Fabrication and characterization of ultra-low noise narrow and wide band Josephson parametric amplifiers

We have fabricated two types of lumped-element Josephson parameter amplifiers (JPAs) by using a multilayer micro-fabrication process involving wet etching of Al films. The first type is a narrow band JPA which shows typical gain above 14 dB in a bandwidth around 35 MHz. The second type is a wideband JPA which is coupled to an input 50 Ω transmission line via an impedance transformer that changes the impedance from about 15 Ω on the non-linear resonator side to 50 Ω on the input transmission line side. The wideband JPA could operate in a 200 MHz range with a gain higher than 14 dB. The amplifiers were used for superconducting qubit readout. The results showed that the signal to noise ratio and hence the readout fidelity were improved significantly.     

Coherent synthesis of ultra-broadband optical parametric amplifiers

We report on coherent synthesis of two ultra-broadband optical parametric amplifiers, each compressed by chirped mirror pairs, resulting in almost-octave-spanning (520-1000 nm) spectra supporting nearly single-cycle sub-4 fs pulse duration. Synthesized pulse timing is locked to less than 30 as by a balanced optical cross-correlator. The synthesized pulse is characterized by two-dimensional spectral interferometry and has a 3.8 fs duration.     

Low noise Schottky barrier diode mixers for wavelengths < 1 mm

Recent progress in realizing low noise Schottky diode mixers in the submillimetre region is reviewed. Schottky diodes built on epitaxial material must be carefully optimized through use of E-beam lithography to obtain lowest conversion loss in a particular frequency region. Satisfactory diplexing schemes exist and a number of promising mixer configurations have been developed. The principal problem is a lack of suitable tunable sources of local oscillator power.     

Raman-noise-induced noise-figure limit for chi(3) parametric amplifiers

The nonzero response time of the Kerr [chi(3)] nonlinearity determines the quantum-limited noise figure of chi(3) parametric amplifiers. This nonzero response time of the nonlinearity requires coupling of the parametric amplification process to a molecular-vibration phonon bath, causing the addition of excess noise through Raman gain or loss at temperatures above 0 K. The effect of this excess noise on the noise figure can be surprisingly significant. We derive analytical expressions for this quantum-limited noise figure for phase-insensitive operation of a chi(3) amplifier and show good agreement with published noise-figure measurements.     

Thermal noise for SBS suppression in fiber optical parametric amplifiers

We demonstrate a new and simple solution to suppress stimulated Brillouin scattering in fiber optical parametric amplifiers. Cumbersome PRBS or sinusoidal generators used to broaden the pump spectrum are replaced by a filtered microwave noise source. Stimulated Brillouin scattering threshold can be increased up to large values still keeping an excellent quality of amplification of nonreturn to zero signals. The simplicity and the performances of this setup open the way for a wide variety of applications for FOPAs.     

Optimization of the power ratios of the bidirectional pumping at two wavelengths for erbium-doped fiber amplifiers

The gain and noise factor spectra of erbium-doped fiber amplifiers with pumped according to a copropagating three-level scheme and according to a counterpropagating quasi-two-level scheme in the regime of unsaturated gain in the C band have been simulated numerically. It has been shown that, at the total pump power up to 30 mW and at the optimized power ratio of the copropagating and counterpropagating pumps, the inhomogeneity of the gain in the C band does not exceed 0.25 dB at the noise factor of 4.2–4.7 dB.     

Bandwidth enhancement for parametric amplifiers operated in chirped multi-beam mode

In this paper we discuss the bandwidth enhancement that can be achieved in multi-Joule optical parametric chirped pulse amplification (OPCPA) systems exploiting the tunability of parametric amplification. In particular, we consider a pair of single pass amplifiers based on potassium-dideuterium-phosphate (DKDP), pumped by the second harmonic of Nd:glass and tuned to amplify adjacent regions of the signal spectrum. We demonstrate that a bandwidth enhancement upto 50% is possible in two configurations; in the first case, one of the two amplifiers is operated near its non-collinear broadband limit; to allow for effective recombination and recompression of the outgoing signals this configuration requires filtering and phase manipulation of the spectral tail of the amplified pulses. In the second case, effective recombination can be achieved simply by spectral filtering: in this configuration, the optimization of the parameters of the amplifiers (pulse, crystal orientation, and crystal length) does not follow the recipes of non-collinear OPCPA.     

Influence of the sum frequency on optically pumped parametric amplifiers

Parametric traveling-wave interactions are calculated with the aid of a plane wave approximation, considering the 4 frequencies ω _s , ω _p , ω _I =ω _p ?ω _s and ω _Σ =ω _p +ω _s . Special attention is paid to the case where ω _p ?ω _s . Competition between parametric amplification and upconversion is studied as a function of phase matching and the results are illustrated by means of numerical examples. It is shown that parametric gain disappears if the linear combination of wave vectors, 2k _p-k_I-k_Σ, vanishes. In this situation upconversion with power gain up to about (ω _Σ /ω _s )² is possible. It is concluded that fork _p?k_s the sum frequency ω _Σ can significantly influence parametric forward amplification but does not affect backward wave amplification.     

