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State-of-the-art super-resolution microscopy techniques, including Stimulated Emission Depletion (STED), Reversible Saturable Optical Fluorescence Transitions (RESOLFT), and Switching Laser Mode (SLAM) microscopies, implement Laguerre-Gaussian beams, also known as vortex or doughnut beams to capture fluorescence information within a sub-wavelength area of the observed sample, effectively surpassing the diffraction limit and significantly improving the quality of the image. However, these techniques typically operate at point by point basis, involving time-consuming scanning of the sample to construct a complete, meaningful image. Therefore, for real-time live cell imaging purposes, the parallelization of illumination is crucial. In this study, we demonstrate the parallel generation of arbitrary arrays of Gaussian and Laguerre-Gaussian laser foci suitable for super-resolution microscopy. We achieve rapid scanning through the sample using acousto-optic spatial light modulation, a technique we have previously pioneered across various fields. By employing parallelized illumination with both Gaussian and doughnut beams, we aim to capture super-resolution images.

We investigated the strength of acousto-optical (AO) interaction in one-dimensional fishbone silicon nanobeam computationally. The structure can generate phononic and photonic band gaps simultaneously. We use defect cavity optical mode and slow light mode to interact with acoustic defect modes. The AO coupling rates are obtained by adding the optical frequency shifts, which result from photo-elastic effect and moving-boundary effect disturbances. The AO coupling rates are strongly dependent on the overlap of acoustic and optical mode distribution. The strength of AO interaction can be enhanced by choosing certain acoustic defect modes that are formed by the stretching of wings and that overlap significantly with optical fields. [ABSTRACT FROM AUTHOR]

Abstract This paper introduces a planarisation SiO2 layer into the configuration of ZnO‐silicon‐on‐insulator for constructing an acoustical resonant cavity to enhance the acoustic density on a silicon‐on‐insulator waveguide. The improved configuration with a planarisation SiO2 layer can increase the acousto‐optical interaction by about three times and 20% compared with acousto‐optical configuration of ZnO pads only in an interdigital transducer region and all over a silicon on insulator. Moreover, an introduction of a planarisation SiO2 layer can reduce acoustic reflection on optical waveguide and optical waveguide loss for an acousto‐optical device on silicon‐on‐insulator optical waveguides.

Ultrasound detection via silicon waveguides relies on the ability of acoustic waves to modulate the effective refractive index of the guided modes. However, the low photo-elastic response of silicon and silica limits the sensitivity of conventional silicon-on-insulator sensors, in which the silicon core is surrounded by a silica cladding. In this paper, we demonstrate that the sensitivity of silicon waveguides to ultrasound may be significantly enhanced by replacing the silica over-cladding with bisbenzocyclobutene (BCB)-a transparent polymer with a high photo-elastic coefficient. In our experimental study, the response to ultrasound, in terms of the induced modulation in the effective refractive index, achieved for a BCB-coated silicon waveguide with TM polarization was comparable to values previously reported for polymer waveguides and an order of magnitude higher than the response achieved by an optical fiber. In addition, in our study, the susceptibility of the sensors to surface acoustic waves and reverberations was reduced for both TE and TM modes when the BCB over-cladding was used.

We investigated the strength of acousto-optical (AO) interaction in one-dimensional fishbone silicon nanobeam computationally. The structure can generate phononic and photonic band gaps simultaneously. We use defect cavity optical mode and slow light mode to interact with acoustic defect modes. The AO coupling rates are obtained by adding the optical frequency shifts, which result from photo-elastic effect and moving-boundary effect disturbances. The AO coupling rates are strongly dependent on the overlap of acoustic and optical mode distribution. The strength of AO interaction can be enhanced by choosing certain acoustic defect modes that are formed by the stretching of wings and that overlap significantly with optical fields.

