Reduction Of Excess Noise Research Articles

On the noise reduction mechanisms of over-tip liners.

The application of acoustic liners near/directly over a sound source has gained significant interest for the excess noise reduction achieved with Over-the-Rotor (OTR) liners compared to the conventional liner installations at the intake of an aero-engine. However, the mechanism of noise reduction achieved in the OTR liners is not clearly understood. This paper aims to explain this mechanism by considering a static monopole source placed over a finite liner insert with a zero background mean flow. This has been investigated numerically using COMSOL Multiphysics in a half-space domain and compared with reference analytical solutions for infinite lined walls. One of the key findings of the paper is the underlying physics of the source modification mechanism, which has been found to be the interference between the primary noise source and a secondary noise source forming on the liner surface. It is identified through an optimal impedance study that this back-reaction mechanism is dominant when the source is located for a normalised tip gap, e/λ<0.25, where e is the distance between the source and the liner surface and λ is the acoustic wavelength. Within this region, there exists an optimum normalised liner length, L / e providing a maximum insertion loss.

Continuous and long-term stabilization of degenerate optical parametric oscillators for large-scale optical hybrid computers.

The minimum requirements for an optical reservoir computer, a recent paradigm for computation using simple algorithms, are nonlinearity and internal interactions. A promising optical system satisfying these requirements is a platform based on coupled degenerate optical parametric oscillators (DOPOs) in a fiber ring cavity. We can expect advantages using DOPOs for reservoir computing with respect to scalability and reduction of excess noise; however, the continuous stabilization required for reservoir computing has not yet been demonstrated. Here, we report the continuous and long-term stabilization of an optical system by introducing periodical phase modulation patterns for DOPOs and a local oscillator. We observed that the Allan variance of the optical phase up to 100 ms was suppressed and that the homodyne measurement signal had a relative standard deviation of 1.4% over 62,500 round trips. The proposed methods represent important technical bases for realizing stable computation on large-scale optical hybrid computers.

Excess noise reduction with ear protector applying mathematical algorithm: A case of medium density fiber industry

Consistent exposure to elevated sound levels results in noise health effects. The industrial environment represents a major source of such effects. There is significant variation in noise at different sections of such industries due to which most of the workers are exposed to these sounds at one or another level. In this study, a noise level measuring methodology is used for fixed and moving workers. This article introduces an algorithm for optimum selection of earmuff and earplug for different working places depending upon the exposure to noise. Medium density fiber industry is considered as a case for this study. It considers workers who are busy at a single point and face a consistent amount of noise as well as the workers who move and are exposed to a varying level of the noise. Noise level meters are used to measure the noise level at different points. At each point, the average value of the samples is taken. Based on the data collected, earmuff with high noise reduction rate is assigned to the workers closed to the machines. Implementation of the developed algorithm reduced the effect of noise on workers by 6.9%, 5%, and 16.3% for the chipper machine, pneumatic fan, and sanding machine, respectively, that were identified as the major source of noise at medium density fiber industry. This percentage reduction helped the workers to bring them to the optimum safe level of noise that is 85 dB and protect them from hearing loss severity due to frequency variations.

Ge/graded-SiGe multiplication layers for low-voltage and low-noise Ge avalanche photodiodes on Si

A new structure is examined for low-voltage and low-noise Ge-based avalanche photodiodes (APDs) on Si, where a Ge/graded-SiGe heterostructure is used as the multiplication layer of a separate-absorption-carrier-multiplication structure. The Ge/SiGe heterojunction multiplication layer is theoretically shown to be useful for preferentially enhancing impact ionization for photogenerated holes injected from the Ge optical-absorption layer via the graded SiGe, reflecting the valence band discontinuity at the Ge/SiGe interface. This property is effective not only for the reduction of operation voltage/electric field strength in Ge-based APDs but also for the reduction of excess noise resulting from the ratio of the ionization coefficients between electrons and holes being far from unity. Such Ge/graded-SiGe heterostructures are successfully fabricated by ultrahigh-vacuum chemical vapor deposition. Preliminary pin diodes having a Ge/graded-SiGe multiplication layer act reasonably as photodetectors, showing a multiplication gain larger than those for diodes without the Ge/SiGe heterojunction.

