Fiber Optical Reflectometry Research Articles

Reflectometric temperature measurement using a single-mode-multimode-single-mode" fiber optic structure

It is shown the "single-mode-multimode-single-mode" structure allows carrying out remote temperature measurement with optical time domain reflectometer. A multimode fiber length was 10 mm. We used the temperature range from 30 to 70oC and wavelengths of 1310 and 1550 nm. The total length of a single-mode fiber-optic line for reflectometric measurements was 20 km. Keywords: fiber optics, fiber optic sensors, optical fiber reflectometry, multimode interference.

Suppression of amplitude fluctuation in Brillouin optical fiber reflectometry employing polarization beam splitter and pre-amplification technique

We propose and validate the suppression effect on amplitude fluctuation in Brillouin optical time domain reflectometry sensing system with a polarization beam splitter and pre-amplification technique. The p - and s -components of local oscillator interfere respectively with two halves of Brillouin scattering amplified by a Erbium doped fiber amplifier. Theoretical analysis indicates that the polarization influence on the beat amplitude is eliminated with the proposed scheme; and experimental results show that the amplitude variation along the sensing fiber could be extracted accurately, and the temperature sensing error is about 5%. The proposed method is helpful to improve the measurement accuracy of the BOTDR sensing system.

Long-Range Distributed Solar Irradiance Sensing Using Optical Fibers.

Until recently, the amount of solar irradiance reaching the Earth surface was considered to be a steady value over the years. However, there is increasing observational evidence showing that this quantity undergoes substantial variations over time, which need to be addressed in different scenarios ranging from climate change to solar energy applications. With the growing interest in developing solar energy technology with enhanced efficiency and optimized management, the monitoring of solar irradiance at the ground level is now considered to be a fundamental input in the pursuit of that goal. Here, we propose the first fiber-based distributed sensor able of monitoring ground solar irradiance in real time, with meter scale spatial resolutions over distances of several tens of kilometers (up to 100 km). The technique is based on an optical fiber reflectometry technique (CP-ϕOTDR), which enables real time and long-range high-sensitivity bolometric measurements of solar radiance with a single optical fiber cable and a single interrogator unit. The method is explained and analyzed theoretically. A validation of the method is proposed using a solar simulator irradiating standard optical fibers, where we demonstrate the ability to detect and quantify solar irradiance with less than a 0.1 W/m2 resolution.

Fully Distributed Optical Fiber Strain Sensor With 10−12 ϵ/√Hz Sensitivity

Advanced optical fiber reflectometry techniques enable spatially distributed measurements of true relative deformations over the length of a conventional optical fiber cable. This methodology is attractive for many applications ranging from intrusion monitoring to seismology. However, accurate quantification of the applied stimulus in general implies sophisticated implementations with poor sensitivity performance. Coherent reflectometry using chirped pulses is an appealing solution, as it provides fast dynamic strain measurements with a simple experimental deployment. Here, we analyze for the first time to our knowledge the lower performance bounds of this technique as a function of the signal-to-noise ratio of the acquired optical signal. We demonstrate that implementations realized so far have been limited by the temporal sampling used instead of the optical signal quality. Through post-processing interpolation approaches, we reach the performance limit for a given set of signal parameters, attaining unprecedented strain sensitivities (10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> ε/√Hz) for km-length distributed sensors in conventional single-mode fibers.

Optical Fiber Sensor with Distributed Parameters Based on Optical Fiber Reflectometry

His paper deals with the two-stage two-phase electronic systems with orthogonal output voltages and currents - DC/AC/AC. Design of two-stage DC/AC/AC high frequency converter with two-phase orthogonal output using single-phase matrix converter is also introduced. Output voltages of them are strongly nonharmonic ones, so they must be pulse-modulated due to requested nearly sinusoidal currents with low total harmonic distortion. Simulation experiment results of matrix converter for both steady and transient states for IM motors are given in the paper, also experimental verification under R-L load, so far. The simulation results confirm a very good time-waveform of the phase current and the system seems to be suitable for low-cost application in automotive/aerospace industries and application with high frequency voltage sources.

Low Coherent Optical Frequency Domain Reflectometry Interrogates Fiber Bragg Grating Sensors

A novel fiber optical reflectometry is proposed for long distance measurements and sensing applications. The reflectrometric information is included in the phase difference of two interfering light beams reflected at the same scattering point on the fiber under test (FUT). The reflection position and local information can be determined by modulating the frequency difference and analyzing the reflecting signal in frequency domain. Theoretical analysis and experimental demonstration are presented. Two adjacent reflection points 50 km away from the reflectometry with a gap of 11 meters between each other is distinguished. It is estimated that the operating range could be over 500 km theoretically by employing a light source with 0.3 nm bandwidth. This novel reflectometry is applied as a fiber Bragg grating interrogation solution as an example.

Measurement of tissue optical properties by the use of oblique-incidence optical fiber reflectometry

Fiber-optic-based oblique-incidence reflectometry is a simple and accurate method for measuring the absorption and reduced scattering coefficients mu(a) and mu?(s) of semi-infinite turbid media. Obliquely incident light produces a spatial distribution of diffuse reflectance that is not centered about the point of light entry. The amount of shift in the center of diffuse reflectance is directly related to the medium's diffusion length D. We developed a fiber-optic probe to deliver light obliquely and sample the relative profile of diffuse reflectance. Measurement in absolute units is not necessary. From the profile, it was possible to measure D, perform a curve fit for the effective attenuation coefficient mu(eff), and then calculate mu(a) and mu?(s). This method was verified with Monte Carlo simulations and tested on tissue phantoms. Our measurements of D and mu(eff) had an accuracy of approximately 5%, thus giving us 10% and 5% accuracy for mu(a) and mu?(s), respectively.

Review of long wavelength single-mode optical fiber reflectometry techniques

This paper reviews the worldwide activity on long-wavelength ( >1.1-\mu m) single-mode optical fiber reflectometry and compares and contrasts the many different approaches being taken to equipment design.