Using a new laser process to custom shape optical fibers

Tue, 05/19/2015 - 11:24am Fraunhofer-Gesellschaft Thanks to a new laser process, optical fibers can now be inserted into even smaller vein branches. In this prototype, the tip is inside the fiber probe. © Fraunhofer IZMModern medicine relies on optical fibers to cauterize unhealthy veins in a minimally invasive way. Now, Fraunhofer researchers have developed a laser processing method that facilitates automated series manufacture of these fibers at a much finer quality than ever before. The scientists presented a fiber probe prototype manufactured using the new technique at the measurement fair SENSOR+TEST 2015 in Nuremberg. Venous disease is fairly widespread in Germany: According to the German Venous League, one in five women and one in six men suffer from varicose veins, thrombosis or other vein problems. Endovenous laser vein therapy is one remedy. For this procedure, a plastic-coated optical fiber 0.5 millimeters in diameter is inserted into the affected blood vessel. Laser light is conducted through the middle of the fiber to the fiber tip. At a temperature of several hundred degrees, the emitted light cauterizes the tissue and causes the veins to collapse. To ensure that the light strikes the side walls of the vein directly, the fiber tip is tapered with a cone-shaped indentation that forms a reflective surface for the laser light. A protective glass cap ensures that no blood deposits directly on the tip could change the optical characteristics of the laser light. The cap also protects the patient from any injury from the fiber tip. In the LaserDELight project, researchers at the Fraunhofer Institute for Reliability and Microintegration IZM have developed a new, laser-based process for precisely shaping this sort of optical fiber. They use the FiberTurningLaser, which is a laser for glass processing. “The method enables the first automated series production,” explains Dr. Henning Schröder from Fraunhofer IZM. Until now, producing the fibers required complicated mechanical and manual processes that not only took significantly longer, but cost more too. “What’s more, replicating a suitable product is extremely difficult,” adds Schröder. Automation ensures consistent high quality. The project is being funded by the German Federal Ministry of Education and Research BMBF. Optical fiber tip inside the probe Using a laser beam, the researchers can shape the optical fiber tip. In a later production step, the protective cap is fused onto the fiber so that no additional fixture is needed. “The new process has demonstrated that it is more practical to fashion a cone-shaped indentation in the fiber than have a tapered shape like the tip of a pencil,” explains Schröder. This offers yet another advantage: the cap on the fiber end is smaller because the tip of the cone is eliminated, making the fiber probe head in general more compact and versatile. Now, it can be inserted into even smaller vein branches. With help from laser technology, the scientists are trying to achieve even finer dimensions, which can no longer be produced by hand: the goal is optical fibers with a diameter of only 100-200 micrometers. These could open up new applications in the area of optical sensors, for instance as micro optics for visible light communication (VLC) —a technology for optical data transmission. To put it simply, for VLC, the process is the reverse of the endovenous laser procedure. “The fiber tip collects data from the environment and sends it back through the fiber to a detector,” Schröder explains. This detector—a photodiode or CMOS chip—converts the optical information into electrical signals for evaluation. Schröder and his Fraunhofer IZM colleagues will present the fiber probe prototype May 19-21 at the measurement fair SENSOR+TEST in Nuremburg (Hall 12, Booth 537). SOURCE: Fraunhofer-Gesellschaft

New technique doubles the distance of optical fiber communications

 

February 3, 2015 University College London - UCL A new way to process fibre optic signals could double the distance at which data travels error-free through transatlantic sub-marine cables. The new method has the potential to reduce the costs of long-distance optical fibre communications as signals wouldn't need to be electronically boosted on their journey, which is important when the cables are buried underground or at the bottom of the ocean. Optical fiber (stock image). A new way to process fibre optic signals has been demonstrated by UCL researchers, which could double the distance at which data travels error-free through transatlantic sub-marine cables. The new method has the potential to reduce the costs of long-distance optical fibre communications as signals wouldn't need to be electronically boosted on their journey, which is important when the cables are buried underground or at the bottom of the ocean. As the technique can correct the transmitted data if they are corrupted or distorted on the journey, it could also help to increase the useful capacity of fibres. This is done right at the end of the link, at the receiver, without having to introduce new components within the link itself. Increasing capacity in this way is important as optical fibres carry 99% of all data and demand is rising with increased use of the internet, which can't be matched by the fibres' current capacity, and changing the receivers is far cheaper and easier than re-laying cables. To cope with this increased demand, more information is being sent using the existing fibre infrastructure with different frequencies of light creating the data signals. The large number of light signals being sent can interact with each other and distort, causing the data to be received with errors. The study published in Scientific Reports today and sponsored by the EPSRC reports a new way of improving the transmission distance, by undoing the interactions that occur between different optical channels as they travel side-by-side over an optical cable. Study author Dr Robert Maher (UCL Electronic & Electrical Engineering), said: "By eliminating the interactions between the optical channels, we are able to double the distance signals can be transmitted error-free, from 3190km to 5890km, which is the largest increase ever reported for this system architecture. The challenge is to devise a technique to simultaneously capture a group of optical channels, known as a super-channel, with a single receiver. This allows us to undo the distortion by sending the data channels back on a virtual digital journey at the same time." The researchers used a '16QAM super-channel' made of a set of frequencies which could be coded using amplitude, phase and frequency to create a high-capacity optical signal. The super-channel was then detected using a high-speed super-receiver and new signal processing techniques developed by the team enabled the reception of all the channels together and without error. The researchers will now test their new method on denser super-channels commonly used in digital cable TV (64QAM), cable modems (256QAM) and Ethernet connections (1024QAM). Study author Professor Polina Bayvel (Electronic & Electrical Engineering) who is Professor of Optical Communications and Networks and Director of UNLOC, said: "We're excited to report such an important finding that will improve fibre optic communications. Our method greatly improves the efficiency of transmission of data -- almost doubling the transmission distances that can be achieved, with the potential to make significant savings over current state-of-the art commercial systems. One of the biggest global challenges we face is how to maintain communications with demand for the Internet booming -- overcoming the capacity limits of optical fibres cables is a large part of solving that problem."

