It is an important way to effectively improve applied optics experimental teaching effect and motivate the undergraduates’ practice ability and creativity by means of scientific and systematic setting teaching contents and link. Based on the research and analysis of applied optics experiment teaching present condition at home and abroad, this paper aims to solve the existed problems and deficiencies during the experiment teaching in our university, and also puts forward some reform ideas and practice method from several aspects such as teaching thought, teaching content and mode, examination and evaluation and so on. Simultaneously, this paper also gives some suggestions on the future course development.
The need of understanding and teaching about wave-particle duality if light with gets more and more apparent in the background of the attention of modern physics. As early as the beginning of twentieth Century, Einstein dared to "deny" the development of a very perfect light electromagnetic theory, so that the quantum of light can be developed. In 1924, De Broglie put forward wave-particle duality if light to other micro particles and the concept of matter wave, pointed out that all micro particle has wave-particle duality. This is a very abstract concept for students, most college physics teaching all lack of demonstration about particle duality of light. The present article aims to contribute to demonstrate the wave-particle duality of light at the same time using a simple way based on fiber optical tweezers. It is hoped that useful lesson can be absorbed so that students can deepen the understanding of the particle and wave properties of light. To complement the demonstration experiment for this attribute light has momentum.
FBG inscribed on splice joint is proposed to be used as a sensor. It could realize temperature and strain measurement simultaneously because of the different strain responses of the different parts of the FBG inscribed on splice joint, while the temperature responses are same. The strain responses of four overlap values are discussed, which is used to optimize the discrimination capability of the strain and temperature response of the FBG device.
We propose a novel dual-channel Surface Plasmon Resonance (SPR) fiber sensors based on the incident angle adjusting method. By grinding fiber tip to form wedge-shape with different angles, we can easier adjust the incident angle in fiber, and then the SPR wavebands will change corresponding. The simulation and experiment demonstrate that the SPR wavebands will red-shift with increasing of the fiber grinding angle. Based on this, we cascade two fiber tips whose grinding angles are 5° and 15° respectively. Under the tests of the refractive index (RI) range from 1.333 to 1.385, the SPR wavebands are 576~683nm and 677~955nm respectively. Therefore, we can demodulate SPR signal by wavelength division multiplexing (WDM) technology. Sequentially, we can detect two analytes simultaneously. This dual-channel SPR fiber sensor has important significance in the fields of multichannel liquid refractive indices and temperature selfreference measurements.
We propose a novel single fiber optical tweezers based on a graded-index multimode fiber (GIMMF), whose length is arbitrary (when the length is larger than 5mm). The optical fiber tweezers based on GIMMFs can propagate larger light field intensity and trap particles easily. The optical fiber tweezers based on precise length GIMMF had been achieved. In this paper, the optical fiber tweezers applies the GIMMF with arbitrary length, which ensure the fabrication of the optical tweezers based on the GIMMF simple, convenient and repeatability.
In this paper, the fabrication of a novel refractive index sensor based on helical long period grating (HLPG) written in a dual-hole elliptical core fiber (DHECF) was demonstrated and the sensing characteristic was experimentally investigated. Due to the structure of the DHECF, The proposed HLPG sensor could work with ultra-small dose testing samples. In addition, since the sample is isolated from the external environment, the testing is immunity to the external interference. The experimental results showed that the testing sensitivity of the sensor was 194nm/RIU with the refractive index range of 1.333 to 1.385. The proposed structure will have a good practicability in the microfluidic sensing system.
We propose a novel method to gather or arrange multiple micro particles by using the thermal convection effect in the water. We fabricate the fiber tip to be a nonadiabatic-tapered shape and then plate a gold film on the fiber tip. The gold film coated on the fiber tip absorbs the light output from the fiber and then generate lots of heat in the water, which causes the thermal convection. The convection forces bring the micro particles moving towards the fiber tip where the temperature is much higher. By using this thermal convection effect, we can realize the multiple micro particles gathering or arranging quickly, easily and simply.
