Fiber Optics and Optical Communications
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We propose and demonstrate a dual-channel microfluidic sensor based on a side-hole fiber (SHF) with two long-period fiber grating (LPFG) structures. There are two air holes in the SHF, which are natural microfluidic channels. We fabricate two LPFGs (long-period gratings LPG-A and LPG-B) in the SHF with the resonance wavelengths of 1268.7 nm and 1385.8 nm, respectively. Results show that the refractive index sensitivities of LPG-A and LPG-B are ?76.0 nm/RIU and ?71.1 nm/RIU, respectively. One can measure the refractive index of liquid samples in two channels simultaneously. The proposed dual-channel microfluidic sensor has advantages of good linearity response, fluidic technology compatibility, and easy light input/output coupling and system integration, which helps the sensor to have a potential application in environmental detection and food safety detection.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.020601
We have demonstrated the highly efficient excitation of the linearly polarized mode (LP01) in ring-core fibers (RCFs) by tapering the spliced point between the RCF and the standard single-mode fiber (SMF) to optimize all-fiber orbital angular momentum (OAM) generation. The tapering technique has been investigated theoretically and experimentally. Before tapering, only 50% of light can be coupled from SMFs to RCFs. The modal interference spectrum with an extinction ratio (ER) of ～9 dB is observed, showing that higher-order modes are excited in RCF. By tapering the spliced point, 90% of light is coupled, and the ER is minimized to be ～2 dB, indicating that the higher-order modes are effectively suppressed by tapering. Such tapered spliced points of RCF–SMF are further applied for all-fiber OAM generation. The efficiencies of OAM+1 and OAM?1 generation are found to be enhanced by approximately 11.66% and 12.41%, respectively, showing that the tapered spliced point of the RCF–SMF is a feasible way to optimize OAM generation.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.020602
We propose a radio frequency (RF) transfer technique with passive phase noise compensation over a fiber-optic ring. By adopting different frequencies and same wavelength transmission and double sideband (DSB) with carrier suppression (DSBCS) modulation, the impact of backscattering can be effectively suppressed. A stable RF signal can be obtained via frequency mixing at an arbitrary access site along the fiber-optic ring. As the two directional transmissions adopt the same fiber and same wavelength from the same laser, the bidirectional propagation symmetry can be maximally guaranteed. We experimentally demonstrate 2 GHz RF signal transfer along a 100 km standard single-mode fiber-optic ring.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.020603
The influences of nutation trail accuracy, simplification of coupling model, spot position jitter, and power variation of incident light on the detection error are analyzed theoretically. Under the condition of satisfying the requirements, the nutation radius is less than 1.13 μm, the accuracy of the nutation trail is less than 0.04 μm, and the detection range is [?5 μm, +5 μm]. The nutation frequency is 160 times spot position jitter frequency and 100 times intensity jitter frequency of incident light. The analysis is of great significance for determining nutation radius and frequency in the tracking system based on fiber nutation.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.020604
Lens-less Fourier-transform holography has been actively studied because of its simple optical structure and its single-shot recording. However, a low-contrast interferogram between the reference and object waves limits its signal to noise ratio. Here, multi-reference lens-less Fourier-transform holography with a Greek-ladder sieve array is proposed in the experiment and demonstrated effectively to improve the signal to noise ratio. The key technique in our proposed method is a Greek-ladder sieve array, which acts as not only a wave-front modulator but also a beam splitter. With advantages of the common path, single shot, and no need for a lens, this system has enormous potential in imaging and especially in extreme ultraviolet and soft X-ray holography.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.020901
Systems containing multiple graphics-processing-unit (GPU) clusters are difficult to use for real-time electroholography when using only a single spatial light modulator because the transfer of the computer-generated hologram data between the GPUs is bottlenecked. To overcome this bottleneck, we propose a rapid GPU packing scheme that significantly reduces the volume of the required data transfer. The proposed method uses a multi-GPU cluster system connected with a cost-effective gigabit Ethernet network. In tests, we achieved real-time electroholography of a three-dimensional (3D) video presenting a point-cloud 3D object made up of approximately 200,000 points.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.020902
