Yonas Muanenda

Cyclic pulse coding for fast BOTDA fiber sensors

A cyclic pulse coding technique is proposed and experimentally demonstrated for fast implementation of long-range Brillouin optical time-domain analysis (BOTDA). The proposed technique allows for accurate temperature and strain measurements with meter-scale spatial resolution over kilometers of standard single-mode fiber, with subsecond measurement times.

A Cost-Effective Distributed Acoustic Sensor Using a Commercial Off-the-Shelf DFB Laser and Direct Detection Phase-OTDR

We propose and experimentally demonstrate the use of cyclic pulse coding for enhanced performance in distributed acoustic sensing based on a phase-sensitive optical time-domain reflectometry (φ-OTDR) using direct detection. First, we present a theoretical analysis showing that to make cyclic pulse coding effective in φ-OTDR, the laser linewidth and stability must be optimized to simultaneously guarantee intrapulse coherence and interpulse incoherence. We then confirm that commercial off-the-shelf distributed feedback (DFB) lasers can satisfy these conditions, providing coding gain consistent with theoretical predictions. By externally modulating such lasers with cyclic pulse coding, we demonstrate a distributed acoustic sensor capable of measuring vibrations of up to 500 Hz over 5 km of standard single-mode fiber with 5-m spatial resolution with ~9-dB signal-to-noise ratio (SNR) improvement compared with the single-pulse equivalent. We also show that the proposed solution offers sensing performances that are comparable to similar sensors employing highly coherent and stabilized external cavity lasers and a single-pulse φ-OTDR.

Long-range accelerated BOTDA sensor using adaptive linear prediction and cyclic coding

We propose and experimentally demonstrate a long-range accelerated Brillouin optical time domain analysis (BOTDA) sensor that exploits the complementary noise reduction benefits of adaptive linear prediction and optical pulse coding. The combined technique allows using orders of magnitude less the number of averages of the backscattered BOTDA traces compared to a standard single pulse BOTDA, enabling distributed strain measurement over 10 km of a standard single mode fiber with meter-scale spatial resolution and 1.8 MHz Brillouin frequency shift resolution. By optimizing the system parameters, the measurement is achieved with only 20 averages for each Brillouin gain spectrum scanned frequency, allowing for an eight times faster strain measurement compared to the use of cyclic pulse coding alone.

Optimized Hybrid Raman/Fast-BOTDA Sensor for Temperature and Strain Measurements in Large Infrastructures

An optimized hybrid Raman/BOTDA optical fiber sensor based on cyclic Simplex pulse coding is proposed to overcome temperature and strain cross-sensitivity issues, allowing at the same time fast implementation of Brillouin optical time domain analysis with subsecond measurement times. By providing a real-time diagnostic system for safe operation, the proposed sensor can play a key role for in-service monitoring of large critical infrastructures. Experimental results demonstrate the capability of the proposed technique to effectively discriminate the Brillouin frequency shift contributions due to strain and temperature variations simultaneously applied to the same fiber section along 10 km of standard single mode optical fiber, with 1-m spatial resolution and a worst-case strain resolution value of 62 με. The proposed scheme uses a single narrowband laser source and one sensing fiber only.

Hybrid distributed acoustic and temperature sensor using a commercial off-the-shelf DFB laser and direct detection

We demonstrate a hybrid distributed acoustic and temperature sensor (DATS) using a commercial off-the-shelf (COTS) distributed feedback (DFB) laser, a single-mode optical fiber, and a common receiver block. We show that the spectral and frequency noise characteristics of the laser, combined with a suitable modulation scheme, ensure the inter-pulse incoherence and intra-pulse coherence conditions required for exploiting the fast denoising benefits of cyclic Simplex pulse coding in the hybrid measurement. The proposed technique enables simultaneous, distributed measurement of vibrations and temperature, with key industrial applications in structural health monitoring and industrial process control systems. The sensor is able to clearly identify a 500 Hz vibration at 5 km distance along a standard single-mode fiber and simultaneously measure the temperature profile along the same fiber with a temperature resolution of less than 0.5°C with 5 m spatial resolution.

A distributed acoustic and temperature sensor using a commercial off-the-shelf DFB laser

In this paper, we experimentally demonstrate a hybrid distributed acoustic and temperature sensor (DATS) based on Raman and coherent Rayleigh scattering processes in a standard singlemode fiber. A single commercial off-the-shelf DFB laser and a common receiver block are used to implement a highly integrated hybrid sensor system with key industrial applications. Distributed acoustic sensing and Raman temperature measurement are simultaneously performed by exploiting cyclic Simplex pulse coding in a phase-sensitive OTDR and in Raman DTS using direct detection. Suitable control and modulation of the DFB laser ensures inter-pulse incoherence and intra-pulse coherence, enabling accurate long-distance measurement of vibrations and temperature with minimal post-processing.

Relative change measurement of physical quantities using dual-wavelength coherent OTDR

We propose the use of alternating pulse wavelengths in a direct-detection coherent optical time domain reflectometry (C-OTDR) setup not only to measure strain and temperature changes but also to determine the correct algebraic sign of the change. The sign information is essential for the intended use in distributed mode shape analysis of civil engineering structures. Correlating relative backscatter signal shifts in the temporal/signal domain allows for measuring with correct magnitude and sign. This novel approach is simulated, experimentally implemented and demonstrated for temperature change measurement at a spatial resolution of 1 m.

Advanced Coding Techniques for Long-Range Raman/BOTDA Distributed Strain and Temperature Measurements

We describe the use of pulse coding for long-range distributed Raman and Brillouin optical time domain analysis (BOTDA) sensors and for implementing hybrid Raman/BOTDA distributed sensors for simultaneous strain and temperature measurement on the same fiber.

High performance distributed acoustic sensor using cyclic pulse coding in a direct detection coherent-OTDR

We propose and experimentally demonstrate a Distributed Acoustic Sensor exploiting cyclic Simplex coding in a phase-sensitive OTDR on standard single mode fibers based on direct detection. Suitable design of the source and use of cyclic coding is shown to improve the SNR of the coherent back-scattered signal by up to 9 dB, reducing fading due to modulation instability and enabling accurate long-distance measurement of vibrations with minimal post-processing.

Cyclic pulse coding for hybrid fast BOTDA/Raman sensor

We propose and experimentally demonstrate a fully hybrid distributed sensing scheme that uses a single narrow-band laser to perform fast measurement of the BFS using BOTDA and simultaneous temperature measurement based on spontaneous Raman scattering over 10 km of single mode fiber. The use of cyclic pulse coding effectively reduces the pump peak power levels required for accurate Raman-based distributed temperature measurement, enhancing at the same time the speed of the BFS measurement in the BOTDA technique.