We propose and demonstrate a novel fiber surface plasmon resonance (SPR) sensor based on a twin-core fiber (TCF). We grind the TCF tip into a frustum wedge shape, and plate a 50nm sensing gold film on the end face, two 500nm reflected gold films on the side faces of the wedge. We launch light source into the core of the TCF by using the high accuracy three-dimensional adjusting mount and microscope objective system. This SPR probe can be combined with microfluidic chip, and realize the real-time monitoring of the refractive index (RI) sensing of flow liquid in the microfluidic channel. The probe successfully monitors the refractive index of liquid ranged from 1.33 to 1.37 and the average sensitivity reaches to 5213nm/RIU in the solution.
We propose and demonstrate a transverse self-accelerating Bessel-like beam generator based on a graded index multimode optical fiber(GIF). The single-mode fiber and the graded-index multimode fiber are spliced with a defined offset. The offset Δx and the GIF length L affect the final properties of the Bessel-like beam, here we choose the offset Δx=20μm and the GIF length L=430μm to be optimal. The beam accelerates along the designed parabolic path up to 250μm in z direction and 40μm in x direction, the curvature of bending is 16% (40μm/250μm, x/z). This transverse self-accelerating Bessel-like beam generator based on the graded index multimode optical fiber constitutes a new development for high-precision micro particles experiments and manipulations because of its simple structure, high integration and small size.
A novel hybrid Michelson-FP (M-FP) interference fiber sensor based on a twin-core fiber has been proposed. It consists
of an in-fiber integrated Michelson interferometer and an air FP cavities. The radial strain and axial strain sensing
properties are explored and analyzed. By using this novel structure, we can measure radial strain and axial strain
simultaneously.
We present a method to measure the polarization mode dispersion (PMD) of the LiNbO3 multifunctional integrated waveguide modulator (MFIWM) which is consist of a Y-waveguide, two extended polarization maintaining (PM) fibers, lead-in PM pigtail and lead-out PM pigtail. This method is based on an all-fiber time-domain scanning white light interferometer and utilizes fast Fourier transform (FFT) technology to obtain interferometric phase. The PMD of each part of MFIWM was measured and distinguished accurately. It’s demonstrated that, the PMD of Y-waveguide is 13.5 ps/nm/km@1555nm which is approximately 40~160 times of the PMD of PM fibers in the MFIWM under test.
We propose and demonstrate a mode division multiplexing single fiber optical tweezers. By using this tweezers, one can trap a yeast cell and then launch it away from the fiber tip with a certain speed to a certain position without moving the optical fiber in a single fiber optical trapping apparatus. We excite both LP01 and LP11 mode beams in a same normal communication fiber core to generate the optical launching force and trapping force by molding the fiber tip into a special tapered-tip shape. A yeast cell of 6μm diameter is trapped and then being launched away. We construct the optical trapping and launching potential wells by controlling the power of two mode beams. This micro particle directional launching function expands new features of fiber optical tweezers based on the normal communication fiber, providing for the possibility of more practical applications in the biomedical research fields.
We present and demonstrate a novel single fiber optical tweezers which can trap and launch (clean) a target polystyrene (PS) microsphere (diameter~10μm) with independent control by using two wavelengths beams: 980nm and 1480nm. We employ 980nm laser beam to trap the target PS microsphere by molding the fiber tip into a special tapered-shape; and we employ 1480nm laser beam to launch the trapped PS microsphere with a certain velocity by using the thermophoresis force generated from the thermal effect due to the high absorption of the 1480nm laser beams in water. When the launching force is smaller than the trapping force, the PS microsphere will be trapped near the fiber tip, and the launching force will blow away other PS microspheres in the workspace realizing the cleaning function; When the launching force is larger than the trapping force, the trapped PS microsphere will be launched away from the fiber tip with a certain velocity and towards a certain direction, realizing the launching function. This PS microsphere launching and cleaning functions expanded new features of single fiber optical tweezers, providing for the possibility of more practical applications in the micro manipulation research fields.
A method of simultaneous evaluation for two branches of a multi-functional integrated optic chip (MFIOC) with a dual channel system is proposed. The difference between the two branches of the MFIOC can be tested simultaneously with a high precision. In the system, the chip is used as a 1×2 splitter and its two branches are combined by a 2×2 coupler. The characteristic peaks of the two branches are distinguished by selecting proper length of the extended fibers which connected to each polarization-maintaining (PM) pigtails. Temperature responses of the two branches of the MFIOC are experimented. Results show that the dual channel system can simultaneously measure the characteristics of the two branches of MFIOC with resolution of over -85 dB and dynamic range of 85dB.
