Rotating Doppler velocimetry of a target has gained huge development in decade, from the initially required alignment between optical and rotary axes to lateral and angular deviations of them. However, signal-to-noise ratio (SNR) and measured error are still salient for rotating velocimetry of an arbitrary pose-varied target, especially when the deviations (including lateral or/and angular conditions) inevitably exist. Here, we proposed and demonstrate a feed-back compensation scheme for overcoming these difficulties, based upon measuring and manipulating orbital-angular-momentum (OAM) phase spectrum. The conjugate OAM superposed states are firstly launched to a rotating surface with lateral or/and angular deviations and then we measure the OAM complex spectrum and rotating Doppler spectrum of the echo photons, respectively. We further modulate the measured specific OAM phase spectrum components and combine the original OAM amplitude spectrum to reconstruct the updated emitted light on a diffractive phase element. In doing so, the measured SNR and the accuracy of the rotating Doppler velocimetry are gradually improved. As a consequence, we thus develop a high-sensitive and high-accuracy rotating Doppler velocimeter This laboratory-constructed prototype might be additionally pushed for applications in astrophysics, industrial manufacturing and meteorological monitoring, etc.
Laser active detection is a remote sensing technology that utilizes laser beams to detect various attributes of a target such as distance, orientation, height, and speed. The direct detection Signal-to-Noise Ratio (SNR) achieved by traditional array imaging systems is usually unsatisfactory because of different types of interferences, including backscattering effects and background noise. Related to this, the performance of existing methods for noise filtering are bounded by the classical detection signal-to-noise ratio. In particular, and there is no effective filtering method when the wavelength of the signal and noise is the same. To address this challenge, this study presents a novel approach to enhancing the Signal-to-Noise Ratio (SNR) of array imaging through the use of quantum state engineering. At the transmitter, we modulate the signal photons with orbital angular momentum to distinguish them from the photons of noise without orbital angular momentum. This modulation makes the signal and noise have differences in spatial intensity distribution. Due to this spatial difference, the signal and noise can be non-destructively separated after passing through the filter at the receiver, which gives enhanced SNR. The results show that this method can effectively filter out the noise with the same wavelength as the signal, and can improve the performance of array imaging detection.
Imaging through turbid medium has many potential applications such as looking through clouds, seeing into seawater and observing through biological tissues. The transmission matrix (TM) method is one of the main imaging technologies that has potential in imaging of large targets. With aid of pre-measured TM, several optimization models are proposed to recover targets from speckle patterns, including ℓ2 norm optimization model, sparse representation (SR) framework and total variation (TV) model. However, the solution of ℓ2 norm optimization model contains large reconstruction noise, while the SR framework and TV model are two kinds of compressive sensing strategies, which require that the targets are sparse. In this paper, in order to image non-sparse targets and suppress the reconstruction noise, we apply the maximum entropy method (MEM) model to recover the target images from speckle patterns. Simulation results show that, for non-sparse target, the MEM model has better reconstruction performance under different noise levels compared with the TV model. For example, peak signal-to-noise ratio (PSNR) and correlation coefficient (CC) of images reconstructed by MEM model at SNR=15 dB are comparable with those by TV model at SNR=35 dB.
Scattering medium is always a problem to be overcome in traditional optical imaging technology. In recent years, a speckle intensity correlation technique has been proposed to achieve high quality reconstruction of targets hidden in the scattering medium. Unfortunately, the imaging field of view (FOV) of this technology is seriously limited by the optical memory effect (OME) range. Here, we propose an iterative point-spread-function deconvolution (IPSFD) method to reconstruct multiple targets. According to the reversibility of the deconvolution algorithm, the IPSFD method starts from a small known target, and estimates the adjacent targets and point-spread-functions continuously by the iterative deconvolution algorithm, and finally reconstructs all targets within around three times the optical memory effect range. Theoretical and experimental results confirm that our method can achieve multi-target reconstruction of the single-shot large FOV speckle pattern. This method may have potential in practical applications biomedical imaging, astronomical imaging, and atmospheric turbulence imaging.
A graphene-assisted microwave photonics filter based on micro-ring resonators is proposed. This setup demonstrated a filter with a flat transmission band and significantly enhanced tunability that a more than 70 GHz frequency shift of the center frequency has realized. The filter will be able to switch by electrical gating on different modes including lowpass, bandpass, and highpass. In the simulation results, the proposed filter exhibits the advantages of high sideband suppression, outstanding rectangular coefficient, and high tunability. Moreover, the construction of filters based on the SOI platform adapts to the developmental requirement of monolithic integration in microwave photonic devices.
