Interlaced spin grating for optical wave filtering

Interlaced Spin Grating is a scheme for the preparation of spectro-spatial periodic absorption gratings in a inhomogeneously broadened absorption profile. It relies on the optical pumping of atoms in a nearby long-lived ground state sublevel. The scheme takes advantage of the sublevel proximity to build large contrast gratings with unlimited bandwidth and preserved average optical depth. It is particularly suited to Tm-doped crystals in the context of classical and quantum signal processing. In this paper, we study the optical pumping dynamics at play in an Interlaced Spin Grating and describe the corresponding absorption profile shape in an optically thick atomic ensemble. We show that, in Tm:YAG, the diffraction efficiency of such a grating can reach 18.3% in the small angle, and 11.6% in the large angle configuration when the excitation is made of simple pulse pairs, considerably outperforming conventional gratings.Comment: 11 pages, 13 figures in Physical Review A, 201

Rate equation reformulation including coherent excitation: application to periodic protocols based on spectral hole-burning

International audienceA large number of signal-processing protocols are based on recording a spectral pattern via spectral hole-burning in an inhomogeneously broadened absorption profile. We present a simulation method specifically designed for periodic excitation sequences leading to the creation of a spectral pattern. This method is applicable to any multi-level atomic structure. The atomic variables' coherent dynamics are solved for a single temporal excitation step. The result is expressed as an equivalent population transfer rate. This way, the whole sequence is described as a matrix product and the steady state of the system under periodic excitation is easily derived. The propagation through the atomic medium is fully decoupled from the temporal evolution. We apply this method to the engraving of a spectral grating in a large-absorption Tm:YAG sample for wideband spectral analysis

Dynamic saturation in semiconductor optical amplifiers: accurate model, role of carrier density, and slow light

We developed an improved model in order to predict the RF behavior and the slow light properties of the SOA valid for any experimental conditions. It takes into account the dynamic saturation of the SOA, which can be fully characterized by a simple measurement, and only relies on material fitting parameters, independent of the optical intensity and the injected current. The present model is validated by showing a good agreement with experiments for small and large modulation indices.Comment: 9 pages, 5 figure

Optical coherence and spin population dynamics in 171^{171}Yb3+^{3+}:Y2_2SiO5_5 single crystals

$^{171}$Yb$^{3+}$-doped Y$_2$SiO$_5$ crystals are a promising platform for optical quantum memories in long-distance quantum communications. The relevance of this material lies in $^{171}$Yb long optical and spin coherence times, along with a large hyperfine splitting, enabling long quantum storage over large bandwidths. Mechanisms affecting the optical decoherence are however not precisely known, especially since low-temperature measurements have so far focused on the 2 to 4 K range. In this work, we performed two- and three-pulse photon echoes and spectral hole burning to determine optical homogeneous linewidths in two 171 Yb:YSO crystals doped at 2 and 10 ppm. Experiments were performed in the 40 mK to 18 K temperature range, leading to linewidths between 320 Hz, among the narrowest reported for rare-earth ions, and several MHz. Our results show that above 6 K the homogeneous linewidth is mainly due to an elastic two-phonon process which results in a slow broadening with temperature, the homogeneous linewidth reaching only 25 kHz at 10 K. At lower temperatures, interactions with $^{89}$Yb nuclear spin-flips, paramagnetic defects or impurities, and also Yb-Yb interactions for the higher concentrated crystal, are likely the main limiting factor to the homogeneous linewidth. In particular, we conclude that the direct effect of spin and optical excited state lifetime is a minor contribution to optical decoherence in the whole temperature range studied. Our results indicate possible paths and regimes for further decreasing the homogeneous linewidths or maintaining narrow lines at higher $^{171}$Yb concentration.Comment: 11 pages, 7 figure for the manuscrip

20 GHz instantaneous bandwidth RF spectrum analyzer with high time-resolution

International audienceWe report on the experimental demonstration of a multi-gigahertz bandwidth RF spectrum analyzer exhibiting a resolution below 20 MHz, based on spectral hole burning in a rare-earth ion-doped crystal. To be compatible with demanding real-time spectrum monitoring applications, our demonstrator is designed to reach a high time resolution. For this purpose, we implemented the so-called "rainbow" architecture in which the spectral components of the incoming signal are angularly separated by the crystal, and are then acquired with a pixelated photodetector. The Tm 3+ :YAG crystal is programmed with a semiconductor DFB laser which frequency scan is servo-controlled and synchronized with the angular scan of a resonant galvanometric mirror, while a high-speed camera is used to acquire the spectra. In the perspective of future implementation within a system, the crystal is cooled below 4 K with a closed-cycle cryostat. With this setup, we have been able to monitor and record the spectrum of complex microwave signals over an instantaneous bandwidth above 20 GHz, with a time resolution below 100 µs, 400 resolvable frequency components and a probability of intercept of 100 %

Slow light fiber systems in microwave photonics

Slow light systems are particularly attractive for analog signal processing, since their inherent limitation to a delay-bandwidth product of 1 is less critical for analog systems such as those used in microwave photonics. We present here the implementation of two basic functions - phase shifting and true time delaying - fully optically controlled using stimulated Brillouin scattering in optical fibers. The combination of these two functions makes possible the implementation of true time delays without limitation on the microwave carrier frequency using the separate carrier tuning technique. This is illustrated by the implementation of the delaying system for the realization of a microwave tunable notch filter

