The kinetic power theorem for parametric, longitudinal, electron-beam amplifiers

A power theorem is developed for parametric, longitudinal, electron-beam amplifiers which may be considered as a generalization of Chu's well-known kinetic power theorem. The new power theorem is used to explore the limitations on noise performance of parametric electron-beam amplifiers. It is shown that the electron-beam noise does not impose a basic limit on the noise performance of a parametric electron-beam amplifier in the way a basic limit is imposed upon the noise performance of conventional longitudinal electron-beam amplifiers. The new power theorem can be employed for understanding the operation of parametric beam amplifiers in the same way as Chu's kinetic power theorem has been used for interpreting the opoeration of longitudinal beam amplifiers.     

Two-diode parametric amplifiers

Analysis suggests that very useful performance may be achieved in parametric amplifiers incorporating two varactor diodes. The most interesting configuration is a bandpass amplifier in which the varactors are the shunt capacitive elements, operated with a phase shift between diodes of 90° at the centre signal frequency and with the diodes mounted with opposite polarities. With inphase pumping this gives unilateral operation and a large potential bandwidth.     

Simulating parametric amplifiers

In this paper, the problems of producing a general simulator model of a parametric amplifier are discussed. This model is to be simple, accurate, and applicable to many forms of parametric amplifiers. A brief discussion of the theory behind parametric amplification is followed by proposals for three models. Each of these is discussed in terms of its limitations and applications. The results of tests on two of these models are presented, and these results are discussed. Some emphasis is placed on the most sucessful of the models, which has been used to simulate a subharmonic oscillator.     

Intermodulation in parametric amplifiers

Third-order intermodulation products due to the charge-voltage nonlinearity of the varactor diode in a parametric amplifier have been computed. Some experimental data obtained from a two-carrier measurement have been reported. Finally, the noise power density in a telephone channel due to parametric amplifier intermodulation has been calculated as a function of total input power into the amplifier.     

Detuning effects in parametric amplifiers

Some detuning effects in parametric amplifiers have been observed when the pump frequency is above and below the optimum value. A possible explanation of these effects is suggested.     

Low-noise room-temperature wideband parametric amplifiers

Two room-temperature parametric amplifiers are described which have gains of 26 dB. One has an excess noise temperature of between 74 and 85 K across the band 3.7?4.2 GHz, and the other has an excess noise temperature of between 85 and 99 K across the band 7.25?7.75 GHz.     

Subharmonic pumping of parametric amplifiers

The purpose of this paper is to present in some detail the operation of a parametric amplifier pumped subharmonically as compared to being directly pumped. As considered here, subharmonic pumping does not involve harmonic pump power generation (external to the varactor) but the utilization of higher-order time-dependent capacitances to yield parametric amplification by employing, basically, only a three-frequency system. The analysis given here is based on an evaluation of the Fourier series representation of the time-dependent capacitance resulting from large-signal ("hard") pumping of varactors. This evaluation indicates that significant values of higher-order time-dependent capacitances suitable for parametric amplification are obtained with relative pump swings in excess of about 90 per cent. Utilizing these higher-order time-dependent capacitances, the amplifier operation for various orders of subharmonic pumping is treated, including such factors as pump power requirements, gain, and noise figure. It is shown that, under certain conditions, less pump power is required to generate the same negative conductance than with direct fundamental pumping. Furthermore, for the same pump power and fundamental pump frequency, it is determined that significant improvements in amplifier noise figure are achieved by employing subharmonic pumping, provided varactor losses are small. From the results obtained by both analysis and experiment, it is concluded that subharmonic pumping, even without harmonic power generation, is not only feasible but can be very useful up to C-band signal frequencies with existing varactors.     

Nondegenerate electron beam parametric amplifiers

Cyclotron wave amplifiers with a pump-to-signal frequency ratio of 5:1 (rather than the usual 2:1) have been built and have given a single-channel noise figure of 2 db. This paper reports on the difficulties which had to be overcome and the restrictions which had to be observed before achieving what, at the start, had looked deceptively simple. The paper begins with a discussion of the relative merits of assigning signal, idler and pump waves in various ways to beam and circuit. In the preferred arrangement the circuit carries only the pump wave; signal and idler are cyclotron waves on the beam. The validity of Tien's equations for the propagation constants and of the Manley-Rowe relations for the power-frequency ratio is demonstrated for the case of cyclotron waves. It is also shown that in a nondegenerate tube, idler noise must be extracted, no matter how high the idler frequency may be. Early experiments by C. B. Crumly, using interdigital couplers for signal and idler, gave very poor noise figures. The twisted coupler, a new structure with high coupling efficiency, was introduced but failed to reduce the high noise. It was then found that a signal carried by a cyclotron wave of low phase velocity was attenuated as it traveled along the beam, and that the noise extraction process worked poorly. This was traced to the spread of axial electron velocities, a source of trouble mentioned by C. P. Lea-Wilson and later by E. I. Gordon. P.G. Everett's measurements of this effect are described. It is then shown how the consequences of the effect may be minimized. Nondegenerate tubes are described in which the velocity spread effect is rendered almost harmless. The twisted coupler structure is particularly well adapted to experiments with synchronous waves; a brief report on such experiments is included.     

