Showing papers in "Journal of The Optical Society of America B-optical Physics in 2007"
TL;DR: In this paper, the authors provide experimental design guidelines tailored ytterbium and erbium-based pumps around 1060 and 1550 nm, respectively, for supercontinuum generation in optical fibers.
Abstract: We review supercontinuum generation in optical fibers for particular cases where the nonlinear spectral broadening is induced by pump radiation from fiber-format sources. Based on numerical simulations, our paper is intended to provide experimental design guidelines tailored ytterbium and erbium-based pumps around 1060 and 1550 nm, respectively. In particular, at 1060 nm, we consider conditions under which the generated spectra are phase and intensity stable, and we address the dependence of the supercontinuum coherence on the input pulse parameters and the fiber length. At 1550 nm, special attention is paid to the case of dispersion-flattened dispersion-decreasing fiber, where we revisit the underlying physics in detail and explicitly examine the use of such fiber for supercontinuum generation with pumps of peak power in the range 200-1200 W and sub-10 m fiber lengths. We show that supercontinuum generation under such conditions can be highly coherent and can be applied to nonlinear pulse compression.
292 citations
TL;DR: In this paper, the phase matching between a plasmon and a core mode can be enforced by introducing air-filled microstructures into the fiber core, where the effective refractive index can be lowered to match that of a plasmus by introducing a small central hole into the fibre core.
Abstract: Design strategies for microstructured-optical-fiber (MOF-) based surface-plasmon-resonance (SPR) sensors are presented. In such sensors, plasmons on the inner surface of the large metallized channels containing analyte can be excited by a fundamental mode of a single-mode microstructured fiber. Phase matching between a plasmon and a core mode can be enforced by introducing air-filled microstructures into the fiber core. Particularly, in its simplest implementation, the effective refractive index of a fundamental mode can be lowered to match that of a plasmon by introducing a small central hole into the fiber core. Resolution of the MOF-based sensors is demonstrated to be as low as 3×10−5 RIU, where RIU means refractive index unit. The ability to integrate large-size microfluidic channels for efficient analyte flow together with a single-mode waveguide of designable modal refractive index is attractive for the development of integrated highly sensitive MOF-SPR sensors operating at any designable wavelength.
261 citations
TL;DR: In this paper, the experimental and theoretical aspects of a low-noise fiber-laser frequency comb were discussed, including the experimental configuration and the major contributions to the frequency noise and linewidth of the individual comb modes.
Abstract: We discuss experimental and theoretical aspects of a low-noise fiber-laser frequency comb, including the experimental configuration and the major contributions to the frequency noise and linewidth of the individual comb modes. Intracavity noise sources acting on the mode-locked laser determine the free-running comb linewidth and include environmental changes, pump noise, and amplified spontaneous emission (ASE). Extracavity noise sources acting outside of the laser typically determine the signal-to-noise ratio on the comb lines and include environmental effects, shot noise, and noise generated during supercontinuum generation. Feedback strongly suppresses these intracavity noise contributions, yielding a system that operates with comb linewidths and timing jitter below the quantum limit set by the intracavity ASE. Finally, we discuss correlations in the residual noise across a phase-locked comb.
246 citations
TL;DR: In this article, the authors demonstrate good beam quality from the combination of three fiber amplifiers, and discuss system scaling and design trades between laser linewidth, beam width, grating dispersion, and beam quality.
Abstract: Fiber lasers are well suited to scaling to high average power using beam-combining techniques. For coherent combining, optical phase-noise characterization of a ytterbium fiber amplifier is required to perform a critical evaluation of various approaches to coherent combining. For wavelength beam combining, we demonstrate good beam quality from the combination of three fiber amplifiers, and we discuss system scaling and design trades between laser linewidth, beam width, grating dispersion, and beam quality.
213 citations
TL;DR: In this article, the authors present a self-consistent theory based on wave kinetic equations that describes the generation spectrum and output power of a Raman fiber laser (RFL), and show that the quasi-degenerate four-wave mixing between different longitudinal modes is the main broadening mechanism in the one-stage RFL at high powers.
