Atomic and molecular physics
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A vapor cell provides a well-controlled and stable inner atmosphere for atomic sensors, such as atomic gyroscopes, atomic magnetometers, and atomic clocks, and its hermeticity affects the stability and aging of atomic sensors. We present the micro-fabrication of a micro-electromechanical system wafer-level hermit vapor cell based on deep reactive ion etching and vacuum anodic-bonding technology. The anodic-bonding process with the voltage increasing in steps of 200 V had a critical influence on vapor cell hermeticity. Further, the silicon–glass bonding surface was experimentally investigated by a scanning electron microscope, which illustrated that there were no visual cracks and defects in the bonding surface. The leak rate was measured using a helium leak detector. The result shows that the vapor cells with different optical cavity lengths comply with the MIL-STD-883E standard (5 × 10?8 mbar·L/s). Moreover, D2 absorption spectroscopy was characterized via optical absorption. The bonding strength was determined to be 13 MPa, which further verified the quality of the vapor cells.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.100201
The impulse response for a phase-change material Ge2Sb2Te5 (GST)-based photodetector integrated with a silicon-on-insulator (SOI) waveguide is simulated using finite difference time domain method. The current is calculated by solving the drift-diffusion model for short pulse (～10 fs) excitation for both of the stable phases. Full width at half-maximum values of less than 1 ps are found in the investigation. The crystalline GST has higher 3 dB bandwidth than the amorphous GST at a 1550 nm wavelength with responsivities of 21 A/W and 18.5 A/W, respectively, for a 150 nm thick GST layer biased at 2 V. A broad spectrum can be utilized by tuning the device using the phase-change property of material in the near infrared region.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.100401
Fiber optics and optical communications
A complex-coefficient microwave photonic filter with continuous tunability is proposed and demonstrated, which has a compact structure and stable performance without splitting the optical path and tuning the polarization state. By only controlling the DC biases of the modulator, the amplitudes and the phases of the filter taps can both be tuned. The phase difference between the two filter taps covers a full 360° range from 10 GHz to 32 GHz. Frequency responses of the proposed filter are measured within 10–20 GHz with different center frequencies.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.100601
High-rate techniques, such as optical orthogonal frequency division multiplexing (OFDM) and color shift keying (CSK), have been proposed for visible light communication (VLC). To fully exploit their advantages, in this Letter, we design a modulation scheme called rotated polarity modulation (RPM) aided complex CSK (CCSK) for OFDM-based VLC systems and derive its theoretical bit error rate and an optimal scaling factor. Analytical and simulation results show that in comparison to the existing schemes, the new RPM-CCSK-OFDM system offers an improved link performance and data rate under a modest complexity. It can also be applied to VLC systems equipped with different types of LED devices, thus enabling flexible deployments.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.100602
Inspired by recent rapid deep learning development, we present a convolutional-neural-network (CNN)-based algorithm to predict orbital angular momentum (OAM) mode purity in optical fibers using far-field patterns. It is found that this image-processing-based technique has an excellent ability in predicting the OAM mode purity, potentially eliminating the need of using bulk optic devices to project light into different polarization states in traditional methods. The excellent performance of our algorithm can be characterized by a prediction accuracy of 99.8% and correlation coefficient of 0.99994. Furthermore, the robustness of this technique against different sizes of testing sets and different phases between different fiber modes is also verified. Hence, such a technique has a great potential in simplifying the measuring process of OAM purity.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.100603
Using the few-mode erbium-doped fiber (FM-EDF) with a simple two-layer erbium-doped structure, we demonstrate an all-fiber FM-EDF amplifier. The gain equalization among the six spatial modes supported by the FM-EDF is achieved when only the pump in the fundamental mode (LP01) is applied. When the signals in six spatial modes are simultaneously amplified, the average modal gain is about 15 dB, and differential modal gain is about 2.5 dB for the signal at 1550 nm.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.100604
Lasers and laser optics
