Cardiovascular disease is a major risk to human health, which needs long-term monitoring for prevention and early diagnosis. Optical sensors present the advantage of immunity to electromagnetic field and high sensitivity, and have been growing in a variety of emerging medical applications to monitor human cardiac parameters. Most of the current optical sensors can only measure limited cardiovascular information such as the heart rate, therefore, the optics-based approach for cardiac electrophysiology has attracted the attention of more researchers. In this paper, we developed a method to evaluate the availability of our proposed anti-EMI optical sensor. The sensitivity of optical sensor based on electro-optic modulation can achieve 266.4μW/V and detect the electrocardiogram (ECG) by attached to the chest and edge of clavicle. A series of ECG signals over 1 hour were analyzed using proposed method, which is driven by the optimization of R-peak location, Lorenz plot and statistical correlation. ECG monitoring results of the optical sensors are in accordance with a standard clinical device (SOMNOtouch™ RESP) among different subjects. Moreover, both the sensors are tested in daily electromagnetic conditions, and it causes some obvious signal artifacts to the SOMNO system, but almost no effect on the optical sensors during the long-term test. We provide further grounds for such clinical applications by demonstrating, for the first time to our knowledge, optics-based device used in long-term ECG monitoring, an essential tool in modern cardiac monitoring applications.
We designed an annular blazed grating to achieve maximum optical power in the +1st transmitted order at a fixed diffraction angle. We performed theoretical analysis and simulations on the designed grating, where the incident beam (wavelength: 1550 nm) was perpendicular to the grating surface. The diffraction efficiency in the +1st transmitted order was dependent on the blaze angle (or modulation depth) and period for a refractive index of 1.49. The diffraction efficiency in the +1st transmitted order was maximum (85.94%) at a modulation depth and period of 2.18 μm and 3.96 μm, respectively, and the corresponding diffraction angle was 45.3°.
White light interferometry is used to measure distributed polarization coupling in high-birefringence polarization-maintaining fibers (PMFs). When there are multiple intrinsic coupling points (CPs), multiple-order ghost CPs will produce. The quantity of multiple-order coupling modes can be calculated recursively. A graphical method is proposed to distinguish the multiple-order ghost CPs from intrinsic CPs. Overlapping of CPs is affected by the positions of disturbance points. Experiments on two and three disturbance points imposed on PMFs are performed. Experimental results show the positions of multiple-order CPs are agree well with graphical analysis. Additionally, the graphical method can be used to analyze other polarization-sensitive optical devices.
The light scattering properties of a transparent spheroidal particle is investigated using defocused interferometric particle imaging. Based on optical transfer matrix theory, the out-of-focus images are simulated using Matlab. We found that the angular variation of a spheroidal particle exhibits isometric with angular variation of the speckle of out-of-focus image. The out-of-focus images of transparent spheroidal particles under different angle of rotation are experimentally acquired using interferometric particle imaging system. The experimental results showed agreement with the simulation results. Thus, we propose a method for obtaining the angular variation of a spheroidal particle using out-of-focus image.
In this paper, we proposed a distributed stress sensor based on white light interferometer. The measurement including two steps: firstly, the moveable mirror of Michelson interferometer scans to detect the interferogram, and the position of dynamic stress can be obtained from the interferogram. Secondly, the moveable mirror of Michelson interferometer adjusted to compensate the optical path difference generated in the polarization maintaining fiber, and the photodiode detect the interference intensity. By applying wavelet transform to the detect signal, the frequency of dynamic stress can be demodulate. In our experiments, the measurement errors for 100 Hz and 1 kHz sinusoidal stress are 0.26 Hz and 0.3 Hz, respectively. And 20 Hz - 60 Hz chirp signal is also measured successfully. In the end, the harmonics in the time frequency distribution image and the factors resulting in the measurement error are discussed in detail.
We propose an effective image denoising filter that combines an improved spin filter (ISF) and wave atoms thresholding (WA) to remove the noise of fringe patterns in electronic speckle shearing pattern interferometry. The WA is first employed to denoise the fringe to save the processing time, and then the ISF is further used to remove noise of the denoised image using WA to obtain a better denoising performance. The performance of our proposed approach is evaluated by using both numerically simulated and experimental fringes. At the same time, three figures of merit for denoised fringes are also calculated to quantify the performance of the combined denoising filter. The denoised results produced by ISF, WA, and bilateral filtering are compared. The comparisons show that our proposed method can effectively remove noise and an improvement of 12 s in processing time and 0.3 in speckle index value is obtained with respect to ISF.
