| 11. |
- Burza, Matthias, et al.
(författare)
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Dispersion and monochromatization of x-rays using a beryllium prism
- 2015
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Ingår i: Optics Express. - 1094-4087. ; 23:2, s. 620-627
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate experimentally and numerically that an x-ray prism made of beryllium can be used to disperse and monochromatize x-rays. A polished beryllium cuboid was employed as refractive and dispersive optics. The results of a proof-of-principle experiment and methods of performance optimization are presented. The spatial separation of undulator harmonics and their subsequent selection using a slit are described. A numerical study, assuming realistic beam and beamline parameters, suggests that undulator harmonics can be spatially separated in the range from 3 keV to beyond 20 keV, while maintaining throughput above 50%. Refractive optics is particularly suitable for low-repetition-rate sources such as free-electron lasers and other LINAC-based short-pulse sources. (C) 2015 Optical Society of America
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| 12. |
- Caleman, Carl, et al.
(författare)
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Ultrafast self-gating Bragg diffraction of exploding nanocrystals in an X-ray laser
- 2015
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Ingår i: Optics Express. - 1094-4087. ; 23:2, s. 1213-1231
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Tidskriftsartikel (refereegranskat)abstract
- In structural determination of crystalline proteins using intense femtosecond X-ray lasers, damage processes lead to loss of structural coherence during the exposure. We use a nonthermal description for the damage dynamics to calculate the ultrafast ionization and the subsequent atomic displacement. These effects degrade the Bragg diffraction on femtosecond time scales and gate the ultrafast imaging. This process is intensity and resolution dependent. At high intensities the signal is gated by the ionization affecting low resolution information first. At lower intensities, atomic displacement dominates the loss of coherence affecting high-resolution information. We find that pulse length is not a limiting factor as long as there is a high enough X-ray flux to measure a diffracted signal.
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| 13. |
- Calil Kores, Cristine, et al.
(författare)
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Temperature dependence of the spectral characteristics of distributed-feedback resonators
- 2018
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Ingår i: Optics Express. - 1094-4087. ; 26:4, s. 4892-4905
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Tidskriftsartikel (refereegranskat)abstract
- We characterize the spectral response of a distributed-feedback resonator when subject to a thermal chirp. An Al2O3 rib waveguide with a corrugated surface Bragg grating inscribed into its SiO2 top cladding is experimentally investigated. We induce a near-to-linear temperature gradient along the resonator, leading to a similar variation of the grating period, and characterize its spectral response in terms of wavelength and linewidth of the resonance peak. Simulations are carried out, showing good agreement with the experimental results and indicating that the wavelength of the resonance peak is a result only of the total accumulated phase shift. For any chirp profile we are able to calculate the reflectivities at the resonance wavelength, and this information largely explains how the linewidth of the resonance changes. This result shows that the increase in linewidth is governed by the increase of the resonator outcoupling losses.
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| 14. |
- Camara, Alexandre R., et al.
(författare)
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Optical creation and erasure of the linear electrooptical effect in silica fiber
- 2015
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 23:14, s. 18060-18069
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Tidskriftsartikel (refereegranskat)abstract
- We study the creation and erasure of the linear electrooptical effect in silicate fibers by optical poling. Carriers are released by exposure to green light and displaced with simultaneous application of an internal dc field. The second order nonlinear coefficient induced grows with poling bias. The field recorded (similar to 10(8) V/m) is comparable to that obtained through classical thermal poling of fibers. In the regime studied here, the second-order nonlinearity induced (similar to 0.06 pm/V) is limited by the field applied during poling (1.2 x 10(8) V/m). Optical erasure with high-power green light alone is very efficient. The dynamics of the writing and erasing process is discussed, and the two dimensional (2D) field distribution across the fiber is simulated. (C) 2015 Optical Society of America
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| 15. |
- Cao, Yuan, et al.
(författare)
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Multi-tenant secret-key assignment over quantum key distribution networks
- 2019
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Ingår i: Optics Express. - : OPTICAL SOC AMER. - 1094-4087. ; 27:3, s. 2544-2561
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Tidskriftsartikel (refereegranskat)abstract
- Quantum key distribution (QKD) networks are promising to progress towards widespread practical deployment over existing fiber infrastructures in the near future. Given the high cost and difficulty of deploying QKD networks, multi-tenancy becomes promising to improve cost efficiency for future QKD networks. In a multi-tenant QKD network, multiple QKD tenants can sham the same QKD network infrastructure to obtain secret keys for securing their data transfer. Since the secret-key resources are finite and precious in QKD networks, how to achieve efficient multi-tenant secret-key assignment (MTKA) to satisfy the secret-key demands of multiple QKD tenants over QKD networks becomes a significant problem. In this regard, this study addresses the MTKA problem over QKD networks. A new multi-tenant QKD network architecture is proposed based on software defined networking (SDN) and quantum key pool (QKP) techniques. A secret-key rate sharing scheme is presented and a heuristic algorithm is designed to implement efficient MTKA over QKD networks. A new performance metric, namely matching degree (MD) that reflects the balance between QKD network secret-key resources and QKD tenant requests, is defined and evaluated. Simulation studies indicate that high QKD tenant requests accommodation and efficient secret-key resource usage can be achieved via maximizing the value of MD.
