Showing papers in "Optics Letters in 1992"
TL;DR: Laser beams that contain phase singularities can be generated with computer-generated holograms, which in the simplest case have the form of spiral Fresnel zone plates.
Abstract: Laser beams that contain phase singularities can be generated with computer-generated holograms, which in the simplest case have the form of spiral Fresnel zone plates.
1,251 citations
TL;DR: A new low-loss fast intracavity semiconductor Fabry-Perot saturable absorber operated at anti-resonance both to start and sustain stable mode locking of a cw-pumped Nd:YLF laser is introduced.
Abstract: We introduce a new low-loss fast intracavity semiconductor Fabry-Perot saturable absorber operated at anti-resonance both to start and sustain stable mode locking of a cw-pumped Nd:YLF laser. We achieved a 3.3-ps pulse duration at a 220-MHz repetition rate. The average output power was 700 mW with 2 W of cw pump power from a Ti:sapphire laser. At pump powers of less than 1.6 W the laser self-Q switches and produces 4-ps pulses within a 1.4-micros Q-switched pulse at an approximately 150-kHz repetition rate determined by the relaxation oscillation of the Nd:YLF laser. Both modes of operation are stable. In terms of coupled-cavity mode locking, the intra-cavity antiresonant Fabry-Perot saturable absorber corresponds to monolithic resonant passive mode locking.
674 citations
TL;DR: This work monitors the induced phase change produced by a cascaded chi((2)):chi((2)) process in KTP near the phase-matching angle on a picosecond 1.06-microm-wavelength beam using the Z-scan technique and predicts the maximum small-signal effective nonlinear refractive index.
Abstract: We monitor the induced phase change produced by a cascaded χ(2):χ(2) process in KTP near the phase-matching angle on a picosecond 1.06-μm-wavelength beam using the Z-scan technique. This nonlinear refraction is observed to change sign as the crystal is rotated through the phase-match angle in accordance with theory. This theory predicts the maximum small-signal effective nonlinear refractive index of n2eff≅±2×10−14 cm2/W (±1 × 10−11 esu) for an angle detuning of ±5° from phase match for this 1-mm-thick crystal with a measured deff of 3.1 pm/V For a fixed phase mismatch, this n2eff scales linearly with length and as deff2; however, for the maximum n2eff the nonlinear phase distortion becomes sublinear with irradiance for phase shifts near π/4.
614 citations
TL;DR: In this article, a high-speed optical coherence domain reflectometer was proposed for noninvasive measurement of anterior eye structure in a rabbit inυiυo and the characterization of reflections and interelement spacing in a multielement lens.
Abstract: We describe a high-speed optical coherence domain reflectometer. Scan speeds of 40 mm/s are achieved with a dynamic range of >90 dB and a spatial resolution of 17 μm. Two applications are presented: the noninvasive measurement of anterior eye structure in a rabbit inυiυo and the characterization of reflections and interelement spacing in a multielement lens.
457 citations
TL;DR: A new beam-propagation method is presented whereby the exact scalar Helmholtz propagation operator is replaced by any one of a sequence of higher-order Pade approximant operators, resulting in a matrix equation of bandwidth 2n + 1 that is solvable by using Standard implicit solution techniques.
Abstract: A new beam-propagation method is presented whereby the exact scalar Helmholtz propagation operator is replaced by any one of a sequence of higher-order (n, n) Pade approximant operators. The resulting differential equation may then be discretized to obtain (in two dimensions) a matrix equation of bandwidth 2n + 1 that is solvable by using Standard implicit solution techniques. The final algorithm allows (for n = 2) accurate propagation at angles of greater than 55 deg from the propagation axis as well as propagation through materials with widely differing indices of refraction.
421 citations
TL;DR: Characterizations of low-loss mirrors by measurements of cavity-decay time and of cavity finesse are reported and the lowest observed mirror loss is 1.6 x 10^-6 (transmission plus absorption and scatter).
