Frequency Noise Power Research Articles

An appropriate model for the noise power spectrum produced by traps at theSi–SiO2 interface: a study of the influence of a time-dependent Fermi level

In this work we have developed an appropriate and novel model for computing the contribution of all trapsat the Si–SiO2 interface to the low frequency (LF) noise power spectrum. In our approach we have usedtheoretical and experimental convex ‘U’-shape curves to model the density of states oftraps distributed at the interface, predicting the qualitative and quantitative behavior forthe reduction of LF noise. In the model development, basic discrete device physicsquantities are used. The low frequency noise behavior of metal–oxide–semiconductordevices under cyclo-stationary excitation is evaluated through analytical and numericalcalculations, and a comparison to relevant experimental data found in the literature isprovided.

Study of the frequency fluctuations of a semiconductor diode laser

Frequency fluctuations of an inexpensive single-mode semiconductor diode laser, which operates in the 822 nm region, are investigated by direct measurement of the error signal. The linear slope of first derivative signal of a transition in the (2,1,1) vibration-rotation band of water vapour is used as a frequency discriminator. A balanced photodetector is used to reduce the intensity noise and to improve the S/N ratio. Frequency stability of the diode laser is investigated when the laser is under a free-running condition and is locked to the line center of the reference transition. An integrator is used to provide feedback voltage to the laser current driver. After frequency stabilization, a more than 60-fold improvement in long-term laser-frequency stability is attained over the performance provided by the free-running semiconductor diode laser. The frequency-noise power spectrum of the diode laser is extracted from the error signal for the Fourier-frequency range ~100 Hz. The Allan variance curve for the laser system is obtained from the frequency-noise power spectrum of the error signal by using a suitable mathematical relation under certain approximations. The extracted values of the Allan variance are compared with the theoretical τ–1 model. The experimental setup is easy to implement in graduate laboratory classes. PACS Nos.: 42.55.Px, 42.62.Fi, 33.70.Jg

Influence of grating parameters on the linewidths of external-cavity diode lasers

We investigate experimentally the influence of the grating reflectivity, grating resolution, and diode facet antireflection (AR) coating on the intrinsic linewidth of an external-cavity diode laser built with a diffraction grating in a Littrow configuration. Grating lasers at 399, 780, and 852 nm are determined to have typical linewidths between 250 and 600 kHz from measurements of their frequency noise power spectral densities. The linewidths are little affected by the presence of an AR coating on the diode facet but narrow as the grating reflectivity and grating resolution are increased, with the resolution exerting a greater effect. We also use frequency noise measurements to characterize a laser mount with improved mechanical stability.

Noise in carbon nanotube field effect transistor

Low frequency noise power spectrum density of carbon nanotubes is presented. It is shown that the input-referred noise of carbon nanotubes increases quadratically as gate voltage is overdriven, suggesting that mobility fluctuation is the dominant mechanism contributing to the noise in carbon nanotube field effect transistors. The comparison of source-drain current noise power spectrum densities of carbon nanotubes in air and in vacuum indicates that a part of device noise is due to charge fluctuations from attached air molecules.

High Temperature Performance and Low Frequency Noise Characteristics of AlGaN/GaN/AlGaN Double Heterostructure Metal-Oxide-Semiconductor Heterostructure Field-Effect-Transistors with Photochemical Vapor Deposition SiO2 Layer

High quality SiO2 films were successfully deposited onto AlGaN using photochemical vapor deposition (photo-CVD). The interface state density, Dit, of photo-CVD SiO2 was estimated to be only 1.1×1011 cm-2eV-1 at room temperature and still only 3.5×1012 cm-2eV-1 even at 175°C. With a 1 µm gate length, it was found that the maximum saturated drain-source current (Ids), maximum transconductance (gm) and gate voltage swing (GVS) of the AlGaN/GaN/AlGaN double heterostructure metal-oxide-semiconductor heterostructure field-effect-transistors (MOS-HFETs) fabricated were 755 mA/mm, 95 mS/mm and 8 V, respectively. Even at 300°C, the maximum saturated Ids and maximum gm of the MOS-HFETs fabricated were still kept at 527 mA/mm and 77 mS/mm, respectively. Furthermore, from the low frequency noise power spectrum, it was found that noise power density of the AlGaN/GaN/AlGaN double heterostructure was lower and presented pure 1/f noise with smaller trapping effects than conventional structures.

Steady state visual evoked potential abnormalities in schizophrenia

Objective The steady state visual evoked potential (SSVEP) can be used to test the frequency response function of neural circuits. Previous studies have shown reduced SSVEPs to alpha and lower frequencies of stimulation in schizophrenia. We investigated SSVEPs in schizophrenia at frequencies spanning the theta (4 Hz) to gamma (40 Hz) range. Methods The SSVEPs to seven different frequencies of stimulation (4, 8, 17, 20, 23, 30 and 40 Hz) were obtained from 18 schizophrenia subjects and 33 healthy control subjects. Power at stimulating frequency (signal power) and power at frequencies above and below the stimulating frequency (noise power) were used to quantify the SSVEP responses. Results Both groups showed an inverse relationship between power and frequency of stimulation. Schizophrenia subjects showed reduced signal power compared to healthy control subjects at higher frequencies (above 17 Hz), but not at 4 and 8 Hz at occipital region. Noise power was higher in schizophrenia subjects at frequencies between 4 and 20 Hz over occipital region and at 4, 17 and 20 Hz over frontal region. Conclusions SSVEP signal power at beta and gamma frequencies of stimulation were reduced in schizophrenia. Schizophrenia subjects showed higher levels of EEG noise during photic stimulation at beta and lower frequencies. Significance Inability to generate or maintain oscillations in neural networks may contribute to deficits in visual processing in schizophrenia.

