A new algorithm for a high-modulation frequency and high-speed digital lock-in amplifier

Laser interferometers can achieve a nanometer-order uncertainty of measurements when their frequencies are locked to the reference frequencies of the atom or molecule transitions. There are three types of displacement-measuring interferometers: homodyne, heterodyne, and frequency modulation (FM) interferometers. Among these types of interferometer, the FM interferometer has many advantageous features. The interference signal is a series of time-dependent harmonics of modulation frequency, so the phase shift can be detected accurately using the synchronous detection method. Moreover, the FM interferometer is the most suitable for combination with a frequency-locked laser because both require frequency modulation. In previous research, low modulation frequencies at some tens of kHz have been used to lock the frequency of laser diodes (LDs). The low modulation frequency for the laser source means that the maximum measurement speed of the FM interferometers is limited. This paper proposes a novel contribution regarding the application of a high-frequency modulation for an LD to improve both the frequency stability of the laser source and the measurement speed of the FM interferometer. The frequency of the LD was locked to an I2 hyperfine component at 1 MHz modulation frequency. A high bandwidth lock-in amplifier was utilized to detect the saturated absorption signals of the I2 hyperfine structure and induce the signal to lock the frequency of the LD. The locked LD was then used for an FM displacement measuring interferometer. Moreover, a suitable modulation amplitude that affected the signal-to-noise ratio of both the I2 absorption signal and the harmonic intensity of the interference signal was determined. In order to verify the measurement resolution of the proposed interferometer, the displacement induced by a piezo electric actuator was concurrently measured by the interferometer and a capacitive sensor. The difference of the displacement results was less than 20 nm. To evaluate the measurement speed, the interferometer was used to measure the axial error of a high-speed spindle at 500 rpm. The main conclusion of this study is that a stable displacement interferometer with high accuracy and a high measurement speed can be achieved using an LD frequency locked to an I2 hyperfine transition at a high modulation frequency.

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Lock-in Phase Mapping of Modulated Reflectance in Dynamically Operating Mixed-Signal IC Devices

ISTFA 2012: Conference Proceedings from the 38th International Symposium for Testing and Failure Analysis ◽

10.31399/asm.cp.istfa2012p0217 ◽

2012 ◽

Author(s):

Zhongling Qian ◽

Christof Brillert ◽

Christian Burmer

Keyword(s):

Modulation Frequency ◽

Free Carrier ◽

Mapping Technique ◽

Free Carrier Absorption ◽

Absorption Mechanism ◽

Mixed Signal ◽

High Modulation ◽

Phase Mapping ◽

Lock In ◽

Mixed Signal Ic

Abstract The lock-in phase mapping technique with modulated reflectance is introduced for the first time. With its help, the modulated reflectance mechanisms using thermal laser in operating FETs, particularly in the pinch off region, are clarified. The free carrier absorption mechanism dominates at a high modulation frequency, while thermo-reflectance mechanisms at a low modulation frequency. In the pinch-off region, thermo-reflectance mechanism cannot be neglected due to extremely low free carrier concentration. The modulated reflectance signal was unexpectedly observed at passive poly/oxide/poly capacitance. The advantages of lockin phase mapping in dynamically operating mixed-signal IC devices are shown in several case studies.

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Neuro-Inspired Computing with Spin-VCSELs

Applied Sciences ◽

10.3390/app11094232 ◽

2021 ◽

Vol 11 (9) ◽

pp. 4232

Author(s):

Krishan Harkhoe ◽

Guy Verschaffelt ◽

Guy Van der Sande

Keyword(s):

