- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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25 nJ, 634 ps and 1 MHz all-fiber passively mode-locked fiber laser based on a GaAs saturable absorber
摘要： We demonstrate an all-fiber passively mode-locked Tm-Ho co-doped fiber laser based on a GaAs saturable absorber (SA) fiber laser at 1875.2 nm. With a 10% output coupler, the fiber laser outputs 1.13 MHz, 634 ps and 25 nJ pulses at 1875.2 nm with a 3 dB-bandwidth of 18.4 nm. The Q-switched mode-locking (QML), the mode-locking at fundamental repetition rate (FRR) and the mode-locking at second harmonic of repetition rate (SHRR) are also observed with the increase of the pump power. The main reason of the SHRR is soliton pulse energy quantization effect.
关键词： Low repetition rate,Mode-locked fiber laser,Soliton pulse,Nanosecond pulse,Soliton pulse energy quantization effect
更新于2025-11-28 14:24:03
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Lossless Information Hiding in Images || Lossless Information Hiding in JPEG- and JPEG2000-Compressed Images
摘要： This chapter focuses on the lossless information hiding in JPEG and JPEG2000 images. For JPEG images, seven typical methods including two schemes from the authors were introduced. For the first five schemes, we introduced the basic ideas, whereas for the schemes from the authors, we provided a detailed introduced detail with experimental results. In the first method of ours, our high-capacity reversible JPEG-to-JPEG data hiding scheme is introduced. Through lowering certain quantization table entries and lifting corresponding quantized DCT coefficients, space is made for embedding data. Using the proposed embedding strategy, our scheme can achieve high embedding capacity and keep the distortion introduced by embedding very low; meanwhile the original cover JPEG image can be restored after the secret data are extracted. Experiments results demonstrate that the proposed scheme maintains the image quality of a stego JPEG image when the embedding capacity is high. Besides, the file size after embedding with not too huge data is acceptable. Compared with Chang et al.’s method and Xuan et al.’s method, the proposed method is superior in terms of the image quality, hiding capacity, and file size. Our scheme is very practical for image files stored and transmitted in the JPEG format. In the second method of ours, a lossless data hiding scheme with file size preservation is proposed. Through analyzing the code space and the statistics of both used and unused VLCs, we find there is still potential free space in the JPEG bitstream that can be explored to hide data. The best of unused VLCs are made and mapped to the used VLCs in specific mapping manners. The proposed scheme embeds data into the VLC codes and whatever mapped VLCs are present are not changed, therefore the image content after data hiding is exactly the same as the original one. Experimental results demonstrate that the proposed scheme can reach better performance irrespective of whether file size preservation is required or not. For JPEG2000 images, we first introduced two schemes from the literature, and then introduce our scheme. In our scheme, high-frequency subbands of the cover image are divided into blocks. In each block, a new histogram shifting method is applied to the histogram of the block for embedding data. Every coefficient that is associated with the peak point embeds 2 bits of data. In addition, we shift the histogram to the left or right adaptively according to a direction sign. Experimental results show that the proposed scheme has high embedding capacity and good invisibility of hidden data.
关键词： steganography,histogram shifting,data hiding,quantization table,reversible watermarking,JPEG2000,Lossless information hiding,JPEG,VLC mapping,DCT coefficients
更新于2025-09-23 15:23:52
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Non-Uniform Quantization Codebook Based Hybrid Precoding to Reduce Feedback Overhead in Millimeter Wave MIMO Systems
摘要： In this paper, we propose two non-uniform quantization (NUQ) codebook based hybrid precoding schemes for two main hybrid precoding implementations, i.e., the full-connected structure and the sub-connected structure, to reduce the feedback overhead in millimeter wave single user multiple-input multiple-output (SU-MIMO) systems. Specifically, we firstly group the angles of the arrive/departure (AOAs/AODs) of the scattering paths into several spatial lobes by exploiting the sparseness property of the millimeter wave in the angular domain, which divides the total angular domain into effective spatial lobes' coverage angles and ineffective coverage angles. Then, we map the quantization bits non-uniformly to different coverage angles and construct NUQ codebooks, where high numbers of quantization bits are employed for the effective coverage angles to quantize AoAs/AoDs and zero quantization bit is employed for ineffective coverage angles. Finally, two low-complexity hybrid analog/digital precoding schemes are proposed that utilize the NUQ codebooks. Simulation results demonstrate that, the proposed two NUQ codebook based hybrid precoding schemes achieve near-optimal spectral efficiencies and show the superiority in reducing the feedback overhead compared with the uniform quantization codebook based works.
