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Schematic design of the customized EO phase modulator. The modulator is modified to have a single optical port where the output port is terminated with a metallic mirror that acts as the external reflector.
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Optical sensing offers an attractive option for detection of surface biopotentials in human subjects where electromagnetically noisy environments exist or safety requirements dictate a high degree of galvanic isolation. Such circumstances may be found in modern magnetic resonance imaging systems for example. The low signal amplitude and high source...
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Context 1
... design of the customized EO phase modulator is illustrated in figure 1. The modulator was designed from an existing EO phase modulator produced for optical communications use with lithium niobate (LiNbO 3 ) as the waveguide material. ...
Context 2
... insertion loss and polarization dependent loss on a single propagation path were measured to be 6.5 dB and greater than 30 dB, respectively. The modulator was designed to have a single optical port where the other optical port (output) was replaced by a metallic mirror (see figure 1). The mirror acts as an external target which reflects the optical signal back into the cavity of the vertical-cavity surface-emitting laser (VCSEL). ...
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Citations
... Previously this technique has been shown to visualize acoustic and pressure waves waves in air [28][29][30][31] and in turbid media [32], by measuring the effect the acoustic wave has on compressing the medium it travels and thus altering the index of refraction along the path of the laser beam. The LFI technique has also been previously used to measure static changes in refractive index of transparent solid materials [33], dynamic index changes in the wave-guides of electro-optic modulators [34], as well as small changes in relative refractive index between different materials [35][36][37][38][39]. Most importantly this technique has been demonstrated effectively with cheap (sub ten dollars a piece in bulk) widespread telecommunications lasers, [21] and with simple customized electronics could easily create a sub-hundred-dollar sensing system. ...
The use of ultrasonic elastic waves is a well established technique for non-destructive testing of materials and structures, in particular to exploit the interaction of waves with structural features to detect and characterize defects. Optical methods offer the advantage of visualising the distribution of elastic waves in a non-contact manner without disturbing the elastic wave. In this work we propose a laser feedback interferometry (LFI) based system as a cost effective, non-contact, alternative to a well established laser Doppler vibrometer technique. We demonstrate the visualization of the elastic waves, using an example of an elastic wave propagating through a prismatic acrylic rod. We show that the ultra-compact and simple implementation of LFI enables accurate visualization of the elastic waves in solids, and opens the pathway to a range of new opportunities in ultrasonic non-destructive testing and evaluation.
... Compared with the traditional interferometer, SMI has the advantages of simplicity, compactness and low cost [5][6][7][8]. It has been applied in the fields of fault diagnosis [9], real-time hole depth monitoring [10], integrated pressure sensors [11], human pulse detection [12], and human skin vibration detection [13]. ...
The self-mixing interference (SMI) signal carries the information of the external moving object, which has great physical significance and application prospects for extracting and analyzing the information of the external object. In this paper, we propose a vibration measurement method based on a reverse point recognition algorithm on the SMI laser signal. By extracting and analyzing the hill and valley values of the SMI signal to determine the reverse point, combined with the semifringe counting method, the vibration information of external objects can be accurately extracted. The method we propose simplifies the displacement reconstruction process with high accuracy. The simulation and experimental results show that this method can achieve high-precision measurements of microvibration with an absolute error of less than 19 nm.
... Compared with typical interferometers, the LFI provides a single and self-aligned apparatus used with a diffusive target [28] . Furthermore, there is only one optical axis that can be easily controlled for beam alignment. ...
... The number of fringes was due to the magnitude of the PZT displacement controlled by the amount of the driver voltage. In this experiment, we measured the phase shift based on the fringes with respect to the sinusoidal input signal due to the different concentrations detected by the LFI SPR [28] . ...
This work reports a phase-interrogated surface plasmon resonance sensor based on a laser feedback interferometer to detect a small refractive index change. The laser feedback interferometer technique is introduced to demonstrate the sensing technique's performance, which offers several inherent advantages, such as compact, optically self-aligned, and high accuracy measurement. Moreover, this technique doubles the interrogating light beam propagation to the solution under the test, leading to an improvement of intrinsic sensitivity measurement up to two-fold. The proposed technique was characterized, and the performance was compared to another phase-interrogated surface plasmon resonance (SPR) based on the Mach-Zehnder interferometer. Laser feedback interferometer SPR has shown significant improvement to the performance parameter under test, namely sensitivity, drift, repeatability, and resolution.
... However, the calculations involve a combination of Fourier and inverse Fourier transformations, which requires a long time to calculate. Rakic et al. have demonstrated the viability of using the SMI technique with a customized EOM as a transducer to detect the electrocardiographic signals on surface skin [20], and they suggested directions for future optimization of the EOM for improved SNR and system gain. The group of Rakic also worked out a concise algorithm for arbitrary feedback levels [21], which was used in our paper on the simulation process. ...
