Acousto-optic Transducer Research Articles

Beyond GHz optical frequency up-converted modulation of LEDs with integrated acousto-optic transducer.

Traditional visible light communication (VLC) via light-emitting diodes (LEDs) employs the on-off keying (OOK) modulation scheme. Even though optical frequency modulation has many advantages, it is hardly used for LED VLC because a high carrier frequency cannot be applied to the LED cavity due to the resistance-capacitance limit. Here, by monolithically integrating an LED with an integrated digital transducer, we experimentally demonstrate the intermixing of gigahertz surface acoustic waves and electrical data signals in the LED cavity at room temperature. An optical transmitter was realized by in situ frequency up-conversion of the data signals from an LED, which has the advantages of improving transmission performance by up-shifting the data spectrum away from low-frequency noise. Our proposed integrated acousto-optic transducer opens a new developing scheme on the frequency up-mixed data encoding of an LED beyond its inherent modulation bandwidth for future VLC.

Gigahertz Optomechanical Photon-Phonon Transduction between Nanostructure Lines.

High-frequency surface phonons have a myriad of applications in telecommunications and sensing, but their generation and detection have often been limited to transducers occupying micron-scale regions because of the use of two-dimensional transducer arrays. Here, by means of transient reflection spectroscopy we experimentally demonstrate optically coupled nanolocalized gigahertz surface phonon transduction based on a gold nanowire emitter arranged parallel to linear gold nanorod receiver arrays, that is, quasi-one-dimensional emitter-receivers. We investigate the response up to 10 GHz of these individual optoacoustic and acousto-optic transducers, respectively, by exploiting plasmon-polariton longitudinal resonances of the nanorods. We also demonstrate how the surface phonon detection efficiency is highly dependent on the nanorod orientation with respect to the phonon wave vector, which constrains the symmetry of the detectable modes, and on the nanorod acoustic resonance spectrum. Applications include nanosensing.

Development of highly sensitive fiber-optic acoustic sensor and its preliminary application for sound source localization

A metal diaphragm-based omnidirectional fiber-optic acoustic sensor with high sensitivity has been developed in this work. The acousto-optic transducer of the sensor is a single-wavelength extrinsic Fabry–Pérot interferometer (EFPI) that is highly sensitive to the displacement of the diaphragm’s center. The sensor can stably work in the linear response region of the EFPI in a wide range of temperature from −20 to 60 °C. The pressure sensitivity of the sensor is larger than 800 mV/Pa, and the sensitivity fluctuation in the frequency range from 100 Hz to 6 kHz is smaller than 3 dB. The noise-limited minimum detectable pressure obtained at 1 kHz of the sensor is 126 μPa/Hz1/2. In addition, the above-prepared fiber-optic acoustic sensors present excellent phase consistency with each other, which facilitates the formation of a sensor array for sound source localization. In this work, a cross-shaped fiber-optic sensor array was prepared and then used to detect and track a small drone flying in the field. The experimental results show that the sensor array can capture the acoustic fingerprint of the drone at a distance as far as 300 m. This detection distance is more than ten times longer than that of a conventional electret condenser microphone. The azimuth angle of the drone obtained with the fiber-optic acoustic sensor array has a deviation of smaller than 10° relative to the GPS data from the drone.

Low-Frequency Bi-Directional Microphone Based on a Combination of Bionic MEMS Diaphragm and Fiber Acousto-Optic Transducer

This paper reports on a fiber-optic directional microphone with a bionic MEMS diaphragm for low-frequency sound source localization. The diaphragm consists of two 3 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times3$ </tex-math></inline-formula> mm wings connected by a 1 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times1$ </tex-math></inline-formula> mm bridge, and two 0.2 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.1$ </tex-math></inline-formula> mm torsion beams anchor the diaphragm to the Silicon-On-Insulator (SOI) frame along the bridge’s central axis. The bridge causes the mechanical coupling between the two wings, resulting in rocking and bending vibration modes of the diaphragm. The designed microphone contains a closed back cavity and works by measuring vibration at one of the diaphragm’s distal edges by a fiber-optic Fabry-Perrot interferometer (FPI). Simulation and experimental results demonstrated that the microphone can make a significant directional response in a wide low-frequency band centered on the rocking-mode eigenfrequency, giving a typical bi-directional polar pattern, but its directionality disappears at the bending-mode eigenfrequency. The directional sensitivity of the microphone was determined to be 1.86 mV/° at 300 Hz based on the measured linear response to the incident angle in an angular range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta =0$ </tex-math></inline-formula> to 60°. The minimum detectable pressure (MDP) of the microphone relies on both the incident angle and sound frequency, and MDP was measured to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12.68\mu $ </tex-math></inline-formula> Pa/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula> Hz at 300 Hz and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta = 100^{\circ }$ </tex-math></inline-formula> . The fiber-optic FPI serving as the acousto-optic transducer offers the directional microphone high sensitivity and strong immunity to electromagnetic interference, rendering it suitable for low-frequency sound source localization in harsh environments, especially for tracing the environmental noise sources.