Abstract: Characterizations of low-loss mirrors by measurements of cavity-decay time and of cavity finesse are reported near 850 nm The lowest observed mirror loss is 16 x 10^-6 (transmission plus absorption and scatter), which corresponds to a reflectivity of 09999984 and to a cavity finesse of 19 x 10^6
402 citations
TL;DR: By gradually translating the peak frequency of guiding filters along its length, this trick allows the use of stronger filters, and hence greater jitter reduction, without incurring the usual penalty of exponentially rising noise from the excess gain required to overcome filterloss.
Abstract: By gradually translating the peak frequency of guiding filters along its length, we create a fiber transmission line that is substantially opaque to noise while remaining transparent to solitons. This trick allows the use of stronger filters, and hence greater jitter reduction, without incurring the usual penalty of exponentially rising noise from the excess gain required to overcome filter loss.
398 citations
TL;DR: A volume holographic data storage scheme that employs counterpropagating reference and image beams and wavelength multiplexing for page differentation and a reduction in holographic cross talk is predicted.
Abstract: We propose a volume holographic data storage scheme that employs counterpropagating reference and image beams and wavelength multiplexing for page differentation. This method is compared with that based on angular multiplexing. A reduction in holographic cross talk is predicted. Further cross-talk reduction that is due to sidelobe suppression is observed in experiments by using photorefractive crystals and the proposed orthogonal data storage.
380 citations
TL;DR: It is reported that small particles with diameters of 1-27 microm have moved in the evanescent fields produced by a laser beam.
Abstract: We report that small particles with diameters of 1–27 μm have moved in the evanescent fields produced by a laser beam. The evanescent field in the experiment was produced in the near field of the surface of a high-refractive-index sapphire prism illuminated by a 1.06-μm YAG laser beam with an incident angle larger than the critical angle. Both polystyrene latex spheres and glass spheres bounced and ran along the surface of the prism when the laser beam was on. The maximum running speed obtained was approximately 20 μm/s. A micrograph of the running particles is shown with plots of the measured velocity versus the incident angle of the laser beam. Applications of this phenomenon are also discussed.
355 citations
TL;DR: The method is effective in controlling the random walk of solitons caused either by initial jitter and/or by amplifier noise (the Gordon-Haus effect) and in overcoming the bit-rate limitation that they provide.
Abstract: By a proper design of the frequency-dependent gain characteristic of optical amplifiers, the parameters (amplitude η and velocity κ) of optical solitons in fibers can be made to approach a desired fixed point in κ − η space. The method is effective in controlling the random walk of solitons caused either by initial jitter and/or by amplifier noise (the Gordon–Haus effect) and in overcoming the bit-rate limitation that they provide.
335 citations
TL;DR: A new type of lightmodulator, the deformable grating modulator, based on electrically controlling the amplitude of a micromachined phase grating is described, which allows the use of structures with high mechanical resonance frequencies.
Abstract: A new type of light modulator, the deformable grating modulator, based on electrically controlling the amplitude of a micromachined phase grating is described. Mechanical motion of one quarter of a wavelength is sufficient for switching in this device. The small mechanical motion allows the use of structures with high mechanical resonance frequencies. We have developed a deformable grating modulator with a bandwidth of 1.8 MHz and a switching voltage of 3.2 V and have demonstrated modulation with 16 dB of contrast. Smaller devices with bandwidths of as much as 6.1 MHz and predicted switching voltages of less than 10 V were also fabricated.
TL;DR: Self-focusing in conjunction with an intracavity aperture creates a power-dependent amplitude modulation in laser oscillators, which allows passive mode locking, and design issues for this mode-locking technique are discussed.
Abstract: Self-focusing in conjunction with an intracavity aperture creates a power-dependent amplitude modulation in laser oscillators, which allows passive mode locking. A simple analytical formalism yields closed-form expressions for the depth of passive amplitude modulation introduced by either the spatial gain profile or a hard aperture inserted in the resonator. Design issues for this mode-locking technique are discussed.
TL;DR: A single-mode linear-cavity fiber laser that utilizes intracore Bragg reflectors for cavity feedback has been continuously tuned, without mode hopping, when both the gratings and enclosed fiber are stretched uniformly.
