Fibers lasers are a very commonly used type of laser. Whether they are being used for communication purposes, materials processing, or medicine, they have come a long way from their humble beginning. This article covers the invention, development, and ultimately, the rise of fiber lasers.
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The inventor of the fiber laser was Elias Snitzer. When he started at American Optics (AO), despite the company's desire to officially establish themselves as a prominent force in fiber optics through more publications, Snitzer was not initially working towards creating a fiber-based laser. He was hired to work on projects dealing with exploring waveguide-mode propagation. Snitzer built a setup at AO to create his own fibers for his wave-guide mode studies. Creating thin enough fibers, he realized, made them act as single-mode waveguides. Snitzer thought that these supported waveguide modes in the glass fiber could make a good host for a maser, since the waveguide structure already existed.
At that time, most colleagues Snitzer encountered maintained the stance that lasing could not (and would not) occur using glass. Undeterred, Snitzer and his group at AO pressed on using different types of doped glasses. Through their attempts, they realized that by cladding the fiber and having a good interface between the core and cladding made the quality of the end reflectors less critical to the fiber's success.
One of the other keys to creating the fiber laser was using the right material to dope the glass. They realized that visible fluoresces were not going to work, so they moved into the infrared. In collecting the data, he realized neodymium gave very high signals when fluorescing. From that, the research continued using different compositions of glasses doped with rare earth elements. In , they were finally able to observe lasing using the neodymium glass rods. The work was published in Physical Review Letters in .
Fiber Laser ProgressionWhile the fiber laser was invented in , it took a good twenty years before it was developed and integrated into the commercial market. Snitzer had a hand here as well, with the invention of the double-clad fiber laser in . Double-clad fiber lasers facilitate a higher power output. In double-clad fibers, the laser light propagates through the core, but the pump light travels through the inner cladding that surrounds the core. The inner core is then encased in an outer cladding. The refractive index of the inner cladding is lower than that of the core but higher than that of the outer cladding.
Double-clad fiber lasers are still used today. There are double-clad fiber lasers available with different geometries for the inner core. The different geometries make it easier to match properties of the pump source to the fiber for improved coupling. Snitzer contributed a substantial amount to the field of fiber optics, which, among other things and the lasers mentioned, also included inventing fiber amplifier.
In , work by IPG Photonics in Moscow improved ytterbium-doped fiber lasers to output power of 1 W. By , they recorded a single-mode fiber output of 10-kW. IPG has continued to innovate fiber lasers since that then. As fiber grew more popular and for telecommunications industry was on the rise, unsurprisingly, fiber laser research grew too, though keeping a lower profile than fiber communications.
Fiber Lasers TodayFiber lasers today are available in multiple configurations. They can be continuous wave (CW), Q-switched, mode-locked, gain-switched, and quasi-continuous wave (QCW) to list a few. Most single-mode fiber lasers tend to be CW. QCW lasers are one of the newer types of fiber lasers. When compared to CW lasers, QCW lasers have both a higher peak power and lower average power. QCW lasers come in both the single-mode and multi-mode variety.
Most fiber lasers have erbium, neodymium, and ytterbium as their gain medium and are diode-pumped. There are different methods to pumping fiber lasers. One method of pumping is side pumping. In side pumping, the pump light is directed into the fiber from an angle close to perpendicular to the laser. Side pumping also distributes absorbed pump power smoothly. This method makes it possible to use pump sources with low spatial coherence allowing to combine different light sources to use as a pump. The other commonly used method of pumping is end pumping. End pumping usually results in a better-quality beam and higher gain than side pumping. A downside of end pumping is that unwanted higher order resonant modes can be present. While double-clad fiber lasers are usually end pumped, they can be side pumped.
Advantages of Fiber LasersFiber lasers have some advantages over other laser types, dependent upon their intended use. One of the benefits of fiber lasers is their sensitivity. Since they are meant to be coupled into fiber, it is difficult to move them out of alignment, unlike other lasers. They are typically more compact than your general laser. Comparatively, fiber lasers also have a lower heat output and lower power consumption with better beam quality than their non-fiber counterparts.
ConclusionFiber lasers have gone from milliwatt output powers at the time of their invention to now being capable of outputting power on the order of kilowatts. For instance, the US Navy was in the process of developing a of a 30-kW laser and intends to build a weapon system housing a 150-kW fiber laser. Through the years, it is clear that innovation has improved fiber laser versatility and has rendered them invaluable to a range of industries.
Do you know any interesting or odd facts about fiber lasers? Please comment below.
If you liked this article you might also like our comprehensive guide on gas lasers.