KEYWORDS: Photons, Single photon, Signal detection, Polarization, Metrology, Sensors, Super resolution, Crystals, Quantum information, Biological research
Quantum process tomography, as an advanced means of metrology, has a capacious range of applications for estimating numerous meaningful parameters. The parameter estimate precision of using coherent state and single photon state as probe are limited by the shot noise limit. Here we demonstrate a quantum enhanced rotating angle measure scheme based on the four-photon Holland-Burnett state can achieve the Heisenberg scaling by the coincidence counting technology. At the same time, the output signal of our scheme has an 8-fold super-resolution compared to the Malus law. In addition, the accuracy achieved by four photons is consistent with using 12 photons of single photon probe. That has incomparable preponderance in a situation in which only weak light can be exploited, like the measure of frangible biological specimens and photosensitive crystals. Moreover, the four-photon Holland-Burnett state can be generated by a polarization-entangled light source. These ensure that our scheme has a champaign application prospect.
Lidar based on Geiger-mode Avalanche Photodiode Detector (Gm-APD), also called Gm-APD Lidar for short, has the advantages of the ultra-high sensitivity and ranging accuracy, and therefore it is widely used in the weak signal detection over a long distance. Time-Correlated Single Photon Counting (TCSPC) is a more commonly used signal processing method of Gm-APD Lidar. However, after each avalanche response, Gm-APD needs a certain time to quench avalanche current, which is called the dead time. In the dead time, Gm-APD can't response any signal. This will result in the uneven response by Gm-APD, and the response probability of the front of the echo pulse signal is higher than that of the back of the echo pulse signal. The peak of photon counting results will deviate from the real peak of the echo signal, and this deviation will become larger with the increase of the echo pulse width. In many application environments (for example, underwater, battlefield smoke, fog and dust, etc.), the broadening effect of the echo pulse signal is obvious, and this will seriously impact the ranging accuracy of Gm-APD Lidar. In this paper, an improved method uses the multi-gate detection to response the complete waveform of the echo pulse signal, and thus improves the ranging accuracy of GmAPD due to obtaining more accurate echo pulse peak.
The polarization of the light is an excellent information carrier, but polarization information of coherent state in the quantum measurement of the past has not been clearly expressed. We refer to some ideas of quantum computation and quantum information, considering the polarization mode of the electromagnetic field to describe polarization information of a coherent state. And on this basis we put forward a polarization rotation angle measurement device based on a Mach-Zehnder interferometer and two polarizers. We also consider the intensity detection, parity detection and Z detection as detection strategies. The results show that this device can realize the super-resolution and shot noise limit with parity detection and Z detection. By simulation analysis, we finally find parity detection is the best method for our scheme, and we also discuss the effects of some parameters on sensitivity and resolution with parity detection.
We propose a novel strategy of asymmetric triangular-wave modulation for photon-counting chirped amplitude
modulation (PCCAM) lidar. Earlier studies use the symmetric triangle wave modulation, by which the velocity can be
detected only when the Doppler shift caused by a moving target is greater than Full Width Half Maximum (FWHM) of
Intermediate Frequency (IF). We use an alternative method known as the asymmetric triangular wave modulation
method, in which the modulation rates of the up-ramp and the down-ramp are different. This new method avoids the
overlapping of the up-ramp and the down-ramp IF peaks, and breaks the limit of the FWHM of IF peak to improve the
velocity measuring sensitivity (also called the minimum detectable velocity). Finally, a proof-of-principle experiment is
carried out in the laboratory. The experimental results agree well with the theoretical results and show the improvement
of the minimum detectable velocity.
Since Geiger mode Avalanche Photodiode (GmAPD) device was applied in laser radar system, the performance of
system has been enhanced due to the ultra-high sensitivity of GmAPD, even responding a single photon. However, the
background noise makes ultra-high sensitive GmAPD produce false alarms, which severely impacts on the detection of
laser radar system based on Gm-APD and becomes an urgent problem which needs to be solved. To address this
problem, a few times accumulated two-GmAPDs strategy is proposed in this paper. Finally, an experimental
measurement is made under the background noise in sunny day. The results show a few times accumulated two-
GmAPDs strategy can improve the detection probability and reduce the false alarm probability, and obtain a clear 3D
image of target.
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