Atmospheric optics and oceanic optics
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Vortex splitting is one of the main causes of instability in orbital angular momentum (OAM) modes transmission. Recent advances in OAM modes free-space propagation have demonstrated that abruptly autofocusing Airy vortex beams (AAVBs) can potentially mitigate the vortex splitting effect. However, different modes of vortex embedding will affect the intensity gradients of the background beams, leading to changes in the propagation characteristics of vortex beams. This study presents the unification of two common methods of coupling autofocusing Airy beams with vortices by introducing a parameter (m), which also controls the intensity gradients and focusing properties of the AAVBs. We demonstrate that vortex splitting can be effectively reduced by selecting an appropriate value of the parameter (m) according to different turbulence conditions. In this manner, the performance of OAM-based free-space optical systems can be improved.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.040101
Atomic and molecular physics
Hoyt W. Chad
We study a Zeeman slower using the magnetic field generated by a pair of coils for a magneto-optical trap. The efficiency of the Zeeman slower is shown to be dependent on the intensity and frequency detuning of the laser light for slowing the atoms. With the help of numerical analysis, optimal experimental parameters are explored. Experimentally, the optimal frequency detuning and intensity of the slowing beam are explored, and 4?×?107 ytterbium atoms are trapped in the magneto-optical trap.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.040201
As the key part of chip-scale atomic clocks (CSACs), the vapor cell directly determines the volume, stability, and power consumption of the CSAC. The reduction of the power consumption and CSAC volumes demands the manufacture of corresponding vapor cells. This overview presents the research development of vapor cells of the past few years and analyzes the shortages of the current preparation technology. By comparing several different vapor cell preparation methods, we successfully realized the micro-fabrication of vapor cells using anodic bonding and deep silicon etching. This cell fabrication method is simple and effective in avoiding weak bonding strengths caused by alkali metal volatilization during anodic bonding under high temperatures. Finally, the vapor cell D2 line was characterized via optical-absorption resonance. According to the results, the proposed method is suitable for CSAC.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.040202
Diffraction and gratings
The two-dimensional angular filter based on volume Bragg gratings in photothermorefractive glass for a nanosecond (ns) laser pulse is demonstrated. The experimental results show that the near-field beam quality of the laser pulse was effectively improved. The near-field modulation and contrast ratio were improved by 1.75 and 4.48 times, respectively. The power spectral density curves showed that the spatial frequencies more than 0.9 mm?1 in the x direction and 1.2 mm?1 in the y direction were effectively suppressed.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.040501
Fiber optics and optical communication
Chun Hong Kang
Tien Khee Ng
Boon S. Ooi
This tutorial focuses on devices and technologies that are part of laser-based visible light communication (VLC) systems. Laser-based VLC systems have advantages over their light-emitting-diode-based counterparts, including having high transmission speed and long transmission distance. We summarize terminologies related to laser-based solid-state lighting and VLC, and further review the advances in device design and performance. The high-speed modulation characteristics of laser diodes and superluminescent diodes and the on-chip integration of optoelectronic components in the visible color regime, such as the high-speed integrated photodetector, are introduced. The modulation technology for laser-based white light communication systems and the challenges for future development are then discussed.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.040601
This Letter investigates the impact of the photodiode (PD) saturation in a sub-sampled photonic analog-to-digital converter (PADC) with two individual pulse lasers. It is essentially proved that when the optical power to the saturated PD increases, the optical–electrical conversion (OEC) responsivity and digitized output power of the PADC decrease. If femtosecond pulses are employed for the PADC sampling clock, the time-stretching process in a dispersive medium is necessary to decrease the impact of the PD saturation. In contrast, when the sampling clock with picosecond pulses is utilized, the PD saturation is more tolerable, and thus, the OEC responsivity can be improved by an increase of the optical power to the PD no matter if the time-stretching process is employed.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.040602
