Diffraction and gratings
and Shaojun Fu
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Near-field holography (NFH), with its virtues of precise critical dimensions and high throughput, has a great potential for the realization of soft x-ray diffraction gratings. We show that NFH with reflections reduced by the integration of antireflective coatings (ARCs) simplifies the NFH process relative to that of setups using refractive index liquids. Based on the proposed NFH with ARCs, gold-coated laminar gratings were fabricated using NFH and subsequent ion beam etching. The efficiency angular spectrum shows that the stray light of the gratings is reduced one level of magnitude by the suppression of interface reflections during NFH.
PDF全文 (下载：197) Chinese Optics Letters ，2016年第14卷第9期 pp.090501
Fiber optics and optical communication
and Chongqing Wu
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Polarization-based optical communications are attracting more attention recently, where the crucial points are polarization features and their measurements. Based on the Müller matrix method, we obtain measurable expressions for the polarization-dependent gain (PDG) and the loss of polarization orthogonality (LPO), while give the boundary of the LPO for any PDG devices. We experimentally demonstrate that non-linear LPO can be created in a semiconductor optical amplifier and find that the LPO will slightly skim over the boundary near the threshold of the injected current. Furthermore, an empirical formula is achieved to gauge the LPO-induced power penalty, which is proven to be valid in differential polarization shift-keying transmission by executing a bit error rate measurement. Our conclusions are applicable to non-orthogonal polarization cases and valuable to polarization-related communications, even orbital angular momentum multiplexing.
PDF全文 (下载：132) Chinese Optics Letters ，2016年第14卷第9期 pp.090601
and Aiying Yang
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Indoor visible light positioning becomes attractive due to the increasing demands of location-based services. This Letter proposes an indoor imaging visible light positioning scheme with a sampled sparse light source, image sensor, and gyro. An indoor positioning cellular with a single reference light source and an off-the-shelf mobile device is demonstrated. Experimental results show that the 3-dimensional positioning error is only several centimeters even with a rotated, rolled, and pitched mobile device. The proposed scheme is convenient and cost effective because the transmitter takes advantage of the existing lighting infrastructure and the receiver is a commercial mobile phone without any extra accessories.
PDF全文 (下载：98) Chinese Optics Letters ，2016年第14卷第9期 pp.090602
and Xiaojun Guo
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Based on the peak to valley ratio (PTVR) of the average magnitude difference function (AMDF), we present a novel optical signal to noise ratio (OSNR) and symbol rate (SR) estimation method for commonly used auxiliary amplitude modulations (AAMs). Moreover, it is demonstrated that the influence of chromatic dispersion (CD) on the method can be mitigated by maximizing the PTVR of the AMDF with additional tunable dispersion compensators. The results of simulations show that the OSNR estimation error can be kept within 0.8 dB in the wide OSNR range of (12, 32) dB, while the SR estimation error is below 0.079% for four widely used 10 Gsymbol/s AAM signals.
PDF全文 (下载：100) Chinese Optics Letters ，2016年第14卷第9期 pp.090603
and Jian'gang Lu
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An adaptive modulation system for a liquid crystal (LC) phase modulator is demonstrated. The phase retardation may be modulated by resetting the driving voltage automatically by matching the measured and ideal transmittance of an LC cell sandwiched by crossed polarizers. By using this system, an LC phase modulator can get a low error function of 0.25% in a short modulation time, which is less than the 10% obtained using a conventional modulation method.
PDF全文 (下载：81) Chinese Optics Letters ，2016年第14卷第9期 pp.090604
and Yunlong Sheng
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We give a brief overview on the more than 50 years of development of the moment-based image description, the moment invariants, and the orthogonal moments. Some basic ideas for significantly improving the performance of the image moment-based methods, such as the use of the low-order radial moments for reducing information suppression drawback and the separation of the radial basis from the circular harmonic basis for a free selection of the orthogonal radial polynomials, are presented. Performance measures for the orthogonal moments are discussed from the point of view of image analysis. A moment family list is proposed, which includes most of the representative moments in use and the discrete orthogonal moments.