Lasers and Laser Optics
A 1.5 J Nd:LuAG ceramic active mirror laser amplifier with a high beam quality is demonstrated in which a 0.8% (atomic fraction) Nd-doped Nd:LuAG ceramic disk with a diameter of 64 mm and a thickness of 5.5 mm is used as a laser gain medium. A maximum single-pass small-signal gain of 2.59 is measured when the pump energy is 11.5 J, with an injected seed energy of 0.4 J; a maximum output energy of 1.5 J is obtained at the repetition rate of 10 Hz. A far-field beam spot 1.25 times the diffraction limit (DL) is achieved by using a stimulated Brillouin scattering phase conjugation mirror (SBS-PCM) for wavefront correction.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.021401
High-power fiber-to-fiber coupling is extensively used in fiber laser applications, and its performance is determined by coupling efficiency. We demonstrate a novel method for alignment and monitoring efficiency by detecting backscattering power at the fiber end cap. The relationship between alignment error and backscattering power is determined by simulations and experiments. Through this method, a state-of-the-art kW-level fiber-to-fiber optic switch is developed (transmission efficiency >97%). It performs well for longer than 60 min. To the best of our knowledge, it is the first time to establish the mathematical model based on this method. Our results can provide guidance in high-power fiber-to-fiber coupling.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.021402
The laser-induced damage threshold of a calcium fluoride (CaF2) single crystal was obtained by a 193 nm ArF excimer laser. The damage morphology of the crystal was analyzed. The results showed that the surface of CaF2 single crystal broke along the natural cleavage plane under ArF excimer laser irradiation, some fragments fell off, and Newton’s rings were observed on the curved fragments. Laser-induced periodic stripe structures (LIPSS) appeared on the surface layer beneath the fragments that peeled off. The spacing of LIPSS was measured, and the formation mechanism of LIPSS was analyzed based on the interference model.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.021403
Recently, fundamental properties and practical applications of two-dimensional (2D) materials have attracted tremendous interest. Micro/nanostructures and functional devices in 2D materials have been fabricated by various methods. Ultrafast direct laser writing (DLW) with the advantages of rich light-matter interactions; unique three-dimensional processing capability; arbitrary-shape design flexibility; and minimized thermal effect, which enables high fabrication accuracy resolution, has been widely applied in the fabrication of 2D materials for multifunctional devices. This timely review summarizes the laser interactions with 2D materials and the advances in diverse functional photonics devices by DLW. The perspectives and challenges in designing and improving laser-fabricated 2D material photonic devices are also discussed.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.023601
In this Letter, we report the existence and relaxation properties of a critical phenomenon on called a 3D super crystal that emerges at T = TC ? 3.5°C, that is, in the proximity of the Curie temperature of a Cu:KTN sample. The dynamics processes of a 3D super crystal manifest in its formation containing polarized nanometric regions and/or polarized clusters. However, with strong coupling and interaction of microcomponents, the characteristic relaxation time measured by dynamic light scattering demonstrates a fully new relaxation mechanism with a much longer relaxation time. As the relaxation mechanism of a relaxator is so-far undetermined, this research provides a novel perspective. These results can help structure a fundamental theory of ferroelectric relaxation.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.021901
Alloying in two-dimension has been a hot spot in the development of new, versatile systems of optics and electronics. Alloys have been demonstrated to be a fascinating strategy to modulate the chemical and electronic properties of two-dimensional nanosheets. We firstly reported ultra-broadband enhanced nonlinear saturable absorption of Mo0.53W0.47Te2 alloy at 0.6, 1.0, and 2.0 μm. The nonlinear saturable absorption of Mo0.53W0.47Te2 saturable absorber (SA) was measured by the open aperture Z-scan technique. Compared to MoTe2 and WTe2 SAs, the Mo0.53W0.47Te2 SA showed five times deeper modulation depth, 8.6% lower saturable intensity, and one order larger figure of merit. Thus, our research provides a method of alloys to find novel materials with more outstanding properties for optics and optoelectronic applications.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.021902
Optical Sensing, Measurements, and Metrology