A fiber Bragg grating (FBG) and Fabry–Perot (FP) cavity cascaded fiber sensing system was manufactured for temperature and pressure sensing. Temperature sensing as high as 175°C was performed by an FBG for the linear variation of an FBG wavelength with temperature. After the temperature was sensed, the demodulation system can find the original FP cavity length and its pressure and cavity length correlation coefficient; thus, the ambient pressure would be calculated. The sensing pressure can be as high as 100 MPa with a repeatability of 1/10,000 and high stability. This kind of fiber sensor has been used in the Shengli Oil Field.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.040603
Optical frequency combs, which are generated by the cascade of a phase modulator and a Mach–Zehnder intensity modulator, are used as a polychromatic signal source in the terahertz imaging system to improve imaging quality. The interference effect caused by the monochromatic wave has been greatly suppressed. The required optical power in the presented system is as low as ～30% of that in the system using the Er-doped fiber amplifier as a source, which can reduce cost and protect photodiodes from damage. This work provides an effective, low power consumption, low cost, and easy way to realize terahertz imaging with high quality and can be used in future security inspections.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041101
Instrumentation, measurement and metrology
This study introduced the research and development of a portable and miniaturized system for the measurement of the refractive index of sub-microliter liquid based on a microfluidic chip. A technical method of double-beam interference, was proposed for use in the measurement. Based on this, by using a laser diode as a light source, changes in the refractive index were calculated by utilizing a complementary metal–oxide–semiconductor to detect the movement of interference fringes of the liquid. Firstly, this study simulated the effects of influencing factors on the interference infringes of two Gaussian beams, such as their spot sizes, distance between two beam spots, and detection range. Secondly, this research introduced the system design and construction of the double-beam interference method and analyzed the results of refractive index tests on sub-microliter aqueous glucose solutions with different concentrations. The measurement accuracy reached 10?4 refractive index units. This system has a compact structure and is rendered portable by using batteries for its power supply. The entire system is designed to be a double Z-shaped structure with a length of about 15 cm, a width of 5 cm, and a height of about 10 cm. It can be used to measure changes in the refractive index of sub-microliter to nanoliter liquids based on the use of a microfluidic chip.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041201
An integrated optoelectronic chip pair, which can transmit and receive optical signals simultaneously, is proposed in this Letter. The design and optimization of its key structure, the vertical cavity surface emitting laser’s distributed Bragg reflector, are presented. Analysis is also done for its influence on the integrated chip’s performance. Moreover, the chip pair’s performance under dynamic conditions is analyzed. Their 3 dB modulation bandwidths are higher than 10 GHz, and their 3 dB photo-response bandwidths are around 23 GHz. Their applications will further improve the performances of the optical interconnects.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041301
Lasers and laser optics
Gold nanorods (GNRs) with two different aspect ratios were successfully utilized as saturable absorbers (SAs) in a passively Q-switched neodymium-doped lutetium lithium fluoride (Nd:LLF) laser emitting at 1.34 μm. Based on the GNRs with an aspect ratio of five, a maximum output power of 1.432 W was achieved, and the narrowest pulse width was 328 ns with a repetition rate of 200 kHz. But, in the case of the GNRs with the aspect ratio of eight, a maximum output power of 1.247 W was achieved, and the narrowest pulse width was 271 ns with a repetition rate of 218 kHz. Our experimental results reveal that the aspect ratios of GNRs have different saturable absorption effects at a specific wavelength. In other words, for passively Q-switched lasers at a given wavelength, we are able to select the most suitable GNRs as an SA by changing their aspect ratio.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041401
We demonstrate a 0.95 GHz repetition rate fully stabilized Yb:fiber frequency comb without optical amplification. Benefitting from the high mode power and high coherence, this comb achieved 35 to 42 dB signal to noise ratio on the direct heterodyne beat signals with at least six continuous wave lasers (at 580, 679, 698, 707, 813, and 922 nm) while keeping >40 dB carrier envelope frequency signal. It can be used for the direct measurement of optical frequencies at visible and near-infrared wavelengths and has great potential on simultaneous comparison of multiple optical frequencies.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041402
We demonstrate a coherent synthesis system based on femtosecond Yb-doped fiber laser technology. The output pulse of the amplification system is divided into two replicas and seeded into photonic crystal fibers of two parallel branches for nonlinear pulse compression. Because of the different nonlinear dynamics in the photonic crystal fibers, the compressed pulses show different spectra, which can be spliced to form a broad coherent spectrum. The integrated timing jitter between the pulses of two branches is less than one tenth of an optical cycle. By coherently synthesizing pulses from these two branches, 8 fs few-cycle pulses are produced.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041403