Spectral enhancement in optical parametric amplifiers in the saturated regime

We present numerical and experimental studies on a front-end laser system for seeding a sub-picosecond multi-terawatt/petawatt light source based on two highly saturated optical parametric amplifiers. Numerical results showing energy gain, spectral gain, and stability as saturation is approached are presented. An experimental realisation of the system has been constructed, and its performance has been found to be in good agreement with the numerical simulations. The total gain is in excess of 10⁵ over a few picosecond gain window, and the pulse energy is ～100 μJ with 4 % root mean square stability.     

Fabrication and characterization of all-Nb lumped-element Josephson parametric amplifiers

Josephson parametric amplifiers (JPAs) with nearly quantum-limited noise performance have become indispensable devices for the measurements of superconducting quantum information. We have developed an all-Nb lumped-element flux-driven JPA operating in the three-wave mixing mode. Our Nb-based JPA comprises Nb/Al-AlO_x/Nb Josephson junctions, a parallel-plate capacitor with SiO₂ dielectric sandwiched between two Nb layers, a bottom coplanar waveguides layer, and a top Nb wiring layer. We experimentally demonstrate a 20 dB gain over a 190 MHz bandwidth, a mean 1 dB compression of -123 dBm, and near quantum-limited noise performance. This fabrication process can be further used to design impedance transformed parametric amplifiers for multiple-qubit readout.     

Ku波段微波小功率放大器的设计

文中论述了利用修正的S参数法,设计了Ku波段微波小功率放大器,具有功率增益高和可靠性高的优点。利用这种设计方法,设计并制作了两个实验的功率放大器,并且它们的性能与设计数据很接近     

Crosstalk in double-pumped fiber optic parametric amplifiers for wavelength division multiplexing systems

We study experimentally inter-channel crosstalk in double-pumped fiber optic parametric amplifiers constructed with conventional dispersion shifted fibers (DSFs) having different lengths (L_A = 13.8, L_B = 6.8, L_C = 4.3, and L_D = 0.8 km). For long fibers (L_A and L_B), eye diagram measurements in a 5-channel (100 GHz spacing) system show that in order to have negligible crosstalk, the output signal power per channel, P_s, should be limited to P_s < 0 dBm. By decreasing the fiber length (to L_C) it is possible to increase the output signal power and/or the number of signals while keeping the crosstalk on negligible levels. This trend was further confirmed by using a very short DSF (L_D = 0.8 km).Finally, we experimentally demonstrate that a general trend in 2P-FOPAs is that spurious FWM increases with the number of signal channels up to a given number of channels when a saturation regime is reached. This saturation of the generation of spurious tones occurs when the bandwidth occupied by the signals exceeds ∼4-5 nm.     

Spatial-temporal frequency band of optical parametric amplifier

The spatial-temporal frequency band of optical parametric amplifier for collinear as well as for noncollinear phase-matching is analyzed taking into account angular dispersion of amplified pulsed beam. The simple formulae are derived which make possible determination of the largest frequency bands of parametric amplifiers in noncollinear geometry. It has been demonstrated that a shape of the spatial-temporal frequency band of optical parametric amplifier essentially depends on pump and signal wavelengths, and certain angular dispersion as well as proper beamwidth of signal pulse enable amplification of ultrashort pulses with duration of a few femtoseconds.     

8 mm二次谐波回旋速调管谐振腔设计研究

 结合回旋速调管研究的相关理论,考虑到高次谐波工作时带来的模式竞争,以及注-波互作用的耦合关系,讨论了在半径、腔长、杂模抑制以及腔内媒质涂层的介电参量等诸多因数影响的情况下,如何设计二次谐波回旋速调管谐振腔的问题。结合设计方法建模,优化设计出了5个适于8 mm二次谐波工作的谐振腔,通过漂移段连接成两种高频结构,其中一种结构在注-波互作用非线性模拟中取得了251 kW的输出功率,电子效率 23.9%,增益 27.2 dB,3 dB带宽大于0.4%;另一种结构初步取得了246 kW的输出功率,其它参数正在测试之中。     

Analysis of Mach-Zehnder interferometer with two degenerated optical parametric amplifiers

We have analyzed a Mach-Zehnder interferometer with one or two degenerated parametric amplifiers, one for each arm. The photocurrent, its variance, and the phase fluctuation are obtained. The photon statistics of the entangled state exiting the interferometer is described by means of the Mandel Q parameter.     

Quantum properties of the three-mode squeezed operator: Triply concurrent parametric amplifiers

In this paper, we study the quantum properties of the three-mode squeezed operator. This operator is constructed from the optical parametric oscillator based on the three concurrent χ⁽²⁾ nonlinearities. We give a complete treatment for this operator including the symmetric and asymmetric nonlinearity cases. The action of the operator on the number and coherent states is studied in the framework of squeezing, second-order correlation function, Cauchy-Schwartz inequality and single-mode quasiprobability function. The nonclassical effects are remarkable in all these quantities. We show that the nonclassical effects generated by the asymmetric case-for certain values of the system parameters-are greater than those of the symmetric one. This reflects the important role for the asymmetry in the system. Moreover, the system can generate particular types of the superposition states.