Using a heavily erbium-doped aluminosilicate fiber prepared by the sol-gel method combined with high temperature sintering, the temperature dependence of the spectrum around the 1.55 nm band and single-mode fiber laser properties were investigated, respectively. The absorption cross section increases 29.2% at ～1558 nm with the temperature increasing from 20°C to 140°C, while the emission cross section slightly increases 4.3%. In addition, the laser slope of the heavily erbium-doped aluminosilicate fiber at 1558 nm decreases 4.4% from 10.8% to 6.4% with the temperature increasing from 18°C to 440°C. Meanwhile, an experiment lasting 3 h proves that the fiber laser has excellent stability below 440°C.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.101401
Particle ejection is an important process during laser-induced exit surface damage in fused silica. Huge quantities of ejected particles, large ejection velocity, and long ejection duration make this phenomenon difficult to be directly observed. An in situ two-frame shadowgraphy system combined with a digital particle recognition algorithm was employed to capture the transient ejecting images and obtain the particle parameters. The experimental system is based on the principle of polarization splitting and can capture two images at each damage event. By combining multiple similar damage events at different time delays, the timeline of ejecting evolution can be obtained. Particle recognition is achieved by an adaptively regularized kernel-based fuzzy C-means algorithm based on a grey wolf optimizer. This algorithm overcomes the shortcoming of the adaptively regularized kernel-based fuzzy C-means algorithm easily falling into the local optimum and can resist strong image noises, including diffraction pattern, laser speckle, and motion artifact. This system is able to capture particles ejected after 600 ns with a time resolution of 6 ns and spatial resolution better than 5 μm under the particle recognition accuracy of 100%.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.101402
Phosphor in glass (PiG) employing Ce:Y3Al5O12 (YAG)-doped boro-bismuthate glass via low-temperature co-sintering technology was successfully prepared, using Bi2O3-B2O3-ZnO glass as the base material. The photoluminescence (PL) of PiG co-sintered at times ranging from 20 min to 60 min at 700°C was investigated. As a result, the relative PL intensity of PiG under a reducing atmosphere of CO showed significant enhancement of about 7–14 times that under air atmosphere sintering for 20–50 min. The PL intensity decreased gradually with the co-sintering time, which may be due to the corrosion of the YAG lattice structure.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.101601
A 50 Gb/s four-level pulse amplitude modulation (PAM4) underwater wireless optical communication (UWOC) system across the water–air–water interface is demonstrated in practice. In practical scenarios, laser beam misalignment due to oceanic turbulence degrades performance in UWOC systems. With the adoption of a reflective spatial light modulator (SLM) with an electrical controller, not only can the laser be arbitrarily adjusted to attain a water–air–water scenario, but oceanic engineering problems can also be resolved to establish a reliable UWOC link. Brilliant bit error rate performance and clear PAM4 eye diagrams are attained by adopting a Keplerian beam expander and a reflective SLM with an electrical controller. This proposed PAM4 UWOC system presents a feasible state that outperforms existing UWOC systems due to its feature providing a high-speed water–air–water link.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.100004
Underwater Wireless Optical Communication
In this paper, the current research of an underwater optical wireless communication (UWOC) network is reviewed first. A hybrid laser diode (LD) and light-emitting diode (LED)-based UWOC system is then proposed and investigated, in which hybrid cluster-based networking with mobility restricted nodes is utilized to improve both the life cycle and throughput of the UWOC network. Moreover, the LEDs are utilized for the coarse alignment, while the LDs are used for high-precision positioning to reduce the difficulty of optical alignment. Finally, challenges and trends for UWOC are pointed out to provide some insight for potential future work of researchers.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.100002
One fast simulation method using Markov chains was introduced to simulate angular, energy, and temporal characteristics of pulsed laser beam propagation underwater. Angular dispersion of photons with a different number of collisions was calculated based on scattering function and the state transition matrix of Markov chains. Temporal distribution and energy on the receiving plane were obtained, respectively, by use of a novel successive layering model and receiving ratio. The validity of this method was verified by comparing it with the Monte Carlo ray tracing (MCRT) method. The simulation results were close to those obtained by MCRT but were less time consuming and had smoother curves.