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| 16. |
- Carpenter, J., et al.
(författare)
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Polarization-resolved cross-correlated (C2) imaging of a photonic bandgap fiber
- 2016
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 24:24, s. 27785-27790
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate polarization-resolved frequency domain cross-correlated (C2) imaging to characterize a 5m length of hollow-core photonic bandgap fiber. We produce a spectrogram of the fiber response to investigate the spatial, polarization, spectral, and temporal behavior. We then show how this temporally-resolved technique can be used to characterize multiple fiber launch conditions simultaneously by assigning each a unique time delay.
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| 17. |
- Cen, Min, et al.
(författare)
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Full monitoring for long-reach TWDM passive optical networks
- 2016
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 24:14, s. 15782-15797
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel and simple fiber monitoring system based on multi-wavelength transmission-reflection analysis for long-reach time and wavelength division multiplexing passive optical networks. For the first time, the full localization functionality of long-reach passive optical networks is possible with the proposed monitoring scheme, including supporting fault detection, identification, and localization in both feeder and distribution fiber segments. By measuring the transmitted and reflected/backscattered optical powers launched by an unmodulated continuous-wave optical source, the proposed solution is able to supervise the network with good spatial accuracy, a high detection speed and a low impact on data traffic. Both the theoretical analysis and experimental validation show that the proposed scheme is capable of providing an accurate fault monitoring functionality for long-reach time and wavelength division multiplexing passive optical networks.
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| 18. |
- Centeno, R., et al.
(författare)
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External cavity diode laser-based detection of trace gases with NICE-OHMS using current modulation
- 2015
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Ingår i: Optics Express. - 1094-4087. ; 23:5, s. 6277-6282
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Tidskriftsartikel (refereegranskat)abstract
- We combine an external cavity diode laser with noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) using current modulation. With a finesse of 1600, we demonstrate noise equivalent absorption sensitivities of 4.1 x 10(-10) cm(-1) Hz(-1/2), resulting in sub-ppbv detection limits for Doppler-broadened transitions of CH4 at 6132.3 cm(-1), C2H2 at 6578.5 cm(-1) and HCN at 6541.7 cm(-1). The system is used for hydrogen cyanide detection from sweet almonds.
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| 19. |
- Chang, Lantian, et al.
(författare)
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Chip based common-path optical coherence tomography system with an on-chip microlens and multi-reference suppression algorithm
- 2016
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 24:12, s. 12635-12650
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an integrated optical probe including an on-chip microlens for a common-path swept-source optical coherence tomography system. This common-path design uses the end facet of the silicon oxynitride waveguide as the reference plane, thus eliminating the need of a space-consuming and dispersive on-chip loop reference arm, thereby obviating the need for dispersion compensation. The on-chip micro-ball lens eliminates the need of external optical elements for coupling the light between the chip and the sample. The use of this lens leads to a signal enhancement up to 37 dB compared to the chip without a lens. The light source, the common-path arm and the detector are connected by a symmetric Y junction having a wavelength independent splitting ratio (50/50) over a much larger bandwidth than can be obtained with a directional coupler. The signal-to-noise ratio of the system was measured to be 71 dB with 2.6 mW of power on a mirror sample at a distance of 0.3 mm from the waveguide end facet. Cross-sectional OCT images of a layered optical phantom sample are demonstrated with our system. A method, based on an extended Fourier-domain OCT model, for suppressing ghost images caused by additional parasitic reference planes is experimentally demonstrated.
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| 20. |
- Chang, Lantian, et al.
(författare)
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Waveguide-coupled micro-ball lens array suitable for mass fabrication
- 2015
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Ingår i: Optics Express. - : Optica Publishing Group. - 1094-4087. ; 23:17, s. 22414-22423
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a fabrication procedure for the direct integration of micro-ball lenses on planar integrated optical channel waveguide chips with the aim to reduce the divergence of light that arises from the waveguide in both horizontal and vertical directions. Fabrication of the lenses is based on photoresist reflow which is a procedure that allows for the use of photolithography for careful alignment of the lenses with respect to the waveguides and enables mass production. We present in detail the design and fabrication procedures. Optical characterization of the fabricated micro-ball lenses demonstrates a good performance in terms of beam-size reduction and beam shape. The beam half divergence angle of 1544 nm light is reduced from 12.4 degrees to 1.85 degrees.
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