Compact magneto-optical traps using planar optics

Magneto-optical traps (MOTs) composed of magnetic fields and light fields have been widely utilized to cool andconfine microscopic particles. Practical technology applications require miniaturized MOTs. The advancement of planaroptics has promoted the development of compact MOTs. In this article, we review the development of compact MOTs basedon planar optics. First, we introduce the standardMOTs. We then introduce the gratingMOTs with micron structures, whichhave been used to build cold atomic clocks, cold atomic interferometers, and ultra-cold sources. Further, we introducethe integrated MOTs based on nano-scale metasurfaces. These new compact MOTs greatly reduce volume and powerconsumption, and provide new opportunities for fundamental research and practical applications.

Encrypted optical fiber tag based on encoded fiber Bragg grating array

Optical fibers are typically used in telecommunications services for data transmission,where the use of fiber tags is essential to distinguish between the different transmission fibers or channels and thus ensure the working functionality of the communication system.Traditional physical entity marking methods for fiber labeling are bulky,easily confused,and,most importantly,the label information can be accessed easily by all potential users.This work proposes an encrypted optical fiber tag based on an encoded fiber Bragg grating(FBG)array that is fabricated using a point-by-point femtosecond laser pulse chain inscription method.Gratings with different resonant wavelengths and reflectivities are realized by adjusting the grating period and the refractive index modulations.It is demonstrated that a binary data sequence carried by a fiber tag can be inscribed into the fiber core in the form of an FBG array,and the tag data can be encrypted through appropriate design of the spatial distributions of the FBGs with various reflection wavelengths and reflectivities.The proposed fiber tag technology can be used for applications in port identification,encrypted data storage,and transmission in fiber networks.

Hollow and filled fiber bragg gratings in nano-bore optical fibers

To combine the technical functions and advantages of solid-core fiber Bragg gratings(FBGs) and hollow-core optical fibers(HCFs), the hollow and filled FBGs in nano-bore optical fibers(NBFs) with nano-bore in the GeO2-doped core are proposed.The fundamental mode field, effective mode index, and confinement loss of NBF with 50 nm–7 μm-diameter hollow and filled nano-bore are numerically investigated by the finite element method.The reflected spectra of FBGs in NBFs are obtained by the transmission matrix method.The hollow FBGs in NBFs can be acheived with ~5% power fraction in the bore and the ~0.9 reflectivity when bore diameter is less than 3 μm.The filled FBGs can be realized with^1% power fraction and 0.98 reflectivity with different fillings including o-xylene, trichloroethylene, and chloroform for 800-nm bore diameter.The feasibility of the index sensing by our proposed NBF FBG is also analyzed and discussed.The experimental fabrication of hollow and filled FBGs are discussed and can be achieved by current techniques.The aim of this work is to establish a principle prototype for investigating the HCFs and solid-core FBGs-based fiber-optic platforms,which are useful for applications such as the simultaneous chemical and physical sensing at the same position.

Convention of Optical Vortices in Two-Helix Long-Period Fiber Gratings

An effective method to fabricate two-helix long-period fiber gratings （TH-LFGs） is presented. Based on the coupling mode theory, the conversion of optical vortices （OVs） in TH-LFGs are analyzed in detail. The conversions of OVs with different topological charges： 0 → ±2 and 1 → 3 are simulated as three examples and the conversion efficiency higher than 98% can be realized.

Optical Switching and Digital Signal Amplification Using an Optical Fiber Grating OBD

It is proposed that an optical fiber grating bistability device may be used for an all optical switching or an all optical digital signal amplifier with low power and high speed. The principle, characteristic and paremeter are analysed, and some design ideas are given.

Optical Fiber Grating Bistability

It is proposed that a segment of Er doped fiber with a couple of fiber gratings on the ends may be used as a novel optical bistability device with low power and high speed. Operation and bistability threshold of device are analysed in accordance with the distributed feedback couple mode theory and the nonlinear characteristic of Er doped fiber. It is shown that a nanoseconds microwatts bistable operation of a centimeter device is realizable under nowaday technological condition.

Characteristics of Smart Concrete with Fiber Optical Bragg Grating Sensor

Based on the advantages of the fiber Bragg grating sensing technology,this paper presents a principle of a novel smart concrete with fiber optical Bragg grating sensor,analyses the theory and characteristics,illustrates the key technology and method to make the fiber Bragg grating sensor for the smart concrete,and proves the feasibility with experiments.The results indicate that the smart concrete with fiber Bragg grating sensors is feasible in the structure monitoring and damage diagnosing in the long run.