We report a hybrid femtosecond laser system based on a femtosecond Yb-doped fiber laser and a Yb-doped potassium gadolinium tungstate (Yb:KGW) regenerative amplifier. To match the central wavelength of the seed source, a Yb:KGW crystal is used in the regenerative amplifier for Np polarization. We study and optimize the dynamics of nonlinear amplification to alleviate the gain narrowing effect. With optimization, the system can output 270 fs pulses with 21 ?μJ pulse energy at a 60 kHz repetition rate.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041404
Fractional density of states (FDOS) hinders the accurate measuring of the overall spontaneous emission (SE) control ability of a three-dimensional (3D) photonic crystal (PC) with the current widely used SE decay lifetime measurement systems. Based on analyzing the FDOS property of a 3D PC from theory and simulation, the excitation focal spot position averaged FDOS with a distribution broadening parameter was proposed to accurately reflect the overall SE control ability of the 3D PC. Experimental work was done to confirm that our proposal is effective, which can contribute to comprehensively characterizing the SE control performance of photonic devices with quantified parameters.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041601
This Letter presents a double-layer structure combining a cracked cross meta-surface and grating surface to realize arbitrary incident linear terahertz (THz) wave polarization conversion. The arbitrary incident linear polarization THz wave will be induced with the same resonant modes in the unit cell, which results in polarization conversion insensitive to the linear polarization angle. Moreover, the zigzag-shaped resonant surface current leads to a strong magnetic resonance between the meta-surface and gratings, which enhances the conversion efficiency. The experimental results show that a more than 70% conversion rate can be achieved under arbitrary linear polarization within a wide frequency band. Moreover, around 0.89 THz nearly perfect polarization conversion is realized.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041602
Medical optics and biotechnology
We demonstrated a method for measurement of central corneal thickness (CCT) with a sub-micrometer sensitivity using a spectral domain optical coherence tomography system without needing a super broad bandwidth light source. By combining the frequency and phase components of Fourier transform, the method is capable of measurement of a large dynamic range with a high sensitivity. Absolute phases are retrieved by comparing the correlations between the detected and simulated interference fringes. The phase unwrapping ability of the present method was quantitatively tested by measuring the displacement of a piezo linear stage. The human CCTs of six volunteers were measured to verify its clinical application. It provides a potential tool for clinical diagnosis and research applications in ophthalmology.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041701
N. P. Yadav
This Letter tackles the issue of non-contact detection of ultrasonic fields by utilizing a novel optical method based on the parametric indirect microscopic imaging (PIMI) technique. A general theoretical model describing the three-dimensional anisotropic photoelastic effect in solid was developed. The mechanism of polarization status variations of light passing through the stress and strain fields was analyzed. Non-contact measurements of the ultrasonic field propagating in an isotropic quartz glass have been fulfilled by the PIMI technique under different ultrasonic excitation conditions. PIMI parameters such as sin?δ, Φ, and the Stokes parameters have been found to be sensitive to ultrasonic fields.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041702
Echinococcosis—a parasitic disease caused by Echinococcus granulosus or Echinococcus multilocularis larvae—occurs in many regions in the world. This disease can pose a serious threat to public health and thus requires a convenient and cost-effective method for early detection. So, we developed a novel method based on visual saliency and scale-invariant features that detects the tapeworm parasites. This method improves upon existing bottom-up computational saliency models by introducing a visual attention mechanism. The results indicated that the proposed method offers a higher level of both accuracy and computational efficiency when detecting Echinococcus granulosus protoscoleces, which in turn could improve early detection of echinococcosis.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.041703
Remote sensing and sensors
Using theoretical simulations for optical fiber surface plasmon resonance (SPR) sensors and prism-based SPR sensors coated with negative permittivity material (NPM), we investigated the effect of the permittivity of NPM on the transmitted spectrum of optical fiber SPR sensors and the reflected spectrum of prism-based SPR sensors and then obtained optimum permittivity of the NPM, which can excite the sharpest SPR spectrum in the white light region (400–900 nm).
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第4期 pp.042801
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All-optical ultrasound probe, which contains a photoacoustically based ultrasound generator paired with a photonic acoustic sensor, provide promising imaging modality for diagnostic and MRI compatible applications. Here, we demonstrate the fabrication of a fiber-based all-optical ultrasound probe and its application in pulse-echo ultrasound imaging. The ultrasound generator is fabricated on a 125-μm multimode optical fiber by forming a light-absorbing multiwalled carbon nanotubes (MWCNTs)-polydimethylsiloxane (PDMS) composite coating on its distal end. A peak-to-peak acoustic pressure 0.95 MPa has been achieved at nearly the damage threshold 2.46 μJ, by chemically functionalizing the fiber surface to enable strong nanotube adsorption. Ultrasound reception was performed by a fiber-laser ultrasound sensor which translates ultrasound pressure into differential lasing-frequency changes. By linearly scanning the probe, ex vivo two- and three-dimensional imaging of a segment of swine trachea has been demonstrated, by detecting the echo ultrasound signals and reconstructing the acoustic scatters. The probe presents axial and lateral resolutions at 150 and 62 μm, respectively. The small-sized, side-looking all-fiber ultrasound probe presents a promising approach for assembling an interventional endoscopy.
PDF全文 (下载：1) Chinese Optics Letters ，2019年第17卷第7期 pp.07
We demonstrate frequency stabilization of a 1.55 μm erbium-doped fiber laser by locking it to a 5-km-long optical fiber delay line (FDL). The stabilized laser is characterized via comparison with a second identical laser system. We obtain fractional frequency stability of better than 3*10-15 over timescales of 1–10 s and a laser linewidth of 0.2 Hz, which is the narrowest linewidth of an FDL-stabilized laser observed to date.
PDF全文 (下载：3) Chinese Optics Letters ，2019年第17卷第7期 pp.07
We reported here a single-pass 1.56 μm fiber gas Raman laser in a deuterium-filled hollow-core fiber and a 2.86 μm cascade fiber gas Raman laser with methane in the second stage. The maximum output power of 1.56 μm and 2.86 μm is 27 mW and 8.5 mW with Raman conversion efficiency of 30% and 42% respectively. The results offer a new method to produce 1.5 μm fiber source and prove the potential of the cascade fiber gas Raman laser in extending the available wavelength.
A novel predictive dynamic bandwidth allocation (DBA) method based on Long Short-Term Memory (LSTM) neural network is proposed for 10-Gigabit-capable passive optical network in mobile front-haul (MFH) links. By predicting the number of packets that arrive at the optical network unit buffer based on LSTM, the round-trip time delay in traditional DBAs can be eliminated to meet the strict latency requirement for MFH links. Our study shows that LSTM has better performance than feed-forward neural network. Based on extensive simulations, the proposed scheme is found to be able to achieve the latency requirement for MFH and outperforms the traditional DBAs in terms of delay, jitter and packet loss ratio.
PDF全文 (下载：2) Chinese Optics Letters ，2019年第17卷第7期 pp.07
All-optical logic gates including AND, XOR, and NOT gates, as well as a half-adder, are realized based on two-dimensional lithium niobate photonic crystal (PhC) circuits with PhC micro-cavities. The proposed all-optical devices have an extinction ratio as high as 23 dB due to the effective all-optical switch function induced by two-missing-hole micro-cavities. These proposed devices can have potential implementation of complex integrated optical functionalities including all-optical computing in lithium niobate slab or thin film.
We present a Er:fiber based femtosecond laser at 780 nm with 256-MHz repetition rate, 191-fs pulse duration, and over 1-W average power. Apart from the careful third-order dispersion management, we introduce moderate self-phase modulation to broaden the output spectrum of the Er:fiber amplifier and achieve 193-fs pulse duration and 2.43-W average power. Over 40% frequency doubling efficiency was obtained by a periodically poled lithium niobate crystal. Delivering through a hollow-core photonics bandgap fiber, this robust laser becomes an ideal and convenient light source for two-photon autofluorescence imaging.
A method is proposed to optimize the recording structure of the photorefractive volume grating to compensate the high spatial frequency in the distorted wavefront by optical phase conjugation. Based on coupled-wave equation, the diffraction efficiency of the recorded grating formed by the scattered beams in different recording structures is simulated. The theoretical results show that the recorded modulations with high spatial frequency can be significantly improved in the small recording angle. In experiment, three recording structures with the recording angle 7.5°, 30° and 45° are chosen to verify the compensation effect. Compared with the reconstructed image in the large recording angle 45°, the signal to noise ratio of image recorded in 7.5° increases to 3.2 times.
Squeezed states belong to the most prominent nonclassical resources. They have compelling applications in precise measurement, quantum computation and detection. Here, we report on the direct measurement of 13.8 dB squeezed vacuum states by improving the interference eciency and gain of balanced homodyne detection. By employing an auxiliary laser beam, the homodyne visibility is increased to 99.8%. The equivalent loss of the electronic noise is reduced to 0.05% by integrating a junction eld-eect transistor
(JFET) buering input and another JFET bootstrap structure in the balanced homodyne detector.
PDF全文 (下载：14) Chinese Optics Letters ，2019年第17卷第7期 pp.07
In this work, a soliton mode-locked erbium-doped fiber laser (EDFL) with a high-quality molecular beam epitaxy (MBE) grown topological insulator (TI) Bi2Se3 saturable absorber (SA) is reported. To fabricate the SA device, a 16-layer Bi2Se3 film was grown successfully on a 100 μm thick SiO2 substrate and sandwiched directly between two fiber ferrules. The TI-SA had a saturable absorption of 1.12 % and a saturable influence of 160 MW/cm2. After inserting the TI-SA into the unidirectional ring-cavity EDFL, self-starting mode-locked soliton pulse trains were obtained at a fundamental repetition rate of 19.352 MHz. The output central wavelength/pulse energy/pulse duration/signal to noise ratio (SNR) of radio frequency spectrum were 1530 nm/18.5 pJ/1.08 ps/60 dBm, respectively. These results demonstrate that MBE technique could provide a controllable and repeatable method for the fabrication of identical high-quality TI-SAs, which is critical important for ultrafast pulse generation.
PDF全文 (下载：10) Chinese Optics Letters ，2019年第17卷第7期 pp.07
We demonstrate a strain compensated long lifetime SESAM with a high modulation depth for fiber lasers. The SESAM was measured to have a damage threshold of 9.5 mJ/cm<sup>2</sup>, a modulation depth of 11.5%, a saturation fluence of 39.3 μJ/cm<sup>2</sup>, and an inversed saturable absorption coefficient of 630 mJ/cm<sup>2</sup>. The SESAM has been applied to a linear cavity mode-locked Yb:fiber laser, which has been working for more than a year without damage of the SESAM.
PDF全文 (下载：7) Chinese Optics Letters ，2019年第17卷第7期 pp.07
We report on the elemental redistribution behavior in oxyfluoride glasses with a high repetition rate near-infrared femtosecond laser. Elemental analysis by Electro-Probe Microanalyzer demonstrates that the redistributions of Ca2+ and Yb3+ ions change dramatically with pulse energy, which are quite different compared with previous reported results. Confocal fluorescence spectra of Yb3+ ions demonstrate that the luminescence intensity changes obviously with the elemental redistribution. The mechanism of the observed phenomenon is discussed. This observation may have potential applications in the fabrication of micro-optical devices.
For most of atom interferometers, vibration isolation unit is applied to reduce vibration noise. In our experiment, instead of isolation, the vibration signals are monitored, combining with the sensitive function, the compensation phase shift for the atom interferometer is obtained. We focused on the correction over a wide spectrum rather than on “monochromatic” frequencies. The sensitivity of the atom gravimeter can be upgraded by a factor of more than two. Furthermore, we demonstrated that the atom interferometer can still produce a good measurement result without passive vibration isolation in extremely noisy environments by using vibration compensation.
PDF全文 (下载：4) Chinese Optics Letters ，2019年第17卷第7期 pp.07
We propose and experimentally demonstrate a novel Raman-based distributed fiber-optics temperature sensor for improving the temperature measurement accuracy and engineering applicability. The proposed method is based on the double-ended demodulation with a reference temperature and dynamic dispersion difference compensation method, which can suppress the effect of local external physics perturbation and intermodal dispersion on temperature demodulation results. Moreover, the system can omit the pre-calibration process by using the reference temperature before the temperature measurement. The experimental results of dispersion compensation indicate that the temperature accuracy optimizes from 5.6 ℃ to 1.2 ℃, and the temperature uncertainty decreases from 16.8 ℃ to 2.4 ℃. Moreover, the double-end configuration can automatically compensate the local external physics perturbation of the sensing fiber, which exhibits a distinctive improvement.
