Yang Baodong   Zhang Jinfang   Wang Junmin  

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An experimental investigation of two-color polarization spectroscopy (TCPS) is presented based on the cesium 6S1/2 - 6P3/2 - 8S1/2 (852.3 nm + 794.6 nm) ladder-type system in a room-temperature vapor cell. The dependency of lineshapes of TCPS on the power of 852.3 nm pump and 794.6 nm probe laser are measured in detail, and we confirm that the linewidth of TCPS in counter-propagating configuration between the pump and probe laser beams is obviously narrower than that of co-propagating configuration due to atomic coherence effect. It is helpful for laser stabilization to excited state transition using TCPS without frequency modulation.

       PDF全文 (下载：5)        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Xie Youpeng   Lei Ting   Yang Chuanwu   Du Luping   Yuan Xiao-Cong (Larry)  

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Digital micro-mirror device (DMD)-based optical switch has the advantages of high-speed channels reallocation, miniaturization, stability and large capacity for short reach optical communication in Datacenter. However, the thermal turbulent atmosphere in Datacenter would cause perturbations and channel crosstalk for the optical switch. The self-healing optical beams such as the Bessel beams have the non-diffraction property to mitigate the turbulence issue. Here, we propose and demonstrate Bessel beams enabled DMD-based optical switch to improve the stability and performance of the optical communication in turbulent atmosphere. We statistically characterize the beam wanders of the Gaussian beams and Bessel beams in turbulent atmosphere at the temperatures of 60oC and 80oC. We built the two channels optical switch communication system and measure the bit error rate of the 15Gbit/s OOK signals transmitted by the Gaussian beams and Bessel beams at the temperatures of 60℃ and 80℃, respectively. The optical switch using the Bessel beams shows lower bit error rates with weaker fluctuations compared with the Gaussian beams. The DMD-based optical switch using the Bessel beams has the potential for practical optical communication applications in Datacenter.

       PDF全文 (下载：2)        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Wang Xin-wen   Liu Kangkang   Cheng He-nan   ren wei   xiang jingfeng   Ji Jing-wei   Peng Xiang-kai   Zhang Zhen   zhao jianbo   ye meifeng   Li Lin   Li Tang   wang bin   qu qiuzhi   Liu Liang   lü desheng  

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A high-performance transportable fountain clock is attractive for use in laboratories with high-precision time-frequency measurement requirements. This letter reports the improvement on stability of a transportable rubidium-87 fountain clock because of an optimization of temperature characteristic. This clock integrates its physical packaging, optical benches, microwave frequency synthesizers and electronic controls onto an easily movable wheeled plate. Two optical benches with high vibration resistance is realized in this work. No additional adjustment is required after several times movement of them. The Allan deviation of the fountain clock frequency was measured by comparing it with that of the hydrogen maser. The fountain clock got a short-term stability of 2.3×10⁻¹³@1s and long-term stability to the order of 10⁻¹⁶@100000s

       PDF全文 (下载：3)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Kong Qian   Zhan Yafeng   Wan Peng  

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We report on a DCN architecture based on hybrid Optical Circuit Switching (OCS) and Optical Burst Switching (OBS) interconnect for dynamic DCN connectivity provisioning. With the combination of the centralized and distributed control of the Software Defined Optical Networks (SDON), the proposed interconnect can achieve unprecedented flexibility in dealing with both mice and elephant flow in the DCN. Numerical simulation is employed to investigate the performance of the proposed architecture. The results show that OBS module has preferable performance in dealing with larger burst packet, and the throughput is constrained by the capacity of the server Random Access Memory (RAM) module.

       PDF全文 (下载：2)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Cen Yuan   Xie Jianlan   Liu Jianjun  

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In this Letter, a photonic crystal (PC) flat lens with scatterer-size-gradient is proposed, which simultaneously achieve imaging of point source and sub-wavelength focusing of plane wave in the first, the second and the fifth bands. The imaging of point source breaks through the diffraction limit in the second and the fifth bands. The PC flat lens with scatterer-size-gradient is expected to be used to new multifunctional optical imaging and focusing device, which improves the application potential of PC flat lens.

