Source stabilization for high quality time-domain diffuse optical tomography

Mo, Wei; Chen, Nanguang

doi:10.1117/12.808188

Cited by 9 publications

(7 citation statements)

References 26 publications

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“…This problem can be removed by using a vertical-cavity surface-emitting laser (VCSEL) which has a good modulation response at higher frequencies but the optical power is usually low (few mW). Direct electrical modulation of laser diodes is advantageous to using electro-optics modulators (EOM) such as Mach-Zehnder modulator (MZM) [7], as they do not require any extra controls. A direct RF modulation technique of injection current was used to modulate high speed 2.5 Gbps VCSELs from Thorlabs at two wavelengths: 780nm and 850nm.…”

Section: System Designmentioning

confidence: 99%

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Developing a robust time domain diffuse optical tomography system

et al. 2013

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Section: System Designmentioning

confidence: 99%

“…To keep the modulation depth constant, an automatic bias tracking and control module based on the addictive dither technique was implemented to set the working point (i.e. the positive quadratic point) of the intensity modulator ahead of each scanning [7].…”

Section: Introductionmentioning

confidence: 99%

Developing a robust time domain diffuse optical tomography system

et al. 2013

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“…When φ changes the transfer function of the EOM is shifted accordingly, to the right or to the left, during the operating time. The drift of the EOM transfer function can be explained by different effects such as changes of working temperature, optical coupling efficiency and photo refractive effects [5,6,7,8].…”

Section: The Electro-optic Modulatormentioning

confidence: 99%

Improving Opto-Electronic Oscillator stability by controlling the Electro-Optic Modulator

Bui

Pham

et al. 2012

2012 Fourth International Conference on Communications and Electronics (ICCE)

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This paper presents a study concerning the improvement of the stability of an Opto-Electronic Oscillator (OEO). It seems to be the first publication about this subject. An advanced method for controlling the optical bias point of the Electro-Optic Modulator (EOM) has been developed. The evolution of the modulator characteristics can be followed through its non-linear behavior by detecting the second harmonic of a low-frequency modulating signal. The control system implemented with PSoC microcontrollers is designed in order to keep the bias point at the quadrature position for minimizing the second order non-linear component. By this way the medium term stability can be greatly improved. Without bias point position control the OEO operates only for a few hours (2 or 3 h) but with the control it can operate for at least a working day (8 h).

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“…The control is achieved by a lock-in amplifier. Correlation determination between the modulating signal applied to the modulator and the detected signal at its output is another solution applied for an EOM, which is used in a time-domain diffuse optical tomography application [17]. A square signal at a frequency of 1 Hz and peak-to-peak amplitude of 0.7 V is applied.…”

Section: Different Techniques Developed For Estimating the Drift Of A...mentioning

confidence: 99%

Instrumentation system for determination and compensation of electro-optic modulator transfer function drift

Bui¹,

Nguyên²,

Ledoux‐Rak³

et al. 2011

Meas. Sci. Technol.

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This paper presents an instrumentation system developed to improve the operation of an electro-optic modulator (EOM). During their operating time, EOM are subject to a drift of the optical transfer function; therefore the initial tuning of the bias point no longer corresponds to the best characteristics of the device. Because of this drift the EOM no longer behaves linearly and there is degradation during time of the performances of the system in which the EOM is included. To determine the drift, a low frequency modulation signal (at 500 Hz) is applied to the EOM and the second harmonic component at 1 kHz is detected. A new criterion is introduced for estimating the nonlinearity and for compensating the drift of the transfer function, keeping the optical bias point at the quadrature position. Temperature changes significantly influence the EOM characteristics. Thus, the instrumentation system has to be simultaneously developed with temperature control and drift compensation of the optical transfer function. The design is based on PSOC microcontrollers for tuning the different parameters, for data acquisition and regulation process. By setting the temperature to some specific values, it is possible to test the behaviour of the modulator. Finally, by using both temperature and bias point control, a significant reduction of the nonlinearity can be obtained during 2 h of experiment: the biasing point at the quadrature point of the transfer function which corresponds to the most linear behaviour can be stabilized within ±0.22% of the half-wave voltage. All the works presented here were carried out with a Mach–Zehnder intensity modulator made of lithium niobate, but it is also possible to apply this method to other kinds of material, for example polymer material.

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Source stabilization for high quality time-domain diffuse optical tomography

Cited by 9 publications

References 26 publications

Developing a robust time domain diffuse optical tomography system

Developing a robust time domain diffuse optical tomography system

Improving Opto-Electronic Oscillator stability by controlling the Electro-Optic Modulator

Instrumentation system for determination and compensation of electro-optic modulator transfer function drift

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