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ABSTRACT: We report the first demonstration of a photonic-chip laser frequency sensor using Brillouin mutually-modulated cross-gain modulation (MMXGM). A large sensitivity (∼9.5 mrad/kHz) of the modulation phase shift to probe carrier frequency is demonstrated at a modulation frequency of 50 kHz using Brillouin MMXGM in a ∼7 cm long chalcogenide rib waveguide.
Optics Express 04/2013; 21(7):8605-13. · 3.59 Impact Factor
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ABSTRACT: We report demonstration of a Brillouin dynamic grating (BDG) in a photonic chip. A BDG was characterized in a 6.5 cm long chalcogenide (As<sub>2</sub>S<sub>3</sub>) rib waveguide using CW pumps in x polarization and read using a CW probe in y polarization. The measured reflectivity, on-off ratio, and 3 dB bandwidth (f<sub>3 dB</sub>) for the BDG were 0.4%, ∼28 dB, and ∼6 GHz, respectively.
Optics Letters 02/2013; 38(3):305-7. · 3.40 Impact Factor
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ABSTRACT: We present a first-principles method to compute radiation properties of ultra-high quality factor photonic crystal cavities. Our Frequency-domain Approach for Radiation (FAR) can compute the far-field radiation pattern and quality factor of cavity modes ∼ 100 times more rapidly than conventional finite-difference time domain calculations. We explain how the radiation pattern depends on the perturbation used to create the cavity and on the Bloch modes of the photonic crystal.
Optics Express 09/2012; 20(20):22763-9. · 3.59 Impact Factor
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ABSTRACT: We propose a scheme for on-chip isolation in chalcogenide (As<sub>2</sub>S<sub>3</sub>) rib waveguides, in which Stimulated Brillouin Scattering is used to induce non-reciprocal mode conversion within a multi-moded waveguide. The design exploits the idea that a chalcogenide rib buried in a silica matrix acts as waveguide for both light and sound, and can also be designed to be multi-moded for both optical and acoustic waves. The enhanced opto-acoustic coupling allows significant isolation (> 20 dB) within a chip-scale (cm-long) device (< 10 cm). We also show that the bandwidth of this device can be dramatically increased by tuning the dispersion of the waveguide to match the group velocity between optical modes: we find that 20 dB isolation can be extended over a bandwidth of 25 nm.
Optics Express 09/2012; 20(19):21235-46. · 3.59 Impact Factor
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ABSTRACT: We derive a frequency-domain-based approach for radiation (FAR) from
double-heterostructure cavity (DHC) modes. We use this to compute the quality
factors and radiation patterns of DHC modes. The semi-analytic nature of our
method enables us to provide a general relationship between the radiation
pattern of the cavity and its geometry. We use this to provide general designs
for ultrahigh quality factor DHCs with radiation patterns that are engineered
to emit vertically.
08/2012;
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ABSTRACT: We report the first demonstration of a photonic chip based dynamically reconfigurable, widely tunable, narrow pass-band, high Q microwave photonic filter (MPF). We exploit stimulated Brillouin scattering (SBS) in a 6.5 cm long chalcogenide (As<sub>2</sub>S<sub>3</sub>) photonic chip to demonstrate a MPF that exhibited a high quality factor of ~520 and narrow bandwidth and was dynamically reconfigurable and widely tunable. It maintained a stable 3 dB bandwidth of 23 ± 2MHz and amplitude of 20 ± 2 dB over a large frequency tuning range of 2-12 GHz. By tailoring the pump spectrum, we reconfigured the 3 dB bandwidth of the MPF from ~20 MHz to ~40 MHz and tuned the shape factor from 3.5 to 2 resulting in a nearly flat-topped filter profile. This demonstration represents a significant advance in integrated microwave photonics with potential applications in on-chip microwave signal processing for RADAR and analogue communications.
Optics Express 08/2012; 20(17):18836-45. · 3.59 Impact Factor
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ABSTRACT: A finite element-based modal formulation of diffraction of a plane wave by an absorbing photonic crystal slab of arbitrary geometry is developed for photovoltaic applications. The semianalytic approach allows efficient and accurate calculation of the absorption of an array with a complex unit cell. This approach gives direct physical insight into the absorption mechanism in such structures, which can be used to enhance the absorption. The verification and validation of this approach is applied to a silicon nanowire array, and the efficiency and accuracy of the method is demonstrated. The method is ideally suited to studying the manner in which spectral properties (e.g., absorption) vary with the thickness of the array, and we demonstrate this with efficient calculations that can identify an optimal geometry.
