A grating-based optical readout method for microcantilever biosensor

For measuring the deflections of the microcantilever biosensor, a reflective grating microcantilevers based on SOI were designed and fabricated, a high precision optical readout approach based on diffraction spectrum balancing feedback control was presented. The diffraction spectrum image was collected by a 12-bit digital area array monochrome CCD. According to the sum gray value of the image which subtracted each other at the balancing position and bending position to control a high precision motorized rotation stage revolve make the sum gray value remained in the balancing position always, then the motorized rotation stage revolving angle is just the cantilever bend angle. The resolution of motorized rotation stage is 35 × 10⁻⁶ deg, the system practical measurement resolution is 1 × 10⁻⁴ deg, that is to say, for a length of 250 μm microcantilever, the tip measure resolution is up to 0.043 nm. Measurement results clearly demonstrate that this reflective grating microcantilever biosensor and this read out method have a great potential for biological and chemical applications.     

Correspondence between two types of rating indices for the heavy weight floor impact sound insulation of residential buildings

Of the two types of rating indices for the heavy weight floor impact sound insulation, the method of utilizing a rubber ball impact source combined with A-weighted sound level and the method utilizing a tire impact source combined with L-rating curve, the advantage of the former has been reported. In order to extend the advantage, the possibility was studied of estimating the rating utilizing the rubber ball impact source, based on the measurement results utilizing the tire impact source, especially for the case of a double leaf wooden floor. The correlation between the indices is not high enough to estimate one of them directly from the other with an accuracy not incorrectly estimating the rating grade of 5 dB step. The use of predictor variables, such as the special specifications of the double leaf wooden floor, for example, the use of sound insulation sheet, and the floor impact sound levels in the 31.5-Hz, 63-Hz and 125-Hz bands, is possibly able to increase the accuracy. Three principal types of multiple regression equation were derived through the analysis of measurement results in existing residential buildings.     

A quick algorithm of exposure distribution for fabrication of micro-optical structures

An approximate algorithm of exposure distribution on photoresist for the case of large exposure dose is obtained on the basis of the algorithm reported in [X. Dong, C. Du, S. Li, C. Wang, Y. Fu, Control approach for form accuracy of microlenses with continuous relief, Opt. Express 13 (2005) 1353-1360] via analyzing a PAC concentration distribution inside the photoresist. We analyzed the fabrication errors of the micro-optical structures which are caused by the approximate algorithm. The relief form error originating from the measurement errors of characteristics parameters of the photoresist is analyzed as well. A valid approach for a quick and accurate design of the exposure distribution is provided accordingly. As an example, a saw-tooth grating with 75 μm relief depth was designed and fabricated so as to verify the new algorithm. Our measurement results show that root mean square (rms) value is less than 0.81 μm. The quick algorithm can satisfy the requirements of micro-optical systems for practical applications.     

Heterodyne interferometer for displacement measurement with amplitude quadrature and noise suppression

The high precision displacement measurement in nanoscale is crucial to many applications. We present a heterodyne interferometry with differential phase to amplitude conversion scheme for displacement measurement in nanoscale. In this approach, the differential phase introduced by the displacement is converted into the amplitudes of heterodyne signals in quadrature. Meanwhile, the heterodyne signals in phase quadrature are also achieved so that the displacement can be determined from the amplitude ratio of the quadrature signals, and the direction of displacement can be determined from the phase quadrature. Since the differential phase to quadrature amplitude conversion is achieved through the optical addition and subtraction by polarization tuning, which are based on differential detection concept. Thus the proposed method benefits from the features of differential detection with common phase noise and correlated amplitude noise rejection and that of quadrature detection with real time and wide dynamic range of phase measurement. To demonstrate the capability of proposed method in differential phase measurement, we measure the displacement drove by a commercially available PZT pusher and found close agreement between the experiment and the theory. The experimental evidence of noise suppression is also found with spectral measurements, which demonstrates the resolution of displacement measurement at 60 pm and minimum detectable differential phase of 5.6 × 10⁻⁶ rad/ over 50 kHz.     

Signal processing efficiency of Doppler global velocimetry with laser frequency modulation

Novel Doppler global velocimeters using laser frequency modulation can optically measure flow velocity fields and offer promising perspectives, but so far unknown limits, for achieving low measurement uncertainties. One approach, e.g. is based on sinusoidal frequency modulation and a harmonic signal analysis. In order to determine the minimum achievable measurement uncertainty, the known theorem of Cramér and Rao is applied to a derived signal model, initially excluding the harmonic signal analysis. For a typical scattered light power of 1 nW and a desired temporal resolution of 16 ms, the calculated minimum velocity standard deviation amounts to 0.02 and 0.06 m/s for signal dependent (quantum shot) noise and signal independent (thermal and dark current) noise, respectively. It is subsequently investigated, how efficient the harmonic signal analysis extracts the Fisher information content. The ratio of the Cramér-Rao lower bound and the estimated measurement uncertainty, where the signal processing is taken into account, was found to be >75% in terms of standard deviations in the entire measurement range of about . For the challenge of measuring velocity fields in turbomachine flows (requirements: 5 kHz measurement rate, ≤1% statistical error, velocities (50-240) m/s), the presented results indicate a necessary minimum scattered light power of 1.5 nW, which seems feasible.     