We develop a hybrid wavelength division multiplexing optical fiber network with distributed fiber-optic sensors and quasi-distributed FBG sensor arrays which detect vibrations, temperatures and strains at the same time. The network has the ability to locate the failure sites automatically designated as self-diagnosis and make protective switching to reestablish sensing service designated as self-healing by cooperative work of software and hardware. The processes above are accomplished by master-slave processors with the help of optical and wireless telemetry signals. All the sensing and optical telemetry signals transmit in the same fiber either working fiber or backup fiber. We take wavelength 1450nm as downstream signal and wavelength 1350nm as upstream signal to control the network in normal circumstances, both signals are sent by a light emitting node of the corresponding processor. There is also a continuous laser wavelength 1310nm sent by each node and received by next node on both working and backup fibers to monitor their healthy states, but it does not carry any message like telemetry signals do. When fibers of two sensor units are completely damaged, the master processor will lose the communication with the node between the damaged ones.However we install RF module in each node to solve the possible problem. Finally, the whole network state is transmitted to host computer by master processor. Operator could know and control the network by human-machine interface if needed.
A novel curved compound eye imaging system is put forward in this paper. Non-uniform hexagonal lens array is
arranged on the inner surface of a plano-concave substrate. Based on the geometrical optics, the parameters of each
microlens are set according to the position of the lens, and even orders of aspheric lens are used to correct some primary aberrations. Optical parameters of this configuration are entered into numerical ray-tracing simulations (ZEMAX). The result shows that the new curved compound eye can enlarge the field of view (FOV) approximately 50% compared to the lateral compound eye, and the FOV can be up to 150°. The principles and functions of all parts of system are described in detail. At last, the feasibility of ultra-precision machining is studied in this paper.
A tunable intracavity fiber laser has been widely used for gas sensing. In order to design a better performance sensor by use of this tunable intracavity fiber laser, the influence factors, including output power such as pump power, intracavity loss, output splitting ratio, and emission wavelength, are investigated based on a theoretical model using the propagation equation. The tunable intracavity fiber laser is set up, and the effects of pump power, intracavity loss, output splitting ratio, and emission wavelength are measured. The experimental results indicate that the theoretical analysis is in good agreement with the experimental measurements; in the process of designing the sensor, the intracavity loss and splitting ratio should be given more attention.
Detection of pollution gas is important in environmental and pollution monitoring, which can be used widely in mining
and petrochemical industry. Fiber optical spectrum absorption (FOSA) at near-IR wavelength is widely used in gas
detection due to its essential advantages. It has attracted considerable attention, and there are several types and methods
in FOSA. Wavelength modulation technique (WMT) is one of them, which will improve the gas detection sensitivity
dramatically. This technique can be realized by detecting the intensity of the second-harmonic component signal.
Intra-cavity laser spectroscopy (ICLS) is another alternative technique for high sensitivity absorption measurement. With
an absorber directly placed within the laser cavity, a short absorption cell can be transformed into a high sensitivity
system. But the practical sensitivity is obviously less than the theoretical value. The authors did some works in these
fields and have obtained some remarkable progress. With broad reflectors instead of FBG as mirror of the cavity and
wavelength sweep technique (WST), several absorption spectra of detected gas can be collected. And the detection
sensitivity can be enhanced sharply by averaging the results of each spectrum, with acetylene sensitivity less than
100 ppm . When ICLS is used combined with WST and WMT, the detection sensitivity of acetylene can be enhanced
further. The sensitivity is less than 75 ppm. By using FBGs as wavelength references, the absorption wavelength of the
detected gas is obtained, which can be used to realize gas recognition. The system is capable of accessing into fiber
intelligent sensing network.
An oral cavity inspecting system is designed and developed to inspect the detail of teeth. The inspecting system is
composed of microscopic imaging part, illuminating part, image capture and processing, display part. The two groups of
cemented lenses were optimized to minimize the optical aberration and the collimated beam light is gotten between the
two lenses. A relay lens is adopted to allow the probe to access the oral cavity depth. The illumination optic fiber is used
and the brightness and color temperature can be adjustable. The illumination fiber end surface is oblique cut and the
optimum angle is 37°. The image of teeth is imaged on CMOS and captured into computer. The illumination intensity
and uniformity were tested and the proper parameter is set. Foucault chart was observed and the system resolution is
higher than 100lp/mm. The oral inspecting system is used to test standard tooth model and patho-teeth model. The tooth
image is clear and the details can be observed. The experimental results show that the system could meet dental medical
application requirements.
