Optical Scheme Research Articles

Optical voice encryption based on speckle-illuminated fourier ptychography and plaintext-related chaotic random phase mask

In this paper, we propose an optical voice encryption scheme based on speckle-illuminated Fourier ptychography (FP) and plaintext-related chaotic random phase mask (CRPM). In this proposed encryption scheme, the plaintext-related CRPMs are generated by chaotic Lozi map and secure hash algorithm (SHA-256). During the encryption process, the voice signal to be encrypted is first converted into a two-dimensional (2D) voice map. Then, with the help of CRPMs and speckle-illuminated FP, the voice map is encrypted into a series of noise-like low-resolution images. During the decryption process, the original voice signal can be recovered from the series of noise-like low-resolution images via Fourier ptychographic phase retrieval algorithm and the CRPMs. To the best of our knowledge, it is the first time to use the Fourier ptychography and chaotic random phase mask to implement the optical encryption of the voice signal. In addition, in this proposed encryption scheme, the chaotic parameters can replace the whole random phase masks as the secret keys, which makes the management and transmission of the secret keys become more convenient. Moreover, since the plaintext-related chaotic parameter keys can be updated dynamically, the security of the proposed encryption scheme can be further improved. The feasibility, security and robustness of the proposed encryption scheme are further analyzed by numerical simulations.

Detection and performance analysis for MIMO visible light communication system using joint optical spatial and pulse amplitude width modulation

Conventional optical spatial modulation (SM) scheme activates one of the light-emitting diodes (LEDs) to transmit an intensity-modulated optical signal, in which the index of the activated LED is determined by spatial symbol and the emitted intensity is controlled by temporal symbol. In order to enhance the spectral efficiency (bits per channel use), we propose a joint SM and pulse amplitude width modulation (PAWM) as a novel optical spatial–temporal signaling scheme. In this paper, the proposed SM-PAWM optical signaling scheme is applied in a multi-input multi-output (MIMO) visible light communication (VLC) system. Employing optimal maximum likelihood (ML) algorithm to extract the spatial and temporal symbols is computationally prohibitive; hence, we develop a novel low-complexity detection scheme that converts the joint optimization problem separately to decode the spatial and temporal symbols. Moreover, theoretical results in terms of the successful identification probability of activated LED as well as the overall symbol error rate are derived. Extensive computer simulations are performed to validate the analytical results. It is shown that the proposed detection scheme is a feasible alternative to the ML detector in the VLC-MIMO system employing SM-PAWM.

Spectroscopic properties and laser cooling feasibility with the X1∏21/2↔X2∏23/2 transition for the PbX (X = F, Cl, Br, and I) molecules

The highly diagonal Frank–Condon factors (FCFs) are necessary for the laser cooling scheme, which means that only the molecules with the appropriate ground and excited electronic states can become candidates. Here, the laser cooling feasibility of the PbX (X = F, Cl, Br, and I) molecules is explored through four-component relativistic calculations. The potential energy curves and transition dipole moments of five Ω states are calculated and used to solve the Schrödinger equation of nuclear motion to obtain the rovibrational energy levels, spectroscopic parameters, the Einstein coefficients, and FCFs. Using the X1 2Π1/2 ↔ X2 2Π3/2 transition with highly diagonal FCFs, we construct optical schemes that can provide 104 ∼ 105 scattering phonons with four pumping lasers for PbX. The Doppler/recoil temperatures of PbX are 419.05 / 57.55, 9.63 / 61.20, 4.95 / 49.98, and 0.71 / 40.17 nK, respectively. Since the 10−4 s of the long spontaneous emission lifetime, the temperatures below microkelvin orders of magnitude can be achieved only if the adequate pre-cooling temperature is satisfied.

A versatile beamline for soft x-ray reflectivity, absorption, and fluorescence measurements at Indus-2 synchrotron source.

