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Tag Archive: sensing

  1. Tuneable Light Waves for Optical Sensing

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    OFS AcoustiSens® Optical Fibers used in random OPO system demonstration 

    Once again, OFS optical fibers are paving the way for researchers to bring cutting-edge technology out of the lab and into practical applications. This time, we’re delving into the realm of optical fiber sensing – a technology that relies on a carefully tuned light source with specific traits like wavelength, power, and pulse width. 

    Generally optical fiber sensing starts with a laser, but they come with a catch: lasers have their materials carefully selected to emit stable light pulses at a specific desired wavelength, limiting their flexibility. A system with wavelength modulation promises exciting innovations for fields as diverse as quantum computing and LiDAR sensing.  

    OPOs can use the deliberate scattering in AcoustiSens optical fiber to change the wavelength of light pulses.
    OPOs can use the deliberate scattering in AcoustiSens optical fiber to change the wavelength of light pulses

    Enter the optical parametric oscillator (OPO). It transforms regular laser light into controlled wavelength pulses by guiding the laser light into an optical cavity, bouncing it around nonlinear crystals and resonators. As the light moves through the cavity and is sent back over itself multiple times the system changes wavelengths and creates parametric amplification.  

    However, there’s a hiccup in this dazzling performance: OPOs are quite sensitive to temperature and environmental changes. Even small changes impact the wavelength and power of the light as it exits the cavity, confining OPOs mostly to high-maintenance lab settings. 

    Researchers theorized that a random laser, which encourages scatter in the light source, would make the system more robust because the scattering would come from the controlled design of the laser and not be at the mercy of environmental changes in the optical cavity. 

    A groundbreaking paper from the University of Ottawa validates this concept. A team demonstrated, for the first time, that an augmented sensing optical fiber like OFS’ AcoustiSens can make this idea a reality. AcoustiSens is manufactured with enhanced Rayleigh scattering and this scattering allowed the OPO system to have stable, tuned wavelengths in a simple and robust optical cavity. 

    Congratulations to the University of Ottawa team and to all the technologists working to unshackle OPOs from the lab. 

  2. Enhancing Distributed Sensing with a Dual-Brillouin-Peak Optical Fiber

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    Dual-Brillouin-Peak Optical Fiber was designed and fabricated by researchers from OFS

    In an era of advanced sensing technologies, the dual-Brillouin-peak optical fiber emerges as a new practical solution forresolving the strain-temperature cross-sensitivity that exists in almost all optical fiber sensors. Its potential spans across a multitude of fields, demanding precision over long distances and high resolutions. This groundbreaking technology is set to redefine the boundaries of Brillouin scattering based distributed fiber sensing.

    Dual-Brillouin-peak single-mode optical fiber can measure both strain and temperature at the same time. This is a very useful feature for applications such as structural health monitoring, oil and gas exploration, and power transmission.

    Dual-Brillouin-peak single-mode optical fiber has two distinct peaks in its Brillouin gain spectrum with similar amplitude levels. By measuring the frequency shifts of these two peaks, we can determine both the strain and the temperature along the fiber.

    This is different from conventional single-mode optical fibers, which have only one dominant Brillouin peak and can only measure either strain or temperature, but not both at the same time. To measure both parameters, we would need to use two different fibers or a special fiber with a coating that has a different thermal expansion coefficient that usually results in an ill-conditioned discrimination.

    The dual-Brillouin-peak optical fiber has several advantages over these methods. First, it simplifies the measurement system by reducing the number of components and connections. Second, it eliminates the need for calibration or compensation of the thermal expansion coefficient. Third, it increases the accuracy and resolution of the measurements by enhancing the Brillouin gain of the higher-order acoustic mode.

    The researchers demonstrated the performance of their optical fiber in a 25-kilometer sensing length with 5-meter spatial resolution. They achieved a temperature resolution of 2°C and a strain resolution of 40 microstrain.

    The fiber and standard single-mode telecom fibers are interchangeable with low splicing loss. The fiber is fully compatible with existing BOTDR/BOTDA (Brillouin Optical Time Domain Reflectometer/Analyzer) interrogators in the market. The dual-Brillouin-peak optical fiber is a promising technology for simultaneous distributed strain and temperature measurement. It has potential applications in various fields that require long-distance and high-resolution sensing.

    To learn more, read the whitepaper: Request PDF | OFS (ofsoptics.com)

  3. Optical Fiber “Senses” Change in Surroundings

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    Companies use optical fiber as a sensor to detect changes in temperature and pressure. This technique is often used to monitor structures including bridges and gas pipelines.

    Now researchers at Ecole Polytechnique Fédérale De Lausanne (EPFL) have discovered a new method where optical fibers can identify when they are in contact with a liquid or a solid. The researchers accomplished this by generating a sound wave with help from a light beam inside the optical fiber.

    A Sensor That Doesn’t Disrupt the Light

    Four factors affect the light carried by a glass optical fiber: intensity, phase, polarization and wavelength. These factors can change when something stretches the fiber or the temperature varies. These changes let the fiber act as a sensor by detecting cracks in structures or temperature changes. However, until now, users could not know what was actually happening around the fiber without letting light escape, which interrupts the light path.

    The method from EPFL uses a sound wave generated inside the fiber. This hyper-frequency wave regularly bounces off of the fiber’s walls. This echo varies at different locations depending on the type of material that the wave contacts. The echoes leave an imprint on the light that users can read when the beam exits the fiber. While users can study this imprint to detect and map out the fiber’s surroundings, it is so faint that it barely disturbs the light within the fiber. In fact, users could employ this technique to sense what is occurring around a fiber and send light-based information at the same time.

    In experiments, the researchers submerged their fibers in water and then in alcohol, and left them out in the open air. Each time, their system correctly identified the change in the fibers’ surroundings. The group expects their technique to have many potential applications by detecting water leakage, as well as the density and salinity of fluids that touch the fiber.

    Spatial and Temporal Detection

    This method discerns changes in the surroundings with a time-based method. Each wave impulse is created with a slight time jag. Then, when the beam arrives, the delay is reflected. The researchers can see what any disturbances were and determine their location. The group can currently locate disturbances to within 10 meters, but have the technical means and expect to increase accuracy down to one meter.

    To read and learn more, go HERE.