scholarly journals External Modulation Laser Module Assembly for Improving Measurement Performance of Homodyne Interferometry

Sensors ◽  
2020 ◽  
Vol 20 (19) ◽  
pp. 5652
Author(s):  
Tao Zhang ◽  
Tao Sun ◽  
Jiean Li ◽  
Xingyu Zhao ◽  
Jiwen Cui
Keyword(s):  
Light Source ◽  
High Frequency ◽  
Phase Modulation ◽  
Optical Measurement ◽  
Modulation Amplitude ◽  
External Modulation ◽  
Measurement Resolution ◽  
Laser Module ◽  
Switching Mode ◽  
Nonlinear Errors

An external modulation laser module assembly (EMLMA) is proposed to suppress nonlinear errors in an interferometry system and improve its measurement performance. The EMLMA employs both phase modulation with radio frequency signal and a specific modulation amplitude switching mode, enabling the suppression of noise introduced by spurious reflections. The amplitude modulation reduces the influence of stray and background light by transforming the signal of interest to a high-frequency bandwidth. Experimental results show that the measurement error and stability of the interferometry system are significantly improved using the proposed light source module. After modulation, the spurious reflection-induced offset is decreased, and the measurement resolution improves from 7 to 2 nm. The EMLMA can replace the light source of any interferometric measurement system without altering the optical measurement structure. The proposed method reduces the influence of nonlinear errors in homodyne interferometry and provides a basis for further improvement of the interferometry performance.

scholarly journals Interferometers with Internal and External Phase Modulation: Experimental and Analytical Comparison

1995 ◽  
Vol 48 (6) ◽  
pp. 971 ◽  
Author(s):  
Andrew J Stevenson ◽  
Malcolm B Gray ◽  
Charles C Harb ◽  
David E McClelland ◽  
Hans-A Bachor
Keyword(s):  
Shot Noise ◽  
High Frequency ◽  
Phase Modulation ◽  
Low Frequency ◽  
Local Oscillator ◽  
Intensity Noise ◽  
Fringe Contrast ◽  
Limited Region ◽  
External Modulation ◽  
Frequency Phase

Optical intensity noise in a light source easily degrades the sensitivity of a shot-noise-limited interferometer which is directly detecting low frequency phase or displacement variations. In this paper we describe and compare two experimental methods in which we use high frequency optical phase modulation to shift low frequency phase signals in an interferometer to a shot noise limited region of the photocurrent spectrum. This phase modulation is applied either within the interferometer arms-internal modulation-or in a local oscillator beam tapped off the main interferometer and coherently recombined with the interferometer output-external modulation. he photocurrent is mixed electronically with the high frequency modulating waveform to extract the signal information free from laser intensity noise. In our experiments, we have been able to detect interferometrically low frequency signals with true shot-noise-limited sensitivity. We find, theoretically and experimentally, that the interferometric sensitivity achievable in each scheme depends critically on non-ideal factors, such as imperfect interferometric fringe contrast and electronic noise in the detectors or amplifiers. This paper examines the relative merits and operating requirements of both modulation schemes in practical interferometers.

scholarly journals Electron-beam–ignited, high-frequency–driven vacuum ultraviolet excimer light source

2011 ◽  
Vol 94 (5) ◽  
pp. 53001 ◽  
Author(s):  
T. Dandl ◽  
H. Hagn ◽  
T. Heindl ◽  
R. Krücken ◽  
J. Wieser ◽  
...  
Keyword(s):  
Electron Beam ◽  
Light Source ◽  
High Frequency ◽  
Vacuum Ultraviolet ◽  
Excimer Light Source

Calibrations of Phase Modulation Amplitude of Photoelastic Modulator

2004 ◽  
Vol 43 (2) ◽  
pp. 827-832 ◽  
Author(s):  
Meng-Wei Wang ◽  
Yu-Faye Chao ◽  
Keh-Chyang Leou ◽  
Fei-Hsin Tsai ◽  
Tsang-Lang Lin ◽  
...  
Keyword(s):  
Phase Modulation ◽  
Modulation Amplitude ◽  
Photoelastic Modulator

Combustion Instability and Emission Control by Pulsating Fuel Injection

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Christian Oliver Paschereit ◽  
Ephraim Gutmark
Keyword(s):  
High Frequency ◽  
Fuel Injection ◽  
Low Frequency ◽  
Nox Emissions ◽  
Modulation Amplitude ◽  
Pulsation Frequency ◽  
Symmetric Mode ◽  
Instability Mode ◽  
Secondary Fuel ◽  
Symmetric Instability

Open-loop control methodologies were used to suppress symmetric and helical thermoacoustic instabilities in an experimental low-emission swirl-stabilized gas-turbine combustor. The controllers were based on fuel (or equivalence ratio) modulations in the main premixed combustion (premixed fuel injection (PMI)) or, alternatively, in the secondary pilot fuel. PMI included symmetric and asymmetric fuel injection. The symmetric instability mode responded to symmetric excitation only when the two frequencies matched. The helical fuel injection affected the symmetric mode only at frequencies that were much higher than that of the instability mode. The asymmetric excitation required more power to obtain the same amount of reduction as that required by symmetric excitation. Unlike the symmetric excitation, which destabilized the combustion when the modulation amplitude was excessive, the asymmetric excitation yielded additional suppression as the modulation level increased. The NOx emissions were reduced to a greater extent by the asymmetric modulation. The second part of the investigation dealt with the control of low frequency symmetric instability and high frequency helical instability by the secondary fuel injection in a pilot flame. Adding a continuous flow of fuel into the pilot flame controlled both instabilities. However, modulating the fuel injection significantly decreased the amount of necessary fuel. The reduced secondary fuel resulted in a reduced heat generation by the pilot diffusion flame and therefore yielded lower NOx emissions. The secondary fuel pulsation frequency was chosen to match the time scales typical to the central flow recirculation zone, which stabilizes the flame in the burner. Suppression of the symmetric mode pressure oscillations by up to 20dB was recorded. High frequency instabilities were suppressed by 38dB, and CO emissions reduced by using low frequency modulations with 10% duty cycle.

Stabilized transverse Zeeman laser as a new light source for optical measurement

1980 ◽  
Vol 19 (3) ◽  
pp. 435 ◽  
Author(s):  
H. Takasaki ◽  
N. Umeda ◽  
M. Tsukiji
Keyword(s):  
Light Source ◽  
Optical Measurement ◽  
Zeeman Laser

Suppression Approaches of Far-Field Radiated Emission Using Common-Mode Inductor

2021 ◽  
Vol 1 (2) ◽  
pp. 1-5
Author(s):  
Mengzi Li ◽  
◽  
Shishan Wang ◽  
Jian Guo
Keyword(s):  
High Frequency ◽  
Reference Value ◽  
Power Converter ◽  
Practical Significance ◽  
Far Field ◽  
Common Mode ◽  
Suppression Method ◽  
Switching Mode ◽  
Emc Design ◽  
Radiated Emission

The miniaturization and integration of Switching Mode Power Supply (SMPS) is increasing, making it more complicated to analyze and predict its far-field radiated emission, and, consequently, studying the suppression method of far-field radiated emission of SMPS is of practical significance and engineering value. In this paper, a high-frequency SMPS is selected as the research object, whose far-field radiated emission is measured under the condition of three typical suppression methods. The experimental results verified the effectiveness of common-mode inductor and are of reference value for EMC design of power converter. Keywords: SMPS; EMC; Far-field Radiated Emission;

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