Dark fringe operation and noise reduction with optical subtraction approach and power allocation

We demonstrate a technique to achieve the reduction of excess noise with dark fringe operation by optical subtraction and power allocation strategy. By performing the subtraction in optical way, the excess noise resulted from the photocurrent is eliminated and the phase information can be extracted with single photoreceiver. Meanwhile, by allocating more optical power to the probe beam, the DC background and the signal amplitude of the photocurrent become very small simultaneously so that the dark fringe operation is achieved. We compare the spectral distributions resulted from the proposed technique with that from the widely employed balanced detection and the modified balanced detection techniques which both are based on electronic subtraction. It is found that the experimental results closely agree to the theoretical predictions.

Monte Carlo investigation of avalanche multiplication process in thin InP avalanche photodiodes

An ensemble Monte Carlo simulation is presented to investigate the avalanche multiplication process in thin InP avalanche photodiodes (APDs). Analytical band structures are applied to the description of the conduction and valence band, and impact ionization is treated as an additional scattering mechanism with the Keldysh formula. Multiplication gain and excess noise factor of InP p+-i-n+ APDs are simulated and obvious excess noise reduction is found in the thinner devices. The effect of dead space on excess noise in thin APD structures is investigated by the distribution of impact ionization events within the multiplication region. It is found that the dead space can suppress the feedback ionization events resulting in a more deterministic avalanche multiplication process and reduce the excess noise in thinner APDs.

Excess noise reduction by optical technique in amplitude-sensitive heterodyne interferometer for small differential phase detection

An amplitude-sensitive technique associated with a heterodyne interferometer for detecting small differential phase is reported. The excess noise with the amplitude-sensitive technique is reduced by optical subtraction instead of electronic subtraction. The differential phase introduced by the orthogonally polarized laser beams is converted to the amplitudes of two heterodyne interferometric signals, which presents amplitude and phase quadrature simultaneously. Thus the excess noise power and quantum noise power are both differential phase dependent. The advantages of differential and additive operations by optical technique and the real time differential phase determination without phase lock in are demonstrated experimentally. The theoretical signal-to-noise ratio (SNR) and minimum detectable differential phase are derived, which takes quantum noise and excess noise into consideration. The experimental results demonstrated the resolutions of differential phase detection closes to 10(-6) rad/square root(Hz) (10(-13) m/square root(Hz)) level over 100 kHz bandwidth and at 10(-8) rad/square root(Hz) (10(-15) m/square root(Hz)) level over 125 MHz bandwidth, respectively, under 2.5 mW incident power.

Modeling of avalanche multiplication and excess noise factor in In0.52Al0.48As avalanche photodiodes using a simple Monte Carlo model

A simple Monte Carlo model has been developed to simulate the avalanche multiplication process in In0.52Al0.48As. The model reproduces avalanche multiplication and excess noise factor measured on a wide range of In0.52Al0.48As p+-n-n+, n+-n-p+, and p+-n+ diodes and confirms that very low excess noise factor can be obtained using pure electron injection in very thick diodes with avalanche region greater than 2.21 μm or in very thin diodes with avalanche region lesser than 0.11 μm. In addition we investigated the effect of an electric field gradient in the avalanche region of avalanche photodiodes and found that the excess noise factor can be reduced with electric field gradients. However in thin diodes with avalanche region lesser than 0.20 μm, the onset of tunneling current negates the excess noise reduction achieved using the electric field gradient. Therefore ideal p+-i-n+ diodes still provide the overall preferred structure.

Laser excess noise reduction in optical phase-shift measurements.

We describe an optical detection scheme that reduces laser excess noise in measurements of small optical phase shifts. The scheme improves the sensitivity of the balanced differential detection. Analysis of the scheme and comparison with the conventional detection are presented. The scheme is applied in electro-optic probing of electrical signals in integrated circuits, where the excess laser noise is reduced by approximately 20 dB.

