The lack of compact and low-cost multi-comb sources has been a hindrance to the development of multi-comb metrology. The multidimensional multiplexing, a new multi-comb generation method, gives consideration to both comb quantity and spectral bandwidth and thus attracts extensive attentions. In this paper, a subring-wavelength multidimensional multiplexing scheme has been proposed. Four optical frequency combs with spectral bandwidths of at least 1.3 nm have been simultaneously generated in one integrated dual-ring mode-locked laser. A dual-ring structure of optical path separation is constructed for the subring multiplexing, while wavelength-dependent spectral filters are made up for the wavelength multiplexing. With necessary adjustment of both the spectral filters and the net-gain balance between subrings, cooperative operation of multiplexing between the two dimensions has implemented the subringwavelength multidimensional multiplexing. In this case, quadruple combs are detected with stable intensity. And the bandwidths of the generated combs are up to 2.8 nm, broader than the schemes with pure wavelength-dimensional multiplexing. Based on the previous research of polarization-wavelength multidimensional multiplexing, this work has proved the extendibility of multidimensional multiplexing schemes. We are convinced that multiplexing of triple or more dimensions could be further developed, promoting potential multi-comb applications.
The resolution of optical microscopy fundamentally limited by diffraction is at best 200 nm. Super-resolution structured illumination microscopy (SR-SIM) provides an elegant way of overcoming the diffraction limit in conventional widefield microscope by superimposing a grid pattern generated through interference of diffraction orders on the specimen while capturing images. The use of non-uniform illumination field “shift” high specimen frequencies which are out-ofband into the pass-band of the microscope through spatial frequency mixing with the illumination field. Therefore the effective bandwidth of SR-SIM is approximately twice as conventional microscopy, corresponding to a 2-fold resolution enhancement, if the difference between excitation and emission wavelength is ignored. However, such a wide-field scheme typically can only image optically thin samples and is incompatible with multiphoton processes. In this paper, we propose a Super-resolution scanning scheme with virtually structured illumination, utilizes detection sensitivity modulation on line by programming or off line by numerical processing together with temporally cumulative imaging, the excitation intensity is constant while capturing images. In this case a nondescanned array detector such as CCD camera is needed. When combined with multiphoton excitation, this scheme can image thick samples with threedimensional optical sectioning and much improved resolution.
In this paper, a design of a novel thermo-structure for measuring thermal drift of optics in a next generation interferometer is presented. The novel thermo-structure is used to change the temperature of interferometer under test (IUT) by radiation since the measurement is operated in vacuum to exclude the affect from air. Besides, the thermo-structure is made of multilayers, intergrated with thermo electric coolers as the source of heat, which can provide a uniform temperature field. In addition, the thermo-structure can also protect the IUT from disturbance of environmental radiation. Performance of the system is evaluated by finite element analysis and simulation results show that it can achieve a uniform temperature field which temperature difference is less than 0.02°C and reduce perturbation of environmental radiation from 2°C down to 0.03°C.
In this paper, the quadrupole electromagnetic tweezer installed in a fluorescent microscope was developed for the purpose of achieving precise control of magnetic microspheres’ motion trajectory. The key technologies of magnetic microsphere control and positioning by such quadrupole magnetic tweezers were systematically studied. An electromagnetic quadrupole magnetic tweezer system was designed and constructed, a current-magnetic force model of the quadrupole magnetic tweezer was established, and the magnetic force-current inverse force model was derived and simplified. A fluorescence microscopy imaging system was set up and the related program design was completed. The position of magnetic fluorescent microspheres was monitored by a high-speed CCD with sampling frequency of 200 Hz. A proportional-integral closedloop feedback controller was built up for magnetic microspheres. The experimental results demonstrated that the magnetic force range available at the center of the work area was [-80pN, 80pN]. Besides, magnetic microspheres were tested to possess a displacement resolution up to 400 nm as well as the capacity of moving in any direction in a two-dimensional plane. Based on the obtained results, it is expected that the quadrupole electromagnetic tweezer can function one of the effective devices for evaluation of cell mechanical properties.
