Showing papers in "Optics Letters in 2009"
TL;DR: This work demonstrates a class of optical fibers in which these beams can be generated and propagated over long lengths with unprecedented stability, even in the presence of strong bend perturbations, opening the door to exploiting nonlinear fiber optics to manipulate such beams.
Abstract: Beams with polarization singularities have attracted immense recent attention in a wide array of scientific and technological disciplines. We demonstrate a class of optical fibers in which these beams can be generated and propagated over long lengths with unprecedented stability, even in the presence of strong bend perturbations. This opens the door to exploiting nonlinear fiber optics to manipulate such beams. This fiber also possesses the intriguingly counterintuitive property of being polarization maintaining despite being strictly cylindrically symmetric, a prospect hitherto considered infeasible with optical fibers.
435 citations
TL;DR: A refractive index sensing geometry exploiting modes beyond cutoff in a selectively infiltrated PCF demonstrates a detection limit of 4.6×10−7 RIU and sensitivity of 30,100nm/RIU, a one-order-of-magnitude improvement over previous PCF sensors.
Abstract: We introduce a microfluidic refractive index sensor based on a directional coupler architecture using solid-core photonic crystal fibers. The sensor achieves very high sensitivity by coupling the core mode to a mode in the adjacent fluid-filled waveguide that is beyond modal cutoff, and with strong field overlap. We demonstrate the device through the selective infiltration of a single hole with fluid along a microstructured optical fiber. A detection limit of 4.6x10(-7) refractive index units has been derived from measurements with a sensitivity of 30,100 nm per refractive index unit, which is the highest for a fiber device to date.
395 citations
TL;DR: This technique does not require calibration of the gamma of the projector, it is easy to implement and thus is promising for developing flexible 3-D shape measurement systems using digital video projectors.
Abstract: We present a 3-D shape-measurement technique using a defocused projector. The ideal sinusoidal fringe patterns are generated by defocusing binary structured patterns, and the phase shift is realized by shifting the binary patterns spatially. Because this technique does not require calibration of the gamma of the projector, it is easy to implement and thus is promising for developing flexible 3-D shape measurement systems using digital video projectors.
349 citations
TL;DR: Using analysis of the image-formation process, an optimized correction scheme permitting image-quality improvement with minimal additional exposure of the sample is developed and it is shown that this correction process induces little photobleaching and significantly improves the quality of images of biological samples.
Abstract: We demonstrate wavefront sensorless aberration correction in a two-photon excited fluorescence microscope. Using analysis of the image-formation process, we have developed an optimized correction scheme permitting image-quality improvement with minimal additional exposure of the sample. We show that, as a result, our correction process induces little photobleaching and significantly improves the quality of images of biological samples. In particular, increased visibility of small structures is demonstrated. Finally, we illustrate the use of this technique on various fresh and fixed biological tissues.
343 citations
JILA1
TL;DR: A high-power optical-parametric-oscillator (OPO) based frequency comb in the mid-IR wavelength region that employs periodically poled lithium niobate and is singly resonant for the signal is presented.
Abstract: We present a high-power optical-parametric-oscillator (OPO) based frequency comb in the mid-IR wavelength region. The system employs periodically poled lithium niobate and is singly resonant for the signal. It is synchronously pumped by a 10 W femtosecond Yb:fiber laser centered at 1.07 microm. The idler (signal) wavelength can be continuously tuned from 2.8 to 4.8 microm (1.76 to 1.37 microm) with a simultaneous bandwidth as high as 0.3 microm and a maximum average idler output power of 1.50 W. We also demonstrate the performance of the stabilized comb by recording the heterodyne beat with a narrow-linewidth diode laser. This OPO is an ideal source for frequency comb spectroscopy in the mid-IR.
311 citations
TL;DR: An integrated approach is followed in which a 1D optical phased array is fabricated on silicon-on-insulator in which continuous thermo-optical steering of 2.3 degrees and wavelength steering of 14.1 degrees is reported.
Abstract: Optical phased arrays are versatile components enabling rapid and precise beam steering. An integrated approach is followed in which a 1D optical phased array is fabricated on silicon-on-insulator. The optical phased array consists of 16 parallel grating couplers spaced 2 mum apart. Steering in one direction is done thermo-optically by means of a titanium electrode on top of the structure using the phased array principle, while steering in the other direction is accomplished by wavelength tuning. At a wavelength of 1550 nm, continuous thermo-optical steering of 2.3 degrees and wavelength steering of 14.1 degrees is reported.