Abstract: We present a detailed analytical self-consistent theory based on wave kinetic equations that describes generation spectrum and output power of a Raman fiber laser (RFL). It is shown both theoretically and experimentally that the quasi-degenerate four-wave mixing (FWM) between different longitudinal modes is the main broadening mechanism in the one-stage RFL at high powers. The shape and power dependence of the intracavity Stokes wave spectrum are in excellent quantitative agreement with predictions of the theory. FWM-induced stochasticity of the amplitude and the phase of each of the ∼106 longitudinal modes generated in the RFL cavity is an example of a light-wave turbulence in a fiber.
204 citations
TL;DR: In this paper, a leakage channel fiber is designed to create large leakage loss for higher-order modes, while maintaining negligible transmission loss for the fundamental mode, which can be used for designing optical fibers with large effective area, which supports robust fundamental mode propagation.
Abstract: Leakage channel fibers, where few air holes form a core, can be precisely engineered to create large leakage loss for higher-order modes, while maintaining negligible transmission loss for the fundamental mode. This unique property can be used for designing optical fibers with large effective area, which supports robust fundamental mode propagation. The large air holes in the design also enable the optical fibers to be bend resistant. The principles of design and operation regime are outlined, demonstrating the potential of this approach for optical fibers that propagate a fundamental mode in core diameter exceeding 100 μm. Performance of a fabricated passive leakage channel fiber, an ytterbium-doped double-clad leakage channel fiber, and an ytterbium-doped polarization-maintaining double-clad leakage channel fiber are also discussed.
190 citations
TL;DR: In this article, the relative frequency stability of a millimeter scale resonator was shown to be at most one part per 10−12 per 1 s integration time, where s is the number of s.
Abstract: We discuss thermodynamic as well as quantum limitations of the stability of resonance frequencies of solid-state whispering-gallery-mode resonators. We show that the relative frequency stability of a millimeter scale resonator can reach one part per 10−12 per 1 s integration time.
190 citations
TL;DR: In this article, the absolute frequency stability of a millimeter-scale whispering gallery mode resonator was shown to reach one part per 10−14 per 1 s integration time if proper crystalline material as well as proper stabilization technique is selected.
Abstract: We show theoretically that the absolute frequency stability of a solid-state millimeter-scale whispering gallery mode resonator can reach one part per 10−14 per 1 s integration time if proper crystalline material as well as proper stabilization technique is selected. Both the fluctuations of the resonator temperature and the fluctuations of the temperature in the mode volume can be measured with the sensitivity better than the fundamental thermodynamic limit and actively compensated.
160 citations
TL;DR: In this article, the unsaturable optical losses in Bi-doped fibers have been revealed and their influence on the Bi-laser operation is investigated, and the frequency doubling of the bi-fiber laser radiation is demonstrated that can be used as a yellow light source (wavelength of 580 nm).
Abstract: Continuous-wave lasing of Bi-doped fiber lasers in a wavelength range of 1150-1215 nm with a power of up to 15 W has been obtained for the first time. The unsaturable optical losses in Bi-doped fibers have been revealed and their influence on the Bi-laser operation is investigated. Frequency doubling of the Bi-fiber laser radiation is demonstrated that can be used as a yellow light source (wavelength of 580 nm).
134 citations
TL;DR: In this paper, the results of pilot experiments carried out at the new infrared beamline SISSI (Source for Imaging and Spectroscopic Studies in the Infrared) operated at the synchrotron laboratory ELETTRA in Trieste, Italy, are compared with the results obtained with conventional IR sources.
Abstract: The results of pilot experiments carried out at the new infrared beamline SISSI (Source for Imaging and Spectroscopic Studies in the Infrared) operated at the synchrotron laboratory ELETTRA in Trieste, Italy, are presented and compared with the results obtained with conventional IR sources. The main figures of merit of the infrared synchrotron radiation (IRSR) such as brightness, spectral quality, and stability are discussed. Using a pinhole scanned across the IRSR beam, the effective beam size, the intensity, and the lateral distribution for different wavelengths are determined. The results obtained on geological and biological samples are used to illustrate how the broadband nature and high brightness of the IRSR beam allow IR spectroscopy experiments on diffraction-limited sample areas in both the mid-IR and far-IR regions.