Abstract: A single-mode linear-cavity fiber laser that utilizes intracore Bragg reflectors for cavity feedback has been continuously tuned, without mode hopping, when both the gratings and enclosed fiber are stretched uniformly. Continuous tuning is achieved in a 1.54-microm erbium fiber laser since the change in the reflected wavelength from a Bragg reflector tracks the change in the cavity resonance wavelength.
TL;DR: A simple dual-wavelength (two-color) Z-scan geometry is demonstrated for measuring nonlinearities at frequency omega(p) owing to the presence of light at omega(e) and this technique gives the nondegenerate two-photon absorption (2PA) coefficient beta(omega(p); omega( e) and the nondEGenerate nonlinear refractive index n(2) i.e., cross-phase modulation.
Abstract: A simple dual-wavelength (two-color) Z-scan geometry is demonstrated for measuring nonlinearities at frequency ωp owing to the presence of light at ωe. This technique gives the nondegenerate two-photon absorption (2PA) coefficient β(ωp; ωe) and the nondegenerate nonlinear refractive index n2(ωp; ωe), i.e., cross-phase modulation. We demonstrate this technique on CS2 for n2 and on ZnSe where 2PA and n2 are present simultaneously.
IBM1
TL;DR: By properly including the linear space–time focusing properties of short pulses, it is found that the trailing half of the self-focusing pulse is greatly enhanced and culminates in the formation of a trailing shock edge.
Abstract: Numerical analysis of the self-focusing of femtosecond optical pulses reveals that the usually invoked slowly varying envelope approximation breaks down long before the temporal structure reaches the time scale of an optical cycle. This breakdown leads to a dramatic departure from the recently predicted symmetric development of the self-focusing pulse. By properly including the linear space–time focusing properties of short pulses, it is found that the trailing half of the self-focusing pulse is greatly enhanced and culminates in the formation of a trailing shock edge.
TL;DR: Optical low-coherence ref lectometry is applied for the first time to the authors' knowledge to investigate diffusive biological tissues with a single-mode fiber probe, and this noninvasive method allows one to determine optical parameters, such as the index of refraction and the transmission properties, and the tissue thickness.
Abstract: Optical low-coherence reflectometry is applied for the first time to our knowledge to investigate diffusive biological tissues with a single-mode fiber probe. Samples of fresh arteries are studied, using the backscattered light from the tissue. The probed volume in the vicinity of the fiber tip is estimated to be below 6.7 × 10−10 cm3. This noninvasive method allows one to determine optical parameters, such as the index of refraction and the transmission properties, and the tissue thickness.
TL;DR: Ultrashort optical pulses have been amplified to 1.7 μJ of energy at a repetition rate of 250 kHz with a novel cw argon-pumped Ti:sapphire regenerative amplifier to generate a white-light continuum in an ethylene glycol jet.
Abstract: Ultrashort optical pulses have been amplified to 1.7 μJ of energy at a repetition rate of 250 kHz with a novel cw argon-pumped Ti:sapphire regenerative amplifier. Acousto-optic switching of the amplifier is used to achieve the high repetition rate. Chirped-pulse amplification is used to avoid nonlinear effects in the amplifier. After recompression, 1-μJ, 130-fs pulses are obtained and are used to generate a white-light continuum in an ethylene glycol jet.
TL;DR: In this paper, the Pade approximant wide-angle propagation operator is factored into a series of simpler Pade (1, 1) operators, thus leading naturally to a multistep method whose component steps are each solvable by using readily available paraxiallike solution techniques.
Abstract: A new beam-propagation method is presented whereby the Pade approximant wide-angle propagation operator is factored into a series of simpler Pade (1, 1) operators, thus leading naturally to a multistep method whose component steps are each solvable by using readily available paraxiallike solution techniques. The resulting method allows accurate approximations to true Helmholtz propagation while incurring only a modest numerical penalty. In addition, the tridiagonal form of the component steps allows the straightforward use of the previously reported transparent boundary condition.