We propose and demonstrate a trapped yeast cell being launched away from the fiber tip with a certain speed to a certain position without moving the optical fiber in a single fiber optical trapping system. We excite both LP01 mode and LP11 mode beams in a same normal communication fiber core to generate the optical scattering force and trapping force by molding the fiber tip into a special tapered-tip shape. A yeast cell of 6μm diameter is trapped and then being launched away. We construct the optical launching well by controlling the power of double mode beams. Besides that, we also built a physical model to analyze the micro particle dynamic behavior characteristics during the launching moment. This micro particle directional launching function expanded new features of fiber optical tweezers based on the normal communication fiber, providing for the possibility of more practical applications in the biomedical research fields.
A novel method for generating cylindrical vector beams with radial and azimuthal polarization is presented. We use the
inner wall waveguide fiber which is a hollow annular symmetry waveguide with air layer, core layer and cladding layer.
We plate on its inner wall surface with a suitable thickness and thin silver film. The incident light will be absorbed and
polarized in the film area and TE mode will be loss retained TM mode. The experiments results demonstrate that the output
optical field distribution is cylindrical vector beams in far field. This method has advantages of simple structure,
convenient operation and low cost.
We present a novel liquid viscosity measuring approach based on the optical trapping technology. We put a “test-micro-particle” enclosed in a confined space built by a quartz capillary tube and two opposite-inserted optical fibers to construct the test cell. In order to make the test cell have the ability of auto-ready and easy-reset, we design and fabricate a special notch-shape in the ends of two fibers. This novel approach provides a new probably development direction for the optical tweezers technology applying on the sensing and measuring fields, and solve the optical tweezers measurement repeatability problems.
We propose a refractive index insensitive temperature sensor based on hollow annular core fiber (HACF) Mach-Zehnder interferometer (MZI). The HACF is composed of a large-diameter air hole, an annular core around the air hole and a cladding. The MZI is fabricated by inserting a short section of the HACF between two short multimode fibers, and the interference occurs between the light beams transmitting along the air hole and the annular core of the HACF. Experimental results show that the MZI is insensitive to external refractive index and has temperature sensitivity of 30 pm/°C.
We propose an ultra-high sensitive temperature sensor based on multimode fiber (MMF) Mach-Zehnder interferometer (MZI). The multimode fiber MZI is composed of a short section of MMF inserting between another two pieces of MMFs with large lateral offset. The sensing head is packaged in a capillary which is filled with glycerol-water solution. At the offset splice interface, part of the light in the lead-in MMF is coupled into the glycerol-water solution around the sensing MMF and the remainder propagates along the cladding of the sensing MMF. Due to the large thermo-optic coefficient of the glycerol-water solution, the transmission spectrum of the MMF-based MZI shift quickly with temperature variation. Experimental results show that the temperature sensitivity is as high as 8.23 nm/°C.
We propose a novel dual optical fiber tweezers integrated in a four-core fiber which can trap, rotate and orient a micro particle immersed in a fluid medium. We design the structures and the functions of this dual optical fiber tweezers, and simulate the optical trapping forces, optical torques exerting on the micro particle. We also give out the experimental setup and the controlling method of this integrated dual optical fiber tweezers.
A novel composite interferometer sensor is presented and its sensing characteristics are investigated. Based on the infiber
integrated Michelson interferometer, a quartz tube is used to encapsulate the ends of the twin-core fiber and single
mode fiber to form the dual extrinsic FP cavities. Thereby, the Michelson and FP configurations are integrated into a
single fiber, which we call it Michelson-FP composite interferometer sensor. The novel sensor can respond to the axial
strain and radial bending simultaneously. We have derived and analyzed the interferometer principle of the new structure.