Theoretical Study of the Spurious-Free Dynamic Range of a Tunable Delay Line based on Slow Light in SOA

We developed a predictive model describing harmonic generation and intermodulation distortions in semiconductor optical amplifiers (SOAs). This model takes into account the variations of the saturation parameters along the propagation axis inside the SOA, and uses a rigorous expression of the gain oscillations harmonics. We derived the spurious-free dynamic range (SFDR) of a slow light delay line based on coherent population oscillation (CPO) effects, in a frequency range covering radar applications (from 40kHz up to 30GHz), and for a large range of injected currents. The influence of the high order distortions in the input microwave spectrum is discussed, and in particular, an interpretation of the SFDR improvement of a Mach-Zehnder modulator by CPOs effects in a SOA is given.Comment: 12 pages, 5 figures (8 attached figures

Broadband true time delay for microwave signal processing, using slow light based on stimulated Brillouin scattering in optical fibers

[EN] We experimentally demonstrate a novel technique to process broadband microwave signals, using all-optically tunable true time delay in optical fibers. The configuration to achieve true time delay basically consists of two main stages: photonic RF phase shifter and slow light, based on stimulated Brillouin scattering in fibers. Dispersion properties of fibers are controlled, separately at optical carrier frequency and in the vicinity of microwave signal bandwidth. This way time delay induced within the signal bandwidth can be manipulated to correctly act as true time delay with a proper phase compensation introduced to the optical carrier. We completely analyzed the generated true time delay as a promising solution to feed phased array antenna for radar systems and to develop dynamically reconfigurable microwave photonic filters. (C) 2010 Optical Society of AmericaWe acknowledge the support from the Swiss National Science Foundation through project 200020-121860 and the support from the European Union FP7 project GOSPEL.Chin, S.; Thevenaz, L.; Sancho Durá, J.; Sales Maicas, S.; Capmany Francoy, J.; Berger, P.; Bourderionnet, J.... (2010). Broadband true time delay for microwave signal processing, using slow light based on stimulated Brillouin scattering in optical fibers. Optics Express. 18(21):22599-22613. https://doi.org/10.1364/OE.18.022599S22599226131821Capmany, J., & Novak, D. (2007). Microwave photonics combines two worlds. Nature Photonics, 1(6), 319-330. doi:10.1038/nphoton.2007.89Dolfi, D., Joffre, P., Antoine, J., Huignard, J.-P., Philippet, D., & Granger, P. (1996). Experimental demonstration of a phased-array antenna optically controlled with phase and time delays. Applied Optics, 35(26), 5293. doi:10.1364/ao.35.005293Yunqi Liu, Jianliang Yang, & Jianping Yao. (2002). Continuous true-time-delay beamforming for phased array antenna using a tunable chirped fiber grating delay line. IEEE Photonics Technology Letters, 14(8), 1172-1174. doi:10.1109/lpt.2002.1022008Mørk, J., Kjær, R., van der Poel, M., & Yvind, K. (2005). Slow light in a semiconductor waveguide at gigahertz frequencies. Optics Express, 13(20), 8136. doi:10.1364/opex.13.008136Su, H., Kondratko, P., & Chuang, S. L. (2006). Variable optical delay using population oscillation and four-wave-mixing in semiconductor optical amplifiers. Optics Express, 14(11), 4800. doi:10.1364/oe.14.004800Shi, Z., & Boyd, R. W. (2009). Discretely tunable optical packet delays using channelized slow light. Physical Review A, 79(1). doi:10.1103/physreva.79.013805Morton, P. A., & Khurgin, J. B. (2009). Microwave Photonic Delay Line With Separate Tuning of the Optical Carrier. IEEE Photonics Technology Letters, 21(22), 1686-1688. doi:10.1109/lpt.2009.2031500Song, K. Y., Herr�ez, M. G., & Th�venaz, L. (2005). Observation of pulse delaying and advancement in optical fibers using stimulated Brillouin scattering. Optics Express, 13(1), 82. doi:10.1364/opex.13.000082Thévenaz, L. (2008). Slow and fast light in optical fibres. Nature Photonics, 2(8), 474-481. doi:10.1038/nphoton.2008.147Nikles, M., Thevenaz, L., & Robert, P. A. (1997). Brillouin gain spectrum characterization in single-mode optical fibers. Journal of Lightwave Technology, 15(10), 1842-1851. doi:10.1109/50.633570Loayssa, A., & Lahoz, F. J. (2006). Broad-band RF photonic phase shifter based on stimulated Brillouin scattering and single-sideband modulation. IEEE Photonics Technology Letters, 18(1), 208-210. doi:10.1109/lpt.2005.861307González Herráez, M., Song, K. Y., & Thévenaz, L. (2006). Arbitrary-bandwidth Brillouin slow light in optical fibers. Optics Express, 14(4), 1395. doi:10.1364/oe.14.001395Weiqi Xue, Sales, S., Mork, J., & Capmany, J. (2009). Widely Tunable Microwave Photonic Notch Filter Based on Slow and Fast Light Effects. IEEE Photonics Technology Letters, 21(3), 167-169. doi:10.1109/lpt.2008.2009468Sagues, M., García Olcina, R., Loayssa, A., Sales, S., & Capmany, J. (2008). Multi-tap complex-coefficient incoherent microwave photonic filters based on optical single-sideband modulation and narrow band optical filtering. Optics Express, 16(1), 295. doi:10.1364/oe.16.00029

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure