As a combination of laser technology and modern photoelectric detection technology, lidar (laser radar) has notable advantages compared with traditional radar such as high resolution, strong anti-interference ability, and good low-altitude detection performance. However, with continuous application in aerospace, military, artificial intelligence and other fields, lidar has reached the limits of classical physics and can’t meet the requirements in detection, measurement and imaging. In order to break the bottleneck, worldwide researchers have developed a new type of radar-quantum lidar, which is based on the combination of traditional radar technology and quantum information technology. Its main principle is to get imaging through squeezed light that is below the noise limit of classical physics and then manipulated by the quantum state to achieve imaging with higher quality. Quantum lidar in the paper injects quantum squeezed light to receiver end and uses quantum phase-sensitive amplifier technology to compensate the photon loss that caused by insufficient quantum power to further improve resolution. In the squeezed light, the generation of quantum squeezed light and detection theory are studied, the resonant cavity locking principle and balanced homodyne detection principle are analyzed, and a mode cleaner with narrow line width is designed to improve beam transverse mode quality of laser and filter high frequency noise. In order to reduce quantum noise and improve resolution, quantum lidar imaging system is developed and the theoretically derivation and numerical simulation results show that the resolution of quantum lidar imaging is 1.71 times higher than that of lidar imaging.
Considering the disadvantages of low definition, low image contrast and brightness, inconspicuous details, which make image analysis more complicate, we developed quantum medical image processing system software. It includes quantum image enhancement module, quantum image denoising module and quantum image segmentation module, which respectively study the quantum enhancement algorithm, quantum denoising algorithm and quantum segmentation algorithm. Quantum denoising algorithm firstly add noise to the image and then carries out a logarithmic transformation and a double density dual-tree complex wavelet transform on the noise-added image, later a denoising of the wavelet coefficients based on Bayesian theory, and the Maxaposterior (MAP) is performed to estimate the variance of the double-tree complex wavelet. Finally the denoised image is obtained from the inverse transform of the dual-tree complex wavelet. Quantum enhancement algorithm improves image quality through quantum inspired and unsharp masking. First, a quantum enhancement operator based on quantum superposition state theory was constructed to enhance image contrast ratio, then the processed image quality was improved by unsharp masking. Quantum segmentation algorithm searches automatically the optimal threshold through improved quantum genetic algorithm, which reduces the complexity of program and improves the information entropy compared with traditional methods. More image information can be retained and more ideal segmentation effect is realized through the algorithm. Experiment show that the peak signal-to-noise ratio (PSNR) for the quantum algorithm is improved by over 2dB and the edge retention index (EPI) is 0.1 higher than that for common methods, image information entropy and clarity index are significantly improved.
Recently, ultrafast optical modulators (OMs) based on atomic transition-metal dichalcogenides (TMDs) film have been intensively explored. Benefited from their remarkable nonlinear saturable absorption properties, TMDs based OMs could be employed as critical devices for pulsed lasers systems to transit continuous wave into pulse trains in laser cavity. Herein, the few-layer TMDs films were grown by chemical vapor deposition (CVD) method in possession of uniform thickness, large areas and high crystal quality. Then two types TMDs based OMs were fabricated by integrating single TMDs film or van der waals heterostructures (VdWHs) on the target substrates. As for VdWHs based OMs, different few-layer TMDs films were vertically stacked in turns on the target substrates to form heterointerfaces, which has been demonstrated with ultrafast carrier relaxation time between neighbor layers recently and is favor for ultrafast pulse generation. In our experiments, the nonlinear optical properties of two types TMDs based OMs were systematically investigated by measuring their nonlinear saturable absorption curves and further compared by embedded them into same fiber laser systems. The results indicate that the VdWHs based OMs owns more excellent nonlinear optical properties (such as larger modulation depth, smaller saturable intensity) and offers a feasible strategy to engineer desired ultrafast photonics devices by modifying the structure of VdWHs.
We propose two schemes for achieving tungsten disulfide (WS2)-based saturable absorber (SA) and saturable absorber mirror (SAM). By utilizing the pulsed laser deposition method, we grow the WS2 film on microfiber to form an evanescent field interaction SA device. Incorporating this SA device into a common ring-cavity erbium-doped fiber (EDF) laser, stably passive mode-locking can be achieved with pulse duration of 395 fs and signal-to-noise ratio of 64 dB. We also produce a fiber tip integrated WS2-SAM by utilizing the magnetron sputtering technique (MST). This new type of SAM combines the WS2 layer as SA and gold mirror as high reflective mirror. By employing the WS2-SAM, we construct the linear-cavity EDF lasers, and achieve passive mode-locking operation with pulse duration of ∼1 ns and SNR of ∼61 dB. We further achieve stably passive Q-switching operation with pulse duration of ∼160 ns and pulse energy of 54.4 nJ. These fiber-integrated SAs and SAMs have merits of compactness and reliability, paving the way for the development of new photonic devices such as SAs for pulsed laser technology.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.