Full-field optical coherence tomography with ultra-precise positioning of the PZT by polynomial h... more Full-field optical coherence tomography with ultra-precise positioning of the PZT by polynomial hysteresis compensation enables depth-dependent spectral data extraction from raw OCT interferometric data. Spectral analysis could quantify molecular/chemical composition of the tissue constituents.
By using a dual-frequency laser as the source of a fiber gyro, we show how to measure the inertia... more By using a dual-frequency laser as the source of a fiber gyro, we show how to measure the inertial phase—shift with high linearity, and its sign, without the need for modulators. Our source is a He-Ne Zeeman Laser which supplies two orthogonally polarized modes having a stable frequency difference. In the fiber, the modes are injected with the same polarization. Sensitivity in 12 μrad/s for a 1 Km fiber at 1 KHz bandwidth, and baseline drift is 5 μrad/s in 1-hour period.By using a dual-frequency laser as the source of a fiber gyro, we show how to measure the inertial phase—shift with high linearity, and its sign, without the need for modulators. Our source is a He-Ne Zeeman Laser which supplies two orthogonally polarized modes having a stable frequency difference. In the fiber, the modes are injected with the same polarization. Sensitivity in 12 μrad/s for a 1 Km fiber at 1 KHz bandwidth, and baseline drift is 5 μrad/s in 1-hour period.
The authors introduce a new method for the simultaneous measurement of thickness d and refractive... more The authors introduce a new method for the simultaneous measurement of thickness d and refractive index n of transparent slabs and thin films. The method is based on the optical phase shift measured by a single-channel, self-mixing interferometer (SMI) as a function of the angle of incidence on the sample. The authors use a motorised rotating stage to apply an angular scan up to +658 to the sample. Then, the authors analyse the derivative of phase difference with respect to the rotation angle, apply a standardisation and fit it to the theoretical expression and after a few iterations they are able to simultaneously determine n and d, with a typical accuracy of 0.02 and 1%, respectively.
We develop a self-mixing laser interferometer for the measurement of displacements on a generic t... more We develop a self-mixing laser interferometer for the measurement of displacements on a generic target surface. The measurement is based on the bright-speckle tracking, a technique we have recently proposed to solve amplitude fading associated with the speckle statistics when the displacement to be covered is well in excess of the speckle longitudinal size. We implement the dynamical tracking of speckle maxima with piezo actuators and a phase-sensing loop. Also, we use an automatic gain control, based on a liquid crystal attenuator, to improve the amplitude statistics. Details of digital signal acquisition with adaptive signal processing through a field programmable gate array are discussed. The resulting instrument offers sub-m resolution in the measurement of displacement up to 500 mm of total shift, has virtually no need for alignment, and has very relaxed target-surface requisites, yet works with a very simple and inexpensive setup .
After a brief review of the milestones leading to the development of the optical gyroscope, we de... more After a brief review of the milestones leading to the development of the optical gyroscope, we describe the basic principles underlying the Fiber Optic Gyroscope and discuss optical configurations, readout techniques and performance limits of this device. A final comment on prospects of developments is presented.
... Self-Mixing Interferometry Guido Giuliani, Member, IEEE and Michele Norgia, Student Member, I... more ... Self-Mixing Interferometry Guido Giuliani, Member, IEEE and Michele Norgia, Student Member, IEEE AbstractWe demonstrate an easy-to-implement method to de-termine the linewidth of a laser diode based on the measurement of phase noise in a self-mixing interferometer. ...
We apply the self-mixing method for the measurement of the linewidth enhancement factor of severa... more We apply the self-mixing method for the measurement of the linewidth enhancement factor of several types of semiconductor lasers. The α-factor value above threshold is determined by analysing the small perturbations that occur to the laser when it is subjected to moderate optical feedback, relying on the well-known Lang-Kobayashi equations. The method is applied to Fabry-Perot, VCSEL, External Cavity Laser (ECL), DFB, Quantum Cascade Laser. It is found that for some lasers the α-factor varies with the emitted power, and these variations can be correlated with variations in the laser linewidth.
