The high current driver accelerator of the SPIRAL 2 project uses independently phased SC resonators working at 88 MHz. Solid state poweramplifiers equipped with circulators are foreseen to drive the cavities with widely ranging conditions of beam loading. These power devices are developed by industrial companies and a test bench has been studied and manufactured to test the prototypes, to commission all the units before their installation on the accelerator and to be used to test repaired modules. Even if designed to be used at 88 MHz, the test bench can be used at higher frequencies too. The poster describes the test bench as well as the results on the first amplifiers bought for the cryomodule power tests.
Linearization of poweramplifiers in wide band communication systems by digital baseband predistortion technique
De nos jours, de nouvelles applications radio fréquences sont conçues et réalisées pour apporter toujours plus de services aux utilisateurs. La ressource spectrale devient de plus en plus rare due à une explosion de demandes de nouveaux services. Pour obtenir une plus grande efficacité spectrale, différentes techniques de modulation ont été développées entraînant le plus souvent une augmentation de la dynamique des signaux. Ces signaux deviennent beaucoup plus sensibles à la non-linéarité présente dans la chaîne de transmission, en particulier celle de l’amplificateur de puissance (AP). De plus, dans les systèmes de communications modernes, la largeur de bande du système devient de plus en plus grande et les effets mémoires de l’amplificateur de puissance ne peuvent plus être négligés. Pour obtenir un rendement optimal, il faut pouvoir travailler avec des puissances moyennes proches de la zone de compression en utilisant des dispositifs supplémentaires permettant de linéariser les APs. L’objectif des techniques de linéarisation est d’obtenir une caractéristique linéaire jusqu’à la zone de saturation de l’AP. Une des techniques les plus prometteuses est la technique de la pré-distorsion numérique en bande de base grâce à sa simplicité, flexibilité et reconfigurabilité. Celle-ci consiste à inverser la non-linéarité de l’AP en bande de base avant l’AP afin de rendre le comportement global du système linéaire. L’objectif de cette thèse est de trouver des solutions efficaces (rapides et simples à implémenter sur des cartes numériques) de linéarisation en bande de base d’amplificateur de puissance ayant des effets mémoires non linéaires.
In addition, high efficiency PA architectures based on supply and load modulation have been explored. The use of supply or load modulation allows maximizing the efficiency at back-off power but generally at the expense of linearity. By adopting an iso-gain optimization scheme, it has been shown that envelope tracking can provide high efficiency together with high linearity without using complex digital pre-distortion. With load modulation, it has appeared that linearization is necessary whatever the optimization scheme, making it inappropriate for handheld devices for which linearization techniques currently consume too much power. In order to assess the performance of load modulation in SOI CMOS technology, a passive load modulation PA demonstrator for 4Gfemto- cell applications was designed. A SOI CMOS tunable matching network has been design to provide optimal load trajectory to the PA at back-off power. Substantial efficiency improvement was reached with this device. The PA delivers 31.5dBm output power with efficiency improvement higher than 50% for back-off power levels ranging from 7dB to 12dB. This prototype is one of the first SOI CMOS PA delivering watt-level output power with high efficiency improvement at back-off. Perspective for this demonstrator is to optimize the layout of the tunable capacitors to improve the performance. The control circuitry of this device could also be studied and optimized to allow dynamic control of the device. This circuit could take the digital information of the digital front-end and decode it to optimize the configuration of the TMN according to the expected output signal. Another possibility would be to process the envelope of the signal, which would be a challenge in terms of high speed electronics.
We now turn our attention to positive envelope feedback, which is the first contribution of the research work presented in this thesis. In chapters 2 and 3, we introduce positive envelope feedback as a novel circuit technique for dynamic biasing of the PA, where the bias signal is a function of the PA’s true output envelope power (Sharma, Constantin, & Soliman, 2017; Sharma & Constantin, January 2018; Sharma & Constantin, April 2018). The CMOS PA’s gate (or BJT PA’s base) bias is varied based on an actual signal flow from the PA’s output node to its bias node. To the best of the author’s knowledge, positive envelope feedback has never been reported in any PA architecture, nor in any analog or RF signal processing function. The proposed approach is simple, requires minimum additional chip area, consumes minimum additional current and does not require any external signal processing. All of the above greatly enhances its feasibility for full on-chip integration as well as facilitates its integration as a functional block into existing state-of-the-art PA architectures to further improve PA performance. The proposed approach does not suffer from excessive delays and the bandwidth limitation, as in the case of negative envelope feedback, and does not require additional circuits for loop stability compensation. It requires a single envelope detector and does not need a high loop gain, which ensures that the PA’s output noise performances are not degraded. All these features contribute towards enhancing the feasibility of implementing positive envelope feedback in PAs as a single-chip stand- alone solution.
cost, and mass [5, 8]. Conducting an accurate comparison of the two technologies can be dif ﬁcult, as there are numerous frequency bands and power requirements to consider .