PDF全文   HTML全文 Chinese Optics Letters, 2019年第17卷第10期 pp.100003
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Coulomb potential may induce a significant angular offset to the 2-dimensional photoelectron momentum distributions for atoms subject to strong elliptically polarized laser field. In the attoclock experiment, this offset usually cannot easily be disentangled from the contribution of tunneling delay and poses a main obstacle to the precise measurement of tunneling delay. Based on semiclassical calculations, here we propose a method to extract the equivalent temporal offset induced solely by Coulomb potential (TOCP) in an attoclock experiments. Our calculations indicate that, at constant laser intensity, the TOCP show distinctive wavelength dependence laws for different model atoms and the ratio of the target atom's TOCP to that of H becomes insensitive to wavelength and linearly proportional to (2I_p )^(-3⁄2), where I_p is the ionization potential of the target atom. This wavelength and I_p dependence of TOCP can be further applied to extract the Coulomb potential influence. Our work paves the way for an accurate measurement of the tunneling delay in the tunneling ionization of atoms subject to intense elliptically polarized laser field.
PDF全文 (下载：2) Chinese Optics Letters ，2020年第18卷第1期 pp.01
Aiming at the application requirements of information optics, this paper proposed a perovskite quantum dot random lasing pumping method suitable for high-speed modulation. At the same time, the luminescence characteristics of perovskite quantum dot films under electron beam pumping conditions are analyzed, and the random lasing mechanism of electron beam pumping CsPbBr3 quantum dot films is revealed. Finally, It is confirmed that perovskite quantum dots are easy to realize random lasing under electron beam pumping conditions.
PDF全文 (下载：9) Chinese Optics Letters ，2020年第18卷第1期 pp.01
In this Letter, we fabricate integrated metasurface of encoded dynamic phases and experimentally generate nonconventional Kagome-type lattices of no second-order phase vortices. The thin metasurface acts analogous to an integration of three conventional optical elements, i.e., six pinholes located at the vertices of two concentric regular triangles of size ratio 1:2, six transparent discs of different thicknesses to introduce a total phase shift difference of 6π and a Fourier lens with focal length in micro-scale. Kagome lattice with required vortex distribution is realized at the “focal” plane of the metasurface under illumination of plane wave.
PDF全文 (下载：7) Chinese Optics Letters ，2020年第18卷第1期 pp.01
In this paper, a dye-doped cholesteric liquid crystal (DDCLC) filled hollow glass microsphere is demonstrate to be a resonator with good temperature response. A diglycerol layer is used to wrap the DDCLCs microdroplet to keep it steady and control its orientation. The whispering gallery mode (WGM) lasing and photonic band gap (PBG) lasing caused by two different mechanisms were obtained under the pump of a pulsed laser, and the temperature response of these two kind of lasing were studied. For the liquid crystal and chiral material used in this paper, both the WGM lasing and the PBG lasing have a blue shift in wavelength with increasing temperature.
PDF全文 (下载：4) Chinese Optics Letters ，2020年第18卷第1期 pp.01
In order to meet the practical needs of all-fiber CTD sensor with high sensitivity, compact structure and easy packaging, this paper uses a microfiber coupler combined with Sagnac loop (MCSL) reflective photonic device to conduct salinity, temperature and deep sensing experiments.These MCSLs’ dynamic range and resolution of salinity, temperature, and depth can meet the requirements of actual marine environment monitoring. This structure opens up a new design idea for the practical research of MC-based marine environmental parameter sensor.
PDF全文 (下载：0) Chinese Optics Letters ，2020年第18卷第1期 pp.01
We demonstrate real-time three-dimensional (3D) color video using color electroholographic system with a cluster of multiple-graphics processing units (multi-GPU) and three spatial light modulators (SLMs) corresponding to respective red, green, and blue (RGB)-colored reconstructing lights. The multi-GPU cluster has a computer-generated hologram (CGH) display node containing a GPU, for displaying calculated CGHs on SLMs, and four CGH calculation nodes using 12 GPUs. The GPUs in the CGH calculation node generate CGHs corresponding to RGB reconstructing lights in a 3D color video using pipeline processing. Real-time color electroholography was realized for a 3D color object comprising approximately 21,000 points per color.