PDF全文 (下载：97) Chinese Optics Letters ，2016年第14卷第9期 pp.091001
Instrumentation, measurement and metrology
and Yudong Zhang
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Compared with binary diffractive super-resolving elements, programmable super-resolution pupil filters permit the analysis of various filter designs and allow the filters to be changed rapidly to modify the response of an optical system. In this Letter, a deformable mirror is employed as a programmable super-resolution pupil phase filter. Continuous phase-only filters based on the Zernike polynomial series are designed by the genetic algorithm and fitted through closed-loop adaptive optics with a piezoelectric deformable mirror. Experimental super-resolution results are in agreement with the theoretical predictions. This method has no polarization light requirement and is convenient for application.
PDF全文 (下载：142) Chinese Optics Letters ，2016年第14卷第9期 pp.091201
Lasers and laser optics
and Xiaoming Duan
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We report a cladding-pumped actively Q-switched ring Tm-doped fiber laser (TDFL). This laser is Q-switched by a free space acousto-optic modulator. A pulse energy up to 150 μJ with a pulse width of 207 ns at a repetition rate of 100 Hz is achieved for a cavity optical length of 6.68 m. The pulse amplitude’s stability at this repetition rate is better than 95%. To the best of our knowledge, this is the first free space structure Q-switched ring TDFL report.
PDF全文 (下载：127) Chinese Optics Letters ，2016年第14卷第9期 pp.091401
and Yang Liu
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We present a hybrid adaptive optics system for a kW-class solid-state slab master oscillator power amplifier laser that consists of both a low-order aberration corrector and a 59-actuator deformable mirror. In this system large defocus and astigmatism of the beam are first corrected by the low-order aberration corrector and then the remaining components are compensated by the deformable mirror. With this sequential procedure it is practical to correct the phase distortions of the beam (peak to valley up to 100 μm) and the beam quality β is successfully improved to 1.9 at full power.
PDF全文 (下载：93) Chinese Optics Letters ，2016年第14卷第9期 pp.091402
M. A. M. Salim
Z. A. Ali
M. F. Ismail
A. A. Latif
and S. W. Harun
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In this work a passively Q-switched dual-wavelength ytterbium-doped fiber laser using a titanium dioxide-based saturable absorber is proposed and proven. The system also utilizes a side-polished fiber in a ring cavity configuration to obtain the desired pulse train. A stable dual-wavelength pulse output is obtained at 1034.7 and 1039.0 nm, with a maximum pulse energy of 2.0 nJ, and a shortest pulse width of 3.2 μs. The generated pulse train is stable, and has a pulse repetition rate from 31.2 to 64.5 kHz.
PDF全文 (下载：100) Chinese Optics Letters ，2016年第14卷第9期 pp.091403
and Kun Qiu
An external-cavity semiconductor laser with nonlinear optical feedback to generate broadband chaos with time delay signature (TDS) suppression is investigated. The system is composed of three semiconductor lasers, one of which is regarded as the chaos generator, while the other two play a role of a built-in nonlinear modulator in the external cavity of the generator. The results show that by properly setting the feedback strength and time delay of the first semiconductor laser in the nonlinear modulator, the TDS embedded in the intensity and phase time-series of the chaos can be effectively concealed in a wide range of frequency detuning.
PDF全文 (下载：123) Chinese Optics Letters ，2016年第14卷第9期 pp.091404
and Pu Wang
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We report a simple and compact all-fiber laser system that is capable of generating widely tunable femtosecond pulses from 1.6 to 2.32 μm. The pulses are produced by utilizing the soliton self-frequency shift in a highly nonlinear fiber pumped by an Er-doped mode-locked fiber laser. Two stages of single-clad Tm:fiber amplifiers are used to amplify the pulses to a higher pulse energy of 10.9 nJ with pulse width of 94 fs, and corresponding to peak power of 105 kW at around 1.93 μm. Running a few hours, the all-fiber laser system exhibits exceptional stability with a signal-to-noise ratio as high as 70 dB.