       PDF全文 (下载：5)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Gao Xin-Xia   Cui Jin-Ming   Huang Yunfeng   Li Chuanfeng   Guo Guangcan  

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We have demonstrated a mode matching method between two different fibers by a hybrid thermal expanded core (TEC) technique, which can be applied to match the modes of fiber-based Fabry-P\'erot cavities (FFPCs). Experimentally, this method has achieved an expansion of the ultraviolet fiber core by 3.5 times while keeping fundamental mode propagation. With the experiment parameters, the fundamental mode coupling efficiency between the fiber and micro-cavity can reach 95% for a plano-concave cavity with a length of 400 \mum. This method can not only have potential in quantum photonics research, but also can be applied in classical optical fields.

       PDF全文 (下载：1)        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Xia Renjie   Wang Changshun   Chen Tianyu   Pan Yujia   Lyu Ziyao   Sun Lili  

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In this paper, an all-optical logic sequence generator based on two different polarization holographic gratings has been proposed and demonstrated, which has one input port and four output ports. The polarization state of input light signal determines logic output signals. It can produce four kinds of logic sequence output signals: 1000, 0100, 0010, and 0001, corresponding to the input light signal of four different polarization states: the p-linear, s-linear, left-handed circular, and right-handed circular. The two polarization gratings have been recorded and the working principle of the logic sequence generator has been proved by diffraction pattern analysis of polarization gratings.

       PDF全文 (下载：1)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Xue Jinxing   Liu Candong   Zeng Zhinan   Li Ruxin   Xu ZhiZhan  

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We theoretically investigate delay-dependent attosecond transient absorption spectra in the helium atom dressed by an infrared laser pulse in the wavelength range of 800–2400 nm. By numerically solving the three-dimensional time-dependent Schrödinger equation, we find that the absorption spectrogram exhibits a multiple-fringe structure for using the longer-wavelength dressing pulse. The quantitative calculation of the transition matrix between different Floquet states provides direct evidence on the origin of the multiple-fringe structure. Our result shows that the wavelength of the dressing pulse is an important parameter and the unique feature of attosecond transient absorption spectroscopy can be induced in the mid-infrared regime.

       PDF全文 (下载：5)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Wang Guoyan   Jiang Lan   Sun Jingya   Hu Jie   Wang Qingsong   Li Ming   Lu Yongfeng  

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Cylindrical shockwave inside PMMA generated simultaneously with two hemispherical shockwaves induced by femtosecond Gaussian beam laser was investigated using ultrafast pump-probe imaging technique. The evolutions of these three shockwaves with probe delay and incident pulse number have been systematically analyzed. The plasma intensity and filament length in the center of cylindrical shockwave both decayed with pulse number. Moreover, the self-focused filament moved downstream towards the output surface with increased pulse number. The experimental results and mechanism illustrated that energy deposition was suppressed by degraded nonlinear effect due to pre-ablated structure in multi-pulses irradiation.

       PDF全文 (下载：2)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Li Yingyi   Yang Ke   Liu Gaoyou   Yao Baoquan   Ju Youlun  

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We demonstrate a Fe:ZnSe laser gain-switched by a ZnGeP₂ (ZGP) optical parametric oscillator (OPO) under the pulse repetition frequency (PRF) of 1 kHz at room temperature. The 2.9 μm signal light of the OPO is employed as the pump for the Fe:ZnSe laser. The maximum output power of the Fe:ZnSe laser is 58 mW with the pulse duration of 2.7 ns under the incident pump power of 280 mW, corresponding to a peak pulse power of 21.5 kW and an optical-to-optical efficiency of 20.7%. The spectrum of the Fe:ZnSe laser has a range of 4030.2-4593.6 nm with a dip in 4187.1-4340.4 nm due to the absorption of CO₂.

       PDF全文 (下载：2)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Ji Jianhua   Zhang Jianjia   Wu Bing   Wang Ke   Xu Ming  

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We experimentally demonstrate a 10 Gb/s FSO wiretap channel based on spatial diversity scheme and optical code division multiple access (OCDMA). In weak and middle turbulence cases, bit error rate of legitimate user can be decreased and physical layer security can be enhanced simultaneously.

