Lower Sideband Frequency Research Articles

Noise characteristics of cross-phase modulation instability light

The noise characteristics of cross-phase modulation instability visible light produced in high-birefringence fibres have been investigated. Noise measurements were made on single sidebands, and on the intensity difference between upshifted and downshifted sidebands using single pass and fibre-laser configurations. The intensity difference noise for the single pass configuration was reduced by more than 25 dB below the single sideband noise, which was typically 35 dB above shot noise. Under certain conditions the intensity difference noise of the modulation instability laser sidebands could be reduced to the shot noise level, while the single sideband noise from the modulation instability laser could be reduced to 2 dB above shot noise. Raman gain on the low frequency sideband and attenuation in the fibre limited the attainable noise reduction.

Nonlinear Trivelpiece–Gould waves: Recurrence, harmonic cascade, and sidebands

A theoretical and experimental study of Trivelpiece–Gould waves propagating in a magnetized plasma column is presented in this paper. In the experiments, these waves are excited by a radio frequency (rf) source, which also serves to create the plasma. Observation of nonlinear effects includes space and time recurrence effects, a wave spectrum containing a large number (up to 25) harmonics, and low-frequency sidebands. The theoretical model explains the recurrence effects as a consequence of multiple nonlinear interactions between the fundamental wave and its harmonics. A good agreement is found between theory and the experiments.

Quantum limited quasiparticle mixers at 100 GHz

Accurate measurements of the noise and gain of superconducting-insulating-superconducting (SIS) mixers using small-area (1 mu m/sup 2/) Ta/Ta/sub 2/O/sub 5//Pb/sub 0.9/Bi/sub 0.1/ tunnel junctions were made. The authors measured an added mixer noise of 0.61+or-0.31 quanta at 95.0 GHz, which is within 25% of the quantum limit of 0.5 quanta. Detailed comparison between theoretical predictions of the quantum theory of mixing has been carried out, and noise and gain have been experimentally measured. The shapes of the I-V curves pumped at the upper and lower sideband frequencies were used to deduce values of the embedding admittances at these frequencies. Using these admittances, the mixer noise and gain predicted by quantum theory are in excellent agreement with experiment.

Quantum-limited heterodyne detection of millimeter waves using superconducting tantalum tunnel junctions

We have made accurate measurements of the noise and gain of heterodyne mixers employing small-area (1 μm2) Ta/Ta2O5/Pb0.9Bi0.1 superconductor-insulator-superconductor tunnel junctions. These junctions have very low subgap leakage current and an extremely sharp current rise at the sum gap. We have measured an added mixer noise of 0.61±0.31 quanta at 95.0 GHz, which is within 25% of the quantum limit of 0.5 quanta for a single-sideband mixer. Values of the imbedding admittances are deduced from the shapes of I-V curves pumped at the upper and lower sideband frequencies. Using these admittances, the mixer performance calculated from the quantum theory is in good agreement with the experiment.

Fiber polarization-rotation switch based on modulation instability

We demonstrate an active fiber polarization-rotation switch based on modulation instability operating near 1.5 microm that exhibits contrast ratios of up to 40:1 and small-signal gains of up to 40 dB. Modulation instability generates upper and lower sideband frequencies with different states of polarization from the pump at the fiber output. The high contrast ratio is achieved in part because intensity fluctuations with the pump alone do not lead to an output from the device.

POWER-side (independent sideband system of AM stereo)

The independent sideband system of AM stereo can, by use of special audio processing, significantly improve mono reception. The resulting transmitted signal, called a 'POWER-side' signal, allows listeners to 'sideband tune' with new types of mono receivers so as to reduce co and adjacent channel interference, improve the effective fidelity of the AM receiver, and make the receiver's tuning significantly less critical. Furthermore, due to the inequality of low frequency sideband components, the system reduces selective fading, antenna null distortion and re-radiation problems when the POWER-side signal is received by both 'sideband tuned' mono receivers as well as digitally tuned stereo and mono receivers which center tune to the carrier frequency. Most importantly, this type of wave substantially reduces co-channel 'beating' effects that have, since the earliest days of broadcasting, plagued AM signal reception.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Sideband noise of a large phase carrier in interferometric sensors

Interferometric sensors using balanced detectors and phase stabilisation schemes remain susceptible to laser intensity noise if phase carrier techniques are employed. An intensity stability of 4 × 10−6 is required for the low-frequency side-band noise to be equivalent to microradian phase shift sensitivity if the phase carrier has a peak phase shift of π/2 rad.