299 citations
TL;DR: A novel and simple iterative phase compensation algorithm is proposed to compensate the nonsinusoidal phase error and experiments show that the proposed algorithm can be used for effective phase error compensation in practical phase-shifting FPP.
Abstract: The nonlinear intensity response of a digital fringe projection profilometry (FPP) system causes the captured fringe patterns to be nonsinusoidal waveforms and leads to an additional phase measurement error for commonly used three- and four-step phase-shifting algorithms. We perform theoretical analysis of the phase error owing to the nonsinusoidal waveforms. Based on the derived theoretical model, a novel and simple iterative phase compensation algorithm is proposed to compensate the nonsinusoidal phase error. Experiments show that the proposed algorithm can be used for effective phase error compensation in practical phase-shifting FPP.
297 citations
TL;DR: This work fabricates photonic metamaterials composed of pairs of twisted gold crosses using two successive electron-beam-lithography steps and intermediate planarization via a spin-on dielectric, finding a fairly broad spectral regime with strong optical activity.
Abstract: Following a recent theoretical suggestion and microwave experiments, we fabricate photonic metamaterials composed of pairs of twisted gold crosses using two successive electron-beam-lithography steps and intermediate planarization via a spin-on dielectric. The resulting two effective resonances of the coupled system lie in the 1-2 microm wavelength regime and exhibit pronounced circular dichroism, while the circular polarization conversion is very small. In between the two resonances, we find a fairly broad spectral regime with strong optical activity, i.e., with a pure rotation of incident linear polarization. The measured optical transmittance spectra agree well with theory.
297 citations
TL;DR: The probability that a detected photon after propagating through the atmosphere has the same value of the orbital angular momentum as the launched photon is found to be given by s(0)=[1+(1.845D/r(0))(2)](-1/2).
Abstract: We analyze the influence of atmospheric turbulence on the propagation of an optical vortex beam having the form V(r,theta)=A(0)e(imtheta). The probability that a detected photon after propagating through the atmosphere has the same value of the orbital angular momentum as the launched photon is found to be given by s(0)=[1+(1.845D/r(0))(2)](-1/2), where D is the aperture diameter and r(0) is the Fried coherence diameter. These vortex beams behave very similarly to Laguerre-Gauss beams under the influence of atmospheric turbulence. These results have important implications for atmospheric laser communication systems that employ quantum encryption.
297 citations
TL;DR: The interaction between localized and propagating surface plasmons is investigated in a structure consisting of a two-dimensional periodic gold nanoparticle array, an SiO2 spacer, and a gold film, demonstrating the strong coupling between localized
Abstract: The interaction between localized and propagating surface plasmons is investigated in a structure consisting of a two-dimensional periodic gold nanoparticle array, an SiO2 spacer, and a gold film. The resonance wavelengths of the two types of surface plasmons supported by the structure are tailored by changing the gold nanoparticle size and the array period. An anticrossing of the resonance positions is observed in the reflection spectra, demonstrating the strong coupling between localized and propagating surface plasmons.
250 citations
TL;DR: A simple and compact modal interferometer for applications in refractometry that is highly stable over time, has low temperature sensitivity, and is suitable for measuring indices in the 1.330-1.440 range is reported.
Abstract: We report a simple and compact modal interferometer for applications in refractometry. The device consists of a stub of large-mode-area photonic crystal fiber (PCF) spliced between standard single-mode fibers. In the splice regions the voids of the PCF are fully collapsed, thus allowing the coupling and recombination of PCF core and cladding modes. The device is highly stable over time, has low temperature sensitivity, and is suitable for measuring indices in the 1.330-1.440 range. The measure of the refractive index is carried out by monitoring the shift of the interference pattern.
TL;DR: A two-stage noncollinear optical parametric chirped-pulse amplification system that generates 7.9 fs pulses containing 130 mJ of energy at an 805 nm central wavelength and 10 Hz repetition rate allows for experiments in a regime of relativistic light-matter interactions and attosecond science.
Abstract: We present a two-stage noncollinear optical parametric chirped-pulse amplification system that generates 7.9 fs pulses containing 130 mJ of energy at an 805 nm central wavelength and 10 Hz repetition rate. These 16 TW light pulses are compressed to within 5% of their Fourier limit and are carefully characterized by the use of home-built pulse diagnostics. The contrast ratio before the main pulse has been measured as 10(-4), 10(-8), and 10(-11) at t=-3.3 ps, t=-5 ps, and t=-30 ps, respectively. This source allows for experiments in a regime of relativistic light-matter interactions and attosecond science.