       PDF全文 (下载：2)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

He Xiaopeng   Huang Panhui   Yang Xiaoyu   Jin Zuanming   Lou shitao   Zhang Xiaolei   Jin Qingyuan  

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The ultrafast spin dynamic of in-plane magnetized Fe/Pt films was investigated by terahertz emission spectroscopy. The amplitude of emitted terahertz wave is proportional to the intensity of the exciting laser beams. Both the amplitude and polarity of the terahertz wave can be adjusted by modifying the external magnetic field. The dependency of the amplitude on external magnetic fields is coincidence to the hysteresis loops of the sample. Also the polarity of terahertz wave is reversed as the magnetization orientation is reversed. The superdiffusive transient spin current with inverse spin Hall effect (ISHE) is attributed to main mechanism of the terahertz emission.

       PDF全文 (下载：4)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Wang Xiaojing   Ren Huaijin   Wang Gang   He Jun  

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In this article, a new method is presented to calculate the interactive length between fundamental wave (FW) and second harmonic generation (SHG) for the configuration of total internal reflection on the inner surface of nonlinear crystal. Three independent experiments are designed to measure bandwidths of this second harmonic wave. The theoretical expression of the intensity of SHG is obtained through nonlinear coupled wave equation. By utilizing the measured bandwidths and the intensity equation through mathematical calculation, the interactive length of this phase-matched SHG can be calculated. Because there is no existing method to obtain the interactive length either from the theoretical calculation or experimental measurement. This method can be applied to estimate the extremely short interactive volume in nonlinear processes.

       PDF全文 (下载：4)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Huang Junchao   Wang Lingke   Duan Yifei   Huang Yafeng   ye meifeng   Li Lin   Liu Liang   Li Tang  

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Excess frequency noise induced by mechanical vibration is the dominant noise source at low Fourier frequencies in fiber-delay-line (FDL) stabilized lasers. To resolve this problem, a double-winding fiber spool is designed and implemented that has ultralow acceleration sensitivity in all spatial directions. By carefully choosing the optimal geometry parameters of the fiber spool, we achieve acceleration sensitivity of 8 × 10−11/g and 3 × 10−11/g in axial and radial directions, respectively.

       PDF全文 (下载：3)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Liu xiaojuan   Hu Ping   Huang Yan   Liu Fangfang   Liu Ying   Guo Liping   Ge Xiaolu  

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A passively Q-switched erbium-doped fiber laser is proposed and demonstrated utilizing a Zirconium Disulfide (ZrS2)-based saturable absorber. ZrS2 nanosheets are prepared whose modulation depth, saturation intensity and nonsaturable absorbance are measured to be 14.7%, 0.34 MW/cm2 and 17.4%, respectively. Then, a Q-switched EDF laser is implemented by the ZrS2-SA. The pulse repetition rate varies from 40.65 kHz to 87.1 kHz when the pump power changes from 55 mW to 345 mW. The shortest pulse width is 1.49 μs with pulse energy of 33.5 nJ. As far as we know, this is the shortest pulse width obtained by ZrS2-SA so far.

       PDF全文 (下载：5)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Fu Shiyao   Zhai Yanwang   Zhou Heng   Zhang Jianqiang   Yin Ci   Gao Chunqing  

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Multi-ring optical vortices are a kind of structured beams that carry orbital angular momentum (OAM) and have concentrical doughnut intensity distributions. In this paper, we present both theoretically and experimentally a scheme that employing the dimensions of both the OAM states and radial index of multi-ring optical vortices simultaneously to accomplish high-dimensional free-space data coding/decoding transmissions. Such scheme can further improve the coding efficiency when limited OAM states are available. In the proof-of-concept experiment, 64-ary coding/decoding employing 16 OAM states and 4 radial indices are present. And the coding/decoding performance when facing various atmosphere turbulence is evaluated. Furthermore, a 64×64 gray image (totally 32768 bits) is also transmitted through multi-ring optical vortices coding in free-space successfully, showing good transmission performance.

