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<jats:p>On the basis of the objective functions, dithering optimization techniques can be divided into the intensity-based optimization technique and the phase-based optimization technique. However, both types of techniques are spatial-domain optimization techniques, while their measurement performances are essentially determined by the harmonic components in the frequency domain. In this paper, a novel genetic optimization technique in the frequency domain is proposed for high-quality fringe generation. In addition, to handle the time-consuming difficulty of genetic algorithm (GA), we first optimize a binary patch, then join the optimal binary patches together according to periodicity and symmetry so as to generate a full-size pattern. It is verified that the proposed technique can significantly enhance the measured performance and ensure the robustness to various amounts of defocusing.</jats:p>

<jats:p>As a typical technology for optical encryption, phase retrieval algorithms have been widely used in optical information encryption and authentication systems. This paper presents three applications of two-dimensional (2D) phase retrieval for optical encryption and authentication: first, a hierarchical image encryption system, by which multiple images can be hidden into cascaded multiple phase masks; second, a multilevel image authentication system, which combines (<jats:italic>t</jats:italic>, <jats:italic>n</jats:italic>) threshold secret sharing (both <jats:italic>t</jats:italic> and <jats:italic>n</jats:italic> are positive integers, and <jats:inline-formula> <jats:tex-math> <?CDATA $t\le n$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>t</mml:mi> <mml:mo>≤</mml:mo> <mml:mi>n</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_8_084203_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) and phase retrieval, and provides both high-level and low-level authentication; and finally, a hierarchical multilevel authentication system that combines the secret sharing scheme based on basic vector operations and the phase retrieval, by which more certification images can be encoded into multiple cascaded phase masks of different hierarchical levels. These three phase retrieval algorithms can effectively illustrate phase-retrieval-based optical information security. The principles and features of each phase-retrieval-based optical security method are analyzed and discussed. It is hoped that this review will illustrate the current development of phase retrieval algorithms for optical information security and will also shed light on the future development of phase retrieval algorithms for optical information security.</jats:p>

<jats:p>Ghost imaging (GI) is thought of as a promising imaging method in many areas. However, the main drawback of GI is the huge measurement data and low signal-to-noise ratio. In this paper, we propose a novel mask-based denoising scheme to improve the reconstruction quality of GI. We first design a mask through the maximum between-class variance (OTSU) method and construct the measurement matrix with speckle patterns. Then, the correlated noise in GI can be effectively suppressed by employing the mask. From the simulation and experimental results, we can conclude that our method has the ability to improve the imaging quality compared with traditional GI method.</jats:p>

<jats:p>A method of single-shot phase-shifting digital holography with a photon-sieve-filtering telescope is proposed. Three copy images with different phases are first generated by use of a monofocal photon-sieve filter in Kepler telescope, and then interfere with the reference plane wave by a beam combiner. The hologram is captured by a charge-coupled device (CCD) in one single exposure. The complex-valued amplitude of the test object can be reconstructed by three-step phase-shifting interferometry through three frames of extracted sub-interferograms from the single-exposure hologram. The principle and simulation experiments are carried out and verified the validity of our proposed method. This method can be applied for snapshot imaging and three-dimensional object construction.</jats:p>

<jats:p>Based on the Weyl expansion representation of Wigner operator and its invariant property under similar transformation, we derived the relationship between input state and output state after a unitary transformation including Wigner function and density operator. It is shown that they can be related by a transformation matrix corresponding to the unitary evolution. In addition, for any density operator going through a dissipative channel, the evolution formula of the Wigner function is also derived. As applications, we considered further the two-mode squeezed vacuum as inputs, and obtained the resulted Wigner function and density operator within normal ordering form. Our method is clear and concise, and can be easily extended to deal with other problems involved in quantum metrology, steering, and quantum information with continuous variable.</jats:p>

<jats:p>A Q-switched erbium-doped fiber laser (EDFL) incorporating zinc-oxide (ZnO) nanoparticles-based saturable absorber (SA) is proposed and demonstrated. To form the SA, the ZnO nanoparticles, which are originally in the powder form, are first dissolved in ethanol and subsequently deposited onto the surface of fiber ferrule by using the adhesion effect with the evaporation technique. By integrating the ZnO nanoparticle-based SA into a laser cavity of an EDFL, a self-started and stable Q-switching is achieved at a low threshold power of 20.24 mW. As the pump power is increased, the pulse repetition rate is tunable from 10.34 kHz to 25.59 kHz while pulse duration decreases from <jats:inline-formula> <jats:tex-math> <?CDATA $21.39\,{\rm{\mu }}{\rm{s}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>21.39</mml:mn> <mml:mspace width="0.50em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">s</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_8_084207_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> to <jats:inline-formula> <jats:tex-math> <?CDATA $3.65\,{\rm{\mu }}{\rm{s}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>3.65</mml:mn> <mml:mspace width="0.50em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">s</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_8_084207_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Additionally, this Q-switched laser has a maximum energy per pulse of 19.34 nJ and an average output power of 0.46 mW. These results indicate the feasibility and functionality of the ZnO nanoparticles-based SA for Q-switched generation, which offers the flexibility and easy integration of the SA into a ring laser cavity.</jats:p>

<jats:p>As a preferable material in the field of photo-detection and catalysis, the characteristics of FePS<jats:sub>3</jats:sub> in broad wavelength range have been proven by many experimental studies. However, FePS<jats:sub>3</jats:sub> has not been used as a saturable absorber (SA) in fiber lasers yet. We propose and demonstrate the generation of a single wavelength and dual-wavelength based on an Er-doped fiber laser (EDFL) at <jats:inline-formula> <jats:tex-math> <?CDATA $1.5\,{\rm{\mu }}{\rm{m}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1.5</mml:mn> <mml:mspace width="0.50em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_8_084208_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> by using an innovative FePS<jats:sub>3</jats:sub> saturable absorber for the first time. The result shows that a stable passively Q-switched pulse can be generated, which demonstrates that the new two-dimensional (2D) material FePS<jats:sub>3</jats:sub> served as SA provides a valid method to realize passively Q-switched laser. In addition, we achieve the output of the dual-wavelength pulse by properly rotating the polarization controller. To the best of our knowledge, the dual-wavelength pulse EDFL could be applied in biomedicine, spectroscopy, and sensing research.</jats:p>

<jats:p>Fiber-based mid-infrared (MIR) supercontinuum (SC) sources benefit from their spectral brightness and spatial coherence that are needed for many applications, such as spectroscopy and metrology. In this paper, an SC spanning from <jats:inline-formula> <jats:tex-math> <?CDATA $2\,{\rm{\mu }}{\rm{m}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2</mml:mn> <mml:mspace width="0.50em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_8_084209_ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> to <jats:inline-formula> <jats:tex-math> <?CDATA $6\,{\rm{\mu }}{\rm{m}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>6</mml:mn> <mml:mspace width="0.50em" /> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_8_084209_ieqn6.gif" xlink:type="simple" /> </jats:inline-formula> is demonstrated in cascaded ZrF<jats:sub>4</jats:sub>–BaF<jats:sub>2</jats:sub>–LaF<jats:sub>3</jats:sub>–AlF<jats:sub>3</jats:sub>–NaF (ZBLAN) and As<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> step-index fibers. The pump source is a ZBLAN fiber-based MIR SC laser with abundant high-peak-power soliton pulses between 3000 nm and 4200 nm. By concatenating the ZBLAN fiber and the As<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> fiber, efficient cascading red-shifts are obtained in the normal dispersion region of the As<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> fiber. The spectral behavior of cascaded SC generation shows that the long-wavelength proportion of MIR SC generated in the ZBLAN fiber plays a critical role for further spectral extension in the As<jats:sub>2</jats:sub>Se<jats:sub>3</jats:sub> fiber.</jats:p>

<jats:p>Multi-wavelength continuous-wave self-Raman laser with an <jats:italic>a</jats:italic>-cut composite YVO<jats:sub>4</jats:sub>/Nd:YVO<jats:sub>4</jats:sub>/YVO<jats:sub>4</jats:sub> crystal pumped by an 879-nm wavelength-locked laser diode is demonstrated for the first time. Multi-wavelength Raman lasers at 1168.4, 1176, 1178.7, and 1201.6 nm are achieved by the first Stokes shift of the multi-wavelength fundamental lasers at 1064, 1066.7, 1073.6, 1084, and 1085.6 nm with two Raman shifts of 890 and 816 cm<jats:sup>−1</jats:sup>. A maximum Raman output power of 2.56 W is achieved through the use of a 20-mm-long composite crystal, with a corresponding optical conversion efficiency of 9.8%. The polarization directions of different fundamental and Raman lasers are investigated and found to be orthogonal <jats:italic>π</jats:italic> and <jats:italic>σ</jats:italic> polarizations. These orthogonally polarized multi-wavelength lasers with small wavelength separation pave the way to the development of a potential laser source for application in spectral analysis, laser radar and THz generation.</jats:p>

<jats:p>We demonstrate a non-crossover sub-Doppler dichroic atomic vapor laser locking (DAVLL) in selective reflection scheme, which allows us to obtain a modulation-free laser locking with wide tuneable range. The dependence of peak-to-peak amplitude, tuneable range and the slope near the zero-crossing point of error signal on the frequency shift induced by the magnetic fields are studied. The adjustable error signal by the varying external magnetic field can offer the laser locking from the order of tens MHz to hundreds MHz. The ultimate dither of locked laser frequency is less than 0.5 MHz. The square root of Allan variance of the error signals reaches a minimum of 3 × 10<jats:sup>−10</jats:sup> for an averaging time of 130 s.</jats:p>