Praseodymium ion doped gain materials have the superiority of lasing at various visible wavelengths directly. Simple and compact visible lasers are booming with the development of blue laser diodes in recent years. In this paper, we demonstrate the watt level red laser with a single blue laser diode and Pr:YLF crystal. On this basis, the passively Q-switched pulse lasers are obtained with monolayer graphene and Co:ZnO thin film as the Q-switchers in the visible range.
PDF全文 (下载：6) Chinese Optics Letters ，2019年第17卷第7期 pp.07
A large-mode-area (LMA) ytterbium doped photonic crystal fiber (PCF) with core NA of 0.034 and core diameter of 50 μm was made by stack-and-draw technique. The core is formed by Yb3+/Al3+/F-/P5+ co-doped silica glass containing 0.09 mol% Yb2O3 with absorption coefficient at 976 nm up to 3.2 dB/m. The core glass with homogeneous distribution of Yb3+ ions and refractive index difference of 4×10-4 compared with pure silica was prepared by sol-gel method and heat homogenization at 2000°C. Laser power amplification of this LMA PCF was studied using a seed source of 21 picosecond pulse duration and 48.7MHz repetition rate at 1030 nm wavelength. With pump power of 520 W, a maximum 272 W (266 KW peak power) quasi single-mode laser output with M2 of 2.2 was achieved in a 4.7 m fiber length bent at a diameter of 47 cm with slope efficiency of 52%, and no obvious mode instability, SRS or thermal damage on end facet of fiber were observed.
The high-resolution frequency domain spectroscopy (FDS) is set up using coherent and continuous wave terahertz emitter and receiver. Terahertz waves are generated and detected by two photomixers with two distributed feedback (DFB) lasers. Atmospheric water vapor with different relative humidity is systematically investigated by the FDS. A high frequency resolution of ~14 MHz is obtained with the help of Hilbert transformation, leading a well resolved and distinct transmittance characterization of water vapor. Compared with conventional THz time domain spectroscopy (TDS), the high-resolution continuous wave THz spectrometer is one of the most practical system in gas-phase molecular sensing, identification, and monitoring.
In this letter, we propose a simple and effective approach for transforming conventional Talbot array illuminator (TAI) with multilevel phase steps into a binary-phase Talbot array illuminator (BP-TAI) through the detour phase encoding. The BP-TAI is a binary (0 π) phase-only diffractive optical element, which can be utilized to generate a large-scale focal spots array with a high compression ratio. As an example, we design a square BP-TAI with the fraction parameter β=15 for achieving a square multifocal lattice with a high compression ratio β^2. Theoretical analysis and experimental results demonstrate that the detour phase encoding is efficient for designing the BP-TAI, especially with the high compression ratio. Such results may be exploited in practical large-scale optical trapping and X-ray imaging.
PDF全文 (下载：12) Chinese Optics Letters ，2019年第17卷第7期 pp.07
A refractive index intensity detecting sensor with long-period grating written in the single mode - thin core - single mode fiber structure is proposed and optimized theoretically. The sensor is composed of two single-mode fibers connected by a section of long period fiber grating fabricated on thin-core fiber. After optimization and benefit from phase matching point, the loss peak of the structure can reach to 62.8dB theoretically. The wavelength of the characteristic peak is fixed at the phase matching point, so the intensity detection can be achieved. The sensitivity can reach to 272.5dB/RIU. The structural optimization of this paper provides a reference for the fabrication of an easy-made all-fiber sensor without extra cladding.
The precise alignment of high-performance telescope is a key factor to ensure the imaging quality. However, for telescopes with wide field of view, the images are sometimes under-sampled. To study the effects of under-sampled images on the precision of telescope alignment, numerical simulations are implemented with stochastic parallel gradient descent (SPGD) algorithm. The results show that the alignment program can converge stably and quickly. However, with the reduction of full width at half maximum (FWHM) of images, the relative residual errors increase from 9.5% to 19.5%, and the wavefront errors raise from 0.0972λ to 0.1074λ, indicating the accuracy of alignment decreases.
