| 381. |
- Krückel, Clemens, 1984, et al.
(författare)
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Linear and nonlinear characterization of low-stress high-confinement silicon-rich nitride waveguides
- 2015
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 23:20, s. 25827-25837
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we introduce a low-stress silicon enriched nitride platform that has potential for nonlinear and highly integrated optics. The manufacturing process of this platform is CMOS compatible and the increased silicon content allows tensile stress reduction and crack freelayer growth of 700 nm. Additional benefits of the silicon enriched nitride is a measured nonlinear Kerr coefficient n2 of 1.4*10^18 m2/W (5 times higher than stoichiometric silicon nitride) and a refractive index of 2.1 at 1550 nm that enables high optical field confinement allowing high intensity nonlinear optics and light guidance even with small bending radii. We analyze the waveguide loss (~1 dB/cm) in a spectrally resolved fashion and include scattering loss simulations based on waveguide surface roughness measurements. Detailed simulations show the possibility for fine dispersion and nonlinear engineering. In nonlinear experiments we present continuouswave wavelength conversion and demonstrate that the material does not show nonlinear absorption effects. Finally, we demonstrate microfabrication of resonators with high Q-factors (~10^5).
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| 382. |
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| 383. |
- Krückel, Clemens, 1984, et al.
(författare)
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Optical bandgap engineering in nonlinear silicon nitride waveguides
- 2017
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 25:13, s. 15370-15380
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Tidskriftsartikel (refereegranskat)abstract
- Silicon nitride is a well-established material for photonic devices and integrated circuits. It displays a broad transparency window spanning from the visible to the mid-IR and waveguides can be manufactured with low losses. An absence of nonlinear multi-photon absorption in the erbium lightwave communications band has enabled various nonlinear optic applications in the past decade. Silicon nitride is a dielectric material whose optical and mechanical properties strongly depend on the deposition conditions. In particular, the optical bandgap can be modified with the gas flow ratio during low-pressure chemical vapor deposition (LPCVD). Here we show that this parameter can be controlled in a highly reproducible manner, providing an approach to synthesize the nonlinear Kerr coefficient of the material. This holistic empirical study provides relevant guidelines to optimize the properties of LPCVD silicon nitride waveguides for nonlinear optics applications that rely on the Kerr effect.
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| 384. |
- Krzempek, Karol, et al.
(författare)
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Stabilized all-fiber source for generation of tunable broadband fCEO-free mid-IR frequency comb in the 7–9 µm range
- 2019
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 27:26, s. 37435-37445
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Tidskriftsartikel (refereegranskat)abstract
- A compact and robust all-fiber difference frequency generation-based source of broadband mid-infrared radiation is presented. The source emits tunable radiation in the range between 6.5 µm and 9 µm with an average output power up to 5 mW at 125 MHz repetition frequency. The all-in-fiber construction of the source along with active stabilization techniques results in long-term repetition rate stability of 3 Hz per 10 h and a standard deviation of the output power better than 0.8% per 1 h. The applicability of the presented source to laser spectroscopy is demonstrated by measuring the absorption spectrum of nitrous oxide (N2O) around 7.8 µm. The robustness and good long- and short-term stability of the source opens up for applications outside the laboratory.
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| 385. |
- Kumpera, Ales, 1980, et al.
(författare)
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Parametric coherent receiver
- 2015
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Ingår i: Optics Express. - : The Optical Society. - 1094-4087 .- 1094-4087. ; 23:10, s. 12952-12964
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Tidskriftsartikel (refereegranskat)abstract
- We present the parametric coherent receiver based on a two-mode pump-degenerate fiber optical parametric amplifier (FOPA). The receiver is inherently single-ended and offers a simultaneous gain and coherent mixing of the received signal and a reference wave (known as a local oscillator signal) with, in principle, arbitrary wavelength separation. We analyze the receiver theoretically and in a proof-of-concept experiment. As a reference we compare the performance to a standard single-ended homodyne coherent receiver.
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| 386. |
- Kvarnström, Mats, 1974, et al.
(författare)
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Image analysis algorithms for cell contour recognition in budding yeast
- 2008
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 16:17, s. 12943-12957
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Tidskriftsartikel (refereegranskat)abstract
- Quantification of protein abundance and subcellular localization dynamics from fluorescence microscopy images is of high contemporary interest in cell and molecular biology. For large-scale studies of cell populations and for time-lapse studies, such quantitative analysiscan not be performed effectively without some kind of automated image analysis tool. Here, we present fast algorithms for automatic cell contour recognition in bright field images, optimized to the model organismbudding yeast (Saccharomyces cerevisiae). The cell contours can be used to effectively quantify cell morphology parameters as well as protein abundance and subcellular localization from overlaid fluorescence data.