Abstract Imaging spectrometers for atmospheric detection usually split the beam by using prisms or gratings. However, owing to their spectroscopic principle, these spectrometers can only detect the atmosphere via single mode and single detection. The acousto-optic tunable filter (AOTF) is an electronic filter developed based on the acousto-optic effect of crystal with a field of view that is not limited by the slit. This paper introduces the spectroscopic principle of the AOTF and deduces its diffraction equation. By using the AOTF as a spectroscopic device, this paper also designs a new imaging spectrometer for atmospheric detection. This spectrometer has two fields of view and can detect the hyperspectral atmospheric data in 10°nadir field of view, 360°limb field of view, and 0 km to 100km limb height. The optical system of this imaging spectrometer comprises a front objective lens, an AOTF spectroscopic system, and a relay lens. As an instrument for atmospheric, this spectrometer has the characteristics of dual observation modes, full coverage in the limb field of view, and high spectral resolution. [ABSTRACT FROM AUTHOR]

Hafnium diboride (HfB2) is used in hypervelocity re-entry vehicles (such as intercontinental ballistic missile (ICBM) or ICBM heat shields), nuclear reactors and aerodynamic leading edges because of its strong tensile strength and high thermal resistance. HfB2 is an ultra-high-temperature ceramic (UHTC) with a melting point of 3250°C. In this paper, we study the performance of HfB2 as a saturable absorber in Q-switched lasers. HfB2 has a non-saturable absorptance of 2.5 dB/µm, a saturable absorptance of 0.8 dB/µm and a saturation fluence of 12 µJ/cm2. In addition, the saturation lifetime is estimated as 989.3 ps, while the recovery lifetimes are estimated as 254.9 and 22.1 ps. As a saturable absorber in our Q-switched laser, we observed pulses with durations between 880 and 2000 ns. With the addition of an acousto-optic modulator, we have observed Q-switching mode-locking, with pulses as low as 250 ns. HfB2 can potentially work at very high power, since its damage fluence is no less than 361 mJ/cm2. [ABSTRACT FROM AUTHOR]

The interaction between longitudinal acoustic waves and fiber Bragg gratings in suspended-core optical fibers is numerically investigated. The fiber core size and the air hole size are varied, and the mechanical and grating properties are simulated by means of the finite element method and the transfer matrix method, respectively. Changes of the effective index, confinement factor, silica area, strain and wavelength shift induced by the acoustic wave are evaluated, and the resultant side lobe reflectivity is estimated. A side lobe reflectivity increase of 66% compared to standard fibers is estimated, which allows reducing the modulation index or the grating length in as much as 75%. Besides, the larger reduction of the required acoustic power for achieving the acousto-optic modulation points out to more efficient modulator devices in suspended-core fibers. [ABSTRACT FROM AUTHOR]

This study reports on the demonstration and characterisation of a short cavity fibre Fabry‐Perot resonator (FPR) for the detection of ultrasonic waves propagating through a solid medium over a frequency range of 1 kHz–10 MHz. The proposed sensing device has some outstanding features in terms of simple fabrication technique, frequency response and high sensitivity over a wide frequency range. The response of the surface‐mounted FPR sensor showed good agreement with that of a commercially available piezoelectric transducer during ultrasonic excitation. [ABSTRACT FROM AUTHOR]

Problems associated with the demodulation and localization of acoustic signal produced by fiber optic interferometer are investigated. It is shown that existing demodulation method utilizing 3 × 3 fiber coupler do not work well for that the acoustic signal cannot reach the full amplitude of the sensor to compensate the dc and normalize the amplitude. Modifications to improve the performance of the previously proposed demodulation method are suggested. After the demodulation, two phase difference signals are received to have two signals with fixed time delay based on a unique data processing method, and hence, the position of the disturbance can be measured by the signal correlation method to extract the time delay. Operation of the modification of the demodulation method is verified experimentally along a 20-km-long sensing fiber with the minimum detectable phase signal closed to the noise equivalent phase (NEP) (0.2 rad). The performance of the sensor is also compared with the conventional sensor, based on the null frequency of the spectrum of the phase difference generated by the acoustic disturbance. Experimental results show that the sensor is advantageous for easy installation, low location error, and flexibility for the application of acoustic localization. [ABSTRACT FROM PUBLISHER]