Power spectrum of directly modulated single-mode semiconductor lasers: Chirp-induced fine structure

The time-averaged power spectrum of a single-mode semiconductor laser under direct current modulation is calculated using the small-signal analysis of the stochastic rate equations. The general formalism includes the effect of frequency chirping owing to current modulation as well as the effect of phase diffusion related to spontaneous emission. Chirp-induced dynamic line broadening is shown to result from a superposition of the additional unresolved sidebands generated at multiples of the modulation frequency on both sides of the optical line. The effect of intensity modulation is to introduce an asymmetry such that the low-frequency sideband has a relatively higher amplitude. The theory explains reasonably well the reported experimental observations. At the same time it provides physical insight into the dynamic process of frequency chirping and its relation to the frequency modulation. In particular, the frequency and the decay rate of transient relaxation oscillations govern the interplay between simultaneously occurring intensity and frequency modulations.

Parametric upconvertors as receiver first mixers at high frequencies

The system requirements of h.f.receivers make unusual demands on any parametric upconvertor designed to form the first mixer stage. These requirements are considered in detail and design equations formulated for two upconvertors, both of the four-frequency type with wanted sideband power extracted at upper- or lowersideband frequencies, respectively. It is demonstrated that values of gain, noise figure and port impedances may be obtained that are compatible with system requirements. The design of an experimental upconvertor is described, and the observed performance is shown to agree with the theoretical predictions

Test Wave Coexisting with a Large-Amplitude Electron Plasma Wave

The behavior of a small test wave launched simultaneoualy with a large- amplitude electron plasma wave is calculated by treating the test wave as a slow modulation of the larger wave's amplitude and phase. Test-wave experiments show agreement with the calculation when the test-wave frequency is between the large wave's frequency ( omega₀) and omega₀-4 pi /T, where T is the maim wave's transit time through the experiment. When the spontaneously unstable lower sideband frequency is within this range, the sideband's slow amplitude oscillations agree with the calculation. (auth)

Effect of Upper Sideband Impedance on a Lower Sideband Up-Converter

An analysis is given of a lower sideband up-converter which includes a finite circuit reactance X/sub 33/ at the upper sideband frequency, in addition to the circuit impedances at the input signal and output lower sideband frequencies. The expressions developed for the gain, gain sensitivity to pump power variation, and noise figure show the extent to which gain and gain sensitivity decrease, and noise figure increases when X/sub 33/ is finite, as compared to the case when X/sub 33/ is infinite. For a simple circuit configuration the gain-bandwidth product changes markedly when X/sub 33/ is small at the center frequency. In addition, when second-harmonic pump power is allowed to flow through the varactor diode, the performance of the lower sideband up-converter can be improved.

Anharmonic interaction between localised modes and lattice modes in alkali halides

Abstract Infrared active localized modes are created in alkali halide crystals by substituting for halide ions H− or D− ions in low concentrations (“U-centers”). The infrared absorption bands due to these defects (in KCl at 500 cm−1 (H−) and 360 cm−1 (D−)) show to principal features: 1 A strongly temperature-dependent peak with a half-width decreasing as T2 between 300° and 60°K and becoming very narrow at lowest temperatures (Δ = 1,6 cm−1 at 60°K for H− in KCl). 2 Two side bands spaced about equally at frequencies higher and lower than the main peak. The high-frequency satellite undergoes little change to lowest temperatures (11 °K). The absorption under the low-frequency side band may be fitted to a function exp (— ħω/kT), where the experimental value of ω is of the order of the frequency difference between side-band maximum and main peak (corresponding to ≈ 60 cm−1 in KCl). Excitation of the localized mode by absorption in the side bands must be due to interaction with lattice vibrations leading to a simultaneous excitation (high-frequency side band) or decay (low-frequency side band) of lattice phonons. The observed side-band structures in different substances and types of defect (H− or D−) are discussed in view of that model.

Noise in reflex klystrons and backward-wave oscillators

The paper describes a.m. and f.m. direct-detection and superheterodyne noise spectrum measurements on various types of backward-wave oscillator and reflex klystron. A procedure has been developed by which the individual a.m., f.m. and background noise components can be separated. The results show that the predominant component at low sideband frequencies is f.m. noise and at high sideband frequencies is background noise. The a.m. noise is not a significant component. The presence of positive ions in the beam of a backward-wave oscillator causes noise peaks at frequencies near 1 Mc/s and an increase of modulation noise over a wide frequency range. Positive ions can be relatively easily removed by transverse ion drainage. Large noise peaks may also be generated at frequencies near those of spurious oscillations. The results of measurements of carrier frequency deviation, and of correlation between a.m. and f.m. noise, and between modulation and beam noise are also given.