In this paper, an electronic speckle-shearing pattern interferometer with pulsed laser and pulse frequency controller
is fabricated. The principle of measuring the vibration in the object using electronic stroboscopic speckle--shearing
pattern interferometer is analyzed. Using a metal plate, the edge of which is clamped, as an experimental specimen,
the shear interferogram are obtained under two experimental frequencies, 100 Hz and 200 Hz. At the same time, the
vibration of this metal plate under the same experimental conditions is measured using the time-average method in
order to test the performance of this electronic stroboscopic speckle-shearing pattern interferometer. The result
indicated that the fringe of shear interferogram become dense with the experimental frequency increasing. Compared
the fringe pattern obtained by the stroboscopic method with the fringe obtained by the time-average method, the
shearing interferogram of stroboscopic method is clearer than the time-average method. In addition, both the
time-average method and stroboscopic method are suited for qualitative analysis for the vibration of the object. More
over, the stroboscopic method is well adapted to quantitative vibration analysis.
In the optical rotary joints, the Dove Prism is employed to rotate an image about the optical axis and compensate optical
path of optical signals so that the optical signals can be transferred across the rotating interface. However, manufacturing
errors and assembling errors of Dove Prism will affect the coupling efficiency of Dove Prism. In this paper, the analytical
expressions for errors of the rotating coupling efficiency are presented when the prism is manufactured with errors in its
base angle and pyramidal angle. The analytical result showed that the coupling losses that arise from manufacturing errors would increase as the base angles deviate from the traditional value of 45° and the pyramidal angle increase. At the same time, the influence of assembling errors on coupling efficiency is also analyzed using the method of light ray tracing. The assembling errors of Dove Prism included angular tilt misalignment, height misalignment, and inclining misalignment. The results indicated that these misalignments cause the coupling efficiency of Dove Prism decreased. The coupling efficiency is more sensitive to the height misalignment and angular tilt misalignment than the inclining misalignment.
Distributed stress sensor with a scanning Michelson white light interferometer can be used to detect stress distribution
and its value by analyzing polarization mode coupling caused by stress field in PMFs (polarization maintaining fibers).
In the measurement of polarization coupling, the birefringence in sensing fiber is usually considered to be
wavelength-independent. The spatial resolution of the distributed stress sensor is invariable, when the optical source
spectrum is given. In practical measurement, however, the birefringence in PMF is related with optical wavelength, the
birefringence dispersion exists in PMF. Due to the birefringence dispersion, the spatial resolution of the distributed stress
sensor descends obviously with the fiber length increasing. In this paper, the influence of external force position and
optical source spectrum on spatial resolution in the distributed stress sensor is analyzed, while the birefringence
dispersion is considered.
A white light interferometer is designed to measure the distributed polarization coupling (DPC) in
polarization-maintaining fiber (PMF). By using a Michelson interferometer to compensate the optical path difference
induced by the modal birefringence of PMF, both the coupling strength and position of the coupling point can be
acquired. The two reflective mirrors on the fixed and scanning arms should be vertical to each other. But in practice, the
movable reflective mirror can't be vertically aligned exactly to the fixed mirror, which would lead to angle misalignment.
The angle misalignment would induce the variance of the optical path difference (OPD), which would reduce the fringe
visibility. Finally, the angle error would lead to a decrease on the signal noise ratio (SNR) and miscalculation of the
polarization coupling intensity. The angle misalignment and diameter of the incident light beam both have an effect on
the fringe visibility. The simulation results show that the requirement of angle error becomes stricter with the increasing
of the light beam diameter. To decrease the angle misalignment, the two plane reflective mirrors should be replaced with
the corner cube prisms. A revised coupling strength calculation equation was proposed to minimize the influence of angle
misalignment.
One of the key issues in establishing an optical fiber sensing system based on fiber Bragg gratings (FBGs) is the
selection of a suitable wavelength shift detection scheme in terms of the performance it offers. By use of a compact
Fabry-Perot (F-P) tunable filter, the Bragg wavelength variation can be detected with a relatively high speed and
satisfying resolution. In this paper, a dynamic strain sensing system based on F-P tunable filter is described, and the F-P
tunable filter is demonstrated to have a significant impact on the system. The relationship between the collected spectrum
of grating and the 3-dB bandwidth of the F-P tunable filter is discussed. The optimum 3-dB bandwidth of the F-P tunable
filter for most FBGs is obtained. It is exhibited in this paper that the demodulation precision and sensitivity of the strain
sensing system is influenced by the nonlinearity between the transmission wavelength of the F-P tunable filter and the
drive voltage. The drive voltage is rectified using interpolation algorithm. The experimental results illustrate that the
average error and the maximum error of the transmission wavelength are decreased by 96.4% and 80.9% respectively.
