Distributed acoustic sensing – DAS

Install and forget!

If you deliver Distributed Acoustic Sensing (DAS) systems for pipeline monitoring, perimeter security, or border control (to name a few), then it is likely that your systems will be installed in harsh environments in remote places.

Wouldn’t it be nice if you could install the system and forget all about it? With our robust and reliable Koheras fiber lasers, you can.

Designed for real-life

We understand that the laser is a key component in your interrogator. It dictates the sensitivity, range, reliability, and failure rate.

Our Koheras lasers are designed for real life. We have combined the all-fiber distributed feedback design with field-proven components from the telecom industry to give you a robust, reliable, maintenance-free, and service-free laser. They’re as low-maintenance as a cactus!

When we say reliable, we mean a typical lifetime of more than 10 years and a return rate of less than 1%.

Over the last 20 years, our customers have deployed more than 15,000 Koheras lasers in the harshest environments. We have lasers on oil rigs, submarines, wind turbines, and even in space.

You do not have to worry about laser supply. We can deliver all the lasers you need when you need them. Every year, our customers deploy more than a thousand Koheras lasers across the planet.

Long-range and high accuracy

To obtain long measurement ranges, our customers typically look for lasers with a long coherence length and low noise to get a high dynamic range. With a Koheras laser, it is possible to obtain measurement ranges of up to 100 km which makes it easier for you to handle your system and lets you save money on equipment.

Ultra-low phase noise (or frequency noise) is a key laser parameter for the sensitivity and accuracy of the sensing system. The high sensitivity of the Koheras laser ensures an excellent detection of acoustic signals.

Due to their intrinsic low-noise design, you get sub-picometer stability and mode-hop-free performance. Do you want to mount them upside-down? No problem. The all-fiber design keeps the laser stable. Install them in the desert? No problem. Temperature changes do not affect stability. Take them for a ride? No problem. Vibration and noise do not distort the signals.

Pick the right laser

If you need a flexible system with more wavelengths, our Koheras lasers are a bit like Lego (although less colorful). You can combine lasers to get the system that best suits you. Use the Koheras ACOUSTIK rack integration to combine up to 16 Koheras BASIK fiber lasers and two matching BOOSTIK line card amplifiers. The ACOUSTIK provides power and control to all modules and you can add and change channels as needed.

References

Here are some publications where others describe their work within DAS, using our Koheras lasers.

• Integrated sensing and communication in an optical fibre by Haijun He, Lin Jiang, Yan Pan, Anlin Yi, Xihua Zou, Wei Pan, Alan E. Willner, Xinyu Fan, Zuyuan He & Lianshan Yan, published in Light: Science & Applications, vol. 12, article 25, 2023.
• Indoor optical fiber eavesdropping approach and its avoidance by Haiqing Hao, Zhongwang Pang, Guan Wang, Bo Wang published in Optics Express, Vol. 30, issue 20, 2022.
• Non-Invasive Acoustic Monitoring of Gas Turbine Units by Fiber Optic Sensors by Konstantin V. Stepanov, Andrey A. Zhirnov, Stanislav G. Sazonkin, Alexey B. Pnev, Alexander N. Bobrov, and Dmitriy A. Yagodnikov, published in Sensors, 2022.
• Demodulation Scheme with Low Harmonic Distortion for PMDI-TDM Based Fiber-Optic Sensor Array by Jianxiang Zhang, Kun Cheng, Wenzhu Huang, Wentao Zhang, Fang Li published at the 27th International Conference on Optical Fiber Sensors, Technical Digest Series, Optica Publishing Group, 2022.
• The sparsity of the response of a quasi-distributed fiber optic sensing system allows ‘overclocking’ its interrogation by Nadav Arbel, MayaYanko, Avishay Eyal, published in Optical Fiber Technology, Volume 61, January 2021, 102373, 2021.
• Time-expanded phase-sensitive optical time-domain reflectometry by Miguel Soriano-Amat, Hugo F. Martins, Vicente Durán, Luis Costa, Sonia Martin-Lopez, Miguel Gonzalez-Herraez, María R. Fernández-Ruiz published in Light: Science & Applications, 2021.
• On the phase fading effect in the dual-pulse heterodyne demodulated distributed acoustic sensing system by Xiangge He, Xiaohu Xu, Min Zhang, Shangran Xie, Fie Liu, Lijuan Gu, published in Optics Express, Vol. 28, No. 22, 26 October 2020, Optics Express 33433, 2020.
• Performance Improvement of Dual-Pulse Heterodyne Distributed Acoustic Sensor for Sound Detection by Xiangge He, Min Zhang, Lijuan Gu, Shangran Xie, Fei Liu, Hailong Lu, published at Sensors (Basel). 2020 Feb; 20(4): 999. 2020.
• Combined frequency and phase domain time-gated reflectometry based on a fiber with reflection points for absolute measurements by V.A. Yatseeva, A.M. Zotovb, O.V. Butova, published in Physics, 2020.
• Cost-effective solution for phase-OTDR distributed acoustic/vibration sensing by V. V. Spirin, C. A. López-Mercado, J. Jason, J. L. Bueno-Escobedo, P. Mégret, M. Wuilpart, D. A. Korobko, I. O. Zolotovskii, S. G. Sokolovskii, A. A. Fotiadi, published in SPIE LASE proceedings 10903, 2019.