A versatile beamline for performing reflectivity, fluorescence, and absorption experiments in the soft x-ray region of 100-1500eV is commissioned on a bending magnet port of the Indus-2 synchrotron source. A high vacuum 2-axis reflectometer with x, y, and z sample scanning stages is installed. This reflectometer is used to measure the reflectivity of large samples up to 300mm in length and 5kg in weight. This feature is useful for characterizing x-ray optical elements, such as mirrors, gratings, and multilayers. A flange mounted silicon drift detector is installed in the downstream of the reflectometer for soft x-ray fluorescence measurements. The soft x-ray absorption measurements are carried out in the total electron yield and partial fluorescence yield modes. Integration of three different experimental techniques in the experimental station makes the beamline versatile for materials science applications as it provides structural, chemical, and electronic state information by performing the required experiments in an identical environment. The beamline uses a varied line spacing plane grating monochromator and gives a high flux (∼109 to 1011 photon/s) with a moderate resolution (λ/Δλ ~1000-5000). A three-mirror-based higher harmonic setup is incorporated to get rid of harmonics and to get a high spectral purity monochromatic beam with less than 0.1% harmonic content. In the present article, the beamline optical scheme, mechanical configuration, and details of the experimental setups are presented, along with a few representative results of each experimental mode.

16QAM optical signal generation scheme based on weighted optimal Euclidean distance.

A two-dimensional signal constellation scheme for binary uniform memoryless source transmission in optical fiber channels is studied in this paper. In geometric shaping (GS), optimization algorithms are usually used to change the overall position of constellation points while maintaining the probability of constellation points unchanged. Different optimization functions are used to allocate the position of constellation symbols, thereby improving constellation performance. A 16 quadrature amplitude modulation (QAM) optical signal generation scheme based on weighted optimal Euclidean distance is proposed in this paper. In order to obtain the best constellation diagram and increase the shaping gain, the weighted optimal Euclidean distance that can minimize the bit error rate (BER) over multiple iterative optimizations is used as the objective function. On the one hand, the proposed 16QAM optical signal generation scheme based on weighted optimal Euclidean distance always outperforms the uniform square 16QAM and the uniform circle 16QAM schemes in the back to back (BTB) transmission. On the other hand, after analyzing the simulation demonstration in a 50GBaud coherent optical communication system over 3000km, results demonstrate that the optical signal to noise ratio (OSNR) performance of this system is better than that of the uniform square 16QAM and the uniform circle 16QAM, which is improved by 0.52dB and 0.85dB, respectively. In addition, the proposed 16QAM system increases the transmission distance by 989km and 741km, respectively, compared to the other two systems. The performance confirms that the proposed novel 16QAM scheme, to the best of our knowledge, can effectively improve the reliability and transmission distance. Therefore, the proposed scheme has a certain development prospect in the future long-distance transmission of high-speed optical fiber communication.

Multiplexed imaging in live cells using pulsed interleaved excitation spectral FLIM.

Multiplexed fluorescence detection has become increasingly important in the fields of biosensing and bioimaging. Although a variety of excitation/detection optical designs and fluorescence unmixing schemes have been proposed to allow for multiplexed imaging, rapid and reliable differentiation and quantification of multiple fluorescent species at each imaging pixel is still challenging. Here we present a pulsed interleaved excitation spectral fluorescence lifetime microscopic (PIE-sFLIM) system that can simultaneously image six fluorescent tags in live cells in a single hyperspectral snapshot. Using an alternating pulsed laser excitation scheme at two different wavelengths and a synchronized 16-channel time-resolved spectral detector, our PIE-sFLIM system can effectively excite multiple fluorophores and collect their emission over a broad spectrum for analysis. Combining our system with the advanced live-cell labeling techniques and the lifetime/spectral phasor analysis, our PIE-sFLIM approach can well unmix the fluorescence of six fluorophores acquired in a single measurement, thus improving the imaging speed in live-specimen investigation.