Competition Noise in DBR Tunable Lasers

Tunable Lasers are key-components for Wavelength Division Multiplexing optical communication applications at 1.55μ m . In this paper, we report the study of low to mid frequency noise power spectral densities and correlation factors in various spectral purity configurations, using the Bragg section tunability around a mode-hopping situation.

A comprehensive study on XPM- and SRS-induced noise in cascaded IM-DD optical fiber transmission systems

A comprehensive study of XPM- and SRS-induced crosstalk noise evolution as well as their interaction along lossy, nonlinear dispersive fiber in a cascaded IM-DD system is performed analytically and numerically. XPM-induced intensity noise (XPMN) comes mainly from few adjacent channels, featuring in higher frequency and higher noise power per contributing channel; while SRS-induced intensity noise (SRSN) comes mainly from all the distant channels, featuring in lower frequency and lower noise power per contributing channel. Interaction between XPMN and SRSN depends on the relative wavelength location between pump and probe as well as dispersion management scheme, and may add either constructively or destructively. SRSN may even exceed XPMN in some cases. In a system with complete dispersion compensation in each span, XPMN, SRSN, and their interaction are all proportional to the square of span number. In dispersion-managed systems, SRSN can be enhanced significantly by resonance effect between fiber spans. On the other hand, XPMN can be markedly suppressed by dispersion management, due mainly to much weaker phase-to-intensity noise conversion through residual dispersion.

Current density and ac field effects on 1/f noise in spin valve sensors

Low frequency noise in patterned NiFe/Co/Cu/Co/FeMn (ΔR/R>9%) spin valves was investigated. The spin valves were sputter deposited and patterned by lift-off to form 75 μm×1000 μm lines. Noise power spectra were measured in the frequency range from 1 Hz to 10 kHz for ac and dc fields applied both parallel and perpendicular to the easy axis. An increase in the low frequency noise power spectrum was observed for an ac field applied along the easy axis. Increasing the ac drive frequency from 500 Hz to 5 kHz reduced the low frequency noise power to near the zero field background level.

Wideband and high frequency stabilization of an injection-locked Nd:YAG laser to a high-finesse Fabry–Perot cavity

High frequency stabilization of a 2.2-W injection-locked laser-diode-pumped Nd:YAG laser to a high-finesse optical cavity has been realized by frequency control of the master laser. With the help of an external electro-optical modulator, the feedback bandwidth was extended to 1 MHz and the frequency noise relative to the reference cavity was suppressed to 3 x 10(-4) Hz/Hz(1/2) below 1 kHz. This feedback laser system is an ideal laser source for gravitational wave detectors, which require both ultralow frequency noise and high output power.

Frequency noise analysis of optically self-locked diode lasers

Recent progress on frequency stabilization of a diode laser emitting near 850 nm is discussed. A confocal Fabry-Perot cavity is used to feed back the beam from the diode laser and provide resonant optical stabilization of the semiconductor laser. A detailed theoretical analysis of the static and dynamic frequency noise power spectrum of the coupled cavity laser field is presented. Static-frequency noise reduction of 50-60 dB and reduction of the laser linewidth from 20 MHz to less than 4 kHz are obtained. Finally, a detailed analysis of the beat-note spectra of two optically self-locked diode lasers shows a nonLorentzian RF power spectrum. >

Efficient frequency noise reduction of GaAlAs semiconductor lasers by optical feedback from an external high-finesse resonator

The reduction of frequency noise power level of non-antireflection-coated GaAlAs laser diodes by several orders of magnitude using optical feedback from an external high-finesse Fabry-Perot resonator is discussed. Optimum oscillation parameters were derived from a steady-state model. Long-term performance was obtained by electronic feedback phase control. >

High frequency noise power spectrum, impedance and transmission loss of power line in Japan on intrabuilding power line communications

A communication system for small-scale local area networks using the power transmission line is discussed. With this application in mind and noise power spectrum of a power line at 10 kHz-100 MHz and the impedance characteristics and transmission loss of a power line in the high frequency band (10 kHz-20 MHz) have been measured. Both narrowband and wideband data transmission are considered. The transmission loss of the power line increases with frequency, whereas the intensity of the noise power spectrum decreases rapidly. This means that power line communication by a single-sideband system is possible using a wide frequency band up to 100 MHz. However, the noise, impedance, and transmission characteristics vary greatly with frequency, so special considerations such as line impedance stabilization networks and other techniques are necessary.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A level compensator for telephotograph systems

SINCE 1936, a number of different telephotograph systems1 have been operated over the lines of the Bell System on a leased-wire basis. The requirements which a line facility must meet for such service are in several respects more severe than the requirements for voice-message service. Telephotograph- transmission requirements have usually specified that abrupt variations in line net loss should be limited to ±0.2 decibel, single frequency noise power should be at least 50 decibels below maximum signal power, and throughout the useful frequency band (1,200 to 2,600 cycles per second), the envelope delay should be equalized within ±300 microseconds. Such requirements were originally satisfied by using 4-wire H-44-25 side circuits in cable, where available, and elsewhere by using 2-wire open-wire side circuits. These facilities were delay-equalized over the necessary frequency range, and precautions were taken to minimize various transmission disturbances.