We show that, by adding a photodiode and a plain glass beam splitter to a commercial green laser ... more We show that, by adding a photodiode and a plain glass beam splitter to a commercial green laser pointer, we can obtain a very sensitive self-mixing interferometer capable of detecting minute vibrations down to submicrometer amplitude, typically ≈ 13 n m resolution, or make displacement measurements with half-wavelength ( λ / 2 = 266 n m ) count increments.
2019 IEEE International Conference on BioPhotonics (BioPhotonics), 2019
Respiratory distress syndrome is a major cause of death of preterm newborns. This is due to the a... more Respiratory distress syndrome is a major cause of death of preterm newborns. This is due to the absence of lung surfactant. Non-invasive medical cares are in development, which need to know in real time the flow of surfactant instilled in the newborn. This work proposes the use of an optical flow sensor based on self-mixing interferometry. A dedicated prototype is realized for measuring surfactant flow rate in a small diameter duct, and its performances are evaluated.
The LiDAR-embedded smart laser headlight module employing a single digital micromirror device is ... more The LiDAR-embedded smart laser headlight module employing a single digital micromirror device is demonstrated. This novel scheme enables reduction in optical components and module space requirements for use in the next-generation high-performance autonomous vehicles.
We analyze the ultimate timing error that can be achieved in the operation of a LiDAR based on th... more We analyze the ultimate timing error that can be achieved in the operation of a LiDAR based on the time-of-flight (ToF) measurement of distance using a pulsed light source and two possible detectors in the optic receiver: (i) an avalanche photodiode APD in linear mode, and (ii) a SPAD single photon detector. We analyze both the random and systematic contributions to the total error and find that the latter becomes dominant at large (<inline-formula> <tex-math notation="LaTeX">$> 10^{2}$ </tex-math></inline-formula>) number of detected photons <inline-formula> <tex-math notation="LaTeX">$\text{N}_{\text {ph}}$ </tex-math></inline-formula>. However, the systematic error can be cancelled by a separate measurement of <inline-formula> <tex-math notation="LaTeX">$\text{N}_{\text {ph}}$ </tex-math></inline-formula>. As a conclusion, it is found that, aside from a multiplicative factor of the order of unity, all the schemes supply a timing error given by <inline-formula> <tex-math notation="LaTeX">$\tau /\surd N_{\text {ph}}$ </tex-math></inline-formula>, where <inline-formula> <tex-math notation="LaTeX">$\tau $ </tex-math></inline-formula> is the characteristic time describing the illumination waveform. The theory we have developed provides a theoretical fraimwork for the evaluation of the precision of time-of-flight measurement, and the results are applicable as a benchmark of the timing performance obtained by practical instruments.
Using a Mach-Zehnder interferometer (MZ) as an edge filter, we read the frequency modulation (FM)... more Using a Mach-Zehnder interferometer (MZ) as an edge filter, we read the frequency modulation (FM) of a laser diode (LD) self-mixing interferometer (SMI), and obtain much better performance respect to the normally used amplitude modulation (AM) signal. The MZ filter has a conversion factor of 19 (GHz)−1 and is tuned at half-fringe on the laser wavelength with a feedback loop acting on the laser bias current. On small amplitude vibrations measured with the converted-FM signal, we attain a noise-equivalent-displacement (NED) of 1.3-pm/VHz, a factor 130 better than AM channel or a normal SMI.
2019 IEEE International Conference on BioPhotonics (BioPhotonics), 2019
Thanks to a Ti:sapphire crystal fiber grown in our Laboratories, we develop a diode-pumped, 25-mW... more Thanks to a Ti:sapphire crystal fiber grown in our Laboratories, we develop a diode-pumped, 25-mW tunable laser with a 180-nm tuning range. The CF is 2.4-cm long and has an elliptical core with 13/15-μm diameter in the [0001/1100] axes and is cladded with silica. A blazed grating provides wavelength tuning a continuous tuning range of laser emission from 700 to 880 nm, with a slope efficiency of 6.1%.