123 citations
TL;DR: In this article, a range of measurements for characterizing two-qubit gates are discussed, ranging from simple measurement routines to full quantum state and process tomography, and the authors highlight connections between them, and discuss which measures are appropriate, given the stage of development of the gate.
Abstract: Accurate characterization of two-qubit gates will be critical for any realization of quantum computation. We discuss a range of measurements for characterizing two-qubit gates. These measures are architecture-independent and span a range of complexity from simple measurement routines to full quantum-state and process tomography. Simple indicative measures, which flag but do not quantify gate operation in the quantum regime, include the fringe visibility, parity, Bell-state fidelity, and entanglement witnesses. Quantitative measures of gate output states include linear entropy and tangle; measures of, and error bounds to, whole-gate operation are provided by metrics such as process fidelity, process distance, and average gate fidelity. We discuss which measures are appropriate, given the stage of development of the gate, and highlight connections between them.
TL;DR: In this article, the first pulse compression of ultrabroadband white-light continuum generated using both induced and self-phase modulations in an Ar-gas-filled hollow fiber was demonstrated.
Abstract: We demonstrate the first pulse compression of ultrabroadband white-light continuum generated using both induced- and self-phase modulations in an Ar-gas-filled hollow fiber. By feedback chirp compensation with a liquid crystal spatial light modulator and a modified spectral interferometry for direct electric-field reconstruction, 2.6-fs, 1.4-GW, 1.3-cycle transform-limited pulses are generated in the visible to near-infrared region.
TL;DR: Simulations demonstrating the possibility of precompensating for feature size when designing intensity shapers are presented, and it is shown that the transmission degradation is highly predictable for this algorithm.
Abstract: An error diffusion algorithm is used to design binary pixelated beam shapers. Beam shapers based on pixels with transmission equal either to 0 or 1 can be synthesized with this deterministic algorithm to provide continuous intensity shaping after Fourier filtering. The capabilities of these shapers are studied for high-power lasers. A particular emphasis is placed on the influence of the feature size on the performance of the designed shapers, and it is shown that the transmission degradation is highly predictable for this algorithm. Simulations demonstrating the possibility of precompensating for feature size when designing intensity shapers are presented.
TL;DR: In this paper, the optical nonlinearity of an aqueous colloid containing silver nanoparticles (NPs) was investigated using the Z-scan technique using a laser at 532 nm that delivers single 80 ps pulses at a low repetition rate.
Abstract: The optical nonlinearity of an aqueous colloid containing silver nanoparticles (NPs) was investigated using the Z-scan technique. Values for the third-, fifth-, seventh-, and ninth-order susceptibilities were obtained, and their dependence with the volume fraction occupied by the NPs was determined. The experiments were performed with intensities between 0.1 and 1.5 GW/cm2 using a laser at 532 nm that delivers single 80 ps pulses at a low repetition rate.
TL;DR: Optical fibers with large diameter cores having a negative index step from cladding to core combined with an adequately large gain coefficient in the core provide near-optimal mode properties for fiber lasers delivering robust single transverse mode operation with very large mode areas as mentioned in this paper.
Abstract: Optical fibers with large diameter cores having a negative index step from cladding to core combined with an adequately large gain coefficient in the core provide near-optimal mode properties for fiber lasers delivering robust single transverse mode operation with very large mode areas. Basic properties and simple design formulas for such fibers are presented.
Journal Article•
TL;DR: In this paper, the linear and nonlinear optical properties of the novel organic crystal 4-N, N-dimethylamino-4′-N′-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS) were reported.
Abstract: We report on the linear and nonlinear optical properties of the novel organic crystal 4-N, N-dimethylamino-4′-N′-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS). The principal refractive indices n1, n2, and n3 have been determined by a direct measurement of the group index dispersion over a broad wavelength range from 0.6 to 1.6 μm. The linear absorption coefficients for light polarized along the dielectric axes have been measured in the transparency range from 600 to 2000 nm. DSTMS crystals show a large birefringence of Δn=0.5 and low absorption α<0.7 cm−1 in the telecommunication wavelength range at 1.55 μm. Furthermore, the nonlinear optical tensor elements d111, d122, and d212 have been determined by the Maker-fringe technique at the fundamental wavelength of 1.9 μm. DSTMS crystals exhibit a very large nonlinear activity with a nonlinear optical coefficient d111=214±20 pm/V. Phase-matching curves determined from our optical data showed that parametric oscillation can be achieved in the wavelength range from 1 to 2.2 μm with effective nonlinear optical coefficients larger than 25 pm/V.
