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(Color online) Schematic block diagram of optical transceiver unit with pulsed serrodyne modulation.
Source publication
We report a new pulsed coherent laser transmitter for wind sensing that combines a semiconductor optical amplifier (SOA) with a phase modulator operated at pulsed serrrodyne modulation. Using pulsed serrodyne modulation, we demonstrate the correction of the instantaneous frequency deviation caused by the direct modulation of the SOA within a single...
Citations
... It has a laser transceiver, an erbium-doped fiber amplifier (EDFA), a circulator, a bidirectional wavelength division multiplexing (WDM) coupler based on a thin-film-filter and free-space optics technology, a balanced receiver made of indium gallium arsenide-based photodetectors, and a field-programmable gate array (FPGA)-based signal processor. The laser transceiver has basically the same configuration as the one in [9]. It consists of a micro-integrable tunable laser assembly (Micro-ITLA) made of aluminum gallium indium arsenide-based laser diodes, a phase modulator made of lithium niobate, a semiconductor optical amplifier (SOA) made by indium phosphide/indium gallium arsenide phosphide, a divider, and a coupler. ...
... A part of the divided light is sent to the optical coupler as a local light. The other part is frequency shifted and pulsed by the phase modulator and the SOA using the pulsed serrodyne modulation [9]. The pulsed light is amplified by the EDFA. ...
... At the time, our development of the telescope had not been completed. Therefore, a conventional telescope [9] was used for each output port of the WDM coupler. The conventional telescopes are roughly aligned for the same measurement direction. ...
We have developed a new, to the best of our knowledge, beam swinging coherent Doppler wind lidar (BS-CDWL) by employing a wavelength switching method using mass-produced components for wavelength division multiplexing (WDM) optical communication systems. This BS-CDWL also has a single and position-to-angle conversion telescope for multiple LOS measurement which contributes to cost-effectiveness. Preliminary wind sensing result is shown with measurable range of up to 350 m.
... The wind sensing coherent light detection and ranging (lidar) [1,2] is a remote sensor which measures the Doppler shift of the backscattered lights from the aerosols. This lidar is suitable for the wind sensing under the clear sky condition; therefore, many researchers have developed the lidars for the wavelength regions of 10.6 µm [3][4][5], 1 µm [6,7], 2 µm [8][9][10][11][12][13][14], 1.5 µm [15][16][17][18][19][20][21][22][23][24][25][26][27][28], and 1.6 µm [29,30]. ...
We have developed an active alignment of receiving beam (AARB) function for coaxial optics in wind sensing coherent Doppler lidar using feedback control based on the heterodyne-detected signal processing of backscattered light from the aerosols. The proposed method needs only the simple alignment components and contributes to the robustness for the coherent lidars with the high-power laser transmitter under the risky condition of misalignment, for example, in the airborne application. The concept, design, and evaluation results of the alignment precision are shown. The effect of the AARB is demonstrated for both cases of the hard target and soft target (i.e., wind sensing). To the best of our knowledge, this is the first demonstration of the AARB concept for the wind sensing coherent lidar.
... On the other hand, coherent detection can effectively suppress the influence of background light by interfering with the received signal with a local oscillator, making it one of the most sensitive optical detection techniques [10,11]. It is widely used in Doppler lidar, coherent laser communication and other fields [12][13][14][15][16][17][18][19][20][21]. Pulsed coherent lidar has reduced the range ambiguity for long-distance ranges [22][23][24]. ...
The decoherence in coherent lidar becomes serious with the increase in distance. A small laser spot can suppress the decoherence of the echo light from noncooperation targets. However, it is very difficult to keep a small light spot over a long distance. In this paper, a pulsed coherent lidar with high sensitivity at the few-photon level was demonstrated. A phase plate was used to modulate the wavefront of the laser to achieve 100 m focusing which reduced the decoherence effect. Based on coherent detection and time-of-flight (TOF) measurements, long-distance laser ranging and imaging on all days was realized. A signal classification and superposition method was used to extract the echo signal submerged in noise. The system was experimentally demonstrated by ranging different noncooperation targets within 105.0 m. The measurement rate was 10 k/s, and the measurement uncertainty was 1.48 cm. In addition, laser imaging was realized at ~50.0 m. The system was simple and portable as well as eye safe, and it may offer new application possibilities in automated vehicle lidar.
... The 1.65-µm coherent DIAL for simultaneous profiling of methane concentration and wind speed has been demonstrated recently [10]. On the other hand, the de-facto standard wavelength of the coherent lidar has moved to the 1.5-µm region [11][12][13][14][15][16][17][18][19][20][21] because of eye-safety and the evolution of devices for optical fibers. Recently, we proposed the 1.53-µm coherent DIAL for the simultaneous profiling of H 2 O density and wind speed, and showed its theoretical feasibility in ground-based measurements [22], with the motivation of future ground-based network stations using this DIAL. ...
... The influence of the ASE in the SNR for the received signal can be negligible by carefully designing the isolation level of the circulator. The self-phase modulation in the fiber amplifier causes an additional up-shift frequency of 2 MHz [16]. Consequently, the sum of this shift frequency and that of AOM is 162 MHz, and is the intermediate frequency of this DIAL system. ...
... The speckle-noise-related SNR is solely derived based on the number of accumulation. The total SNR is calculated using these two SNRs (see, Eqs. (14)- (16) in Appendix B). It is seen that the calculated SNR for OFF wavelength is in good agreement with the experimental one. ...
The 1.53-µm coherent differential absorption lidar (DIAL) is demonstrated for the simultaneous profiling of water vapor (H2O) density and wind speed. The optical setup is fiber-based. The wavelength locking circuit can achieve precise locking of 13.0 MHz by the combination of the line center locking to the hydrogen cyanide (HCN) absorption line and offset locking to the H2O absorption wavelength. The measurable range for the simultaneous profiling is up to 1.2 km. The DIAL-measured H2O density is compared with the one measured by an in-situ sensor. Qualitative good agreement is shown with the random error of 0.56 g/m³.
