Jiun-You Lin

Small-angle measurement with highly sensitive total-internal-reflection heterodyne interferometer

In this paper, a high-sensitivity total-internal-reflection (TIR) heterodyne interferometer is proposed for measuring small angles. In the proposed interferometer, a half-wave plate and two quarter-wave plates that exhibit specific optic-axis azimuths are combined to form a phase shifter. When a rhomboid prism is placed between the phase shifter and an analyzer that exhibits suitable transmission-axis azimuth, it shifts and enhances the phase difference of the s- and p-polarization states at double TIR. The enhanced phase difference is dependent on the incident angle; thus small angles can be easily and accurately measured by estimating the phase difference. The experimental results demonstrate the feasibility of this method. Angular resolution and sensitivity levels superior to 1.2×10⁻⁴ deg (2.1×10⁻⁶ rad) and 100 (deg/deg), respectively, were attainable in a dynamic range of 0.5 deg.

Multiport optical circulator by using polarizing beam splitter cubes as spatial walk-off polarizers

Optical circulators are necessary passive devices applied in optical communication systems. In the design of optical circulators, the implementation of the function of spatial walk-off polarizers is a key technique that significantly influences the performance and cost of a device. This paper proposes a design of a multiport optical circulator by using polarizing beam splitter cubes as spatial walk-off polarizers. To show the feasibility of the design, a prototype of a six-port optical circulator was fabricated. The insertion losses are 0.94-1.49 dB, the isolations are 25-51 dB, and return losses are 27.72 dB.

Optical method for measuring optical rotation angle and refractive index of chiral solution.

Based on the phenomena of Brewsters angle and the principles of common-path heterodyne interferometry, we present an optical method for measuring the optical rotation angle and the refractive index of a chiral solution simultaneously in one optical configuration. A heterodyne light beam and a circularly polarized heterodyne light beam are separately guided to project onto the interface of a semicircle glass and a chiral solution. One of the beams is transmitted through the solution, and the other is reflected near Brewsters angle at the interface. Then the two beams pass through polarization components respectively for interference. The phase differences of the two interference signals used to determine the rotation angle and the refractive index become very high with the proper azimuth angles of some polarization components, hence achieving an accurate rotational angle and a refractive index. The feasibility of the measuring method was demonstrated by our experimental results. This method should bear the merits of high accuracy, short sample medium length, and simpler operational endeavor.

Determination of the refractive index and the chiral parameter of a chiral solution based on chiral reflection equations and heterodyne interferometry

This study develops a method for determining the chiral parameter and the refractive index of an isotropic chiral medium using chiral reflection equations and critical angle phenomena. Linearly polarized light propagates back and forth in a parallelogram prism between two parallel compartments with chiral solutions. A beam splitter then divides the light that emerges from the prism into a reflected light beam and a transmitted light beam. The two beams pass through a compensator and an analyzer, respectively, to cause phase compensation and interference of s and p polarizations. The phase difference between the two interference signals are initially optimized by a suitable optical arrangement and subsequently measured by heterodyne interferometry. Additionally, the refractive index of the solution is determined from the critical angle that occurred at the discontinuity of the phase difference between the two interference signals. These results are substituted into derived equations to calculate the chiral parameter. The approach has the merits of both common-path interferometry and heterodyne interferometry.

An alternative design of holographic polarization-selective elements

The feasibility of conventional polarization-selective substrate-mode holograms is usually limited by the finite refractive index modulation strength. Therefore, in this study, a novel design of polarization selective element with a large diffraction angle is proposed based on the coupled-wave theory. The polarization selective element for 632.8nm is fabricated with VRP-M silver-halide recording material. The diffraction efficiencies of s- and p- components are 83% and 5%, and the calculated extinction ratios are 5.58 and 275, respectively. Polarization selective elements fabricated by the proposed method have all the merits of conventional substrate-mode hologram but not limited by the finite refractive index modulation of common recording materials.

Simple method for measuring small wavelength differences

A simple method is presented to determine small wavelength differences based on the dispersion properties of a uniaxial crystal and circularly polarized heterodyne interferometry. A circularly polarized heterodyne light beam is incident on a uniaxial crystal at the Brewsters angle, and the reflected light beam passes through an analyzer for interference. Owing to proper azimuth angles of the transmission axis of the analyzer and the optical axis of the crystal, the variation of the phase difference determined with the heterodyne interferometric technique of the interference signal is significantly enhanced, resulting in an accurate wavelength variation. The feasibility of this method was demonstrated, and the sensitivity of wavelength differences is about 0.001 nm. The proposed approach has a simple structure, straightforward operation, high stability, and high sensitivity.

Measurement of two-dimensional distribution of temperature with surface plasmon resonance

This study proposes a simple method for measuring two-dimensional temperature distributions. Using the significant phase difference between p- and s-polarizations of the reflected light of a surface plasmon resonance (SPR) detector, the variation in the phase difference, which is caused by a variation in the temperature, can be accurately measured by phase-shifting interferometry. Then, by substituting the phase distribution into special derived equation, the temperature distribution can be determined. In order to show the feasibility of this method, different temperature distributions were measured. The measurement resolution is about 0.186°C. Due to the introduced common-path configuration and the high-sensitivity characteristic of surface plasmon resonance, this method should have merits of easy operation, high sensitivity, high accuracy and rapidly measurement.

High sensitivity glucose sensor based on optical heterodyne phase detection

Measurements of glucose concentration are important parts of biochemical analyses. Based on the principles of the common-path heterodyne interferometry, we develop a high sensitivity optical sensor for measuring glucose concentration. A heterodyne light beam after transmitted through a glucose solution passes through some polarization components for interference. The phase difference determined with heterodyne interferometric technique of the interference signal is greatly enhanced as a result of proper azimuth angles of some polarization components, and a high sensitivity measurement of glucose concentration can be achieved. The feasibility of the measuring method was demonstrated by our experimental results. This optical sensor should bear the merits of high accuracy, short sample medium length, and simpler operational endeavor.

A simple method for measuring the small displacements

In this study, a simple method for measuring the small displacements is presented. When a circularly polarized heterodyne light beam reflected from a mirror is incident into a hemi-spherical prism and is reflected at the base of the prism. Then the reflected light beam passes through an analyzer for interference. With properly chosen azimuth angles of transmission axis of the analyzer, the phase difference between s- and p- polarized light is sensitive to the incident angle near the internal reflection polarization angle. The phase difference can be accurately measured with the heterodyne interferometry. The small displacement of the mirror causes a small variation of incident angle and a phase change. Therefore, substituting the phase difference into special derived equations; the small displacement can be determined. The proposed method has advantages of common-path configuration and heterodyne interferometry.