The analysis results show that the interferometer sensor could be considered as the superposition of Michelson
interferometer and FP interferometer. Moreover, we establish a testing system and conduct a series of experiments to
investigate the strain and bending characteristics. We measure the reflection spectra with the spectrum analyzer. The
spectral response of the composite interferometer sensor presents two pattern fringes with different frequencies due to
the respective optical path interferometers. The experimental results indicate that the composite interferometer sensor is
very sensitive to the strain and bending characteristics, and the presented sensor has different strain and bending
sensitivity coefficients. Due to these characteristics, the presented sensor might be able to measure the strain and bending
characteristics simultaneously. In conclusion, the presented novel interferometer sensor is of compact structure, high
integration and good strain and bending sensing characteristics. Thus, many types of fiber-optic sensors may be built
based on it.
As the special core structure of the helical-core fiber, it has high fabrication difficulty. It has a high precision of
fabrication system requirement. The coaxality of optical fiber rotation is one of the key technologies. Under the premise
of a helical-core fiber fabrication system designed and manufactured, this paper puts forward micro-imaging test method
based on the centroid method. This method gets the image of fiber core spot through the microscopic imaging system,
and calculates the energy center of the spot image by using the centroid method. Thus we get the center and radius of
rotation of the spot image after the fabrication system rotated a period. Thereby the testing and adjustment of the
fabrication system coaxality are realized. The experimental results show that this method can complete the coaxality
testing of helical-core fiber fabrication system; make offset of the core be less than 10 μm. This method solves the
disalignment problem of optical fiber rotation during the process of helical-core fiber fabrication well.
We propose a novel tapered-tip single fiber optical tweezers, which can realize micro particles multi-trapping. The
theory analysis about multi-trapping was finished with the finite difference time domain (FDTD) method. The theory and experiment results showed that the particle refractive index affects the multi-trapping obviously.
An all-fiber optical coherence domain polarimetry (OCDP) is presented, which can increase the detection sensitivity and dynamic range simultaneously. An all-fiber OCDP system has been built, and the detecting sensitivity of polarization crosstalk can reach -98dB, meanwhile, the dynamic range can keep in 98dB. This method realizes the highest performance of the date OCDP technology, and provides an effective measurement and evaluation tools for high performance fiber optic devices and sensor system.
KEYWORDS: Refractive index, Sensors, Optical fibers, Near field optics, Near field, Data acquisition, Optical amplifiers, Optical testing, Signal detection, Computer simulations
This paper developed an intelligent optical fiber refractive index profile measurement system. This system is based on
the principle of the refracted near-field measurement. The whole system is the use of a unique high-resolution
non-contact capacitive displacement sensor to monitor the scanning position of the fiber measured. At the same time we
used a shading screen which was embedded into the sample pool. Using this method, we can totally save space. Finally,
we used a high curvature condenser to collection of reflected light which we used a photo detector to collect. The
collected signal was brought into the computer to calculate the optical fiber refractive index. The whole system is totally
enclosed operating instrument with an easy-to-use software interface for performing measurements of both multi mode
and single mode optical fiber, which can easy pick up the signal automatically and processing in computer. Measurement
accuracy can reach 10-4. It is fit for measuring the refractive index of single-mode fibers and multi-mode fibers.
The newly interfere and integrated fiber electro-optic intensity modulator was researched, it was made into
Michelson interferometer by thermal poled hollow two-core fiber, and researched the modulation effect of the
electro-optic intensity modulator. The result indicate that the poled fiber modulator have low half-wave
voltage, and achieved a good effect on intensity modulate, it also realized electro-optic fiber modulator and
Michelson interferometer integrated in one optical fiber. The electro-optic intensity modulator have good
stability, simple structure and so on.
In order to develop the near- field optical tweezers with perfect function , We design the near-field optical fiber optical
tweezers basing on the multi-core of the optical fiber. Combining the total internal reflection and multi-core optical
fiber, we form evanescent wave on the fiber water interface forming , and realize the capture of object .It can separate the
near-field optical tweezers and its control from the microscopic observation system effectively, so It enhance the
operability of near-field optical tweezers and the ability of active capture greatly. The Multi-core optical fiber constitutes
the Near-field optical tweezers, the superposition of the coherent light from opposite transmission forms a area of capture.
Interference effect makes light intensely, at the same time the capture space becomes more and more narrow. They can
improve the capture function of the new generation of all-fiber near-field optical tweezers greatly. And we quantitatively
calculating the optical trap force of the micron-grade particle. In this passage, there is a new progress in setting up the
near field optical tweezers' model and the calculation method. Moreover, it improves the using value of the near field
optical tweezers technology in the life sciences.