TL;DR: In this paper, the authors developed a metal hollow waveguide as a flexible delivery medium of terahertz waves, and they measured transmission losses in the region of hollow waveguides with inner silver coating.
Abstract: We developed a metal hollow waveguide as a flexible delivery medium of terahertz waves. Theoretical evaluation shows that a metal waveguide mainly supports TE modes and that the TE11 mode shows a high coupling coefficient to linearly polarized light. Also the TE11 mode brings less mode conversion to high-order modes than the TE01 mode giving the lowest loss. We measured transmission losses in the terahertz region of hollow waveguides with inner silver coating; the losses were ∼7.5-8dB/m at the wavelengths from 190-250μm for waveguides with an inner diameter of 1mm. These losses coincide well with theoretical ones, and this shows that in these waveguides, the TE11 mode is dominant when a linearly polarized beam is launched into them. The waveguides are flexible because we use a thin-wall glass capillary as the base tubing. Our experiment revealed low additional losses due to bending even when complicated bends were applied to the waveguides. The metal-coated hollow fiber with an inner diameter of 1mm is sufficiently small and flexible for use in endoscopic applications.
TL;DR: In this paper, the authors demonstrate wideband, low-noise, highly coherent, and ultraflat supercontinuum (SC) generation using soliton pulse and normal dispersion highly nonlinear fibers.
Abstract: Recently, widely broadened supercontinuum (SC) has been generated using ultrashort pulse and highly nonlinear fibers. However, inherent noise and fine structures have been the problem for the application of SC. We demonstrate wideband, low-noise, highly coherent, and ultraflat SC generation using soliton pulse and normal dispersion highly nonlinear fibers. Characteristics of generated SC are experimentally evaluated, and they are compared with those of the conventional SC. Octave spanning high-quality SC is also generated using high-power soliton pulse.
TL;DR: In this article, the authors examined the sensor capability of whispering gallery mode (WGM) evanescent waves to detect adsorption of molecules to the surface of microsphere sensors and more particularly to the utilization of a high refractive index surface layer to increase the sensitivity thereof.
Abstract: The use of whispering gallery mode (WGM) evanescent waves to detect adsorption of molecules to the surface of microsphere sensors and more particularly to the utilization of a high refractive index surface layer to increase the sensitivity thereof. The present invention examines the sensor capability of WGM in a dielectric sphere coated with a thin uniform dielectric layer of a high refractive index. Among the utilities of such a modified resonator for the sensing are to have an evanescent field of a different penetration depth without using a non-silica based microsphere or changing the laser wavelength, to further enhance the sensitivity by drawing the optical field of WGM into the coating layer, and to realize the same relative shifts for WGM of different radial modes, thus eliminating ambiguities in the measurement of a refractive index change in the surrounding medium.
TL;DR: In this article, the effect of hydrostatic pressure on solid and hollow microsphere optical resonators was investigated and the feasibility of a micro-optical pressure sensor based on whispering gallery modes (WGMs) and quantifying the deleterious effect of environmental pressure changes on other WGM-based sensors was explored.
Abstract: The effect of hydrostatic pressure on solid and hollow microsphere optical resonators was investigated. The primary goal was to explore the feasibility of a micro-optical pressure sensor based on whispering gallery modes (WGMs) and to quantify the deleterious effect of environmental pressure changes on other WGM-based sensors. Expressions were developed for WGM shifts due to changes in hydrostatic pressure of the environment surrounding the spherical resonators. These expressions were validated through experiments in which the pressure-induced WGM shifts of hollow polymethyl methacrylate microspheres were monitored. The effect of atmospheric pressure variations on silica resonators is negligible, but hydrostatic pressure may be effective in the optical tuning of hollow polymer spheres.
TL;DR: In this paper, the authors review the ways in which photonic crystal fibers are affecting and may further affect the development and deployment of fiber laser technology, and present a review of some of the most significant developments in this area.
