizer (DDFS) was proposed to improve frequency and phase agility, reduce spurious performance, and minimize direct analog circuitry.
Abstract: A direct digital-to-analog microwave frequency signal synthesizer device which employs both wideband and narrowband direct digital frequency synthesizer (DDFS) circuitry to improve frequency and phase agility, reduce spurious performance, and minimize direct analog circuitry. A clock output having an extremely precise and highly stabilized frequency is fed to the wideband DDFS circuit and to the narrowband DDFS circuit. One or the other is selectively enabled by control logic circuitry. When the former is enabled, precision, high frequency resolution, low spurious, fast frequency switching is achieved at the microwave output. When the latter is enabled, precision, high frequency and phase resolution, low spurious, is achieved, providing frequency chirp, and frequency phase control at the microwave output. The output of the wideband DDFS circuit is processed to reduce the spurious response and up-converted, while the output of the narrow band DDFS circuit is directly up-converted. The selected DDFS circuit, is frequency up-converted to provide a synthesized microwave output signal.
74 citations
TL;DR: In this article, a method for compensating large amounts of second-and third-order material dispersion is described, and two simple, compact and robust stretcher-compressor systems for microjoule and millijoule-level chirped-pulse amplification are presented.
Abstract: We describe a method for compensating large amounts of second- and third-order material dispersion, and we present two simple, compact and robust stretcher-compressor systems for microjoule-and millijoule-level chirped-pulse amplification. These systems, which use dispersive material to stretch and a modified grating pair to compress the pulse, provide expansion and compression with full cubic-phase compensation. Unlike previous fiber-stretcher systems which were limited to picosecond pulse durations, these systems can be used effectively with 50-fs microjoule pulses or 100-fs millijoule pulses. The results of our model are described, including the quartic-phase limitations for both systems. We discuss other applications of this grating pair to other areas of ultrafast optics, including intracavity dispersion compensation for femtosecond oscillators. >
TL;DR: In this article, the effect of the second post-Newtonian correction on the accuracy of the estimation of the parameters of the gravitational-wave signal from a coalescing binary is investigated.
Abstract: The effect of the recently calculated second post-Newtonian correction on the accuracy of the estimation of the parameters of the gravitational-wave signal from a coalescing binary is investigated. It is shown that the addition of this correction degrades considerably the accuracy of the determination of the individual masses of the members of the binary. However the chirp mass and the time parameter in the signal are still determined to a very good accuracy. The possibility of estimating the effects of other theories of gravity is investigated. The performance of the Newtonian filter is investigated and it is compared with the performance of post-Newtonian search templates introduced recently. It is shown that both search templates can extract accurately useful information about the binary.
TL;DR: In this paper, the lasing characteristics and dynamic properties of partly gain-coupled 1.55/spl mu/m DFB lasers with a gain corrugation in the strained-layer MQW active region are presented.
Abstract: The lasing characteristics and dynamic properties of partly gain-coupled 1.55-/spl mu/m DFB lasers with a gain corrugation in the strained-layer MQW active region are presented. Narrow spectral linewidth, which is associated with the low linewidth enhancement factor, was experimentally measured. By analyzing data from RIN measurements, the damping rate, the damping factor, the intrinsic bandwidth and the effective differential gain were obtained. From the small-signal frequency response, a measured 3 dB bandwidth of 22 GHz at 10 mW output power was achieved. The high bandwidth is believed to be related to the high differential gain, resulting from the combination of longitudinal gain and index-coupling mechanisms and the reduction of the carrier transport time, which is due to an efficient lateral carrier injection along the longitudinal interface. Experimental results show that under 10 Gbit/s pseudorandom NRZ modulation, the devices have small wavelength chirp and clear eye openings making them suitable for long haul and high bit-rate applications. >
TL;DR: An exact analytical expression for the time-bandwidth product DeltatDeltaf of chirped sech(2) pulses is derived and an experimental measurement of the alpha factor that relies on this formula is discussed.
Abstract: An exact analytical expression for the time-bandwidth product DeltatDeltaf of chirped sech(2) pulses is derived. The relation can be expressed by DeltatDeltaf = 0.1786 arcosh(cosh pialpha + 2) as a function of the laser's phase-amplitude coupling factor alpha. An experimental measurement of the alpha factor that relies on this formula is discussed.
TL;DR: The classical dynamics of a diatomic molecule modeled by a Morse oscillator interacting with a chirped infrared laser pulse is studied, which requires a much lower threshold laser intensity to achieve dissociation.
Abstract: The classical dynamics of a diatomic molecule modeled by a Morse oscillator interacting with a chirped infrared laser pulse is studied. When the chirping rate is small, the system can be described approximately in the moving frame by a time-independent Hamiltonian, which produces single-node separtrices (buckets) in phase space. Systems trapped in the buckets undergo convection to dissociation. This route to dissociation is different from the chaotic diffusion route for monochromatic excitation and requires a much lower threshold laser intensity to achieve dissociation.