Investigation into road vehicle noise reduction by drainage asphalt pavement.

Regarding the reduction of road vehicle noise by drainage asphalt pavement, two kinds of experimental investigations were performed. Firstly, sound propagation was observed on two types of drainage asphalt pavements and a dense asphalt pavement. In this experiment, an omnidirectional sound source was located under the body of a passenger car and a heavy truck. As a result, it was found that the excess noise reduction on drainage asphalt pavement can be attributed to the sound absorption during multiple reflection uncle': the vehicle body and this effect depends on the vehicle type. Secondly, pass-by tests were performed on the three kinds of pavements using the same test vehicles. In this experiment, tire/road noise was measured on each pavement and by comparing the results, the reduction of tire/road noise due to the porosity of drainage asphalt pavement was estimated. Based on the results of these investigations, a calculation model for the prediction of vehicle noise propagation on drainage asphalt pavement has been proposed.

Ultrafast optical pulse noise suppression using a nonlinear spectral filter: 23 dB reduction of fiber laser 1/f noise

Nonlinear spectral filtering provides a simple method for reducing noise in optical pulses to below the shot noise level. We show its effectiveness for excess noise reduction in an ultrafast optical pulse train by demonstrating 23 dB reduction of low frequency 1/f noise in pulses from a passively mode-locked erbium-doped fiber laser. The noise reduction is achieved by spectrally filtering pulses propagated as solitons through a 1.5 km length of optical fiber.

Excess noise reduction in GaInP/GaAs heterojunction bipolar transistors

In this paper an annealing procedure which gives an excess noise reduction both of heavily C-doped resistive structures and GaInP/GaAs Heterojunction Bipolar Transistors (HBTs) of 5 dB is proposed. The investigation of the correlation between the noise generators indicate that the annealing leads to a decrease of noise voltage attributed to a strain reduction both in the intrinsic and in the extrinsic base related to a site switching effect of carbon atoms. The reduction of noise current with annealing is attributed to the surface improvement related passivation process by hydrogen atoms.

Excess noise reduction in fiber gyroscope using broader spectrum linewidth Er-doped superfluorescent fiber laser

The minimum detectable rotation rate of a fiber gyroscope employing a rare-earth-doped superfluorescent laser (SFL) is theoretically proportional to the inverse square root of the spectrum linewidth Delta lambda of the employed SFL due to its excess noise. The short-term resolution of a fiber gyroscope using an Er-doped SFL with Al codoping that has a larger Delta lambda value than that without Al, is examined. The experimental results agree well with the theoretical prediction. The ER-doped SFL with Al can successfully improve the resolution as compared with that without Al.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

GaAs Schottky devices for submillimeter wavelengths

The above analyses assume the absence of excess noise in the Schottky barrier mixer diode. Achievement of such a condition is dependent not only on the absence of interfacial stress in the device structure, but also on device surface properties. Reduction of excess noise caused by these two mechanisms is discussed by Sherrill, et al.,(10) and Kattman, et al.(11)

Measurements of residual defects and 1/f noise in ion-implanted p-channel MOSFET's

This paper describes the measurements of excess noise and residual defects of extremely low concentrations (<1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> ) in ion-implanted p-channel MOSFET's. The activation energy and the density of the residual defects after high-temperature annealing were measured using a transient capacitance technique. The test FET's were ion-implanted with fluences of 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> to 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> using <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup> p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , or <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup> Si <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> species. A post-implant anneal was carried out in an N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> or an Ar ambient for 20 min at various temperatures. For <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -implanted MOSFET's after annealing above 1000°C, a high residual defect concentration was observed near the conduction band edge; whereas after annealing the defect density as a result of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">28</sup> Si <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> or <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup> p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> implantation was equal to that of control MOSFET's. The density-of-state data agree with the equilibrium measurements of excess ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/f</tex> ) noise power. The excess noise was measured as a function of the drain current. The distribution of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/f</tex> noise power versus potential minimum of holes in the equilibrium condition is similar to that of interface state density. In nonequilibrium operation, a reduction of excess noise was achieved owing to the presence of buried channel created by ion implant.