Center Wavelength Shift Research Articles

Enhanced Interferometric Weak Value Amplification With Multiple Reflection

A multiple-reflection scheme was proposed to improve the sensitivity and resolution of interferometric weak measurement by introducing a cuboid prism device in the optical path. Increasing the number of reflection in a total internal reflection weak value amplification (WVA) system resulted in a 3.8 fold improvement in the sensitivity of the central wavelength shift to refractive index unit (RIU) (from 1788 nm/RIU to 6821 nm/RIU). Using the multiple reflection device, a RIU resolution of $2.7\times 10$ -7 RIU was obtained. The real-time deposition process of dopamine is monitored.

Reconfigurable thin film filter for compensating AOI deviation effects using LC coupled cavities

An efficient technique to enhance thin-film filters’ angular tolerance is described and numerically demonstrated. The spacer refractive index is controlled using a liquid crystal (LC) in the multi-cavity thin-film filter. The angle of incident (AOI) deviation causes significant degradation in the filter performance. To circumvent the influence of the AOI deviation, a correction effect is introduced through controlling the LC refractive index, while maintaining the normal incident performance of the filter. The proposed LC-based approach has proven effective in increasing the angular tolerance of the thin-film filter. Simulation results indicate an angle-insensitive performance under a 20o incident angle cone deviation. The results illustrate the effectiveness of this approach over the C-band, where the change in the center wavelength shift was reduced from 107.57 nm to 0.38 nm. Moreover, the change in the transmission filter bandwidth was reduced by 70%. The proposed compensation approach offers flexibility in the central wavelength and in the filter bandwidth estimated at the 0.5 dB, 3 dB, and 25 dB passband ranges.

A Random-displacement Measurement by Combining a Magnetic Scale and Two Fiber Bragg Gratings.

Long-distance displacement measurements using optical fibers have always been a challenge in both basic research and industrial production. We developed and characterized a temperature-independent fiber Bragg grating (FBG)-based random-displacement sensor that adopts a magnetic scale as a novel transferring mechanism. By detecting shifts of two FBG center wavelengths, a full-range measurement can be obtained with a magnetic scale. For identification of the clockwise and counterclockwise rotation direction of the motor (in fact, the direction of movement of the object to be tested), there is a sinusoidal relationship between the displacement and the center wavelength shift of the FBG; as the anticlockwise rotation alternates, the center wavelength shift of the second FBG detector shows a leading phase difference of around 90° (+90°). As the clockwise rotation alternates, the center wavelength shift of the second FBG displays a lagging phase difference of around 90° (-90°). At the same time, the two FBG-based sensors are temperature independent. If there is some need for a remote monitor without any electromagnetic interference, this striking approach makes them a useful tool for determining the random displacement. This methodology is appropriate for industrial production. As the structure of the whole system is relatively simple, this displacement sensor can be used in commercial production. In addition to it being a displacement sensor, it can be used to measure other parameters, such as velocity and acceleration.

FBG wavelength demodulation based on bandwidth of radio frequency signals

A FBG sensor real-time demodulation system based on radio frequency signals’ bandwidth monitoring is proposed. To the best of authors’ knowledge, this is the first FBG sensor demodulated by using radio frequency signals’ bandwidth. Beat frequency signals (BFS) are generated by multi-longitudinal mode laser in a laser cavity which is made of a sensing FBG, a static FBG and a piece of fiber. The sensing FBG’s center wavelength shift is in proportion to a bandwidth change of BFS. The demodulation system has a high sensitivity of 50.0 MHz/με. Measurement results demonstrated the system’s high accuracy, sensitivity and stability.

A Bio-molecular Sensor Based on Optical Weak Measurement

We developed a phase-sensitive sensor based on the optical weak measurement for label-free detection of biomolecular interaction. The weak value amplification system can be implemented in common-path with total internal reflection structure. The phase difference between p and s polarizations caused by biomolecular recognition is measured by the central wavelength shift of the frequency domain weak measurement system. Structure of p and s polarizations in common-path makes system robust and stable. The applicability is illustrated by real-time monitoring interaction of biomolecules.

