查看更多>>摘要：Super-hemispherical solid immersion lens (s-SIL) has proved its superiority in high-numerical aperture (NA) and aberration-free characteristics, however, its applications are limited by high cost, difficulty in manufacturing, sample mounting and narrow detection fields. One alternative solution is to utilize a coverslip-based two-piece solid immersion lens (t-SIL) modified from conventional s-SIL. However, one severe issue associated with t-SIL is that its practical imaging performances of t-SIL (e.g. effective NA, aberration, etc.) is not as good as expected. Previous literatures mentioned the problems but gave different explanations. Actually, the fundamental reason is the mismatch among the hemispherical ball, the coupling liquid and the additional coverslip. This work is to investigate the refractive-index-mismatch issues of t-SIL. More specifically, we elaborate two typical cases of mismatches and the corresponding influences on practical aberration and effective NA. In both cases, we prove the feasibility of t-SIL when the refractive indices of three parts are not strictly matched, and give tolerance to mismatch. Besides, solutions to aberration compensation and application suggestions are also given to guide the practical operations.
查看更多>>摘要：Accurate characterization of the inner surface of X-ray monocapillary optics (XMCO) is of great significance in X-ray optics research. Compared with other characterization methods, the micro computed tomography (micro-CT) method has its unique advantages but also has some disadvantages, such as a long scanning time, long image reconstruction time, and inconvenient scanning process. In this paper, sparse sampling was proposed to shorten the scanning time, GPU acceleration technology was used to improve the speed of image reconstruction, and a simple geometric calibration algorithm was proposed to avoid the calibration phantom and simplify the scanning process. These methodologies will popularize the use of the micro-CT method in XMCO characterization.
查看更多>>摘要：In this paper, we extend a circular Pearcey beam (CPB) to an elliptical Pearcey beam (EPB) with the elliptical parameterstheoretically and experimentally. In contrast to the CPB and the elliptical Airy beam, the EPB is more diverse and tunable, endowed with double focusing property due to the convergence process out of synchronization along the short axis and the long axis. We can flexibly adjust the normalized focusing intensity, the beam shape, the focusing position of the EPB by controlling the elliptical parameter. The experiment results match well with the theoretical ones. Additionally, the optical bottle is verified by embedding the vortex into the EPB, which can variegate the optical tweezers applications for multi microparticle manipulation.
查看更多>>摘要：Weakly-coupled Space-Division-Multiplex (SDM) fiber is a promising candidate transmission medium for the remote true-time-delay (TTD) beamforming system. However, the signal-to-crosstalk beating interference (SCBI) can result in severe phase difference (or time delay) variation between TTD channels, which deteriorates the beam direction stability. Here, we develop a model to illustrate the phase variation problem when employing the coherent light source. To obtain a stable beam direction, we propose using an ASE source instead of a coherent source as the optical carrier. When utilizing the ASE source, the signal-to-noise ratio (SNR) of the remote RF signals is also thoroughly derived. It indicates that the RF signal with high SNR can be achieved via increasing the ASE source bandwidth and pre-compensating the fiber link dispersion. We carry out a proof-of-concept experiment of the remote beamforming system with the ASE source at the end. The variation of the phase difference between different channels is less than 3 degrees. The SNR of the RF signal is over 110 dB with a 1 Hz bandwidth. These results pave the way for exploring the SDM fiber in the remote beamforming system.
查看更多>>摘要：In the extreme environment, the signal of the target object is very weak, even reaching the photon level. The single-photon detection technology can detect the weak signal effectively. Ghost imaging (GI) system with single-photon detection technology has a good application in weak light imaging, but the quality of the photon-level GI is still poor. In this paper, we develop a conditional generative adversarial network (CGAN) algorithm to restore images, and the network is trained with simulation data. The results show that the CGAN algorithm has an excellent performance, and the average PSNR and SSIM of test results increase to about 20.8 dB and 0.87 respectively, proving the proposed method is feasible. It is of great significance for imaging under low photon conditions.