Processing Speed ◽

Delay Time ◽

High Speed ◽

State Of The Art ◽

Polarization Modulation ◽

Time Interval ◽

Computing Technique ◽

High Modulation ◽

Short Time ◽

Modulation Speed

Delay-based reservoir computing (RC), a neuromorphic computing technique, has gathered lots of interest, as it promises compact and high-speed RC implementations. To further boost the computing speeds, we introduce and study an RC setup based on spin-VCSELs, thereby exploiting the high polarization modulation speed inherent to these lasers. Based on numerical simulations, we benchmarked this setup against state-of-the-art delay-based RC systems and its parameter space was analyzed for optimal performance. The high modulation speed enabled us to have more virtual nodes in a shorter time interval. However, we found that at these short time scales, the delay time and feedback rate heavily influence the nonlinear dynamics. Therefore, and contrary to other laser-based RC systems, the delay time has to be optimized in order to obtain good RC performances. We achieved state-of-the-art performances on a benchmark timeseries prediction task. This spin-VCSEL-based RC system shows a ten-fold improvement in processing speed, which can further be enhanced in a straightforward way by increasing the birefringence of the VCSEL chip.

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A New Method to Verify the Measurement Speed and Accuracy of Frequency Modulated Interferometers

Applied Sciences ◽

10.3390/app11135787 ◽

2021 ◽

Vol 11 (13) ◽

pp. 5787

Author(s):

Toan-Thang Vu ◽

Thanh-Tung Vu ◽

Van-Doanh Tran ◽

Thanh-Dong Nguyen ◽

Ngoc-Tam Bui

Keyword(s):

Phase Change ◽

High Speed ◽

Measurement Accuracy ◽

Slow Motion ◽

New Method ◽

Virtual Displacement ◽

Electro Optic ◽

Lock In ◽

Speed And Accuracy ◽

Electro Optic Modulator

The measurement speed and measurement accuracy of a displacement measuring interferometer are key parameters. To verify these parameters, a fast and high-accuracy motion is required. However, the displacement induced by a mechanical actuator generates disadvantageous features, such as slow motion, hysteresis, distortion, and vibration. This paper proposes a new method for a nonmechanical high-speed motion using an electro-optic modulator (EOM). The method is based on the principle that all displacement measuring interferometers measure the phase change to calculate the displacement. This means that the EOM can be used to accurately generate phase change rather than a mechanical actuator. The proposed method is then validated by placing the EOM into an arm of a frequency modulation interferometer. By using two lock-in amplifiers, the phase change in an EOM and, hence, the corresponding virtual displacement could be measured by the interferometer. The measurement showed that the system could achieve a displacement at 20 kHz, a speed of 6.08 mm/s, and a displacement noise level < 100 pm//√Hz above 2 kHz. The proposed virtual displacement can be applied to determine both the measurement speed and accuracy of displacement measuring interferometers, such as homodyne interferometers, heterodyne interferometers, and frequency modulated interferometers.

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Sources of the Scalp-Recorded Amplitude-Modulation Following Response

Journal of the American Academy of Audiology ◽

10.1055/s-0040-1715963 ◽

2002 ◽

Vol 13 (04) ◽

pp. 188-204 ◽

Cited By ~ 53

Author(s):

Shigeyuki Kuwada ◽

Julia S. Anderson ◽

Ranjan Batra ◽

Douglas C. Fitzpatrick ◽

Natacha Teissier ◽

...

Keyword(s):

Animal Model ◽

Amplitude Modulation ◽

Single Unit ◽

Modulation Frequency ◽

Multiple Sources ◽

High Modulation ◽

Before And After ◽

Single Unit Recordings ◽

Composite Response ◽

The Brain

The scalp-recorded amplitude-modulation following response (AMFR)” is gaining recognition as an objective audiometric tool, but little is known about the neural sources that underlie this potential. We hypothesized, based on our human studies and single-unit recordings in animals, that the scalp-recorded AMFR reflects the interaction of multiple sources. We tested this hypothesis using an animal model, the unanesthetized rabbit. We compared AMFRs recorded from the surface of the brain at different locations and before and after the administration of agents likely to enhance or suppress neural generators. We also recorded AMFRs locally at several stations along the auditory neuraxis. We conclude that the surface-recorded AMFR is indeed a composite response from multiple brain generators. Although the response at any modulation frequency can reflect the activity of more than one generator, the AMFRs to low and high modulation frequencies appear to reflect a strong contribution from cortical and subcortical sources, respectively.