Gain stabilisation of parametric amplifiers

A method of stabilising the gain of a parametric amplifier from the pumped conduction current of a varactor diode is described. Long-term stabilities of 0.1dB/week have been achieved on a 13dB-gain amplifier with diode currents of less than 1 ?A.     

Discharge and kinetics modeling in electron-beam controlled CO2laser amplifiers

The specific computational methods used to model the spatial and temporal behavior of large pulsed electron-beam controlled CO2laser amplifiers are presented. The interactions between the various physical processes which occur in these devices are related to the logical structure of the model, so that the key approximations can be identified. We show that, in most cases, the uniformity of the gain can be adequately described with a two-dimensional (2-D) analysis, which uses the discharge conditions present at a single "snapshot" time corresponding to the peak of the discharge power. We apply these techniques to model an experiment in which the nonuniformities play an important role; and, as a second example, we demonstrate that the modeling capabilities can show the consequences of design modifications in large-aperture amplifiers.     

Active reactance compensation of parametric amplifiers

The increase in bandwidth potential of a simple parametric amplifier obtained by adding active rather than passive filter elements to the signal circuit is discussed. Measured performance data of an amplifier constructed for the 4GHz satellite-communication band is given; by using this technique, a sevenfold increase in bandwidth at 20dB gain was obtained     

Gain limitations in optical parametric amplifiers

Factors limiting the gain of parametric amplifiers pumped by the 266 nm harmonic of aQ-switched Nd:YAG laser have been investigated, and the advantages of combined parametric/dye amplifiers in the visible are discussed.     

Backward optical parametric oscillators and amplifiers

Degenerate backward optical parametric oscillators and amplifiers have been considered, for the first time, to the best of our knowledge. When the pump intensity is four times the threshold pump intensity, the conversion efficiency reaches a maximum value. On the other hand, for nondegenerate optical parametric oscillators, the conversion efficiency always increases as the pump intensity increases. This behavior is different from those for forward optical parametric oscillators. In either configuration, the oscillation can occur without an external feedback. There is, however, a distributed feedback provided through the opposite propagation directions of the signal and idler. The threshold pump intensities for the oscillators can be achieved by the lasers currently available based on quasi-phase matching in several structures. As the input intensity for the backward parametric wave increases, the gain for this wave decreases dramatically if the pump intensity is on the order of the threshold or higher. When the input intensity is much larger than the threshold pump intensity, there is almost no gain regardless of the level of the pump intensity     

Phase mismatch in traveling-wave parametric amplifiers

A misunderstanding is corrected regarding the effect of phase mismatch on the gain in traveling-wave parametric amplifiers. It is shown that gains greater than unity can be obtained even when the signal and idler waves do not grow exponentially.     

Noise characteristics of dual-pump fiber-optic parametric amplifiers

The noise figure (NF) properties of an undepleted and lossless dual-pump fiber-optic parametric amplifier (FOPA) are theoretically and numerically investigated. The theoretical study takes into account the noise characteristics of the two pump waves that are considered to have parallel polarization states for gain maximization. It is shown that noisy pump waves degrade the amplifier's NF, especially when the amplifier is operating at high gain values and when the input signal is high. The theoretical observations are validated by Monte Carlo numerical simulations, and the agreement between them is excellent. Finally, a comparative study concerning the noise characteristics of dual-pump and single-pump FOPAs is performed.     

Maximum and resonant gains in parametric amplifiers

It has generally been assumed that, in three-frequency negative-resistance parametric amplifiers incorporating resonant circuits, maximum gain is obtained when the signal and idler circuits are resonant. It is shown that this assumption is not, in general, justified.     

Gain reciprocity in fibre optical parametric amplifiers

A fibre optical parametric ampifier operating in the small-signal gain regime can exhibit the same gain when amplifying in either direction. This is true even in the presence of random dispersion and birefringence variations along the fibre.     

Fibre optical parametric amplifiers with circularly-polarised pumps

A fibre optical parametric amplifier with orthogonal circularly-polarised pumps requires only half the pump power of an amplifier with linearly-polarised pumps to achieve a given gain. The gain is also independent of the polarisation of the input signal.