Nd3+ doped fiber lasers at around 900 nm based on the 4F3/2 → 4I9/2 transition have obtained much research attention since they can be used as the laser sources for generating pure blue fiber lasers through frequency doubling technique. Here, all-fiber laser at 915 nm was realized by polarization-maintaining Nd3+ doped silica fiber. A net gain per unit length of up to 1.0 dB/cm at 915 nm was obtained from a 4.5 cm fiber, which to our best knowledge is the highest gain coefficient reported in this kind of silica fiber. The optical-to-optical conversion efficiency varies with active fiber length and the reflectivity of output fiber Bragg grating (FBG), presenting an optimal value of 5.3% at 5.1 cm fiber length and 70% reflectivity of LR-FBG. Additionally, the linear DBR short cavity was constructed to explore its potential in realizing single frequency 915 nm fiber laser. The measurement result of longitudinal mode properties shows it is still multi-longitudinal modes laser operation with 55 mm laser cavity. These results indicate that the Nd3+ doped silica fiber could be used to realize all-fiber laser at 915 nm, which presents potential to be the seed source of high power fiber laser.
PDF全文 (下载：0) Chinese Optics Letters ，年第卷第期 pp.
D. Bernal Olivier
Self-mixing interferometry (SMI) is an attractive sensing scheme which typically relies on mono-modal operation of employed laser diode. However, change in laser modality can occur due to change in operating conditions. So, detection of occurrence of multi-modality in SMI signals is necessary to avoid erroneous metric measurements. Typically, processing of multi-modal SMI signals is a difficult task due to the diverse and complex nature of such signals. However, the proposed techniques can significantly ease this task by identifying the modal state of SMI signals with 100% success rate, so that interferometric fringes can be correctly interpreted for metric sensing applications.
The polarization of D-shaped fiber is modulated after immersing it in the magnetic fluid (MF) and applying a magnetic field. Theoretical analysis predicts that magneto-optical dichroism of MF plays key role in the light polarization modulation. During the light polarization modulation, the evanescent wave polarized parallel to the magnetic field has greater loss than its orthogonal component. The light polarization of D-shaped fiber with a wide polished surface can be modulated easily. High concentration MF and large magnetic field all have great ability to modulate light polarization.
Ooi B. S.
Conventional line-of-sight underwater wireless optical communication (UWOC) links suffer from huge signal fading in the presence of oceanic turbulence due to misalignment, which is caused by variations in the refractive index in the water. Non-line-of-sight (NLOS) communication, a novel underwater communication configuration, which has eased the requirements on the alignment, is supposed to enhance the robustness of the UWOC links in the presence of such turbulence. This paper experimentally and statistically studies the impact of turbulence that arises from temperature gradient variations and the presence of different air bubble populations on NLOS optical channels. The results suggest that temperature gradient-induced turbulence causes negligible signal fading to the NLOS link. Furthermore, the presence of air bubbles with different populations and sizes can enhance the received signal power by seizing the scattering phenomena from an ultraviolet 377-nm laser diode.
PDF全文 (下载：1) Chinese Optics Letters ，2019年第17卷第10期 pp.10
In this paper, recent advances in underwater wireless optical communication (UWOC) are reviewed for both LED- and LD-based systems,
mainly from a perspective of advanced modulation formats. Volterra series based nonlinear equalizers, which can effectively counteract the
nonlinear impairments induced by the UWOC system components, are discussed and experimentally demonstrated. Both the effectiveness
and robustness of the proposed Volterra nonlinear equalizer in UWOC systems under different water turbidity are validated. To further
approach the Shannon capacity limit of the UWOC system, probabilistic constellation shaping (PCS) technique is introduced, which can
overcome the inherent gap between a conventional regular quadrature amplitude modulation (QAM) format and the Shannon capacity of
the channel. The experimental results have shown significant system capacity improvement compared to the cases using a regular QAM.
Underwater visible light communication (UVLC) is expected to act as an alternative candidate in next-generation underwater 5G wireless optical communications. To realize high-speed UVLC, the challenge is that the absorption, scattering, turbulence of water medium and the nonlinear response from imperfect optoelectronic devices, which can bring large attenuation and nonlinearity penalty. Nonlinear adaptive filters are commonly used in optical communication to compensate for nonlinearity. In this paper, we compare RLS based Volterra filter, LMS based DP filter and LMS based Volterra filter in terms of performance and computational complexity in underwater visible light communication. We experimentally demonstrate 2.325 Gb/s transmission at a distance of 1.2 m water with a commercial blue LED. Our goal is to assist the readers in refining the motivation, structure, performance and cost of powerful nonlinear adaptive filters in the context of future underwater visible light communication in order to tap into hitherto unexplored applications and services.