SO2 and NO2 are the most important pollution in atmosphere. An optimized long path (LP) differential optical absorption spectroscopy (DOAS) system of high light intensity at an ultraviolet (UV) wavelength is proposed and used to measure the concentration of SO2 and NO2 simultaneously. In contrast to the traditional DOAS, the system adopted a Y-type optical fiber structure instead of a combination of mirrors in the telescope. The UV light intensity test shows that the light intensity of UV can arrive to above 80% of the max measuring range when the light path reaches 135 m, and the integral time of the spectrograph is only 15 ms. The system is proved to be efficacious through laboratory calibration. The maximum error of SO2 calibration is 4.19%, and is 5.22% for NO2. The error of the SO2 and NO2 mixture calibration is within 10%. Field measurement is implemented in a wastewater treatment plant in winter. The measurement light path is 738 m. The concentration of SO2 varies from 6 μg/m3 (2.26 ppb) to 20 μg/m3 (7.52 ppb), and the concentration of NO2 varies from 100 μg/m3 (53.2 ppb) to 200 μg/m3 (106.4 ppb) approximately. The results are in accordance with the data from a monitoring station nearby in magnitude order and variation tendency mostly.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.021201
An all-reflective self-referenced spectral interferometry based on the transient grating (TG) effect is proposed for single-shot measuring of the amplitude and phase of ultrashort pulses in a broadband spectral range. Except for a thin third-order nonlinear medium, which was used to generate the TG signal, no transmitted optics were used in the proposed device, and few-cycle pulses in a broad spectral range from deep UV to mid-IR can be characterized. With a homemade compact and alignment-free device, a 5.0 fs pulse at 800 nm corresponding to about two cycles and a 14.3 fs pulse at 1800 nm corresponding to less than three cycles were successfully characterized.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.021202
A novel phase-shifted long-period fiber grating (PS-LPFG) for the simultaneous measurement of torsion and temperature is described and experimentally demonstrated. The PS-LPFG is fabricated by inserting a pre-twisted structure into the long-period fiber grating (LPFG) written in single-mode fiber (SMF). Experimental results show that the torsion sensitivities of the two dips are ?0.114 nm/(rad/m) and ?0.069 nm/(rad/m) in the clockwise direction, and ?0.087 nm/(rad/m) and ?0.048 nm/(rad/m) in the counterclockwise direction, respectively. The temperature sensitivities of the two dips are 0.057 nm/°C and 0.051 nm/°C, respectively. The two dips of the PS-LPFG exhibit different responses to torsion and temperature. Simultaneous measurement of torsion and temperature can be implemented using a sensor. The feasibility and stabilization of simultaneous torsion and temperature measurement have been confirmed, and hence this novel PS-LPFG demonstrates potential for fiber sensing and engineering applications.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.021203
We propose a new non-intrusive flow measurement method using the distributed feedback fiber laser (DFB-FL) as a sensor to monitor flow in the pipe. The relationship between the wavelength of the DFB-FL and the liquid flow rate in the pipeline is derived. Under the guidance of this theory, the design and test of the flow sensor is completed. The response curve is relatively flat in the frequency range of 10 Hz to 500 Hz, and the response of the flow sensor has high linearity. The flow from 0.6 m3/h to 25.5 m3/h is accurately measured under the energy analysis method in different frequency intervals. A minimum flow rate of 0.046 m/s is achieved. The experimental results demonstrate the feasibility of the new non-intrusive flow measurement method based on the DFB-FL and accurate measurement of small flow rates.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.021204
We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses. This emission line corresponds to the B2Σu+(v′=4)?X2Σg+(v=3) transition of nitrogen ions. In the presence of an external seeding pulse, the 353.8 nm signal was amplified by 3 orders of magnitude. Thanks to the much enhanced intensity, we performed time-resolved measurement of the amplified 353.8 nm emission based on the sum-frequency generation technique. It was revealed that the built-up time and duration of these emissions are both inversely proportional to the gas pressure, while the radiation peak power grows up nearly quadratically with pressure, indicating that the 353.8 nm radiation is of the nature of superradiance.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.023201
To make further understanding of terahertz (THz) wave generation from liquid water, we study THz wave emission from water lines of different diameters. The water line with a smaller diameter generates a stronger THz electric field for the diameters from 0.2 mm to 0.5 mm. The THz electric field strength and polarity change with the relative position between the incident laser and water line. Moreover, the THz energy has an optimal radiation angle of about 60°. A two-dimensional dipole array model is introduced to illustrate the phenomenon. Our observations contribute to optimizing the scheme of the liquid THz source.