Conventional optical fiber tweezers are unsuitable for operation inside cells, due to their big-size
fiber tip to realize beam focusing. In this letter, new
micro-optical tweezers with no focusing are
demonstrated, which only demand a uniform thin-fiber to realize 3D capture and manipulation. The
fused biconical taper method is adopted to produce micro-optical tweezers with a diameter of 0.75 μm,
the finite-difference time-domain (FDTD) calculation method is used in the simulation and in the
discussion of trapping ability, and the possibility of using this method is confirmed with experiments.
These optical tweezers have a small size, tight structure, and simple production method, and it is hoped
that they will become an effective tool in cell capture and manipulation.
Refracted near-field method is a very mature and reliable method for the measure of fiber refractive index profiles. In
this paper, we use refracted near-field technique and set up the experimental device to measure special optical fiber
refractive index profiles. We build a simulation model which refers to air-core photonic crystal fiber based on refracted
near-field method, determine the structure parameters and the relationship between refractive index profiles and light
intensity distribution, calculate fiber refractive index profiles deviation caused by the special fiber structure, and give the
correction method. The experimental result is modified by the above and obtains a good treatment effect.
Micro crack and pits of Side-polished fiber (SPF) is polished by fine sand paper and by an arc discharge, and their effects
are compared. When there is no light through SPF after polishing, we will find that using an arc discharge method is
better than fine sand paper polishing method especially their images being compared. When light passes SPF after
polishing, we will find that transmitted light of SPF by using an arc discharge method is less than the others. In
conclusion, using an arc discharge method is obviously better than fine sand paper polishing method.
We present a novel method to calibrate fiber optical tweezers. This paper proposed a new calibrating method solving the
problem, which makes the calibration for fiber optical tweezers in a wide range of output optical field possibly. Based on
electromagnetic field momentum conservation law and
finite-difference time-domain method, we calculated and
analyzed the force of multiple particles are simultaneously trapped, and get the f-x (trapping fore-distance from the fiber
tip) curve, which is consistent to the experimental results. Theoretical and experimental results show that the fiber optical
tweezers is more conducive to study the precise mechanical properties of biological cells in a larger range.
We propose and fabricate a twin-half hollow elliptical core polarization maintaining fiber. The shape of the core in the
polarization maintaining fiber is designed to be elliptical for generating a geometry birefringence. In the cladding, two
half-hollows are symmetrically distributed with respect to the elliptical core for producing a stress birefringence.
Therefore, the birefringence in such a polarization maintaining fiber is the mixed effect of the geometry and stress
birefringence. The birefringence generating mechanism is analyzed in detail and a theoretical formula depicting the
birefringence is built up. The simulation results for the twin-half hollow elliptical core fiber at different structural
parameters are obtained by using finite element method. Through adjusting the structural parameters of the fiber, the
relationships between the birefringence and the core diameter as well as the width of the core bridge are discussed.
A novel microfiber vibration sensor based on optical trapping mechanism is proposed. In the vibration sensor, a
polystyrene microsphere with a diameter of 10μm is used as the mass block. The polystyrene microsphere is enclosed in
a sensing cavity filled with refractive index matching liquid. The sensing cavity is composed of a quartz capillary with an
inner diameter of 40μm whose two ends are inserted with two optical fibers with an outer diameter of about 40μm. The
end surface of the each fiber is fabricated to be a concave tip to generate scattering and gradient forces for trapping the
mass block. By adjusting light power outgoing from the two concave tips, the mass block can be suspended at center of
the sensing cavity. When a vibration is applied on the sensing cavity, the location of the microsphere will change with
the vibration, which results the light power from one tip collected by the other tip also varies with the vibration. The
response of the vibration sensor is experimentally demonstrated at frequency range from 15Hz to 1000Hz. The vibration
sensor has advantages of simple configuration, small size, light weight as well as good vibration response.