PDF全文 (下载：2) Chinese Optics Letters ，2019年第17卷第10期 pp.10
In this work, a blue gallium nitride (GaN) micro-LED based underwater optical communication (UWOC) system was built, and UWOCs with varied Maalox, chlorophyll and sea salt concentrations were studied. Data transmission performance of the UWOC and the influence of light attenuation were investigated systematically. Maximum data transmission rates at the distance of 2.3 m were 933, 800, 910 and 790 Mbps for experimental conditions with no impurity, 200.48 mg/m3 Maalox, 12.07 mg/m3 chlorophyll and 5kg/m3 sea salt, respectively, much higher than previously reported systems with commercial LEDs. It was found that increasing chlorophyll, Maalox and sea salt concentrations in water resulted in an increase of light attenuation, which led to the performance degradation of the UWOC. Further analysis suggests two light attenuation mechanisms, e.g. absorption by chlorophyll and scattering by Maalox, are responsible for the decrease of maximum data rate and the increase of bit error rate. Based on the absorption and scattering models, excellent fitting to the experimental attenuation coefficient can be achieved and light attenuation by absorption and scattering at different wavelengths was also investigated. We believe this work instructive to apply UWOC for practical applications.
PDF全文 (下载：9) Chinese Optics Letters ，2019年第17卷第10期 pp.10
The growing number of underwater activities is giving momentum to the development of new technologies, such as buoys, Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs). The data collected by these vehicles needs to be transmitted to a central unit with high speed. Clearly, wired solution are not suitable, since they strongly impact the mobility. In this scenario, a promising solution is offered by Underwater Optical Wireless Communication (UOWC) technology, which can achieve both high-speed and wireless operation. Here, we provide a comprehensive survey on the challenges, the experimental realizations and the state of the art in UOWC researches.
PDF全文 (下载：0) Chinese Optics Letters ，2019年第17卷第10期 pp.10
Foreseeing the proliferation of underwater vehicles and sensors, underwater wireless optical communication (UWOC) is a key enabler for ocean exploration, with strong competitiveness in short-range bandwidth-intensive applications. We provide a tutorial on the basic concepts and essential features of UWOC as well as an overview of work being conducted in this field. Research challenges, arising from the characteristics of underwater channels, and possible roadmaps are discussed in detail. This review is expected to be of great use to the link designers of this field.
PDF全文 (下载：8) Chinese Optics Letters ，2019年第17卷第10期 pp.10
We systematically investigate the bubble-induced performance degradation for underwater wireless optical communication (UOWC) with different bubble sizes and positions. By using different transmit and receive diversities, we investigate the effectiveness of spatial diversity on the mitigation of the bubble-induced impairment to the UOWC link. With the help of a 2×2 MIMO using repetition coding (RC) and maximum ratio combining (MRC), a robust 780-Mbit/s UOWC transmission is achieved. The corresponding outage probability can be significantly reduced from 34.6% for the system without diversity to less than 1%.
PDF全文 (下载：3) Chinese Optics Letters ，2019年第17卷第10期 pp.10
This letter investigates the performance of the two-way multi-hop system for underwater optical wireless communications. With the decode-and-forward (DF) relaying, the two-way multi-hop system is modeled, where the effects of absorption, scattering, and oceanic turbulence are all taken into account. An exact closed-form expression for outage probability is derived under the assumption that the oceanic turbulence obeys a log-normal distribution. Numerical results demonstrate the impacts of various parameters on the outage performance and indicate that the two-way multi-hop system significantly improves the performance in comparison to both the one-way multi-hop system and the two-way two-hop system.
The received signal intensity fluctuation and communication performance of an underwater optical wireless communication (UOWC) system under the air bubble effects are experimentally investigated. For different bubble density and size, Lognormal, Gamma, Weibull and generalized extreme value distributions are tested to fit the fluctuation of the signal intensity at the receiving end. The best fitting distribution is found to vary with bubble parameters. The communication system performance with OOK and pulse position modulation is further studied.