Fiber lasers are everywhere in the modern world. Due to the different wavelengths they can generate, they are widely used in industrial environments to perform cutting, marking, welding, cleaning, texturing, drilling and a lot more. They are also used in other fields such as telecommunication and medicine.
Fiber lasers use an optical fiber cable made of silica glass to guide light. The resulting laser beam is more precise than with other types of lasers because it is straighter and smaller. They also have a small footprint, good electrical efficiency, low maintenance and low operating costs.
If you want to learn everything you need to know about fiber lasers, keep reading.
Elias Snitzer invented the fiber laser in and demonstrated its use in . Serious commercial applications only emerged in the s, however.
Why did it take so long? The main reason is that fiber laser technology was still in its infancy. For example, fiber lasers could only emit a few tens of milliwatts whereas most applications require at least 20 watts. There was also no means of generating high-quality pump light, as laser diodes did not perform as well as today.
Here are some of the key moments in the history of fiber laser technology, going back as early as when Albert Einstein established its foundations.
Today, important advances are still being made in fiber laser technology, making it more efficient, powerful and accessible. Some of the most upcoming applications include laser cleaning and laser texturing, which can replace polluting technologies and help make the world greener.
Generally speaking, fiber lasers can be categorized using the following criteria:
Fiber lasers can be categorized in many other ways, but the categories mentioned here are the most common. Follow these links if you want to see examples of fiber lasers integrated into products:
The main difference between fiber and CO2 lasers is the source where the laser beam is created. In fiber lasers, the laser source is silica glass mixed with a rare-earth element. In CO2 lasers, the laser source is a mixture of gases which includes carbon dioxide.
Due to the state of their source, fiber lasers are considered solid-state lasers, and CO2 lasers are considered gas-state lasers.
These laser sources also produce different wavelengths. Fiber lasers, for example, produce shorter wavelengths, with some examples ranging between 780 nm and nm. CO2 lasers, on the other hand, produce longer wavelengths that typically range between 9,600 nm and 10,600 nm.
They are used for different applications due to their different wavelengths. For example, nm fiber lasers are usually preferred for metal processing applications. Laser cutting is a notable exception, where CO2 lasers are often preferred to cut metals. CO2 lasers also react well with organic materials.
If you're debating between the two, read our post on choosing between a CO2 and a fiber laser.
When a fiber laser system is engineered into a solution that is ready to be used, that solution is called a fiber laser machine. Whereas the OEM laser system is the tool that performs the operation, the laser machine is the framework in which the tool is integrated.
Laser machines can make sure that:
For example, the fiber laser machine shown here includes a rotary table, a rotary indexer, a Class-1 laser safety enclosure, a fume extractor, a vision camera and an HMI.
Follow these links if you want to see more examples of fiber laser machines:
Most online sources claim that fiber lasers last 100,000 hours whereas CO2 lasers last 30,000 hours. This is not entirely true. These numbers refer to a value called 'mean time between failures' (MTBF), which isn't the same for all fiber lasers. In reality, you will see different numbers for different types of fiber lasers.
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The MTBF measures the reliability of a laser by indicating how many hours the laser is expected to function before a failure occurs. It is obtained by testing multiple laser units, and then dividing the total number of operational hours by the total number of failures.
Although this value does not exactly tell you how long a fiber laser can last, it still provides a good idea of the laser's reliability.
If you really want to know the exact lifespan of a fiber laser, you'll be disappointed as there's no real answer. In truth, fiber lasers have critical points in their lifetime when they can fail.
Here's what you need to know if your laser experiences failures at any of these moments:
Fiber lasers use pump light from what is called laser diodes. These diodes emit light that is sent into the fiber-optic cable. Optical components located in the cable are then used to generate a specific wavelength and amplify it. Finally, the resulting laser beam is shaped and released.
Here's how each component is used to perform this operation.
Laser diodes transform electricity into photons'or light' to be pumped into the fiber-optic cable. For this reason, they are also known as the 'pump source'
To generate light, diodes use two semiconductors charged differently:
When the positive and negative charges meet, they try to combine. But to do so, the free electron must be released as a photon. As current flows through the semiconductors, the quantity of photons quickly increases.
The resulting light is pumped into the fiber-optic cable and will be used to generate the laser beam.
In nature, light goes in all directions. To focus light into a single direction and obtain a laser beam, fiber-optic cables use two basic components: the fiber core and the cladding.
Total internal reflection occurs because the cladding has a lower refractive index than the core. You can see similar effects in nature. For example, if you look at submerged objects, they appear deformed. This is because when light travels from air to water, it hits a different refractive index and changes direction. The same applies when light travels from the core to the cladding, except that the change in direction produces a reflection.
Without the cladding, light would go in all directions and exit the core. But thanks to the cladding's refractive index, light remains in the core and continues its path.