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Quantitative FM Spectroscopy at High Temperatures: The Detection of 1CH2 behind Shock Waves

Zeitschrift für Physikalische Chemie ◽

10.1524/zpch.2000.214.12.1723 ◽

2000 ◽

Vol 214 (12) ◽

Cited By ~ 7

Author(s):

G. Friedrichs ◽

H.Gg. Wagner

Keyword(s):

High Temperature ◽

Shock Waves ◽

High Temperatures ◽

Frequency Modulation ◽

Modulation Frequency ◽

Optical Power ◽

Time Resolved ◽

Signal Conversion ◽

High Modulation ◽

Singlet Methylene

The technique of time resolved frequency modulation (FM) spectroscopy has been shown to provide a very sensitive means to detect small radicals behind shock waves. Features of high temperature FM spectroscopy behind shock waves will be discussed and a general signal conversion procedure to carry out quantitative concentration measurements will be presented.Using a high modulation frequency, a high modulation index and high total optical power, singlet methylene radicals (α

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Neural Rate and Timing Cues for Detection and Discrimination of Amplitude-Modulated Tones in the Awake Rabbit Inferior Colliculus

Journal of Neurophysiology ◽

10.1152/jn.00776.2006 ◽

2007 ◽

Vol 97 (1) ◽

pp. 522-539 ◽

Cited By ~ 51

Author(s):

Paul C. Nelson ◽

Laurel H. Carney

Keyword(s):

Inferior Colliculus ◽

Dynamic Range ◽

Modulation Depth ◽

Average Rate ◽

Modulation Frequency ◽

Detection Threshold ◽

Depth Functions ◽

Depth Discrimination ◽

High Modulation ◽

Envelope Processing

Neural responses to amplitude-modulated (AM) tones in the unanesthetized rabbit inferior colliculus (IC) were studied in an effort to establish explicit relationships between physiological and psychophysical measures of temporal envelope processing. Specifically, responses to variations in modulation depth ( m) at the cell’s best modulation frequency, with and without modulation maskers, were quantified in terms of average rate and synchronization to the envelope over the entire perceptual dynamic range of depths. Statistically significant variations in the metrics were used to define neural AM detection and discrimination thresholds. Synchrony emerged at modulation depths comparable with psychophysical AM detection sensitivities in some neurons, whereas the lowest rate-based neural thresholds could not account for psychoacoustical thresholds. The majority of rate thresholds (85%) were −10 dB or higher (in 20 log m), and 16% of the population exhibited no systematic dependence of average rate on m. Neural thresholds for AM detection did not decrease systematically at higher SPLs (as observed psychophysically): thresholds remained constant or increased with level for most cells tested at multiple sound-pressure levels (SPLs). At depths higher than the rate-based detection threshold, some rate modulation-depth functions were sufficiently steep with respect to the across-trial variability of the rate to predict depth discrimination thresholds as low as 1 dB (comparable with the psychophysics). Synchrony, on the other hand, did not vary systematically with m in many cells at high modulation depths. A simple computational model was extended to reproduce several features of the modulation frequency and depth dependence of both transient and sustained pure-tone responders.

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Polymer colour converter with very high modulation bandwidth for visible light communications

Journal of Materials Chemistry C ◽

10.1039/c7tc03787b ◽

2017 ◽

Vol 5 (35) ◽

pp. 8916-8920 ◽

Cited By ~ 7

Author(s):

D. A. Vithanage ◽

A. L. Kanibolotsky ◽

S. Rajbhandari ◽

P. P. Manousiadis ◽

M. T. Sajjad ◽

...

