Photodiode Output Research Articles

Структура и элементная база приёмо-передающего модуля для организации подводной оптической беспроводной системы передачи данных

In the paper, the results of theoretical study of a wireless optical data transmission channel, as well as experimental study of its characteristics, taking into account different configurations of the optical component base of receiving and transmitting modules, were presented. The model of the wireless underwater optical communication channel with pulse-position modulation (4 bits per symbol) of digital data traffic with 100 Mbps is proposed. The model showed that to organize a communication channel on a 10 m path, the use of an array of light-emitting diodes (LEDs) is requires (the amount is up to 20 LEDs). For this case, a sufficiently large route budget will be provided, even with additional factor that reduce the efficiency of light propagation in seawater. The LEDs were chosen to organize the data transmission channel, since they have a wide radiation pattern and allow the implementation of a relatively simple driver circuit. The required optical radiation power is realized with the use of an array of LEDs. Schematic diagrams of the LEDs driver and power supply for the receiving and transmitting modules have been designed. A measuring layout with optical transmitter and receiver blocks has been implemented. The test signal is a regular sequence of pulses with a duty cycle of 2, and a frequency of 1 MHz. In the receiving module, the signal from the output of the pin photodiode is amplified using a wideband operational amplifier. Sets of 3 pin photodiodes and 10 LEDs were selected and tests were carried out to determine options for optical components that provide the best time characteristics of the output electrical signal in terms of delay time, rising and falling edges of pulses in a wireless optical airborne communication channel. Also, measurements were done on an air path with a length of 0.25-3 m using one or two LEDs as part of the transmitting module. It has been experimentally confirmed that the organization of a communication channel with a length of up to 10 m requires about 15-20 light-emitting diodes. Further study involves the designing and testing of a driver for the LEDs array and a prototype transceiver module.

COHERENT AMPLITUDE MODULATION IN A LASER GAS SENSOR

The article is devoted to a current topic in science and technology -determining the type and concentration of gas using a laser. At close values of green laser radiation intensity and bias voltage, interference patterns of the time series of the photodiode output signal were obtained. The degree of coherence (more than ~0.1) made it possible to distinguish between the types of gases and their concentrations. Signal coherence was controlled by Allan deviation values.The novelty of the research method is the choice of the harmonic of the electrical network asthe main modulation frequency. It is shown that the correlation functions and the corresponding power spectra are sensitive to low-frequency fluctuations of molecules and their clumps. This allows the results and methods of this work to be used in specific cases instead of large-sized and expensive complexes of optical instruments at room pressure and temperature.

New Crystal Photodiode Combination for Environmental Radiation Measurement

Here, a new design will be introduced to detect radiation in the environment with high efficiency. The designed structure consists of placing ZnS–Si APD and PIN photodiodes at the ends of conventional crystals such as NaI(Tl) and CsI(Tl). Since ZnS is transparent to photons with wavelengths between 340 and 10000 nm, photons coming from the crystals are absorbed directly in the depletion region and generate primary particles. With an increase in the number of generated primary particles, a stronger and cleaner signal is obtained. In the simulation work, the light generated by 30 keV–3 MeV gamma rays in the crystals was obtained using the Geant4 simulation code. The single-particle Monte Carlo technique was used to calculate the photodiode output signal for the crystal emission spectrum. The simulation results showed that the crystals and ZnS–Si photodiode structures formed a good combination. The high quantum efficiency and low excess noise factor make the ZnS–Si structure an excellent choice for scintillating light detection.

BiGRU-Based Adaptive Receiver for Indoor DCO-OFDM Visible Light Communication

Nonlinear devices and channel interference can significantly impact the received signal in visible light communication (VLC). While recent research has explored receiver recovery using deep learning, existing approaches often involve replacing traditional channel estimation and equalization modules with neural network models. However, these models introduce additional data processing steps after fast Fourier transform (FFT), leading to increased complexity. To address these challenges, this study introduces a novel direct time-domain waveform equalization approach using a bidirectional gated recurrent unit (BiGRU) neural network for indoor VLC employing direct current (DC)-biased orthogonal frequency division multiplexing (DCO-OFDM). Unlike previous methods, our proposed scheme utilizes time-domain waveform data from photodiode outputs for direct balancing, harnessing the potent nonlinear processing capabilities of the BiGRU model. We first analyze the nonlinear processing capacity of the BiGRU model and subsequently compare the performance of different receiving methods on a constructed indoor visible-light communication platform. Experimental results demonstrate that the BiGRU-based approach exhibits low complexity and exceptional nonlinear channel learning capabilities. Notably, the proposed method outperforms other strategies in terms of bit error rate without the need for pilot signals. These findings validate the potential of the BiGRU-based DCO-OFDM receiving scheme as a promising solution for future VLC systems.