Breakthrough in optical fiber communications

 

December 19, 2014 University of Southampton Researchers from the University of Southampton have revealed a breakthrough in optical fiber communications. They developed an approach that enables direct modulation of laser currents to be used to generate highly advanced modulation format signals. The research explores a radically new approach to the generation of spectrally-efficient advanced modulation format signals as required in modern optical communication systems. This is a constellation diagram of one of the mainstream modulation formats of the future system: Sixteen Quadrature-Amplitude modulation. Researchers from the University of Southampton have revealed a breakthrough in optical fibre communications. Academics from the University's Optoelectronics Research Centre (ORC) have collaborated with colleagues at Eblana Photonics Inc, in Ireland, to develop an approach that enables direct modulation of laser currents to be used to generate highly advanced modulation format signals. The research, published in the journal Nature Communications, explores a radically new approach to the generation of spectrally-efficient advanced modulation format signals as required in modern optical communication systems. This new technology, patented by the University of Southampton and licensed to Eblana Photonics Inc, avoids the need for costly and power-inefficient external modulator schemes that are currently used to generate such signals.. Dr Radan Slavik, Principal Research Fellow at the ORC, said: "Our paper highlights the exquisite control that we have achieved over the optical field generated directly from a current-modulated semiconductor laser." Direct current modulated lasers are of huge commercial relevance and are already widely used in optical communications, telecommunications and sensor and high power fibre laser systems. However, the inability to accurately control the full optical field emitted directly from such lasers has been a fundamental problem limiting applications. Dr Slavik explains: "The new capability we have demonstrated will be of relevance and could be of significant impact within many scientific and engineering communities that are directly concerned with or exploit laser radiation. "We have previously presented some of the results included in this paper at conferences, including a post-deadline presentation at Optical Fibre Communications (OFC), and at an international symposium and this has already generated a lot of interest from senior academics in our community, as well as from leading industrial players." Dr Rob Lennox, Director of Sales at Eblana Photonics Ltd., Dublin, said: "We are very pleased to have collaborated on this innovative development work performed by the ORC team and are looking towards making this new approach a commercial reality." Story Source: The above story is based on materials provided by University of Southampton. Note: Materials may be edited for content and length. Journal Reference: Zhixin Liu, Joseph Kakande, Brian Kelly, John O’Carroll, Richard Phelan, David J. Richardson, Radan Slavík. Modulator-free quadrature amplitude modulation signal synthesis. Nature Communications, 2014; 5: 5911 DOI: 10.1038/ncomms6911

Subwavelength optical fibers to diffuse light

 

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A laser beam (emitting at a wavelength of 600 nanometers) is guided into an optical microfiber.

Researchers at the Femto-ST Institute (CNRS/UFC/UTBM/ENSMM)(1), working in collaboration with colleagues from the Charles Fabry Laboratory (CNRS/Institut d'Optique Graduate School), have just discovered a new type of light diffusion in tiny optical fibers 50 times thinner than a strand of hair! This phenomenon, which varies according to the fiber's environment, could be used to develop sensors that are innovative and highly sensitive. The work is published in the journal Nature Communications on October 24, 2014.

Optical microfibres are silica fibres tapered down to a size 50 times smaller than a strand of hair, with an approximate diameter of one micrometer (a thousandth of a millimeter) or even less. To produce these tiny objects, researchers at the Charles Fabry Laboratory heated and stretched optical fibres used in telecommunications, measuring 125 micrometers in diameter. The remainder of the study was carried out at the Femto-ST Institute in Besançon. By injecting a laser beam in these silica microwires, the CNRS researchers observed a new type of Brillouin light scattering (2) for the first time, involving surface acoustic waves. This discovery was subsequently confirmed by a numerical simulation, which helped verify the physical mechanism at play. (3)

Since the diameter of the fibers is smaller than the wavelength of the light used (1.5 micrometers, in the infrared), the light is extremely confined inside. As it travels, it infinitesimally shakes the wire, displacing it by a few nanometers (one millionth of a millimetre). This distortion gives rise to an acoustic wave that travels along the fiber surface at a velocity of 3,400 meters per second, according to the results of the researchers. The wave in turn affects the propagation of the light, as part of the light radiation returns with a different wavelength in the opposite direction.

This phenomenon had never been observed previously, for it only occurs when light is confined in a subwavelength-diameter fiber. In standard optical fibers, light travels essentially in the core of the fiber (with a 10-micrometrer diameter), and consequently does not generate surface waves.

Since the waves generated by the confinement of the light travel along the surface of the microfibers, they are sensitive to environmental factors such as temperature, pressure and ambient gas. This makes it possible to design highly sensitive and compact optical sensors for industry(4). These results also help improve our knowledge of the fundamental interaction between light and sound on an infinitesimally small scale.

1. Femto-ST: Franche-Comté électronique mécanique thermique et optique -- sciences et technologies (CNRS/Université de Franche-Comté/Université de technologie de Belfort-Montbéliard/Ecole nationale supérieure de mécanique et des microtechniques de Besançon).
2. "Inelastic" scattering of light by acoustic waves of a medium. In other words, the properties of the medium modify the path of light waves as well as their wavelength.
3. Waves of the same nature as the sound waves perceived by our ears, but with a much higher frequency, and therefore inaudible.
4. As opposed to electrical sensors, optical sensors are passive sensors (that do not need electricity), and which use the properties of light.