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| 387. |
- König, Lorenzo, et al.
(författare)
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Optimal Design of the Annular Groove Phase Mask Central Region
- 2022
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Ingår i: Optics Express. - 1094-4087. ; 30:15, s. 27048-27063
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Tidskriftsartikel (refereegranskat)abstract
- Vortex phase masks have been shown to be an efficient means to reduce the blinding stellar light in high-contrast imaging instruments. Once placed at the focal plane of the telescope, the helical phase ramp of a vortex phase mask diffracts the light of a bright on-axis source outside the re-imaged telescope pupil, while transmitting the light of a faint off-axis companion nearly unaffected. The Annular Groove Phase Mask (AGPM) is a broadband metasurface implementation of a vector vortex phase mask using the artificial birefringence of a circular subwavelength grating etched onto a diamond substrate. To date, the AGPM design has been optimized using rigorous coupled-wave analysis (RCWA), which is a valid tool to simulate periodic straight gratings. However, we have now reached a performance level where the curvature of the grating lines at the center becomes a limiting factor. Here, we use a finite-difference time-domain (FDTD) method to correctly describe the AGPM performance, including the effect of the curved grating close to its center. We confirm the validity of this simulation framework by comparing its predictions with experimental results obtained on our infrared coronagraphic test bench, and we show that RCWA fails at reproducing correctly the central AGPM performance, confirming the need for a full 3d simulation tool such as FDTD. Finally, we use FDTD to optimize the grating parameters at the AGPM center, and conclude with a new optimal design.
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| 388. |
- Laakso, Miku, 1989-, et al.
(författare)
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Water in contact with the backside of a silicon substrate enables drilling of high-quality holes through the substrate using ultrashort laser pulses
- 2020
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 28:2, s. 1394-1408
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Tidskriftsartikel (refereegranskat)abstract
- Holes through silicon substrates are used in silicon microsystems, for example in vertical electrical interconnects. In comparison to deep reactive ion etching, laser drilling is a versatile method for forming these holes, but laser drilling suffers from poor hole quality. In this article, water is used in the silicon drilling process to remove debris and the shape deformations of the holes. Water is introduced into the drilling process through the backside of the substrate to minimize negative effects to the drilling process. Drilling of inclined holes is also demonstrated. The inclined holes could find applications in radio frequency devices.
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| 389. |
- Lagatsky, A. A., et al.
(författare)
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Efficient Doubling of Femtosecond Pulses in Aperiodically and Periodically Poled KTP Crystals
- 2007
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Ingår i: Optics express. - 1094-4087. ; 15:3, s. 1155-1160
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Tidskriftsartikel (refereegranskat)abstract
- Efficient doubling of femtosecond pulses in periodically and aperiodically poled KTP crystals is demonstrated by employing the quasi-phasematched frequency conversion technique. Conversion efficiencies as high as 60% were achieved using either aperiodically or periodically poled KTP nonlinear crystals in an extracavity, single-pass configuration using a diode-pumped femtosecond Yb:KYW laser as the pump source. The temporal characteristics of the frequency-doubled pulses as a function of focusing conditions in a "thick" nonlinear crystal regime have been investigated experimentally and pulses as short as 177 fs have been generated at around 520 nm under strong focusing conditions using a KTP crystal with aperiodic poling.
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| 390. |
- Landström, Lars, et al.
(författare)
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Extraordinary transmission through metal-coated monolayers of microspheres
- 2009
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Ingår i: Optics Express. - 1094-4087. ; 17:2, s. 761-772
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Tidskriftsartikel (refereegranskat)abstract
- The spectral dependence of the extraordinary transmission through monolayers of close-packed silica or polystyrene microspheres on a quartz support, covered with different thin metal films (Ag, Au and Ni) was investigated. The measured spectra were compared with modeled transmission spectra using finite difference time domain (FDTD) calculations. Measured and modeled spectra show good overall agreement. The supported modes in the sphere array were found to be of utmost importance for the transmission mechanism and the results also suggest that the presence of guided modes in the photonic crystal may further enhance the extraordinary transmission through the metal film.
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