MATHEMATICAL MODELING OF FIBER-OPTIC TRANSMISSION SYSTEM WITH INTENSITY MODULATION

Fibre optic transmission systems are widespread in the transport network. Optical Transport Hierarchy (OTH) transmission systems are the basis of the transport network. The principle of wavelength multiplexing of channels is used to increase the technical and economic performance. Technically a simpler type of intensity modulation is used to transmit OTU1 and OTU2 OTH frames. Erbium-doped fibre-based optical amplifiers also generate amplified spontaneous emission noise, which degrades the performance of the transmission system. The qualitative characteristics of the optical channel of OTH transmission system with intensity modulation are investigated in this paper. In the simulation process, it is possible to neglect the nonlinear signal distortion in the optical fiber at the nominal signal power of the transponder transmitter. Therefore, in the studied transmission system model, an optical oscillation consisting of two components (signal and noise) arrives at the receiver input. In this case, an electrical signal consisting of three summands (signal-signal, signal-noise and noise-noise) will be generated at the output of the photodiode. A simplified formula for calculating the Q-factor of the optical signal, which affects the error probability in the optical channel, is proposed in most of the specialized literature. Numerical Q-factor values were calculated for OTU1 and OTU2 frames. They were compared with the reference results which were obtained by simulation in Optiwave Optisystem software. The analysis of the obtained data has proved that the simplified formula for the calculation of the Q-factor has a relative error of the order of 39-59%. A more accurate result can be obtained by using an expression that takes into account both components of the noise at the photodiode output.

Research and Design of Photoelectric Converter for Quantum Gravimeter

In the control system of a quantum gravimeter, the optical signal containing phase information is weak and usually at the nV level. This situation puts forward high requirements for the measurement performance of the system. As the coupling input component of the measurement system, the noise level of the preamplifier has a dramatic influence on the noise performance. In this paper, the input current signal is provided by the photodiode. According to the photodiode output characteristics, we design three preamplifiers with different gain and bandwidth, which is verified by the optical system. Under the condition of meeting the design requirements, the noise performance is compared with the common commercial detector Model 2307. The results show that the noise performance of the photoelectric converter designed in this paper is about 1.5 times that of model 2307.

Portable Water Quality Measurenment System for Sanitation

ABSTRACTWater is one of the essential needs that play an essential role in supporting life on earth. Water for sanitary hygiene purposes is used for several things to maintain individual hygiene, such as bathing and toothbrushes. Water is also for washing foodstuffs, tableware, and washing clothes. In addition, water for hygiene sanitation can be used as raw water for drinking water. This research designs a water quality measurement tool using parameters following water quality for sanitary hygiene purposes issued by the Ministry of Health. These parameters include turbidity, acidity (pH), temperature, and solids in water. The tool is designed to use Arduino Uno as a controller, sensors according to the parameters of photodiode sensors, pH, temperature, TDS (Total Dissolved Solids), and output systems using an LCD 20 x 4. This study concluded that the water quality detection system is running well, using photodiode sensors that can read each level of turbidity based on the value of ADC (Analog Digital Converter). The TDS sensor has an accuracy rate of 93.2% with a 6.8% error percentage. The pH sensor has an occurrence rate of 97.5% with a 2.5% error percentage, and a temperature sensor has an accuracy of 97.84% with a 2.16% error percentage.

Cross-Axis Dynamic Field Compensation of Optically Pumped Magnetometer Arrays for MEG

