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Effect of dual-channel optical feedback on self-mixing interferometry system
摘要： Laser feedback interference is widely used for displacement measurement of non-cooperative targets due to its ultra-high sensitivity. However, by the same token, laser feedback interferometry (LFI) suffers from multi-channel optical feedback, which compromises measurement stability and accuracy. We perform both simulations and experiments to study the effect of dual-channel optical feedback on LFI systems based displacement measurement. Dual-channel optical feedback interference is the simplest and most representative form of multi-channel feedback interference. We evaluate system performance by varying ,a which is the ratio of feedback level in the primary channel to the one in the secondary channel. The results indicate that the measured displacement curve is a linear line superimposed with nonlinear periodic errors when the target in the primary channel moves linearly and the target in the secondary channel stays stationary. Whereas, the curve is a periodic curve instead of a linear one, for the case when the target in the secondary channel moves linearly while the one in the primary channel stays stationary. Furthermore, the amplitude and shape of the periodic curves also depend on the parameter .a When a is much less than 1, the displacement curve is sinusoidal, whereas the curve has a saw-tooth shape with larger amplitude for a close to 1. In view of this situation, a new displacement measurement method, counting the cycles of the periodic displacement curves, is proposed. The current work can provide theoretical and experimental suggestions for improving the performance of existing self-mixing interferometry systems, and implementing ones with multi-channel optical feedback channels.
关键词： rate equations,interferometry,self-mixing,laser feedback
更新于2025-09-23 15:23:52
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Broad Range and High Precision Self-Mixing Interferometer Based on Spectral Analysis with Multiple Reflections
摘要： In this paper, a novel self-mixing interferometer is proposed with spectral analysis by multiple reflection vibration technique. The relationship between the vibration amplitude, the dominant frequency and the reflection time is deduced, which indicates that the theoretical minimum measurable vibration amplitude is 0.21λ/G(N,θ) and the precision is about 0.08λ/G(N,θ). The displacement sensitivity gain G(N,θ) increases with the reflection time. Theoretical analysis results show that the proposed method for vibration measurement has the advantages of high precision and broad measurement range, especially for the measurement of amplitude much smaller than λ/2. The validity of the method is tested by several experiments with different amplitudes and reflection times. An amplitude of 75 nm has been proved to be measurable and the absolute error is 5.43 nm, which is within the theoretical error range. The proposed method plays an important role in high precision and nanoscale measurement.
关键词： self-mixing,multiple reflections,spectral analysis
更新于2025-09-23 15:21:21
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High Resolution Laser Self-Mixing Displacement Sensor under Large Variation in Optical Feedback and Speckle
摘要： Self-Mixing interferometry signal characteristics are highly dependent on both the operating optical regime and target surface. In this paper, a method is proposed to overcome some identified limitations of the even power scalable algorithm (EPSA) [1], such as the required operating regime to be weak feedback. In addition, by using the up-sampling techniques, the number of stages involved in the even-power scalable algorithm can be drastically increased without any data acquisition bandwidth modification. Here, 10 successive stages have been successfully implemented to achieve a theoretical resolution of λ0/213. It is further shown that the proposed method can handle and process weak, moderate and strong feedback regime as well as speckle affected SMI signals more efficiently. Lastly, FPGA based hardware emulation of EPSA is also done for later embedded implementation of this high-resolution algorithm. FPGA synthesis results show that the designed system can measure maximum target velocity up to 1.18 m/s while consuming total power of 1.4W.
关键词： Self-mixing,Speckle,Signal processing
更新于2025-09-23 15:21:01
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A Method of Human Eye Parameter Measurement Based on Laser Self-Mixing Interference
摘要： The eye is the most important sensory organ of the human body, and the cornea and anterior chamber are very important components In surgeries like vision correction, it is necessary to know the accurate corneal thickness and anterior chamber depth of human eyes. Their accurate measurement cannot only provide a reference for doctors, but also provide a strong guarantee of surgical results. In order to achieve high-precision measurements of human corneal thickness and anterior chamber depth, we develop an equivalent human-eye optical system and a measurement method for the thickness. This method designs an equivalent double-membrane system to simplify the physiological structure of the cornea and anterior chamber of the human eye and irradiate the double-membrane system through laser. The re?ected light returns to the laser cavity and the original light self-mixing interference, and a photodetector collects and processes the interference signals to obtain the corneal thickness and anterior chamber depth. The correctness of the theoretical calculations is veri?ed by the experimental system, and the measurement accuracy can reach the micrometer level.
关键词： self-mixing interference,anterior chamber depth,corneal thickness,confirmatory experiment,double-membrane system
更新于2025-09-23 15:21:01
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A tunable self-mixing chaotic laser based on high frequency electro-optic modulation
摘要： A tunable self-mixing chaotic laser based on high frequency electro-optical modulation is proposed. A laser dynamics system is designed and tested for tunable chaotic laser generation and provides optical feedback and electro-optic modulation with two degrees of freedom. The chaotic laser is generated by optical feedback, and it becomes tunable by high frequency electro-optic modulation. The frequency is modulated from 10 MHz to 10 GHz to test this system, and an ultra-wide band chaotic laser from 0.8 GHz to 24 GHz is measured by an electrical spectrum analyzer (ESA). The experimental results show the generation of a tunable chaotic laser via electro-optic modulation. At the same time, this tunable chaotic laser has a highly sensitive dynamic response near the 2.0 GHz range of frequency modulation. The system is proved to be suitable for applications in high-speed broadband communication and sensing.
