Multimode Interference Optical Power Splitter in Proton-Exchange LiNbO_3 Waveguides

The self imaging effect in graded index waveguides using annealed proton exchange (APE) technique in lithium niobate (LiNbO 3) waveguides is analyzed and simulated using the three dimensional nonparaxial beam propagation method (BPM).On this basis,a 1×8 multimode interference (MMI) optical power splitter by APE technique in X cut LiNibO 3 with Y propagation substrate is fabricated.Measurements show that the device has realized eight powers splittings.

Low power consumption 4-channel variable optical attenuator array based on planar lightwave circuit technique

The power consumption of a variable optical attenuator（VOA） array based on a silica planar lightwave circuit was investigated. The thermal field profile of the device was optimized using the finite-element analysis. The simulation results showed that the power consumption reduces as the depth of the heat-insulating grooves is deeper, the up-cladding is thinner,the down-cladding is thicker, and the width of the cladding ridge is narrower. The materials component and thickness of the electrodes were also optimized to guarantee the driving voltage under 5 V. The power consumption was successfully reduced to as low as 155 mW at an attenuation of 30 dB in the experiment.

Optically powered gas monitoring system using single-mode fibre for underground coal mines

We present an optically powered,intrinsically safe gas monitoring system to measure four essential environmental gases(CH_(4),CO_(2),CO and O_(2)),together with ambient temperature and pressure,for underground mines.The system is based on three key technologies developed at UNSW:(1)power-over-fbre(PoF)at 1550 nm using a single industry-standard,low-cost single-mode fbre(SMF)for both power delivery and information transmission,(2)liquid–crystal-based optical transducers for optical telemetry,and(3)ultra-low power consumption design of all electronics.Together,this approach allows each gas monitoring station to operate with less than 150 mW of optical power,meeting the intrinsic safety requirements specifed by the IEC60079-28 standard.A 2-month feld trial at BMA’s Broadmeadow underground mine proved the cabling compatibility to the mine’s existing optical network and the stability of the system performance.Compared with conventional electrically powered gas sensors,this technology bypasses the usual roadblocks of underground gas monitoring where electrical power is either unsafe or unavailable.Furthermore,using one fbre for both power delivery and communication enables longer distance coverage,reduces optical cabling and increases multiplexing possibilities and data throughput for better awareness of underground environment.

Universal form of the power spectrum of the aero-optical aberration caused by the supersonic turbulent boundary layer

Based on the measurement of one-dimensional （1D） optical path difference （OPD） of the supersonic turbulent bound- ary layer, an analytical form for the power spectrum of the two-dimensional （2D） OPD is obtained with its structure function and under the locally homogeneous isotropic assumption. The universality of this spectrum is argued, and its validity is checked by the comparison with experimental result. The potential applications of this model in theoretical and numerical studies are emphasized. Another contribution of this work is around the application of correlation function to analyzing the statistics of OPD. Based on our results and other results published elsewhere, we show that the OPD is often not stationary, and one should be cautious about using this tool.

Optical power limiting of ultrashort hyper-Gaussian pulses in cascade three-level system

Propagation of strong femtosecond hyper-Gaussian pulses in a cascade three-level molecular system is studied by solving numerically the Maxwell–Bloch equations by the iterative predictor-corrector finite-difference time-domain method.Optical power limiting behavior induced by strong nonlinear two-photon absorption is observed for different orders of the femtosecond hyper-Gaussian pulses. Pulses of a higher order temporal profile are found to have a wider power range of optical limiting but a larger output saturation intensity. Both the output saturation value and the damage threshold of optical power limiting decrease with pulse duration increasing. The decrease of the pulse area along the pulse propagation is much slower than that obtained from the two-photon area theorem due to invalidity of the slowly varying amplitude approximation and the monochromatic field hypothesis.

Computer Modeling and Simulation Evaluation of High Power LED Sources for Secondary Optical Design

Proposed and demonstrated is a novel computer modeling method for high power light emitting diodes(LEDs). It contains geometrical structure and optical property of high power LED as well as LED dies definition with its spatial and angular distribution. Merits and non-merits of traditional modeling methods when applied to high power LEDs based on secondary optical design are discussed. Two commercial high power LEDs are simulated using the proposed computer modeling method. Correlation coefficient is proposed to compare and analyze the simulation results and manufacturing specifications. The source model is precisely demonstrated by obtaining above 99% in correlation coefficient with different surface incident angle intervals.