A new self-mixing interferometry quadrature demodulation method based on a lock-in amplifier technique is proposed. Sinusoidal phase modulation of the beam is obtained by an electro-optic modulator (EOM) in the external cavity. Then the real phase of the external target can be calculated by lock-in amplifier analysis method. In this paper, the validity of the proposed method is confirmed by theoretical analysis and means of simulated signals, and then it is demonstrated by several experimental measurements for target harmonic and arbitrary motion. The results show that the proposed method can get a high-precision measurement, even using a diffusive target.
... OFI (Optical Feedback Interferometry) is a very simple interferometric sensing technology based on the optical feedback effect in lasers. It was early proposed to measure displacement [10], [11], velocity [12]- [15] and vibration [16], [17]. Its principle 2 is the following: a part of the emitted laser beam reflected or scattered by a distant target re-enters the laser cavity where it interacts with the initial laser free-running light. ...
... a rotating mirror was used to apply 2D scan on the skin. Human retina blood 12 perfusion can be measured by a SLDV scheme of a spatial resolution of up to 10μm and a temporal resolution of 2 s for a scan of 256 × 64 pixels [31]. Besides blood velocity or perfusion diagnostics, SLDV can be also used in the diagnosis of burn depth. ...
... 12. 3D reconstruction of the flow field in a micro-scale T-joint mixer where the flow is laminar (Re = 120) assessed by µPIV measurement. ...
Optical feedback interferometry (OFI) is an emerging sensing technique which has been studied in fluidic systems. This sensing scheme is based on the modulation of the laser emission output power and/or the junction voltage induced by the interaction between the back-scattered light from a distant target and the laser inner cavity light. Thanks to the Doppler Effect, OFI can precisely measure the velocity of seeding particles in flowing liquids which is much required in chemical engineering and biomedical fields. In the present thesis, optical feedback interferometry performance for microscale flow sensing is studied theoretically and experimentally. A new numerical modeling approach based on multi-physics numerical simulations for OFI signal simulation in the micro-scale flowmetry configuration is presented that highlight the sensor performances. In this model, many factors are involved such as particle concentration and laser-particle scattering angle distribution and flow velocity distribution. The flow rate measurement shows good agreement with the modeling. The implementation of OFI based sensors in multiple fluidic systems, investigating the impact of the fluidic chip specific configuration on the sensor signal.Finally, a compact OFI flowmetry sensor based on Vertical-Cavity Surface-Emitting Lasers (VCSELs) using micro optical fabrication techniques is demonstrated as well. The simulation method for the design and the microfabrication procedures are detailed. After an evaluation of the experimental results, the capabilities of this new OFI sensor in microfluidic measurements are emphasized, thus demonstrating an open path towards ultra-compact microfluidic systems based on the OFI sensing technique.
... The changing of propagation wave through the EO modulator opens the opportunity to be utilized as sensing instruments. The EO modulator in sensing technologies has a potential to be viably developed as a practical, distinctive method adopted to detect electric fields [4] and bio-potential signals [5]. Optical sensing solutions in biomedical applications have an innate advantage of immunity to both RF and magnetic field interference. ...
... In specific, the optical sensing shows an alternative choice for the sensing of surface bio-potentials, where there is the existence of electromagnetically noisy environments or safety requirements that entail a high level of galvanic isolation in those circumstances. Although, the optical properties, particularly low signal amplitude and high source impedance of typical bio-potentials have provided optical transduction an unfamiliar sensing method [5]. The complexity of directly measuring myocardial signals from the skin surface using the optical technique is compounded because of the amplitude of the bio-potential noted from the cardiac activity is extremely low (being in the 10 s of V range). ...
Electro-optic (EO) modulator is used commonly in optical communication systems. Extensive research has being carried out to optimize the device by improving its design and making use of novel waveguide materials. For bio-sensing applications, optimizing the device to be able to operate in low frequency and low input voltage (half-wave voltage) are substantial. This paper discusses the ability of a selection of EO modulator materials and waveguide designs to increase the modulator's sensitivity by enhancing the value of the EO coefficient and reduce the half-wave voltage needed to modulate the input signal. EO phase modulator with a proper polymer material will produce better results compared to LiNbO3 in terms of length extension and low insertion loss. Furthermore, we show the performance study of a EO polymer phase modulator compared with the LiNbO3 waveguide to gain lower length extension as well low insertion loss. Those parameters are essential for bio-sensing applications like as biomedical tools to sense the response of human body. As well as these parameters are important to design an EO phase modulator that is feasible for measuring bio-potential signal of a human body in biomedical applications.