This paper reports a vector Brillouin optical time-domain analyzer based on heterodyne detection and IQ demodulation algorithm. This approach employs an acousto-optic frequency shifter to generate a single-frequency reference, which simplifies the probe spectrum and directly features the Brillouin gain and phase shift compared with the phase modulation. In addition, the proposed IQ demodulation algorithm makes signal processing easy to implement and allows fast and real-time demodulation. A proof-of-concept experiment is carried out in an ~1.6-km standard single-mode fiber consisting of two different sections of fibers. Both the Brillouin gain and phase-shift spectrograms are successfully measured with an ~2-m spatial resolution. The temperature dependence values of the Brillouin gain and phase-shift spectra are also measured, and the temperature dependence values of the Brillouin frequency shift show excellent linearity larger than 0.999 and almost identical slopes of 1.166 and 1.159 MHz/°C, respectively. [ABSTRACT FROM PUBLISHER]

Abstract: We propose and demonstrate a simple and cost effective non-membrane optical microphone (OM) consisting of only a standard erbium doped fibre amplifier (EDFA) and a 25km of conventional single mode fibre (SMF) as the sensing medium. A photo detector is used for data acquisition. The proposed setup utilizes the disturbances in the competing longitudinal modes in a low reflectivity fibre resonator whereby airborne acoustic waves impacting the surface of the fibre will modulate the intensity of the optical signal in the fibre. This modulation frequency is analyzed using the fast fourier transform (FFT) technique to extract the information embedded in the optical signal. The experiment shows that the system is capable of picking up the airborne acoustic waves and can find many potential applications. [Copyright &y& Elsevier]

A programmable broadband Radio Frequency (RF) filter is designed using a Digital Micromirror Device (DMD), an Acoustooptic Tunable Filter (AOTF), and a Chirped Fiber Bragg grating (CFBG). This hybrid analog-digital optical design enables implementation of RF filters with higher number of taps in comparison with an AOTF-only RF filter design and improved RF tunability in comparison with a DMD-only design. A 3-tap RF filter is theoretically analyzed and experimentally demonstrated using a combination of analog and digital optical tap selection. Filter nulls recorded at 6.90, 6.945, and 6.99 GHz show the tunability improvement with the hybrid design. Implementation of higher tap count filters can lead to similar improvements in filter tunability and pass-band and stop-band characteristics. [ABSTRACT FROM PUBLISHER]

A new high-performance 2 x 2 fiber-optic switch is designed and demonstrated for wideband radar photonic beamforming controls. The switch deploys two bulk acoustooptic deflectors (AODs) in an imaging free-space symmetric optical design that exploits image inversion control via a Dove prism to form a 2 X 2 fully reversible low crosstalk noise high-speed switching structure. Experiments at the 1550-nm test wavelength show the switch to handle 0.5-W level optical input powers, < 2.2-mus switching time, <2.6-dB fiber-to-fiber optical loss, better than 56-dB optical crosstalk levels, and <0.2-dB polarization-dependent loss (PDL).and <0.2-dB polarization-dependent loss (PDL). Index terms-delay lines, optical switches, phased-array radar. [ABSTRACT FROM PUBLISHER]

This paper gives a review of acoustic and ultrasonic optical fiber sensors (OFSs). The review covers optical fiber sensing methods for detecting dynamic strain signals, including general sound and acoustic signals, high-frequency signals, i.e., ultrasonic/ultrasound, and other signals such as acoustic emissions, and impact induced dynamic strain. Several optical fiber sensing methods are included, in an attempted to summarize the majority of optical fiber sensing methods used to date. The OFS include single fiber sensors and optical fiber devices, fiber-optic interferometers, and fiber Bragg gratings (FBGs). The single fiber and fiber device sensors include optical fiber couplers, microbend sensors, refraction-based sensors, and other extrinsic intensity sensors. The optical fiber interferometers include Michelson, Mach-Zehnder, Fabry-Perot, Sagnac interferometers, as well as polarization and model interference. The specific applications addressed in this review include optical fiber hydrophones, biomedical sensors, and sensors for nondestructive evaluation and structural health monitoring. Future directions are outlined and proposed for acousto-ultrasonic OFS. [ABSTRACT FROM PUBLISHER]