TL;DR: In this article, all solid photonic bandgap optical fiber comprising a core region and a cladding region is disclosed, which includes a background optical material having a first refractive index and elements arranged in a two-dimensional periodic structure.
Abstract: All solid photonic bandgap optical fiber comprising a core region and a cladding region is disclosed. The cladding region surrounding the core region includes a background optical material having a first refractive index and elements arranged in a two-dimensional periodic structure. In one embodiment, each of the elements comprises a center part and peripheral part having a higher refractive than the central part. In other embodiments, each element comprises a plurality of rods having a higher refractive index higher than the fist, the rods of each element arranged in a circle or polygon. Light transmission apparatus and methods of using the fiber are also disclosed.
TL;DR: A 24 W liquid-cooled CW 3 microm fiber laser with a multimode-core Er-doped ZBLAN fiber with stable high-power operation was demonstrated, and this is the highest output power obtained by a 3 micron fiber laser.
Abstract: A 24 W liquid-cooled CW 3 microm fiber laser with a multimode-core Er-doped ZBLAN fiber has been developed. The output power of 24 W and an optical-to-optical efficiency of 14.5% (with respect to incident pump power) were obtained with 975 nm diode pumping. Efficient cooling was implemented by a combination of fluid cooling over the entire length of the fiber and conductive cooling at both end faces of the fiber. Consequently, stable high-power operation was demonstrated. To our knowledge, this is the highest output power obtained by a 3 microm fiber laser. Furthermore, the high power can be further scaled up, since the output power in the present work is limited only by the available pump power.
TL;DR: Room-temperature EL is observed at the direct gap energy from a Ge/Si p-i-n diode exhibiting the same characteristics of the directgap photoluminescence of Ge, indicating a promising future of tensile-strained Ge-on-Si for electrically pumped, monolithically integrated light emitters on Si.
Abstract: We report what we believe to be the first demonstration of direct bandgap electroluminescence (EL) from Ge/Si heterojunction light-emitting diodes (LEDs) at room temperature. In-plane biaxial tensile strain is used to engineer the band structure of Ge to enhance the direct gap luminescence efficiency by increasing the injected electron population in the direct Γ valley. Room-temperature EL is observed at the direct gap energy from a Ge/Si p-i-n diode exhibiting the same characteristics of the direct gap photoluminescence of Ge. The integral direct gap EL intensity increases superlinearly with electrical current owing to an indirect valley filling effect. These results indicate a promising future of tensile-strained Ge-on-Si for electrically pumped, monolithically integrated light emitters on Si.
TL;DR: In this article, the authors demonstrate optical frequency combs using the fluorite whispering gallery mode resonator as a nonlinear Kerr medium and two regimes of generation are observed, giving the record low repetition rate of 13 GHz, equal to the cavity's free spectral range (FSR) or high repetition rates of multiples of cavity FSR.
Abstract: We demonstrate optical frequency combs using the fluorite whispering gallery mode resonator as a nonlinear Kerr medium. Two regimes of generation are observed, giving the record low repetition rate of 13 GHz, equal to the cavity's free spectral range (FSR) or high repetition rates of multiples of cavity FSR. An intermediate regime was also observed. Raman lasing spectrum similar to modulation instability in fibers was observed for the first time to the best of our knowledge.
TL;DR: Preliminary experimental results carried out with a perturbation frequency up to 98 Hz demonstrate the validity of the proposed dynamic strain measurements in optical fibers based on the stimulated Brillouin scattering interaction between two counterpropagating optical pulses.
Abstract: We present a technique for dynamic strain measurements in optical fibers based on the stimulated Brillouin scattering interaction between two counterpropagating optical pulses. The technique allows for a high sampling rate and permits to addressing dynamically and randomly the position at which vibration is measured. Preliminary experimental results carried out with a perturbation frequency up to 98 Hz demonstrate the validity of the proposed technique.
TL;DR: A mode-locked fiber laser is reported that exploits dissipative-soliton pulse shaping along with cladding pumping for high average power and dechirped pulses at 70 MHz repetition rate.
Abstract: We report a mode-locked fiber laser that exploits dissipative-soliton pulse shaping along with cladding pumping for high average power. The laser generates 31 nJ chirped pulses at 70 MHz repetition rate, for an average power of 2.2 W. After dechirping outside the laser, 80 fs pulses, with 200 kW peak power, are obtained.