Brightness improvement in a graphene inserted GaN/ZnO heterojunction light emitting diode

Heat dissipation is a crucial issue for heterojunction light emitting diodes (LEDs) because the requirement of high brightness necessitates higher current densities that would trigger more joule heating. We demonstrate that the embedded graphene in a ZnO/MgO/GaN LED alleviates self-heating issues by virtue of its heat-spreading ability and improves the brightness of the device. The effect of graphene was studied by optical characteristics, energy band structure and thermal field simulation of the devices. The optimized device acts as an LED with ultraviolet emission at 397.4 nm. Compared with the one without graphene, a 6.2-fold improvement in intensity and a 16.8 nm blue shift in central wavelength were obtained. The graphene induced heat sinking on the junction area was proposed to explain this optical improvement. Followed by thermal simulation, the joule heat related photoluminescence suppression of individual ZnO microrods further proves the mechanism.

Simultaneous measurement of refractive index and temperature with high sensitivity based on a multipath fiber Mach-Zehnder interferometer.

We present and experimentally demonstrate a highly sensitive sensor for simultaneously measuring the refractive index (RI) and temperature based on a multipath fiber Mach-Zehnder interferometer. The sensor is fabricated by sandwiching a segment of weak-coupling seven-core fiber (SCF) with two short multimode fibers, and then splicing it with lead-in and lead-out single-mode fibers, respectively. Six outer cores of the SCF are half-etched chemically for enhancing the interaction between light and matter. A high-quality transmission spectrum with 23dB fringe visibility is obtained. Due to the strong interaction between the outer core modes and cladding modes with the surrounding medium, the proposed fiber structure exhibits not only an extremely high RI sensitivity of -1802.26 nm/RI unit from 1.427 to 1.442, but also a superior temperature sensitivity of 82pm/°C from 10°C to 90°C. Moreover, RI and temperature can be discriminated simultaneously by measuring the central wavelength shifts of two transmission notches. This sensor has outstanding advantages of high sensitivity, easy fabrication, simple structure, and low cost, and may find applications in multiparameter highly sensitive sensing.

Influences of Physical Processes and Parameters on Simulations of TOA Radiance at UV Wavelengths: Implications for Satellite UV Instrument Validation

Numerous factors can influence the radiative transfer simulation of hyper-spectral ultraviolet satellite observation, including the radiative transfer scheme, gaseous absorption coefficients, Rayleigh scattering scheme, surface reflectance, aerosol scattering, band center wavelength shifts of sensor, and accuracy of input profiles. In this study, a Unified Linearized Vector Radiative Transfer Model (UNL-VRTM) is used to understand the influences of various factors on the top of atmosphere (TOA) normalized radiance in the ultraviolet (UV) region. A benchmark test for Rayleigh scattering is first performed to verify the UNL-VRTM accuracy, showing that the model performances agree well with earlier peer-reviewed results. Sensitivity experiments show that a scalar radiative transfer approximation considering only ozone and a constant surface reflectance within the UV region may cause significant errors to the TOA normalized radiance. A comparison of the Ozone Mapping and Profiler Suite (OMPS) radiances between simulations and observations shows that the surface reflectance strongly influences the accuracy for the wavelengths larger than 340 nm. Thus, using the surface reflectivity at 331 nm as a proxy for simulating the whole OMPS hyperspectral ultraviolet radiances is problematic. The impact of rotational Raman scattering on TOA radiance can be simulated through using SCIATRAN, which can also reduce the difference between measurements and simulations to some extent. Overall, the differences between OMPS simulations and observations can be less than 3% for the entire wavelengths. The bias is nearly constant across the cross-track direction.

