Fabrication of Beta-Barium Borate Sensing Head for Non-Invasive Measurement of Fluidic Concentration Variations.

In this study, a beta-barium borate sensing head (BBO-SH) was fabricated and evaluated for the measurements of fluidic concentration variations by using a non-invasive technique. The BBO-SH could be coupled to a fluidic container through thin interlayer water in a heterodyne interferometer based on the phase interrogation. To ensure the sensing head's stability, the package of BBO-SH uses the prism and the coverslip bounded with UV glue, which can resist environmental damage due to moisture. After each use, the sensing head could be easily cleaned. The sensitivity of the BBO-SH remained stable after repeated measurements over a period of 139 days. Finally, the achievable measurement resolutions of the concentration and refractive index are 52 ppm and 1 × 10-6 RIU, respectively, for the sodium chloride solution. The achievable measurement resolutions of the concentration and refractive index were 55 ppm and 8.8 × 10-7 RIU, respectively, for the hydrochloric acid solution.

Low-Cost Polyethylene Terephthalate Fluidic Sensor for Ultrahigh Accuracy Measurement of Liquid Concentration Variation.

A low-cost polyethylene terephthalate fluidic sensor (PET-FS) is demonstrated for the concentration variation measurement on fluidic solutions. The PET-FS consisted of a triangular fluidic container attached with a birefringent PET thin layer. The PET-FS was injected with the test liquid solution that was placed in a common path polarization interferometer by utilizing a heterodyne scheme. The measured phase variation of probe light was used to obtain the information regarding the concentration change in the fluidic liquids. The sensor was experimentally tested using different concentrations of sodium chloride solution showing a sensitivity of 3.52 ×104 deg./refractive index unit (RIU) and a detection resolution of 6.25 × 10-6 RIU. The estimated sensitivity and detection resolutions were 5.62 × 104 (deg./RIU) and 6.94 × 10-6 RIU, respectively, for the hydrochloric acid. The relationship between the measured phase and the concentration is linear with an R-squared value reaching above 0.995.

Reflection-induced linear polarization rotation and phase modulation between orthogonal waves for refractive index variation measurement.

An optical phase interrogation is proposed to study reflection-induced linear polarization rotation in a common-path homodyne interferometer. This optical methodology can also be applied to the measurement of the refractive index variation of a liquid solution. The performance of the refractive index sensing structure is discussed theoretically, and the experimental results demonstrated a very good ability based on the proposed schemes. Compared with a conventional common-path heterodyne interferometer, the proposed homodyne interferometer with only a single channel reduced the usage of optic elements.

Homodyne chiral polarimetry for measuring thermo-optic refractive index variations.

Novel reflection-type homodyne chiral polarimetry is proposed for measuring the refractive index variations of a transparent plate under thermal impact. The experimental results show it is a simple and useful method for providing accurate measurements of refractive index variations. The measurement can reach a resolution of 7×10-5.

A comparison between two heterodyne light sources using different electro-optic modulators for optical temperature measurements at visible wavelengths.

In this paper we have successfully demonstrated a z-propagating Zn-indiffused lithium niobate electro-optic modulator used for optical heterodyne interferometry. Compared to a commercial buck-type electro-optic modulator, the proposed waveguide-type modulator has a lower driving voltage and smaller phase variation while measuring visible wavelengths of 532 nm and 632.8 nm. We also demonstrate an optical temperature measurement system using a homemade modulator. The results show that the measurement sensitivities are almost the same values of 25 deg/°C for both the homemade and the buck-type modulators for a sensing light with a wavelength of 632.8 nm. Because photorefractive impacts are essential in the buck-type modulator at a wavelength of 532 nm, it is difficult to obtain reliable phase measurements, whereas the stable phase operation of the homemade one allows the measurement sensitivity to be improved up to 30 deg/°C with the best measurement resolution at about 0.07 °C for 532 nm.

Dual-channel optical phase measurement system for improved precision.

Developments and applications of a dual-channel phase measurement system are being proposed and experimentally studied by utilizing an optical homodyne technique. In this measurement system, the phase modulation was adopted by using a near-stable Zn-indiffused lithium niobate phase modulator. The proposed method was successfully applied on the simultaneous measurements of the phase-retardation difference between a transmitted light and a reflected light after passing through a nonpolarization beam splitter. The measured stability of the phase-retardation difference was approximately 0.0013 rad.

An optical homodyne technique to measure photorefractive-induced phase drifts in lithium niobate phase modulators.

In this paper, we develop an optical measurement system with capabilities of phase unwrapping, real-time and long-term monitoring for measuring a phase drift caused by photorefractive effects in lithium niobate phase modulators. To extract the phase-drift variations, the measurement setup uses a homodyne interferometer with a phase modulation and a Fast Fourier Transform (FFT) demodulation scheme. The phase-drift characteristics of a traditional Ti-indiffused and a Zn-indiffused phase modulator have been investigated under different applied voltages and throughput powers. These experiments were conducted as a proof-of-concept to demonstrate that the apparatus worked successfully to measure the phase drift of a device in the presence of photorefractive effects. The results indicate that the Zn-indiffused phase modulators have better photorefractive stability than the Ti-indiffused phase modulators.

A novel Zn-indiffused mode converter in x-cut lithium niobate.

A novel Zn-indiffused mode converter has been proposed and experimentally studied in an x-cut/z-propagation lithium niobate at a wavelength of 0.632 mum for the first time. The optimized phase-matching and mode-conversion voltages for maximum conversion are 12 V and -?5 V, respectively. The results show that the proposed mode converter can operate with a stable conversion efficiency of about 99.5% between TM and TE polarizations at a throughput power of 25 muW in a period of 60 min. Moreover, a comparison of optical power-handling stability between the Ti-indiffused and the Zn-indiffused channel waveguides, was explored. The encouraging results indicate that the Zn-indiffused waveguide has better power stability than the Ti-indiffused waveguide. Thus, it is expected that the proposed mode converter will have better stability than the conventional Ti-indiffused ones, especially in the visible wavelength region.