An enzymatic glucose sensor was fabricated and integrated into a heterodyne refractometer. A heterodyne light source was incident into the sensor which the circular birefringence refractive index of sample was changed as the chemical reaction between glucose oxidase and glucose progressed. Therefore, the phase difference before and after chemical reaction could be measured by a lock-in amplifier with phase-lock technology. The optical configuration and measurement procedures indicated that the alignment of the measurement system was straightforward and that it reduced the misalignment effect. The phase stability of the proposed system was superior to 0.04 deg within 1 min. The glucose sensor can be reused 100 times while retaining favorable performance. The results indicated that the resolutions of the proposed method were ∼1.5 and 1.29 mg / dl for the glucose solution and serum-based sample (SRM 965b), respectively. The calibration curve revealed high linearity within the dynamic range of 0 to 300 mg / dl. Based on these findings, the proposed method has a potential to measure the whole blood glucose concentration for daily monitoring.
The thermal optical properties of a holographic material were measured using total internal reflection heterodyne interferometry. The effective thermal expansion coefficients (ETECs) of the holographic material were determined at various exposure times. Our results showed that the holographic material exhibited a smaller thermal expansion coefficient (TEC) with a longer exposure time than those materials with short exposure times. Thus the diffraction power increased as the exposure time of the holographic material increased. Furthermore, the proposed method provides a highly accurate means of measurement for determination of the TEC. The theoretical ETEC error of the proposed method is better than 1.1×10−7 and the practical ETEC error under the precision measurement conditions can reach to 2.3×10−6.
In this study, we proposed an alternative displacement sensor which constructed with reflection type holographic diffraction grating. To integrate with the truly phase detection heterodyne interferometer, and then the in-plane displacement can be measured with sub-nanometer displacement resolution. The smallest variation can be observed of proposed method is approximately 20 pm and there are no significant differences between proposed method and comparison methods. Furthermore, we evaluated the thermal property of the hologram and showed that the grating pitch variation is smaller than 0.1 nm for temperature variations within 1 °C. According to these findings, we can conclude that the holographic grating can be an alternative displacement sensor with high sensitivity and high stability.
In this paper a novel common-path laser encoder system for nanopositioning is proposed, that can effectively reduce the environmental disturbance at its lowest level. It has promising potential for nanometer resolution and large range
applications. The experimental results of the proposed laser encoder match well with ones of HP5529A for large ranges.
The tested results also show that it has the capability of nanometer scale measurement resolution.
Grating interferometers overcome the diffraction limit of optical waves. They can provide nano-scale displacement
resolution, and will have great potential for nano-metrology applications. The optical configurations of used grating
interferometers are Michelson's type with different paths between the measurement beam and reference beam. Environmental
disturbance can directly enter the measured signals and cannot be essentially slashed. Thus the accuracy of
the used grating interferometers becomes dramatically worse. In this paper, a homodyne common-path grating interferometer
is proposed, that can reduce the environmental disturbance at its lowest level. It has promising potential for
nanotechnology applications. The measurement principle and experimental verifications are done in the work.
A novel laser encoder is presented for sub-nanometer displacement measurement. It is based on optical heterodyne
interferometry and two arms of compensation optics with a symmetric and quasi-common-path optical configuration in
polarization space. High stability and resolution can be achieved for displacement measurements. The theoretical
analysis shows that our method can effectively compensate misalignments resulting from the dynamic runout in laser
encoders. Experimental results reveal that the laser encoder can measure a displacement in subnanometer scale and in
millimeter travel range.
Laser encoders as an optical displacement measurement technique have many applications such as modern
manufacturing, scanning probe microscopy (SPM) and nanomanipulation. For the measurement scale down to the
nanometer range, the stability, sensitivity and tolerance to dynamic runout are the key issues for laser encoders. This
paper presents a novel laser encoder for sub-nanometer displacement measurement. It is based on optical heterodyne
interferometry and conjugate optics with a symmetric and quasi-common-path optical configuration. It offers high
stability, high resolution, low uncertainty displacement measurements and can break through the dynamic runout
problem in laser encoders. Experimental results reveal that the laser encoder can detect a displacement variation of 26
pm, and can thus be applied to sub-nanometer or even picometer positioning.
A novel method of the measurement of in-plane displacement is presented. This method includes a heterodyne light source, a moving grating and a lock-in amplifier for phase measurement. The phase variation which resulted from the grating movement is measured by an optical heterodyne interferometer. The short and long displacement can be measured by our method. The theoretical resolution is about 1 pm. If considering the high frequency noise, the measurement error or resolution is about 0.2 nm yet.
Laser encoders overcome the fundamental resolution limit of geometrical optical encoders by cleverly converting the diffraction limit to phase coded information so as to facilitate nanometer displacement measurement. As positioning information is coded within the optical wavefront of laser encoders, interferometry principles must be adopted in the design of the laser encoders. This effect has posed a very strong alignment tolerance among various components of the whole laser encoder, which in turn imposes a serious user adaptation bottleneck. Out of all alignment tolerances, the head-to-scale alignment tolerance represents the most important hindrance for wider ap-plications. This paper presents a novel laser planar encoder, which serves as a two-dimensional position detection apparatus for precision machine applications and can provide a measuring resolution less than 1 nm. Improving the IBM laser optical encoder design by taking into consideration manufacturing tolerance of various optical components, an innovative two-dimensional laser encoder with ultra high head-to-scale tolerance is presented. It was identified that this newly proposed laser encoder design could avoid the effect of differences in polarization diffraction efficiencies for the 2-D grating scale used. Optimizing the system performance by cleverly designing the profile of the 2-D grating scale was also detailed. The effect of non-uniform temperature field within the head-to-scale range that can yield a nonzero initial phase so as to decrease the system measurement accuracy was analyzed. In addition, misalignment of the polarizers located in front the photodiodes were identified to be the main cause for imperfect Lissajous circles, which may lower the measuring resolution when traditional arctangent algorithm was adopted for circular polarization interferometers. The resolution of the newly developed laser planar encoder was verified by experiments and was found to agree well with the theoretical predictions.
Laser encoders overcome the fundamental resolution limit of geometrical optical encoders by cleverly converting the diffraction limit to phase coded information so as to facilitate nanometer displacement measurement. As positioning information was coded within the optical wavefront of laser encoders, interferometry principles thus must be adopted within the design of the laser encoders. This effect has posed a very strong alignment tolerance among various components of the whole laser encoder, which in turn impose a serious user adaptation bottleneck. Out of all alignment tolerance, the head-to-scale alignment tolerance represents the most important hindrance for wider applications. Improving the IBM laser optical encoder design by taking into the consideration of manufacturing tolerance of various optical components, an innovative linear laser encoder with very high head-to-scale tolerance is presented in this article. Efficiency of the TE/TM incident light beams on the grating scale used are examined theoretically and verified experimentally so as to provide design optimizations of the grating scale. Effect of various grating scale, quartz master or polymer-based grating replicate, is also detailed. Signal processing used to decoded the quadrature based positioning optical signal is also studied. Experimental results that verify the resolutions of the tabletop laser encoder prototype by comparing the decoded quadrature signal and a HP laser interferometer output signal is also presented.
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