关键词： Optical injection,Laser self-mixing,Electro-optic modulation,Chaotic laser
更新于2025-09-23 15:19:57
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The origin of distorted intensity pattern sensed by a lens and antenna coupled AlGaN/GaN-HEMT terahertz detectors
摘要： Here, we report artefacts in the intensity pattern of a focused terahertz beam around 1 THz by scanning photocurrents as a function of the beam location and the frequency. Although the exact distortion is found with our specific antenna design, we believe similar artefacts could be commonplace in antenna-coupled FET terahertz detectors when the beam spot becomes comparable with the antenna size. To eliminate such artefact, new antenna designs are welcomed to achieve strong asymmetry in the terahertz field distribution under the gate while maintaining a more symmetric radiation pattern for the whole antenna.
关键词： high electron mobility transistor,terahertz detector,self-mixing,local electrical field
更新于2025-09-23 15:19:57
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Smaller antenna-gate gap for higher sensitivity of GaN/AlGaN HEMT terahertz detectors
摘要： We report an attempt to improve the sensitivity of terahertz detection based on self-mixing in antenna-coupled ?eld-effect transistors by enhancing the ?eld-effect factor and the antenna factor with a reduced gate length and a reduced antenna-gate gap, respectively. An optical noise equivalent power (NEP) of 3:7 pW= ??????Hz at 0.65 THz was achieved in a GaN/AlGaN high-electron-mobility transistor (HEMT) with a gate length of 300 nm and an antenna-gate gap of 200 nm at room temperature. It was found that the antenna factor was inversely proportional to the antenna-gate gap, and the responses upon coherent/incoherent terahertz irradiation were well described by the self-mixing model. To ?ll the NEP gap of 0:1 (cid:2) 1 pW= ??????Hz between room-temperature and cryogenic detectors by HEMT-based detectors at room temperature, impedance match needs to be carefully considered.
关键词： terahertz detection,GaN/AlGaN HEMT,self-mixing,field-effect transistors,antenna-coupled
更新于2025-09-23 15:19:57
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[IEEE 2019 International Topical Meeting on Microwave Photonics (MWP) - Ottawa, ON, Canada (2019.10.7-2019.10.10)] 2019 International Topical Meeting on Microwave Photonics (MWP) - 300 GHz Photonic Self-Mixing Imaging-System with vertical illuminated Triple-Transit-Region Photodiode Terahertz Emitters
摘要： In this paper, we report a phase-sensitive photonic THz two-tone self-mixing imaging system, comprising a self-developed vertical illuminated triple transit region photodiode (TTR-PD) and a commercial square law Schottky barrier diode as THz emitter and THz detector, respectively. Using the two-tone self-mixing approach, the phase information of a device-under-test can be extracted by down-mixing two THz signals inside the SBD, whereas the phase information remains in the output signal. The THz tones are generated by two free-running lasers and the TTR-PD, while one optical signal is externally modulated for double sideband carrier suppression. By means of the self-mixing, the phase noises of the free running lasers are canceled out. Using a second PD for the trigger, lock-in detection allows fast imaging speed, only limited by the integration constant. Beside the imaging system, we present the characteristics of the used vertically illuminated terahertz triple transit region photodiodes with thin depletion zone and small active areas. Numerical analysis by energy-balance model based TCAD simulations show transit-time limitations over 200 GHz, due to the electron field management within the active photodiode layers and the resulting high electron velocities. Therefore, the fabricated TTR-PDs show a flat ±2 dB frequency response within the frequency range from 225 GHz to 305 GHz. By employing the proposed photonic two-tone imaging system with the fabricated TTR-PDs, amplitude and phase difference vector images are taken at 299.5 GHz and 300.5 GHz. Metal and acrylic glass items inside a paper envelope are clearly visible, which demonstrates the potential of the system.
关键词： energy balance,self-mixing,TCAD,Terahertz spectroscopy,terahertz imaging,terahertz photodiodes
更新于2025-09-19 17:13:59
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Vibration Measurement Based on the Local Maximum Detection Algorithm for Laser Self-Mixing Interferometry
摘要： A novel laser self-mixing interferometry vibration measurement algorithm based on the local maximum detection technique is proposed, that can reconstruct micro vibrations rapidly and easily. In this article, the principles of the local maximum detection algorithm are analyzed in detail, and the process of solving the window function is emphasized. The major advantage of the method is that it does not involve any complicated calculations and removes the need for optical/electromechanical components. The validity of the presented method is confirmed by means of simulated signals and demonstrated via several experiments for harmonic and aleatory motion.
关键词： local maximum detection,self-mixing interferometry,vibration measurement
更新于2025-09-19 17:13:59
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Doppler-shifted laser self-mixing interferometry for enhanced detection sensitivity
摘要： Laser self-mixing interferometry (SMI) is a well-known measurement technique having been applied to the fields of geometrical quantities detection, medical treatment and industry manufacturing. Its detection sensitivity can be improved by frequency shifting towards the laser’s relaxation oscillation frequency (ROF), which has always been implemented by a pair of acousto-optic modulators (AOM). This manuscript presents a novel method based on Doppler effect for frequency shifting, which is based on a rotating disk and has the advantages of convenient adjustment and low cost. The theoretical analysis in the form of Doppler shift and time-delayed rate equations is followed, and simulative and experimental results are included to prove its validity. To our knowledge, this technique has not been used in practice till now, and the proposed structure, with these advantages, can find significant applications in designing high performance SMI sensors, and can extend SMI measurement to more kinds of non-cooperative surfaces.
关键词： Self-mixing interferometry,signal to noise ratio,Doppler shift,sensitivity,relaxation oscillation frequency
更新于2025-09-19 17:13:59