PDF全文 (下载：4) Chinese Optics Letters ，2019年第17卷第6期 pp.06
Forward-scattering-light interferometry has become the most commonly used position detection scheme in optical levi-tation system. Usually, 3-set detectors are required to obtain the 3-dimensional motion information. Here, we simplify the 3-set detectors to one set by inserting a Dove prism. With an optical levitation system in vacuum, we investigate the role of Dove prism in the position measurement process. The relationship between power spectral density and ro-tation angle of Dove prism is experimentally demonstrated and analyzed. This work shows that the Dove prism can much reduce the complexity of experimental setup, which can be applied in the compact optical levitation system for studies in metrology, quantum physics and biology.
PDF全文 (下载：12) Chinese Optics Letters ，2019年第17卷第6期 pp.06
Based on natural protein materials, a series of lenses with different height and focal length were assembled on glass substrates by femtosecond laser non-contact, masking and cold processing. This lens array itself possesses unique and characteristic optical performance in three-dimensional parallel imaging and bending imaging. What is more profound is that by using equilibrium swelling of protein-hydrogel, once the lens array was placed in liquid environment, with the change of ion concentration (eg. pH), the refractive index and curvature of the protein-hydrogel would change, which leads to the flex of focal plane of the lens, finally realizes the dynamically tunable of protein microlens. These smart stress device may have great potential in optical biosensing and microfluidic chip integrated field.
PDF全文 (下载：2) Chinese Optics Letters ，2019年第17卷第6期 pp.06
Abstract: Monitoring the chemical and structural changes in protein side chains and endpoints by infrared spectroscopy is important to study the chemical reaction and physical adsorption process of proteins. However, the detection of side chains and endpoints in nanoscale proteins is still challenging due to its weak infrared response. Here, by designing a double-layered graphene plasmon sensor on MgF2/Si substrate in the IR fingerprint region, we detect the vibrational modes in side chains and endpoints (1397 cm-1 and 1458 cm-1) of monolayer protein. The sensor could be applied on biochemistry to investigate the physical and chemical reaction of biomolecules.
PDF全文 (下载：9) Chinese Optics Letters ，2019年第17卷第6期 pp.06
Atomic Doppler broadening thermometry(DBT) potentially is an accurate and practical approach for the thermodynamic temperature measurement. However, previous reported atomic DBT had a long acquisition time and had only been proved at the triple point of water, 0℃, for the purpose of determination of the Boltzmann constant. This research implemented the Cesium atomic DBT for fast room temperature measurement. Cs133 D1(6S1/2→6p1/2 transition) line was measured by direct laser absorption spectroscopy, and quantity of thermal-induced linewidth broadening was precisely retrieved by the Voigt profile fitting algorithm. The preliminary results showed the proposed approach had a 4 minutes single-scan acquisition time and a 0.2% reproducibility. It is expected that the atomic DBT could be used as an accurate, chip-scale, and calibration-free temperature sensor and standard.
With tin diselenide (SnSe2) film as saturable absorber (SA), the passively Q-switched self-frequency doubling (SFD) lasers were realized in Nd3+:ReCa4O(BO3)3 (Re = Y, Gd) crystals. For Nd:YCOB crystal, the maximum average output power at 532 nm was 19.6 mW, and the corresponding pulse repetition frequency, pulse duration, single pulse energy and peak power were 17.6 kHz, 91.9 ns, 1.1 μJ, 12.1 W, respectively. For Nd:GdCOB crystal, these values were 14.5 mW, 22.1 kHz, 48.7 ns, 0.66 μJ and 13.5 W.
PDF全文 (下载：11) Chinese Optics Letters ，2019年第17卷第6期 pp.06
High power LASER diodes (LD) with a lasing wavelength between 700-780 nm have great potential in various medical use. Here we report our recent efforts in developing InGaAsP/AlGaInP based commercial high power edge-emitting LD which has 755 nm emission peak with a world-record continuous wave (CW) output power of 12.7 W, the highest reported so far. The lack of Al atoms in active region significantly lowers the chance of catastrophic optical damage (COD) during high power laser operation. Meanwhile, with accumulated 3800 running hours, our ongoing aging tests reveal excellent reliability of our devices.