TL;DR: A wavelength-division multiplexer with no polarization dependence is demonstrated, based on an arrayed-waveguide grating fabricated with silica-based optical waveguides on a silicon substrate, designed to operate in the 115th order for high wavelength resolution.
Abstract: A wavelength-division multiplexer with no polarization dependence is demonstrated. It is based on an arrayed-waveguide grating fabricated with silica-based optical waveguides on a silicon substrate. The polarization dependence that is due to the birefringence of the waveguide is eliminated by inserting a quartz λ/2 plate in the middle of the arrayed waveguide. Moreover the grating is designed to operate in the 115th order for high wavelength resolution. The polarization insensitivity and the high resolution lead to the successful multiplexing of 13 wavelength channels with 1-nm spacing. A passband width of 0.3 nm and a cross-talk level of −30 dB are achieved.
TL;DR: It is shown that a saturable absorber and a frequency limiter are required for the ring laser to self-start, i.e., to mode lock from initial noise and to operate stably, and that nonlinear polarization rotation with polarization selectivity inside the ring can act as a saturables absorber.
Abstract: A fiber ring laser that can produce nearly transform-limited soliton pulses is simulated. This laser has an erbium-doped optical-fiber amplifier and allows wavelength tuning through the interplay of fiber chromatic dispersion and the round-trip delay time of the laser. We show that a saturable absorber and a frequency limiter are required for the ring laser to self-start, i.e., to mode lock from initial noise and to operate stably. We also show that nonlinear polarization rotation with polarization selectivity inside the ring can act as a saturable absorber.
TL;DR: The present approach is robust and should permit the modeling of two- and three-dimensional optical soliton propagation, scattering, and switching from the full-vector Maxwell’s equations.
Abstract: The initial results for femtosecond electromagnetic soliton propagation and collision obtained from first principles, i.e., by a direct time integration of Maxwell's equations are reported. The time integration efficiently implements linear and nonlinear convolutions for the electric polarization and can take into account such quantum effects as Kerr and Raman interactions. The present approach is robust and should permit the modeling of 2D and 3D optical soliton propagation, scattering, and switching from the full-vector Maxwell's equations.
IBM1
TL;DR: The numerical simulations show that the dispersion causes the splitting of a pulse before it self-focuses into two temporally separated pulses, which then continue to self-focus and compress rapidly, results in periodic modulation of the generated continuum spectrum, as was recently observed in continuum generation by focused femtosecond pulses in gases.
Abstract: The self-focusing of femtosecond optical pulses in a normally dispersive medium is studied numerically. This situation represents a general problem that may be modeled by a 3 + 1-dimensional nonlinear Schrodinger equation, where two dimensions are self-focusing and the third is self-defocusing. The numerical simulations show that the dispersion causes the splitting of a pulse before it self-focuses into two temporally separated pulses, which then continue to self-focus and compress rapidly. The calculated behavior results in periodic modulation of the generated continuum spectrum, as was recently observed in continuum generation by focused femtosecond pulses in gases.
TL;DR: The dye-induced optical torque exceeds significantly the normal optical torque for all anthraquinone dyes investigated and with one of the dyes, optical Freedericksz transition in a planar layer is demonstrated.
Abstract: Optical reorientation measurements in dye-doped nematic liquid crystals are reported. The dye-induced optical torque exceeds significantly the normal optical torque for all anthraquinone dyes investigated. With one of the dyes, optical Freedericksz transition in a planar layer is demonstrated.
TL;DR: Two-photon-induced conductivity has been observed in Si and GaAsP photodiodes and in a CdS photo-conductive cell at room temperature and applied to the ultrashort optical pulse measurement with a simplified Michelson-type arrangement.