Label-free and Non-destruction Determination of Single- and Double-Strand DNA based on Quantum Weak Measurement

The process of unwinding and renaturation of DNA has been widely used in studies of nucleotide sequence organization. Compared with traditional methods for DNA unwinding and renaturation, the label-free and non-destruction detection technology is significant and desiderated. We realized an optical system based on optical rotation via weak measurement for detection of single- and double-strand state of DNA. The optical rotation, which was induced by the status change of single and double DNA strands, was exploited to modulate the preselected polarization of a weak measurement system. With this modulation, the optical rotation caused by the separation of DNA strands can be determined through the center wavelength shift of the output spectrum. By monitoring the wavelength shift in real time, the separation processes of the DNAs with different base ratio (25% and 70%) and length (4nt and 40nt), and DNAs with three terminally modified cholesterol molecules were experimentally explored in varied pH and temperature conditions. In addition, the detection limit of the DNA concentration was obtained to be 5 × 10−6 mol/L. Our work based on optical rotation detection of single- and double-strand DNA exhibits the unique advantages of real-time monitoring, label-free, non-destruction and simplicity.

Shape monitoring of morphing wing using micro optical sensors with different embedded depth

Abstract Considering the complex and variability of flight environment of the morphing aircraft, usually it is difficult to solve the real-time wing shape monitoring problem when the aircraft changes its motion state or suffering the wind and waves. In this paper, with the goal of supporting real-time wing shape monitoring of morphing aircraft, three-dimensional (3D) shape monitoring of polyimide film skin for morphing wing based on the embedded Fiber Bragg Grating (FBG) sensor is designed and analyzed. Firstly, the sensitively of FBG sensors with different embedded depth in the polyimide film was analyzed, and the finding is that when the ratio value of upper/lower embedded depth is larger, the sensitively of FBG sensor is higher. Secondly, the wavelength of FBG sensors at different states were obtained, and the center wavelength shift of FBG sensors can be used to measure the bending curvatures of the wing, besides, according to the obtained bending curvatures, the 3D shape of polyimide skin of the morphing wing at different deformation states are reconstructed through interpolation and curve fitting functions. Moreover, several shape reconstruction experiments of the morphing wing were carried out with precise visual measurement, and the maximum error between FBG sensing and visual measurement is 5%. Consequently, the effectiveness of FBG sensing method for wing shape monitoring of morphing aircraft is demonstrated, as well as more potentiality and applicability for the shape monitoring in the field of soft robotics and flexible biosensor monitoring.

A Stable Wavelength Operation Ho:YAG Laser with Orthogonally Polarized Pump**Supported by the Cooperation Foundation of Changchun Science and Technology Bureau under Grant No 17DY027, the Foundation of Education Department of Jilin Province under Grant No JJKH20181105KJ, and the Foundation of Jilin Province Science and Technology Department under Grant No 20180101033JC.

A stable wavelength operation Ho:YAG laser dual-pumped by two orthogonally polarized Tm:YLF lasers is reported. Under the cw operation mode, a laser output power of 24 W is measured. The corresponding optical-optical conversion efficiency is 44.75% and the slope efficiency is 50.12%. Under the Q-switched operation mode, the output maximum average power is 22.8 W at the re-frequency of 6 kHz. The corresponding optical-optical conversion efficiency and slope efficiency are 42.64% and 48.01%, respectively. The output central wavelength is 2090.73 nm, the linewidth is 0.40 nm, and the beam quality is . Moreover, the shift of the output central wavelength is less than 0.01 nm, and the linewidth shift is also less than 0.01 nm.

Temperature and stress sensing characteristics of symmetrically fused tapered fiber grating