Free-electron interaction with nonlinear optical states in microresonators.

The short de Broglie wavelength and strong interaction empower free electrons to probe structures and excitations in materials and biomolecules. Recently, electron-photon interactions have enabled new optical manipulation schemes for electron beams. In this work, we demonstrate the interaction of electrons with nonlinear optical states inside a photonic chip-based microresonator. Optical parametric processes give rise to spatiotemporal pattern formation corresponding to coherent or incoherent optical frequency combs. We couple such "microcombs" to electron beams, demonstrate their fingerprints in the electron spectra, and achieve ultrafast temporal gating of the electron beam. Our work demonstrates the ability to access solitons inside an electron microscope and extends the use of microcombs to spatiotemporal control of electrons for imaging and spectroscopy.

Geometric-Optical Model of Digital Holographic Particle Recording System and Features of Its Application

The paper proposes an equivalent optical scheme of an in-line digital holographic system for particle recording and a mathematical model that establishes a one-to-one correspondence between the dimensional and spatial parameters of a digital holographic image of a particle and the imaged particle itself. The values of the model coefficients used to determine the real size and longitudinal coordinate of a particle according to its holographic image are found by calibration. The model was tested in field and laboratory conditions to calibrate a submersible digital holographic camera designed to study plankton in its habitat. It was shown that four calibration measurements are sufficient enough to determine the model coefficients, and the developed design of the submersible digital holographic camera makes it possible to perform these measurements during the recording of each hologram. In addition, this neither requires data on the refractive index of the medium with particles nor on the parameters of the optical elements of the scheme. The paper presents the results of marine experiments in the Kara Sea and the Laptev Sea, as well as in fresh water in laboratory conditions and in Lake Baikal. The error in measuring the particle size in seawater without the use of the model is 53.8%, while the error in determining their longitudinal coordinates is 79.3%. In fresh water, the same errors were 59% and 54.5%, respectively. The error in determining the position of a particle with the use of the designed mathematical model does not exceed 1.5%, and the error in determining the size is 4.8%. The model is sensitive to changes in the optical properties of the medium, so it is necessary to perform calibration in each water area, and one calibration is quite sufficient within the same water area. At the same time, the developed design of the submersible holographic camera allows, if necessary, calibration at each holographing of the medium volume with particles.

Near-infrared H2S telemetry system under non-cooperative target with a novel mixed heterodyne optical structure scheme for high efficiency

A gas leakage telemetry system under non-cooperative target was designed and developed based on laser absorption spectroscopy technology, targeting the combination frequency absorption band of Hydrogen sulfide (H2S) gas molecules. A distributed feedback (DFB) laser centered at 1578 nm was adopt, with mature packaging process and high market maturity. The returned signal of diffuse reflection is extremely weak, decreasing exponentially with the increase of telemetry distance, and direct detection technology is difficult to achieve ideal performance at telemetry distance and lower detection limit. Thus, heterodyne detection technology was introduced to significantly amplify diffuse reflection signal and improve the signal-to-noise ratio (SNR) of telemetry system. For further detection sensitivity, wavelength modulation spectroscopy (WMS) technology was combined to suppress background noise through the electrical modulation of DFB laser. Alternating signal was applied to the laser to alter its output characteristics during the process of laser oscillation. Compared with exterior modulation methods, this interior modulation method does not require additional modulator, which avoids optical loss and is more economical. Combining the advantages of fiber structure and space optical path structure, a novel mixed heterodyne optical structure which was more applicable to this system was independently designed after the specific analysis of main noise sources. Then, the effect of heterodyne detection technology was verified in contrast of direct detection technology. Sensor performance was validated through calibration and stability experiments. The limit of detection (LoD) reached a minimum of 3.44 parts-per-million (ppm·m) with a 98 s averaging time. And the packaged system was fully capable of detecting the hazardous critical concentration of H2S and acting as an alarm mechanism.

