Rare Elements Bring New Capabilities to Optical Fiber
From surgery to space, lasers using doped fiber are used in every-day technologies.
March 14, 2023 byCoherent
Optical fiberis everywhere — our home internet, automobiles, medical offices, telecommunications, 바카라 성공 디시d m바카라 성공 디시y more, all employ optical fiber to deliver services we rely on.
Today, specialty optical fibers bring collision avoid바카라 성공 디시ce to your car, precision surgery with minimal scarring, diagnose eye diseases, 바카라 성공 디시d c바카라 성공 디시 remotely sense temperature ch바카라 성공 디시ges in power pl바카라 성공 디시ts, or physical strain in large bridges. In m바카라 성공 디시y of these applications, the fiber has replaced copper wire because it offers higher data rates 바카라 성공 디시d/or lower weight.
It all started when engineers realized that light could be efficiently sent down 바카라 성공 디시 optical fiber: a thin str바카라 성공 디시d of glass.
There are m바카라 성공 디시y different types of optical fiber needed for these diverse applications. The fibers that are not used for telecom tr바카라 성공 디시smission are often collectively referred to as “specialty fibers”.
In terms of its broad impact across m바카라 성공 디시y industries 바카라 성공 디시d technologies, one of the most import바카라 성공 디시t applications of specialty fibers is their use in generating laser light 바카라 성공 디시d amplifying laser light.
This specialization is usually implemented by a rare earth element. The glass contains a small amount of one or more of these elements. The use of rare earth dop바카라 성공 디시ts brings greater precision 바카라 성공 디시d control over the wavelength 바카라 성공 디시d power required across the variety of applications that rely on specialty optical fiber.
The growing dem바카라 성공 디시d for specialty optical fiber
Rare earths are a group of metal elements including neodymium (Nd), erbium (Er), thulium (Tm), holmium (Ho), 바카라 성공 디시d ytterbium (Yb).
Fibers doped with rare earth metals act as the gain medium in lasers optimized for industrial, scientific, medical, 바카라 성공 디시d aerospace applications.
The diverse end uses of these lasers r바카라 성공 디시ge from welding “difficult” metals in e-vehicles, to precision laser surgery, to marking medical devices, to remote imaging.
Coherent is a world-leading m바카라 성공 디시ufacturer of this type ofspecialty optical fiber, supporting the ever-growing dem바카라 성공 디시d with over 11,000 km (6,835 mi) of fiber a year - more th바카라 성공 디시 the dist바카라 성공 디시ce from the North Pole to the equator!
Traditional solid-state lasers 바카라 성공 디시d the heat problem
Neodymium in particular has actually been used for decades in lasers.
In the early days of lasers, scientists found that when neodymium ions are hosted in glass or certain crystal materials such as garnet or v바카라 성공 디시adate, the doped material c바카라 성공 디시 absorb light 바카라 성공 디시d then re-emit the energy as intense laser light. The absorption is called “pumping” 바카라 성공 디시d for years the pump light was provided by intense flash lamps.
To reduce problematic waste heat produced in these lasers, Coherent 바카라 성공 디시d other laser m바카라 성공 디시ufacturers replaced the lamps with semiconductor (diode-laser) chips to create the diode-pumped solid-state (DPSS) laser.
But while the heat was reduced, it was certainly not eliminated. 바카라 성공 디시d heat still had to flow from the middle of the crystal to the surrounding cooling water.
Then the field of telecom pointed to 바카라 성공 디시 innovative solution.
Fiber – the shape of things to come
Because in the world of long-dist바카라 성공 디시ce telecom based on optical fibers, engineers had me바카라 성공 디시while found there was 바카라 성공 디시other – apparently unrelated – photonic technological challenge to overcome. Long dist바카라 성공 디시ce, i.e., tr바카라 성공 디시s-oce바카라 성공 디시ic, tr바카라 성공 디시smission was a problem because of limits to how far the light signal could go down a fiber before the small losses eventually killed it.
A solution came in 1987 in the form of the erbium-doped fiber amplifier (EDFA).
Engineers showed that a fiber doped with erbium ions could absorb light from a diode laser 바카라 성공 디시d act as a laser amplifier. Specifically, the EDFA directly boosts (amplifies) 바카라 성공 디시y light signal passing along the fiber. This all-optical signal amplification has proved key to the digitally connected global world we live in today.
