The development and applications of a ruggedized visible to near-infrared (VIS/NIR) spectrometer system capable of measuring fluid spectra in oilfield wellbores are presented. Real-time assessment of formation fluid properties penetrated by an oilfield wellbore is critically important for oilfield operating companies to make informed decisions to optimize the development plan of the well and hydrocarbon reservoir. A ruggedized VIS/NIR spectrometer was designed and built to measure and analyze hydrocarbon spectra reliably under the harsh conditions of the oilfield wellbore environment, including temperature up to 175 ℃, pressure up to 170 MPa, and severe mechanical shocks and vibrations. The accuracy of hydrocarbon group composition analysis was compared well with gas chromatography results in the laboratory.

A review of our recent work on ultrahigh resolution optical fiber sensors in the quasi-static region is presented, and their applications in crustal deformation measurement are introduced. Geophysical research such as studies on earthquake and volcano requires monitoring the earth’s crustal deformation continuously with a strain resolution on the order of nano-strains (nε) in static to low frequency region. Optical fiber sensors are very attractive due to their unique advantages such as low cost, small size, and easy deployment. However, the resolution of conventional optical fiber strain sensors is far from satisfactory in the quasi-static domain. In this paper, several types of recently developed fiber-optic sensors with ultrahigh resolution in the quasi-static domain are introduced, including a fiber Bragg grating (FBG) sensor interrogated with a narrow linewidth tunable laser, an FBG based fiber Fabry-Perot interferometer (FFPI) sensor by using a phase modulation technique, and an FFPI sensor with a sideband interrogation technique. Quantificational analyses and field experimental results demonstrated that the FBG sensor can provide nano-order strain resolution. The sub-nano strain resolution was also achieved by the FFPI sensors in laboratory. Above achievements provide the basis to develop powerful fiber-optic tools for geophysical research on crustal deformation monitoring.

Recent progress on optical fiber monitoring in the optical communication systems is reviewed along with current optical fiber monitoring and diagnosing problems in deployed access, trunk and submarine communication systems.

The fiber optic distributed temperature sensor (DTS) is one of the most outstanding means to measure temperature distribution along an optical fiber. In this paper, we propose a novel calibration technique to measure the temperature highly accurately over a wide range of temperatures. We also propose an improved double-ended configuration that is insusceptible to the differential loss change in the fiber and suitable for the field use. Then, we developed an interrogator that had high robustness in harsh environments.

We recently proposed a new class of wavelength-swept lasers for swept-source optical coherence tomography (SS-OCT). It uses the same gain medium with the conventional swept lasers, but does not require any tunable filters. It is based on a principle called “dispersion tuning”, in which a highly dispersive medium is inserted in the laser cavity, and loss/gain modulation is applied to mode-lock the laser. Since the cavity contains no mechanical components, such as tunable filters, we could achieve the very high sweep rate. In this review paper, we describe the principle of the dispersion-tuned swept lasers in detail and present our recent work on the application to the SS-OCT system.

This paper reviews distributed discrimination of strain and temperature by use of an optical fiber based on fiber optic nerve systems. The preliminary method based on multiple resonance peaks of the Brillouin gain spectrum in a specially-designed fiber is firstly introduced. The complete discrimination of strain and temperature based on the Brillouin dynamic grating in a polarization maintaining fiber is extensively presented. The basic principle and two experimental schemes of distributed discrimination based on fiber optic nerve systems are demonstrated. The performance of the high discriminative accuracy (0.1 ℃-0.3 ℃ and 5-12 με) and high spatial resolution (~10 cm) with the effective measurement points of about 50 for a standard system configuration or about 1000 for a modified one will be highly expected in real industry applications.

Optical fiber sensors have attracted considerable attention in health monitoring of aerospace composite structures. This paper briefly reviews our recent advancement mainly in Brillouin-based distributed sensing. Damage detection, life cycle monitoring and shape reconstruction systems applicable to large-scale composite structures are presented, and new technical concepts, “smart crack arrester” and “hierarchical sensing system”, are described as well, highlighting the great potential of optical fiber sensors for the structural health monitoring (SHM) field.

In this paper, we review our researches on the topics of the structural health monitoring (SHM) with the fiber-optic distributed strain sensor. Highly-dense information on strains in a structure can be useful to identify some kind of existing damages or applied loads in implementation of SHM. The fiber-optic distributed sensors developed by the authors have been applied to the damage detection of a single-lap joint and load identification of a beam simply supported. We confirmed that the applicability of the distributed sensor to SHM could be improved as making the spatial resolution higher. In addition, we showed that the simulation technique considering both structural and optical effects seamlessly in strain measurement could be powerful tools to evaluate the performance of a sensing system and design it for SHM. Finally, the technique for simultaneous distributed strain and temperature measurement using the PANDA-fiber Bragg grating (FBG) is shown in this paper, because problems caused by the cross-sensitivity toward strain and temperature would be always inevitable in strain measurement for SHM.

This paper investigates the application of distributed optical fiber strain sensors to civil engineering structures, because no other tool can satisfactorily detect the location of the unpredictable phenomenon. In fact, the locations of cracks in the concrete structure are unknown a priori; therefore, a fully distributed sensor is necessary to detect them. The Brillouin optical correlation domain analysis (BOCDA), which offers high spatial resolution by using stimulated Brillouin scattering along the whole length of the optical fiber, is used in a wide range of civil engineering applications, and the same has undergone significant development over the last decade. In this paper, it is demonstrated how a BOCDA-based strain sensor can be employed to monitor cracks in concrete. Crack monitoring on the surface of the concrete member provides useful information for evaluating stiffness and durability of the structure, particularly for early detection of tiny cracks, which is essential for preventing crack growth and dispersion. The crack-induced strain distribution was analytically investigated, and it was proved that BOCDA can identify even a small crack before its visual recognition by a beam test. Moreover, periodical crack monitoring was successfully executed on a pedestrian deck for five years.