A cost-effective joint multi-parameter optical performance monitoring scheme for high baud rate mode division multiplexing system

Inter-symbol interference (ISI), mode coupling (MC) and other impairments present in high baud rate mode division multiplexing (MDM) systems significantly degrade the reliability and accuracy of optical signal transmission. Therefore, performing joint multi-parameter optical performance monitoring (OPM) is crucial to ensure the efficient operation of the system. We propose a scheme that combines asynchronous single channel sampling (ASCS) images with a multi-task residual neural network (MT-ResNet) to enable cost-effective joint OPM at intermediate nodes in a 100 GBaud MDM system. The scheme requires only one photodetector to receive the signal. Based on the distinct characteristics exhibited by ASCS images for different parameters in the MDM system, the MT-ResNet is improved to capture correlations among parameters and learn residual information between inputs and outputs. This enables high-precision and rapid simultaneous implementation of modulation format identification (MFI), MC estimation, optical signal-to-noise ratio (OSNR) estimation, and chromatic dispersion identification (CDI) in the intermediate nodes of a 100 GBaud MDM system. The effectiveness of the proposed scheme is verified using a 100 GBaud QPSK/8QAM/16QAM/32QAM/64QAM MDM simulation transmission system with five spatial modes (LP01/LP11a/LP11b/LP21a/LP21b). The results show that under the influence of different linewidth (LW) of laser and differential mode group delay (DMGD), a 100 % identification success rate can be achieved for five commonly used MFs and eight different cumulative CD values in high baud rate MDM systems, across a wide range of OSNR. Additionally, the mean absolute error (MAE) of OSNR estimation corresponding to the five MFs is 0.22 dB, 0.26 dB, 0.30 dB, 0.32 dB, and 0.36 dB, respectively. The MAE of the eight different MC intensities fluctuate between 0.015 and 0.030. These results fully demonstrate the superior performance of the proposed scheme. Furthermore, the scheme exhibits favorable tolerance to large LWs and fiber nonlinear effects. Moreover, the complexity of the scheme is accurately analyzed through floating-point operations (FLOPs) and parameters (Params), which are much less than existing typical schemes, with specific values of 14.8849 M and 1.3798 M.

Compact 20-pass thin-disk multipass amplifier stable against thermal lensing effects and delivering 330 mJ pulses with M2 < 1.17.

We report on an Yb:YAG thin-disk multipass amplifier delivering 100 ns long pulses at a central wavelength of 1030 nm with an energy of 330 mJ at a repetition rate of 100 Hz. The beam quality factor at the maximum energy was measured to be M2 < 1.17. The small signal gain is 21.7, and the gain at 330 mJ was measured to be 6.9. The 20-pass amplifier is designed as a concatenation of stable resonator segments in which the beam is alternately Fourier transformed and relay-imaged back to the disk by a 4f-imaging optical scheme stage. The Fourier transform propagation makes the output beam robust against spherical phase front distortions, while the 4f-stage is used to compensate the thermal lens of the thin-disk and to reduce the footprint of the amplifier.

An affordable optical detection scheme for LSPR sensors

Biosensing technologies are essential for advancing healthcare by enabling rapid point-of-care (POC) testing and diagnosis, potentially saving lives. Biosensors, such as Localized Surface Plasmon Resonance (LSPR) sensors with gold nanoparticles (AuNPs), show promise in early disease diagnosis due to their simple structure and high sensitivity. However, their commercialization is limited by high production costs and the need for precise optoelectronic systems. This article proposes an affordable optical detection scheme for LSPR sensors named BioColor. BioColor uses a color CMOS camera to capture images of light passing through the sensor elements, which are plasmonic papers composed of AuNPs. Variations in the refractive index over the sensor’s surface cause changes in the color of the transmitted light. This color change can be detected through image processing algorithms and the detection results are visualized on the BioColor mobile app, providing instant automated access to sensing outcomes.