... All these early works relied on the 10-µm wavelength from CO 2 lasers due to their maturity as compared with other lasers. After these pioneering works, the de facto standard wavelength ofcoherent lidar has moved to the 1.5-µm region [21][22][23][24][25][26][27][28][29][30][31] because of eye safety and the evolution of devices for optical fibers. Unfortunately, the absorption of water vapor is too weak within the gain wavelength band of the erbium-doped fiber amplifier [32]. ...
A feasibility study of coherent differential absorption lidar is conducted using a 1.53-µm wavelength for simultaneously retrieving the water vapor density and wind speed profiles. We selected the ON and OFF wavelengths to be 1531.383 and 1531.555 nm, respectively, for minimizing the effect of the temperature change in the atmosphere. The systematic measurement error can be reduced to below 5% by stabilizing the ON wavelength from ${-64}$ − 64 to 102 MHz around the center of the water vapor absorption line. Analysis of the speckle and photon statistics errors reveal that the relative error of the water vapor density is less than 10% at the altitude from 0.1 to 1.7 km with the 100 m range resolution with 10 min data accumulation time. The simultaneous measurement of wind speed and direction can also be achieved by employing a conical scan mechanism.
This work focuses on the investigation of surface defects in small bearings. Based on the theory of rough surface scattering and the dual-beam ratio measurement method, fiber optic sensing technology is applied in identifying surface defects in bearings. To facilitate the extraction of features for surface defects in bearings, a sensor probe fiber array with three concentric circles around the central emission is determined. A reflective intensity-modulated fiber optic sensor (FOS) is employed to detect surface defects on bearings. The structural parameters of the FOS are simulated through Matlab, considering the inner/outer diameter, numerical aperture, and axial spacing of the sensor. This work involves designing modulation light source excitation circuits, photoelectric conversion module circuits, pre-amplification differential amplifier circuits, infinite gain bandpass filtering circuits, and window function comparison circuits. This effectively amplifies the defect feature signals and eliminates noise interference. In experiments, the sensor probe is fixed on the support of a micro-displacement measurement platform. By adjusting the distance between the probe and the side surface through rotation, initial tests are conducted using standard roughness samples. The results indicate that installing the sensor probe at a distance of 0.92 mm from the side surface provides better measurement of surface roughness. The oscilloscope waveform reveals that the FOS can identify defects on different bearing surfaces. Furthermore, the bearing surface is divided into sections with engraved text (seal cover part) and without engraved text (inner and outer rings of the bearing). Using computer vision (CV) technology, a FOS detection system is designed, achieving a defect recognition rate of 99% for bearings, in line with the intended design goals.
The 1550 nm band semiconductor optical amplifier (SOA) has great potential for applications such as optical communication. Its wide-gain bandwidth is helpful in expanding the bandwidth resources of optical communication, thereby increasing total capacity transmitted over the fiber. Its relatively low cost and ease of integration also make it a high-performance amplifier of choice for LiDAR applications. In recent years, with the rapid development of quantum-well (QW) material systems, SOAs have gradually overcome the shortcomings of polarization sensitivity and high noise. The research on quantum-dot (QD) materials has further improved the noise characteristics and transmission loss of SOAs. The design of special waveguide structures—such as plate-coupled optical waveguide amplifiers and tapered amplifiers—has also increased the saturation output power of SOAs. The maximum gain of the SOA has been reported to be more than 21 dB. The maximum saturation output power has been reported to be more than 34.7 dBm. The maximum 3 dB gain bandwidth has been reported to be more than 120 nm, the lowest noise figure has been reported to be less than 4 dB, and the lowest polarization-dependent gain has been reported to be 0.1 dB. This study focuses on the improvement and enhancement of the main performance parameters of high-power SOAs in the 1550 nm band and introduces the performance parameters, the research progress of high-power SOAs in the 1550 nm band, and the development and application status of SOAs. Finally, the development trends and prospects of high-power SOAs in the 1550 nm band are summarized.
The coherent transceiver for visible wavelength is demonstrated. Successful heterodyne-detection is shown including the Doppler shift detection. The experimental results indicate the future possibility for the coherent communication and Doppler lidar for underwater applications.
The photoelectric tracking control system is a system composed of photoelectric signal detection, signal processing, servo control system and mechanical structure, which plays a crucial role in the field of target tracking. The turret needs to be tested when it leaves the factory, including high-low direction, horizontal direction, aiming speed and other indicators. Moreover, there are large errors in the manual testing methods such as recorder and recording pen, so the photoelectric tracking device is used for the detection of the turret system. First, the hardware of the photoelectric tracking system is designed, including the main control circuit, peripheral expansion module circuit, intelligent power drive circuit and a detection circuit. The system is connected to the camera. The optical signal sent by the system will hit the fixed target. The upper computer will track the trajectory of the light in real-time and then track the trajectory of the turret to obtain the coordinates of the optical signal and the offset angular velocity of the turret. First, color conversion is conducted on the image data collected by photoelectric tracking through the weighted average method. The complete motion path of the turret is obtained through an image denoising algorithm to obtain the motion speed of the turret. In the test, the photoelectric tracking system is first connected to the motor, and enters a stable state when the motor rotor is 80 ms. The rotor speed is faster. When the rotor speed decreases, the system’s current ripple is large, and then decreases rapidly. After the control system is installed in the turret, its display can be driven by FPGA programming. The VGA display of influence time is set, the editing program is downloaded to the FPGA development board, and the gray image of the turret motion track can be seen through the VGA display.
