Acousto-optic Filter Research Articles

Ultra-Widely Tunable Acousto-Optic Add-Drop Filter Based on Acoustically-Induced Polarization Conversion of Single Mode Fiber

An ultra-widely tunable acousto-optic add-drop filter is proposed and demonstrated based on the acoustically-induced polarization conversion of cladding-etched single-mode fiber, which covers wavelengths from 1081 nm to 1582 nm with a tuning band larger than 500 nm. The constructed filter has reconfigurable band-pass and band-rejection filtering characteristics, and obtains the advantages of ultra-wide wavelength tuning range, fast tuning speed, simple fabrication and zero frequency shift. It has potential applications in the fields of WDM communication, ultra-wide tunable laser, signal processing, swept-source optical coherence tomography (SS-OCT) and wideband spectroscopy.

Development of a Hyperspectral System with Controlled Spectral, Spatial, and Radiometric Resolution

An approach to the construction of a hyperspectral system is proposed and justified, providing control of spectral, spatial, and radiometric (brightness) resolution, which opens up the possibility of hyperspectral monitoring of objects with limited computing resources and bandwidth of the video data transmission channel. Spectral resolution control is supposed to be carried out on the basis of tuneable, software-controlled acousto-optic filters, spatial resolution control – based on modern CMOS matrix technologies with the “active pixel” function, digitalization control of the images obtained – based on the developed analogy-to-digital converter with tuneable quantization level. Modelling using experimental data has shown the possibility of implementing a sufficiently reproducible classification of hyperspectral images with a decrease in their spectral, spatial, and radiometric resolutions.

О возможности использования данных геостационарного детектора молний для исследования плазменных явлений

The article deals with scientific and technical problems associated with the functionality of the geostationary lightning mapper, which is currently used for meteorological monitoring. Results of the study into the Schumann resonance phenomenon and the technical parameters of the mapper were analyzed simultaneously. A hypothesis is offered which suggests that there are pulsations in the time dependences of the radiation power of lightning activity at frequencies corresponding to Schumann resonance. A new application of the geostationary lightning mapper for studying plasma phenomena is proposed. Adding to the mapper an acousto-optic filter and a camera, which has the functions of switching the resolution/frame rate parameters, is shown to be useful for both meteorological and plasma studies.

Possibility of using GLM data for studying plasma phenomena

The article deals with scientific and technical problems associated with the functionality of the geostationary lightning mapper, which is currently used for meteorological monitoring. Results of the study into the Schumann resonance phenomenon and the technical parameters of the mapper were analyzed simultaneously. A hypothesis is offered which suggests that there are pulsations in the time dependences of the radiation power of lightning activity at frequencies corresponding to Schumann resonance. A new application of the geostationary lightning mapper for studying plasma phenomena is proposed. Adding to the mapper an acousto-optic filter and a camera, which has the functions of switching the resolution/frame rate parameters, is shown to be useful for both meteorological and plasma studies.

Ultrashort near-infrared pulse generation by non-collinear optical parametric amplification in LiInS2

We demonstrate non-collinear optical parametric amplification (NOPA) in LiInS2 to generate ultrashort near-infrared pulses. White light pulses around 1400 nm generated in yttrium aluminum garnet are amplified by five orders of magnitude up to 1.0 µJ by three-stage NOPA in LiInS2. The dispersion of the amplified pulses is compensated by an acousto-optic programmable dispersive filter, resulting in the pulse compression down to 40 fs, which is 1.1 times the pulse width of the Fourier-transform limited pulse. The successful demonstration of NOPA in LiInS2 indicates the possibility as a new light source to obtain high peak intensity which enables us to access the regime of non-perturbative physics.

Equal-efficiency diffraction of unpolarized wideband light with acousto-optic filters

We present the diffraction of unpolarized light over a broad wavelength range using paratellurite Acousto-Optic Tuneable Filters. The diffraction of unpolarized light usually relies on a specific operating point that is sensitive to the wavelength and angle of incidence, resulting in an operating ability over a narrow bandwidth. We present a detuning strategy to eliminate the angular dependence and obtain equal diffraction efficiency for both the linear polarization states over a broad bandwidth. We explain how to find the optimum operating frequency and present its dependency as a function of the wavelength. With the quasi-phase matching condition presented, the diffraction of unpolarized light over the 400 nm to700 nm band is possible with an efficiency of over 80%.