The strain sensitivity of the optimized system is below
3με. The error between the practical strain value demodulated
by the system and theoretical value is below 5%.
A vertical-shaft-type Mirau white-light phase-shifting interferometer is designed based on white-light phase-shifting interference microscopy in this paper. The interferometer is composed of an illumination and interference imaging part, a piezoelectric transducer in the vertical direction, a two-dimensional scanning part in the test surface, image collection and interferograms analysis part. The light illuminates the sample and the test surface uniformly, and the interferogram is formed. In order to get phase-shifting, the move of the objective is driven by PZT. The three-dimensional scanning system consists of a two-dimensional horizontal motorized stage and a vertical piezoelectric transducer. Multi-aperture stitching extends the measurement range in the test surface. A new pixel divided phase-extracting algorithm was put forward in combination with a residues-pretreatment phase-unwrapping algorithm based on image segmentation. The algorithm is used to minimize the phase-shifting error and nonlinearity error of the detector. The surface profile of a fiber connector with fiber inserted was measured. Mean value of the protrusion between fiber and fiber connector was measured to be 45.7nm, with 0.9 nm error. The mean height of a spot on the end surface of fiber connector was measured to be 23.6nm, with 0.7nm error.
A white light Michelson interferometer is designed to measure the distributed polarization mode coupling in High birefringence polarization-maintaining fibers (HiBi-PMFs). Using a Michelson interferometer to compensate the optical path difference induced by the modal birefringence of PMF, both power coupling intensity and position of the coupling point can be acquired. Traditionally, this technique requires only one polarization mode in the PMF to be exited or both polarization modes to be exited with equal intensity. This needs precise alignment of the polarization direction with the principal axis of the PMF. In practice, it's not easy to realize. In this paper, the influence of the incident polarization extinction ratio (PER) on the measurement result was evaluated theoretically and experimentally. A polarization state adjusting mechanism is designed. An analyzer can be oriented at any angle of the PMF's principle axes. By alternating this angle between 0o, 90o and 45o, the incident PER can be calculated and the measurement can be carried out with random exited polarization mode. An instrument was designed and implemented to verify this scheme. Spatial resolution better than 7cm and coupling strength sensitivity less than -75dB are realized.
A microstructure inspection endoscope, based on directly imaging, is proposed. It is designed for detecting defects on the surface of optical fiber end. It is matched with FC or SC female fiber connector. The inspection head of the endoscope can be put into a 2.5-millimeter-diameter micro-pore. Its numerical aperture is not restricted by tiny dimension of object lenses. System resolution is increased to 600 line-pairs per millimeter. The endoscope consists of object lenses, scanner slab and kohler illumination system. The design provides possibility of various utilities such as aiming at a smaller subject by micro optical scanner and modeling the surface by tri-dimensional vision. And the optical system includes low-magnification lenses and high-magnification zoom lenses. Rough observation at low-magnification and particularly inspection at high-magnification are provided. The instrument has the advantages of high identification, compact configuration and flexible manipulation.
The numerical aperture (NA) of the double beam interferometers (DBI) can affect the accurate measurement of surface profiles. Based on the double beam interference microscope imaging theory, the fringe spacing will vary wide nonlinearly with the increasing of numerical aperture. The double beam interferometers require oblique incidence illumination, including Michelson, Mirau and Linnik types. The intensity distribution of the illumination across its stop is constant so the correction factor depends mainly on the NA in the Michelson and Linnik interferometers. The correction factor expression is derived in the Michelson interferometer. The reference surface is a central obscuration in the beam, which will reduce the effective numerical aperture in the Mirau interferometer. At the same numerical aperture, larger central obscuration has a much effect on the correction factor. The correction factor expression is determined by considering the influence of central obscuration and oblique incidence in the Mirau interferometer.
White light interferometry has been adopted to measure the distributed polarization coupling in high birefringence fibers. A superluminescent diode is adopted as the optical source in the white light interferometer. To enlarge the measurement range, the light beam in the scanning arm of the Michelson interferometer is reflected three times. Thus the scanning range of the interferometer is doubled. The full-width half-maximum spectrum of the SLD is 50 nm, and the central wavelength is 1300 nm. If the modal birefringence of the HBF is 5×10-4, a spatial resolution of 70 mm can be achieved. A high sensitivity photo detector and a high-resolution analog to digital converter have been adopted. The polarization coupling intensity measurement accuracy can be up to -75 dB.