A simulation program for analysing fiber optic Bragg gratings

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Optical fiber Bragg grating sensors in smart structures

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The Application of Optical CDMA-Based Fiber Radio Networks in Wireless Sensor Networks

One fiber radio scheme using shifted prime codes for interference elimination is proposed for optical code-division multiple-access (OCDMA) network. By taking advantage of the cyclic property of the shifted prime codes in the same code groups, the proposed compact decoder is low cost and suitable to be used in the task manager node in the applications of wireless sensor networks. The performance comparison for sev-eral OCDMA-based fiber radio networks is also given to clarify the advantage of the proposed one.

Magneto-Optic Fiber Bragg Gratings with Application to High-Resolution Magnetic Field Sensors

Magneto-optic fiber Bragg gratings （MFBG） based on magneto-optic materials have a lot of potential applications for sensing and optical signal processing. The transmission and reflection spectra of guided optical waves in the MFBG are investigated. According to the sensitivity of MFBG spectral lines to the magneto-optic coupling intensity varying with applied magnetic field, a novel magnetic field sensor of high-resolution up to 0.01 nm/（kA/m） is predicted.

NOVEL FIBER GRATING SENSOR DEMODULATION TECHNIQUE BASED ON OPTICAL WAVELET FILTERING

The optical wavelet filter is designed. It can filter and choose frequency swiftly. It can realize demodulation of distributed fiber Bragg grating（FBG） measurement system. Its scanning resolution and scanning period depend on wavelet function. Wavelet function is controlled by computer. Compared to conventional scan filter, optical wavelet filtering has some advantages such as simple structure, high scan frequency, high resolution and good linearity. At last, the error of optical wavelet filter scanning procedure is analyzed. Scanning step length refers to the shifting of optical wavelet window＇s central frequency. It affects system precision directly. If scanning step length is different, the measured signal is different. The methods of reducing step length guarantee scanning periodic time are presented.

Extraordinary Optical Confinement in a Silicon Slot Waveguide with Metallic Gratings

We present a silicon slot waveguide with metallic gratings embedded on the silicon surface in the slot region. The dependence of the optical coupling between two silicon wires on the width of the metal gap and the slot size are studied in detail. The results show that the optical field in the slot region with metallic gratings is significantly enhanced compared with the traditional slot waveguide due to the surface plasmon polaritons coupling on metallic gratings. The extraordinary optical confinement is attributed to the low effective dielectric constant of metallic gratings. The effective dielectric constant decreases with the increasing wavelength, and reaches the minimum when the width of the metal gap is about 0.01 times the wavelength.

Surface Plasmon Resonance Sensors Based on Polymer Optical Fiber

Surface Plasmon Resonance （SPR） is a powerful technique for directly sensing in biological studies, chemical detection and environmental pollution monitoring. In this paper, we present polymer optical fiber application in SPR sensors, including wavelength interrogation surface enhanced Raman scattering SPR sensor and surface enhanced Raman scattering （SERS） probe. Long-period fiber gratings are fabricated on single mode polymer optical fiber （POF） with 120 μm period and 50% duty cycle. The polarization characteristic of this kind of birefringent grating is studied. Theoretical analysis shows it will be advantageous in SPR sensing applications.

Code synchronization based on lumped time-delay compensation scheme with a linearly chirped fiber Bragg grating in all-optical analog-to-digital conversion

We propose a novel lumped time-delay compensation scheme for all-optical analog-to-digital conversion based on soliton self-frequency shift and optical interconnection techniques. A linearly chirped fiber Bragg grating is optimally designed and used to compensate for the entire time-delays of the quantized pulses precisely. Simulation results show that the compensated coding pulses are well synchronized with a time difference less than 3.3 ps, which can support a maximum sampling rate of 151.52 GSa/s. The proposed scheme can efficiently reduce the structure complexity and cost of all-optical analog-to-digital conversion compared to the previous schemes with multiple optical time-delay lines.

FIBER OPTIC TEMPERATURE MEASURING SYSTEM

This paper presents a fiber optic temperature measuring system used for measuring the temperature in many occasions. The system is of reflective type and composed of thermostatic bimetal plate, lever piston framework, optical grating and optical fiber probes. When the temperature changes, the thermostatic bimetal plate deforms. Through lever piston framework, the optical grating produces displacement in the upright direction. Thus the change of the temperature is transformed into the upright displacement of the optical grating. Optical fiber probes are used for detecting the number of streak lines of the optical grating′s displacement depending on the change of temperature. The detected signal can be transmitted to the control center through optical fiber cable up to distance of 1 km. The measurable range of this system reaches 100℃ with accuracy of ±0.2℃.