Acceleration response spectrum for predicting floor vibration due to occupant walking

Annoying vibrations caused by occupant walking is an important serviceability problem for long-span floors. At the design stage the floor?s structural arrangement may frequently change to cater for the owner?s varying requirements. An efficient and accurate approach for predicting a floor?s acceleration response is thus of great significance. This paper presents a design-oriented acceleration response spectrum for calculating a floor?s response given the floor?s modal characteristics and a specified confidence level. 2204 measured footfall traces from 61 test subjects were used to generate 10 s peak root-mean-square acceleration response spectra, on which a piecewise mathematical representation is based. The proposed response spectrum consists of three main parts: the first harmonic plateau ranging from 1.5 to 2.5 Hz, the second harmonic plateau ranging from 3.0 to 5.0 Hz and the descending part going with frequencies from 5.0 to 10.0 Hz. The representative value of each plateau and the mathematical representation for the descending curve were determined statistically for different confidence levels. Furthermore, the effects of factors, such as floor span, occupant stride length, higher modes of vibration, boundary conditions and peak acceleration response, on the proposed spectrum have been investigated and a modification measure for each factor is suggested. A detailed application procedure for the proposed spectrum approach is presented and has been applied to four existing floors to predict their acceleration responses. Comparison between predicted and field measured responses shows that the measured accelerations of the four floors are generally close to or slightly higher than the predicted values for the 75 percent confidence level, but are all lower than the predicted values for the 95 percent confidence level. Therefore the suggested spectrum-based approach can be used for predicting a floor?s response subject to a single person walking.     

An absolute phase to world coordinates method for the defocusing structured light shape measurement system

This paper proposes a flexible calibration method for the defocusing structured light three-dimensional (3D) imaging system. Neither a high accuracy translation stage nor the parameters of the projector is required. Therefore the method is more flexible in many practical applications. World coordinates for calibration are obtained based on the method of coordinates from known plane. The monotonic nonlinear relationships between the absolute phase and each world coordinate have been investigated. Different from other methods, in our method, the 3D shape is directly recovered by the absolute phase to world coordinates method. Experimental results show that, when polynomial curve fitting methods are used, the root-mean-squared (RMS) error for the flat plate reconstruction is less than 0.12 mm, and the measurement error of 3D points is less than −0.34%. Furthermore, when comparing the measurement results of our method with the method of coordinates from known plane based on camera calibration, the relative error is less than −0.05%. Therefore, camera calibration is considered as the major error source.     

Fabry-Perot interference-based fiber-optic sensor for small displacement measurement

A simple fiber-optic sensor based on Fabry-Perot interference for small displacement measurement is investigated both theoretically and experimentally. A broadband light source is coupled into a Fabry-Perot cavity formed by the surfaces of a sensing fiber end and the measured object. The interference signals from the cavity are reflected back into the same fiber. A small displacement via changes in cavity length can be obtained by measuring the wavenumber spacing of the interference fringes. The experimental data meet with the theoretical values very well. Given the light source bandwidth of 40 nm and the initial distance of 30 μm, the proposed displacement sensing system could achieve high resolution measurement of 16 nm.     

Optical beams in sub-strongly non-local nonlinear media: A variational solution

Discussed is the propagation of optical beams in non-local nonlinear media modelled by 1 + 1D non-local nonlinear Schrödinger equation (NNLSE). In the sub-strongly non-local case, an approximate analytical solution is obtained for an arbitrary response function by a variational approach. Described by a combination of the Jacobian elliptic functions, the solution is periodic, and its period depends on not only the input power but also the initial beam width, which is confirmed by the numerical simulation of the NNLSE.     

Computer modeling of a large-area integrating sphere uniform radiation source for calibration of satellite remote sensors

To meet the pre-launch radiometric calibration requirements of large field of view (FOV) imaging remote sensors, a large-area integrating sphere uniform radiation source (ISURS) based on a 1600 mm diameter internally illuminated integrating sphere with a 620 mm diameter exit port was designed. The software TracePro based on ray-tracing method was applied to computer modeling of the ISURS. It is shown that the angle of internal radiation source from the center of the sphere is an important factor affecting the spatial radiance uniformity at exit port. Taking this factor into account, the model established is able to obtain the important characteristics of the sphere source. With the characteristics obtained, the ISURS was manufactured and its optical parameters were measured. The measurement result of the spatial radiance uniformity of the large-area ISURS was 99.19%. There is a discrepancy of 0.12% between measured and simulated results. It is demonstrated that the method used and the model established can increase the efficiency of designing large-area sphere radiation source.     