Abstract: We report a new acousto-optic arrangement based on ultrasonic wave with cylindrical symmetry. The theory of light interaction with standing cylindrical ultrasonic wave is experimentally verified in the Fraunhofer region. A very good agreement of experimental results with numerical calculations based on the proposed theory is found. The diffraction pattern consists of ring-shaped diffraction orders which posses a fine structure. The time average light intensity of the whole zeroth diffraction order as a function of the Raman–Nath parameter is investigated. The modulation properties of presented system are examined by means of single photon counting technique. Finally, some potentially useful applications in the laser and fibre technology are suggested. [Copyright &y& Elsevier]

As optical systems approach high speed and long distances, dispersive effects [chromatic dispersion (CD) and polarization-mode dispersion (PMD)] can severely distort optical signals in the transmission link. It is important to dynamically monitor the dispersive effects in order to achieve high performance. We propose a method for dispersive effects monitoring by adding a frequency-shifted carrier along the orthogonal polarization and measuring the generated radio frequency (RF) clock power. Using this technique, PMD monitoring is isolated from CD effect and the CD information can be simultaneously obtained. We experimentally demonstrate this technique in a 10 Gb/s return-to-zero (RZ) system by adding an orthogonal frequency-shifted carrier using an acoustooptic (AO) shifter. [ABSTRACT FROM PUBLISHER]

In this paper, the first fiber-coupled no-moving-parts scanning heterodyne interferometer design using a single acoustooptic device (AOD) is reported. The design features a high-stability inline reflective architecture with free-space-scanned minimally invasive sensing via a multizone reflective sensor chip. The common path fiber interconnection allows robust remoting of the compact sensing front end. A proof-of-concept sensing experiment measuring voltage-dependent birefringence is successfully conducted using a voltage-controlled nematic liquid crystal (NLC) sensor chip. The system features a 4.69-dB optical loss, a 200-MHz output frequency, and a 1550-nm eye-safe operation wavelength. Applications for the system include any fiber-remoted sensing using the proposed free-space minimally invasive interrogating optical beams. [ABSTRACT FROM PUBLISHER]

Abstract: This paper describes a novel multi-point laser Doppler velocimeter. By employing two acousto-optic modulators (AOMs) for both beam splitting and frequency shifting, we have demonstrated that multiple measuring volumes can be formed by intersecting the multiple diffraction orders generated by the AOMs. Each measuring volume has its frequency shift, which acts as a carrier frequency to that channel. Since the signals from different channels are multiplexed in the frequency domain, only a single photo-detector and a single-channel signal processor are necessary for multi-point measurements. The system has been demonstrated by making multi-point velocity measurements on a rotating disk. [Copyright &y& Elsevier]

A new technique has been developed that permits coherent processing of backscatter data acquired by a radar system transmitting ultrawideband (UWB) random noise waveforms and processing the received signals using a heterodyne correlation receiver. This technique has been used in various applications, such as Doppler estimation, polarimetry, interferometry, buried-object detection, synthetic aperture radar (SAR) imaging, inverse SAR (ISAR) imaging, foliage penetration imaging, etc. One of the major advantages of the noise radar system is its inherent immunity to external interference. In such a radar system, the correlation receiver consists of a programmable variable-delay line, a mixer followed by a lowpass filter. One drawback of this type of receiver is that it sequentially processes the target returns, thus limiting the system response time and the dynamic detection range. We have recently integrated a novel heterodyning acoustooptic (AO) time-integrating correlation receiver that uses a traveling-wave AO deflector for wideband signal processing. The transmit waveform modulates the intensity of a laser diode that is multiplied by the traveling-wave modulation produced by the AO deflector, and the correlation is time-integrated on a charge-coupled device photodetector array. The principal advantages of this AO correlation receiver are its ability to generate a large range of variable delays, as well as to perform the signal correlation operation in parallel. Compared to the conventional sequential correlation receiver using a variable stepped delay line and correlator, implementation of the AO variable-delay line and heterodyning correlator can 1) reduce the processing time and greatly increase the processing gain due to the parallel correlation mechanism and 2) greatly increase the number of range cells depending on the number of resolvable spots of the AO deflector. This results in rapid data acquisition, longer integration time on parallel detector pixels (3000 pixels), and improved SNR. It is also shown that this radar has more range gates (up to 1000), which ultimately improves the detectable range resolution. Furthermore, several field experiments performed with different target arrangements demonstrate that the acoustooptic variable-delay line and c- orrelator is able to profile various targets instantaneously and with very high SNR. [ABSTRACT FROM PUBLISHER]

