Showing papers in "Optics Letters in 1989"
TL;DR: A simple yet highly sensitive single-beam experimental technique for the determination of both the sign and magnitude of n(2), where the sample is moved along the z direction of a focused Gaussian beam while the repetitively pulsed laser energy is held fixed.
Abstract: We present a simple yet highly sensitive single-beam experimental technique for the determination of both the sign and magnitude of n2. The sample is moved along the z direction of a focused Gaussian beam while the repetitively pulsed laser energy is held fixed. The resultant plot of transmittance through an aperture in the far field yields a dispersion-shaped curve from which n2 is easily calculated. A transmittance change of 1% corresponds to a phase distortion of ≃ λ/250. We demonstrate this method on several materials using both CO2 and Nd:YAG laser pulses.
2,254 citations
TL;DR: Bragg gratings have been produced in germanosilicate optical fibers by exposing the core, through the side of the cladding, to a coherent UV two-beam interference pattern with a wavelength selected to lie in the oxygen-vacancy defect band of germania, near 244 nm.
Abstract: Bragg gratings have been produced in germanosilicate optical fibers by exposing the core, through the side of the cladding, to a coherent UV two-beam interference pattern with a wavelength selected to lie in the oxygen-vacancy defect band of germania, near 244 nm. Fractional index perturbations of approximately 3 x 10(-5) have been written in a 4.4-mm length of the core with a 5-min exposure. The Bragg filters formed by this new technique had reflectivities of 50-55% and spectral widths, at half-maximum, of 42 GHz.
1,987 citations
IBM1
TL;DR: By analyzing the propagation of terahertz electromagnetic pulses through water vapor, this work has made what it is believed are the most accurate measurements to date of the absorption cross sections of the water molecule for the nine strongest lines.
Abstract: We describe the application of a new high-brightness, terahertz-beam system to time-domain spectroscopy. By analyzing the propagation of terahertz electromagnetic pulses through water vapor, we have made what we believe are the most accurate measurements to date of the absorption cross sections of the water molecule for the nine strongest lines in the frequency range from 0.2 to 1.45 THz.
830 citations
TL;DR: A general criterion to describe this limitation that must be satisfied by all materials is derived and experimentally evaluated this criterion for a lead-glass fiber.
Abstract: Two-photon absorption can place a fundamental limitation on waveguide all-optical switching devices. We have derived a general criterion to describe this limitation that must be satisfied by all materials. As a specific example, we have experimentally evaluated this criterion for a lead-glass fiber.
424 citations
TL;DR: It should become possible, with a temporal microscope, to expand ultrafast optical phenomena to a time scale that is accessible to conventional high-speed photodiodes.
Abstract: A temporal imaging system is presented consisting of a dispersive input path, a phase modulator producing a phase modulation substantially equal to A+Bt 2 , and an output dispersive path. This temporal imaging system can be combined with other temporal lenses to image input signals in the same manner that spatial lenses can be used to image light from spatial sources. In particular, this temporal imaging system can be used to expand, compress and or invert input temporal signals.
411 citations
TL;DR: The microchip lasers demonstrate ways to reduce greatly the cost and complexity offabricating small lasers and electro-optic devices.
Abstract: Optically pumped, single-frequency, Nd-doped, solid-state lasers have been constructed using flat-flat cavities, which were diced from large dielectrically coated wafers of various crystals. For example, a Nd:YAG laser with a cavity length of 730 microm has operated at room temperature in a single longitudinal mode from a threshold of less than 1 mW to greater than 40 times the threshold. Theslope efficiency was greater than 30%. Heterodyne measurements showed an instrument-limited linewidth of 5 kHz. The microchip lasers demonstrate ways to reduce greatly the cost and complexity offabricating small lasers and electro-optic devices.
358 citations
TL;DR: The use of a coupling electromagnetic field is described to provide a general method of producing inversion-free laser systems and the interference between dressed states produces a zero in absorption while allowing gains of the order of that of the uncoupled system.
Abstract: We describe the use of a coupling electromagnetic field to provide a general method of producing inversion-free laser systems. The interference between dressed states produces a zero in absorption while allowing gains of the order of that of the uncoupled system.
258 citations
TL;DR: It is argued that optics can reduce the energy for irreversible communication of logic-level signals inside digital switching and processing machines due to an effective impedance transformation that matches the high impedances of small devices to the low impedances encountered in electromagnetic propagation.
Abstract: I argue that optics can reduce the energy for irreversible communication of logic-level signals inside digital switching and processing machines. This is because quantum detectors, quantum sources, and modulators can perform an effective impedance transformation that matches the high impedances of small devices to the low impedances encountered in electromagnetic propagation. Current physics and device concepts are sufficient to realize this advantage over electrical communications given appropriate integration technology. This energy argument suggests that all except the shortest intrachip communications should be optical.