TL;DR: In this paper, two measurement techniques for estimating the /spl alpha/ parameter of a laser, the frequency f/sub c/ for which the adiabatic and transient chirp of the laser have the same magnitude, and the dispersion coefficient D of an optical fiber are compared.
Abstract: Two measurement techniques for estimating the /spl alpha/ parameter of a laser, the frequency f/sub c/ for which the adiabatic and transient chirp of a laser have the same magnitude, and the dispersion coefficient D of an optical fiber are compared. The techniques rely on either a single measurement of the transfer function of a dispersive optical fiber using direct modulation of the laser, or two measurements of the fiber transfer function using external and direct modulation of the laser. Compared to the two measurement technique, the single measurement technique yields a smaller estimate of /spl alpha/ and a nearly identical estimate of f/sub c/, and can produce an unreliable estimate of D unless the frequency span in the parameter extraction procedure is sufficiently large. >
TL;DR: In this article, a wavelength scanning interferometric technique has been used to provide phase dispersion and time delay measurements of photorefractive fiber gratings with sub-picosecond time delay and 3pm wavelength resolutions for the first time.
Abstract: A wavelength scanning interferometric technique has been used to provide phase dispersion and time delay measurements of photorefractive fibre gratings with sub-picosecond time delay and 3pm wavelength resolutions for the first time. Chirped fibre grating filters for dispersion compensation in long fibre telecommunications links have been fully characterised.
TL;DR: In this article, a 120 mm long fibre Bragg grating, adjustably chirped by an offset-core technique, compensates for dispersion in a 10 Gbit/s optical communication system operating at 1054 mu m over 270 km of non-dispersion-shifted fibre.
Abstract: A 120 mm long fibre Bragg grating, adjustably chirped by an offset-core technique, compensates for dispersion in a 10 Gbit/s optical communication system operating at 1054 mu m over 270 km of non-dispersion-shifted fibre. Simultaneous compensation of fibre dispersion and source chirp in a directly modulated system is also described.
TL;DR: In this article, the authors demonstrate a method for producing chirped fiber Bragg gratings with a phase mask of uniform period by a simple stretch and write technique, which can be used for writing a controllable length, chirp and shading.
Abstract: The authors demonstrate a method for producing chirped fibre Bragg gratings with a phase mask of uniform period by a simple stretch and write technique. Gratings with widths of up to 10 nm have been fabricated by this method and the technique lends itself to writing gratings with controllable length, chirp and shading.
TL;DR: In this paper, a bending waveguide-based chirped gratings of ultra-high spatial precision is implemented using bent waveguides on homogeneous grating fields.
Abstract: DFB lasers with continuously and arbitrarily chirped gratings of ultrahigh spatial precision are implemented by a method we proposed recently, using bent waveguides on homogeneous grating fields. Choosing individual bending functions we generate special chirping functions and obtain additional degrees of freedom to tailor and improve specific device performances. We present two applications for lasers showing several improved device properties and the effectiveness of our method. First, we implement continuously distributed phase-shifted lasers, revealing a considerably reduced photon pile-up, higher single-longitudinal mode stability, higher output power, lower linewidth, and higher yield than conventional abruptly phase-shifted lasers. Second, a novel tuning principle is applied in chirped multiple-section DFB lasers, showing 5.5-nm wavelength tuning, without any gaps, maintaining high side-mode suppression. >
TL;DR: In this paper, static and dynamic thermal processes are incorporated into the modeling and simulation of DFB lasers, and analytical expressions for AM/FM responses considering both carrier and thermal effects are obtained.
Abstract: Static and dynamic thermal processes are incorporated into the modeling and simulation of DFB lasers. Analytical expressions for AM/FM responses considering both carrier and thermal effects are obtained. The self-consistency of this model is verified by comparing with experiment. Thermal effects on the laser performance such as L-I characteristics, lasing wavelength chirp, small signal AM/FM and large signal modulation responses are examined. It is noted that there is a trade-off between static and dynamic thermal wavelength chirps. >
TL;DR: In this article, a three-port MZI wavelength converter enables strong improvement of extinction ratios up to 11 dB in dynamic operation and signal chirp reduction by optical crossphase modulation.
Abstract: 2.5 Gbit/s all-optical wavelength conversion is reported with a novel monolithically integrated Mach-Zehnder interferometer realised in InGaAs/InP MQW technology. The three-port MZI wavelength converter enables strong improvement of extinction ratios up to 11 dB in dynamic operation and signal chirp reduction by optical crossphase modulation. This improvement of signal quality by wavelength conversion is confirmed by a gain of 2.3 dB in system sensitivity after transmission over 100 km (nondispersion-shifted) fibre compared to the standard 2.5 Gbit/s direct modulation performance of a DFB laser. >
TL;DR: In this article, a chirped grating has been written in a hydrogen-loaded standard telecommunication fibre, achieving a peak reflectivity of 96% and a bandwidth of 6.0 nm.