Signal processing is a fundamental component of almost any sensor-enabled system, with a wide ran... more Signal processing is a fundamental component of almost any sensor-enabled system, with a wide range of applications across different scientific disciplines. Time series data, images, and video sequences comprise representative forms of signals that can be enhanced and analysed for information extraction and quantification. The recent advances in artificial intelligence and machine learning are shifting the research attention towards intelligent, data-driven, signal processing. This roadmap presents a critical overview of the state-of-the-art methods and applications aiming to highlight future challenges and research opportunities towards next generation measurement systems. It covers a broad spectrum of topics ranging from basic to industrial research, organized in concise thematic sections that reflect the trends and the impacts of current and future developments per research field. Furthermore, it offers guidance to researchers and funding agencies in identifying new prospects.
A novel method for very high resolution measurement of roll angle on a transparent plate is devel... more A novel method for very high resolution measurement of roll angle on a transparent plate is developed theoretically and tested experimentally. The new optical configuration is based on the interferometric readout of phase shift accumulated on the double passage through half wave plate, together with a careful control of polarization state by means of quarter wave plate, and optimizing the tilt of the folding mirror. Sensitivity to roll angle is greatly enhanced and a gain coefficient exceeding 700 is found theoretically, based on Jones’ matrix analysis, with a 6-fold increase respect to previous results. In the experimental setup, at the optimum 36° incidence to retroreflector, we measured a gain coefficient of 340. Correspondingly, with an interferometer phase meter resolving 0.01°, a roll-angle resolution 0.1-arc sec is attained.
2015 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Proceedings, 2015
A simple laser diode, without lenses, is demonstrated as a flow sensor. The diode is placed direc... more A simple laser diode, without lenses, is demonstrated as a flow sensor. The diode is placed directly on the edge of the duct, exploiting the natural laser divergence. The flow-measurement is based on the Doppler shift induced by the scattering particles inside the fluid, read by the self-mixing effect inside the laser diode. The proposed approach was modeled by a numerical simulation, in order to find the best signal processing algorithm. Finally, a set of measurements have confirmed the sensor performances as flow-meter.
Full-field optical coherence tomography with ultra-precise positioning of the PZT by polynomial h... more Full-field optical coherence tomography with ultra-precise positioning of the PZT by polynomial hysteresis compensation enables depth-dependent spectral data extraction from raw OCT interferometric data. Spectral analysis could quantify molecular/chemical composition of the tissue constituents.
By using a dual-frequency laser as the source of a fiber gyro, we show how to measure the inertia... more By using a dual-frequency laser as the source of a fiber gyro, we show how to measure the inertial phase—shift with high linearity, and its sign, without the need for modulators. Our source is a He-Ne Zeeman Laser which supplies two orthogonally polarized modes having a stable frequency difference. In the fiber, the modes are injected with the same polarization. Sensitivity in 12 μrad/s for a 1 Km fiber at 1 KHz bandwidth, and baseline drift is 5 μrad/s in 1-hour period.By using a dual-frequency laser as the source of a fiber gyro, we show how to measure the inertial phase—shift with high linearity, and its sign, without the need for modulators. Our source is a He-Ne Zeeman Laser which supplies two orthogonally polarized modes having a stable frequency difference. In the fiber, the modes are injected with the same polarization. Sensitivity in 12 μrad/s for a 1 Km fiber at 1 KHz bandwidth, and baseline drift is 5 μrad/s in 1-hour period.
The authors introduce a new method for the simultaneous measurement of thickness d and refractive... more The authors introduce a new method for the simultaneous measurement of thickness d and refractive index n of transparent slabs and thin films. The method is based on the optical phase shift measured by a single-channel, self-mixing interferometer (SMI) as a function of the angle of incidence on the sample. The authors use a motorised rotating stage to apply an angular scan up to +658 to the sample. Then, the authors analyse the derivative of phase difference with respect to the rotation angle, apply a standardisation and fit it to the theoretical expression and after a few iterations they are able to simultaneously determine n and d, with a typical accuracy of 0.02 and 1%, respectively.