Underwater Acoustic Signal Detection and Down-Conversion Using Optomechanical Resonance and Oscillation

We have studied the performance of optomechanical resonators and oscillators as high sensitivity underwater acousto-optical receivers and signal processors. In the absence of optomechanical oscillation, optomechanical resonator functions as a very sensitive acousto-optical transducer with low-power consumption. In the presence of optomechanical oscillation we show that optomechanical oscillator can simultaneously function as an acousto-optical transducer and frequency down-converter that extracts the IF or baseband signal from an ultrasonic carrier without the need for RF local oscillator and mixer.

Application of the flexoelectric effect in liquid crystals to create acousto-optic transducers

The flexoelectric effect in nematic liquid crystals was studied using acoustic modulation spectroscopy. A cell consisting of three plates separated by spacers was used. The movable plate made shear oscillations in the plane of the cell. We studied thin layers of liquid crystals with homeotropic orientation of molecules with a thickness of from 20 to 100 microns. The frequency of exposure is 1 kHz. In the framework of the de Gennes model, near the phase transition liquid crystal - isotropic phase, the resulting signal has a flexoelectric nature and is due to a dipole mechanism. In this work, the temperature dependences of the flexosignal, the temperature effect on the value of the average constant angle of inclination (θc) and the amplitude of the oscillations of the director (θd) of a liquid crystal are investigated. The dependences of flex coefficients e33 on temperature are obtained. It was found that dipole and quadrupole mechanisms contribute to the observed molecular orientational polarization. The results of this study are proposed to be used to create liquid crystal transparencies of the new generation, as well as acousto-optic transducers for automated vibration control systems, since the use of liquid crystals provides a number of advantages (lightweight construction, low power consumption and overall dimensions, low cost).

Acousto-Optical Transducer With Optomechanical Gain

The acousto-optical response of a microtoroidal optomechanical microresonator with optically compensated damping factor is measured and analyzed. We demonstrate that the large optical quality factor combined with the enhanced acoustic response due to radiation pressure make optomechanical microresonators excellent candidates as sensitive acousto-optical transducers with extremely low power consumption.

Optical detection of acoustic waves with surface plasmons.

For broadband and sensitive detection of acoustic waves, the surface plasmon resonance (SPR) can be used, which responds to variations of dielectric properties in close proximity to a metal film supporting surface plasmon waves. When an acoustic wave is incident onto a receiving plate positioned within the penetration depth of the surface plasmons, it creates displacements of the surface of the plate and thus modulates the dielectric properties, affecting the SPR and the reflection of the incident light. Here we study characteristics and determine the optimal configuration of such an acousto-optical transducer with surface plasmons for efficient conversion of an acoustic signal into an optical one. We simulate the properties of this transducer and present estimates showing that it can have a large frequency bandwidth and high sensitivity.

Acousto-optical Transducer with Surface Plasmons

The surface plasmon resonance (SPR) is a sensitive technique for the detection of changes in dielectric parameters in close proximity to a metal film supporting surface plasmon waves. Here we study the application of the SPR effect to an efficient conversion of an acoustic signal into an optical one. Such a transducer potentially has a large bandwidth and good sensitivity. When an acoustic wave is incident onto a receiving plate positioned within the penetration depth of the surface plasmons, it creates displacements of the surface of the plate and, thus, modulates the dielectric properties in the proximity of the gold film. This modulation, in turn, modifies the light reflection under surface plasmon resonance conditions. We simulate characteristics of this acousto-optical transducer with surface plasmons and provide sets of parameters at the optical wavelength of 800 nm and 633 nm for its realization.