PDF全文 (下载：1) Chinese Optics Letters ，2019年第17卷第6期 pp.06
We propose a general guideline on the design of stimulated Brillouin scattering (SBS) based microwave photonic filter (MPF) using directly-modulated pump. Filter gain profiles and passband ripples with the waveform repetition periods of the driving current ranging from 2 ns to 100 ns are measured after transmission of different fiber length. The results show that the filter performance has nothing to do with the fiber length and the DAC bandwidth requirement for the driving current is no more than 500MHz. Therefore the low cost, flexible reconfiguration and miniaturization characteristics make SBS filter using directed-modulated pump a promising choice as MPF.
PDF全文 (下载：13) Chinese Optics Letters ，2019年第17卷第6期 pp.06
The changes of mechanical properties and biological activities of monomeric erythrocytes are studied using the optical tweezers micromanipulation technology. Firstly, the mechanical properties of irradiated erythrocyte membranes are obtained. Weaker power laser irradiation can delay the decay of the mechanical properties of erythrocytes, and promote the biological activity of erythrocytes, while higher power laser irradiation damages erythrocytes. The stronger the laser irradiation is, the more obvious and rapid the damage will be. The temperature of the cell surface will be changed by regulating the laser power and irradiation time, so the biological functions of erythrocyte can be controlled. Secondly, the finite element simulation of the temperature change on the cell surface under the condition of laser irradiation is carried out using a simulation software, and the precise temperature of the cell surface irradiated cumulatively by a laser with different powers is obtained. Finally, the processes of abscission, unfolding and denaturation of hemoglobins in erythrocytes at different temperatures due to the photothermal effect are analyzed using the model. The mechanism of the laser irradiation on the elasticity of erythrocyte membranes is also obtained.
PDF全文 (下载：3) Chinese Optics Letters ，2019年第17卷第6期 pp.06
Space debris laser ranging was achieved with a 60-W, 200-Hz, 532-nm nanosecond slab, single-frequency green laser at the Shanghai Astronomical Observatory's 60-cm satellite laser ranging system. There were 174 passes of space debris measured in 2017, with the minimum radar cross section (RCS) being 0.25 m<sup>2</sup>, and the highest ranging precision up to 13.6 cm. The RCSs of space debris measured with the farthest distances in 174 passes was analyzed. The results show that the farthest measurement distance (R) and RCS (A) was fitting to R=1388.159A<sup>0.24312</sup>, indicating that this laser can measure the distance of 1388.159 km at a RCS of 1 m<sup>2</sup>, which is very helpful to surveillance and research on low-Earth-orbit space debris.
PDF全文 (下载：4) Chinese Optics Letters ，2019年第17卷第5期 pp.05
An external frequency doubling electro-optically Q-switched Nd:YAG 473 nm blue laser was demonstrated. With absorbed pump energy of 48 mJ at 100 Hz repetition rate, about 2 mJ of 473nm blue laser pulse energy was achieved by cascade frequency doubling. The second harmonic conversion efficiency was 64.5% and overall optical-optical efficiency was 4.2%, respectively. The blue laser pulse width was less than 10ns and beam quality factor was less than 2.4.
PDF全文 (下载：2) Chinese Optics Letters ，2019年第17卷第5期 pp.05
Yuan Xiao-Cong (Larry)
Controlling both amplitude and phase of light in subwavelength scale is a challenge for traditional optical devices. Here we propose and numerically investigate a novel plasmonic meta-hologram, demonstrating broadband manipulation of both phase and amplitude in subwavelength scale. In the meta-hologram, phase modulation is achieved by the detour phase distribution of unit cells, and amplitude is continuously modulated by a T-shaped nano-cavity with tunable plasmonic resonance. Compared to phase-only hologram, such meta-hologram could reconstruct 3D images with higher signal-to-noise ratio and better image quality, and thus o?ering great potential in applications such as 3D displays, optical communications, and beam shaping.
PDF全文 (下载：30) Chinese Optics Letters ，2019年第17卷第6期 pp.06