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.
Traditional lidar sensitivity is not up to the requirements in detecting small long-range targets with weak echo signals. Due to the limitation by the background noise of sunlight and complex climate, the high sensitivity detection cannot be realized by a photon counting lidar with Geiger-mode Avalanche Photodiode Detector (Gm-APD). In this paper, a new system is proposed to improve the performance of photon counting lidar ranging based on two-dimensional modulation. The new system uses two modulation methods to modulate the transmitted signal, which are chirp modulation and photon orbital angular momentum modulation. Chirped modulation is used to adjust the transmitted signal waveform in the frequency domain, and the detection performance improvement of Gm-APD can be improved with response probability correction. Photon orbital angular momentum modulation is used to adjust the transmitted signal waveform in the spatial domain, which is used to filter out background noise. The simulation results show that two-dimensional modulation is independent and do not interfere with each other. Comparing with the traditional lidar, the detection probability increased by 52%; the SNR can be increased by up to 115%, the range accuracy can be up to two-thirds of the traditional range accuracy (means increased by 32%). The new system achieves high sensitivity detection in complex environment.
Traditional lidar is not effective in detecting small long-range targets with weak echo signals. Geiger-mode Avalanche Photodiode (Gm-APD) single photon detector has super high sensitivity. By adding photon orbital angular momentum modulation module, a photon-counting chirped amplitude modulation lidar with high sensitivity ranging function is designed. Based on the characteristics of photon orbital angular momentum space transmission, a special demodulation method is used to realize the spatial separation of noise and signal. The above scheme achieves the goal of high sensitivity ranging detection. The simulation results show that the scheme can improve the signal-to-noise ratio of the system effectively and realize the high-sensitivity ranging function of small target in long distance.
In modern radar systems and electronic warfare systems, instantaneous microwave frequency measurement (IFM) is widely used for detecting and roughly classifying unknown signals. However, conventional electrical approaches realizing IFM have hit the bottleneck of limitation in measurement range due to the limited bandwidth of the electronic components. Photonics-based approaches for microwave spectrum analysis are considered to be competitive alternatives because of the advantages such as wide instantaneous bandwidth, low loss and immunity to electromagnetic interference. In the past decades, a few methods of photonic approaches have been proposed. A tunable fiber Fabry-Perot interferometer (FFP)1 and a fiber Bragg grating2 used as an optical scanning receiver were reported, but the response time is long due to the piezoelectric ceramics (PZT) or electric heating driven systems, the scanning speed is only 200 Hz 2. IFM based on frequency-amplitude mapping technique was previously demonstrated.3, 4 However, the measurement range is limited to about 20 GHz and the accuracy varies in the whole range. In recent years, frequency measurement based on stimulated Brillouin scattering (SBS) with high resolution was reported,5, 6 but the existence of a scanning microwave signal source made the system complex and the response time is depended on the sweeping speed of the local oscillator, which is of the order of milliseconds. In Ref. 7, a system integrating SBS and a frequency shifting recirculating delay line (FS-RDL) was demonstrated. The sweeping time is about hundreds of microseconds, but there is a trade-off between sweeping time and measurement range. Measurement period of 5 s in 20 GHz range has been realized by channelized radio frequency measurement scheme.8 However, the implementation of an analog-to-digital converter with bandwidth of 2 GHz made the system complex and costly.
In this work, a novel approach of ultrafast frequency measurement based on electro-optic Fabry-Perot (EOFP) scanning receiver is proposed for the first time. In comparison with other frequency scanning measurement systems, which use methods such as mechanical tuning, electric heating, scanning microwave signal, FS-RDL, etc., our double-EOFP system can measure signals with frequency under 54 GHz in 2 s, which is the fastest scanning rate as far as we know.
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.
Interferometric synthetic aperture lidar (InSAL) can achieve high precision 3D imaging, while the image registration algorithm for generating critical interference figure is very important for InSAL. AS the difference between Interferometric Synthetic Aperture Radar (InSAR) and InSAL in dealing with the noise, it is hard for registration algorithmto be used directly in InSAL. To solve this problem, this paper proposes a combination registration algorithm, using the correlation function method both in rough registration and fine registration in the data of Doppler away from zero, and using the spectrum registration method in the data of near zero point by Doppler. The registration accuracy can reach 0.1 a pixel. The simulation results show that the accuracy of the proposed algorithm is improved to 1.43% compared with the traditional spectral registration algorithm.
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.
Fiber Doppler lidar systems the advantage of high velocity precision over conventional differential velocity measurement. However, the velocity precision of fiber Doppler lidar systems may be degraded by the complex motion of the target, the roughness of the target and the discrete digital data processing. In this paper, a setup of 1064 nm fiber Doppler lidar system is proposed to measure the velocity of radial moving targets. Detailed theoretical analysis was conducted with the influence factors on the velocity precision of the system, and simulations were conducted with an optimized design. A prototype was constructed in the laboratory and experiments were carried out with the prototype. The experimental velocity was 2.65 cm/s, and the relative velocity precision was superior to 0.3%, which proved the validity of the research.
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.