PDF全文 (下载：4) Chinese Optics Letters ，2019年第17卷第10期 pp.10
A sunlight communication system is proposed that uses Sr2Si5N8:Eu2+ phosphors to concentrate sunlight signals in strong background-light noise; thus, a wide spectrum sunlight communication system is converted into a narrow spectrum one. A communication method is proposed to enable compression to the dark line H-α (656.28 nm) spectrum. A 50% solar energy conversion efficiency is achieved, with a 0.3 μs code delay, a 0.2 μs code rise time (20%–80%), and a 96% optical transmittance. Experimental results show that phosphors enhance the sunlight intensity 1.5 times with the same distance. This method has immense potential in future long-distance sunlight communication.
PDF全文 (下载：4) Chinese Optics Letters ，2019年第17卷第12期 pp.12
Experimental generation of stable mode-locked pulses and cylindrical vector beams (CVBs), from an all few-mode fiber (FMF) ring laser is firstly reported, to the best of our knowledge. In this laser, a section of few-mode erbium-doped fiber (FM-EDF) is used as the gain medium. The FM-EDF is pumped by 976 nm laser light with LP11 mode, which is simultaneously converted and multiplexed through a homemade hybrid device, i.e. wavelength division multiplexing-mode selection coupler (WDM-MSC). All the components in our experiment are connected using FMF. The resulted CVB pulses have a spectral width of 0.33 nm with a repetition rate of 30.58 MHz under the pump power of 340 mW. Moreover, both azimuthally and radially polarized CVBs have been achieved with high purity of >95%. This mode-locked CVB fiber laser with all FMF configuration open the way to manipulate the transverse mode in mode-locked fiber lasers.
PDF全文 (下载：1) Chinese Optics Letters ，2019年第17卷第12期 pp.12
A 50 Gb/s four-level pulse amplitude modulation (PAM4) underwater wireless optical communication (UWOC) system across the water–air–water interface is demonstrated in practice. In practical scenarios, laser beam misalignment due to oceanic turbulence degrades performance in UWOC systems. With the adoption of a reflective spatial light modulator (SLM) with electrical controller, not only can the laser be arbitrarily adjusted to attain a water–air–water scenario, but oceanic engineering problems can also be resolved to establish a reliable UWOC link. Brilliant bit error rate performance and clear PAM4 eye diagrams are attained by adopting a Keplerian beam expander and a SLM electrical controller. This proposed PAM4 UWOC system presents a feasible state that outperforms existing UWOC systems due to its feature providing a high-speed water–air–water link.
Spontaneous optical emission properties of laser-produced plasma during laser damage events at input and exit surfaces of fused silica were retrieved and compared. We show that plasma at the input surface is much larger in size and exhibits significantly higher electron number density and excitation temperature even when smaller laser energy was used. This effect was attributed to the stronger laser-plasma coupling at the input surface. In addition, a strong continuum background containing three peaks at 1.3 eV, 1.9 eV and 2.2 eV was observed at the exit surface and possible origins for this effect are also discussed.
PDF全文 (下载：2) Chinese Optics Letters ，2019年第17卷第12期 pp.12
The extraordinary optical transmission (EOT) in subwavelength metal structure has been studied widely. Herein, we proposed a strategy for tuning the EOT of bullseye structure. Specifically, the bullseye structure was immersed in a nonlinear medium, and a controlling light was employed to change the refractive index of the medium. At different intensities and distributions of controlling light, the transmission property of signal light in the bullseye structure was simulated. The results show that, a variable transmission spectrum in the bullseye structure can be realized. Moreover, the position of central transmission peak shifts linearly with the increasing intensity of controlling light.
PDF全文 (下载：8) Chinese Optics Letters ，2019年第17卷第12期 pp.12
We demonstrate a novel type of miniature spectrometer based on a Fourier transform spectrometer (FTS) chip with dense output array and a commercial photodetector (PD) array. The FTS chip has an output array cycle of 20 μm and consists of 51 Mach-Zehnder interferometers (MZIs), the PD array is a commercial linear charged coupled device (CCD). An achromatic triplet lens is used to image the MZI output interferogram onto the CCD with a small aberration. Our experimental result shows that a free spectral range (FSR) from 489 nm to 584 nm and a retrieved spectral resolution of 3.5 nm at 532 nm are obtained. The achieved properties shows that our spectrometer has the potential to outperform the best commercial compact one in terms of most performance indices.
