arXiv subjects
Publications and source records attributed to Michael Eiselt.
A deployed fiber with in-house and underground sections is interrogated with a coherent correlation OTDR. The origin and propagation speed of a hammer-generated pressure wave in the underground section is detected and acoustic signals are monitored.
Distributed fiber sensing based on correlation-aided phase-sensitive optical time domain reflectometry is presented. The focus is on correlation as an enabler for high spatial resolution. Results from different applications are presented.
A coherent optical subassembly (COSA) is evaluated for coherent-correlation optical time domain reflectometry (CC-OTDR) based fibre sensing. Even though the COSA was originally designed for digital communication applications, acoustic signals with frequencies up to 360 Hz can be detected after 50 km of transmission.
Fiber optic sensing is becoming an important means to physically secure today's network infrastructure. However, a network-wide deployment of the monitors will require cost reduction of the interrogator system, which can only be achieved by highly integrated system components. In this contribution, we report on the use of an in-house designed single-chip coherent transceiver for acoustic fiber sensing. The transceiver on the basis of silicon photonics contains a high-speed dual-polarization IQ-modulator as well as a coherent receiver with balanced photodiodes and trans-impedance amplifiers, as defined by the OIF integrated coherent transmit-receive optical sub assembly (IC-TROSA) implementation agreement. The laser, used for transmission and as local oscillator, is provided external to the photonic integrated circuit and can be chosen according to the line-width requirements of the sensing system. The acoustic sensing demonstration is using a correlation-based optical time domain reflectometry with coherent detection. This method is able to detect, besides the amplitude information, the phase of the back-scattered signal, which has a significantly higher sensitivity to environmental effects on the fiber, like temperature and strain. As a proof of concept, sensing of an acoustic signal after a fiber span of 20 km is demonstrated by evaluating the obtained phase information, providing information on external dynamic events up to a frequency of 1.75 kHz.
Superimposed temperature variations and dynamic strain applied through a 400 Hz acoustic signal on a 195 m single-mode fiber section are successfully measured using a coherent correlation optical time domain reflectometry as an interrogator.
In this paper, we report on the development progress of correlation-based optical time domain reflectometry (OTDR). Substituting the direct detection receiver with a coherent receiver enables to extract the phase and polarization information of the reflected signal. Furthermore, due to the mixing of a weak probe signal with a strong local oscillator the sensitivity of the receiver improved. This improvement was demonstrated by analyzing the reflection from an angled physical contact (APC) connector. To further quantify the improvements, we compare the direct detection correlation OTDR (C-OTDR) with the coherent detection correlation OTDR (CC-OTDR) with respect to the spatial and amplitude resolution.
The use of optical fiber as sensor as well as transmission medium for sensing data is discussed, enabling the use of optically active sensors without power supply at distances of tens of kilometers. Depending on the interrogation system, a spatial resolution of less than a millimeter can be achieved. The basic sensing principle is optical time-domain reflectometry (OTDR) with direct detection or coherent detection of the Rayleigh back-scattered or Fresnel reflected signal. Spatial resolution is improved by a cross-correlation between the transmitted sequence and the received signals.
The temperature dependence of the latency of an optical signal transmitted over an optical fiber was investigated by means of a correlation OTDR. While the bare fiber showed a linear latency increase over temperature, the jumper cable inside a jacket with tight buffer as inner jacket showed an increased elongation effect, especially in the range of lower tempera-tures. This could be attributed to the tight buffer. For future latency sensitive applications in the area of 5G networks these effects have to be taken into account.
Using a Correlation-OTDR, we characterized the temperature-induced group delay variations of two nested antiresonant nodeless hollow core fibers. The temperature sensitivity of both is substantially less than for SSMF with some dependency on coating type.
In this paper, we report on the integration of a Correlation-OTDR into a portable unit (30 cm x 30 cm), based on a multi-processor system on chip (MPSoC) and a small formfactor pluggable (SFP) 2.5G transceiver. Going beyond telecommunication applications, this system is demonstrated for temperature measurements, based on the change of propagation delay with temperature in a short section of optical fiber. The temperature measurement accuracy is investigated as a function of the fiber length from 4 to 25 meters.
By means of C-OTDR (Correlation - Optical Time Domain Reflectometry), we measured the latency of100 km fiber with an accuracy of a few picoseconds. Based on iterating 49 measurements, we calculated a standard deviation of 12 ps between the round-trip latency values. To verify the reflection measurements, we used a single pass setup without reflector, which showed a maximum difference of only 11 ps.
Several multi-core fibers (MCF) were characterized using Correlation Optical Time Domain Reflectometry (C-OTDR) in terms of propagation delay and polarization mode dispersion (PMD). The results show that the propagation delay in the cores depends on the position of the core in the fiber and that the differential delay between the cores varies with temperature.
Using a Correlation-OTDR and a modulation phase shift method we characterized four multi-core fibers. The results show that the differential delay depends on the position of the core in the fiber and varies with temperature.
We measured the latency of a 100 km fibre link using a Correlation OTDR. Improvements over previous results were achieved by increasing the probe signal rate to 10 Gbit/s, using dispersion compensation gratings, and coupling the receiver time base to an external PPS signal.
We review some currently discussed solutions for 400 Gbit/s inter-data center WDM transmission for up to 100 km. We focus on direct detected solutions, namely PAM4 and DMT, and present two WDM systems based on these formats.
We demonstrate up to 12 km, 56 Gb/s DMT transmission using high-speed VCSELs in the 1.5 um wavelength range for future 400Gb/s intra-data center connects, enabled by vestigial sideband filtering of the transmit signal.
We review currently discussed solutions for 80 km DWDM transmission targeting inter data-center connections at 100G and 400G line rates. PDM-64QAM, PAM4 and DMT are investigated, while the focus lies on directly detected solutions.
Discrete multi-tone transmission (DMT) is a promising candidate for future 400G data center interconnects. Eight channels, each carrying 56 Gb/s of data can be combined in a 50-GHz channel grid to form a 400 Gb/s superchannel. For a fully loaded 96 channel DWDM system this leads to a total capacity of 4.8 Tb/s. To meet the requirements of the targeted application in terms of cost efficiency and low power consumption, it is important to keep the complexity for the digital signal processing as low as possible. For DMT, the complexity is mainly determined by the length of the fast Fourier transformation (FFT). Since data center interconnects only have to bridge a distance of typically 80 km, we here investigate among other parameters the influence of the FFT length among other parameters on the achievable performance for 56 Gb/s DMT only for this distance. Transmission is performed in C-band to enable DWDM and no optical dispersion compensation is applied. We consider double sideband (DSB) as well as vestigial sideband (VSB) DMT. It can be seen that an FFT length of 128 is sufficient to reach the required performance in terms of bit error ratio, however, a higher length can significantly improve the performance.