TL;DR: A laser-scanning optical-resolution photoacoustic microscopy method that can potentially fuse with existing optical microscopic imaging modalities is developed, and the data acquisition time for an image consisting of 256 x 256 pixels was less than 2 min.
Abstract: We have developed a laser-scanning optical-resolution photoacoustic microscopy method that can potentially fuse with existing optical microscopic imaging modalities. To acquire an image, the ultrasonic transducer is kept stationary during data acquisition, and only the laser light is raster scanned by an x-y galvanometer scanner. A lateral resolution of 7.8 microm and a circular field of view with a diameter of 6 mm were achieved in an optically clear medium. Using a laser system working at a pulse repetition rate of 1,024 Hz, the data acquisition time for an image consisting of 256 x 256 pixels was less than 2 min.
TL;DR: The spin-dependent nanometer-sized displacements of the spin Hall effect of the reflected light from a planar air-glass interface are measured and the displacement is found to increase with the incident angle and decrease after approximately 48 deg, while in the case of the horizontal polarization, it changes rapidly near the Brewster angle.
Abstract: We have measured the spin-dependent nanometer-sized displacements of the spin Hall effect of the reflected light from a planar air-glass interface. In the case of the vertical polarization, the displacement is found to increase with the incident angle and subsequently decrease after approximately 48 deg, while in the case of the horizontal polarization, it changes rapidly near the Brewster angle. For a fixed incident angle of 30 deg, the displacement decreases to zero as the polarization angle approaches approximately 39 deg from 0 deg (the horizontal polarization) and then increases in the opposite direction until 90 deg (the vertical polarization).
TL;DR: A full-field phase-gradient imaging method: asymmetric illumination-based differential phase contrast (AIDPC), which does not require phase shifting for quantitative imaging of phase gradient, provides artifact-free images of birefringent specimens, requires shorter camera exposure, and has larger depth of focus.
Abstract: We describe a full-field phase-gradient imaging method: asymmetric illumination-based differential phase contrast (AIDPC). Imaging properties of AIDPC are evaluated using the phase-gradient transfer-function approach and elucidated with experimental images of an optical fiber and a histochemical preparation of a skeletal muscle section. In comparison with full-field differential interference contrast, AIDPC does not require phase shifting for quantitative imaging of phase gradient, provides artifact-free images of birefringent specimens, requires shorter camera exposure, and has larger depth of focus. It is amenable to transfer-function engineering, simultaneous fluorescence imaging, and automated live cell imaging.
TL;DR: This work provides what it believes to be the first experimental demonstration of linear Shockley-like surface states in an optically induced semi-infinite photonic superlattice.
Abstract: We provide what we believe to be the first experimental demonstration of linear Shockley-like surface states in an optically induced semi-infinite photonic superlattice. Such surface states appear only when the induced superlattice consisting of alternating strong and weak bonds is terminated properly at the surface. Our experimental results are in good agreement with our theoretical analysis.
TL;DR: A silicon waveguide-fiber grating coupler that uses a subwavelength microstructure to achieve a continuously variable grating strength yet can be fabricated using only a single etch step is proposed.
Abstract: We propose a silicon waveguide-fiber grating coupler that uses a subwavelength microstructure to achieve a continuously variable grating strength yet can be fabricated using only a single etch step. By adjusting the subwavelength microstructure at every point along the grating, the grating coupler can be optimized to give high field overlap with the optical fiber mode and also minimize backreflections along the incident waveguide path. Our design example is optimized for quasi-TM mode in a silicon photonic-wire waveguide, as required for waveguide evanescent-field-sensing applications. A field overlap of up to 94% with a standard single-mode optical fiber (SMF-28) is achieved by coupler apodization. Backreflection from the grating is reduced to ~0.1%, and the total predicted photonic wire to fiber coupling efficiency is 50%.
TL;DR: The metamaterial modified bolometers modified by metallic resonant absorber elements are suitable for multispectral thermal imaging systems in the mid-IR and terahertz regime.
Abstract: Microbolometers are modified by metallic resonant absorber elements, leading to an enhanced responsivity at selectable wavelengths. The dissipative energy absorption of tailored metamaterials allows for engineering the response of conventional bolometer microbridges. The absorption peak position and height are determined by the geometry of the metamaterial. Square-shaped metal/dielectric/metal stacks as absorber elements show spectral resonances at wavelengths between 4.8 and 7.0 microm in accordance with numerical simulations. Total peak absorptions of 0.8 are obtained. The metamaterial modified bolometers are suitable for multispectral thermal imaging systems in the mid-IR and terahertz regime.