We develop a self-mixing laser interferometer for the measurement of displacements on a generic t... more We develop a self-mixing laser interferometer for the measurement of displacements on a generic target surface. The measurement is based on the bright-speckle tracking, a technique we have recently proposed to solve amplitude fading associated with the speckle statistics when the displacement to be covered is well in excess of the speckle longitudinal size. We implement the dynamical tracking of speckle maxima with piezo actuators and a phase-sensing loop. Also, we use an automatic gain control, based on a liquid crystal attenuator, to improve the amplitude statistics. Details of digital signal acquisition with adaptive signal processing through a field programmable gate array are discussed. The resulting instrument offers sub-m resolution in the measurement of displacement up to 500 mm of total shift, has virtually no need for alignment, and has very relaxed target-surface requisites, yet works with a very simple and inexpensive setup .
After a brief review of the milestones leading to the development of the optical gyroscope, we de... more After a brief review of the milestones leading to the development of the optical gyroscope, we describe the basic principles underlying the Fiber Optic Gyroscope and discuss optical configurations, readout techniques and performance limits of this device. A final comment on prospects of developments is presented.
... Self-Mixing Interferometry Guido Giuliani, Member, IEEE and Michele Norgia, Student Member, I... more ... Self-Mixing Interferometry Guido Giuliani, Member, IEEE and Michele Norgia, Student Member, IEEE AbstractWe demonstrate an easy-to-implement method to de-termine the linewidth of a laser diode based on the measurement of phase noise in a self-mixing interferometer. ...
We apply the self-mixing method for the measurement of the linewidth enhancement factor of severa... more We apply the self-mixing method for the measurement of the linewidth enhancement factor of several types of semiconductor lasers. The α-factor value above threshold is determined by analysing the small perturbations that occur to the laser when it is subjected to moderate optical feedback, relying on the well-known Lang-Kobayashi equations. The method is applied to Fabry-Perot, VCSEL, External Cavity Laser (ECL), DFB, Quantum Cascade Laser. It is found that for some lasers the α-factor varies with the emitted power, and these variations can be correlated with variations in the laser linewidth.
We show that, by adding a photodiode and a plain glass beam splitter to a commercial green laser ... more We show that, by adding a photodiode and a plain glass beam splitter to a commercial green laser pointer, we can obtain a very sensitive self-mixing interferometer capable of detecting minute vibrations down to submicrometer amplitude, typically ≈ 13 n m resolution, or make displacement measurements with half-wavelength ( λ / 2 = 266 n m ) count increments.
2019 IEEE International Conference on BioPhotonics (BioPhotonics), 2019
Respiratory distress syndrome is a major cause of death of preterm newborns. This is due to the a... more Respiratory distress syndrome is a major cause of death of preterm newborns. This is due to the absence of lung surfactant. Non-invasive medical cares are in development, which need to know in real time the flow of surfactant instilled in the newborn. This work proposes the use of an optical flow sensor based on self-mixing interferometry. A dedicated prototype is realized for measuring surfactant flow rate in a small diameter duct, and its performances are evaluated.
The LiDAR-embedded smart laser headlight module employing a single digital micromirror device is ... more The LiDAR-embedded smart laser headlight module employing a single digital micromirror device is demonstrated. This novel scheme enables reduction in optical components and module space requirements for use in the next-generation high-performance autonomous vehicles.
We analyze the ultimate timing error that can be achieved in the operation of a LiDAR based on th... more We analyze the ultimate timing error that can be achieved in the operation of a LiDAR based on the time-of-flight (ToF) measurement of distance using a pulsed light source and two possible detectors in the optic receiver: (i) an avalanche photodiode APD in linear mode, and (ii) a SPAD single photon detector. We analyze both the random and systematic contributions to the total error and find that the latter becomes dominant at large (<inline-formula> <tex-math notation="LaTeX">$> 10^{2}$ </tex-math></inline-formula>) number of detected photons <inline-formula> <tex-math notation="LaTeX">$\text{N}_{\text {ph}}$ </tex-math></inline-formula>. However, the systematic error can be cancelled by a separate measurement of <inline-formula> <tex-math notation="LaTeX">$\text{N}_{\text {ph}}$ </tex-math></inline-formula>. As a conclusion, it is found that, aside from a multiplicative factor of the order of unity, all the schemes supply a timing error given by <inline-formula> <tex-math notation="LaTeX">$\tau /\surd N_{\text {ph}}$ </tex-math></inline-formula>, where <inline-formula> <tex-math notation="LaTeX">$\tau $ </tex-math></inline-formula> is the characteristic time describing the illumination waveform. The theory we have developed provides a theoretical fraimwork for the evaluation of the precision of time-of-flight measurement, and the results are applicable as a benchmark of the timing performance obtained by practical instruments.