PDF全文   HTML全文 Chinese Optics Letters, 2020年第18卷第2期 pp.023202
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We report the first demonstration of group delay tuning with stimulated Raman scattering induced dispersion in a hydrogen-filled hollow-core optical fiber. A pump laser induces sharp refractive index change near the S0(0) Raman transition of hydrogen molecules, enabling the control of the group velocity of signal pulses around the Stokes wavelength. Experiment with an 80-m-long hollow-core fiber filled with 2.5-bar hydrogen achieved continuously tuning of pulse delay up to 1.42 ns by varying the Raman gain from 0-10 dB. Tunable pulse delay is realized by changing pump power as well as hydrogen pressure. This work provides a new technique for controlling pulse propagation in optical fibers with high flexibility.
PDF全文 (下載：1) Chinese Optics Letters ，2020年第18卷第6期 pp.06
Polarization aberration caused by material birefringence can be partially compensated by lens clocking. In this paper, we propose a fast and efficient clocking optimization method. Firstly, the material birefringence distribution is fitted by the orientation Zernike polynomials. On this basis, the birefringence sensitivity matrix of each lens element can be calculated. Then we derive the rotation matrix of the orientation Zernike polynomials and establish the mathematical model for clocking optimization. Finally, an optimization example is given to illustrate the efficiency of the new method. The result shows that the maximum RMS of retardation is reduced by 64% using only 48.99s.
PDF全文 (下載：0) Chinese Optics Letters ，2020年第18卷第6期 pp.06
Refractive index enhancement is crucial in the field of lithography, imaging, optical communications, solar devices and many more. We present a review of advancements in the process of designing high refractive index metamaterials, starting from quantum coupling and photonic bandgap materials to metamaterials utilizing deep subwavelength coupling to achieve ever-high values of refractive index. A particular interest is given to experimentally verified schemes in engineering high index of refraction. The Understanding of evolution of material design from intrinsic electronic states manipulation to meta-atoms design is not only fascinating but prerequisite to developing successful devices and applications.
Photonic waveguide arrays provide a simple and versatile platform for simulating conventional topological systems. Here we investigate a novel one-dimensional (1D) topological band structure, a dimer chain, consisting of silicon waveguides with alternating self-coupling and inter-coupling. Coupled mode theory is used to study topological features of such model. It is found that topological invariants of our proposed model are described by the global Berry phase instead of the Berry phase of the upper or lower energy band, which is commonly used in the 1D topological models such as SSH model. Next, we design an array configuration composed of two dimer patterns with different global Berry phases to realize the topologically protected waveguiding. The topologically protected propagation feature is simulated based on Finite-Difference Time-Domain (FDTD) method and then observed in the experiment. Our results provide an in-depth understanding of the dynamics of the topological defect state in a 1D silicon waveguide array, and may provide different routes for on-chip lightwave shaping and routing.
PDF全文 (下載：21) Chinese Optics Letters ，2020年第18卷第5期 pp.05
We propose here a novel method for position fixing in micron-scale by combining the convolutional neural networks (CNN) architecture and speckle patterns generated in a multimode fiber. By varying the splice offset between a single mode fiber and a multimode fiber, speckles with different patterns can be generated at the output of the multimode fiber. The CNN is utilized to learn these specklegrams and then predict the offset coordinate. Simulation results show that predicted positions with the precision of 2 μm account for 98.55%. This work provides a potential high-precision two-dimensional positioning method.
PDF全文 (下載：4) Chinese Optics Letters ，2020年第18卷第5期 pp.05
In this paper, the surface-enhanced Raman scattering (SERS)signal of BRC patient serum obtained by a porous silicon (PSi) Bragg reflector with silve nanoparticles(Ag NPs). Based on these advantages, the serum SERS of 30 normal people and 30 BRC patients were detected by this substrate. After abaseline correction of the experimental data, principal component analysis and linear discriminant analysis (PCA-LDA) were used to complete the data processing. The results showed that the diagnostic accuracy, specificity and sensitivity of the PSi Bragg reflector SERS substrate with composite Ag NPs were 95%, 96.7%, and 93.3%respectively. The results of this exploratory study prove that the detection of BRC serum based on the composite Ag NPs PSi Bragg reflector SERS substrate is a stable, strong SERS signal, unmarked and noninvasive BRC diagnosis technology. In the future, this technology can serve as anoninvasiveclinical tool to detect cancer diseases and have a consider able impact on clinical medical detection.
