Correlation Optical Time Domain Reflectometry Research Articles

Optical time domain reflectometry based on a self-chaotic circular-sided microcavity laser.

A self-chaotic circular-sided square microcavity laser, with a chaos bandwidth of 12.9GHz and a flatness of ±3d B, was applied in optical time domain reflectometry (OTDR). Using the broadband chaos laser, we demonstrated a range resolution of 4.5mm and a 25-km detection distance experimentally. The solitary wide-bandwidth microcavity chaos laser, without the extra correlation peaks in optical feedback chaotic lasers, has shown potential advantages for correlation OTDR in practical application.

Correlation optical time domain reflectometry based on broadband random optoelectronic oscillator

Correlation optical time domain reflectometry based on broadband random optoelectronic oscillator

Ultra-long chaotic FBG sensing with high-order random fiber lasing amplification.

We propose and demonstrate an ultra-long chaotic fiber Bragg grating (FBG) sensing system based on wavelength-scanning correlation optical time-domain reflectometry (COTDR) assisted by sixth-order random fiber lasing amplification (RFLA). Cascaded random Raman fiber lasing generated in the long fiber span can provide up to sixth-order distributed Raman amplification for the chaotic probe light and its echo signal without ruining the chaotic behavior, which can significantly extend the sensing distance of COTDR. As a result, a 152-km-long wavelength-scanning COTDR is experimentally demonstrated to simultaneously realize FBG sensing and location with a spatial resolution as high as 6 cm, which is the longest COTDR to the best of our knowledge. Temperature sensing of the specific FBG is performed, and the temperature sensitivity of the proposed system is 0.25 dB/°C with a good linearity. The proposed chaotic FBG sensing system with high-order RFLA can act as a new platform for ultra-long, large-capacity FBG sensing, which has potential applications in overhead transmission powerline monitoring and structural health monitoring.

Accurate Single-Ended Measurement of Propagation Delay in Fiber Using Correlation Optical Time Domain Reflectometry

A correlation optical time-domain reflectometry (COTDR) method is presented, which measures the propagation delay with an accuracy of a few picoseconds. This accuracy is achieved using a test signal data rate of 10 Gbit/s and employing cross-correlation and pulse fitting techniques. In this paper we introduce and evaluate the basic signal processing steps, investigate the measurement accuracy, and discuss applications for monitoring link delay and chromatic dispersion of long fiber spans as well as temperature sensing applications.

Correlation technique using of-the-shelf CW DFB laser for interrogation of fiber optic sensors

The paper presents a simple fiber-optic sensor technique based on methods of correlation optical time domain reflectometry. A correlation reflectometry technique can measure distribution of reflection coefficient along the optical fiber by calculating the correlation function between a probe optical signal (reference) and the signal returned back due to reflections or/and back-scattering from the fiber under the test. To obtain the best sensor performance, the probe signal power should be a truly random function of time. As an optical source we use a free-running DFB laser diode operating in a continuous wave regime without any external modulation. To generate the probe test signal, laser light is passed through an interferometer with an optical path difference much longer than the coherence length of the laser light. The light intensity at the interferometer output has a truly random fluctuations and its auto correlation function is suitable for correlation optical reflectometry. We present results of experimental verification of the techniques in different sensor configurations. Multipoint sensor using very low reflective fiber Bragg gratings with reflectivity of 0.01% printed in a long SMF-28 optical fiber was demonstrated.

Long-range and high-resolution correlation optical time-domain reflectometry using a monolithic integrated broadband chaotic laser.

We experimentally demonstrate a compact, long-range, high-resolution chaotic correlation optical time-domain reflectometry based on a monolithic integrated chaotic laser (MICL). The MICL can directly generate a broadband chaotic signal covering a RF frequency range of over 40 GHz. Multi-reflection events can be precisely located in a detection range of ∼47 km with a range-independent resolution of 2.6 mm.

Long-range and high-precision correlation optical time-domain reflectometry utilizing an all-fiber chaotic source.

We propose a long range, high precision optical time domain reflectometry (OTDR) based on an all-fiber supercontinuum source. The source simply consists of a CW pump laser with moderate power and a section of fiber, which has a zero dispersion wavelength near the laser's central wavelength. Spectrum and time domain properties of the source are investigated, showing that the source has great capability in nonlinear optics, such as correlation OTDR due to its ultra-wide-band chaotic behavior, and mm-scale spatial resolution is demonstrated. Then we analyze the key factors limiting the operational range of such an OTDR, e. g., integral Rayleigh backscattering and the fiber loss, which degrades the optical signal to noise ratio at the receiver side, and then the guideline for counter-act such signal fading is discussed. Finally, we experimentally demonstrate a correlation OTDR with 100km sensing range and 8.2cm spatial resolution (1.2 million resolved points), as a verification of theoretical analysis.

