On March 20, 2018, according to the American Optical Society, researchers for the first time optically captured and excited a particle-based centimeter-level laser inside a fiber. The new high-speed propagating microlaser enables high sensitivity along the length of the fiber. Temperature measurements, and can provide a novel way to accurately transmit light to distant and difficult-to-reach locations.
'This high-speed microlaser has great potential for transmitting light in the body.' Said Richard Zeltner, Marx Planck Institute for Optical Science, Germany. 'By inserting the fiber into the skin, the microlaser can provide the appropriate wavelength and position the light accurately. Photosensitive drugs. This concept can also be applied to optofluidic lab-on-a-chip devices to provide light sources with high spatial resolution for various bioanalytical techniques or on-chip temperature measurements. 'On the Optical Society (OSA) Journal of Optics Researchers led by Philip St.J. Russell reported that high-speed microlasers can perform position-sensitive temperature-sensing measurements with millimeter-scale spatial resolution. This example demonstrates the utility of high-speed microlasers in distributed sensing. And real-time, continuous measurements along the fiber's direction.
The high-speed transmission microlaser is based on a whispering gallery mode resonator, which is a small particle that limits and enhances certain wavelengths of light. The name comes from the phenomenon that light waves propagate along the curved inner surfaces of these particles. Like sound waves spread in the whispering wall of Paul Cathedral, the whispered sound is clearly heard on the other side of the gallery.
'This is the first time that a distributed sensing demonstration of a whispering gallery mode resonator has been used,' Zeltner said. 'This unique sensing approach opens up many new possibilities for distributed measurements and remote physical performance evaluation with high spatial resolution. For example, it is useful for temperature sensing in harsh environments.
Making high-speed transmission lasers
A key part of the realization of high-speed transmission microlasers is a special type of optical fiber, called hollow-core photonic crystal fiber. As the name implies, unlike the traditional glass solid glass, the core part of this fiber is empty. The hollow part is Glass microstructure coating, the glass microstructure can confine the light inside the fiber.
"For quite some time, our research team has been developing the necessary technology for light trap particles in hollow photonic crystal fibers," said research team member Shangran Xie. 'In this new job, we can apply this technology. Not only to capture a particle, but also to make it a laser capable of long-distance detection in an optical fiber.
A whispering gallery mode particle is transported along an air-core fiber, and the fiber-embedded metal V-groove performs the heating function. Initially, only a constrained laser beam is introduced into the fiber from the left end of the fiber. About 37 seconds later, the second constrained laser The beam is introduced from the right end of the fiber, causing the particles to stop transmitting and capture in the center of the V-shaped groove.
In order to achieve high-speed transmission of micro-lasers, the researchers injected the laser into a water-filled hollow core to capture the particles optically. Like the materials used to make conventional lasers, the particles also contained a gain medium. The researchers used a second beam. The laser excites this kind of gain medium, causing particles to emit light or lasing. The position of the particles in the fiber is controlled by the optical force generated by the capturing laser or by the internal water flow in the core region.
Accurate temperature sensing
To test the ability of the new system to sense temperature changes, the researchers advanced the laser particles along two areas heated to 22 degrees Celsius above room temperature. By measuring the shift in wavelength of the laser light emitted from the micro-laser as it passes through the fiber, Accurately detect changes in temperature. The temperature change detected by the sensor is less than 3 degrees Celsius and provides a spatial resolution of a few millimeters.
'The spatial resolution of this distributed sensor is ultimately limited by the size of the particle.' Zeltner said. 'This means that we can achieve a spatial resolution as small as a few microns in a very long measurement range, with other types of distribution Compared to temperature sensors, this is a huge advantage of our system.
Using laser Doppler velocimetry, the researchers determined that during the experiment, the particles moved at a speed of 250 micrometers per second. They said that using fiber filled with air instead of water can increase the speed of advancement to centimeters per second or even meters.
Although the microparticles used in the experiment caused photobleaching, which caused the loss of excitation after about one minute, the researchers stated that particles with different gain materials can solve this problem. They are also exploring whether multiple fibers can be manipulated simultaneously inside the fiber. Micro laser, and is improving the particle position detection scheme.
'With the accelerating commercialization of hollow photonic crystal fibers, all the technology needed for this system to become a practical sensor is already available,' Zeltner said.
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