PDF全文 (下載：5) Chinese Optics Letters ，2020年第18卷第5期 pp.05
Laser induced discharge plasma (LDP) can be used as inspection and metrology EUV sources for its simplicity. To avoid the tin electrode erosion, a LDP EUV source, in which a tin pool was used as cathode, was developed. A CO2 pulse laser was focused on the liquid tin target surface, and then a breakdown occurred in a very short time. The voltage-current characteristics of the discharge oscillated, and lasted for several microseconds, and a RLC fitting model was used to obtain the inductance and resistance. An ICCD camera was used to investigate the dynamic of LDP, which can explain the formation of a discharge channel. The EUV spectra of laser induced liquid tin discharge plasma were detected by a grazing incident ultraviolet spectrometer, compared with laser produced tin droplet plasma EUV spectrum. To explain the EUV spectra difference of laser induced liquid tin discharge plasma and laser produced tin droplet plasma, the collision radiation (CR) model combined with COWAN code was used to fit the experimental EUV spectrum, which can estimate the electron temperature and density of the plasma.
PDF全文 (下載：3) Chinese Optics Letters ，2020年第18卷第5期 pp.05
The ultimate capacity of cladding-pumped 10/130 Tm: fiber is experimentally investigated with a 793nm LD bidirectionally pumped amplifier. The laser system works stably at the output power of 52W, 65W, and 87W. Eventually, the damage of the amplifier occurs when the output power reaches about 103.5 W with a total incident pump power of 176.8W. Considering the incident seed power of 12.3W, the amplifier conversion efficiency is estimated about 51.6% before it is damaged. With the valuable exploration, we achieve the first air-cooling 60 W Tm: fiber laser at 1945.845 nm with a spectra linewidth of 0.4 nm. The laser power stability reaches 1.24% during a continuous test time of >65 hours. The beam quality is measured as Mx2=1.16, My2=1.14.
PDF全文 (下載：9) Chinese Optics Letters ，2020年第18卷第5期 pp.05
A high repetition rate, picosecond THz parametric amplifier (TPA) with a LiNbO3 (LN) crystal has been demonstrated in this work. At 10 kHz repetition rate, a peak power of 200 W and an average power of 12 μW have been obtained over a wide range around 2 THz; at 100 kHz repetition rate, a maximum peak power of 18 W and average power of 10.8 μW have been obtained. The parametric gain of the LN crystal was also investigated and a modified Schwarz-Maier model was introduced to interpret the experimental results.
PDF全文 (下載：8) Chinese Optics Letters ，2020年第18卷第5期 pp.05
To introduce ordered nano-structure inside transparent amorphous matrix with superior optical and mechanical properties bears scientific and technological importance, yet limited success has been achieved. Here, via simple melting-quenching and subsequent thermal activation, we report the successful preparation of a transparent nano-structured glass ceramics embedded with Sr<sub>2</sub>LuF<sub>7</sub> nano-crystals (~26 nm), as evidenced by XRD, TEM and HRTEM. The successful incorporation of dopants into formed Sr<sub>2</sub>LuF<sub>7</sub> nano-crystals with low phonon energy results in highly tunable blue-green photo-emission, which depending on excitation wavelength, dopant type and temperature. We found that Eu<sup>3+</sup> and Eu<sup>2+</sup> ions co-exist in this hybrid optical materials, accompanied by the broadband blue emission of Eu<sup>2+</sup> and sharp red emissions of Eu<sup>3+</sup>. Series of optical characterizations are summoned, including emission, excitation spectra and decay curve measurement, to reveal the reduction mechanism of Eu<sup>3+</sup> to Eu<sup>2+</sup>. Furthermore, near green-white photo-emission is achieved via the enrichment of Tb<sup>3+</sup>/Eu<sup>3+</sup> into crystallized Sr<sub>2</sub>LuF<sub>7</sub> nano-crystals. The temperature-dependent visible photo-emission reveals thermal activation energy increases with the precipitation of Sr<sub>2</sub>LuF<sub>7</sub> nano-crystals in glass matrix, suggesting better thermal stability of glass-ceramics than precursor glasses. These results could not only deepen the understanding of glass-ceramics but also indicate the promising potential of Eu<sup>3+</sup>/Tb<sup>3+</sup> ions doped-Sr<sub>2</sub>LuF<sub>7</sub> glass-ceramics for UV pumped WLEDs with good thermal stability.