Multi-tap Optical Delay Line-based Optical-Electrical Dispersion Compensation Scheme in High-speed IM/DD Systems

Multi-tap Optical Delay Line-based Optical-Electrical Dispersion Compensation Scheme in High-speed IM/DD Systems

Design and Analysis of a Telescope Optical Path Length Stability Measurement Scheme

Design and Analysis of a Telescope Optical Path Length Stability Measurement Scheme

An optimized LSTM-based equalizer for 100 Gigabit/s-class short-range fiber-optic communications

&lt;p&gt;Intensity modulation/direct detection (IM/DD) remains to be the preferred optical transmission scheme for short-range applications for its simplicity of application, inexpensiveness, and small footprint. However, the impairments of low-cost device and fiber chromatic dispersion lead to the limitation of system performance when the data rate rises to 100 Gbps or higher. In this paper, we demonstrated that an equalizer using neural networks can effectively improve the transmission performance of high-speed IM/DD systems. An optimization of a long short-term memory (LSTM) structure in terms of network depth and distribution of neurons in hidden layers leads to an enhancement of the overall performance of the 50 Gbaud PAM4 communications. Furthermore, the results for a system using a LSTM-based equalizer give the better outcome than the traditional feed-forward equalizer (FFE) or artificial neural network (ANN)-based equalizer.&lt;/p&gt;

Acousto-Optic Deflector-Principles, Working and Applications

Acoustic optic deflectors (AOD) have gained a lot of popularity as a fast way to scan the laser beam in optical coherence systems. It produces an acoustic wave that deflects the laser beam in a single direction. There are many factors to consider when choosing different solutions for acousto-optic spectral systems, but no comprehensive analysis or summary of these factors exists. In addition to summarizing the most popular optical schemes for acousto-optic spectral systems, this paper explains the basic principles of acousto-optic devices. A simulation study has also been performed to represent the characteristics of AOD in a practical environment. Additionally, applications of acousto-optic spectral systems in a few common fields are presented.

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ ТА АНАЛІЗ ТЕХНОЛОГІЧНОЇ ПОХИБКИ ЗАСОБУ ВИМІРЮВАННЯ ГЕОМЕТРИЧНИХ ХАРАКТЕРИСТИК КАНАЛІВ СТВОЛІВ ВОГНЕПАЛЬНОЇ ЗБРОЇ

The parameters of the optical scheme of a laser triangulation sensor, whose deviation from their nominal (calculated) values will affect the transformation function, are determined. It is shown that the presence of a technological error during the processing of measurement information will be perceived as an apparent change in the measured value with a constant input signal. Mathematical models of the components of technological error are obtained, which are presented in the form of error limits at the input of the measuring instrument. The expressions for determining the confidence limits of the total technological error, taking into account the correlation between its components, are substantiated. A quantitative assessment of the technological error for characteristic combinations of weapon parameters is carried out. The results of the quantitative evaluation are presented in the form of graphs of the dependence of the limits of relative and absolute technological error on the increase in the radius of the bore in the measurement range.

