As milk consumption increases, rapid detection of milk concentration is becoming more and more crucial. In this research, we propose an LED-based milk concentration detection system, which is a new detection method that detects milk concentration by loading the LED with RF signals. The system includes an arbitrary waveform generator (AWG), LED, lampshade, silicon photo dioxide (PD), oscilloscope, and other components. After passing through different concentrations of milk solution, the light signal carrying a specific frequency is received by the PD, and after photoelectric conversion, the signal carrying a specific frequency in the light signal is converted out, and the concentration of the milk solution to be measured is obtained by reading the peak value measured by the oscilloscope. The experiments validated different brands of milk solutions with varying concentrations, demonstrating the feasibility of LED-based milk concentration detection, and the test analysis was performed for the same brand of milk solutions with varying concentrations, yielding a quadratic fit R2=0.9169, confirming that the system has good sensing performance for milk concentration and validating the method's feasibility.
Time of flight light detection and ranging (TOF LiDAR) is the main detection technology solution used in the mainstream LiDAR products at present. Smog has a certain interference effect on the laser, which affects the ranging accuracy of TOF LiDAR system. This paper focuses on the accuracy of TOF LiDAR ranging under smog conditions and the error analysis. A vertical cavity surface emitting laser is selected to emit a pulsed laser through a smog-filled smog chamber, a CMOS sensor is used to receive the reflected light, and the experimental data are collected using the host computer software. The collected data are then extracted from the effective area and processed with algorithms such as average filtering. Finally, the image of each pixel with the measured distance and the error situation are obtained. The effect of smog is simulated by increasing the system delay time to obtain the simulated image under smog conditions. The results obtained from the TOF LiDAR smog experiment are compared with the simulation results, and it can be seen that the smog has a significant attenuation effect on the laser transmission, with the attenuation ratio up to 63.99%, and the range error under the smog condition decreases by 53.55%, and the accuracy of the range measurement is improved.
Reducing carbon emissions is a global priority due to human impact on atmospheric pollution and the greenhouse effect. Achieving carbon peak and neutrality requires real-time monitoring of CO2 concentrations. However, developing high-sensitivity, portable, and anti-jamming gas detection solutions is challenging. Among spectroscopic techniques, Tunable Diode Laser Absorption Spectroscopy (TDLAS) is highly sensitive for detecting CO2 concentrations. This paper elaborates on the principles of TDLAS for detecting CO2 concentrations and proposes a noise reduction algorithm to meet diverse environmental requirements. Simulations were performed using software to simulate CO2 absorption spectra at approximately 1.57866535μm under high-intensity noise (0.1mW - 1mW). Based on this simulation, we applied the Wavelength Modulation Spectroscopy (WMS) technique to calculate the ratio of the output differential signal's second harmonic intensity to the first harmonic S2f/1f(T) and output power to reduce light intensity influence and improve concentration inversion linearity. The weighted convolutional moving average filtering was utilized to optimize WMS denoising, utilizing weight transfer to make the process more precise and reliable. After analyzing various window functions, it was concluded that a window length of 9 would be the most optimal. The algorithm improved the signal-to-noise ratio (SNR) by 22.435% under these conditions. When the noise level increased fourfold from the original signal, the algorithm enhanced the SNR by 59.514%, enabling reliable CO2 monitoring even under challenging conditions.
When the optical fiber ring is used as interferometer in microwave photonics (MWP) filter, researchers usually pay much attention to the sensing sensitivity, but are lack of experimental research on the deterioration of sensing linearity caused by the noise in this structure. Therefore, this paper studies the deterioration of the temperature sensing linearity in MWP filter, which is caused by the noise in optical fiber ring structure. In experiment, a sinusoidal microwave signal with the radio frequency(RF) amplitude of 4Vpp and the frequency range of 127MHz -147MHz are selected to modulate the broad-band light, and the bias voltage of the electro-optic modulator(EOM) is 3V. In the experiment, the 50m sensing fiber is heated, with the temperature range of 25°C-55°C. The filtered microwave signal is realized by the beating process in photodiode(PD), and then the signal is sent to the electrical spectrum analyzer (ESA). When the RF sweeping curves are recorded, the maximum peak detection(MPD) method is used to extract the resonant frequency of two resonant peaks at different temperatures respectively. Finally, the mean values of these resonant frequencies are calculated, and the first and multiple order polynomial is used to fit the above data. These results show that the resonant frequencies corresponding to different resonant peaks vary with the temperature with poor linearity. The first order fitting R-square of the resonant peak 1 and peak 2 are only 0.3855 and 0.2545, while the quartic fitting R-square can reach 0.8583 and 0.9589. It can be seen that there is a large noise in the optical fiber ring structure, which seriously affects the sensing performance of the MWP filter.