Quantum acousto-optic transducer for superconducting qubits

We propose theory for reversible quantum transducer connecting superconducting qubits and optical photons using acoustic waves in piezoelectrics. The proposed device consists of integrated acousto-optic resonator that utilizes stimulated Brillouin scattering for phonon-photon conversion, and piezoelectric effect for coupling of phonons to qubits. We evaluate the phonon-photon coupling rate, and show that the required power of optical pump as well as the other device parameters providing full and faithful quantum conversion are feasible for implementation with the state of the art integrated acousto-optics.

Acousto-Optic Cerebral Blood Flow Monitoring During Induction of Anesthesia in Humans.

Past transcranial Doppler (TCD) studies have documented the effects of the sequence of anesthesia induction followed by intubation on cerebral blood flow (CBF) velocity. The purpose of this study was to determine whether acousto-optic CBF monitoring would detect changes in CBF which are known to occur with propofol and subsequent endotracheal intubation. Seventy-two patients scheduled for elective non-intracranial surgery were evaluated. A Cerox 3215F (Ornim Medical) acousto-optic CBF monitor was used. The acousto-optic transducers were applied bifrontally prior to induction. Baseline cerebral flow index (CFI) values were obtained for at least 2min prior to induction, set to a unitless value of 100. Subsequent relative changes in CFI from baseline were determined at the lowest value over 3min after propofol injection but before laryngoscopy; and the highest value over 5min after the start of laryngoscopy. CFI data were evaluated using Friedman's test. The median dose of propofol [interquartile range] given was 200mg [160-250]. CFI decreased to 84% of baseline after propofol and increased to 147% of baseline after endotracheal intubation (both p<0.001); MAP decreased after intravenous induction of anesthesia from 103±15 to 86±15mmHg (p<0.001) and then returned following endotracheal intubation to 104±20mmHg. Our data are congruent with previous observations made with TCD under similar experimental conditions. Such observations support the notion that acousto-optic monitoring yields valid real-time measures of changes in CBF in humans. Further validation against other quantitative measures of CBF would be appropriate.

Ultrasonic Laser Diagnostics of Residual Stresses

The ultrasonic laser method and an instrument for the measurement of residual stresses with an inclined acousto-optical transducer (UDL-2M laser ultrasonic flaw detector) are presented. The results of experimental investigations of variations in the rate of propagation of an ultrasonic wave in samples made of steel in compression testing are presented. The results demonstrate that the method is sufficiently sensitive for the purpose of determining the stresses in a subsurface layer of the sample. External factors that tend to vary the rate of propagation of ultrasonic waves are considered.

Miniaturized fiber-optic ultrasound probes for endoscopic tissue analysis by micro-opto-mechanical technology

A new Micro-Opto-Mechanical System (MOMS) technology for the fabrication of optoacoustic probes on optical fiber is presented. The technology is based on the thermoelastic emission of ultrasonic waves from patterned carbon films for generation and on extrinsic polymer Fabry-Perot acousto-optical transducers for detection, both fabricated on miniaturized single-crystal silicon frames used to mount the ultrasonic transducers on the tip of an optical fiber. Thanks to the fabrication process adopted, high miniaturization levels are reached in the MOMS devices, demonstrating fiber-optic emitters and detectors with minimum diameter around 350 and 250 μm respectively. A thorough functional testing of the ultrasound emitters mounted on 200 and 600 μm diameter optical fibers is presented, in which the fiber-optic emitter with a diameter of 200 μm shows generated acoustic pressures with peak-to-peak value up to 2.8 MPa with rather flat emission spectra extended beyond 150 MHz. The possibility to use the presented optoacoustic sources in conjunction with the fiber-optic acousto-optical detectors within a minimally invasive probe is also demonstrated by successfully measuring the ultrasonic echo reflected from a rigid surface immersed in water with various concentration of scatterers. The resulting spectra highlight the possibility to discriminate the effects due to frequency selective attenuation in a very wide range of frequencies within a biological medium using the presented fiber-optic probes.