In this paper, an apparatus has been designed to inspect the end surface of fiber optic connectors. A white-light high-brightness light emitting diode has been adopted to offer enough light power. Zoom lenses comprise field lens and achromatic lens with a large range of magnification from 1.25 to 60. They can be used to inspect not only the whole ferrule but also the details of the core. The illumination system has two modes: perpendicular and oblique. In oblique illumination, the relation on the maximum length of shadow
along the incident direction and the angle of oblique illumination is disclosed and the curvature of shadow is drawn. Fiber undercut and protrusion can be judged whether they are satisfied the tolerance with the curvature.
A noncontact system for detecting and monitoring the grain and contour of optical connector end face based on Mirau-type interferometer is proposed in this paper. In this system, phase shift technique has been adopted. A five steps algorithm is presented. By this algorithm, the computer can analyze the interference pattern and unwrapped the phase information of the detected surface. Then we can get the differential height of every point on the surface. This
method is capable of measuring fiber height to ±0.003 microns and radius of curvature and offset of polish to ±0.30 mm and ±2.0 microns respectively. So we can get not only 2-D and 3-D topography of testing surface, but also the evaluation parameters of surface roughness.
A multi-pipeline optical interconnection network for distributed computing system has been designed. Each sub-layer network is connected to the ring with an access node (AN), which can transmit data at every wavelength with a tunable laser diode. The data transmission speed at each wavelength is 1.25 Gbit/s. With 8 wavelengths, a total bandwidth of 10 Gbit/s can be obtained. Each AN only receives a certain wavelength. With a band pass filter, the desired optical signal can be dropped down. Pipelining data transmission is achieved among different wavelengths. This network is a multi-pipeline structure. So the communication latency and communication overheads can be decreased. Meanwhile, the ring topology has good scalability. The scale of the network can be expanded adopting more wavelengths at each access node.
A high-performance metropolitan area network has been designed with the combination of coarse wavelength division multiplexing (CWDM) and electrical time division multiplexing (ETDM) techniques. The network consists of n access nodes with each node transmitting and receiving m wavelengths. Virtual multi-channel (VMC) has been achieved at each wavelength via ETDM technique to minimize the data blocking possibility. This network structure has high bandwidth, low communication latency and high performance-to-cost ratio. A prototype network of 6 access nodes has been implemented with 4 virtual channels at each wavelength. The data transmission speed at each wavelength is 1.25 Gbit/s. It can be upgraded to 2.5 Gbit/s. The network has high flexibility and scalability. To further expand the network capacity, multi-wavelength window CWDM technique can be adopted at 1300 nm and 1550 nm simultaneously.
KEYWORDS: Data transmission, Field programmable gate arrays, Clocks, Human-machine interfaces, Data communications, Interfaces, Local area networks, Switching, Computer networks, Time division multiplexing
A giga-bit per second optical ring has been designed. The data link layer bandwidth of the network is 1.5 Gbit/s. Hardware routing has been achieved by field programmable gate array (FPGA) to minimize the communication latency. As a result, the point-to-point communication latency between adjacent node computers is less than 300 ns. To reduce the data communication latency and have a more efficient usage of the data link layer bandwidth, virtual multi-channel transmission mechanism has been achieved with hardware. The network supports a maximum of four virtual channels for each physical data link. Time slots can be dynamically assigned to each virtual channel. The length of each time slot can also be dynamically selected based on the length of each data packets. Zero wait time has been achieved for the switching between different virtual channels. The relationship between the network performance and the number of virtual channels has also been analyzed in this paper.
In this paper, high-density and large-capacity parallel data reliable transmission has been accomplished in high electro-magnetic interference environments via virtual- parallel optical transmission technique. Through time division multiplexing (TDM), all the parallel data signals and control signals are converted to high-speed serial data stream. Each bit is transmitted in a time slot during a frame period Thus, the parallel signals can be transmitted using only one opto-electronic device. Each optical transmission channel consists of two optical fibers, can achieve full-duplex transmission of 24 bits parallel signals. The maximum frame rate is 75 MHz. This data transmission card can be expanded to 6 channels, has a maximum data throughput of 15 Gbps. This optical data transmission link can work properly for a wide range of supply voltage. When the supply power voltage varied from 4.2 to 7.0 volts, the bit error rate (BER) is still below 10E-12.
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