254 citations
TL;DR: A simple model is presented to describe mode locking in a laser coupled to a nonlinear resonator, which reveals a new mechanism for pulse shortening and shows that shortening does not rely on dispersion in the auxiliary cavity.
Abstract: A simple model is presented to describe mode locking in a laser coupled to a nonlinear resonator. It reveals a new mechanism for pulse shortening and shows that shortening does not rely on dispersion in the auxiliary cavity. Experimental results are given to support the basic predictions of the model.
223 citations
TL;DR: Equations describing the pulse-front delay in singlet lenses, achromats, and compound lenses are presented, which is several orders of magnitude larger than the broadening caused by group-velocity dispersion in the lens material.
Abstract: Large temporal front distortion of femtosecond pulses occurs in lenses having chromatic aberration. The effect is due to the difference between the phase and group velocities. Equations describing the pulse-front delay in singlet lenses, achromats, and compound lenses are presented. The pulse-front delay is several orders of magnitude larger than the broadening caused by group-velocity dispersion in the lens material. Delays occurring in Fresnel-type zone plates are also described.
206 citations
TL;DR: This work presents a new iterative algorithm that holds promise of being a robust estimator and corrector for arbitrary phase errors and demonstrates its ability to focus scenes containing large amounts of phase error regardless of the phase-error structure or its source.
Abstract: Uncompensated phase errors present in synthetic-aperture-radar data can have a disastrous effect on reconstructed image quality. We present a new iterative algorithm that holds promise of being a robust estimator and corrector for arbitrary phase errors. Our algorithm is similar in many respects to speckle processing methods currently used in optical astronomy. We demonstrate its ability to focus scenes containing large amounts of phase error regardless of the phase-error structure or its source. The algorithm works extremely well in both high and low signal-to-clutter conditions without human intervention.
TL;DR: This work demonstrates the potential of solitons as the natural bits in ultrafast optical processing by observing switching of 93% of the total reflected energy in a partially transmitting integrated fiber loop mirror that makes up the interferometer.
Abstract: We demonstrate, for the first time to our knowledge, the switching of optical solitons. We observe switching of 93% of the total reflected energy in a partially transmitting integrated fiber loop mirror that makes up the interferometer. This result demonstrates the potential of solitons as the natural bits in ultrafast optical processing.
TL;DR: It is shown experimentally the trapping of orthogonally polarized solitons in birefringent optical fibers with polarization dispersions as high as 90 psec/km.
Abstract: We show experimentally the trapping of orthogonally polarized solitons in birefringent optical fibers with polarization dispersions as high as 90 psec/km. Solitons along two axes of a fiber compensate for the polarization dispersion by shifting their frequencies, and we observe frequency splitting up to 1.03 THz for a polarization dispersion of 80 psec/km. For a 20-m fiber the energy required to compensate for the polarization dispersion is ~84 pJ, and for a 76-m fiber the energy required reduces to ~64 pJ.
TL;DR: Experiments with a 5.2-km-long single-mode fiber reveal that the output signal is approximately 100 times that of the Rayleigh backscattered signal observed in conventional optical time-domain reflectometry.
Abstract: A new technique for measuring optical-fiber-attenuation characteristics is described The technique uses stimulated Brillouin scattering in the fiber between a counterpropagating pulsed pump wave and a cw Stokes probe wave Fiber attenuation is estimated nondestructively from amplification of the probe wave through stimulated Brillouin scattering Experiments with a 52-km-long single-mode fiber reveal that the output signal is approximately 100 times that of the Rayleigh backscattered signal observed in conventional optical time-domain reflectometry The signal fluctuation due to polarization-dependent Brillouin gain is successfully removed by polarization averaging
TL;DR: In this paper, the effects of saturation-induced cross talk and intermodulation distortion associated with multichannel signal amplification were investigated in erbium-doped fiber amplifiers.
Abstract: Transient gain saturation and recovery with 110–340-μsec time constants were observed in erbium-doped fiber amplifiers. This slow response reduces the effects of saturation-induced cross talk and intermodulation distortion associated with multichannel signal amplification. In a two-channel amplification experiment, negligible saturation-induced cross talk was measured at signal modulation frequencies >5 kHz. Increased suppression of saturation-induced cross talk was achieved through feed-forward compensation to reduce low-frequency gain fluctuations.
TL;DR: It is shown that these chirowaveguides cannot support individual TE, TM, or TEM modes and that they exhibit mode bifurcation in hybrid modes.