Application of the ultrashort pulse position modulation method in the frequency domain and dual optical sideband modulation, based on the acoustic-optical filter of photonic crystal fibers to obtain optical logic gates

An acousto-optical filter with tunable polarization based on photonic crystal fibers is used to propose a method of optical modulation, from the modulation by positions of ultrashort pulses in the frequency domain (PPFDM) and the modulation in dual optical sideband simultaneously. So apply this method for generating optical logic gates. It can be shown that AND and OR logic gates can be obtained when a soliton of 55.5-fs time width is encrypted initially generating two bits of information by the modulation method proposed here. We analyzed the optical double-sideband PPFDM modulation for the pulses (bits), polarized in the two input modes, allowing a variation in the εcod encoding parameter for each pulse. One input pulse in relation to another is allowed a phase difference Δϕ = 1.28π, because analyzing the frequency curve as a function of a phase variation, it is observed that it is in this phase that we obtain the most reliable logic gates.

Carrier-envelope phase control of synthesized waveforms with two acousto-optic programmable dispersive filters.

We demonstrate the scanning and control of the carrier-envelope phases (CEPs) of two adjacent spectral components totally spanning more than one-octave in the short-wave infrared (SWIR) wavelength region by operating two individual acousto-optic programmable dispersive filters (AOPDFs) applied to each of the two spectral components. The total CEP shift of the synthesized sub-cycle pulse composed of the two spectral components is controlled with simultaneous scans of the two CEPs. The resultant error of the controlled CEP was 642 mrad, so that this technique is useful for searching zero CEP of the synthesized pulse with the maximum field amplitude. In addition, we conduct a closed feedback loop to compensate for the CEP fluctuation by using the two AOPDFs together. As a result, we succeed to reduce the rms error of the CEP from 399 mrad to 237 mrad.

Acousto-optic spatial frequency filter operating in the intermediate region of acousto-optic interaction

The characteristics of an acousto-optic spatial frequency filter designed for processing of two-dimensional images and operation in the intermediate region of acousto-optic diffraction are investigated. The advantage of such filters over filters operating in a Bragg regime is the possibility of operation at significantly lower acoustic frequencies, which allows the passband of spatial frequencies to be increased and the limiting resolution to be decreased. Transfer functions of diffraction orders are obtained. The use of the first diffraction order is demonstrated to allow selection of the two-dimensional image contour. The two-dimensional image edge enhancement of the image transmitted by optical emission at a wavelength of 0.63×10−4cm is experimentally demonstrated using a TeO2 spatial filter operating at a frequency of 15 MHz.

Formation of contrast images of specified objects by acousto-optic hyperspectrometer by selective spectral registration

The method of selecting the most informative spectral channels when using an acousto-optic hyperspectrometer in the mode of selective spectral registration is presented. The developed technique makes it possible to select spectral channels in which the maximum contrast of objects is observed against a certain background, provided that their spectral properties are known. The results of experimental studies of the technique confirm an increase in contrast compared with panchromatic and hyperspectral shooting modes in the entire optical range. The choice of spectral channels according to the presented technique can also be used both for the formation of transmission functions in a multi-window acousto-optic hyperspectrometer, and for the rapid formation of their high-contrast color-synthesized images. Keywords: hyperspectral images, spectral contrast, visualization, acousto-optical filter, spectral density of energy brightness.

Analysis of the effectiveness of schematic diagrams of a tunable source based on an acousto-optic filter

Analysis of the effectiveness of schematic diagrams of a tunable source based on an acousto-optic filter

Modes of wide-aperture acousto-optic diffraction in a uniaxial birefringent crystal

Acousto-optic (AO) anisotropic interaction in uniaxial birefringent crystals is a widespread and versatile approach to tunable spectral filtration of light. Its principal constraints are limited values of spectral and angular bandwidth restricting the light transmission and imaging performance of AO filters. A way to overcome these drawbacks is simultaneous Bragg diffraction of two or more light beams. In this paper, we discuss and compare the main features of four available modes of anisotropic wide-aperture AO interactions in uniaxial birefringent crystals. We calculate the angular aperture, spectral resolution and other parameters and estimate the spectral image quality features related to each one. Theoretical consideration and computational modeling are carried out for tellurium dioxide (TeO2)—the main AO crystal. Derived results are important for the development of AO imaging devices, particularly multi-channel AO tunable filters.

Optical system of 3D AOTF-based microscopic imager

In this paper, we propose a novel approach of calculating optical stereoscopic systems containing acousto-optic tunable filters. Each channel is designed separately as a simple imaging system. It is formed by an entrance lens, a radiation receiver lens, and an acousto-optic filter. The optimization of the depth of field and the magnification of the optical system is carried out during the calculations. The numerical values of the overall parameters obtained satisfy the given initial requirements. The Zemax simulation of the built optical system is in strong agreement with the calculation.

