| 391. |
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| 392. |
- Larsson, Jim, et al.
(författare)
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Atmospheric CO2 sensing using Scheimpflug-lidar based on a 1.57-mu m fiber source
- 2019
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 27:12, s. 17348-17358
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Tidskriftsartikel (refereegranskat)abstract
- A molecular laser-radar system, based on the Scheimpflug principle, has been constructed and demonstrated for remote sensing of atmospheric CO2 concentrations using Differential Absorption Lidar (DIAL) in the (30012 <- 00001) absorption band. The laser source is a Continues Wave (CW) Distributed-FeedBack (DFB) diode laser seeding an Erbium-doped fiber amplifier, emitting narrowband (3 MHz) tunable radiation with an output power of 1.3 W at 1.57 mu m. The laser beam is expanded and transmitted to the atmosphere. The atmospheric backscattered signal is collected with a Newtonian telescope and detected with a linear InGaAs array detector satisfying the Scheimpflug condition. We present range-resolved measurements of atmospheric CO2 concentration from a test range of 2 km located in the city of Lund, Sweden. We discuss and provide scalable results for CO2 profiling with the Scheimpflug-lidar method.
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| 393. |
- Larsson, Rasmus, 1994, et al.
(författare)
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Coherent combining of low-power optical signals based on optically amplified error feedback
- 2022
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 30:11, s. 19441-19455
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Tidskriftsartikel (refereegranskat)abstract
- In free-space optical communication links, the combining of optical signals from multiple apertures is a well-known method to collect more power for improved sensitivity or mitigation of atmospheric disturbances. However, for analog optical combining no detailed analysis has been made in cases when the optical signal power is very low (<-60 dBm) as would be the case in very long-haul free-space links. We present a theoretical and experimental study of analog coherent combining of noise-limited signals from multiple independent apertures by applying low frequency optical phase dithering to actively compensate the relative phases. It is experimentally demonstrated that a 97% combining efficiency of four 10 GBaud QPSK signals is possible with a signal power per aperture exceeding -80 dBm, in fair agreement with theory. We also discuss the scaling aspects to many apertures.
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| 394. |
- Larsson, Rasmus, 1994, et al.
(författare)
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Low-noise phase-sensitive optical parametric amplifier with lossless local pump generation using a digital dither optical phase-locked loop
- 2023
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 31:22, s. 36603-36614
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Tidskriftsartikel (refereegranskat)abstract
- The low noise figure of phase-sensitive amplifiers (PSAs) is attractive for optically pre-amplified measurement and communication systems. However, a major practical implementation difficulty pertains to the requirement of phase-locked signal, idler, and pump waves. Previously, injection locking to a co-propagating weak pump pilot or tapping portions of the received signal (lossy) for carrier re-generation have been used. Here we present a novel, lossless approach without any pump pilot, that generates a phase-locked receiver-local pump within the PSA using a digital dither-based optical phase-locked loop. We experimentally demonstrate a 2 dB noise figure with a low 0.3 dB penalty due to imperfect locking. By comparing the phase-locking performance in a PSA to that in a 50/50-coupler, we discuss and predict potential performance improvements connected to loop delay and laser phase characteristics.
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| 395. |
- Laurell, Fredrik, et al.
(författare)
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Laser-written waveguides in KTP for broadband Type II second harmonic generation
- 2012
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Ingår i: Optics Express. - 1094-4087. ; 20:20, s. 22308-22313
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Tidskriftsartikel (refereegranskat)abstract
- Femto-second laser writing was used to fabricate waveguides in a z-cut KTP sample with losses below 0.8 dB/ cm. They were used for efficient, broad bandwidth, Type II birefringent second harmonic generation to the green. The temperature and wavelength bandwidth were, 28 degrees C.cm and 0.85 nm.cm, respectively.
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| 396. |
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| 397. |
- Lebugle, Maxime, et al.
