Modified homodyne laser interferometer based on phase modulation for simultaneously measuring displacement and angle.

Many researchers from scientific and industrial fields have devoted their efforts to the laser interferometer, aiming to improve the measurement accuracy and extend the practical applications. Here, we present a modified homodyne laser interferometer based on phase modulation for simultaneously measuring displacement and angle. The active sawtooth wave phase modulation enhances immunity of this interferometer to the environmental fluctuations and laser power drift. Based on polarized optic theory and the sinusoidal measurement retro-reflector, a modified Michelson-type interferometer configuration is designed to simultaneously measure displacement and angle. Phase difference between the reference and measurement interference signals can be obtained using the sawtooth wave phase modulation and zero crossing detection technique, where the real-time displacement and angle values can be derived directly. Experimental results demonstrate our proposed interferometer has good static and dynamic performance.

Sinusoidal Phase-Modulated Angle Interferometer for Angular Vibration Measurement.

Primary angular vibration calibration devices based on laser interferometers play a crucial role in evaluating the dynamic performance of inertial sensing devices. Here, we propose a sinusoidal phase-modulated angle interferometer (SPMAI) to realize angular vibration measurements over a frequency range of 1-1000 Hz, in which the sinusoidal measurement retro-reflector (SMR) and the phase generation carrier (PGC) demodulation algorithm are adopted to track the dynamic angle variation. A comprehensive theoretical analysis is presented to reveal the relationship between demodulation performance of the SPMAI and several factors, such as phase modulation depth, carrier phase delay and sampling frequency. Both the simulated and experimental results demonstrate that the proposed SPMAI can achieve an angular vibration measurement with amplitude of sub-arcsecond under given parameters. Using the proposed SPMAI, the frequency bandwidth of an interferometric fiber-optic gyroscope (IFOG) is successfully determined to be 848 Hz.

All-fiber optic displacement sensing system for an Ilizarov transverse tibial bone transport device.

A single-mode-multimode-single-mode (SMS) optical fiber-based displacement sensing system mounted on an Ilizarov transverse tibial bone transport device for microcirculation reconstruction is reported. Wide-range displacement is approximated as a uniform extension of a spring that is connected to an SMS optical fiber structure acting as the displacement sensor and allowing full displacement characterization. Transmission spectrum changes are measured, providing a displacement range of 24 mm with a sensitivity of $ - {55.42}\;{\rm pm/mm}$-55.42pm/mm and a resolution of 45.2 µm. The experimental results are characterized using a polynomial response curve for measuring the displacement due to transverse distraction of the Ilizarov device. The SMS fiber interrogation system is based on a macrobending fiber edge filter-based ratiometric measurement system. The use of SMS fibers together with the macrobending fiber-based interrogation system eliminates the influence of temperature on the displacement measurement. The implementation of the all-fiber sensing system of this investigation has uniquely facilitated a smart clinical device with a wide displacement range as well as operating in real-time monitoring when attached to the Ilizarov transverse tibial bone transport device. It also means that this fiber-optic sensing device can be made more cost-effective, simpler in construction, and more versatile while providing a high degree of measurement accuracy and resolution.

Multimode-interference-effect-based all-fiber displacement sensing system for an orthopedic Ilizarov apparatus device.

The paper describes a multimode-interference-effect-based single-mode-multimode-single-mode (SMS) fiber optic sensing system for wide-range displacement monitoring on an Ilizarov orthopedic external fixation device. Displacement measurement is implemented as the uniform extension of a spring, which is connected to an SMS optical fiber displacement sensor, allowing full displacement characterization. SMS fiber structures are used together with a macrobending-fiber-based interrogation system to measure temperature perturbation and hence eliminate its effect on the displacement measurement. Transmission spectra are measured, achieving a displacement measurement range of 110 mm with maximum sensitivity of -53 pm/mm and a resolution of 500 µm. The all-fiber sensing system has facilitated a clinical device with a wide displacement range operating in real-time when attached to the Ilizarov apparatus.