Optimisation of axially segmented liners for aeroengine broadband noise

A practical two-stage method for optimising an acoustic liner divided into axial segments for aeroengine broadband noise is presented. The principles are explained based on a three segment design but extension to more segments is straightforward. Initially, the optimisation focuses on the material properties of the individual segments. The second stage determines the optimum axial segment lengths and the optimum permutation of segments along the duct by evaluating the fully scattered acoustic field. This method is deployed to optimise an absorber for a broadband source noise of bandwidth 900 Hz-1.8 kHz. The axial order of the segments is found to have a dramatic influence on the optimum axial segment lengths. In the case study, comparisons with optimised uniform liners over this frequency range demonstrate only a small noise reduction. A simple optimisation that neglects scattering between axial segments significantly overestimates the available attenuation and provides a poor estimate of the optimum segment lengths.     

Photonic instantaneous measurement of microwave frequency using fiber Bragg grating

A photonic approach to realizing instantaneous measurement of microwave frequency based on optical monitoring using a fiber Bragg grating (FBG) is proposed and demonstrated. In the approach, a frequency-unknown microwave signal is modulated on an optical carrier in a Mach-Zehnder modulator biased at the minimum transmission point. After detecting the transmission and reflection optical powers at the output of the FBG, the microwave frequency can be determined according to the value of transmission-to-reflection power ratio, due to the fixed relationship between the microwave frequency and the power ratio. A proof-of-concept experiment has been performed, which demonstrates that a measurement resolution of ±0.08 GHz over a 10 GHz measurement bandwidth is achieved. The measurement performance in terms of resolution is better than previously reported results.     

Weak solutions for partial differential equations with source terms: Application to the shallow water equations

Weak solutions of problems with m equations with source terms are proposed using an augmented Riemann solver defined by m + 1 states instead of increasing the number of involved equations. These weak solutions use propagating jump discontinuities connecting the m + 1 states to approximate the Riemann solution. The average of the propagated waves in the computational cell leads to a reinterpretation of the Roe’s approach and in the upwind treatment of the source term of Vázquez-Cendón. It is derived that the numerical scheme can not be formulated evaluating the physical flux function at the position of the initial discontinuities, as usually done in the homogeneous case. Positivity requirements over the values of the intermediate states are the only way to control the global stability of the method. Also it is shown that the definition of well-balanced equilibrium in trivial cases is not sufficient to provide correct results: it is necessary to provide discrete evaluations of the source term that ensure energy dissipating solutions when demanded. The one and two dimensional shallow water equations with source terms due to the bottom topography and friction are presented as case study. The stability region is shown to differ from the one defined for the case without source terms, and it can be derived that the appearance of negative values of the thickness of the water layer in the proximity of the wet/dry front is a particular case, of the wet/wet fronts. The consequence is a severe reduction in the magnitude of the allowable time step size if compared with the one obtained for the homogeneous case. Starting from this result, 1D and 2D numerical schemes are developed for both quadrilateral and triangular grids, enforcing conservation and positivity over the solution, allowing computationally efficient simulations by means of a reconstruction technique for the inner states of the weak solution that allows a recovery of the time step size.     

Critical power for self-focussing of a femtosecond laser pulse in helium

The critical power for self-focussing of a femtosecond laser pulse in helium has been measured using the moving focus method. The experimental value is (1 atm) ∼268 GW. Using this value, the nonlinear refractive index is inferred to be  ∼ 3.6 × 10^-21 cm²/W. In addition, the plots of the electron densities versus energy and pressure have also been used to determine the critical power of helium, based on the intensity clamping of the filamentation process. The value agrees well with the one by the moving focus method.     

High-power multi-mode laser to single-mode pump conversion

A novel pump-sharing module for multi-channel amplifiers based on integration of high-power multimode semiconductor lasers and planar waveguide circuits is proposed. The feedback-free modules are designed for optimum coupling, throughput and power uniformity on silicon using BPM method and fabricated via the sol-gel process of photo patternable precursors. Modal properties of the multimode lasers are considered by studying spectrum and spatial distribution of laser output power at different temperatures. Employing an 1500 mW 980 nm multimode laser (TE polarized), via lens and Butt coupling up to 1250 mW of laser output is coupled into the multimode channel waveguides, which are tapered and branched to four single mode waveguides. The measured pump power from splitter outputs, randomly polarized, exceeds 600 mW. At constant temperatures ranging from 22 °C to 30 °C, the pump-sharing modules exhibit good stability with a power uniformity of <0.5 dB over hours.     

