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

Optical fibre-based sensors for oil and gas applications.

Oil and gas (O&G) explorations moving into deeper zones for enhanced oil and gas recovery are causing serious safety concerns across the world. The sensing of critical multiple parameters like high pressure, high temperature (HPHT), chemicals, etc., are required at longer distances in real-time. Traditional electrical sensors operate less effectively under these extreme environmental conditions and are susceptible to electromagnetic interference (EMI). Hence, there is a growing demand for improved sensors with enhanced measurement capabilities and also sensors that generates reliable data for enhanced oil and gas production. In addition to enhanced oil and gas recovery, the sensing technology should also be capable of monitoring the well bore integrity and safety. The sensing requirements of the O&G industry for improved sensing in deeper zones include increased transmission length, improved spatial coverage and integration of multiple sensors with multimodal sensing capability. This imposes problems like signal attenuation, crosstalks and cross sensitivities. Optical fibre-based sensors are expected to provide superior sensing capabilities compared to electrical sensors. This review paper covers a detailed review of different fibre-optic sensing technologies to identify a feasible sensing solution for the O&G industry

Microwave Photonics for Distributed Sensing

In the past few years, microwave-photonics technologies have been investigated for optical fiber sensing. By introducing microwave modulation into the optical system, the optical detection is synchronized with the microwave modulation frequency. As a result, the system has a high SNR and thus an improved detection limit. In addition, the phase of the microwave-modulated light can be obtained and Fourier transformed to find the time-of-arrival information for distributed sensing. Recently, an incoherent optical-carrier-based microwave interferometry (OCMI) technique has been demonstrated for fully distributed sensing with high spatial resolution and large measurement range. Since the modal interference has little influence on the OCMI signal, the OCMI is insensitive to the types of optical waveguide. Motivated by the needs of distributed measurement in the harsh environment, in the first part of this paper, several OCMI-based sensing systems were built by using special multimode waveguides to perform sensing for heavy duty applications. Driven by an interest on the high-resolution sensing, in the second part of the paper, I propose a coherence-gated microwave photonics interferometry (CMPI) technique, which uses a coherent light source to obtain the optical interference signal from cascaded weak reflectors. The coherence length of the light source is carefully chosen or controlled to gate the signal so that distributed sensing can be achieved. The experimental results indicate that the strain resolution can be better than 0.6 µε using a Fabry-Perot interferometer (FPI) with a cavity length of 1.5 cm. Further improvement of the strain resolution to the 1 nε level is achievable by increasing the cavity length of the FPI to over 1m. The CMPI has also been utilized for distributed dynamic measurement of vibration by using a new signal processing method. The fast time-varying optical interference intensity change induced by the sub-scan rate vibration is recorded in the frequency domain. After Fourier transform, distinctive features are shown at the vibration location in the time domain signal, where the vibration frequency and intensity can be retrieved. The signal processing method supports vibration measurement of multiple points with the measurable frequency of up to 20 kHz

Microfabricated tactile sensors for biomedical applications: a review

During the last decades, tactile sensors based on different sensing principles have been developed due to the growing interest in robotics and, mainly, in medical applications. Several technological solutions have been employed to design tactile sensors; in particular, solutions based on microfabrication present several attractive features. Microfabrication technologies allow for developing miniaturized sensors with good performance in terms of metrological properties (e.g., accuracy, sensitivity, low power consumption, and frequency response). Small size and good metrological properties heighten the potential role of tactile sensors in medicine, making them especially attractive to be integrated in smart interfaces and microsurgical tools. This paper provides an overview of microfabricated tactile sensors, focusing on the mean principles of sensing, i.e., piezoresistive, piezoelectric and capacitive sensors. These sensors are employed for measuring contact properties, in particular force and pressure, in three main medical fields, i.e., prosthetics and artificial skin, minimal access surgery and smart interfaces for biomechanical analysis. The working principles and the metrological properties of the most promising tactile, microfabricated sensors are analyzed, together with their application in medicine. Finally, the new emerging technologies in these fields are briefly described

Fiber Bragg Gratings as e-Health Enablers: An Overview for Gait Analysis Applications

Nowadays, the fast advances in sensing technologies and ubiquitous wireless networking are reflected in medical practice. It provides new healthcare advantages under the scope of e-Health applications, enhancing life quality of citizens. The increase of life expectancy of current population comes with its challenges and growing health risks, which include locomotive problems. Such impairments and its rehabilitation require a close monitoring and continuous evaluation, which add financial burdens on an already overloaded healthcare system. Analysis of body movements and gait pattern can help in the rehabilitation of such problems. These monitoring systems should be noninvasive and comfortable, in order to not jeopardize the mobility and the day-to-day activities of citizens. The use of fiber Bragg gratings (FBGs) as e-Health enablers has presented itself as a new topic to be investigated, exploiting the FBGs’ advantages over its electronic counterparts. Although gait analysis has been widely assessed, the use of FBGs in biomechanics and rehabilitation is recent, with a wide field of applications. This chapter provides a review of the application of FBGs for gait analysis monitoring, namely its use in topics such as the monitoring of plantar pressure, angle, and torsion and its integration in rehabilitation exoskeletons and for prosthetic control

Temperature And Strain Sensing With Hybrid Interferometer

A hybrid interferometer for simultaneous measurement of strain and temperature is proposed and investigated experimentally. This hybrid design is composed of Fabry-Perot interferometer (FPI) and Michelson Interferometer (MI) cascaded with each other. It is developed by fusion splicing a single mode fiber (SMF), a multimode fiber (MMF), a dual side hole fiber (DSHF), a hollow core fiber (HCF) and a tapered-SMF. The tapered SMF was inserted into the HCF to form a reflection mirror for the FPI. The maximum temperature and strain sensitivity of the hybrid interferometer achieved through experiments is 11.6 pm/°C and 6.8 pm/mu varepsilon , respectively. The different sensitivities of FPI and MI to temperature and strain enable us to achieve simultaneous measurement. The proposed hybrid interferometer sensor has many attractive features such as, novel design, low cost, easy fabrication, compact size, and good sensitivity. Therefore, the proposed hybrid sensor could be widely deployed in plenty of applications, for instance, structural health monitoring, civil engineering, food manufacturing, chemical and medical fields