       PDF全文 (下载：3)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

tellal azeddine   ziane omar   Baldeck Patrice  

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The diffraction of a dielectric microline pair is optimized by numerical simulations to generate an efficient focusing pattern with a micron-scale footprint. Microlines separated by 1.12 µm are fabricated by two-photon polymerization on a glass substrate, and their diffraction pattern is characterized by 3D wide-field transmission microscopy. A line pair, having a width W = 0.4 µm and a height H = 0.8 µm, leads to a diffraction-limited focusing in the visible spectrum. Depending on wavelength, its focal length, lateral resolution, and depth of focus are in the ranges of 0.8-1.3 µm, 0.22-0.44 µm, and 1.7-2.13 µm, respectively. Such microlens based on the diffraction of only two subwavelength scatterers could be used for the design of miniature optical sensors with micron and sub-micron pixels.

       PDF全文 (下载：0)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

KOIRALA ISHWOR   Park Chul-Soon   Lee Sang-Shin   Choi Duk-Yong  

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Angle tolerant transmissive subtractive color filters incorporating a metasurface exploiting hydrogenated amorphous silicon (a-Si:H) nanopillars (NPs) on a glass substrate, were proposed and demonstrated. The achieved transmission efficiency ranged from 75% to 95% at off-resonance wavelengths. For NP resonator, electric and magnetic field distributions in conjunction with absorption cross-sections were investigated to confirm resonant transmission dip which is primarily governed by the absorption resulting from simultaneous excitation of magnetic and electric dipoles via Mie scattering. The proposed devices exhibit higher angular tolerance and lower crosstalk for the absorption spectra and therefore be applicable with photodetectors, image sensors, and imaging/display devices.

       PDF全文 (下载：1)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Che Abd Rashid Nurfatihah   Ngajikin Nor Hafizah   Azmi Asrul Izam   Arsat Rashidah   Isaak Suhaila   Cholan Noran Azizan   Azmi Nur Ellina  

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Spectrophotometer with LED being the light source for uric acid detection is proposed in this work. The mechanism of the uric acid detection is based on energy absorbed by sodium urate, which is a chemical product of uric acid and sodium hydroxide (NaOH) solution. For the performance validation, comparison between the spectrophotometer with LED and halogen lamp is carried out. Measurement results suggest that spectrophotometer system with LED light has better sensitivity than that with halogen light. At 460 nm wavelength, the sensitivity for the spectrophotometer with LED is 0.0046 dL/mg, which is 73% higher than that with halogen light that records 0.0012 dL/mg. This enhanced sensitivity is attributed to the higher luminous efficacy of the LED light beam. As a result, a larger amount of flux interacts with the sample, leading to the sensitivity enhancement. The spectrophotometer with LED is also applied for detection of uric acid in real human urine sample. Based on the experimental data at 460 nm wavelength, the method manages to achieve the sensitivity of 0.0016 dL/mg, accuracy of 96.01%, limit of detection (LOD) of 4.79 mg/dL and limit of quantification (LOQ) of 14.52 mg/dL. These findings show that the use of LED as the input light is promising for the spectrophotometer.

       PDF全文 (下载：3)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Xie Yafeng   Zhang Saifeng   Zhang Xiaoyan   Dong Ningning   Kislyakov Ivan   Luo Song   Chen Zhanghai   Nunzi Jean-Michel   Zhang Long   Wang Jun  

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Mechanically exfoliated (ME) and chemical vapor deposition (CVD) MoS₂ monolayers have been extensively studied, but the large differences of nonlinear optical performance between them have never been clarified. Here, we prepared MoS₂ monolayers using ME and CVD methods and investigated the two-photon absorption (TPA) response and its saturation. We found TPA coefficient of ME monolayer was about (1.88±0.21)×10³ cm/GW, nearly two times of CVD one, (1.04±0.15)×10³ cm/GW. Furthermore, we simulated and compared the TPA-induced optical pulse modulation in multilayer cascaded structures, which is instructive and meaningful for the design of optical devices such as beam shaper, optical limiter.