关键词： feedback overhead,non-uniform quantization,spatial lobe,Millimeter wave communication,hybrid precoding
更新于2025-09-23 15:23:52
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To the Theory of the Polarized Radiation Absorption in a Semiconductor (001) Quantum Well
摘要： The paper considers absorption of linearly polarized radiation in a semiconductor size-quantized well related to optical transitions both between the branches of light and heavy holes and between the size-quantized subbands. Main features of the light absorption in an infinitely deep symmetric well are elucidated. These features are characterized by intraband absorption of light and associated with the direct optical transitions of holes between the subbands of the semiconductor valence band formed due to the size quantization.
关键词： optical transition,semiconductor,size quantization,light absorption coefficient,polarized light,holes
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE 10th Sensor Array and Multichannel Signal Processing Workshop (SAM) - Sheffield (2018.7.8-2018.7.11)] 2018 IEEE 10th Sensor Array and Multichannel Signal Processing Workshop (SAM) - Super-Resolution Pulse-Doppler Radar Sensing via One-Bit Sampling
摘要： This paper investigates the delay-Doppler estimation problem of a pulse-Doppler radar which samples and quantizes the noisy echo signals to one-bit measurements. By applying a multichannel one-bit sampling scheme, we formulate the delay-Doppler estimation as a structured low-rank matrix recovery problem. Then the one-bit atomic norm soft-thresholding method is proposed to recover the low-rank matrix, in which a surrogate matrix is properly designed to evaluate the proximity of the recovered data to the sampled one. With the recovered low-rank matrix, the delays and Doppler frequencies can be determined and paired. Numerical experiments are performed to demonstrate the effectiveness of our method compared with the one-bit sparse signal recovery method based on discrete dictionary.
关键词： Delay-Doppler estimation,atomic norm,compressive sensing,1-bit quantization
更新于2025-09-23 15:22:29
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[IEEE 2018 Asia Communications and Photonics Conference (ACP) - Hangzhou, China (2018.10.26-2018.10.29)] 2018 Asia Communications and Photonics Conference (ACP) - Performance Improvement of IM-DD OFDM Systems by Nonuniform DAC Output Levels
摘要： We propose and experimentally demonstrate a nonuniform quantization scheme to improve the signal-to-quantification noise ratio (SQNR) for low-bit resolution digital-to-analog converter (DAC) based intensity-modulated direct-detection (IM-DD) orthogonal frequency division multiplexing (OFDM) transmission systems. In this scheme, the discrete output levels of DAC are nonuniform and properly assigned based on the A-law and Lloyd algorithm. The effectiveness of the proposed method is verified by IM-DD OFDM transmission systems with various modulation formats and resolution. The experimental results show maximal 3.9 dB performance improvement after 10-km standard single mode fiber (SSMF) transmission.
关键词： OFDM,IM-DD,Nonuniform quantization,DAC
更新于2025-09-23 15:22:29
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Vector quantization using the improved differential evolution algorithm for image compression
摘要： Vector quantization (VQ) is a popular image compression technique with a simple decoding architecture and high compression ratio. Codebook designing is the most essential part in vector quantization. Linde–Buzo–Gray (LBG) is a traditional method of generation of VQ codebook which results in lower PSNR value. A codebook affects the quality of image compression, so the choice of an appropriate codebook is a must. Several optimization techniques have been proposed for global codebook generation to enhance the quality of image compression. In this paper, a novel algorithm called IDE-LBG is proposed which uses improved differential evolution algorithm coupled with LBG for generating optimum VQ codebooks. The proposed IDE works better than the traditional DE with modifications in the scaling factor and the boundary control mechanism. The IDE generates better solutions by efficient exploration and exploitation of the search space. Then the best optimal solution obtained by the IDE is provided as the initial codebook for the LBG. This approach produces an efficient codebook with less computational time and the consequences include excellent PSNR values and superior quality reconstructed images. It is observed that the proposed IDE-LBG find better VQ Codebooks as compared to IPSO-LBG, BA-LBG and FA-LBG.