Prior to 1990, there had been very few published studies comparing SSPAs and TWTAs. Since then, only a few major studies have compared the capabilities of the two technologies. These studies took place in 1991, 1993, and 2005. The 1991 study was funded by the European Space and Technology Center (ESTEC) and focused on satellites launched between 1984 and 1992. In 1993, National Aeronautics and Space Administration (NASA) sponsored a study expanding on the 1991 ESTEC study [8, 11], and in 2005, Boeing supported a study comparing SSPAs and TWTAs onboard satellites launched from the mid-1980s to 2004 . Updates to the Boeing 2005 study were made in 2008 and 2013 [20, 42].
series of ALS 1 shown in Figure 4.36 should therefore reflect the intrinsic character of the fiber amplifier.
Figure 4.35: ALS fiber amplifiers: output power vs. laser diode pump current. The most important objective in monitoring the output power was to gain some insight on lifetime and stability of fiber amplifiers, as photo-darkening [ 102 , 103 , 160 ] has long been a concern in high-power ytterbium-doped fiber amplifiers for long-term operation. Both ALS 1 and ALS 2 experienced gradual loss of output power. Simple linear fitting of the output power trend between ∼ 3800 h and ∼ 6400 h indicates loss rate of 1.1 mW h −1 for ALS 1 and 0.9 mW h −1 for ALS 2. It should be noted that there was no measurement dedicated to photo-darkening, so the loss of output power was a collective effect of many factors including but not limited to photo-darkening. For example, the degradation of the fiber coupler bringing together the signal beam the two pumping beams might also be liable for the loss of output power.
Our approach to make CBC of diode lasers more attractive for future applications is to make use of high-brightness tapered amplifiers in order to reach similar power levels but with a reduced number of elements. Tapered laser diodes are a promising building block for CBC architectures as they can deliver high power in a close to diffraction limited beam out of one monolithic device. However, one important drawback to tapered devices is the slightly degraded beam quality at high powers with about 70% power-content in the diffraction limited central lobe while the rest of the power is distributed in side lobes. TPAs are nevertheless our preferred choice for power scaling by CBC to simplify the optical setup by using only a limited number of high-poweramplifiers. At the same time as demonstrated in this study, CBC is one way to reduce the relative power content in the side lobes since CBC with non-perfect Gaussian beams favors the diffraction-limited power content leading to an improved beam quality . In our previous studies, an output power of 11.5 W was reached by CBC of a monolithically integrated array of five TPAs, but it was limited by thermal effects caused by emitter to emitter heating of the laser bar . For this reason, we make use of separate individual amplifiers that can be efficiently cooled in order to be able to operate them at higher currents and achieve a higher combined power per element . Additionally one can develop a simplified optical setup with standard optical elements, as splitting and combining the beam is simpler.
2. Experimental setup
The experimental setup starts with a femtosecond oscillator delivering 200 fs pulses, centered at 1030 nm, at 55 MHz repetition rate. It is followed by a pulse picker allowing to reduce the pulse repetition rate, a 500 ps Chirped- Fiber Bragg Grating used for chirped-pulse amplification and a pulse-shaper. The beam is then split into eight channels, seven of which are used for the beam combining. These seven sub-beams are seeded through variable optical delay lines in free-space followed by piezo-driven fiber stretchers allowing to match the delay and the phase between the pulses, respectively. A second pulse picker stage allows for a further reduction of the pulse repetition rate down to 2 MHz. The output beams are pre-amplified in large-mode area core-pumped ytterbium-doped fiber amplifiers before seeding seven poweramplifiers of 30-µm mode-field diameter generating 25 W average power each. The fiber outputs are then stacked into a hexagonal array and individually collimated by a hexagonal microlens array. The common image focal plane represents the tiled-aperture and defines the near field of the global beam. The combined beam is directly found in the far field, obtained in the image focal plane of a lens. Hence, no combining elements are needed.