Journal of the Optical Society of America A 05/2012; 29(5):817-31. · 1.56 Impact Factor
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ABSTRACT: We report the first (to our knowledge) demonstration of photonic chip based tunable slow and fast light via stimulated Brillouin scattering. Slow, fast, and negative group velocities were observed in a 7 cm long chalcogenide (As(2)S(3)) rib waveguide with a group index change ranging from ~-44 to +130, which results in a maximum delay of ~23 ns at a relatively low gain of ~23 dB. Demonstration of large tunable delays in a chip scale device opens up applications such as frequency sensing and true-time delay for a phased array antenna, where integration and delays ~10 ns are highly desirable.
Optics Letters 03/2012; 37(5):969-71. · 3.40 Impact Factor
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ABSTRACT: We analyze the absorption of solar radiation by silicon nanowire arrays, which are being considered for photovoltaic applications. These structures have been shown to have enhanced absorption compared with thin films, however the mechanism responsible for this is not understood. Using a new, semi-analytic model, we show that the enhanced absorption can be attributed to a few modes of the array, which couple well to incident light, overlap well with the nanowires, and exhibit strong Fabry-Pérot resonances. For some wavelengths the absorption is further enhanced by slow light effects. We study the evolution of these modes with wavelength to explain the various features of the absorption spectra, focusing first on a dilute array at normal incidence, before generalizing to a dense array and off-normal angles of incidence. The understanding developed will allow for optimization of simple SiNW arrays, as well as the development of more advanced designs.
Optics Express 09/2011; 19 Suppl 5:A1067-81. · 3.59 Impact Factor
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ABSTRACT: We demonstrate on-chip stimulated Brillouin scattering (SBS) in an As2S3 chalcogenide rib waveguide. SBS was characterized in a cm long waveguide with a cross-section 4 μm x 850 nm using the backscattered signal and pump-probe technique. The measured Brillouin shift and its full-width at half-maximum (FWHM) linewidth were ~7.7 GHz and 34 MHz, respectively. Probe vs. pump power measurements at the Brillouin shift were used to obtain the gain coefficient from an exponential fit. The Brillouin gain coefficient obtained was 0.715 x 10(-9) m/W. A probe gain of 16 dB was obtained for a CW pump power of ~300 mW.
Optics Express 04/2011; 19(9):8285-90. · 3.59 Impact Factor
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ABSTRACT: We investigate the modes of double heterostructure cavities where the underlying photonic crystal waveguide has been dispersion engineered to have two band-edges inside the Brillouin zone. By deriving and using a perturbative method, we show that these structures possess two modes. For unapodized cavities, the relative detuning of the two modes can be controlled by changing the cavity length, and for particular lengths, a resonant-like effect makes the modes degenerate. For apodized cavities no such resonances exist and the modes are always non-degenerate.
Optics Express 12/2010; 18(25):25693-701. · 3.59 Impact Factor
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ABSTRACT: We present a numerically improved multipole formulation for the calculation of resonances of multiple disks located at arbitrary positions in a 2-d plane, and suitable for the accurate computation of the resonances of large numbers of disks and of high-wavenumber eigenstates. Using a simple reformulation of the field expansions and boundary conditions, we are able to transform the multipole formalism into a linear eigenvalue problem, for which fast and accurate methods are available. Observing that the motion of the eigenvalues in the complex plane is analytic with respect to a two parameter family, we present a numerical algorithm to compute a range of multiple-disk resonances and field distributions using only two diagonalizations. This method can be applied to photonic molecules, photonic crystals, photonic crystal fibers, and random lasers.
Optics Express 08/2009; 17(15):13178-86. · 3.59 Impact Factor
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ABSTRACT: We demonstrate a direct, single measurement technique for characterizing the dispersion of a photonic crystal waveguide (PCWG) using a tapered fiber evanescent coupling method. A highly curved fiber taper is used to probe the Fabry-Pérot spectrum of a closed PCWG over a broad k-space range, and from this measurement the dispersive properties of the waveguide can be found. Waveguide propagation losses can also be estimated from measurements of closed waveguides with different lengths. The validity of this method is demonstrated by comparing the results obtained on a 'W1' PCWG in chalcogenide glass with numerical simulation.
Optics Express 10/2008; 16(18):13800-8. · 3.59 Impact Factor