We have designed a small type of endoscopic 2D fiber scanner probe to incorporate OCT with endoscopy imaging. The
new probe consists with two piezoelectric ceramics plated with electrode, a conductive thin-film with non-inverse
piezoelectric effect and a piece of nude fiber with coating layers removed. To accomplish the scanning, the only thing
need to be done is to drive the two piezoelectric ceramic sheets which provides simpler structure and at the same time
minimizes the probe effectively. Here we have obtained some preliminary results and verified the feasibility of the
program.
We present an abruptly tapered twin-core fiber optical tweezers, which is fabricated by fusing and drawing the twin-core
fiber (TCF). The two beams guided by the TCF, and a larger converge angle between the two beams are made due to the
abrupt tapered shape. The two beams converged at the micro-lensed tip, then forming a fast divergent optical field. The
microscopic particle trapping performance of this special designed tapered TCF tip is investigated. The distribution of
the optical field emerging from the tapered fiber tip is simulated based on the beam propagation method (BPM). By
using this two-beam combined technique, a strong enough gradient forces well is obtained for microscopic particles
trapping in three-dimensional. The abruptly tapered TCF optical tweezers is rigid and easy to handle, especially useful
for build-up a multi-tweezers system for trapping and manipulating micro-scale particles.
A novel fiber optic flow velocity sensor based on a twin-core fiber Michelson interferometer has been proposed and
demonstrated. The sensor only is a segment of twin-core fiber acting as cylinder cantilever beam. The force exerted on
the cylinder by the flow of a fluid with unknown velocity bends the fiber, which corresponding to the shift of the phase
of the twin-core in-fiber integrated Michelson interferometer. This twin-core fiber sensing technique could automatically
compensate the variation of environmental temperature and pressure due to both arms of the interferometer would be
affected equally by such changes.
By using spherical designed three-core fiber, a micro structured light pattern generator for sensing of 3-D object shapes
has been demonstrated. The square or hexagon grid interferometric fringe pattern formed by the fiber optic
interferometric grid generator is projected on an object's surface. The deformed grid pattern containing information of
the object's surface topography is captured by a CCD camera and is analyzed using a 2-D Fourier transforming
profilometry. The use of fiber optic grid interferogram technique greatly simplifies the holographic interferometry system
and the carrier grid interferogram can be conveniently generated without the use of excessive auxiliary components or
sophisticated experimental devices, and moreover, the three-core fiber can be used in very narrow places due to its small
size. Finally, the square or hexagon grid interferometric fringe pattern provides a data fusion ability, which could further
improve the accuracy of the 3-D shape sensing results.
A novel two-core optical fiber probe is proposed and fabricated by grinding method. The distribution of the optical field
emerging from the probe was simulated using BPM method. With the probe, a single fiber optic tweezers system was
constructed and successfully used to trap and rotate microscopic particles. The structure of this system is simple and
compact. With the merit of easily controlling and adjusting, this novel system can adapt to the optical micromanipulation
need of more biological cells and molecular.
Based on Jones matrices theory, the error source and action mechanism of polarized interferometer using four-channel
orthogonal signals in nanometer level measurement are researched. It opens a door for selecting optical components,
adjusting light set-up and compensating error.The mechanism of nonlinear errors and the variance law of nonlinear errors
in laser interferometer, which is caused by nonideal factors of 1/4 wave plates or 1/2 wave plate or all of them, based on
polarized phase-shift technology. In this paper, every single error on the polarized interferometer is discussed with the
isolation of each wave plate, so that the character of nonlinear error will be reached with composite error. In the
experiments, difference delay angle error of two 1/4 wave plates and location angle error is -5°∼5°in interferometer. The
aim of this paper is to realize the mechanism of nonlinear errors and the varying rule of nonlinear errors in laser
interferometer. All above provide error remove or compensation for laser interferometer in nanometer level measurement
with theoretical foundation and search after application.
A novel flat-faced thin fiber optic tweezers is proposed. It was fabricated by heating and drawing method under the
condition of laying aside the conventional focusing method. With this fiber optic probe, the single fiber optic tweezers
realized trapping a yeast cell in water. The experiment results were in good agreement with the simulated results which
were carried out using FDTD method.