We present dynamic field compensation (DFC), whereby three-axis field measurements from reference magnetometers are used to dynamically maintain null at the alkali vapor cells of an array of primary sensors that are proximal to a subject's scalp. Precision measurement of the magnetoencephalogram (MEG) by zero-field optically pumped magnetometer (OPM) sensors requires that sensor response is linear and sensor gain is constant over time. OPMs can be operated in open-loop mode, where the measured field is proportional to the output at the demodulated photodiode output, or in closed-loop, where on-board coils are dynamically driven to maintain the internal cell at zero field in the measurement direction. While OPMs can be operated in closed-loop mode along all three axes, this can increase sensor noise and poses engineering challenges. Uncompensated fluctuations in the ambient field along any statically nulled axes perturb the measured field by tipping the measurement axis and altering effective sensor gain – a phenomenon recently referred to as cross-axis projection error (CAPE). These errors are particularly problematic when OPMs are allowed to move in the remnant background field. Sensor gain-errors, if not mitigated, preclude precision measurements with OPMs operating in the presence of ambient field fluctuations within a typical MEG laboratory. In this manuscript, we present the cross-axis dynamic field compensation (DFC) method for maintaining zero field dynamically on all three axes of each sensor in an array of OPMs. Together, DFC and closed-loop operation strongly attenuate errors introduced by CAPE. This method was implemented by using three orthogonal reference sensors together with OPM electronics that permit driving each sensor's transverse field coils dynamically to maintain null field across its OPM measurement cell. These reference sensors can also be used for synthesizing 1st-gradient response to further reduce the effects of fluctuating ambient fields on measured brain activity and compensate for movement within a uniform field. We demonstrate that, using the DFC method, magnetic field measurement errors of less than 0.7% are easily achieved for an array of OPM sensors in the presence of ambient field perturbations of several nT.

An Extensive Large Signal Equivalent Circuit Model of GaAs-PIN Photodiode

Based on the variation trend of the depletion layer of GaAs-PIN photodiode (PD) under different optical power and reverse bias voltages, an extensive large-signal equivalent circuit model that characterizes PD in non-punch-through and punch-through states is proposed in this article. According to the analysis of the PD’s depletion layer variation, the nonlinear parameters of the model are described by exponential function and Gaussian function. To verify the reliability of equivalent circuit model, on-chip measurements were performed on PIN-PD fabricated by commercial GaAs process, and the measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> and reflection coefficient agree with the proposed model simulation results well. Furthermore, using the proposed model for simulation with CAD tools shows that reducing junction capacitance has potential in improving PD output power and gain flatness. At the same time, the model provides a certain reference for selecting bias condition in the design of the PD matching network and fabricating PD with high power output.

All-optical microwave feedback oscillator with atomic cell resonator

We report the demonstration of an all-optical self-sustained cell-based microwave feedback oscillator. In this scheme, a microwave resonance, optically induced in a buffer-gas filled vapor cell resonator through coherent population trapping (CPT), is detected by a fast photodiode, amplified, and used to drive back, through a frequency divider, a Mach–Zehnder electro-optic modulator in a sustaining loop configuration. The total gain and phase of the system was measured in an open-loop configuration with a network analyzer. In good agreement with values predicted by the Leeson effect, the CPT feedback oscillator demonstrates an absolute phase noise of −24 dB rad2/Hz at 1 Hz offset frequency, compatible with a fractional frequency stability of 8 × 10−12 at 1 s, and a phase noise floor of −112 dB rad2/Hz, limited by the low microwave power available at the photodiode output. The amplitude noise of the oscillator shows a comparable noise floor and, for offset frequencies lower than 200 Hz, a 1/f dependence, due to the presence of the frequency divider in the loop.

Broadband micro-transient absorption spectroscopy enabled by improved lock-in amplification.

Recent breakthroughs in material development have increased the demand for characterization methods capable of probing nanoscale features on ultrafast time scales. As the sample reduces to atomically thin levels, an extremely low-level signal limits the feasibility of many experiments. Here, we present an affordable and easy-to-implement solution to expand the maximum sensitivity of lock-in detection systems used in transient absorption spectroscopy by multiple orders of magnitude. By implementation of a tuned RC circuit to the output of an avalanche photodiode, electric pulse shaping allows for vastly improved lock-in detection. Furthermore, a carefully designed "peak detector" circuit provides additional pulse shaping benefits, resulting in even more lock-in detection signal enhancement. We demonstrate the improvement of lock-in detection with each of these schemes by performing benchmark measurements of a white-light continuum signal and micro-transient absorption spectroscopy on a few-layer transition metal dichalcogenide sample. Our results show the practicality of ultrafast pump-probe spectroscopy for many high-sensitivity experimental schemes.