关键词： Improved differential evolution (IDE) algorithm,Improved particle swarm optimization (IPSO) algorithm,Bat algorithm (BA),Firefly algorithm (FA),Vector quantization,Image compression,Codebook,Linde–Buzo–Gray (LBG) algorithm
更新于2025-09-23 15:22:29
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[IEEE 2019 Compound Semiconductor Week (CSW) - Nara, Japan (2019.5.19-2019.5.23)] 2019 Compound Semiconductor Week (CSW) - $\mathbf{1545}\ \mu \mathbf{m}$ Quantum Dot Vertical Cavity Surface Emitting Laser with low threshold
摘要： Approximate Nearest Neighbor (ANN) search has become a popular approach for performing fast and efficient retrieval on very large-scale datasets in recent years, as the size and dimension of data grow continuously. In this paper, we propose a novel vector quantization method for ANN search which enables faster and more accurate retrieval on publicly available datasets. We define vector quantization as a multiple affine subspace learning problem and explore the quantization centroids on multiple affine subspaces. We propose an iterative approach to minimize the quantization error in order to create a novel quantization scheme, which outperforms the state-of-the-art algorithms. The computational cost of our method is also comparable to that of the competing methods.
关键词： vector quantization,Approximate nearest neighbor search,subspace clustering,large-scale retrieval,binary codes
更新于2025-09-23 15:21:01
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Electromagnetically induced grating with second field quantization in spherical semiconductor quantum dots
摘要： A new approach for diffracting the weak probe beam into higher-order directions is proposed via electromagnetically induced grating in second field quantization formalism, offering a new way for implementations of quantum information with semiconductor quantum dots. The formalism of second field quantization allows describing atoms and photons as a many-body system. An induced diffraction grating is formed based on the electromagnetic induced transparency when a standing-wave coupling field is applied to a spherical quantum dot as a three-level system. Due to phase modulation, the zeroth-order light intensity becomes weak, and the first-order diffraction is improved affectedly. On the contrary, the probe beam is barely diffracted via absorption modulation. The simulation results verify that photon numbers of probe and control fields, as well as other parameters in the QD, can lead to the diffraction efficiency of phase grating to be improved. Phase diffraction grating accompanied with a high transmissivity is demonstrated, and the first-order diffraction efficiency reaches 30%. Also, the impact of QD dimensions on its optical response is investigated. This model may find potential applications in designing the semiconductor quantum dot-based photonic devices in optical communications and quantum information networks.
关键词： Electromagnetically induced grating (EIG),Semiconductor quantum dot (SQD),Second field quantization
更新于2025-09-23 15:21:01
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Hybrid Plasmonic Waveguide based 3??3 Multimode Interferometer for Compact 120?° Optical Hybrid
摘要： The Kinect system is arguably the most popular 3-D camera technology currently on the market. Its application domain is vast and has been deployed in scenarios where accurate geometric measurements are needed. Regarding the PrimeSense technology, a limited amount of work has been devoted to calibrating the Kinect, especially the depth data. The Kinect is, however, inevitably prone to distortions, as independently confirmed by numerous users. An effective method for improving the quality of the Kinect system is by modeling the sensor’s systematic errors using bundle adjustment. In this paper, a method for modeling the intrinsic and extrinsic parameters of the infrared and colour cameras, and more importantly the distortions in the depth image, is presented. Through an integrated marker- and feature-based self-calibration, two Kinects were calibrated. A novel approach for modeling the depth systematic errors as a function of lens distortion and relative orientation parameters is shown to be effective. The results show improvements in geometric accuracy up to 53% compared with uncalibrated point clouds captured using the popular software RGBDemo. Systematic depth discontinuities were also reduced and in the check-plane analysis the noise of the Kinect point cloud was reduced by 17%.
关键词： 3D/stereo scene analysis,quality assurance,quantization,camera calibration,Kinect
更新于2025-09-23 15:21:01