Abstract: We introduce here a new class of waveguides, chirowaveguides, which exhibit some novel and unique properties owing to electromagnetic chirality. These waveguides consist of cylindrical waveguides containing chiral, or optically active, materials. Owing to the optical activity of the material inside the waveguide, several unique and novel features are associated with this type of guided-wave structure. It is shown that these waveguides cannot support individual TE, TM, or TEM modes and that they exhibit mode bifurcation in hybrid modes. As an illustrative example the parallel-plate chirowaveguide is analyzed, and the corresponding dispersion relations and Brillouin diagrams are obtained. Some of the novel applications of chirowaveguides to integrated-optical devices and optical communications systems are presented.
TL;DR: Ultrashort pulses are generated in a Ti:Al(2)O(3) laser by using a coupled nonlinear external cavity to achieve passive mode locking without the need for synchronous pumping or acousto-optic modulation.
Abstract: Ultrashort pulses are generated in a Ti:Al2O3 laser by using a coupled nonlinear external cavity. The external cavity uses self-phase modulation in an optical fiber to achieve passive mode locking without the need for synchronous pumping or acousto-optic modulation. A stable train of chirped 1.4-psec pulses is generated. After dispersive compensation, pulses as short as 200 fsec are obtained.
TL;DR: A significant enhancement in the mode locking of a KCl:Tl color-center laser has been observed when a length of optical fiber having positive group-velocity dispersion was incorporated within an external control cavity.
Abstract: A significant enhancement in the mode locking of a KCl:Tl color-center laser has been observed when a length of optical fiber having positive group-velocity dispersion was incorporated within an external control cavity. Pulse durations of ~260 fsec were obtained by this method, representing a compression factor ~60× that with the color-center laser alone. Similar results have also been observed with an InGaAsP semiconductor diode amplifier as the nonlinear element within the control cavity.
TL;DR: By adiabatic amplification of a periodically modulated cw signal in an optical fiber, a train of approximately independent solitons can be generated at a high repetition rate (up to the terahertz range).
Abstract: By adiabatic amplification of a periodically modulated cw signal in an optical fiber, a train of approximately independent solitons can be generated at a high repetition rate (up to the terahertz range). These pulse trains can be produced with fibers having slowly varying dispersion as well.
TL;DR: Evidence that soliton pulse shaping is playing a key role in the formation of the pulses is presented, showing that mode-locked erbium-doped fiber laser pulses are generated from a wide-bandwidth, lithium niobate guided-wave modulator.
Abstract: We have generated pulses as short as 4 psec at 1530 nm from a mode-locked erbium-doped fiber laser. The mode locker is a wide-bandwidth, lithium niobate guided-wave modulator, and the fiber laser is completely integrated. We present evidence that soliton pulse shaping is playing a key role in the formation of the pulses.
TL;DR: Numerical solution of a general rate-equation model of an erbium-doped fiber amplifier highlights several important features of the device and shows that the detriment in the noise figure previously associated with counterpropagating schemes for only small-signal conditions is similar for strong signals.
Abstract: Numerical solution of a general rate-equation model of an erbium-doped fiber amplifier highlights several important features of the device. A difference in strong-signal gain between copropagating and counterpropagating signal pump schemes in the presence of pump excited-state absorption is predicted, and this is confirmed by experiment. The detriment in the noise figure previously associated with counterpropagating schemes for only small-signal conditions is shown to be similar for strong signals, corresponding to a power-amplifier operating regime. In addition, a correction to the noise figure is given for the limit of a low-gain amplifier.
TL;DR: Computer-simulation results indicate that binary phase IDO encoding is capable of generating two-dimensional spot arrays with diffraction efficiencies larger than 70% and can be employed to encode arbitrary images with twofold rotation symmetry.
Abstract: An iterative discrete on-axis encoding method for computer-generated holograms (termed IDO encoding) has been developed. The binary IDO method employs simulated annealing to optimize the hologram phase delay and reduce sensitivity to fabrication tolerances. Computer-simulation results indicate that binary phase IDO encoding is capable of generating two-dimensional spot arrays with diffraction efficiencies larger than 70%. An experimentally fabricated hologram, designed to account for a 6% manufacturing hologram thickness tolerance, produced a 3 × 3 array of spots with 59% diffraction efficiency. The binary IDO algorithm can be employed to encode arbitrary images with twofold rotation symmetry.
TL;DR: It is shown that nonlinear dark pulses in optical fibers are more stable than bright pulses with respect to loss and noise.
Abstract: We numerically study the initial-value problem of the nonlinear Schrodinger equation in the normal-dispersion regime of an optical fiber. A nonchirped hyperbolic tangent input pulse having arbitrary amplitude is found to evolve into a primary dark soliton having a constant amplitude and speed. The effect of the input amplitude is to alter the pulse width of the primary dark soliton. In addition, a set of secondary dark solitons of smaller amplitude moving away from the primary pulse is also generated. It is also shown that nonlinear dark pulses in optical fibers are more stable than bright pulses with respect to loss and noise.