PDF全文 (下載：2) Chinese Optics Letters ，2020年第18卷第5期 pp.05
In this paper, we propose a broadband NIR absorber based on the phase transition material VO2. By designing different arrangements of the VO2 square lattice at high and low temperatures on fused silica substrates, the absorption rate reaches more than 90% in the entire 1.4-2.4 μm range. Using a finite-difference time-domain simulation method and thermal field analysis, the results prove that the absorber is polarization-independent and has wide-angle absorption for incident angles of 0°-70°. The proposed absorber has a smoother absorption curve and is superior in performance, and it has many application prospects in remote sensing geology.
PDF全文 (下載：1) Chinese Optics Letters ，2020年第18卷第5期 pp.05
We propose and demonstrate a novel scheme of the semi-open-loop polarization control (SOL-PC), which controls the state of polarization (SOP) with high accuracy and uniform high speed. For any desired SOP, we firstly adjust the initial SOP by the open-loop control (OLC) based on the matrix model of a three-unit piezoelectric polarization controller, and quickly move it close to the objective one. Then the close-loop control (CLC) will be performed to reduce the error and reach precisely the desired SOP. The response time is three-order faster than that of the present close-loop polarization control, while the average deviation is on a par with it. Finally the SOL-PC system is successfully applied to realize the suppression of polarization mode dispersion (PMD) effect, and reduce the first-order PMD to near zero. Due to its perfect performance, the SOL-PC will energize the present polarization control to pursue an ideal product, which can meet the future requirements in ultrafast optical transmission and quantum communication.
PDF全文 (下載：10) Chinese Optics Letters ，2020年第18卷第5期 pp.05
A switchable microwave photonic filter (MPF) using a phase modulator (PM) and a silicon-on-insulator (SOI) micro-ring resonator (MRR) is proposed and demonstrated. By adjusting the polarization controller (PC) between the PM and the MRR, the filtering function of the MPF can be switched between a band-stop filter and a band-pass filter. In a proof-of-concept experiment, an MPF with a rejection ratio of 30 (or 15 dB) for the band-stop (or band-pass) response and a frequency tuning range from 9.6 to 27.6 GHz is achieved.
PDF全文 (下載：18) Chinese Optics Letters ，2020年第18卷第5期 pp.05
Quantum walks, a counterpart of classical random walks, have many applications due to its neoteric features. Since was firstly proposed, quantum walks have been explored in many fields theoretically and also been demonstrated experimentally in various physical systems. In this article, we review the experimental realizations of discrete-time quantum walks in photonic systems with different physical structures, such as bulk optics and time-multiplexed framework. And then some typical applications using quantum walks are introduced. Finally, the advantages and disadvantages of these physical systems are discussed.
PDF全文 (下載：0) Chinese Optics Letters ，2020年第18卷第5期 pp.05
A grating-coupled surface plasmon resonance sensor based on bilayer aluminum nanowire arrays is fabricated by laser interfere lithography. The device presents impressive reflective sharp peaks by lateral surface plasmon resonances even for aluminum thickness merely of several nanometers. Distinct reflective peaks and dramatic color shifts under different analytes are observed within a wide range of incident angle, metal thickness, and refractive index. The sensitivity of 307 nm per refractive index unit is experimentally obtained. The reflective-peak-typed surface plasmon resonance sensors are suitable for practical applications, because of easy fabrication, low cost wide range, and high signal visibility.
The unamplified spontaneous emission（SE）is one of important physical processes of the light-matter interaction in a diode laser, in terms of Einstein’s theory. The recent research on a kind of new indium-rich cluster (IRC) laser structure did not reveal SE characteristics of the IRC structure, as its unusual quantum confined structure made it difficult to acquire correctly the SE spectra through theoretical simulation or previous experimental techniques. Thus, in this paper we firstly established a convenient and effective experimental approach to acquire SE spectra of the IRC structure by the measurement of amplified spontaneous emissions from dual facets of a single edge-emitting chip with little sample processing. With the proposed method, the special SE spectra due to the IRC effect were observed. Then, the SE formation mechanism and characteristics in the IRC structure were analyzed by comparing the experimental data with theoretical SE spectra using a standard InGaAs/GaAs quantum well with the similar material composition. This research provides a useful tool to investigate the SE characteristics of any non-standard diode laser structure and is very meaningful to developing a new type of IRC lasers.