VISUAL DATA COMPUTER PROCESSING IN EDUCATIONAL DIY PROJECTS

The software tools for processing visual data in an educational chemical experiment, the experience of their usage, and a number of DIY (Do it yourself) projects developed on their basis were analyzed. Particular attention was paid to the role of self-made devices during the forced online education caused by COVID-19 and the full-scale war in Ukraine. The results of the development of the software tool ColorKit, which is being developed at the Department of Physics and Chemistry of H.S. Skovoroda Kharkiv National Pedagogical University are presented. The basic principles were covered, the interface was described, the main functions of the application and their areas of usage were given. The principle of operation of the modules: "Spectrophotometer", "Colorimeter", "Refractometer", "Polarimeter" was characterized. The features of the structure of optical computer devices for physico-chemical analysis developed by teachers, students of higher education and students, members of the Academy of Medical Sciences were considered, and the results of their testing were highlighted. The design of an absorption spectrophotometer based on a reflective diffraction grating made from a DVD disc was described; a new method of its calibration using a diamond green solution was proposed. The operating model was tested and it was established that the accuracy of the device was sufficient for demonstration and educational chemical experiments. The operating principle of the "Colorimeter" module of the ColorKit software tool was considered. It was shown that, unlike other software tools, it had built-in approximation tools, which significantly facilitated the processing of visual data; displaying the results of mathematical processing in a graphic form, which made the experiment visual. It should be noted that for the correct operation of the virtual spectrophotometer and colorimeter in real time, the correct setting of the video device driver is quite important. A number of optical schemes of refractometers developed on the basis of the ColorKit software tool were presented: with liquid and V-prisms; i.e. the device whose principle of action is based on changing the optical properties of the lens in contact with the solution. It was shown that the simultaneous display of the course of the rays and the results of mathematical processing provides a high level of visibility. The results of the approval of the LED DIE refractometer with a V-prism are outlined. Further prospects for the development of the ColorKit project are planned.

M-Cube — towards correlative multi-scale light-sheet imaging using a compact, modular and moving illuminator

The crossed arrangement of excitation and collection optics is the defining feature of selective plane illumination microscopes. It results in an axial sectioning given by the thickness of the light sheet, whereas the lateral resolution depends on the numerical aperture of the collection optics. One disadvantage of this optical scheme is that it has been difficult to image large fields-of-view at high spatial resolution. Yet, it is often not necessary to image the entire sample at high resolution. Instead, a zoom from mm-scale over-views to regions-of-interest that are imaged at μm is often sufficient, e.g., for studying neuronal networks that simultaneously comprise cm-long connections and tiny (sub-μm) synaptic contacts, spanning 6 orders of magnitude. Observations over such different spatial scales typically require the use of different instruments. We here describe our ongoing efforts to build and characterise a compact light-sheet module designed for correlative micro- meso- and macroscopic imaging. Its particularity is that moves with the sample between micro- and macroscopic imaging arms. Based on a compact illuminator and flexible sample carrier the module is mounted on a motorised long-range, high-precision microscope table. The ability to perform seamless back-and-forth multi-scale imaging comes from a strict registering of image coordinates.

Twelve Times Faster yet Accurate: A New State‐Of‐The‐Art in Radiation Schemes via Performance and Spectral Optimization

AbstractRadiation schemes are critical components of Earth system models that need to be both efficient and accurate. Despite the use of approximations such as 1D radiative transfer, radiation can account for a large share of the runtime of expensive climate simulations. Here we seek a new state‐of‐the‐art in speed and accuracy by combining code optimization with improved algorithms. To fully benefit from new spectrally reduced gas optics schemes, we restructure code to avoid short vectorized loops where possible by collapsing the spectral and vertical dimensions. Our main focus is the ecRad radiation scheme, where this requires batching of adjacent cloudy layers, trading some simplicity for improved vectorization and instruction‐level parallelism. When combined with common optimization techniques for serial code and porting widely used two‐stream kernels fully to single precision, we find that ecRad with the TripleClouds solver becomes 12 times faster than the operational radiation scheme in ECMWF's Integrated Forecast System (IFS) cycle 47r3, which uses a less accurate gas optics model (RRMTG) and a more noisy solver (McICA). After applying the spectral reduction and extensive optimizations to the more sophisticated SPARTACUS solver, we find that it’s 2.5 times faster than IFS cy47r3 radiation, making cloud 3D radiative effects affordable to compute in large‐scale models. The code optimization itself gave a threefold speedup for both solvers. While SPARTACUS is still under development, preliminary experiments show slightly improved medium‐range forecasts of 2‐m temperature in the tropics, and in year‐long coupled atmosphere‐ocean simulations the 3D effects warm the surface substantially.