Nowadays, Microwave photonics has been extensively studied. Microwave photonic filter(MPF) is a new method in recent years that is widely used in optical sensing, which is a new method developed in recent years. In microwave photonic sensing technology, microwave photonic interference is the key method. In this experiment, the microwave photonic interference technology is used to complete the identification of different types of fiber connector, which can be identify optical fiber connectorr or certain types of optical devices in the optical fiber sensing link. MPF is formed by Mach-Zehnder interferometer(MZI) composed of coupler and optical fiber. People usually use the optical path differences between the upper and lower arms to form microwave photon interferometer for optical sensing. We form the optical path difference by adding optical fibers of different lengths. The formation of MPF is due to the interference of light modulated by the microwave signal interferometer. We has found that the different fiber connector of the optical fiber also have a greater impact on the performance of the microwave photonic filter. This paper selects the optical fiber of 3 meter with different fiber connectors, and measures optical power and radio frequency intensity at different temperature. This paper mainly discusses the differences of different connectors of the fiber and the microwave photonic sensing at different temperatures.
When we use FBG to filter the optical signal, we pay more attention to its optical power spectrum and less attention to its dispersion fluctuation. However, if the dispersion fluctuation of FBG is too large, it may lead to signal distortion, so it is very important to detect the dispersion fluctuation of FBG. In this paper, we choose the FBG with wavelength of 1550nm and reflectivity of 95%, and use the method of phase to amplitude conversion to detect the second-order dispersion fluctuation of FBG. In the temperature range of 23 ° - 33.6 °, we have measured the optical power spectrum and the second-order dispersion fluctuation curve of the fiber grating, and analyzed the experimental results. Then we find that when the FBG with flat optical power spectrum but large dispersion fluctuation is used for filtering, the output signal will be distorted.
The silicon Mach–Zehnder modulator is a significant type of optical modulator, which is widely utilized in optical communication and microwave photonics. The performance of the second harmonic microwave generation by a silicon Mach–Zehnder modulator is simulated and analyzed. The power and the purity of the second harmonic microwave mainly depend on two significant parameters: 1) the electrical nonlinearity of the diodes on arms of the modulator, 2) the bias voltage on the diode. Simulations show following results:1) when the built-in voltage Vb decreases from 8V to 3.5V, the incremental amounts of second harmonics and the fourth harmonics are 7.9dB and 15.6dB under the condition that the RF power is 15dBm and the bias voltage is 0V; 2) when the bias voltage increases from -0.5V to 4V, the ratio between second harmonics and the fourth harmonics varies from 20.0dB to 11.3dB under the condition that the RF power is 15dBm and the built-in voltage Vb is 3.5V. 3) when the RF power increases from 5dBm to 20dBm, the ratio between second harmonics and the fourth harmonics varies from 27.6dB to 11.6dB under the condition that is the bias voltage is 2V and the built-in voltage Vb is 3.5V. To conclude, the powers of second harmonics will increase with the reduction of the ratios between the second harmonics and the fourth harmonics.
Microwave photonic filter is one of the key technologies of microwave photonics. Its main purpose is to replace the traditional method to process radio frequency signal, modulate optical carrier by radio frequency signal, and process it directly in the optical domain. The advantage of FIR microwave photonic filter is that it has no system poles and is more stable. It guarantees linear phase, which is very important in signal processing. In this paper, the incoherent microwave photon sensor cascaded by FBG is verified experimentally. In the experiment, three FBG wavelengths are 1530 nm, 1550.12nm and 1539.5nm respectively to form a high-order FIR microwave photon filter, two 3dB couplers and three km fibers to form an unbalanced M-Z interferometer. The incoherent light generated by EDFA is modulated by a filter electro-optic modulator through an optical fiber Bragg grating, demodulated by an M-Z interferometer, and eventually received by a photodetector. In the experiment, 60 MHz near notch is chosen as the modulation frequency, the amplitude of modulation signal is 4 Vpp, the temperature range is 30-40°C with the temperature interval of 1°C. The sensitivities of 0.2219dBm/°Care obtained by processing the average values of 3 points, 5 points, 7 points, 10 points and 15 points.
For a VLC system, it transmits information by modulating LED with electrical signal. To ensure the sufficient optical power at the receiver, the electrical signal with large amplitude is hope to be applied on the LED , however, the LED has the turn-on voltage and the saturated voltage, so large electrical signal in transmitter will lead to the clipping distortion on the LED in theory. In this paper, the modulating efficiencies of white light LED with the rated power 1W, 0.5W and 0.1W are measured in experiment with the biased voltage 3.4V, and their modulating property are compared when the peak-peak AC voltage of the frequency 500KHz are in the range 0.5V-2.1Vpp and 2.2-5Vpp. In the experiment, an Arbitrary waveform generator (AWG) with the voltage bias function is utilized to generate a biased sine waveform Experimental results show that the slopes of Pe-Vt curve(modulating efficiency) increase with the drop of the rated power of LED at the frequency 500KHz in region I. In region II, the slopes of 1W LED and 0.1W LED are larger than that of 0.5W LED. The modulating efficiency is higher in region II than that in region I. When LED operate at the clipping distortion region, it has large modulating efficiency. Data fitting analysis shows that the 1W LED has the poor linearity in both region because its R-squares in both regions are smaller than other LEDs. The nonlinearity of the Pe-Vt curve will affect the modulating efficiency.
A novel photonic scheme of instantaneous frequency measurement (IFM) using analog modulation
links with interferometric detection assisted by a polarizer is proposed and demonstrated
experimentally. This scheme is simple, cost-effective as it only requires the basic
modulation-demodulation elements in typical analog optical links. The measurement errors as shown in
experimental results can be kept in 0.1GHz over a frequency range of 0.1GHz-6.5GHz.
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