Instantaneous frequency measurement using two parallel I/Q modulators based on optical power monitoring

A scheme for instantaneous frequency measurement(IFM)using two parallel I/Q modulators based on optical power monitoring is proposed.The amplitude comparison function(ACF)can be constructed to establish the relationship between the frequency of radio frequency(RF)signal and the power ratio of two optical signals output by two I/Q modulators.The frequency of RF signal can be derived by measuring the optical power of the optical signals output by two I/Q modulators.The measurement range and measurement error can be adjusted by controlling the delay amount of the electrical delay line.The feasibility of the scheme is verified,and the corresponding measurement range and measurement error of the system under different delay amounts of the electrical delay line are given.Compared with previous IFM schemes,the structure of this scheme is simple.Polarization devices,a photodetector and an electrical power meter are not used,which reduces the impact of the environmental disturbance on the system and the cost of the system.In simulation,the measurement range can reach 0 GHz-24.5 GHz by adjusting the delay amount of the electrical delay lineτ=20 ps.The measurement error of the scheme is better at low frequency,and the measurement error of low frequency 0 GHz-9.6 GHz can reach-0.1 GHz to+0.05 GHz.

Power Equilibrium in Dense Wavelength Division Multiplexing Optical Communication Systems

The disequilibrium of the optical power among different channels is analyzed for the dense wavelength division multiplexing optical communication systems. And the new technologies and devices for optical amplifying, filtering, adding /dropping,etc,have been reviewed, which can be used to equalize dynamically the optical power in optical networks.

Laser shaping and optical power limiting of pulsed Laguerre–Gaussian laser beams of high-order radial modes in fullerene C60

We study the strong nonlinear optical dynamics of nanosecond pulsed Laguerre–Gaussian laser beams of high-order radial modes with zero orbital angular momentum propagating in the fullerene C60molecular medium. It is found that the spatiotemporal profile of the incident pulsed Laguerre–Gaussian laser beam is strongly reshaped during its propagation in the C60molecular medium. The centrosymmetric temporal profile of the incident pulse gradually evolves into a noncentrosymmetric meniscus shape, and the on-axis pulse duration is clearly depressed. Furthermore, the field intensity is distinctly attenuated due to the field-intensity-dependent reverse saturable absorption, and clear optical power limiting behavior is observed for different orders of the input pulsed Laguerre–Gaussian laser beams before the takeover of the saturation effect;the lower the order of the Laguerre–Gaussian beam, the lower the energy transmittance.

Influence of corneal power on circumpapillary retinal nerve fiber layer and optic nerve head measurements by spectral-domain optical coherence tomography

AIM：To evaluate the influence of corneal power on circumpapillary retinal nerve fiber layer（cp RNFL）and optic nerve head（ONH）measurements by spectral-domain optical coherence tomography（SD-OCT）.METHODS：Twenty-five eyes of 25 healthy participants（mean age 23.6±3.6y）were imaged by SD-OCT using horizontal raster scans.Disposable soft contact lenses of different powers（from-11 to＋5 diopters including 0diopter）were worn to induce 2-diopter changes in corneal power.Differences in the cp RNFL and ONH measurements per diopter of change in corneal power were analyzed.RESULTS：As corneal power increased by 1 diopter,total and quadrant cp RNFL thicknesses,except for the nasal sector,decreased by-0.19 to-0.32μm（P〈0.01）.Furthermore,the disc,cup,and rim areas decreased by-0.017,-0.007,and-0.015 mm2,respectively（P〈0.001）;the cup and rim volumes decreased by-0.0013 and-0.006 mm3,respectively（P〈0.01）;and the vertical and horizontal disc diameters decreased by-0.006 and-0.007 mm,respectively（P〈0.001）.CONCLUSION：For more precise OCT imaging,the ocular magnification should be corrected by considering both the axial length and corneal power.However,the effect of corneal power changes on cp RNFL thickness and ONH topography are small when compare with those of the axial length.

Thiophene-fluorene derivatives with high three-photon absorption activities and their application to optical power limiting

The three-photon absorption （3PA） properties of two thiophene-fluorene derivatives （abbreviated as MOTFTBr and ATFTBr） have been determined by using a Q-switched Nd：YAG laser pumped with 38ps pulses at 1064nm in DMF. The measured 3PA cross-sections are 152×10^-78cm^6s^2 and 139× 10^-78cm^6s^2, respectively. The optimized structures were obtained by AM1 calculations and the results indicate that these two molecules show nonplanar structures, and attaching different donors has different effects on the molecular structure. The charge density distributions during the excitation were also systematically studied by using AM1 method. In addition, an obvious optical power limiting effect induced by 3PA has been demonstrated for both derivatives.

Optical fiber-based power and data delivery system for high voltage electronic current transformer

This paper describes a prototype power delivery system developed for high voltage electronic current transformer （ECT） that uses laser light to transfer power to and communicates with the primary converter. The design is based on optical-to-electrical power converters, solid-state diode lasers and optical fibers. Command signals are transmitted via the same up-fiber used to send power from secondary power supply to primary converter. The upward data transmission is completed during the brief interruption of power delivery without affecting steady power-supply. A simple comparator added to the primary converter can take the command data. Experimental results show that the fibers can provide reliable up-link for data transmission at 200 kb/s from the secondary to the primary converter. Based on the delivery system, the secondary converter can control three auxiliary channels to provide additional information. These monitoring channels are used in a time-multiplexing mode to provide information about the operation temperature, voltage and current at the remote unit for monitoring the ECT. This preventive maintenance or built-in test can increase reliability by giving early warning for necessary maintenance request.