Université de Nice-Sophia Antipolis, Parc Valrose 06108 Nice, France E-mail: firstname.lastname@example.org
Abstract. We present a co-axial dual-core resonant leaky optical fibre design, in which the outer core
is made highly leaky. A suitable choice of parameters can enable us to resonantly couple power from the inner core to the outer core. In a large-core fibre, such a resonant coupling can considerably increase the differential leakage loss between the fundamental and the higher order modes and can result in effective single-mode operation. In a small-core single-mode fibre, such a coupling can lead to sharp increase in the wavelength dependent leakage loss near the resonant wavelength and can be utilized for the suppression of amplified spontaneous emission and thereby gain equalization of an optical amplifier. We study the propagation characteristics of the fibre using the transfer matrix method and present an example of each, the large-mode-area design for high poweramplifiers and the wavelength tunable leakage loss design for inherent gain equalization of optical amplifiers.
 A. Alizade, M. Forounchi and A. Medi, ”On Design of Wideband Compact-Size Ka/Q-Band High-PowerAmplifiers”,IEEE Trans. Microw. Theory Tech., vol. 64, no. 6, pp. 1831–1842, 2016.  S. Narayanan, ”Application of Volterra series to intermodulation distortion analysis of transistor feedback amplifies”, IEEE Trans. Microw. Theory Tech., vol. 17, pp. 518–527, 1970.
 T. W. Kim, B. Kim and K. Lee, ”Highly linear receiver front-end adopting MOSFET transconductance linearization by multiple gated transistors”,IEEE Journal of Solid-State Circuits, vol. 39, pp. 223–229, 2004.  Y. Ding and R. Harjani, ”A +18 dBm IIP3 LNA in .35 um CMOS”, IEEE International Solidstate Circuits Conference, 2001.
pump absorption and power loss (P in decreases). Regions
with initially higher (resp. lower) pump power will experience more (resp. less) efficient PB so their RIA, together with their local EDL, will increase slowly (resp. rapidly). In other words, lower EDLs are less rapidly damaged (raised). As regards the PB efficiency, the notion of high and low pump power is obviously related to the dose rate. A high power, i.e. yielding very efficient PB, refers to a power which is capable of photo-ionizing color centers at a frequency which is comparable to that of their formation (set by D’). For space-based applications, concerned with very low dose rates, “high pump powers” can be actually low. Not only the small D’ will make initial EDLs low (2-3 dB/m at
Départment de Physique, Université de Sherbrooke, Sherbrooke, Québec, Canada and
3 Canadian Institute for Advanced Research, Toronto, Canada
(Dated: October 27, 2014)
Achieving individual qubit readout is a major challenge in the development of scalable supercon- ducting quantum processors. We have implemented the multiplexed readout of a four transmon qubit circuit using non-linear resonators operated as Josephson bifurcation amplifiers. We demon- strate the simultaneous measurement of Rabi oscillations of the four transmons. We find that multiplexed Josephson bifurcation is a high-fidelity readout method, the scalability of which is not limited by the need of a large bandwidth nearly quantum-limited amplifier as is the case with linear readout resonators.
Key words: Semiconductor optical amplifiers, all-optical regeneration
Until now, signal processing in long distance transmission systems is performed by optoelectronic repeaters. However the higher the bit rate, the more expensive and complex the optoelectronic repeaters. In this circumstance, all-optical devices become attractive solutions. Therefore, an all-optical solution should have criteria such as stability, compactness, simplicity of operation and low-power consumption. The two functionalities which are closest to implementation in real systems are wavelength conversion and regeneration.
We report on the first coherent beam combining of 60 fiber chirped-pulse amplifiers in a tiled-aperture configuration along with an interferometric phase measurement technique. Relying on coherent beams recombination in the far field, this technique appears well suited for the combination of a large number of fiber amplifiers. The 60 output beams are stacked in a hexagonal arrangement and collimated through a high fill factor hexagonal microlens array. The measured residual errors within the fiber array yields standard deviations of 4.2 μm for the fiber pitch and 3.1 mrad for the beam-to-beam pointing, allowing a combining efficiency of 50 %. The phasing of 60 fiber amplifiers demonstrates both pulse synchronization and phase stabilization with a residual phase error as low as /100 RMS.
The theory of I.F. amplifiers with negative feedback Ferguson, Alex J.
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