Nowadays LADAR system set on practical moving platform is purposed to detect real-time velocity as well as precise distance and direction evaluation for safe landing or obstacles avoiding. On account of narrow band, brief algorithm, non-modulated CW Doppler LADAR based on optical heterodyne principle could acquire the velocity of multiple targets with high frame frequency, high SNR ratio while no velocity ambiguity. In this paper, a non-modulated 1064nm CW Doppler fiber LADAR system with high frame frequency as well as high velocity precision is proposed. The experimental result of the system shows a velocity precision of 6.65mm/s, and a velocity detection frame frequency of 20FPS, which essentially meet the practical demands.
The conventional phase coded lidar systems require the collection of every returned laser pulse and are restricted in
range resolution by sampling frequency and subpulse width. A phase coded lidar system with high range resolution is
proposed with the accumulated m-sequence acquisition method by utilizing detector characteristics for signal detection.
The detector accumulates kN-1 or kN+1 bits of the emitted laser sequence to deduce the a single bit of the sequence. The
indoor experiment achieved 2 us resolution with the sampling period of 28 and 32 us by employing a 15-bit m-sequence.
This method achieves the acquisition of m-sequence with narrow subpulse width whereas the sampling frequency is kept
low. The experiment results showed an approach to implement the phase coded imaging lidar into practical application.
Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
Based on the classical optical coherence theory, a single detector virtual ghost imaging (VGI) with partially coherence hyperbolic cosine Gaussian beam has been demonstrated theoretically. An analytical imaging formula is obtained and the numerical calculation results lead to the influences of the turbulence strength, the propagation distance and the coherent parameters of the beam on the imaging quality. Moreover, we find that the VGI with hyperbolic cosine Gaussian beam can resolve the target better than the VGI with the conventional Gaussian Schell model beam under similar conditions.
A gain-modulated laser range imaging technology is generalized and its range accuracy is deduced. Theoretical results
indicate that the range accuracy is proportional to the ratio of gain function to the derivative of the gain function and
inverse proportional to output SNR. A gain-modulated laser range imaging system is established in our laboratory. It
consists of a pulsed laser which is capable of generating laser pulses with a pulse width of 10ns and a center wavelength
of 532 nm, and a receiver which is a digital 256×256 CCD sensor coupled to a GEN II intensifier with a 10nm bandwidth
optical filter. Image intensifier is electronically driven and can be set to three modulated gain or constant gain. A range
image of the target can be extracted by processing an intensity image with modulated gain and an intensity image with
constant gain. Some indoor experiments are performed with sinusoidal, linear and exponential gain functions. The range
images of the targets from 52 m to 58 m is taken and analyzed. Experimental results demonstrate the range accuracy with
both sinusoidal and linear gain function depends on the relative range but one with exponential gain function
independent of relative range. Specially, in the exponential gain function case the relatively small time constant can
contribute to relatively high range accuracy.
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.
This paper presents an equivalent direct detection receiver model by statistical method which simplifies the random
impulse responses of electrons counting of returned signal, background radiation and dark current as a Gaussian random
process with high enough gain. An investigation based on Gaussian distribution of system output in ICCD scannerless
range-gated Lidar system is conducted with the calculations of error probability, absolute error and relative error. As the
unique manipulated variable, optimized system gains are calculated separately based on the Gaussian model of the
random process to achieve the lowest error probability, the lowest absolute error and relative error. The simulations show
that the values of optimized gains tend to increase along with the target distance, although the increasing speeds are
different. To meet multiple requests, an evaluation model based on cost function is constructed with different weights.
The simulation shows that the evaluation model is capable of setting optimized gains for different circumstances and the
settings of the weights are vital to the performance of Lidar system.
Scannerless laser imaging radar will be the trend of laser imaging radar in future because it has several advantages of
high frame rate, wide field of view, small size and high reliability owing to giving up mechanical scanner. A scannerless
gain-modulated three-dimensional laser imaging radar is developed: Our system consists of a pulsed laser which is
capable of generating 100mJ pulses with a pulse width of 10ns and a center wavelength of 532 nm, and a receiver which
is a digital CCD sensor coupled to a GEN II intensifier with a 10nm bandwidth optical filter. The homogenized light
beam passes through a diverging lens to flood illuminate the targets. The return light is collected by a Nikon camera lens
and amplified by the image intensifier which is electronically driven and can be set to exponentially modulated gain or
constant gain. The CCD sensor can record a 12 bit gray-level image with a resolution of 780×582 pixels at a 50 Hz frame
rate. For a range image of the target can be extracted by processing an intensity image with exponentially modulated gain
and an intensity image with constant gain, the range image is acquired at a 25 Hz frame rate. During our outdoor
experiment, the range image of the targets at 500m is acquired with 2m range accuracy and the range image of the targets
at about 1 kilometer is acquired with 5m range accuracy in daytime.