Acousto-optic filtration in low-coherence spectral-domain interferometry

The basic principles of measurements in spectral-domain low coherence interferometry (optical coherence tomography, optical coherence microscopy) based on acousto-optic filtration are discussed. Relations for extracting information about sample’s spatial structure from a series of spectral interference images acquired with spectral tuning are given. The implementation of measurements in spectral domain using acousto-optic filtration is considered. The effect of the acousto-optic filter characteristics on depth measurement range and depth resolution is estimated. The results of modelling of the interference signal and experimental data obtained in the scheme with acousto-optic filtration of interfering beams at the output of Michelson interferometer are presented.

Energy efficiency of lighting systems based on acousto-optic filtration

Designing systems with an acousto-optical filter requires considering its small numerical aperture and crystal size. These features lead to the low efficiency of using the luminous flux, which may be crucial in practical applications of such systems for spectral analysis. The article discusses ways to increase the energy efficiency in different types lighting systems based on acousto-optic filtration.

Absolute spectral backscatter measurements of large-core multimode PMMA polymer optical fibers.

To our knowledge, we are the first to measure the absolute value of the backscattering coefficient of a standard 1 mm core-diameter, multimode (MM) step-index (SI) polymethylmethacrylate (PMMA) polymer optical fiber (POF) for the spectral range of 450 nm to 700 nm. Our optical time domain reflectometer (OTDR) setup consists of a femtosecond supercontinuum laser with an acousto-optical filter as a tunable light source with short pulses and a time-correlated single-photon counting system as a receiver with a high dynamic range. The backscattering coefficient is calculated from the ratio between the energy within the fiber end reflex and the distributed backscattering level. We also measured the spectral attenuation with our OTDR setup and compared it with a standardized measurement method. At the attenuation minima within the measured spectral range the backscattering level of a 1 ns pulse is about -46dB at 520 nm, -48dB at 570 nm, and -51 dB at 650 nm. We were also able to show by the observed wavelength dependence that Rayleigh scattering causes a majority of the scattering.

Ring-shaped optical trap based on an acousto-optic tunable spatial filter.

We report on a novel, to the best of our knowledge, optical scheme of an annular optical trap based on an acousto-optic tunable spatial filter. Design of the optical trap is proposed and validated. Experimental demonstration with polystyrene microspheres includes controllable arrangement of freely floating particles into a circular pattern, aggregation, and disaggregation of the particles. Dynamical adjustment of the trapping field potential diameter is achieved by programmable frequency-swept controlling of the acousto-optic filter.

Spectral Imaging Experiments with Various Optical Schemes Based on the Same AOTF.

Spectral image filtration by means of acousto-optical tunable filters (AOTFs) has multiple applications. For its implementation, a few different optical schemes are in use. They differ in image quality, number of coupling components, dimensions and alignment complexity. To choose the optical system of AOTF-based spectral imager properly, many factors have to be considered. Though various schemes of acousto-optic (AO) filtration have been tested and discussed, their comparative analysis has not been reported up to now. In this study, we assembled the four most popular schemes (confocal, collimating, tandem and double-path) using the same AO cells and experimentally compared their main features. Depending on the application, each scheme may be the basis of compact cost-effective spectral imaging devices.

Basic FBG apodization functions effects on the filtered optical acoustic signal

<span>This article clarified the basic fiber Bragg grating (FBG) apodization functions effects on the filtered optical acoustic signal (AS). Max optical acoustic power variations after acousto optic filter is clarified with the spectral wavelength variations. FBG apodization functions are uniform, Gaussian, and Tanh. We have tested the max optical acoustic power variations after various apodization FBG functions with the spectral wavelength variations. The max AS power amplitude after the electrical combiner is reported based various Apodization FBG functions. The max optical AS after FBG is studied with various FBG lengths for various FBG apodization functions at the central wavelength of 1.55 μm. The max electrical power after power combiner unit is demonstrated with different FBG lengths for various FBG apodization functions at the central frequency of 193.1 THz. </span>

Two-dimensional image edge enhancement using a spatial frequency filter of two-color radiation

Two-dimensional optical image edge enhancement is investigated using a spatial acousto-optical (AO) filter operating at two wavelengths of optical radiation, which significantly increases the reliability of measurements and also reduces the effect of noise. The filter operates basing on diffraction of light in two diffraction orders. It is shown that, in the general case, it is impossible to obtain a two-dimensional image contour simultaneously at two wavelengths at the same energy and frequency-angular parameters of the AO filter. A regime has been found that makes it possible to switch from one wavelength to another while maintaining the operation of edge enhancement by changing the acoustic power. This regime has been experimentally confirmed by the example of the formation of a two-dimensional image contour using two-colour radiation of an Ar laser emitting at wavelengths of 0.488 × 10−4 and 0.514 × 10−4 cm, and an AO cell made of TeO2, operating at a sound frequency of 57 MHz.