TL;DR: A simple and fast calculation algorithm for a computer-generated hologram (CGH) by use of wavefront recording plane and the total computational complexity is dramatically reduced in comparison with conventional CGH calculations.
Abstract: We present a simple and fast calculation algorithm for a computer-generated hologram (CGH) by use of wavefront recording plane The wavefront recording plane is placed between the object data and a CGH When the wavefront recording plane is placed close to the object, the object light passes through a small region on the wave recording plane The computational complexity for the object light is very small We can obtain a CGH to execute diffraction calculation from the wavefront recording plane to the CGH The computational complexity is constant The total computational complexity is dramatically reduced in comparison with conventional CGH calculations
TL;DR: The real-time monitoring of antibody-antigen reactions using complementary and mismatched immunoglobulin G receptor-analyte pairs and bovine serum albumin is demonstrated.
Abstract: We demonstrate a silicon photonic wire waveguide biosensor array chip for the simultaneous monitoring of different molecular binding reactions. The chip is compatible with automated commercial spotting tools and contains a monolithically integrated microfluidic channel for sample delivery. Each array sensor element is a 1.8-mm-long spiral waveguide folded within a 130 microm diameter spot and is incorporated in a balanced Mach-Zehnder interferometer with a near temperature independent response. The sensors are arranged in a 400 microm spacing grid pattern and are addressed through cascaded 1x2 optical power splitters using light from a single input fiber. We demonstrate the real-time monitoring of antibody-antigen reactions using complementary and mismatched immunoglobulin G receptor-analyte pairs and bovine serum albumin. The measured level of detection for each sensor element corresponds to a surface coverage of less than 0.3 pg/mm(2).
TL;DR: The spiral plAsmonic lens provides efficient plasmonic focusing while it eliminates the requirement of centering the incident beam to the plasMonic lens, making it suitable for full Stokes parameter polarimetric imaging applications.
Abstract: A simple spiral plasmonic lens is studied both analytically and numerically. Owing to the geometric phase effect, a spiral plasmonic lens focuses the left-hand and right-hand circular polarizations into spatially separated plasmonic fields. Such a spatial multiplexing of the field distribution is utilized in miniature circular polarization analyzer design. A circular polarization extinction ratio better than 100 is obtainable with a device size as small as 4lambda(spp). The spiral plasmonic lens provides efficient plasmonic focusing while it eliminates the requirement of centering the incident beam to the plasmonic lens, making it suitable for full Stokes parameter polarimetric imaging applications.
TL;DR: It is discovered that a silicon-on-insulator photonic crystal waveguide whose lattice is shifted along the waveguide generates wideband, low-dispersion, slow light with excellent reproducibility.
Abstract: We discovered that a silicon-on-insulator photonic crystal waveguide whose lattice is shifted along the waveguide generates wideband, low-dispersion, slow light with excellent reproducibility. We observed delayed transmission of picosecond optical pulses, as well as two-photon absorption and self-phase modulation enhanced by a high internal light intensity in the slow-light regime.
TL;DR: This OB-QEPAS configuration not only allows for use of larger excitation optical beams and facilitating optical alignment but also provides higher enhancement of photoacoustic signals than previously published results based on the common on-beam QEPAS under the same experimental conditions.
Abstract: An off-beam (OB) detection approach is suggested and experimentally investigated and optimized for quartz-enhanced photoacoustic spectroscopy (QEPAS). This OB-QEPAS configuration, very simple in assembly, not only allows for use of larger excitation optical beams and facilitating optical alignment but also provides higher enhancement of photoacoustic signals than previously published results based on the common on-beam QEPAS under the same experimental conditions. A normalized noise equivalent absorption coefficient (1σ) of 5.9×10−9 cm−1W/Hz1/2 was obtained for water vapor detection at normal atmospheric pressure.
TL;DR: A chain of four Tm-doped fibers amplified a single-frequency, 2040 nm diode laser to 608 W with M(2)=1.05+/-0.03, to be known as the highest power obtained from any single- frequencies, single-mode fiber laser.
Abstract: A chain of four Tm-doped fibers amplified a single-frequency, 2040 nm diode laser to 608 W with M2=1.05±0.03, limited by available pump power. Stimulated Brillouin scattering limits were investigated by splicing different lengths of passive fiber to the output of the final amplifier stage. Integrated rms phase noise above 1 kHz was less than λ/30, suggesting the possibility of further scaling via coherent beam combining. To our knowledge, this is the highest power obtained from any single-frequency, single-mode fiber laser.