Ladar system simulation is to simulate the ladar models using computer simulation technology in order to
predict the performance of the ladar system. This paper presents the developments of laser imaging radar
simulation for domestic and overseas studies and the studies of computer simulation on ladar system with
different application requests. The LadarSim and FOI-LadarSIM simulation facilities of Utah State University
and Swedish Defence Research Agency are introduced in details. This paper presents the low level of
simulation scale, un-unified design and applications of domestic researches in imaging ladar system
simulation, which are mostly to achieve simple function simulation based on ranging equations for ladar
systems. Design of laser imaging radar simulation with open and modularized structure is proposed to design
unified modules for ladar system, laser emitter, atmosphere models, target models, signal receiver, parameters
setting and system controller. Unified Matlab toolbox and standard control modules have been built with
regulated input and output of the functions, and the communication protocols between hardware modules. A
simulation based on ICCD gain-modulated imaging ladar system for a space shuttle is made based on the
toolbox. The simulation result shows that the models and parameter settings of the Matlab toolbox are able to
simulate the actual detection process precisely. The unified control module and pre-defined parameter settings
simplify the simulation of imaging ladar detection. Its open structures enable the toolbox to be modified for
specialized requests. The modulization gives simulations flexibility.
A novel approach based on the theory of stochastic resonance (SR) for detecting weak signals in heavy noise for detecting distance information for laser ranging is presented in this paper. SR in a nonlinear system is a cooperative effect of noise and periodic signal driving in bi-stable systems. Under the proper condition, increasing input noise level results in an increase in the output signal-to-noise ratio (SNR), which means increasing the disorder of the input leads to increasing the order of the output. Driven by a periodic signal and a Gaussian white noise, stochastic resonance exists in the double-well potential system. This stochastic resonance phenomenon can greatly improve the SNR of a periodic signal with additive Gaussian white noise. In this paper the theoretical derivation for bi-stable system at the SR and the computer simulation have been given. Under the generic adiabatic approximation condition, a numerical simulation on such as the out SNR shows that the output SNR in heavy ground noise has been improved evidently. In laser ranging system, the SR theory was applied in electronic circuits and the out SNR improved obviously.
In optical remote sensing systems especially the imaging systems the quality of the scanner is the key element for obtaining high quality 2-D image of the target. There must be a detection device to verify the scanning performance of the optical scanner. In this paper such a detection device was developed. It consists of large area CCD camera, specific optical lens, electronics shutter, computer control element and scanning performance analysis software. The core technologies in developing the device are to design the specific optical lens, eliminate the delaying trail in the detecting image and recognize and analyze the spot matrix in the detecting image. The detection field of view can be wider than 10o×10o and resolution better than 0.1mrad. This device can not only perform real time detection on line, displaying dynamic values of all the detecting parameters, but also perform off line, displaying values of various detecting parameters for a given image taken at anytime. To consider the objectivity and creditability of the detecting result, there is an adjusting program to ensure the collimation between the detection device and the given optical scanner.
A wavelet analysis is a time-frequency domain analysis between the time-domain analysis and the Fourier frequency- domain analysis, that is, a wavelet function is considered as integral kernel of a wavelet transform, characterized by well-localized property of time-frequency domain. A wavelet function is converted by a mother wavelet shifting and flexing. The sampling interval is self-adjusted, as the signal frequency components are different. So the signal detail can be focused on at will. In this paper, a novel method is presented to detect a rectangle-pulse signal of pulse laser radar, which is submerged from noise, by means of the wavelet transform. As to rectangle-signal, the wavelet transform coefficient can be obtain the maximum value by selecting a couple of optimum wavelet variables and a filter comes into being so that the signal noise ratio is improved to detect the signal.
An IR flare is used as a source in the half-active IR night- viewer system, and the non-scanning IR micro-photoelectric camera as a sensor. The clear image had been obtained at night. Some IR flares and the automatic testing equipment had been developed. Then the integral radiation character of the IR flares had been measured. Some samples with more kind of the fuel components are manufactured, the wavelength of the IR flare for maximum radiant flux have matched with the responded wavelength of the sensor. The clearly reflective image of the targets had been obtained at 400m and 700m in the field tests. In this paper, the we develop a sample of IR flare as radiant point and characters, measuring system and method and test in our field are introduced.
A short coherence length of a laser diode (LD) is required in coherent resolved interferometers. The coherence length of a LD can be reduced by modulating the source with a high frequency signal, which is superposed on the driving current for the LD. A 980nm laser diode in this paper is modulated with a frequency 40MHz and modulation depth 0.5, where its coherence length is compressed 20 times. The first side-band peak in the coherence function is reduced by 10dB, but it is hard to suppress them completely.
In order to navigate through its environment a robot vehicle needs to determine its position relative to a certain target. Now in the robot vision system the light spots measuring technique can be used. A charge coupled device camera is used as a sensor in the technique, but because it needs a complex focusing and processing system, the technique is not simple enough and the method for relative positioning is not quick, the processing is computationally intensive. In order to overcome the these defects a simple and reliable sensor, that is the position sensitive detector (PSD) is used as a close range sensor. In this paper, a new algorithm of measuring light spot, the structure and principle of the PSD are introduced. The scheme of measuring with PSD in the robot vision system is demonstrated. Using the system the robot position relative to the target can be determined.