Ju-Yi Lee

Optical heterodyne laser encoder with sub-nanometer resolution

This paper presents a novel laser encoder for sub-nanometer displacement measurement. It is based on optical heterodyne interferometry and two sets of conjugate optics with a symmetric and quasi-common-path optical configuration. It offers displacement measurements of high stability, high resolution. 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 detect a displacement variation down to sub-nanometer range.

Two-dimensional displacement measurement by quasi-common-optical-path heterodyne grating interferometer

A method based on a specific quasi-common-optical-path (QCOP) configuration for two-dimensional displacement measurement is presented. The measurement system consists of a heterodyne light source, two-dimensional holographic grating, specially designed set of half wave plates, and lock-in amplifiers. Two measurement configurations, for single and differential detection, are designed. The sensitivity, resolution and nonlinear phase error of the differential detection type are better than those of the single detection type. The experimental results demonstrate that the QCOP interferometer has the ability to measure two-dimensional displacement while maintaining high system stability.

Quasi-common-optical-path heterodyne grating interferometer for displacement measurement

A novel heterodyne grating interferometer based on a quasi-common-optical-path design is proposed for displacement measurement. The quasi-common-optical-path design relies on the phase shift between the zeroth and first diffraction grating orders which have been rotated in polarization using a half-wave plate. We achieved a measurement resolution better than 3 nm with a system stability of less than 14 nm over 1 h. We discussed the performances of the system addressing the effect of dominant errors, namely grating pitch, frequency mixing, polarization mixing and polarization?frequency mixing. While the theoretically quasi-common-optical-path heterodyne grating system allows for sub-nanometer resolution, we found that the measurement resolution here is limited by the displacement stage. Relying on heterodyne interferometric phase measurement combined with quasi-common-optical configuration, the proposed and demonstrated method has the advantages of high measurement resolution, relatively straightforward operation and high stability.

Polarization-interferometric surface-plasmon-resonance imaging system

A two-dimensional phase-detection system for a surface-plasmon-resonance sensor is presented. The sensor utilizes polarization interferometry to detect phase differences between the s and p polarizations. We successfully detected a spatial phase-difference variation, resulting from the biomolecular interactions, of less than 1 x 1 mm(2). The phase stability demonstrated in the experimental results was approximately 0.09 degrees, and the corresponding change in the refractive index detection limit was approximately 4.3 x 10(-6). The common-optical-path configuration of the proposed method allowed us to reduce disturbances from ambient conditions. Furthermore, this method is capable of real-time array detection.

Displacement measurement using a wavelength-phase-shifting grating interferometer

A grating interferometer based on the wavelength-modulated phase-shifting method for displacement measurements is proposed. A laser beam with sequential phase shifting can be accomplished using a wavelength-modulated light passing through an unequal-path-length optical configuration. The optical phase of the moving grating is measured by the wavelength-modulated phase-shifting technique and the proposed time-domain quadrature detection method. The displacement of the grating is determined by the grating interferometry theorem with the measured phase variation. Experimental results reveal that the proposed method can detect a displacement up to a large distance of 1 mm and displacement variation down to the nanometer range.

Heterodyne grating interferometer based on a quasi-common-optical-path configuration for a two-degrees-of-freedom straightness measurement

We present a heterodyne grating interferometer based on a quasi-common-optical-path (QCOP) design for a two-degrees-of-freedom (DOF) straightness measurement. Two half-wave plates are utilized to rotate the polarizations of two orthogonally polarized beams. The grating movement can be calculated by measuring the phase difference variation in each axis. The experimental results demonstrate that our method has the ability to measure two-DOF straightness and still maintain high system stability. The proposed and demonstrated method, which relies on heterodyne interferometric phase measurement combined with the QCOP configuration, has the advantages of high measurement resolution, relatively straightforward operation, and high system stability.

Measurement of in-plane displacement by wavelength-modulated heterodyne speckle interferometry

The use of wavelength-modulated light incorporated into an optical-path-difference speckle interferometer is demonstrated as a heterodyne technique for measuring the in-plane displacement of a rough object. The in-plane displacement can be determined from the measured phase variation of the heterodyne speckle signal. We also improved the optical configuration to create a high-contrast interference pattern. Experimental results reveal that the proposed method can detect displacement up to a long range of 220 μm and displacement variation down to the nanometer range. Moreover, the sensitivity can reach up to 0.8°/nm. The performance of the system is discussed.

Heterodyne common-path grating interferometer with Littrow configuration.

This paper presents a heterodyne common-path grating interferometer with Littrow configuration (HCGIL). The HCGIL can effectively overcome environmental disturbance effect and the DC offset and the amplitude variation of the measurement signals. Experimental results match well with the HP5529A results for long-range measurements. Results also show that the estimated measurement resolution is 0.15 ± 0.027 nm. The stability of the HCGIL is -0.41 ± 0.23 nm. Therefore, the HCGIL has potential for subnanometer resolution and long-range applications.

Reusable glucose fiber sensor for measuring glucose concentration in serum

We demonstrate a glucose fiber sensor for measuring glucose concentration in serum. High resolution and rapid measurement are achieved through the integration of highly selective enzymes and heterodyne interferometry. The best resolution and response time obtained are 0.14 mg/dL and 1.3 s, respectively. The stability of the sensor is also verified by investigating the initial phase variation. Experimental results show that the fiber sensor can be reused more than 10 times.

Heterodyne interferometer for measurement of in-plane displacement with subnanometer resolution

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.