Investigation of a novel SMS fiber based planar multimode waveguide and its sensing performance.

A novel, MMI-based all-fiber structure, which consists of two single-mode fibers and a multimode fiber polished on both sides, is described. The light propagation characteristics of this fiber structure, as well as its superior sensing performance, are analyzed theoretically by using the beam propagation method (BPM). This fiber structure demonstrates a significant spectral response to changes of the surrounding refractive index (RI), and the measured results exhibit good agreement with the predicted data. The measured average RI sensitivity is as high as 151.29 nm/RIU over an RI range from 1.3450 to 1.4050, when the polished depth is 30 µm on both sides of the multimode fiber. This fiber structure can be an advantageous platform for various applications, especially for a lab-on-fiber type sensing application.

Highly sensitive displacement sensor based on composite interference established within a balloon-shaped bent multimode fiber structure.

A novel optical fiber displacement sensor based on composite interference established within a balloon-shaped bent multimode (BSBM) fiber structure is described and experimentally demonstrated. The BSBM fiber structure is realized by bending a straight single-mode-multimode-single-mode (SMS) fiber structure into a balloon shape using a length of capillary tube to fix the shape of the structure. Owing to the bend in the multimode waveguide, the original undistorted multimode interference pattern is changed, and an extra Mach-Zehnder interferometer is effectively introduced within the multimode fiber (MMF) section at a suitable bending radius. This established composite interference greatly improves the displacement sensing performance of the SMS fiber structure. A maximum displacement sensitivity of 0.51 dB/µm over the displacement range of 0-100 µm at the operating wavelength of 1564.7 nm is achieved experimentally. Based on its easy fabrication process, low cost, and high measurement sensitivity, the sensor of this investigation could be a realistic candidate in the high-accuracy displacement measurement field.

A Review of Multimode Interference in Tapered Optical Fibers and Related Applications.

In recent years, tapered optical fibers (TOFs) have attracted increasing interest and developed into a range of devices used in many practical applications ranging from optical communication, sensing to optical manipulation and high-Q resonators. Compared with conventional optical fibers, TOFs possess a range of unique features, such as large evanescent field, strong optical confinement, mechanical flexibility and compactness. In this review, we critically summarize the multimode interference in TOFs and some of its applications with a focus on our research project undertaken at the Optoelectronics Research Centre of the University of Southampton in the United Kingdom.

Strain sensor based on gourd-shaped single-mode-multimode-single-mode hybrid optical fibre structure.

A fibre-optic strain sensor based on a gourd-shaped joint multimode fibre (MMF) sandwiched between two single-mode fibres (SMFs) is described both theoretically and experimentally. The cladding layers of the two MMFs are reshaped to form a hemisphere using an electrical arc method and spliced together, yielding the required gourd shape. The gourd-shaped section forms a Fabry-Perot cavity between the ends of two adjacent but non-contacting multimode fibres' core. The effectiveness of the multimode interference based on the Fabry-Perot interferometer (FPI) formed within the multimode inter-fibre section is greatly improved resulting in an experimentally determined strain sensitivity of -2.60 pm/µÎµ over the range 0-1000 µÎµ. The sensing characteristics for temperature and humidity of this optical fibre strain sensor are also investigated.

Simultaneous and independent capture of multiple Rayleigh dielectric nanospheres with sine-modulated Gaussian beams.

This study investigates the propagation properties and radiation forces on Rayleigh dielectric particles produced by novel sine-modulated Gaussian beams (SMGBs) because of the unique focusing properties of four independent light intensity distribution centers and possessing many deep potential wells in the output plane of the target laser. The described beams can concurrently capture and manipulate multiple Rayleigh dielectric spheres with high refractive indices without disturbing each other at the focus plane. Spheres with a low refractive index can be guided or confined in the focus but cannot be stably trapped in this single beam trap. Simulation results demonstrate that the focused SMGBs can be used to trap particle in different planes by increasing the sine-modulate coefficient g. The conditions for effective and stable capture of high-index particles and the threshold of detectable radius are determined at the end of this study.