A novel in-fiber optical switch based on two-core optical fiber is demonstrated. A Mach-Zehnder intereferometer was integrated into a single optical fiber of 125 μm diameter using a novel coupling connection technology. Then embedding the single optical fiber into a universal optical fiber transmission line, the novel in-fiber optical switch is formed. It can make microscale and integrated optical fiber elements into a complex function system, which greatly improve the performance of in-fiber elements and can develop and manufacture fiber optical sensors acceptable for various special situation. The reference and sensing arms of the intereferometer of the perfect in-fiber optical switch based on two-core optical fiber is integrated into a single fiber, which makes the structure more simple and the optical paths relatively stable, so it can effectively avoid the influence of enviroment factors such as vibration, temperature and greatly improve the performance of in-fiber optical swiches.
KEYWORDS: Digital signal processing, Demodulation, Vibrometry, Linear filtering, Modulation, Signal processing, Analog electronics, Filtering (signal processing), Signal detection, Interferometers
The demodulation method of active homodyne laser nanometer vibration measurement system based on digital signal processing (DSP) system is presented. In this paper, the software and hardware designs of low-frequency nanometer vibration measurement system is demonstrated based on the technology of phase generated carrier (PGC). The key technique of PGC based on DSP includes the following aspects: the choice of carrier frequency and the modulation depth of phase are expounded for the need of high sensitivity detection and large dynamic range; the designs of sampling frequency and anti-aliasing filter are introduced. Experiment result indicates that using digital signal processor chip as the core signal processing component has more advantages than analog system: the intrinsic direct current offset from temperature shifting of analog PGC circuit is eliminated; the disturbance of low frequency noise is suppressed; the systemic adaptability and the ability of anti-jamming are improved; besides, this system is easy to be miniaturization. This detecting system can be used for measuring weak vibration of nanometer measurement with frequency ranging from 10 to 100Hz.The result shows that amplitude-detecting resolving power is greater than 0.1nm(value of peak-peak) and the largest detectable amplitude is 10μm. It is a promising practical demodulation scheme for low frequency weak vibration measurement.
A nonlinearity correction using ellipse fitting technique based on orthogonal polarized laser interferometer is
proposed in this paper. In this paper, characteristics of four-channel output signals based on polarized Michelson laser
interferometer are studied. The orthogonal signal's non-orthogonal error which is caused by temperature disturbance and
low frequency vibration noise is compensated. Besides, a new algorithm of demodulating small phase signal is proposed.
Low frequency vibration signal demodulation system based on DSP technique is constructed. It proposed an ellipse
fitting algorithm based on Least-squares theory. This algorithm can achieve correction error of less than ±0.3%.
System's real-time measurement capability and its resolution can be improved.
Based on Jones matrices theory and polarized phase-shift technology, one of the most important elements of polarized interferometer that is the error source and action mechanism of wave plates is researched. There are two reasons that cause wave plate error, one of which is immanent parameter error and the other one is location error. When environmental temperature changes and vibratory jam exists, the error of different elements will couple, which makes nonlinear error on the polarized interferometer more complex. It opens a door for selecting wave plates, adjusting light set-up and compensating error. In this paper, the point is the experiments on the wave plate error, which is on the base of theory. Every single error on the polarized interferometer is discussed with the isolation of each wave plate, so that the character of nonlinear error will be reached with composite error. In the experiments, difference delay angle error of two 1/4 wave plates is -10 degrees~10 degrees and location angle error is -5 degrees~5 degrees in interferometer. The aim of this paper is to realize the mechanism of nonlinear errors' appearance and the varying rule of nonlinear errors in laser interferometer. The effects of the environmental factors (temperature and oscillation) on the measurement accuracy and the compensation for the environmental changes are also studied. All above provide error remove or compensation for laser interferometer in nanometer level measurement with theoretical foundation and search after application.
A double-coating optical fiber sensor which is used for soil deformation measurement is proposed in the paper. It could
be used in non-destructive detection of large scale structures, health evaluation of the civil structures and forecast of
geologic hazard such as landslide. The structure of the double-coating soil mechanical sensor is designed and the
mechanical model of the mutual effects between the optical fiber and the soil is founded. Under the static press, the
deformations of the soil dam model and the slope model are experimentally detected by using the calibrated white-light
fiber soil mechanical sensor. In the experiment, a 500 millimeter length double-coating soil mechanical sensor is chose
to detect the soil deformation. Measuring results indicate that the mechanical transfer coefficient is 0.31 and the
measuring range of deformation is from zero to 10 millimeter. Compared with the outside stickup sensors, the embedded
soil mechanical optical fiber sensor can faithfully represent the deformation inside the soil model, the measuring result is
closer to the real soil deformation and the measuring method is more effective.
