Separate Dimming Controlling and Data Transmission for an Indoor Visible Light Communication System

Simultaneous dimming controlling and data transmission are usually required in a white LED based indoor visible light communication system.However,the diming controlling of LED normally interferes the data transmission due to the modulation nonlinearity of LED.In order to solve this problem,a scheme by separating the LEDs for the functions of dimming control and data transmission respectively is proposed in this paper.In the scheme,the LEDs used for dimming control function are driven by a dc amplified circuit,and the LEDs for data transmission are driven by a digital modulation circuit respectively.In this way,the modulation distortion to the data signal caused by the modulation nonlinearity can be avoided even if the dimming is at high level dc driven current.The proof-of-concept experiment of a 2.5Mbit/s visible light communication system demonstrates that the dimming controlling and data transmission can be realized simultaneously in a simple way,and the data transmission is not affected by the dimming controlling function.Compared to previous methods,the scheme in this paper is simpler and cost effective,and makes sense when high rate data is transmitted in a visible light communication system.

Diode-Pumped Quasi-Three-Level Passively Q-Switched Nd：GGG Laser with a Codoped Nd,Cr：YAG Saturable Absorber

We demonstrate the first quasi-three-level passively Q-switched Nd：GGG laser at 937nm using a Nd, Cr：YAG crystal as the saturable absorber. The dependences of the average output power, the repetition rate and the pulse width on the incident pump power are obtained. A maximum average output power of 1.18 W with repetition rate of 35kHz and pulse width of 45ns is achieved at an incident pump power of 18.3 W. The corresponding optical-to-optical and slope efficiencies are 6% and 10%, respectively.

Possibility to break through limitation of measurement range in dual-wavelength digital holography

By using the beat frequency technique,the dual-wavelength digital holography(DWDH)can greatly increase the measurement range of the system.However,the beat frequency technique has a limitation in measurement range.The measurement range is not larger than a synthetic wavelength.Here,to break through this limitation,we propose a novel DWDH method based on the constrained underdetermined equations,which consists of three parts:(i)prove that the constrained underdetermined equation has a unique integer solution,(ii)design an algorithm to search for the unique integer solution,(iii)introduce a third wavelength into the DWDH system,and design a corresponding algorithm to enhance the anti-noise performance of DWDH.As far as we know,it is the first time that we have discovered that the problem of DWDH can belong in a problem of contained underdetermined equations,and it is also the first time that we have given the mathematical proof for breaking through the limitation of the measurement range.A series of results is shown to test the theory and the corresponding algorithms.More importantly,since the principle of proposed DWDH is based on basic mathematical principles,it can be further extended to various fields,such as dual-wavelength microwave imaging and dual-wavelength coherent diffraction imaging.

Temperature-dependent second harmonic generation process based on an MgO-doped periodically poled lithium niobate waveguide

The temperature dependency of a 5-mo1% MgO-doped periodically poled lithium niobate waveguide was investi- gated in this paper. We started with the temperature-dependent refractive index equation for the waveguide. Secondly, the temperature dependency of the second harmonic generation effect was experimentally researched under different temperatures and pump powers. The quasi-phase matched wavelengths, efficiency bandwidths and peak efficiencies of the waveguide were measured. The experimental results agreed with theoretical simulations, which are indispensable in the following all-optical sampling studies based on the cascaded second harmonic generation/difference-frequency generation process in the current device.

Dynamically tunable terahertz passband filter based on metamaterials integrated with a graphene middle layer

The dynamic tunability of a terahertz（THz） passband filter was realized by changing the Fermi energy（EF） of graphene based on the sandwiched structure of metal-graphene-metal metamaterials（MGMs）. By using plane wave simulation, we demonstrated that the central frequency（ f0） of the proposed filter can shift from 5.04 THz to 5.71 THz; this shift is accompanied by a 3 dB bandwidth（ f） decrease from 1.82 THz to 0.01 THz as the EFincreases from 0 to 0.75 eV.Additionally, in order to select a suitable control equation for the proposed filter, the curves of f and f0 under different graphene EFwere fitted using five different mathematical models. The fitting results demonstrate that the Dose Resp model offers accurate predictions of the change in the 3 dB bandwidth, and the Quartic model can successfully describe the variation in the center frequency of the proposed filter. Moreover, the electric field and current density analyses show that the dynamic tuning property of the proposed filter is mainly caused by the competition of two coupling effects at different graphene EF, i.e., graphene-polyimide coupling and graphene-metal coupling. This study shows that the proposed structures are promising for realizing dynamically tunable filters in innovative THz communication systems.

Magnetic Field Induced Spectroscopy of ^(88)Sr Atoms Probed with a 10 Hz Linewidth Laser

We present our experiment on magnetic field induced spectroscopy of the ^(1)S0–^(3)P0 transition of ^(88)Sr atoms with a 10 Hz linewidth laser.The ^(88)Sr atoms are cooled by two stage laser cooling.After the second stage narrow line laser cooling,the temperature of the atoms is reduced to~3μK.The atoms are then loaded into an 813 nm one-dimensional optical lattice.A homemade 698 nm laser with 10 Hz linewidth and maximum intensity of more than 100 W/cm2 is used to probe the ^(88)Sr atoms in the lattice.By means of a magnetic field of~1 mT and a probe laser with 50 ms pulse and~6 W/cm^(2) intensity,the Doppler free ^(88)Sr ^(1)S0–^(3)P0 transition spectrum with a linewidth of 208 Hz is obtained.