Towards a fast and stable tachypnea monitor:a C_(60)-Lys enabled optical fiber sensor for humidity tracking in breath progress

The pandemic of respiratory diseases enlightened people that monitoring respiration has promising prospects in averting many fatalities by tracking the development of diseases.However,the response speed of current optical fiber sensors is still insufficient to meet the requirements of high-frequency respiratory detection during respiratory failure.Here,a scheme for a fast and stable tachypnea monitor is proposed utilizing a water-soluble C_(60)-Lys ion compound as functional material for the tracking of humidity change in the progression of breath.The polarization of C_(60)-Lys can be tuned by the ambient relative humidity change,and an apparent refractive index alteration can be detected due to the small size effect.In our experiments,C_(60)-Lys is conformally and uniformly deposited on the surface of a tilted fiber Bragg grating(TFBG)to fabricate an ultra-fast-response,high-sensitivity,and long-term stable optical fiber humidity sensor.A relative humidity(RH)detecting sensitivity of 0.080 dB/%RH and the equilibrium response time and recovery time of 1.85 s and 1.58 s are observed,respectively.Also,a linear relation is detected between the resonance intensity of the TFBG and the environment RH.In a practical breath monitoring experiment,the instantaneous response time and recovery time are measured as 40 ms and 41 ms,respectively,during a 1.5 Hz fast breath process.Furthermore,an excellent time stability and high repeatability are exhibited in experiments conducted over a range of 7 days.

Simulation Tools for a Fiber-Optic Based Structural Health Monitoring System

Probability of detection(POD)graphics allow for a change from qualitative to quantitative assessment for every damage detection system,and as such it is a main request for conventional non-destructive testing(NDT)techniques.Its availability can greatly help towards the industrialization of the corresponding Structural health monitoring(SHM)system.But having in mind that for SHM systems the sensors are at fixed positions,and the location of a potential damage would change its detectability.Consequently robust simulation tools are required to obtain the model assisted probability of detection(MAPOD)which is needed to validate the SHM system.This tool may also help for the optimization of the sensor distribution,and finally will allow a probabilistic risk management.INDEUS,simulation of ultrasonic waves SHM system,was a main milestone in this direction.This article deals with the simulation tools for a strain based SHM system,using fiber optic sensors(FOS).FOS are essentially strain/temperature sensors,either with multi-point or with distributed sensing.The simulation tool includes the finite element model(FEM)for the original and damaged structure,and algorithms to compare the strain data at the pre-established sensors locations,and from this comparison to extract information about damage occurrence and location.The study has been applied to the structure of an all-composite unmanned aircraft vehicle(UAV)now under construction,designed at Universidad Politecnica de Madrid for the inspection of electrical utilities networks.Distributed sensing optical fibers were internally bonded at the fuselage and wing.Routine inspection is planned to be done with the aircraft at the test bench by imposing known loads.From the acquired strain data,damage occurrence may be calculated as slight deviations from the baselines.This is a fast inspection procedure without requiring trained specialists,and it would allow for detection of hidden damages.Simulation indicates that stringer partial debondings are detected before they become critical,while small delaminations as those produced by barely visible impact damages would require a prohibited number of sensing lines.These simulation tools may easily be applied to any other complex structure,just by changing the FEM models.From these results it is shown how a fiber optic based SHM system may be used as a reliable damage detection procedure.

Controllable optical multi-well trap and its optical lattices using compounded cosine patterns

This paper proposes a flexible scheme to form various optical multi-well traps for cold atoms or molecules by using a simple optical system composed of an compounded amplitude cosine-only grating and a single lens illuminated by a plane light wave or a Gaussian beam. Dynamic manipulation and evolution of multi-well trap can be easily implemented by controlling the modulation frequency of the cosine patterns. It also discusses how to expand this multi-well trap to two-dimensional lattices with single- or multi-well trap by using an orthogonally or non-orthogonally modulated grating, as well as using incoherent multi-beam illumination, and these results show that all the symmetric structures of two-dimensional Bravais lattices can be obtained facilely by using proposed scheme.

Engineering approach to in-situ bridge health monitoring with fiber bragg gratings

In this presentation the feasibility and capability of fiber Bragg gratings （FBG） employed in bridge health monitoring are demonstrated on a real bridge. FBG＇ s wavelength shift depending on strain variance has been tested. The technique of FBG installation on bridges has been developed. 12 FBG strain sensors and 3 temperature sensors have been successfully embedded in the prestressed concrete box girder during the construction of Heilongjiang Hulan River Bridge. The prestressing tension process and quasi-static loading process of the girder were monitored with those sensors before it was installed onto the bridge. After the bridge was completed, the FBG sensors embedded have been utilized to monitor the strain shift of the beam under quasi-static load, traffic load and temperature. The results show that the traffic fluxes, possible tatigue damage and deflection of the bridge can be revealed conveniently through strain measurements with these FBG sensors, which provide key information for structural health diagnosis. The fact that the FBG strain sensors have withstood the ordeal of harsh construction process and lasted for more than one year proves that their durability and stability can satisfy the requirements for bridge health monitoring. It is also shown that the FBG strain sensor is more adaptive to long-term structural health monitoring than the electric resistance strain gauge.