Time–space–weight calibrated plastic optical fiber-based pressure sensing carpet

We demonstrate time-, space-, and weight-based calibration techniques for pressure monitoring in the low-cost plastic optical fiber (POF) sensor carpet. It is found that the POF-based pressure sensing platform has several limitations, such as output voltage variations and difference in the sensor response for horizontal and vertical fibers due to convex and concave shapes of bend. To surpass the these limitations, we have developed time-based calibration using time windowing technique to reduce the standard deviation of photodiode output voltage variations by 98%. We have also described space and weight calibration techniques based on the convex and concave shapes of fiber bend. These techniques help in improving the Landweber image reconstruction algorithm to obtain significant clarity and improvement in object pressure images. We also report an artificial intelligence-based algorithm to determine the accuracy of positioning of the load. Experimental results demonstrate that this algorithm gives a mean square error of 0.875 cm in position detection on the carpet. We discuss the potential for a compact and cost-effective pressure sensor carpet, which integrates with the living environment and the outside world.

Study of the characteristics of the synchronization algorithm for a quantum key distribution system based on comparing the number of samples from an adjacent pair of time windows with a threshold level

The analysis of time and probabilistic characteristics is carried out for a two-stage synchronization algorithm in a quantum key distribution (QKD) system with automatic compensation of polarization distortions. Formulas are obtained for calculating the missing probabilities a signal pair of windows, false alarm and successful synchronization. The dependences of the missing probability a signal pair on the average number of photons and noise pulses are investigated during the analysis of a pair of windows for different threshold levels. The numerical material obtained in the course of the study indicates the possibility of using for express calculations the probability of detecting a signal pair of windows formulas oriented to the normal distribution of the number of recorded pulses at the output of a single-photon avalanche photodiode.

Application of Bpw34 photodiode and cold white LED as diagnostic X-ray detectors: A comparative analysis

This study compares the real-time dosimetric performance of a bpw34 photodiode (PD) and cold white light-emitting diodes (LEDs) based on diagnostic X-ray-induced signals. Signals were extracted when both the transducers were under identical exposure settings, including source-to-detector distance (SDD), tube voltage (kVp), and current-time product (mAs). The transducers were in a photovoltaic configuration, and black vinyl tape was applied on transducer active areas as a form of optical shielding. X-ray beam spectra and energies were simulated using Matlab-based Spektr functions. Transducer performance analysis was based on signal linearity to mAs and air kerma, and sensitivity dependence on absorbed dose, energy, and dose rate. Bpw34 PD and cold white LED output signals were 84.8% and 85.5% precise, respectively. PD signals were 94.7% linear to mAs, whereas LED signals were 91.9%. PD and LED signal linearity to dose coefficients were 0.9397 and 0.9128, respectively. Both transducers exhibited similar dose and energy dependence. However, cold white LEDs were 0.73% less dose rate dependent than the bpw34 PD. Cold white LEDs demonstrated potential in detecting diagnostic X-rays because their performance was similar to that of the bpw34 PD. Moreover, the cold white LED array's dosimetric response was independent of the heel effect. Although cold white LED signals were lower than bpw34 PD signals, they were quantifiable and electronically amplifiable.

Microfluidic Soil Nutrient Detection System: Integrating Nitrite, pH, and Electrical Conductivity Detection

Soil harbours innumerable microorganisms, nutrients, and other crucial elements, it anchors vegetation and supplies it with the primary factors that make agriculture possible. Soil health is determined by quantifying nutrients and physical parameters that are required to be in optimum range depending on the cropping pattern. In line with this, the current work presents an integrated, low-cost, microfluidic-based system for the detection of three such parameters namely– nitrite, pH and electrical conductivity (EC). A filtration protocol using different grades of Whatman filter paper was established to detect the said parameters using a suspension of soil. A multiplexed polydimethylsiloxane (PDMS) device was designed and fabricated to test for EC and nitrite. The device employed a conductivity cell with copper electrodes, connected in series with a resistor, powered using an oscillating power source. Griess reaction-based photometric detection using an LED and photodiode was used to quantify nitrite. A transimpedance amplifier circuit was designed and fabricated to amplify the photodiode output. pH detection was achieved using a commercially available pH probe and an Arduino pH breakout board. A low-cost 3D printed syringe pump was developed to achieve flow control. Atmega 328P (onboard Arduino Uno) was used to integrate the subsystems. A smartphone application was built to control the system and store geotagged data. Bluetooth protocol was used to communicate between the smartphone application and Arduino. Standards and real soil samples were tested using the developed microfluidic system.

Fully Integrated, Automated, and Smartphone Enabled Point-of-Source Portable Platform With Microfluidic Device for Nitrite Detection.