PDF全文 (下载：3) Chinese Optics Letters ，2019年第17卷第12期 pp.12
In the context of nonlinear plasmonics we review the recently introduced concept of Plasmonic Parametric Resonance (PPR) and discuss potential applications of such phenomenon. PPR arises from the temporal modulation of one or more of the parameters governing the dynamics of a plasmonic system and can lead to the amplification of high-order sub-radiant plasmonic modes. The theory of PPR is reviewed, possible schemes of implementation are proposed, and applications in optical limiting are discussed.
The tilted energy band in the multiple quantum wells (MQWs) arising from the polarization effect causes the quantum confined Stark effect (QCSE) for  oriented III-nitride based near ultraviolet light-emitting diodes (NUV LEDs). Here, we prove that the polarization effect in the MQWs for NUV LEDs can be self-screened once the polarization induced bulk charges are employed by using the alloy-gradient InxGa1-xN quantum barriers. The numerical calculations demonstrate that the electric field in the quantum wells becomes weak and thereby flattening the energy band in the quantum wells, which accordingly increases the spatial overlap for the electron-hole wave functions. The polarization self-screening effect is further proven by observing the blue shift for the peak emission wavelength in the calculated and the measured emission spectra. Our results also indicate that for NUV LEDs with a small conduction band offset between the quantum well and the quantum barrier, the electron injection efficiency for the proposed structure becomes low. Therefore, we suggest doping the proposed quantum barrier structures with Mg dopants.
PDF全文 (下载：6) Chinese Optics Letters ，2019年第17卷第12期 pp.12
Due to the composition-dependent properties of two-dimensional (2D) transition metal dichalcogenides (TMDs), alloying of existing dissimilar TMDs architecture is a novel and controllable route to tailor crystal structure with superior optical and optoelectronic properties. Here, we reported the hexagonal-phase WSe1.4Te0.6 alloy can enable great promise for enhanced saturable absorption response exceeding the parent component WSe2 and WTe2, with larger modulation depth and lower saturable intensity. These advantages allowed the 1070 nm passively Q-switched lasers based on WSe1.4Te0.6 more efficient, with narrowing pulse duration narrowed to 45%, slope efficiency increased by 232%. Our findings highlighted the appropriate alloying of TMDs as an effective strategy for development of saturable absorbers.
One fast simulation method using Markov chains was introduced to simulate angular, energy and temporal characteristics of pulsed laser beam propagation underwater. Angular dispersion of photons with different number of collisions was calculated based on scattering function and state transition matrix of Markov chains. Temporal distribution and energy on the receiving plane were obtained respectively by use of novel successive layering model and receiving ratio. The validity of this method was verified by comparing with Monto Carlo ray tracing (MCRT) method. The simulation results were close to those obtained by MCRT with less time consuming and smoother curves.
We show the intensity control of filamentation in fused silica by temporally shaping the femtosecond laser pulse. The arbitrary control of filamentation intensity has been obtained by the feedback control based on the genetic algorithm, and the peak intensity of filament has changed from about 670 to around 2100 (CCD counts). This modulation is qualitative agreement with the simulation results. It is shown that the control of the intensity is realized by modulating the peak power of the shaped pulse.
Wake fiber Bragg grating (WFBG) is an ideal quasi-distributed optical fiber sensor. Special attention should be paid to the spectrum and sensing performance of WFBG at extreme temperature due to its poor reflection intensity. In this paper, the temperature characteristics of WFBG from -252.75℃ to 200.94℃ are experimentally investigated. Five WFBGs with reflectivity from ~0.25% to ~10% are used in the experiments. The reflectivity variations and wavelength shifts at different temperatures are studied. Experimental results show that the WFBG can survive and work at extreme temperature, but the performance is affected significantly. The reflectivity is affected significantly by both cryogenic temperature and high temperature. The temperature responses of Bragg wavelengths in the wide temperature range are also obtained.