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This paper shows an optical time domain reflectometry (OTDR) system based on an avalanche photodiode (APD) receiver, a 520 nm laser diode transmitter, a high-speed analog-to-digital converter (ADC) and a commercially available field programmable gate array (FPGA). This approach allows OTDR measurements up to 200 m and provides a spatial resolution of 20 cm. Depending on the number of averaging, the measurement time can be between 5 s and 50 s for a range up to 200 m with a good signal to noise ratio.
This paper shows the results on the data transmission over distances of up to 350 m SI-POF with KDPOF Media Converter based on Gigabit POF Transceiver KD1001 (KD-EVK1001MC Evaluation Kit) and laser diode (LD) operating at 520 nm. A bit rate of 1 Gbit/s with 16-PAM modulation scheme can be achieved over 200 m SI-POF. At longer distances, the bit rate is automatically reduced by KDPOF transceiver according to the actual channel capacity.
We report on a proposal for an incoherent optical frequency domain reflectometry (I-OFDR) for 1-mm core diameter PMMA SI-POF. An avalanche photodiode receiver and optimized transmitter based on a 515-nm laser diode allow measurement up to 200 m SI-POF. The measurements have been carried out using a vector network analyzer; the subsequent data processing has been implemented in MATLAB.
We present a robust concept for quasi distributed strain measurement using optical time domain reflectometry (OTDR) in polymer optical fibers (POF). The spatial shifts of discrete reflective events in the OTDR trace are evaluated as reference points. It is shown how such reference reflections can be prepared and which properties can be expected.
B8.3 Influence of Temperature on Distributed Strain Sensing with OTDR in Polymer Optical Fibers
(2021)
Strain in ground and earthworks can be measured by polymer optical fibers (POF) applied to geotextiles. We measure the increase of backscatter (IOB) in the fiber under strain using optical time domain reflectometry (OTDR). The effect of temperature on this measurement principle is investigated. The local backscatter changes by 0.003 dB/K for common ambient temperature. In addition it is shown, that temperature depended viscoelastic properties of the polymer does affect IOB.
Fiber Bragg grating (FBG) sensor technology is expected to make an important contribution to extending the lifetime of polymer electrolyte membrane (PEM) fuel cells. It allows accurate measurements of in-situ operating temperature and humidity, which is essential for an accurate control of both. For these applications an accurate and reliable calibration is crucial. This paper demonstrates the successful use of a 2x2 factorial calibration method for calibration of two standard FBGs for application in a PEM fuel cell. The calibrated low-cost FBG sensor allows temperature and humidity measurements with a RMS error (RMSE) of 0.45°C and 4.8 %RH, respectively.
With polymer optical fibers (POF) attached to geotextiles, optical time domain reflectometry (OTDR) can be used to measure strain of the geotextile spatially resolved in soil. We test the technique in a geotechnical application test and thus demonstrate the functionality of the sensor for field use.
According to the current state of the art, adhesively bonded joints cannot be tested completely non-destructively. This is the main motivation to permanently monitor adhesively bonded joints in order to record their structural integrity and - as a result - to ensure safe load transmission. By the use of permanent non-destructive Structural Health Monitoring (SHM) methods, structural damages in the adhesive bond can be detected at an early stage. This paper presents a new method for monitoring the structural integrity of adhesively bonded joints by integrating a Polymer Optical Fiber (POF) into the adhesive layer. The sensor concept is based on a deformation transfer from the adhesive to the POF, which results in a change in the cross-sectional shape of the POF. The cross-sectional shape influences the optical light propagation in the POF, which can be detected by simple optical measuring devices. The paper describes the general principle and first results of investigations on a structural adhesive (3M Scotch-Weld DP 609). The sensor signal is in a good relation to the stress state of the adhesive layer.
Absolute spectral backscatter measurements of large-core multimode PMMA polymer optical fibers
(2021)
To our knowledge, we are the first to measure the absolute value of the backscattering coefficient of a standard 1 mm core-diameter, multimode (MM) step-index (SI) polymethylmethacrylate (PMMA) polymer optical fiber (POF) for the spectral range of 450 nm to 700 nm. Our optical time domain reflectometer (OTDR) setup consists of a femtosecond supercontinuum laser with an acousto-optical filter as a tunable light source with short pulses and a time-correlated single-photon counting system as a receiver with a high dynamic range. The backscattering coefficient is calculated from the ratio between the energy within the fiber end reflex and the distributed backscattering level. We also measured the spectral attenuation with our OTDR setup and compared it with a standardized measurement method. At the attenuation minima within the measured spectral range the backscattering level of a 1 ns pulse is about −46 dB at 520 nm, −48 dB at 570 nm, and −51 dB at 650 nm. We were also able to show by the observed wavelength dependence that Rayleigh scattering causes a majority of the scattering.