In this work, SF6 as Raman-active medium is investigated to generate multispectral Raman laser by the combination of cascade stimulated Raman scattering and four wave mixing. The Raman frequency comb from the 10th order anti-Stokes to the 9th order Stokes was generated, and its spectral range covered 377-846 nm. The photon conversion efficiency of 16.4% for the first Stokes was achieved, and the Raman gain coefficient at 1.5 MPa of SF6 under the 532 nm pump laser was calculated to be 0.83 cm/GW by the SRS threshold comparison with H2. Using helium as carrier gas, the thermal effect of SF6 Raman laser was improved dramatically under repetition rate of 10 Hz.
We demonstrated absorption spectroscopy on water vapor for the determination of gas temperature. An adaptive dual-comb detection system is utilized to obtain precise spectroscopic data in a broadband range from 7143 to 7240 cm-1 with a spectral resolution of 0.049 cm-1. The measured spectra are in accordance with the simulated results from HITRAN database. Several measurements are investigated in the temperature range of 500-1000 K, revealing relative deviations of less than 5% compared to the thermocouple. This broadband and accurate adaptive dual-comb spectral detection method could be a powerful tool for non-invasive combustion diagnosis.
Laguerre-Gaussian (LG) mode beam has very important applications in many research fields. Here, Theon sieve is first introduced into the laser resonator and to generate petal-like laser beam by coherently superimposing two high-order LG mode. The effectiveness was verified by GLAD software. The petal-like laser beam is derived from the light field redistribution and coherently superposition caused by the diffraction effect of Theon sieve. The relationship between the order of petal-like laser and the cavity structures has also been investigated in detail. Light field operation in laser cavity greatly simplifies the optical structure and is more beneficial to optical diagnostics and imaging.
PDF全文 (下載：2) Chinese Optics Letters ，2020年第18卷第4期 pp.04
Imaging through scattering media via speckle autocorrelation is a popular method based on the optical
memory effect. However, it fails if valid information acquired is insufficient due to a limited sensor size.
In this paper, we reveal a relationship between detector and object sizes for the minimum requirement
to ensure image reconstruction by defining a sampling ratio R, and propose a method to enhance image
quality at a small R by capturing multiple frames of speckle patterns and piecing them together. This
method will be helpful in expanding applications of speckle autocorrelation to remote sensing, underwater
probing and so on.
PDF全文 (下載：0) Chinese Optics Letters ，2020年第18卷第4期 pp.04
We demonstrate a novel multi-functional radar receiver scheme based on the photonic parametric sampling. The working principle of the photonic parametric sampling based on four wave mixing (FWM) process is presented. To experimentally verify the multi-functional feasibility, the scheme is individually implemented to carry out a four-channel phased array radar reception and a dual-band radar reception.
PDF全文 (下載：3) Chinese Optics Letters ，2020年第18卷第4期 pp.04
For the first time, a group-VI single element nanomaterial was used as the optical saturable absorber (SA) to genetate laser pulses. With two-dimensional (2D) tellurene as passively Q-switcher, the 1.06 and 1.3 μm pulse laser operations were realized from a diode-pumped Nd:YAG crystal. The shortest pulse widths were 98 ns, 178 ns, and the highest peak powers were 2.68 W, 2.45 W, respectively. Our research manifests that tellurene is an excellent SA material in near infrared region.
PDF全文 (下載：5) Chinese Optics Letters ，2020年第18卷第4期 pp.04
We experimentally demonstrated optical wireless power transfer (OWPT) using a near-infrared laser diode (LD) as the optical power transmitter. We considered a photovoltaic (PV) cell and a photodiode (PD) as the optical power receivers. We investigated the characteristics of the LD, PD, and PV cell in order to determine the optimum operating condition from the viewpoint of transfer efficiency. We also experimentally demonstrated a whole system optimization process to maximize the DC-to-DC transfer efficiency of the OWPT. Our experimental results showed that the optimization process can improve the OWPT efficiency by upto 48 %.