Influences of atmospheric turbulence effects on the orbital angular momentum spectra of vortex beams

We investigate the atmospheric turbulence effects on orbital angular momentum(OAM) spectra of different kinds of vortex beams, including Laguerre–Gaussian(LG) beams and Bessel beams, numerically. We generate the holograms of atmospheric turbulence with different structure constants of the refractive index. The OAM spectra of distorted single-mode or multiplexed LG beams and Bessel beams are analyzed. Compared with the OAM spectra of the two kinds of vortex beams, the spectrum of the Bessel beams is more dispersive. The results illustrate that Bessel beams suffer more from turbulent atmosphere than LG beams.

Non-probe compensation of optical vortices carrying orbital angular momentum

In this paper, we demonstrate a scheme for compensating distorted optical vortex beams carrying orbital angular momentum. By inputting the intensity profile into the Gerchberg–Saxton algorithm [Optik 35, 237(1972)], the pre-compensation phase mask can be acquired. No additional probe beams are introduced, and all the computing is aiming at the transmitted vortex beams. The distorted vortex beams are investigated experimentally before and after pre-compensation, showing favorable compensation performance. This scheme will find applications in the areas of rotation detection, optical communications, and so on.

Combination of light-emitting diode positioning identification and time-division multiplexing scheme for indoor location-based service

A combination of light-emitting diode（LED） identification and a time-division multiplexing scheme is proposed in this Letter for indoor location-based service. With the scheme, the arrangement of white LED lamps and the structure of a data frame are designed to realize high-accuracy indoor positioning and location-based payload data transmission simultaneously. The results of the experiment demonstrate that the indoor positioning accuracy is 10 cm and 2 Mb/s data transmission with high signal quality is realized.

Investigation of HTSC digital trunking communication receiver subsystem

The application of HTSC (high temperature superconductor) microwave devices in a UHF digital trunking communication system is introduced.The replacement between the HTSC microwave devices and the normal microwave devices is conducted.The digital sensitivity of the base station in complex electromagnetic environment has been increased to 6 dB,as the results of the experiment indicated,and this means that the coverage radius of the base station has been improved about twice,that is to say,the coverage area can be extended to four times as large as that of the current method.

Diagnostics of the topological charge of optical vortex by a phase-diffractive element

A phase-diffractive optical element is designed to measure the topological charge of optical vortices. We use the scalar diffraction theory to calculate the far-field diffraction patterns. The simulation results show that almost all of the power of the incident beams is diffracted to the same diffraction order, and this approach is also effective for multi-ring optical vortices. We upload this phase-diffractive optical element on the liquid crystal spatial light modulator to do the experiment. The observed far-field diffraction patterns fit well with the simulation results.

Wavelength-tunable mode-locked Yb-doped fiber laser based on nonlinear Kerr beam clean-up effect

We demonstrate a novel approach to achieve wavelength-tunable ultrashort pulses from an all-fiber mode-locked laser with a saturable absorber based on the nonlinear Kerr beam clean-up effect.This saturable absorber was formed by a single-mode fiber spliced to a graded-index multimode fiber,and its tunable band-pass filter effect is described by a numerical model.By adjusting the bending condition of the graded-index multimode fiber,the laser could produce dissipative soliton pulses with their central wavelength tunable from 1040 nm to 1063 nm.The pulse duration of the output laser could be compressed externally to 791 fs,and the signal to noise ratio of its radio frequency spectrum was measured to be 75.5 dB.

1319-nm single-frequency output from dif fusion-bonded monolithic nonplanar Nd:YAG ring resonator with undop0ed end

An efficient 1 319-nm Nd：YAG single-frequency laser is demonstrated in a diffusion-bonded nonplanar ring oscillator （NPRO） with an undoped end. The thermal model of diffusion-bonded NPRO is generated to analyze the temperature field and thermal focal length. A stable single-frequency output power of up to 1.55 W is obtained at 1 319 nm.

Dynamical phase alignment of sampling clock in optical performance monitoring system

In an optical performance monitoring system for high-speed optical communications, the ultra-short optical pulse from the laser is divided into two parts. One is to sample high-speed optical communication signal and the other as the sampling clock in an analog/digital converter （ADC） after detecting using a photon-detector. We propose a simple method based on variance calculation to align the phase of sampling clock in an ADC. The experiments demonstrate that, with the proposed method, the eye diagram or constellation diagram of high-speed optical communication signal can be reconstructed by the optical performance monitoring system.

Resonantly pumped 1645 nm Q-switched Er：YAG laser with a ring cavity

这份纸报告 1645 nm 嗯: 在 1532 nm 操作的嗯纤维激光共鸣地抽的钇铝柘榴石激光。有 52% 的斜坡效率的 1.78W continous 波浪(CW ) 产量力量用一个长戒指洞和做的 1 at.% 被获得嗯: 钇铝柘榴石水晶。在切换 Q 的模式，获得的脉搏精力是以 500 Hz 的重复率的 1.6 mJ；为 1 kHz 重复率， 1.2 mJ 产量精力被获得。

Design and demonstration of a foveated imaging system with reflective spatial light modulator

In this paper, a foveated imaging system using a reflective liquid crystal spatial light modulator （SLM） was designed. To demonstrate the concept of foveated imaging, we simulated with software Code V and established a laboratory prototype. The result of the experiment shows that an SLM can be used to correct the aberration of region of interest （ROI） while the resolution of other area was still very low. The vary- resolution system was relative simple compared to the traditional high resolution system and obviously can reduce the amount of data transmission. Such systems will have wide application prospect in various fields.

Passively Q-switched single-frequency output from a diffusion-bonded monolithic Nd:YAG non-planar ring oscillator

A compact monolithic Nd：YAG non-planar ring laser with diffusion-bonded Cr4＋：YAG is demonstrated,and high stable pulsed single-frequency laser at 1.06 μm is realized.Theoretical analysis and simulation results of pulsed laser parameters are illustrated.14.96-kW maximum peak power,pulse-width of 4.8 ns is achieved for single-frequency operation.