... The changing of propagation wave through the EO modulator opens the opportunity to be utilized as sensing instruments. The EO modulator in sensing technologies has a potential to be viably developed as a practical, distinctive method adopted to detect electric fields [4] and bio-potential signals [5]. Optical sensing solutions in biomedical applications have an innate advantage of immunity to both RF and magnetic field interference. ...
... In specific, the optical sensing shows an alternative choice for the sensing of surface bio-potentials, where there is the existence of electromagnetically noisy environments or safety requirements that entail a high level of galvanic isolation in those circumstances. Although, the optical properties, particularly low signal amplitude and high source impedance of typical bio-potentials have provided optical transduction an unfamiliar sensing method [5]. The complexity of directly measuring myocardial signals from the skin surface using the optical technique is compounded because of the amplitude of the bio-potential noted from the cardiac activity is extremely low (being in the 10's of μV range). ...
Electro-optic (EO) modulator is used commonly in optical communication systems. Extensive research has being carried out to optimize the device by improving its design and making use of novel waveguide materials. For bio-sensing applications, optimizing the device to be able to operate in low frequency and low input voltage (half-wave voltage) are substantial. This paper discusses the ability of a selection of EO modulator materials and waveguide designs to increase the modulator's sensitivity by enhancing the value of the EO coefficient and reduce the half-wave voltage needed to modulate the input signal. EO phase modulator with a proper polymer material will produce better results compared to LiNbO3 in terms of length extension and low insertion loss. Furthermore, we show the performance study of a EO polymer phase modulator compared with the LiNbO3 waveguide to gain lower length extension as well low insertion loss. Those parameters are essential for bio-sensing applications like as biomedical tools to sense the response of human body. As well as these parameters are important to design an EO phase modulator that is feasible for measuring bio-potential signal of a human body in biomedical applications.
... In addition, using advantages from the light amplification in the laser cavity where the interferences take place, OFI is sensitive to very low levels of back-scattered optical power. OFI can be considered as a consolidated and mature interferometric technique in mechatronics, typically for velocity, vibration and displacement measurements [13,14] and as an alternative method for multiple biomedical studies [15][16][17]. For a complete overview on the phenomenon and applications related to OFI, we refer the readers to a recent review [18]. ...
Optical feedback interferometry (OFI) is a compact sensing technique with recent implementation for flow measurements in microchannels. We propose implementing OFI for the analysis at the microscale of multiphase flows starting with the case of parallel flows of two immiscible fluids. The velocity profiles in each phase were measured and the interface location estimated for several operating conditions. To the authors knowledge, this sensing technique is applied here for the first time to multiphase flows. Theoretical profiles issued from a model based on the Couette viscous flow approximation reproduce fairly well the experimental results. The sensing system and the analysis presented here provide a new tool for studying more complex interactions between immiscible fluids (such as liquid droplets flowing in a microchannel).
... SMI measuring device has features such as a simple structure, easy collimation, non-contact, and easy integration. Therefore, SMI has been widely used in velocity [3,4], as well as in the measurement of vibration [5][6][7][8][9], distance [10][11][12], displacement [13][14][15][16][17], and biomedicine [18][19][20], three-dimensional imaging [21][22][23] and laser parameters [24][25][26][27], and other measuring fields. ...
We propose a novel algorithm for Multiple Self-Mixing Interferometry (MSMI). The algorithm is able to measure nanometer scale vibration by the power spectrum analysis. In the paper, the principles of the method are introduced in detail. The experimental setup has been built. The validity of the proposed algorithm was confirmed by conducting a series of experimental measurements at different reflection times, feedback factors, and vibrational frequencies using PZT as a reference. Experimental results showed that the method can quickly demodulate parameters of vibration and good correspondence between theory and experiment. The proposed algorithm, thus, furnishes nanometer measurements with a very high resolution using a self-aligned, cost effective and compact experimental setup.
... The SMI system is simpler than conventional interferometers because many optical elements, such as the beam splitter, reference mirror, and external photodetector, are not required [5]. The self-mixing phenomenon occurs when the laser beam is partially reflected by a target in an external cavity and mixed with the light inside the laser cavity, which results in variation in emitted power and lasing frequency [6]. Information about the motion of the target can be deduced by an integrated phototransistor through analyzing the variation. ...
To accurately extract absolute distance information from a self-mixing interferometry (SMI) signal, in this paper we propose an approach based on a particle swarm optimization (PSO) algorithm instead of frequency estimation for absolute distance. The algorithm is utilized to search for the global minimum of the fitness function that is established from the self-mixing signal to find out the actual distance. A resolution superior to $25{\mu}m$ in the range from 3 to 20 cm is obtained by experimental measurement, and the results demonstrate the superiority of the proposed approach in comparison with interpolated FFT. The influence of different external feedback strength parameters and different inertia weights in the algorithm is discussed as well.