To visualize how light travels in fiber cables, you can watch this video:
As pump light travels through the fiber-optic cable, it eventually enters the laser cavity'a small region of the cable where only light of a specific wavelength is produced. Physical engineers say that the fiber is 'doped' in this region because it has been mixed with a rare-earth element.
As particles from the doped fiber interact with light, their electrons rise to a higher energy level. When they fall back to their basic state, they release energy in the form of photons or light. Physical engineers refer to these phenomena as 'electron excitation' and 'electron relaxation'.
The laser cavity also acts as a resonator where light bounces back and forth between what is called 'fiber Bragg gratings'. This leads to 'Light Amplification by the Stimulated Emission of Radiation', or LASER. Put simply, this is where the laser beam is formed.
There are two types of Bragg gratings:
Here's how amplification takes place: when photons hit other excited particles, these particles also release photons; since the Bragg gratings reflect photons back into the cavity, and more pump light is sent into the cavity, an exponential number photons are released.
As a result of this stimulated emission of radiation, laser light is created.
The wavelength produced by the doped fiber varies according to the doping element of the laser cavity. This is very important, as different wavelengths are used for different applications. The doping element could be erbium, ytterbium, neodymium, thulium, and so on. Ytterbium-doped fiber lasers, for example, generate a wavelength of nm and are used for applications like laser marking and laser cleaning.
Different doping elements produce different wavelengths because specific particles release specific photons. As such, photons generated in the laser cavity all have the same wavelength. This explains why each type of fiber laser generates a specific wavelength'and only that wavelength.
Photons that exit the resonant cavity form a laser beam that is extremely well collimated (or straight) due to the fiber's light guiding properties. In fact, it is too collimated for most laser applications.
To give the laser beam a desirable shape, different components can be used, such as lenses and beam expanders. For example, our fiber lasers are equipped with a 254 mm focal length lens for laser applications that dig into the material (i.e., laser engraving and laser texturing). This is because their short focal length allows us to focus more energy onto an area for a more aggressive form of laser ablation.
Other types of lenses provide different advantages, which is why experts choose them carefully when optimizing a laser for a specific application.
Not all lasers and laser applications use the same parameters. For example, different ones need to be adjusted for laser cutting and laser marking. Some parameters, however, are used for all types of fiber lasers. Here are the ones you are most likely to encounter.
The wavelength produced by a fiber laser corresponds to the level of electromagnetic radiation of the laser light. Typically, fiber lasers produce wavelengths between 780 nm and nm, which is located in the infrared spectrum and is invisible to the human eye. This range of infrared light tends to react well with metals, rubber and plastics, making it useful for a wide range of materials processing applications.
Some fiber lasers such as green lasers produce visible light which can react well with soft materials such as gold, copper, silicone and soft glass. Green fiber lasers are also used for holography, therapy and surgery, among other things.
These lasers require additional components to generate visible light. John Wallace from Laser Focus World explains how this is done:
['] there is actually no fiber laser on the market that produces visible laser light from within the lasing fiber itself. Visible light can, however, be obtained from a near-infrared (IR)-emitting fiber laser by external frequency conversion'for example, Raman-shifting, frequency-doubling, frequency sum-mixing, or combinations of these approaches.
Excerpt from
Photonics Products: Fiber Lasers: Visible fiber lasers do red, green, and now bluishby
Laser Focus World
The mode of operation is the way in which the laser beam is released. Fiber lasers typically operate in the continuous-wave or in the pulsed mode.
In the continuous-wave operation mode, a continuous, uninterrupted laser beam is released, which is ideal for applications like laser welding and laser cutting.
In the pulsed operation mode, short pulses are released at a set repetition rate. Pulsed laser beams reach higher peak powers and are ideal for laser engraving and laser cleaning. This mode includes the following parameters:
The laser power is the amount of energy that can be produced by the laser over one second. It is also known as 'average power' and 'output power'.
Pulsed lasers may also indicate a peak power, which is a different parameter. The peak power is the maximum amount of energy reached by a single pulse. For example, a 100W pulsed fiber laser can easily reach 10,000W of peak power. This is because pulsed lasers do not distribute energy evenly over time as opposed to continuous-wave lasers.
The beam quality indicates how close the beam is to what is called a Gaussian beam. In actual applications, this is relevant because it indicates how well focused the laser beam is.
Mathematically speaking, a perfect beam quality is expressed as M2=1. Laser beams that are well-focused concentrate more energy in a smaller area. High-quality laser beams are required for applications like laser engraving and laser cleaning, whereas lower beam qualities may be more appropriate for applications where ablation is not desired, such as laser welding.
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