And don’t miss the short article on how thousands of our low-noise Koheras lasers keep a large-scale data network secure, with SFO Technologies.

Don’t know what DAS is?

Distributed Acoustic Sensing is a sensing system based on light. The system consists of an interrogator and some optical fibers. The optical fibers replace traditional discrete sensors and let you measure sound along with its entire length.

The interrogator has a laser inside which sends light pulses into the optical fibers. Most of the light travels forward but some of it is reflected back to the interrogator.

Sound and movements from the environment affect the light. The interrogator analyses the reflected light to figure out what is going on and if it should send an alert. The ultra-precise detection reveals the exact position of the incident, eliminates uncertainties, and saves time.

Why use DAS for smart cities?

Today’s CCTV and discrete sensors give an incomplete picture of what is going on in the city. A DAS system gives you access to a lot of information otherwise unavailable to you.

DAS systems use optical fibers as sensors and let you measure sound along their entire length. It works over long distances and large areas, without any disruption, and sends responses back in real-time.

You can use the existing grid of fiber optic communication networks that are already laid out across countries and oceans. The long stretches of fiber provide you with thorough and continuous data.

DAS systems can be used for a wide range of monitoring applications in the smart city, such as:

• Traffic patterns and density
• Road conditions
• Vehicle type
• Vehicle acceleration, speed, and direction
• Infrastructure monitoring to prevent deterioration of bridges, roads, and tunnels
• Assisting the development of autonomous driving
• Crime detection

Why is Koheras the ideal laser for DAS?

Our Koheras lasers are an excellent choice for DAS systems. To get the highest detection range, you need the lowest possible phase noise – which you get from the Koheras lasers.

They are industrial-grade OEM lasers with a rugged design, a stable performance unaffected by different environmental conditions, and wide temperature ranges in the field.

World-leading acoustic sensing systems use our Koheras lasers due to the intrinsic low phase-noise, the narrow linewidth, and the long coherence length that enable measurement ranges in the range of 100 km.

The most reliable low-noise laser on the market

We have more than 15,000 Koheras lasers deployed in the harshest environments on – and off – the planet. We have lasers on oil-rigs, submarines, wind turbines, and even in space.

With over 20 years of experience, we know they last.

What are the advantages of using DAS?

Distributed Acoustic Sensing, DAS, is a sensing system based on light. The system listens in on everything that is going on in the city. Intelligent software translates the sounds to information and alerts that let you manage traffic and prevent damage to infrastructure.

Optical fibers are perfect sensors

When you use optical fiber as sensors for smart city applications, you get a long list of advantages:

• Fibers are already installed throughout most cities
• Fibers enable measurements of thousands of locations, continuously
• Fibers can cover a large geographical range
• Fibers are immune to electromagnetic interference
• Fibers do not need or carry any electrical power
• Fibers are highly reliable and cost-efficient

Ultra-precise detection eliminates uncertainties and saves time

DAS systems are based on interferometric sensing. An ultra-stable, low-noise laser – such as our Koheras lasers – is built into an interrogator that sends light into the fiber and detects the backscattered light.