TL;DR: The scattering of a p-polarized beam incident onto a random grating whose grooves are perpendicular to the plane of incidence displays a well-defined peak in the retroreflection direction for metallic and perfectly conductingrandom gratings but not for random gratings on dielectric surfaces.
Abstract: We study the scattering of a p-polarized beam incident onto a random grating whose grooves are perpendicular to the plane of incidence. The scattered field is expressed in terms of the total magnetic field and its normal derivative on the surface of the grating. The integral equations satisfied by these functions are solved numerically for each of several hundred realizations of the surface profile possessing a Gaussian spectrum. The diffuse component of the differential reflection coefficient averaged over these realizations displays a well-defined peak in the retroreflection direction for metallic and perfectly conducting random gratings but not for random gratings on dielectric surfaces.
TL;DR: The phase-gradient algorithm represents a powerful new signal-processing technique with applications to aperture-synthesis imaging, and it is shown that the estimator is in fact a linear, minimum-variance estimator of the phase derivative.
Abstract: The phase-gradient algorithm represents a powerful new signal-processing technique with applications to aperture-synthesis imaging. These include, for example, synthetic-aperture-radar phase correction and stellar-image reconstruction. The algorithm combines redundant information present in the data to arrive at an estimate of the phase derivative. We show that the estimator is in fact a linear, minimum-variance estimator of the phase derivative.
TL;DR: It is shown that interaction between darksolitons as well as between bright solitons is always attractive, but the interaction between bright and dark solitONS may be repulsive.
Abstract: We theoretically examine the interaction between two solitons in a double-mode optical fiber. The bound state between two solitons of different modes is investigated, including both dark and bright solitons. It is shown that interaction between dark solitons as well as between bright solitons is always attractive, but the interaction between bright and dark solitons may be repulsive. Analytical results are in agreement with numerical ones.
TL;DR: Experimental results in a uniform, supersonic, free-jet flow containing water vapor show that enhancement of OH concentration by focused UV photodissociation of H(2)O at 248 nm is an excellent tagging mechanism for velocity measurements.
Abstract: Experimental results in a uniform, supersonic, free-jet flow containing water vapor show that enhancement of OH concentration by focused UV photodissociation of for velocity H2O at 248 nm is an excellent tagging mechanism measurements. Two-dimensional images of OH fluorescence with a vidicon show a narrow initial enhanced OH zone along a straight line limited by the jet diameter. Fluorescence induced by a time-delayed pulsed dye laser documents the convection of this enhanced OH by the uniform core flow and reveals sharply stretched edge regions due to the shear layer with ambient air. The core flow velocity measurements are in agreement with predicted values.
TL;DR: Using numerical simulation, it is shown that solitons of any pulse width can avoid splitting or excessive broadening in response to birefringence of randomly varying orientation as long as the fiber's polarization-dispersion parameter is less than ~0.3D.
Abstract: Using numerical simulation, we show that solitons of any pulse width can avoid splitting or excessive broadening in response to birefringence of randomly varying orientation as long as the fiber’s polarization-dispersion parameter (in psec/km1/2) is less than ~0.3D1/2, where D is the dispersion parameter (in psec nm−1 km−1). Nevertheless, we also find that polarization dispersion tends to produce a significant amount of dispersive wave radiation from the soliton.
TL;DR: An analytical solution is obtained for solitary pulse propagation in an amplified nonlinear dispersive system that has ahyperbolic secant amplitude and a hyperbolic tangent instantaneous frequency variation.
Abstract: An analytical solution is obtained for solitary pulse propagation in an amplified nonlinear dispersive system. For a homogeneously broadened gain medium, this solitary pulse has a hyperbolic secant amplitude and a hyperbolic tangent instantaneous frequency variation. The pulse is a gain-guided pulse in either the positive or the negative dispersion regime as well as in the self-focusing or self-defocusing regime. A dark solitary pulse that has a hyperbolic tangent amplitude and a similar instantaneous frequency variation is also obtained.
TL;DR: A technique is described for imaging components of velocity in a gaseous flow field by using pulsed planar laser-induced fluorescence based on the fluorescence detection of Doppler-shifted absorption that results when a spectrally narrow absorption line is excited with a broadband laser.
Abstract: A technique is described for imaging components of velocity in a gaseous flow field by using pulsed planar laser-induced fluorescence. The technique is based on the fluorescence detection of Doppler-shifted absorption that results when a spectrally narrow absorption line is excited with a broadband laser. Results obtained in a Mach 7 underexpanded supersonic jet, seeded with NO, are presented. The practical extension of this technique to single-shot measurements of two velocity components is discussed.