       PDF全文 (下载：5)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Guan Yan   Wang Fang   Yang Ying   Wang De'en   Zhang Xin   Qiang Yuan   Zhou Wei   Hu Dongxia   Deng Xuewei   Ren Huaijin  

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Collinear phase-matching of sum-frequency generation (SFG) has been studied thoroughly previously, while non-collinear schemes are sometimes more flexible in application. However, this phase-matching type is more difficult to meet and control. We employ a convenient method to obtain harmonic generation in bulk KDP: using an incident wave vector and a reflected wave vector to consist triangle phase-matching relationship. With a simple, flexible set-up, we can observe 351nm SFG and the conversion efficiency is up to ~3.6% per reflection. Furthermore, we believe this approach has potential application value and improvement space.

       PDF全文 (下载：5)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

li qin   Li Wenbo   Chu Wei   Cao Yuxiang   Zhang Wencheng   Ma Hongliang   Jin Zuanming   Dai Ye  

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Spatio-temporal coupling characteristics of ultrafast laser pulse are quantitatively tailored. An asymmetric microstructure is induced in the focal volume when laser scans perpendicular to the direction of spatial chirp in fused silica. The tilted direction reverses when adding a Dove prism into the light path. The sign of pulse front tilt can be turned from positive to negative by changing the group delay dispersion by step. We reveal that tilted direction of microstructure depends on spatial chirp and the interplay between spatio-temporal chirp leads to the change of tilted angles.

       PDF全文 (下载：4)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Liu Shun   Lu Ping   Chen Enci   Ni Wenjun   Liu Deming   Zhang Jiangshan   Lian Zhenggang  

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This letter shows Vernier effect based on two segments of PANDA polarization maintaining fiber (PMF) whose length is 28 cm and 23 cm, respectively. The two PMF is spliced together and the angle between the fast axes is set to 45°. This cascaded PMF is inserted in a Sagnac loop to form an interferometer which can generate Vernier effect. The spectrum consists of finesse fringe and envelope and realize simultaneous measurement of strain and temperature. The envelope can provide strain and temperature sensitivities of 58.0 pm/με and -1.05 nm/°C. The finesse fringe provides sensitivities of 5.9 pm/με and -1.36 nm/°C.

       PDF全文 (下载：5)        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Guo Hui   He Ruyong   Wei Chaopeng   Lin Zequn   Wang Le   zhao shengmei  

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In this paper, we propose an advanced framework of ghost edge imaging, named compressed ghost edge imaging (CGEI). In the scheme, a set of structured speckle patterns with pixel shifting are illuminated on an unknown object. The output is collected by a bucket detector without any spatial resolution. By using compressed sensing algorithm, we obtain horizontal and vertical edge information of the unknown object with the bucket detector detection results and the known structured speckle patterns. The edge is finally constructed via two-dimensional edge information. The experimental and numerical simulations results show that the proposed scheme has a higher quality and reduces the number of measurements, in comparison with the existed edge detection schemes based on ghost imaging.

       PDF全文 (下载：5)        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Zhang Yinlong   Liang YiZhi   Jin Long   Guan Bai-Ou  

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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：8)        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Huang Junchao   Wang Lingke   Duan Yifei   Huang Yafeng   ye meifeng   Liu Liang   Li Tang  

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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：9)        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

huang wei   cui yulong   Li zhixian   zhou zhiyue   Wang Zefeng  

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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.

       PDF全文 (下载：3)        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Zhang Min   Xu Bo   Li Xiaoyun   Cai Yi   Wu Baojian   Qiu Kun  

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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：3)        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Lu Chenghao   Zhu Bing   Zhu Chuanyi   Ge Licheng   Liu Yi'an   Chen Yuping   Chen Xianfeng  

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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.

       PDF全文 (下载：4)        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Wang Aimin   Yang Wan   Wu Danlei   Wu Runlong   Liu Guanyu   Chen Bingying   Feng Lishuang   Zhang Zhigang  

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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.

       PDF全文 (下载：2)        Chinese Optics Letters ，2019年第17卷第7期 pp.07