(författare)
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High-acceptance versatile microfocus module based on elliptical Fresnel zone plates for small-angle X-ray scattering
- 2017
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Ingår i: Optics Express. - 1094-4087. ; 25:18, s. 21145-21158
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Tidskriftsartikel (refereegranskat)abstract
- High-efficiency microfocusing of multi-keV X-rays at synchrotron sources is highly profitable for spatially resolved structural analysis of many kinds. Because radiation from synchrotron sources is typically elongated along the horizontal dimension, generating a microbeam that is isotropic in size requires a carefully designed optics system. Here we report on using a combination of a horizontally tunable slit downstream of the undulator source with elliptical diffractive Fresnel zone plates. We demonstrate the arrangement in context of small-angle X-ray scattering experiments, obtaining a microbeam of 2.2 μm ×1.8 μm (X × Y) with a flux of 1.2 × 1010 photons/s at an energy of 11.2 keV at the sample position.
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| 398. |
- Lee, Kwang Jo, et al.
(författare)
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Analysis of acceptable spectral windows of quadratic cascaded nonlinear processes in a periodically poled lithium niobate waveguide
- 2011
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 19:9, s. 8327-8335
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Tidskriftsartikel (refereegranskat)abstract
- We report a systematic and comparative study of the acceptance bandwidths of two cascaded quadratic nonlinear processes in periodically poled lithium niobate waveguides, namely cascaded second-harmonic generation and difference-frequency generation (cSHG/DFG) and cascaded sum-frequency generation and difference-frequency generation (cSFG/DFG). We first theoretically and experimentally study the acceptance bandwidths of both the individual second-harmonic generation (SHG) and sum-frequency generation (SFG) processes in the continuous wave (CW) and pulsed-pump regimes. Our results show that the SHG bandwidth is approximately half that of the SFG process in the CW regime, whereas the SHG acceptance bandwidth can approach the CW SFG bandwidth limit when pulsed-pump is used. As a consequence we conclude that the tuning bandwidths of both cascaded processes should be similar in the pulsed pump regime once the pump pulse bandwidths approach that of SFG (i.e. the cSHG/DFG bandwidth is not limited by the CW SHG bandwidth). We confirm that this is the case experimentally.
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| 399. |
- Lee, Kwang Jo, et al.
(författare)
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OTDM to WDM format conversion based on quadratic cascading in a periodically poled lithium niobate waveguide
- 2010
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Ingår i: Optics Express. - 1094-4087. ; 18:10, s. 10282-10288
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Tidskriftsartikel (refereegranskat)abstract
- We propose and demonstrate error-free conversion of a 40 Gbit/s optical time division multiplexed signal to 4 x 10 Gbit/s wavelength division multiplexed channels based on cascaded second harmonic and difference frequency generation in a periodically poled lithium niobate waveguide. The technique relies on the generation of spectrally (and temporally) flat linearly chirped pulses which are then optically switched with short data pulses in the nonlinear waveguide. Error-free operation was obtained for all channels with a power penalty below 2dB.
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| 400. |
- Lee, Kwang Jo, et al.
(författare)
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Phase sensitive amplification based on quadratic cascading in a periodically poled lithium niobate waveguide
- 2009
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Ingår i: Optics Express. - 1094-4087. ; 17:22, s. 20393-20400
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Tidskriftsartikel (refereegranskat)abstract
- We propose and demonstrate phase-sensitive amplification based on cascaded second harmonic generation and difference frequency generation within a periodically poled lithium niobate waveguide. Excellent agreement between our numerical simulations and proof-of-principle experiments using a 3-cm waveguide device operating at wavelengths around 1550 nm is obtained. Our experiments confirm the validity and practicality of the approach and illustrate the broad gain bandwidths achievable. Additional simulation results show that the maximum gain/attenuation factor increases quadratically with input pump power, reaching a value of +/- 19.0dB at input pump powers of 33 dBm for a 3 cm-long waveguide. Increased gains/reduced powers for a fixed gain could be achieved using longer crystals.
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