Chaotic laser brings out higher precision OTDR

Professor Wang YunCai and his student Wang AnBang reported a new concept of optical time domain reflectometry (OTDR) based on a chaotic light correlation method. This will be useful for precise fault location in fiber links with high-density events. Their work is reported in Issue 53 (February, 2010) of SCIENCE CHINA Information Sciences. Optical fiber cables often break down due to natural disasters or human destruction. In particular, there are more and more fiber cable breakdowns within a building with the development of local networks and radio over fiber technology. This problem is currently solved by OTDR, the most important tool for fiber fault location. However, the conventional one, based on the pulse-echo method, is not precise enough because of its several meters of spatial resolution and its broad dead zone. By the use of a chaotic light correlation technique, Dr. Wang and Prof. Wang achieved distance-independent resolutions of 6 cm and 25 km measurable distance for single-mode fiber Although the correlation technique was used in a pseudo-random sequence OTDR to improve the trade-off between resolution and dynamic range in a pulse-echo OTDR, it is still limited by the electronic modulation bandwidth. The use of broadband chaotic light generated from a laser diode rather than pseudo-random optical pulses, reached centimeter accuracy for fiber fault location. Its obvious advantage is that a laser diode with optical feedback can easily generate large-amplitudes and multi-GHz bandwidth chaotic light signal, without electro-optical modulator. “This paper reports the first chaotic OTDR experiments, which will be useful for evaluation of optical fibers”, said one of reviewers. After Prof. Wang introduced their work at the CHAOS 2009 International Conference held in Chania, Greece (1–5 June, 2009), the chaotic correlation OTDR was considered to be one of three novel applications according to the summary of the international workshop of Chaos Applications in Telecommunications and Sensors, 2009 (The other two are fast pseudorandom bit generation and chaos steganography, by the way). “The current research emphasizes the high accuracy of fiber fault location and the next aim is to measure the fiber loss and Rayleigh scatters just as the conventional correlation OTDR does”, said Prof. Wang. The achievement of a chaotic correlation OTDR makes it possible for high-accuracy and non-destructive detection of small-size fiber networks.

Chaos correlation optical time domain reflectometry

We propose a novel correlation optical time domain reflectometry (C-OTDR) of using broadband chaotic light. This reflectometry has the advantage over the conventional OTDR and the pseudorandom signal C-OTDR in range-independent spatial resolution. We employ a laser diode with feedback from a long fiber ring cavity as the source of chaotic probe light. Experimental and numerical studies show that the chaotic light has broad and flat spectrum, and excellent correlation properties. Using this broadband chaotic laser, we experimentally demonstrate the proposed chaos C-OTDR for locating the fiber reflection events, and analyze the spatial resolution and dynamic range. The results show that the chaos C-OTDR can realize a range-independent resolution of 6 cm and its dynamic range is at least 25 km.

Wavelength tunable optical time-domain reflectometry based on wavelength swept fiber laser employing two-dimensional digital micro-mirror array

We demonstrate a cost effective wavelength tunable optical time-domain reflectometry (OTDR) for wavelength division multiplexing passive optical networks (WDM-PON). In order to realize the unique wavelength tunable optical time-domain reflectometry (OTDR), the wavelength swept fiber laser was developed by a digital micro-mirror array device (DMD), and the correlation OTDR (COTDR) technique was used. We successfully detected the fault location at the remote node fibers with 20 m resolution and fast wavelength setting speed of ∼15 μs in conventional band (C-band).

High-resolution correlation OTDR for distributed fiber-optic sensors and mobile cabling

Abstract Distributed fiber-optic sensing systems require a spatial resolution of less than 1 meter, which cannot easily be reached by conventional optical time domain reflectometry (OTDR) because of present electronics response times limited to about 10 ns corresponding to a few meter resolution. Correlation optical time domain reflectometry (COTDR) is a powerful technique for high-resolution test of distributed single-mode fiber sensors in the long wavelength range 1.3–1.6 μm. This article describes the realization of a 1.3−μm COTDR using a 200-Mb/s pseudorandom sequence that allows a spatial resolution of 50 cm and gives results obtained on a short single-mode fiber length with localized defects simulating a distributed line of sensors.