查看更多>>摘要：Optical frequency transfer through the atmosphere is needed for diverse free-space applications, e.g. coherent communication, optical clock comparison and relativity experiments. The task requires an appropriate optical link system that provides the multimodal abilities of not only pointing, acquisition, and tracking (PAT) but also phase noise suppression in the presence of air turbulence. Here, we describe a free-space optical (FSO) link system built over a 1.4 km outdoor path to transmit optical frequencies with a fast beam tracking capability together with an active feedback compensation scheme of the atmospheric phase noise. The FSO link is able to offer a frequency transfer stability of 3.51 x 10(-19) at 100 s averaging, which suffices to deliver the current state-of-the-art optical clock signals.
查看更多>>摘要：We demonstrate the similar to 2.8 mu m linearly polarized mu s-scale pulse generation from a polarization-maintaining (PM) Er3+-doped fluoride fiber laser by Q-switching and gain-switching, for the first time to our knowledge. The achieved pulses have a polarization extinction ratio (PER) of up to similar to 23 dB, and a repetition rate of several to tens of kHz with a maximum average power of hundreds of mW. By introducing a ruled reflective diffraction grating into the cavity, the wavelengths are able to be continuously tuned in the spectral range of 2.7 similar to 2.83 mu m. This work represents the first report on a linearly polarized short pulse PM fiber laser in the mid-infrared, opening up new opportunities for some specific applications (e.g., frequency doubling, optical parametric oscillation, coherent combining).
查看更多>>摘要：Herein, a CuSCN/Ga2O3 heterojunction device was fabricated by spin-coating and metal-organic chemical vapor deposition (MOCVD) methods. Under the irradiation of 254 nm deep ultraviolet (DUV) light with an intensity of 1000 mu W/cm(2) , the device shown high sensitivity and favorable self-powered performances with photo-to-dark current ratio (PDCR) of 1.29 x 10(4) , photo responsivity (R) of 5.5 mA/W, rejection ratio (R-270nm/R-600nm) of 4.33 x 10(3) , and specific detectivity (D*) of 3.8 x 10(11) cm Hz(1/2)W(-1) (Jones) at -5 V. In addition, the device has a rise time of 0.45 s and 3.80 s, and a decay time of 0.26 s and 0.26 s. In general, the CuSCN/Ga2O3 heterojunction prepared in this work may well be a potential candidate for achieving a self-powered and high-performance DUV photodetector.
查看更多>>摘要：ReS2 is emerging as a promising saturable absorber for solid-state lasers from visible to mid-infrared. In this paper, we report on a new approach of integrating a ReS2 saturable absorber into Yb:Lu0.74Y0.23La0.01VO4 crystal based Q-switched laser. Under maximum pump power, the highest pulse energy at 1.03 mu m wavelength was measured as 5.3 mu J, which is one order of magnitude higher compared with the previously reported 1 mu m solid-state passively Q-switched lasers based on ReS2 saturable absorber.
查看更多>>摘要：In this paper, we experimentally demonstrate a digital signal processing (DSP)-enabled 50G on-off keying passive optical network (PON) using cost-effective O-band 10G directly modulated laser and 10G avalanche photodiode. The bandwidth-limited devices induce serious spectral distortions, leading to an unacceptable performance. Digital pre-distortion at the transmitter and post-detection at the receiver are proposed to jointly compensate the serious spectral distortions. The digital pre-distortion at the transmitter can compensate for a part of spectral distortions, but cannot deal with the fast power fading within the high-frequency range. At the receiver, the digital post-detection is proposed to compensate the high-frequency distortions, which mainly includes the polynomial nonlinear equalizer, two-tap post filter, and maximum likelihood sequence estimation (MLSE) with channel estimator. Different from the conventional digital post-detection, the channel estimator can estimate more accurate channel information for MLSE, leading to a better bit error rate (BER) performance. By using the proposed digital signal processing, power budget beyond 29 dB is achieved at BER of 2 x 10(-2) after 20 km standard single-mode fiber transmission. In conclusion, the proposed DSP-enabled 50G-PON shows great application potentials for the next-generation PON.
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Elsevier