Characterization and Optimization of Photonic Crystal Optical Power Limiters

In the work, there have been investigated the optical power limiting effects which occur in the nonlinear photonic crys-tals possessing saturable Kerr nonlinearity. The method is proposed which allows exact determination of the parame-ters of the structure as well as the radiation parameters which provide the limiting effect.

The Effects of Power Control on Free-Space Optical Communications during Snowfall and Rainfall

Free-space optical (FSO) communication requires a line-of-sight connection between a transmitter and a receiver in which the information signal is modulated by an optical carrier that propagates in free space. The FSO channel is greatly affected by weather conditions such as fog, rain, and snow. In the literature, several adaptive techniques, such as power control (PC), have been suggested to mitigate channel link degradations. In this paper, we investigate the effects of snow and rain attenuation on the bit error rate (BER) of the FSO system using two types of modulations, the on-off keying (OOK) modulation and the pulse-position modulation (16-PPM). The effect of PC on the performance of FSO communications is also examined in this study. We evaluated the system’s performance with two types of snow, wet snow and dry snow, as well as with different rain regions. Results show that PC improves the BER of the FSO system;a high rate of improvement is found for wet snow and rain. PC has almost no effect with dry snow because of the high attenuation and the limitations on transmitted power. The BER for 16-PPM is better than that for OOK modulation.

Continuous-wave optical enhancement cavity with 30-kW average power

Optical enhancement cavity(OEC)is a powerful tool for fundamental research and diagnostics.In this paper,the progress of a continuous-wave OEC to realize of megawatt cavity for a novel light source based on a steady-state microbunching(SSMB)mechanism,is reported.After efficiently suppressing all external noise and optimizing the alignment,mode-matching,and polarization matching,stable and long-term locking is achieved with the help of two feedback loops.The modal instability phenomenon caused by the surface thermoelastic deformation is observed.A pair of D-shape mirrors are utilized to remove the high-order modes.Finally,an intra-cavity average power of 30 kW is reached.

Efficient loading of ultracold sodium atoms in an optical dipole trap from a high power fiber laser

We report on a research of the loading of ultracold sodium atoms in an optical dipole trap,generated by two beams from a high power fiber laser.The effects of optical trap light power on atomic number,temperature and phase space density are experimentally investigated.A simple theory is proposed and it is in good accordance with the experimental results of the loaded atomic numbers.In a general estimation,an optimal value for each beam with a power of 9 W from the fiber laser is achieved.Our results provide a further understanding of the loading process of optical dipole trap and laid the foundation for generation of a sodium Bose–Einstein condensation with an optical dipole trap.

Design of MMI 1×8 Optical Power Splitters Used Si-based SiO_2 Waveguide

An initial structure design of MMI 1×8 optical power splitters is reported.The waveguide material is Si-based SiO2 Ge-doped and deposited by PECVD method.Embedded strip structure is implied in the section design.By using BPM-CAD,a favorable result is obtained that this device has a sound uniformity and fairly low loss.Meanwhile,simulations of designs with certain changed parameters is also implemented for a better design configuration.

Multiplexing Technique Applied in the Optically Powered Oil-tank Detection System

The method of using multiplexing technique to realize the optically powered multiple detection system is presented. As this system adopted novel time and pulse width multiplexing techniques, reliable separation and error code correcting techniques, it realizes optically powered multiple channel and parameters detection, and successfully applied in the oil tanks for temperature, pressure, liquid level and reserve measurings.

Review of Optical Character Recognition for Power System Image Based on Artificial Intelligence Algorithm

Optical Character Recognition(OCR)refers to a technology that uses image processing technology and character recognition algorithms to identify characters on an image.This paper is a deep study on the recognition effect of OCR based on Artificial Intelligence(AI)algorithms,in which the different AI algorithms for OCR analysis are classified and reviewed.Firstly,the mechanisms and characteristics of artificial neural network-based OCR are summarized.Secondly,this paper explores machine learning-based OCR,and draws the conclusion that the algorithms available for this form of OCR are still in their infancy,with low generalization and fixed recognition errors,albeit with better recognition effect and higher recognition accuracy.Finally,this paper explores several of the latest algorithms such as deep learning and pattern recognition algorithms.This paper concludes that OCR requires algorithms with higher recognition accuracy.

Compact and Economical MMI Optical Power Splitter for Optical Communication

A 1×8 GaAs/GaAlAs optical power splitter based on a MultiMode Interference (MMI) coupler is presented. The input and output single mode waveguides are optimized by the Discrete Spectral Index Method (DSIM) and a moderate square spot on the output in deep etched rib waveguides is obtained. The fabrication tolerance has been analyzed by the Finite Difference Beam Propagation Method (FDBPM). The device was fabricated by the dry etching technique and the near field output obtained. The device shows polarization insensitive, large fabrication tolerance, low theoretical excess loss and low power imbalance.