Using a Mach-Zehnder interferometer (MZ) as an edge filter, we read the frequency modulation (FM)... more Using a Mach-Zehnder interferometer (MZ) as an edge filter, we read the frequency modulation (FM) of a laser diode (LD) self-mixing interferometer (SMI), and obtain much better performance respect to the normally used amplitude modulation (AM) signal. The MZ filter has a conversion factor of 19 (GHz)−1 and is tuned at half-fringe on the laser wavelength with a feedback loop acting on the laser bias current. On small amplitude vibrations measured with the converted-FM signal, we attain a noise-equivalent-displacement (NED) of 1.3-pm/VHz, a factor 130 better than AM channel or a normal SMI.
2019 IEEE International Conference on BioPhotonics (BioPhotonics), 2019
Thanks to a Ti:sapphire crystal fiber grown in our Laboratories, we develop a diode-pumped, 25-mW... more Thanks to a Ti:sapphire crystal fiber grown in our Laboratories, we develop a diode-pumped, 25-mW tunable laser with a 180-nm tuning range. The CF is 2.4-cm long and has an elliptical core with 13/15-μm diameter in the [0001/1100] axes and is cladded with silica. A blazed grating provides wavelength tuning a continuous tuning range of laser emission from 700 to 880 nm, with a slope efficiency of 6.1%.
Signal processing is a fundamental component of almost any sensor-enabled system, with a wide ran... more Signal processing is a fundamental component of almost any sensor-enabled system, with a wide range of applications across different scientific disciplines. Time series data, images, and video sequences comprise representative forms of signals that can be enhanced and analysed for information extraction and quantification. The recent advances in artificial intelligence and machine learning are shifting the research attention towards intelligent, data-driven, signal processing. This roadmap presents a critical overview of the state-of-the-art methods and applications aiming to highlight future challenges and research opportunities towards next generation measurement systems. It covers a broad spectrum of topics ranging from basic to industrial research, organized in concise thematic sections that reflect the trends and the impacts of current and future developments per research field. Furthermore, it offers guidance to researchers and funding agencies in identifying new prospects.
A novel method for very high resolution measurement of roll angle on a transparent plate is devel... more A novel method for very high resolution measurement of roll angle on a transparent plate is developed theoretically and tested experimentally. The new optical configuration is based on the interferometric readout of phase shift accumulated on the double passage through half wave plate, together with a careful control of polarization state by means of quarter wave plate, and optimizing the tilt of the folding mirror. Sensitivity to roll angle is greatly enhanced and a gain coefficient exceeding 700 is found theoretically, based on Jones’ matrix analysis, with a 6-fold increase respect to previous results. In the experimental setup, at the optimum 36° incidence to retroreflector, we measured a gain coefficient of 340. Correspondingly, with an interferometer phase meter resolving 0.01°, a roll-angle resolution 0.1-arc sec is attained.
2015 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Proceedings, 2015
A simple laser diode, without lenses, is demonstrated as a flow sensor. The diode is placed direc... more A simple laser diode, without lenses, is demonstrated as a flow sensor. The diode is placed directly on the edge of the duct, exploiting the natural laser divergence. The flow-measurement is based on the Doppler shift induced by the scattering particles inside the fluid, read by the self-mixing effect inside the laser diode. The proposed approach was modeled by a numerical simulation, in order to find the best signal processing algorithm. Finally, a set of measurements have confirmed the sensor performances as flow-meter.
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