A single tapered fiber optical tweezers is demonstrated experimentally based on a fused tapered fiber probe. Yeast cells
immersed in water were trapped at the tip of the fiber probe and moved in 3 dimensions at a certain velocity. The
trapping force, both axial and transverse, can only be attributed to the force effect of the optical field emerging from the
end of the fiber probe. The output optical field was numerically simulated by using a BPM (beam propagation method)
method. It is qualitatively discussed that such optical field own the ability to form a 3-D optical trap.
Based on Jones matrices theory, the paper researches the error source and action mechanism of the polarized
interferometer in nanometer level measurement. It opens the door for selecting optical component, adjusting light set-up
and compensating error. According to the theoretical analysis, the main reason that causes error is degeneration of
polarization that the imperfect performance of optical components and imperfect adjusting bring. Especially the different
delay angle happens more obviously. The characteristic of the passive homodyne laser interferometer based on the
polarized phase-shift is that the output of interferometer is four-channel signals in quadrature. Using this characteristic,
through strict selecting and fine adjusting components and differential signal processing, the interferometer can perform
nanometer measurement.
Fluorescence fiber sensors are broadly used to measure temperature, concentration, and pH value etc.
The fluorescence sensing systems are based on different principles, namely fluorescence intensity,
fluorescence intensity ratio, and fluorescence lifetime. The fluorescence lifetime is an effective
parameter for sensing purpose, because it is independent on the intensity of the pumping source and
does not need expensive narrow-band filter. An experiment system has been established. Some samples
are produced to measured the fluorescence lifetime of temperature characteristic and get the
relationship of strain and temperature versus the fluorescence lifetime at the same time. The experiment
result was fitted and analyzed. The test results show that the fluorescence lifetime decreased with the
increasing of temperature. The change of fluorescence lifetime with the strain is inconspicuous
comparing to that with the temperature.
A novel laser interferometer which adopts alternating modulation phase tracking homodyne technique is proposed. The
vibration of nanometer-accuracy is measured with the improved Michelson interferometer by adding cat's eye moving
mirror and PZT phase modulation tracking structure. The working principle and the structure of the interferometer are
analyzed and the demodulation scheme of alternating phase modulation and tracking is designed. The signal detection is
changed from direct current detecting to alternating current detecting. The signal's frequency spectrum transform is
achieved, the low-frequency noise jamming is abated, the Signal-to-Noise of the system is improved and the measured
resolution is enhanced. Phase tracking technique effectively suppresses the low-frequency noise which is caused by
outside environment factors such as temperature and vibration, and the stability of the system is enhanced. The
experimental results indicate that for the signal with the frequency of 100Hz and the amplitude of 25nm, the output
Signal-to-Noise is 30dB and the measured resolution is 1nm.
The optimization of parameters for dual fiber optical tweezers is presented in this paper. Mode transmission properties
are analyzed theoretically and characteristics of the optical field in tapered fiber are numerically simulated using FDTD
method. The optimization of fiber's parameters such as the taper angle, radius of the fiber tip-lens and cladding radius at
the tip of the tapered fiber is discussed in detail for the dual fiber optical tweezers. It is indicated that, for a common use,
the taper angle should be as small as possible and the micro lens should be fabricated at the tip of the taper where the
cladding is polished close to the fiber core. Experiments were done to investigate structural parameters including the
arranged angle and the horizontal distance between the two fiber ends. Results indicate that the transverse trapping force
is enhanced as the arranged angle reducing and there is an optimal horizontal distance between two fiber ends.
The combined two-ring-resonator schemes of fiber optic gyroscope are developed and demonstrated. The two-ring topology structure has been classified 2 kinds: two-ring in series and in parallel. The cavity lengths L1 and L2 of the two-ring-resonator are chosen as 623m and 1260m, respectively. A theoretical model of the two-ring Rayleigh backscattering fiber optic gyroscope which including the Sagnac effect is established. The experimental results are agreement with the theoretical prediction.
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