Abstract: A new and simple method for writing chirped fibre gratings is presented. It involves the use of a phase mask combined with a spherical lens and requires a controlled tilt between the fibre and the phase mask surface. A chirped grating has been written in a hydrogen-loaded standard telecommunication fibre. A peak reflectivity of 96% and a bandwidth of 6.0 nm have been achieved. This technique allows the production of a large range of chirp magnitudes.
TL;DR: In this paper, a variable output coupling scheme for a stretched-pulse polarization additive pulse mode-locked (APM) fiber ring laser is described, which allows the coupling percentage to be changed while the laser is running and allows for the maximum possible power extraction before cavity losses inhibit mode•locked operation.
Abstract: A variable output coupling scheme is described for a stretched‐pulse polarization additive pulse mode‐locked (APM) fiber ring laser. The scheme allows the coupling percentage to be changed while the laser is running and allows for the maximum possible power extraction before cavity losses inhibit mode‐locked operation. We describe how the nonlinear pulse dynamics change to compensate the change in cavity loss. Compared to high power output coupling schemes that use the APM rejection port, this method provides cleaner output pulses at comparable output powers. Pulse energies of 0.39 nJ are obtained at 48% output coupling in a diode‐pumped system. 88 fs pulses with time‐bandwidth products of 0.49 are obtained after output chirp compensation using a silicon prism pair.
TL;DR: Continuous tuning of the cubic and quartic phases of the pulse stretcher in a chirped-pulse amplification laser system is demonstrated and near-bandwidth-limited recompression of 100-fs pulses is obtained by minimizing the total phase through fourth order.
Abstract: We demonstrate continuous tuning of the cubic and quartic phases of the pulse stretcher in a chirped-pulse amplification laser system. We obtain near-bandwidth-limited recompression of 100-fs pulses by minimizing the total phase through fourth order.
TL;DR: In this article, a wide-stopband fiber transmission filter with single narrow transmission bands produced using multiply exposed chirped fiber grating resonators is presented, which achieves single passband transmission with an effective finesse of 48.
Abstract: Efficient, wide-stopband fibre transmission filters with single narrow transmission bands produced using multiply exposed chirped fibre grating resonators are reported. Tailored combinations of these structures with additional chirped gratings have achieved single passband transmission with an effective finesse of 48. This demonstrates the feasibility of fabricating all-fibre transmission filters with arbitrary passband/stopband combinations.
TL;DR: In this article, a totally integrated all-fibre femtosecond chirped pulse amplification scheme was described, which was temporally stretched, amplified in a diode pumped Yb-Er fiber amplifier and recompressed to give 900 fs pulses of 1.6 nJ energy and an average power of 4.8 mW.
Abstract: A totally integrated all-fibre femtosecond chirped pulse amplification scheme is described. Transform-limited 670 fs pulses at a 3.1 MHz repetition rate, derived from a diode pumped Yb-Er figure-of-eight fibre laser, were temporally stretched, amplified in a diode pumped Yb-Er fibre amplifier and recompressed to give 900 fs pulses of 1.6 nJ energy and an average power of 4.8 mW. Chirped Bragg fibre gratings were used to stretch and recompress the pulses, in a novel configuration which minimises loss.
TL;DR: Using a simple group delay model, the dispersion terms of quadratically chirped in-fiber Bragg gratings and their design parameters for using such devices to provide cubic and quadratic dispersion compensation were calculated in this article.
08 May 1995
TL;DR: The synthesizer's flexible waveform control provides a means for motion compensation, reducing ambiguities, and correction of nonlinearities in the transceiver's frequency response.
Abstract: A chirp synthesizer promises to have a great impact on waveform generation and local oscillator (LO) configurations for next-generation radar architectures. The flexibility in waveform control provided by the synthesizer offers the potential for improved radar performance. The synthesizer allows the generation of waveforms with a wide range of carrier frequencies, chirp rate, pulse widths, and pulse repetition frequencies. The variation of these parameters allows the radar to transmit different waveforms to achieve various missions such as target acquisition, tracking, or classification. The synthesizer's flexible waveform control provides a means for motion compensation, reducing ambiguities, and correction of nonlinearities in the transceiver's frequency response. Waveform distortion due to propagation path and component and signal processor errors can also be reduced by application of the synthesizer to perform certain error correction techniques. These features are realized in a small lightweight package that can be utilized in various radar scenarios. The paper discusses the salient features of the new chirp synthesizer and its application in various radar configurations.
TL;DR: Experimental and numerical verifications of the relationships between curvature and grating characteristics are presented and linear, quadratic, and square-root chirped gratings are obtained.
Abstract: We can introduce chirping, or a variation in the periodicity of a Bragg grating, into an optical fiber by writing gratings on curved optical fibers. By precisely specifying the curvature, we can obtain linear, quadratic, and square-root chirped gratings. Experimental and numerical verifications of the relationships between curvature and grating characteristics are presented.