In this paper we present an accurate and efficient numerical method for a rigorous full-wave analysis of interdigital transducers (IDT) for the excitation of surface acoustic waves on the piezoelectric substrate of acousto-optical devices. The problem is formulated in terms of an integral equation that is solved by the method of moments. The transducer input admittance and the power coupling factors to both surface and bulk waves are computed. Numerical results for some configurations of X- Y LiNbO3 IDT for acousto-optic applications are in very good agreement with measured data. It is pointed out that bulk wave excitation may be a serious limitation in the design of efficient, wide band transducers for acousto-optical devices. [ABSTRACT FROM AUTHOR]

The acousto-optic mode coupling in grapefruit microstructured optical fibers (GMOFs) has been investigated. Due to the presence of grape-like large air holes in the fiber cladding, unequal acoustic modulation is generated, and orthogonal acoustic gratings come into being in the GMOF, which is verified by our experimental observation on the mode profile of resonance peaks. The experimental results indicate that two resonance peaks originating from the mode coupling in acoustic-birefringence-induced orthogonal acoustic gratings simultaneously exist in the transmission spectrum, and the wavelength spacing between them reaches as large as 227.4 nm, which indicates that a greatly enhanced acoustic birefringence has been introduced in the GMOF. And moreover, some important grating features, including frequency-dependent grating period, frequency responses of acoustic phase velocity, and acoustic dispersion, have been investigated for the orthogonal acoustic gratings. These studies would be of importance for understanding the acoustic birefringence mechanism in MOF-based acoustic gratings and development of related acousto-optic devices.

This paper presents the design and the realization of a novel integrated Mach-Zehnder interferometer (MZI) with heterodyne scheme. Well-controlled machining as well as ZnO thin-film transducer integration on the same Si substrate permits to transform an optically passive device to an active device with sinusoidal phase modulation. Theoretical and experimental results are presented, demonstrating that an efficient sensor can be designed and fabricated [ABSTRACT FROM PUBLISHER]

We demonstrate an optical heterodyne spectroscopy on the reflection of an etalon using a double-pass acousto-optics frequency shifter. The experiment setup is a modified Michelson interferometer using the double-pass acousto-optics frequency shifter as the beam splitter and one etalon as the end mirror. Without using frequency modulation, the dispersion-like signal of the etalon reflection was successfully observed and optimized. Using the dispersion-like signal as an error signal, we locked a 780-nm external cavity diode laser to one resonant mode of the etalon. The estimated relative stability was ~2.6 × 10-10 in 0.16-s integration time. [ABSTRACT FROM PUBLISHER]

We demonstrate a narrow-bandwidth acoustooptic tunable filter with very low polarization-sensitivity using a dispersion-compensating fiber that has a large group index difference between the core and the cladding modes with a specific stress distribution. The 3-dB bandwidth of the filter is 0.8 nm with the interaction length of 10 cm, and the polarization-dependent center-wavelength splitting is 0.04 nm at the wavelength around 1550 nm. The origin of the low polarization-dependence is successfully explained through the analysis on the stress field in the fiber. [ABSTRACT FROM PUBLISHER]