Abstract: Photonic crystal fibers and fiber lasers have been two of the most rapidly evolving areas of optics and photonics over the past few years. Recent developments in the field of photonic crystal fibers are enabling new ways to generate, transform, and deliver light, and have significant implications for fiber laser design and applications. We review the ways in which photonic crystal fibers are affecting and may further affect the development and deployment of fiber laser technology.
TL;DR: In this paper, the upconversion of Er3+-doped metaphosphate glasses with 794nm excitation was investigated and a mechanism, involving excited state absorption and energy transfer upconverting, has been proposed to explain the up-conversion process.
Abstract: Metaphosphate glasses doped with five concentrations of Er3+ ions have been investigated through absorption and emission spectra, decay curves, and upconversion measurements. Judd-Ofelt parameters have been evaluated from absorption spectrum of the 1.0mol.%Er3+-doped glass, which are in turn used to predict radiative properties of some important luminescence levels of Er3+ ions in these glasses. Gain bandwidths of an optical amplifier have been evaluated and are compared with those of reported Er3+:glass systems. Temperature dependence of the 1.5μm emission has been studied for the 2.0mol.%Er3+-doped glass from 13K to room temperature. Lifetimes of the I13/24 level were measured and are found to decrease with concentration of Er3+ ions after 0.1mol.%. Concentration quenching of lifetimes has been analyzed using the theory developed by Auzel [J. Lumin.94-95, 293 (2001); Opt. Mater.24, 103 (2003)]. Infrared to visible upconversion was also measured for three concentrations of Er3+-doped metaphosphate glasses with 794nm excitation. A mechanism, involving excited state absorption and energy transfer upconversion, has been proposed to explain the upconversion process.
TL;DR: In this article, the authors investigated the properties of plasmon polaritons guided by 2D monoangular metal corners with a vector finite-element method and found that both a smaller corner angle and a sharper corner tip help to better confine the mode field.
Abstract: We investigate the properties of plasmon polaritons guided by 2D monoangular metal corners with a vector finite-element method. Such corner waveguides in general include both V-channel- and Λ-wedge-type waveguides. The influences of both geometric parameters (i.e., corner angle, tip sharpness, etc.) and operating wavelength to the mode properties, such as effective mode index, loss, and mode field size, are inspected. It is noticed that both a smaller corner angle and a sharper corner tip help to better confine the mode field. The confinement of the V-channel waveguide is found to be especially sensitive to its angle, while the confinement of the Λ-wedge waveguide is affected about equally by its angle and tip sharpness. Almost all superior mode field confinement is realized at the expense of higher propagation loss for such waveguides. The chromatic dispersion of such waveguides is found to be adequate for applications in integrated optical circuits. The mode behaviors of realistic corner waveguides with finite sidewalls are also studied.
TL;DR: In this article, the dispersion curve of a coupled cavity waveguide and the equifrequency surfaces and polarization properties of a PhC beam splitter are extracted without postprocessing or cumbersome near-field scanning.
Abstract: Photonic crystals (PhCs) act on light in two different ways: confinement and modification of propagation. Both phenomena rely on the complex interplay between multiply scattered waves that can form what is known as a Bloch mode. Here, we present a technique that allows direct imaging of Bloch modes, both in real space and in k-space. The technique gives access to the location of the field maxima inside the PhC, the dispersion relation, equifrequency surfaces, as well as reflection and transmission coefficients. Our key advance is that we retrieve the desired information comprehensively, without postprocessing or cumbersome near-field scanning techniques, even for modes that are nominally lossless, i.e., below the light line. To highlight the potential of the technique, we extract the dispersion curve of a coupled cavity waveguide consisting of as many as 100 cavities, as well as the equifrequency surfaces and polarization properties of a PhC beam splitter.
TL;DR: In this article, the authors consider N-qubit symmetric Dicke states with N/2 excitations and show that for large N these states have the smallest overlap possible with states without genuine multipartite entanglement.