Space-division multiplexing (SDM) has attracted significant attention in recent years, because larger transmission capacity is enabled by more degrees of freedom (DOFs) in few mode fibers (FMFs) compared with single mode fibers (SMFs). To transmit independent information on spatial modes without or with minor digital signal processing (DSP), weakly-coupled FMFs are preferred in various applications. Several cases with different use of spatial DOFs in weakly-coupled FMFs are demonstrated in this work, including single-mode or mode-group-multiplexed transmission, and spatial DOFs combined with time or frequency DOF to improve the system performance.
A deep convolutional neural network is employed to simultaneously measure the beam-pointing and phase difference of sub-beams from a single far-field interference fringe for the coherent beam combining systems. Especially, the amplitudes of sub-beams in measurement path are modulated in order to prevent measuring mistake caused by symmetry of beam-pointing. This method is able to measure beam-pointing and phase difference with an RMS accuracy of about 0.2μrad and λ/250 respectively in a two-beam coherent beam combining system.
PDF全文 (下載：1) Chinese Optics Letters ，2020年第18卷第4期 pp.04
We investigate the influence of the source's energy fluctuation on both computational ghost imaging and computational ghost imaging via sparsity constraint, the reconstruction quality will decrease with the increase of the source's energy fluctuation. In order to overcome the problem of image degradation, a correction approach against the source's energy fluctuation is proposed by recording the source's fluctuation with a monitor before modulation and correcting echo signal or the intensity of computed reference light field with the data recorded by the monitor. Both numerical simulation and experimental results demonstrate that computational ghost imaging via sparsity constraint can be enhanced by correcting echo signal or the intensity of computed reference light field, while only correcting echo signal is valid for computational ghost imaging.
We propose and analyze a silicon hybrid plasmonic polarization splitter-rotator with ultra-short footprint using asymmetric bent directional coupler on silicon-on-insulator platform. Benefiting from the large birefringence induce by bent structure and plasmonic effect, the cross-polarization coupling length is only 5.21 μm. The transverse magnetic to transverse electric polarization conversion efficiency is over 99.9% with extinction ratio of 20.6 dB (32.5 dB) for transverse magnetic (transverse electric) mode at 1.55 μm. Furthermore, the polarization conversion efficiency is higher than 90% while maintaining crosstalk below -19 dB within the bandwidth of 80 nm.
In this paper, vortex phase and sinusoidal phase modulation of Hermite-Gaussian beams are studied theoretically and experimentally. The coding method of experiment is introduced in detail and the evolution law of focus under different beam order (m, n) and topological charge (l) is given. In order to verify the accuracy of generation experiment, the optical field distribution under sinusoidal vortex modulation is analyzed deeply. The relevant analysis and methods provided in this paper have certain practical significance for the development of laser mode analysis, optical communication and other fields.
PDF全文 (下載：6) Chinese Optics Letters ，2020年第18卷第4期 pp.04
A new disordered crystal Nd:SrAl<sub>12</sub>O<sub>19</sub> (Nd:SRA) with an Nd<sup>3+</sup> doping concentration of 5% was successfully grown using the Czochralski method. A diode-pumped Nd:SRA Q-switched laser operating at 1049 nm was demonstrated for the first time. Based on a MXene Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> sheet, a high repetition rate of 201 kHz with a Q-switched pulse width of 346 ns was obtained when the absorbed pump power was 2.8 W. The peak power and single pulse energy were 1.87 W and 0.65 μJ, respectively.
The photoelectric properties of conductive films are improved by doping silver on aluminum-doped zinc oxide (AZO) films by picosecond laser induced forward transfer (LIFT) technology. Firstly, the temperature variation of the electron and lattice in silver films under picosecond laser was numerically calculated by finite element analysis, and the relationship between picosecond laser induced transfer mechanism and film thickness was revealed：As the film thickness increases, the film is transferred from the entire area to the upper film breaking through the underlying film and forming a jet to transfer; Then, different thickness silver films were deposited on the AZO films by picosecond LIFT. We have successfully obtained some AZO films with higher optoelectronic properties under the conditions of thinner silver film and lower laser energy density; under the thick silver film (>100 nm) or the too high laser energy, the AZO films were damaged, but at this time, silver deposits on the surface of the AZO films to produce a special nanostructure.