A combined multiple-SLED broadband light source at 1300 nm for high resolution optical coherence tomography

We demonstrate a compact, inexpensive, and reliable fiber-coupled light source with broad bandwidth and sufficient power at 1300 nm for high resolution optical coherence tomography (OCT) imaging in real-time applications. By combining four superluminescent diodes (SLEDs) with different central wavelengths, the light source has a bandwidth of 145 nm centered at 1325 nm with over 10 mW of power. OCT images of an excised stage 30 embryonic chick heart acquired with our combined SLED light source (<5 μm axial resolution in tissue) are compared with images obtained with a single SLED source (∼10 μm axial resolution in tissue). The high resolution OCT system with the combined SLED light source provides better image quality (smaller speckle noise) and a greater ability to observe fine structures in the embryonic heart.     

Thermal simulation of InP-based 1.3 μm vertical cavity surface emitting laser with AsSb-based DBRs

In this paper, the thermal analysis of double-intracavity tunnel-junction vertical cavity surface emitting laser is theoretically performed using simulation software PICS3D which self-consistently combines 3D simulation of carrier transport, self-heating and optical wave-guiding. Excellent agreement between simulation and measurement is obtained by careful adjustment of material parameter in model. The temperature distribution of the device is obtained at 20 °C and 6o °C stage temperature. Quantum well maximum temperature for operating device is in very good agreement with experimental results.Simulation results show that Joule heating is the main heat source in device. Vertical electron escape into Separate Confinement Heterostructure causes thermal power roll-off. Self-heating and optical reductions are the triggering mechanisms behind the leakage current. Laser design variations are shown to allow a significant increase in the maximum output power. This optimized structure can also enhance the stimulated recombination rate and decrease the Auger recombination rate.     

Proposal for nonlinear refractive index measurement using spectral ratio in modulated OFRR dynamics

A novel method for measuring the nonlinear refractive index of an optical fiber using a spectral ratio between the modulation frequency and a harmonic component in a modulated optical fiber ring resonator (OFRR) is proposed. The spectral ratio between the modulation frequency and the 2nd-harmonics generated by phase-modulation through the OFRR is increased with increasing the input light power and has peaks above 5 W input power, however, the peaks was shifted to the lower input power below 1 W by averaging taken into account of the phase distribution. A experimental setup consisted of an OFRR system and an Ar-laser as a pump light source was used to determine the nonlinear refractive index of an optical fiber. In the experimental results, the peaks of the spectral ratio as a function of the input power was found out at 0.8 W and 0.45 W of the input power corresponding to the input source line at 488.0 nm and 514.5 nm, respectively. The profile was similar to that obtained by the simulation and the nonlinear refractive index of a optical fiber was determined as 1.0 × 10⁻²² m²/V² by a relationship between the input power giving the peak and the nonlinear refractive index.     

Three-dimensional profile stitching based on the fiducial markers for microfluidic devices

Profile acquisition of microfluidic devices is a challenging task due to the competing requirements of both large field of view (FOV) and high-resolution. One strategy for obtaining such measurement is linking or stitching high-resolution profiles, possibly from multiple instruments, into a large FOV profile. As opposed to current stitching techniques relying on precise control and measurement of the translation of the sample stage, our approach presented in this paper takes advantage of the overlapping of fiducial markers, to align and stitch the separately measured profiles of a device. This method allows three-dimensional profiles transformed in six degrees of freedom, so that the pitch, roll and yaw among measurements are compensated, and stitching can be processed in both in-plane and out-of plane directions. Measurements of microfluidic channels recorded by an atomic force microscope and a white-light interferometer are stitched with accuracies evaluated to be 0.086 μm and 0.094 μm, respectively. Stitching experiments for large-scale profile gets an accuracy of 0.047 μm. Special form of stitching for profiles acquired by different tools, i.e. key parts of a device profile measured by a small FOV high-resolution instrument are stitched into a large FOV low-resolution profile by another instrument, is also carried out with an accuracy of 0.224 μm.     

Long distance real-time measurement of multi-points micro-vibration in region by digital holography

Many applications require micro-vibration measurement, especially multi-points detection at long distance in real-time. In this paper, a micro-vibration measurement approach based on digital holographic interferometry is proposed for middle-low frequency detection. It can be used to monitor irregular frequency/amplitude vibration in selected region over 10 m away simultaneously and synchronously. A series of experiments were conducted including real-time measurement of 300 Hz, 1 kHz, 2 kHz and 3 kHz constant frequency/amplitude periodic vibration, precision and frequency response tests with calibration of LDV, 1 kHz irregular amplitude vibration, irregular frequency/amplitude vibration as well as the real-time measurement and simultaneous display of multi-points vibration. The experimental results demonstrate the feasibility of the proposed method and reveal its unique advantages.