Complex algorithms analyze what is going on along the fiber, with high precision.

The interpretation software detects every incident but ensures that only relevant information is passed on to the operators.

Ultra-precise detection reveals the exact position of the incident, eliminates uncertainties, and saves time.

Do you need a laser for your DAS system?

Use DAS systems to monitor all kinds of critical assets and infrastructures, such as power plants, airports, oil-rigs, borders, conveyor belts, pipelines large facilities, etc.

When you point a laser beam at a moving surface, the reflected light is backscattered at a slightly different frequency. This frequency shift is compared to a reference laser beam, allowing you to tell the velocity and displacement of the moving surface.

Koheras lasers are ideal for interferometric sensing

When making interferometric sensing systems – such as laser Doppler vibrometers – it is important to use a laser with a very narrow linewidth to get accurate feedback. With their intrinsic low phase noise and narrow linewidth, the Koheras lasers are ideal for interferometric sensing systems with high demands to dynamic range and sensitivity.

Our unique fiber laser design ensures high wavelength stability and no need for periodic adjustments to the laser’s center wavelength. Furthermore, its true single-mode & mode-hop free operation enables stable system performance.

With documented low failure rates, we proudly deliver the most reliable low-noise lasers on the market. Our lasers boast a long life in demanding industrial environments where uptime is critical due to their inherently compact and robust design.

Useful in many industries

Due to the versatility, the laser Doppler vibrometry method is used to measure a wide range of displacements, from slow to very high-frequency movements.

Precise measurements of mechanical displacement are vital for quality control and structural optimization in the automotive, civil engineering, and aerospace industries.

High optical performance combined with industrial robustness

Our Koheras BASIK MIKRO E15 laser is a popular choice with manufacturers of commercial laser-based vibrometer systems, whether it is single-point, multi-point, or scanning vibrometry. With its robust and compact OEM footprint and very narrow linewidth and low-frequency noise, it combines the best of the scientific and industrial worlds.

Use the Koheras lasers to get:

• Precise measurements of complex and sensitive mechanical structures
• Stable system performance due to true single-mode & mode-hop free laser operation
• Robust fiber laser design suitable for industrial field applications

Publications

• Chun-Hsiung Wang, Hsin Lee, Yu-Hsiang Hsu, Shu-Sheng Lee, Jiun-Woei Huang, Wen-Jong Wu, and Chih-Kung Lee: Photonic Doppler velocimetry for high-speed fragment generator measurements, published in Optics Express, 2020.

Locate oil with Koheras lasers

Optical sensing systems are gaining ground because they offer several advantages over traditional technologies based on electrical transducers, e.g. piezoelectric hydrophones.

New interferometric systems with fiber optical sensors enable longer sensing ranges with high dynamic range and sensitivity. The fibers are passive (no electronics), compact, lightweight, reliable, and can be multiplexed to interrogate extensive sensor arrays. This is key to obtaining a higher return on investment and – ultimately – a lower cost of ownership.

Today only about 30% of an oil well is exploited over time. However, with permanent reservoir monitoring, it is possible to increase the extraction rate and benefit from the existing infrastructure around an oil reservoir.

The optical sensor system listens to an “acoustic signature” from the seafloor, providing means to identify and locate oil “pockets” that are otherwise difficult to access.

Our market-leading low phase noise is crucial for obtaining a high dynamic range and sensitivity in an optical sensor system.

Robust, reliable, and a long lifetime

Our industrial Koheras fiber laser modules have been used in the oil & gas industry for many years and are currently the backbone of several seismic sensor systems.

The fiber laser design is inherently compact and robust. It is developed for a long lifetime in demanding environments where uptime is critical. With documented low failure rates, we proudly deliver the most reliable low noise lasers on the market.

We have more than 15,000 Koheras lasers deployed in the harshest environments on – and off – the planet. We have lasers on oil-rigs, submarines, wind turbines, and even in space. With 20 years of experience, we know they last.

Features

• Low phase-noise provides high dynamic range and sensitivity
• Unsurpassed reliability, suitable for long term operation in harsh environments
• Designed for OEM integration
• Maintenance-free 24/7 operation