Noncontact optical metrologies for Young’s modulus measurements of nanoporous low-k dielectric thin films

Brillouin light scattering (BLS) and picosecond laser ultrasonics (PLU) are two noncontact optical techniques that have garnered significant interest for thin film elastic constant measurements. PLU and BLS measurements were utilized to determine the elastic constants of 100 to 500 nm thick nanoporous low-k dielectric materials of significant interest for reducing capacitive delays in nanoelectronic interconnect circuits. PLU measurements with and without a metal acousto-optic transducer are described in detail and compared to previously reported BLS measurements. The values of Young’s modulus determined by both BLS and PLU were found to be in excellent agreement and consistent with nanoindentation measurements on thicker 2 micrometer films. While successful BLS measurements were achieved for films as thin as 100 nm, PLU measurements were limited to >∼200 nm thick films due to experimental constraints on observing acoustic pulses in thinner films. However, these results clearly demonstrate the capability of both BLS and PLU to determine the elastic constants of low-k dielectric materials at the desired thickness targets for future nanoelectronic interconnect technologies.

LC acousto-optical transducer for nondestructive holographic control systems

LC acousto-optical transducer for nondestructive holographic control systems

Ways to Improve Acoustooptic Transducers Using Liquid Crystals

Ways to Improve Acoustooptic Transducers Using Liquid Crystals

THE STUDY OF EPITAXIAL GROWTH ZnO THIN FILM ON A (0112) SAPPHIRE SUBSTRATE USING ECR PLASMA SPUTTERING METHOD

Epitaxial growth of ZnO film on sapphire substrate has important applications in surface acoustic wave and acousto-optical transducers. An epitaxial ZnO film has been grown on a (0112) sapphire substrate using ECR plasma sputtering method at a substrate temperature of 380℃. The film is colourless, transparent and surface smooth. In order to explore the relationship between the deposition parameter and crystal structure of ZnO film, it have been studied that epitaxied growth of ZnO film in different substrate temperatures and deposition rates by XRD method.

Coupled waveguide acousto-optic hydrophone

Apparatus is provided for detecting the presence of acoustic signals which includes a laser source, and a detector coupled to opposite end of an acousto-optic transducer. The transducer may employ fiber optic waveguides, etched to allow evanescent coupling therebetween, and disposed within a flexible housing. Integrated and planar optic transducers are provided in various forms employing two integrated optic waveguide channels, two planar waveguides, or a planar waveguide and absorber combination. Each configuration is disposed within a flexible housing and the waveguides are separated from each other by a predetermined distance. Any flexing of the housing is transformed into a displacement of the waveguides relative to one another. The coupling between the waveguides is a very sensitive function of distance, and hence detection of variations in the energy coupled by the waveguides provides an indication of the presence of the acoustic signals.

Optical Information Processing Components

This special issue of Optical Engineering addresses a number of critical issues in the continuing invention, development, and characterization of components for optical information processing and computing applications. This is the second in an annual series of related special issues, initiated with the publication of "Spatial Light Modulators: Critical Issues" (Optical Engineering, Vol. 22, No. 6, November/ December 1983). Although the last two decades have witnessed tremendous progress in the invention and development of optical processing techniques, architectures, and algorithms, only limited optical hardware is currently available for the implementation of such concepts. As a result, extensive software and numerous system schematics exist for a multiplicity of processor configurations that in almost all cases have not proven implementable in compact systems capable of high frame rate operation. A notable exception is the excellent performance record of optical processors based on one-dimensional acoustooptic transducers. Such acoustooptic devices have gained wide use and acceptance in military and commercial sectors for applications such as spectrum analysis, signal correlation, light modulation, and laser beam scanning and steering.

Application Of The Radon Transform To Optical Production Of The Wigner Distribution Function

The Wigner distribution function (WDF), a simultaneous coordinate and frequency representation of a signal, has properties useful in pattern recognition. Because the WDF is computationally demanding, its use is not usually appropriate in digital processing. Optical schemes have been developed to compute the WDF for one-dimensional (1 -D) signals, often using acousto-optic signal transducers. Some recent work has demonstrated the computation of two-dimensional (2-D) slices of the four-dimensional (4-D) WDF of a 2-D input transparency. In this latter case, the required 2-D Fourier transformation is performed by coherent optics. We demonstrate that computation of the WDF of real 2-D signals is susceptible to Radon transform solution. The 2-D operation is reduced to a series of 1 -D operations on the line-integral projections. The required projection data are produced optically, and the Fourier transformation is performed by efficient 1 -D processors (surface acoustic wave filters) by means of the chirp-transform algorithm. The resultant output gives 1 -D slices through the 4-D WDF nearly in real time, and the computation is not restricted to coherently illuminated transparencies. This approach may be useful in distinguishing patterns with known texture direction. The optical setup is easily modified to produce the cross-Wigner distribution function, a special case of the complex, or windowed, spectrogram.