The stress-sensitive and temperature-insensitive characteristics of the tapered fiber grating can be used effectively to suppress the cross-sensitive problem of temperature and stress. In this paper, a fiber grating with a symmetric double-cone shape is proposed, which is made by using a fused taper technology. The theoretical model of sensing characteristics is established and analyzed by the transfer matrix method. Firstly, the factors affecting the change of radon coefficient are studied, and the relationship between the radon coefficient and the amount of grate length change is obtained, and then the spectral characteristics of the symmetric fused-tapered fiber grating are analyzed to discuss the origin of dense modulation at the short wavelength of the spectrum. The effects of temperature and stress on the reflection spectrum of symmetrically fused-tapered fiber grating are studied, and the relationship between the corresponding center wavelength and spectral bandwidth is obtained. In order to solve the problem of low stress sensitivity of the fiber grating, a scheme is presented that the radius difference of the optical fiber in the sensing cone region is enhanced by using polymer to coat the tapered area. Finally, a fused taper technology is used to prepare the symmetrically molten fiber grating, and verify the correctness of theoretical simulation in experiment, indicating that its stress sensitivity is 0.11391 nm/N. Firstly, the ripple coefficient of the symmetrically fused-tapered fiber grating is linearly related to the amount of change in the length of the grating. Secondly, because the grating cycle is small at the end of the symmetrically melt-pull-cone fiber-optic grating, and the reflectivity is less than 1, the left-hand transmission light and the right-hand reflected light will produce interference, so the spectral short wavelength will present dense modulation phenomenon. Thirdly, the center wavelength shifts to long wavelength region and the reflection bandwidth is broadened as stress is raised, and the center wavelength and reflection bandwidth are both linearly changed with the applied stress. Finally, the center wavelength shifts to long wavelength region as the temperature rises gradually, and the effect on the spectral bandwidth can be ignored. The stress sensitivity of the fiber grating increases hundreds of times by increasing the difference in fiber optic grating radius in the sensing tapered area, and the stress sensitivity can be further improved by increasing the fused taper variation of the grating. The spectral bandwidth of the symmetrical fused tapered fiber grating is only sensitive to stress but not to temperature. The characteristics can be used to realize the double-parameter measurement of temperature and stress.

On crack propagation monitoring by using reflection spectra of AFBG and UFBG sensors

Due to their light weight, small size and immunity to electromagnetic interference, Fiber Bragg Gratings (FBG) have shown great potential in structural health monitoring (SHM) area. Ordinarily, FBGs are used as the quasi-distributed sensors to detect structural damage by central wavelengths shifting, which has robust problem in real engineering application. It is found that the FBG reflection spectra can also be distorted with the non-uniform strain field caused by crack. Multiple indices can be extracted from the reflection spectra which can provides more information on the crack propagation. However, till now no researches have been investigated regarding the behaviors of different kinds of FBGs for crack propagation monitoring based on the FBG reflection spectra. In this paper, behaviors of the apodized FBG (AFBG) and the uniform FBG (UFBG) sensors for structural crack propagation monitoring are investigated. The reflective spectral behaviors of both UFBG and AFBG sensors under crack-generated non-uniform strain are illustrated by simulation and experiment. Three spectra indices, namely the central wavelength shift, the ratio of side lobe to main lobe and the information entropy, are proposed to indicate the propagation of the crack. The results show the UFBG sensors have better performance than the AFBG sensors which are more suitable for crack propagation monitoring.

Rapid Separation of Enantiomeric Impurities in Chiral Molecules by a Self-Referential Weak Measurement System.

We propose a self-referential fast detection scheme for a frequency domain weak measurement system for the detection of enantiomeric impurities in chiral molecules. In a transmissive weak measurement system, the optical rotation (OR) is used to modify the pre-selected polarization state and the post-selection polarization state. We obtained the sum and difference of the optical rotations produced by the sample and the standard by rotating the quarter wave plate in the system. Then, we estimate the ratio of chiral molecules to enantiomeric impurities using the ratio of the central wavelength shifts caused by the addition and subtraction states described above. In this paper, our system has an optical resolution of 1.88 × 10−5°. At the same time, we completed the detection of the ratio of the two substances in the mixture of L-proline and D-proline in different proportions, which proved that our system can quickly detect the content of enantiomeric impurities in chiral molecules.

Design a bridge scour monitoring system by pressing the fiber Bragg grating with a rolling pulley mechanism

In this paper, we design an optical fiber sensor based on fiber Bragg grating (FBG) for real-time bridge scour monitoring. The sensing element of the FBG is embedded in the silicone rubber, and the two ends of the rubber are fixed on the metal plate. The pulley has a circumference of 0.2 m and will drive the threaded screw, has a pitch of 1 mm, forward to press the rubber. When the rubber is pressed by the threaded screw, we can measure the reflection central wavelength shift from FBG sensor to obtain the scour depth. Bridge scour is one of the main causes of bridge failures that is resulted by the interaction of flood water and soil-structure at the bottom of the river. Monitoring scour is very important to ensure the continued safe operation of the bridge traffic and the passing through person’s life and property. A prototype of temperature-insensitive scour sensing system was designed and fabricated to test its sensing characteristics in the laboratory. The design criterion of scour sensor is to achieve the highest sensing pier scour depth of ≥ 4 m. The robust experimental results prove that the proposed system will ensure the effectiveness and feasibility in the field.