Keyword(s):

Visible Light ◽

High Speed ◽

Visible Light Communication ◽

Modulation Bandwidth ◽

Visible Light Communications ◽

Semiconducting Polymer ◽

High Modulation ◽

Very High

We report the synthesis, photophysics and application of a novel semiconducting polymer as a colour converter for high speed visible light communication.

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Development of a Compact, Configurable, Real-Time Range Imaging System

10.26686/wgtn.16985239 ◽

2021 ◽

Author(s):

◽

Adrian Peter Paul Jongenelen

Keyword(s):

High Speed ◽

Imaging System ◽

Modulation Frequency ◽

Image Sensor ◽

Measurement Precision ◽

Operating Parameters ◽

Range Imaging ◽

Field Range ◽

Full Field ◽

Precision And Accuracy

<p>This thesis documents the development of a time-of-flight (ToF) camera suitable for autonomous mobile robotics applications. By measuring the round trip time of emitted light to and from objects in the scene, the system is capable of simultaneous full-field range imaging. This is achieved by projecting amplitude modulated continuous wave (AMCW) light onto the scene, and recording the reflection using an image sensor array with a high-speed shutter amplitude modulated at the same frequency (of the order of tens of MHz). The effect is to encode the phase delay of the reflected light as a change in pixel intensity, which is then interpreted as distance. A full field range imaging system has been constructed based on the PMD Technologies PMD19k image sensor, where the high-speed shuttering mechanism is builtin to the integrated circuit. This produces a system that is considerably more compact and power efficient than previous iterations that employed an image intensifier to provide sensor modulation. The new system has comparable performance to commercially available systems in terms of distance measurement precision and accuracy, but is much more flexible with regards to its operating parameters. All of the operating parameters, including the image integration time, sensor modulation phase offset and modulation frequency can be changed in realtime either manually or automatically through software. This highly configurable system serves as an excellent platform for research into novel range imaging techniques. One promising technique is the utilisation of measurements using multiple modulation frequencies in order to maximise precision over an extended operating range. Each measurement gives an independent estimate of the distance with limited range depending on the modulation frequency. These are combined to give a measurement with extended maximum range using a novel algorithm based on the New Chinese Remainder Theorem. A theoretical model for the measurement precision and accuracy of the new algorithm is presented and verified with experimental results. All distance image processing is performed on a per-pixel basis in real-time using a Field Programmable Gate Array (FPGA). An efficient hardware implementation of the phase determination algorithm for calculating distance is investigated. The limiting resource for such an implementation is random access memory (RAM), and a detailed analysis of the trade-off between this resource and measurement precision is also presented.</p>

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1.55 μm High Speed Partly Gain-Coupled DFB Lasers with Periodically Etched Strained-Layer Quantum Wells

International Journal of High Speed Electronics and Systems ◽

10.1142/s0129156497000172 ◽

1997 ◽

Vol 08 (03) ◽

pp. 475-494 ◽

Cited By ~ 2

Author(s):

Toshihiko Makino

Keyword(s):

Quantum Wells ◽

High Speed ◽

Carrier Transport ◽

Stop Band ◽

Longitudinal Distribution ◽

Modulation Bandwidth ◽

Carrier Injection ◽

Strained Layer ◽

High Modulation ◽

Dfb Laser

The high speed performance of partly gain-coupled (GC) DFB lasers consisting of periodically etched strained-layer quantum wells (QW's) is reviewed with comparisons to the equivalent index-coupled (IC) DFB lasers with the same active layers. It is shown that the GC DFB laser has a –3 dB modulation bandwidth of 22 GHz at 10 mW with a stable single mode oscillation at the longer side of the Bragg Stop-band due to in-phase gain coupling. A theoretical analysis is also presented based on the local-normal-mode transfer-matrix laser model which takes into account both the longitudinal distribution of laser parameters and carrier transport effects. The mechanism for high modulation bandwidth of the GC DFB laser is attributed to a higher differential gain due to a reduced carrier transport time which is provided by an effecient carrier injection from the longitudinal etched interface of the QW's.

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