Abstract: I present methods for detecting entanglement around symmetric Dicke states. In particular, I consider N-qubit symmetric Dicke states with N/2 excitations. I show that for large N these states have the smallest overlap possible with states without genuine multipartite entanglement. Thus these states are particularly well suited for the experimental examination of multipartite entanglement. I present fidelity-based entanglement witness operators for detecting multipartite entanglement around these states. I then consider entanglement criteria, somewhat similar to the spin squeezing criterion, based on the moments or variances of the collective spin operators. Surprisingly, these criteria are based on an upper bound for variances for separable states. I present criteria detecting entanglement in general and criteria detecting only genuine multipartite entanglement. The collective operator measured for this criteria is an important physical quantity: Its expectation value essentially gives the intensity of the radiation when a coherent atomic cloud emits light.
TL;DR: In this paper, the photorefraction in nematic liquid crystal (LC) doped with nanoferroelectric particles was investigated and the effect originated from an increased birefringence of the colloid and a stronger LC reorientation torque.
Abstract: We report on the first, to the best of our knowledge, studies of photorefraction in nematic liquid crystal (LC) doped with nanoferroelectric particles. We found the strong enhancement of two-beam coupling in the colloid of ferroelectric nanoparticles in LC. The effect originated from an increased birefringence of the colloid and a stronger LC reorientation torque. Our measurements allowed us to suggest that increased birefringence is caused by the contribution of polarizability anisotropy of the ferroelectric particles. Stronger reorientation torque is caused by the permanent dipole moment of the particles contributing to the dielectric anisotropy of the colloid eacol. The enhancement of two-beam coupling in LCs by doping with ferroelectric nanoparticles at extremely small concentration shows the strong potential of ferroelectric nanoparticles for improving the optical response of LCs, especially for those materials where a method of chemical synthesis has reached its limit.
TL;DR: In this article, an experimental apparatus based on coherent population trapping and aimed at detecting a biological (cardiac) magnetic field in a magnetically compensated but unshielded volume is presented.
Abstract: We present encouraging results obtained with an experimental apparatus based on coherent population trapping and aimed at detecting a biological (cardiac) magnetic field in a magnetically compensated but unshielded volume. The work includes magnetic-field and magnetic-field-gradient compensation and uses differential detection to cancel common mode magnetic noise. Synchronous data acquisition with a reference (electrocardiographic or pulse-oximetric) signal makes possible improvement of the signal-to-noise ratio in off-line averaging. The setup has the significant advantages of working at room temperature with a small-size head, and the possibility of fast adjustments of the dc bias magnetic field, which makes the sensor suitable for detecting a biomagnetic signal at any orientation with respect to the axis of the head and in any position on the patient's chest, which is not the case with other kinds of magnetometers.
TL;DR: In this paper, the authors performed a comprehensive experimental investigation of two-photon absorption spectra of a series of 12 symmetrical and asymmetrical cationic polymethine dyes, including complete one and twophoton excitation anisotropy measurements.
Abstract: We performed a comprehensive experimental investigation of two-photon absorption (2PA) spectra of a series of 12 symmetrical and asymmetrical cationic polymethine dyes, including complete one-and two-photon excitation anisotropy measurements. Quantum-chemical calculations were performed with the goal of understanding the nature of 2PA bands and of uncovering structure-property relations. We found that there are 2PA bands in the spectral region between the first absorption band and that for twice its energy. A weakly allowed 2PA band within the short-wavelength shoulder of the first absorption band was observed owing to the effects of vibrational and charge distribution symmetry breaking. The nature of the strongest 2PA band is connected to the electron transition from the molecular orbital localized at the benzene rings of the terminal groups to the lowest unoccupied molecular orbital (LUMO). Structure-property relations revealed that the 2PA cross section tends to be enhanced by either an increase in the length of the polymethine chromophore or an increase in the donor strengths in the terminal groups.
TL;DR: In this article, the degree of second-order coherence for spontaneous parametric downconversion fields was measured using time-to-amplitude converters (TACs).
Abstract: I present measurements of the degree of second-order coherence g(2)(0) for spontaneous parametric downconversion fields and discuss the differences between two-detector (unconditional) and three-detector (conditional) measurements of g(2)(0). An emphasis is placed on comparing measurements made using time-to-amplitude converters (TACs) to those made using a logic circuit, illustrating how the TAC measurements are adversely influenced by dead time effects. Finally, I show how the detrimental effects of dead time when using TACs can be mitigated by renormalizing the measurement results.