Integrated athermal arrayed-waveguide grating multiplexer and demultiplexer with all-metal compensating rod for broadband temperature application.

In this paper, a unique device that can act as both multiplexer and demultiplexer is proposed with two all-metal compensating rods that makes the compensated chip almost the same spectrum profile as the original one. In this way a flat-top athermal arrayed-waveguide grating module of 100-GHz×40-ch is successfully fabricated. A small center wavelength shift of ±25 pm is achieved for the ultra-wide temperature range from -40°C to 85°C with the low insertion loss change of less than ±0.14 dB.

Characterizing the effect of femtosecond photo-treatment on the center wavelength of fiber Bragg gratings.

Various types of pre- and post-treatments to optical fibers are typically used to improve and/or change the properties of fiber Bragg grating (FBG). Here, we investigate experimentally the effects of NIR femtosecond (fs) laser pulses used for pre- and post-treatment on the refractive index of the fiber, and the resulting center wavelength shift of an fs inscribed FBG. We observe "red"-shift when applying a suitable pre-treatment, and both "blue"- and "red"-shifts when applying post-treatment. We characterize the photo-treatment parameters and compare to an FBG inscribed on a fresh fiber without any treatment. We also show that when the photo-treatment is saturated the result is a phase-shifted grating. Our results give further insight into the process of fs photo-treatments and quantify the effects in the case of fs FBG inscription.

Optical rotation based chirality detection of enantiomers via weak measurement in frequency domain

A transmission optical rotation detection scheme based on a weak measurement was proposed for the chirality detection of enantiomers. In this transmission weak measurement system in the frequency domain, the optical activity of the chiral liquid sample was estimated with the central wavelength shift, by modifying the preselected polarization state with the optical rotation (OR). The central wavelength shift of output spectra is sensitive to the OR angle but immune to the interference of the refractive index change caused by measuring circumstances. Two isomers of chiral amino acid acquired opposite responses with this system, and a resolution of 2.17 × 10−9 mol/ml for Proline detection could be obtained. Such a resolution is about 2 orders of magnitude higher than that of common methods, which shows a high sensitivity. This proposed weak measurement scenario suggested an approach to polarimetry and provided a way to accurately assess molecular chirality.

Determination of Tumor Marker Carcinoembryonic Antigen with Biosensor Based on Optical Quantum Weak Measurements.

A phase-sensitive weak measurement biosensor was proposed for the detection of carcinoembryonic antigen (CEA), one common category of tumor markers. The total internal reflection (TIR) at the interface of the prism without precious metal coating was exploited to introduce the phase delay between horizontal and vertical polarizations, which can be determined through the central wavelength shift of output spectra for the sensing of the refractive index of the sample. In the weak measurement analysis, the specific binding reaction of tumor markers with a refractive index change on the surface of the prism can be monitored in real time through the central wavelength shift. With the specific absorption measurement, the feasibility of this weak measurement-based biosensor was experimentally demonstrated. We provide a low cost and convenient approach for tumor marker detection.

Smart Photonic Carbon Brush: FBG Length as Sensing Parameter

This article deals with problem of carbon brush’s length measurements. There are many applications where regular inspection is not feasible because of a number of factors including, for example, time, labor, cost and disruptions due to down time. Thus, there is a need for a system that can monitor the brush’s length to calculate it’s wear rate, while the component is in operation or without removing of the component from its operational position. We propose a novel method for characterization of carbon brush’s length. This method based on the usage of advantages of the multiplicative response of FBGs and FBG arrays: spectral parameters depend on several aspects, such as grating’s period, refractive index, it’s physical length and so on. We are the first, in our point of view, who proposed to use third parameter for sensing application and prospectively all three parameters for complex measurement: the change of FBG’s length is used to measure length of the brush and it’s wear rate, grating’s central wavelength shift for temperature (due to refractive index change) and mechanical stress (due to grating’s period variations) measurements. The results of modelling and experiments are presented.