Abstract: Two-photon-induced conductivity has been observed in Si and GaAsP photodiodes and in a CdS photoconductive cell at room temperature and applied to the ultrashort optical pulse measurement with a simplified Michelson-type arrangement. The efficiency of the two-photon conductivity is found to be 3 × 10−14I A/W, where I is the intensity of the incident pulse in watts per squared centimeter. A single-shot pulse-width measurement has also been performed by using a two-dimensional silicon CCD array. Use of these inexpensive photodetectors with nonlinear characteristics has proved to be convenient for intensity correlators because of their instantaneous response to temporal coincidence of optical pulses and ease of optical arrangement.
TL;DR: It is shown that dark solitons form not only stable waveguides but also structures equivalent to Y-junction splitters and other devices.
Abstract: Dark spatial solitons are created when intense quasi-plane waves containing amplitude or phase discontinuities propagate through self-defocusing, Kerr-like media. We show that dark solitons form not only stable waveguides but also structures equivalent to Y-junction splitters and other devices.
TL;DR: For the first time to the authors' knowledge, transient oscillations were observed in DPS and the spectral shift of a probe pulse was time resolved together with the rise in DPS, which is clear evidence for induced phase modulation in absorptive materials.
Abstract: A new femtosecond time-resolved interferometer was developed that utilizes interference fringes in the frequency domain to obtain simultaneously difference phase spectra (DPS) and difference transmission spectra with a multichannel spectrometer. For the first time to our knowledge, transient oscillations were observed in DPS and the spectral shift of a probe pulse was time resolved together with the rise in DPS, which is clear evidence for induced phase modulation in absorptive materials.
TL;DR: A producing KTiOPO4-based optical parametric oscillator with external-pulse compression, 62-fs pulses at 76 MHz and 175-mW average power (37-kW peak power) is demonstrated.
Abstract: We demonstrate a producing KTiOPO4-based optical parametric oscillator with external-pulse compression, 62-fs pulses at 76 MHz and 175-mW average power (37-kW peak power). The oscillator is pumped synchronously with 800-mW, 110-fs pulses from a Kerr lens mode-locked Ti:Al2O3 laser operating at λ = 765 nm. The oscillator cavity length is actively stabilized, and the total amplitude noise is <1% (rms). With a single mirror set, the signal-beam wavelength is tunable between 1.20 and 1.34 μm. The idler beam tunes from 2.1 to 1.78 μm with an expected (uncompressed) pulse width of <400 fs and ~100-mW average power. Tuning throughout the bandwidth from 0.9 to 4.5 μm should be possible with additional mirror sets.
TL;DR: The magnitude of the nonlinear-optical coefficients of KTiOPO4 are measured relative to those of quartz and an effective d coefficient for type II phase matching at 1.064 μm of 3.35 pm/V is predicted.
Abstract: The magnitude of the nonlinear-optical coefficients of KTiOPO4 are measured relative to those of quartz at 0.88 μm. When we use for quartz d11 = 0.308 pm/V at 0.88 μm (which corresponds to 0.30 pm/V at 1.06 μm), the following results (in pm/V) are obtained for KTiOPO4 (at 0.88 μm): d15 = 2.04, d24 = 3.92, d31 = 2.76, d32 = 4.74, and d33 = 18.5. The accuracy of the measurements is estimated to be ±10%. These results, if corrected for dispersion, predict an effective d coefficient for type II phase matching at 1.064 μm of 3.35 pm/V.
TL;DR: The influence of normal group-velocity dispersion on the self-focusing of light pulses is numerically studied and temporal splitting of the field envelope is observed when the critical power is exceeded along with diffraction of the spatially sharpened central part of the pulse.
Abstract: The influence of normal group-velocity dispersion on the self-focusing of light pulses is numerically studied. Temporal splitting of the field envelope is observed when the critical power is exceeded along with diffraction of the spatially sharpened central part of the pulse. Dispersion increases considerably the self-focusing threshold for short pulse durations.
TL;DR: It is demonstrated that relaxation algorithms for the determination of the lowest-order modes of a refractive-index profile are identical to imaginary-distance propagation procedures.
Abstract: We demonstrate that relaxation algorithms for the determination of the lowest-order modes of a refractive-index profile are identical to imaginary-distance propagation procedures.