This paper reviews ways and means used for reduction or elimination of periodic nonlinearity in heterodyne interferometers. The periodic nonlinearity resulting from polarization mixing or frequency mixing in heterodyne interferometers was modeled into one expression, which included the initial polarization state of the laser source, the rotational alignment of the beam splitter along with different transmission coefficients for polarization states and the rotational misalignment of a receiving polarizer. Three compensation techniques, measuring two orthogonal output signals, Lissajous Compensation and Chu-Ray Algorithm, are described and discussed for reduction of periodic nonlinearity. These algorithms needed at least one fringe of motion or a constant velocity sweep to properly correct the motion. And five types of two spatially separated beam interferometer configurations are described and discussed for elimination of periodic nonlinearity to a picometer level. It is concluded that the main disadvantage of these configurations was their complex architecture with unbalanced long beam paths.
KEYWORDS: Control systems, Control systems design, Mathematical modeling, Device simulation, Systems modeling, Servomechanisms, Error control coding, Inspection, Lithium, Optoelectronics
In order to enable the output response of a precision rapid displacement system to rapidly track the input instructions, and solve the problem of excessive control amplitude in the shortest period of time, deadbeat control with constraint and non-ripple can be used to enhance the system response rate under the constraint. Simulation results show that the steady-state step signal tracking error of a system can reach ±1.5μm under random disturbance, and the step response is rapid and accurate. Compared with general control strategies, this method has a digital control design to increase the speed of response, the fine anti-disturbance ability, and the potential for wide application.
Lateral resolution, as one of the most important parameters of a confocal system, has a direct effect on the measurement
accuracy of a confocal system. The lateral resolution of a confocal system can be improved by introducing a radial
birefringent pupil filter into a differential confocal system. The pupil function of this radial birefringent pupil filter can
be obtained using Jones algorithm and, the angle between the polarization direction of the polarizing film of the lateral
birefringent filter and the optical axis of the birefringent element, and the size of a filter a, can be got by analyzing the
first zero point G. Meanwhile, we analyzed the influence of such factors as the defocusing amount on the lateral response
of the system. It was proved through simulation and experiments that the lateral resolution of a confocal system can be
improved using an optimized radial birefringent pupil filter.
Phase-only pupil-filtering differential confocal measurement, a new approach, is proposed to improve the spatial resolution of a laser probe measurement system (LPMS) for ultraprecise measurement of microstructural workpieces. The proposed approach uses a lateral superresolution pupil filter for sharpening the main lobe of the Airy spot to improve the LPMS lateral resolution and uses the differential confocal measurement method to improve the LPMS axial resolution, thereby improving the LPMS spatial resolution. In addition to improving the spatial resolution, linearity, and antiinterference capability of a confocal measurement system, the proposed approach can be used for bipolar absolute measurement and improvement of the measurement range. Experimental comparison and analyses indicate that the lateral resolution of a phase-only pupil-filtering differential confocal system can be improved by 50% over that of an LPMS with the same parameters, and a lateral resolution better than 0.27 µm and an axial resolution better than 3 nm can be achieved when the wavelength of the incident beam is =632.8 nm, the numerical aperture of the measuring lens is NA=0.65, and uM=4. It is therefore concluded that the phase-only pupil filtering differential confocal measurement method is a new approach to a higher spatial resolution of LPMSs and can be used for ultraprecise measurement of surface microcontours and microdimensions.
Optical sensors have two notable advantages in modern precision measurement. One is that they can be used in nondestructive measurement because the sensors need not touch the surfaces of workpieces in measuring. The other one is that they can strongly resist electromagnetic interferences, vibrations, and noises, so they are suitable to be used in machining sites. But the drift of light intensity and the changing of the reflection coefficient at different measuring positions of a workpiece may have great influence on measured results. To solve the problem, a spectroscopic differential characteristic compensating method is put forward. The method can be used effectively not only in compensating the measuring errors resulted from the drift of light intensity but also in eliminating the influence to measured results caused by the changing of the reflection coefficient. Also, the article analyzes the possibility of and the means of separating data errors of a clinical measuring system for form and position errors of circular workpieces.
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