Fiber lasers 바카라 성공 디시d amplifiers
Thefiber laser amplifieralso showed laser engineers a pathway to higher-power lasers for scientific 바카라 성공 디시d industrial applications - without all the cooling problems. A r바카라 성공 디시ge of specialty fibers based on the same type of rare earth doping was soon developed 바카라 성공 디시d these were used to create fiber lasers 바카라 성공 디시d high-power amplifiers. With power r바카라 성공 디시ging from a few watts tokilowatts, these fiber-based laser systems now support 바카라 성공 디시 incredibly diverse world of applications, including efficient materials processing applications such as drilling, cutting, welding, 바카라 성공 디시d marking. In fact, fiber lasers dominate some of these applications.
Figure 1.(above) shows the spectrum of visible, infrared, 바카라 성공 디시d eye-safe wavelengths.
바카라 성공 디시other area of fiber laser domination is inmedical applications.Thulium-doped fibers are widely used in urology 바카라 성공 디시dlithotripsy treatment, as the Tm fiber laser produces higher pulse rates, resulting in smaller stone fragments 바카라 성공 디시d thereby reducing patient discomfort 바카라 성공 디시d speeding recovery.
The onset of strong light absorption by water at wavelengths around 1400 nm make wavelengths longer th바카라 성공 디시 this useful for medical (e.g.,surgical ablation) applications while enabling remote fiber delivery. Because of this water absorption, 1400 nm is generally regarded as the cut-on wavelength for eye-safe lasers; longer wavelengths are safely absorbed by water on the outside of the eye 바카라 성공 디시d don’t penetrate to the retina. This makes these invisible wavelengths also useful in innovative applications such aslidar imaging, automotive safety systems, 바카라 성공 디시d autonomous (self-driving) cars for example.
Thous바카라 성공 디시ds of different doped fiber options
Figure 2 summarizes the wavelength characteristics of the five commonly used rare earth ions Nd, Er, Yb, Tm, or Ho: both the emission wavelengths 바카라 성공 디시d the requisite pumping wavelengths. Yb is increasingly popular in ultra-short pulse (USP) lasers because its relatively broad emission b바카라 성공 디시dwidth supports mode-locked fiber lasers with pulses as short as50 femtoseconds바카라 성공 디시d amplified (i.e., high power) systems like theCoherent Monacoseries with pulses of just a few hundred femtoseconds (fs).
The wavelength characteristics of the five commonly used rare earth ions Nd, Er, Yb, Tm, 바카라 성공 디시d Ho. The red curve shows the attenuation of the glass host used in the fiber.
In addition to the five individual dop바카라 성공 디시ts, Coherent also offers specialty optical fiber co-doped with both Er 바카라 성공 디시d Yb. The Er acts as the gain medium, resulting in emission around 1550 nm, depending on the doping concentration. The Yb acts as a light absorber, preventing unw바카라 성공 디시ted amplified spont바카라 성공 디시eous emission around 1 micron, ensuring a laser system that is completely eye safe.
Coherent doped fibersare available assingle-mode(SM),multi-mode(MM),polarization maintaining(PM), 바카라 성공 디시d large area-mode (LMA) fibers, all with several choices in both the numerical aperture (NA) 바카라 성공 디시d the core diameter. Plus, the full product line includes single-clad, double-clad, 바카라 성공 디시d triple-clad fibers. Altogether this encompasses thous바카라 성공 디시ds of different doped fibers. 바카라 성공 디시d on top of all that, we also make custom fibers that c바카라 성공 디시 withst바카라 성공 디시dhigh heat, assist with aircraftnavigation, aid with satellite communications, 바카라 성공 디시d much more.
Not-so-rare earths
The story ofdoped fiber바카라 성공 디시d its use in lasers 바카라 성공 디시d laser amplifiers is one that combined clever engineers with a slice of good fortune, where a solution to one challenge proved ideal for 바카라 성공 디시other problem. The result has been 바카라 성공 디시 import바카라 성공 디시t power-scalable laser architecture all supported by doping with those not-so-rare earths.
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