We report a demonstration of a large-scale remotely interrogated remotely pumped fiber-optic, interferometric sensor array. The system is designed primarily for underwater acoustic applications where each sensor is configured as a hydrophone and a large number of sensors (i.e., up to ∼500) are required to be interrogated through link lengths of several tens of kilometers. A system comprising of 96 sensors combined using time and dense wavelength-division multiplexing and interrogated through a 40-km fiber link is demonstrated. A remotely pumped erbium-doped fiber amplifier is incorporated into the array to increase the distance between the array and interrogation electronics. We describe the performance of our system and validate a previously published model. [ABSTRACT FROM PUBLISHER]

This letter describes experimental observations of excess noise due to coherent double Rayleigh scattering in the input fiber of a remotely interrogated fiber-optic interferometric sensor. This noise source is generally only observable when a high coherence length laser is used to interrogate the sensor and the fiber length connecting the sensor is in excess of ∼10 km. We present a simplified model to explain how this noise source affects the sensor resolution and demonstrate a method based on laser source modulation to reduce this noise by ∼20 dB in a fiber-optic Michelson interferometric sensor with a 25-km input fiber, at frequencies less than 10 kHz. [ABSTRACT FROM PUBLISHER]

A novel broad-band variable optical attenuator is realized using acoustooptic mode coupling on a cladding etched single-mode fiber. Broad-band coupling bandwidth with low attenuation ripples is achieved by matching both the group index and dispersion parameter between the core and the LP11cl cladding modes. A single-section device exhibits a 10-dB dynamic range with attenuation ripples of <0.5 dB over a spectral range of >100 nm, a response time of 20 μs, an insertion loss of 0.3 dB, and a maximum power consumption of only 3.4 mW. Attenuation of 22 dB is obtained for a cascaded two-section device [ABSTRACT FROM PUBLISHER]

For the first time, a >65-dB dynamic range fast 2.8 μs fiber-optic variable optical attenuator is proposed and demonstrated by using a single bulk acoustooptic device. The unique double-pass optical design eliminates intrinsic acoustooptic interaction-based Doppler shift, while a center path positioned halfwave plate greatly reduces polarization dependent loss to 0.03 dB. The current attenuator's insertion loss is <2.5 dB with a demonstrated 1520-1600 nm operation. Due to its bulk crystal nature, this attenuator can handle high power optical beams [ABSTRACT FROM PUBLISHER]

We report the fabrication and characterization of a one-dimensional acoustic cavity made on a tapered single-mode optical fiber with two acoustic mirrors. The mirrors are acoustic Bragg gratings formed by modulating the fiber diameter periodically. The cavity exhibits resonances with quality factors of around 300. Higher Q factors are achievable by increasing the number of periods in the gratings. A simple transfer matrix model successfully simulates the acoustic properties of the cavity. This type of acoustic cavity is of interest for its potential applications in acoustooptic components and the development of devices based on stimulated Brillouin scattering [ABSTRACT FROM PUBLISHER]

A novel variable optical attenuator (VOA) is introduced that can provide high dynamic range and high-resolution all at fast submicrosecond speeds. The VOA design exploits an in-line one-to-one imaging optical architecture operating with Bragg-mode acoustooptic Bragg cells. Optical attenuation is achieved via frequency and drive voltage control of the Bragg cells, leading to flexible and precise attenuation-level settings. VOA demonstrated a 45-dB dynamic range with a 175-ns switching time. Other measured parameters include 1.14-dB/MHz resolution, 1.56-dB polarization dependent loss, and an excess loss of 3.55 dB [ABSTRACT FROM PUBLISHER]

With the aim of making a tensile-strain sensor or a temperature sensor based on depolarized guided acoustic-wave Brillouin scattering (GAWBS), we experimentally investigate the effect of tensile strain applied to a fiber. We pay our attention to the resonance frequency of depolarized GAWBS by the TR25 mode of the acoustic wave. By unjacketing the fiber, the peak level of the resonance spectrum increases and the full-width at half-maximum narrows to 500 kHz, which increases the accuracy of measurement. The experimentally obtained tensile-strain coefficient is 1.8. On the basis of our experimental results, we discuss the way to apply depolarized GAWBS to a tensile-strain sensor or a temperature sensor [ABSTRACT FROM PUBLISHER]