Excess limit of Nitrites, which are prevalent within environmental and physiological systems, have severe detrimental effects, thus point-of-source detection becomes an important requirement to take suitable preventive measures. This paper presents the design and development of a standalone, point-of-source, portable, low-cost, automated and integrated microfluidic system for quick detection and quantification of nitrite. Based on multiphysics simulations, a disposable polydimethylsiloxane (PDMS) microfluidic device was employed to carry out the controlled Griess reaction based assay. A low-cost 3D printed syringe pump was developed to inject the sample and reagent. Photometric detection was employed using light emitting diode (LED) and photodiode. A transimpedance amplifier circuit was designed and fabricated to achieve amplified photodiode output with reduced noise. An off-the-shelf microprocessor was used to integrate the whole system and a smartphone application (app) was developed to control the complete system and store the data. Interaction between the application and the microprocessor was achieved using Bluetooth connectivity. Spectrophotometric validation was performed and a calibration equation was obtained which was used to convert the device voltage output to absorption, through specially programmed android app. All the components were integrated in a 3D printed platform whose virtues such as ease of usage and affordability makes, quantification of nitrite, a simple and real time process wherein the limit of detection and limit of quantification values are found to be 0.07103 ppm and 0.21524 ppm respectively with good repeatability.

Highly Spectrally Pure 90-GHz Signal Synthesis Using a Coupled Optoelectronic Oscillator

A 90-GHz frequency reference is synthesized through harmonic generation from a 30-GHz coupled optoelectronic oscillator. The 30-GHz signal and its third harmonic feature an average power level of −5.6 and −15.8 dBm, respectively, at the photodiode output. Phase noise measurements at 30 and 90 GHz have been performed and phase noise levels as low as −114.4 dBc/Hz at 1-kHz offset for the fundamental and −104 dBc/Hz at 1-kHz offset frequency for the 90-GHz signal have been obtained.

Frequency Response Comparison of Photo-Detectors for Visible Light Communication Systems

For Visible Light Communication (VLC) systems, photo receiver is very important for obtaining low noisy modulated signal at receiver side since the pure modulated signal is easy demodulated. Therefore, we give a comparison of performance of three type photo receivers in this paper. In first application, we use a photoresistor to detect the modulated signal. It is referred as CDS (cadmium-sulfide) resistor. Another detector is solar cell unit. The other receiver is selected photodiode detector. It is shown from experimental results that the most appropriate modulated signal is obtained at output of photodiode. The output of solar cell consists of very complex signal compared with output of photoresistor. Additionally, we use PPM (Pulse Position Modulation) technique for transmission of data signal.

Flexible nine-channel photodetector probe facilitated intraspinal multisite transcutaneous photobiomodulation therapy dosimetry in cadaver dogs.

Noninvasive photobiomodulation therapy (PBMT) of spinal cord disease remains speculative due to the lack of evidence for whether photobiomodulatory irradiances can be transcutaneously delivered to the spinal cord under a clinically acceptable PBMT surface irradiation protocol. We developed a flexible nine-channel photodetection probe for deployment within the spinal canal of a cadaver dog after hemilaminectomy to measure transcutaneously transmitted PBMT irradiance at nine sites over an eight-cm spinal canal length. The probe was built upon a 6.325-mm tubular stem, to the surface of which nine photodiodes were epoxied at approximately 1cm apart. The photodiode has a form factor of 4.80 mm×2.10 mm×1.15 mm (length×width×height). Each photodiode was individually calibrated to deliver 1V per 7.58 μW/cm2 continuous irradiance at 850nm. The outputs of eight photodiodes were logged concurrently using a data acquisition module interfacing eight channels of differential analog signals, while the output of the ninth photodiode was measured by a precision multimeter. This flexible probe rendered simultaneous intraspinal (nine-site) measurements of transcutaneous PBMT irradiations at 980nm in a pilot cadaver dog model. At a surface continuous irradiance of 3.14 W/cm2 applied off-contact between L1 and L2, intraspinal irradiances picked up by nine photodiodes had a maximum of 327.48 μW/cm2 without the skin and 5.68 μW/cm2 with the skin.

Generation of octupled microwave signal via frequency multiplication method

We propose experimentally a technique to generate a low noise frequency octupled microwave signal. We demonstrate that by carefully arranging the phase of 90° between two MZMs (out of three), a low noise photonically assisted octupled microwave signal can be generated. A 25.6 GHz optical microwave signal is achieved with 3.2 GHz of local RF oscillator signal. Moreover, the intensity expressions at the output of photodiode are derived for both with and without dispersion terms. Finally, we advocate the impact of the electrical spurious suppression ratio on the extinction ratio of the modulators. Our experimental and simulation results agree well with the theoretical analysis.