PDF全文 (下载：92) Chinese Optics Letters ，2016年第14卷第9期 pp.091405
Medical optics and biotechnology
and Yi Shen
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As a high-resulotion biological imaging technology, photoacoustic microscopy (PAM) is difficult to use in real-time imaging due to the long data acquisition time. Herein, a fast data acquisition and image recovery method named sparse PAM based on a low-rank matrix approximation is proposed. Specifically, the process to recover the final image from incomplete data is formulated into a low-rank matrix completion framework, and the “Go Decomposition” algorithm is utilized to solve the problem. Finally, both simulated and real PAM experiments are conducted to verify the performance of the proposed method and demonstrate clinical potential for many biological diseases.
PDF全文 (下载：129) Chinese Optics Letters ，2016年第14卷第9期 pp.091701
and Zhiwei Lu
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We obtain the output of a 284 ps pulse duration without tail modulation based on stimulated Brillouin scattering (SBS) pulse compression pumped by an 8 ns-pulse-duration, 1064 nm-wavelength Q-switched Nd:YAG laser. To suppress the tail modulation in SBS pulse compression, proper attenuators, which can control the pump energy within a rational range, are added in a generator-amplifier setup. The experimental result shows that the effective energy conversion efficiency triples when the pump energy reaches 700 mJ to 51%, compared with the conventional generator-amplifier setup.
PDF全文 (下载：275) Chinese Optics Letters ，2016年第14卷第9期 pp.091901
and Shining Zhu
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We demonstrate a tunable optical parametric oscillator in a periodically poled congruently grown lithium tantalite whispering gallery mode resonator. The resonator is mechanically polished to millimeter size, and the quality factor is approximately 107 at 1064 nm. Our experiments show that this kind of resonator is capable of reaching a very low threshold and having a wide tuning range. Combined with its narrow resonant linewidth, it is potentially used as a compact, widely tunable, and narrow-linewidth infrared to mid-infrared laser source.
PDF全文 (下载：107) Chinese Optics Letters ，2016年第14卷第9期 pp.091902
and Wenyan He
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To improve the optical performance of an antireflection (AR) coating on a micro-spherical substrate, the ray angle of the incidence distribution and the thickness profile are taken into consideration during the optical coating design. For a convex spherical substrate with a radius of curvature of 10 mm and a clear aperture of 10 mm, three strategies are used for the optimization of the spectral performance of a broadband AR coating in the spectral region from 480 to 720 nm. By comparing the calculated residual reflectance and spectral uniformity, the developed method demonstrates its superiority in spectral performance optimization of an AR coating on a micro-spherical substrate.
PDF全文 (下载：90) Chinese Optics Letters ，2016年第14卷第9期 pp.093101
and Peng Liu
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We experimentally investigate the evolution of the terahertz (THz) waveform and polarization state inside the plasma filament produced by orthogonally polarized two-color pulses. We find that the variation of the THz polarization state along the plasma column is dominantly caused by the relative phase difference and spectra blue shift of the two-color field. Elliptically polarized THz radiation is generated by controlling the initial relative phase and the filament length. The result indicates the coherent control of the polarization state of the THz emission.
PDF全文 (下载：75) Chinese Optics Letters ，2016年第14卷第9期 pp.093201
and Tiqiao Xiao
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Full-field x ray nano-imaging (FXNI) is one of the most powerful tools for in-situ, non-destructive observation of the inner structure of samples at the nanoscale. Owing to the high flux density of the third-generation synchrotron radiation facility, great progress is achieved for FXNI and its applications. Up to now, a spatial resolution of 20 nm for FXNI is achieved. Based on the user operation experiences over the years at the Shanghai Synchrotron Radiation Facility (SSRF) x ray imaging beamline, we know lots of user experiments will rely on a large range of spatial resolutions and fields of view (FOVs). In particular, x ray microscopes with a large FOV and a moderate spatial resolution of around 100 nm have a wide range of applications in many research fields. Driven by user requirements, a dedicated FXNI system is designed and constructed at the SSRF. This microscope is based on a beam shaper and a zone plate, with the optimized working energy range set to 8–10 keV. The experimental test results by a Siemens star pattern demonstrate that a spatial resolution of 100 nm is achieved, while an FOV of 50 μm is obtained.
PDF全文 (下载：104) Chinese Optics Letters ，2016年第14卷第9期 pp.093401