Fiber Laser: How it works, advantages, and application
Fiber lasers have emerged as a game-changer in various industries. Fiber lasers utilize optical fibers as their gain medium, enabling them to deliver exceptional performance across a wide range of tasks. From laser marking and cutting to welding and cleaning, fiber lasers have revolutionized traditional manufacturing processes, providing superior results with greater efficiency.
What is a fiber laser?
Fiber lasers utilize optical fibers as their active gain medium and belong to the category of solid-state lasers. The process involves absorbing raw light from pump laser diodes in a fiber composed of silicate or phosphate glass. Subsequently, the fiber converts this absorbed light into a laser beam characterized by a specific wavelength. To get this, the optical fiber is doped with rare-earth elements.
By employing various doping elements, a wide range of laser beams can be generated, each with its own distinct wavelength. The broad spectrum of wavelengths produced by fiber lasers makes them highly versatile for a multitude of applications. These include machine laser cutting, texturing, cleaning, laser engraving, jewelry engraving, drilling, marking, and welding. Consequently, fiber lasers have found utility across diverse sectors such as medicine, defense, telecommunications, automotive, spectroscopy, electrical, manufacturing, and transportation.
How does a fiber laser work?
Fiber lasers harness pump light emitted by laser diodes, directing the emitted light into a fiber-optic cable. Within the cable, optical components are employed to produce a precise wavelength and amplify it. Subsequently, the laser beam is carefully shaped and released for its intended purpose.
Below is how fiber lasers operate through their several components.
Creation of pump light in the laser diodes
Laser diodes, also referred to as the "pump source," convert electricity into photons or light, which is then pumped into the fiber-optic cable. The process of generating light in diodes involves the utilization of two differently charged semiconductors.
The first semiconductor is positively charged and requires an additional electron. Conversely, the second semiconductor carries a negative charge and possesses either an excess or a free electron.
When the positive and negative charges come into contact, they strive to combine. To facilitate this combination, the free electron is released as a photon. As current flows through the semiconductors, the number of photons rapidly increases.
The resulting light is then directed into the fiber-optic cable, where it will be utilized to produce the laser beam.
Pump light is guided and passes through the optical fiber
Within the optical fiber system, a coupler plays a vital role in combining the light emitted from multiple laser diodes into a unified good source of fiber. This coupler, integrated into the optical fiber, possesses multiple entry points on one side, each connecting to an individual fiber originating from a laser diode. On the opposite side of the coupler, a single exit point is present, linking to the main fiber. Once the light from all the laser diodes is collected, it travels toward the laser medium.
Subsequently, the light emitted by the diode laser traverses the optical fiber, comprising two primary components: the core and the cladding. The core, constructed of silica glass, serves as the pathway for the light, while the cladding encompasses the core. As the light reaches the cladding, it undergoes total internal reflection, redirecting it back into the core.
Although some power is inevitably lost as heat in fiber lasers, the favorable surface area to volume ratio facilitates efficient heat dissipation, resulting in minimal wear and tear due to thermal effects. During its journey through the optical fiber, the light eventually reaches the doped section of the fiber, commonly referred to as the laser cavity.
Stimulated emission in the laser cavity
When laser diode light reaches the doped fiber, it excites electrons in the rare earth element, resulting in a population inversion crucial for laser production. As these excited electrons transition to lower energy levels, they emit photons of a specific wavelength. Through stimulated emission, these photons stimulate other excited electrons to emit similar photons, creating a cascade effect. The equilibrium between excited and relaxed electrons ensures a continuous flow of raw laser light. However, further refinement is necessary for the light to be utilized in various applications.
Amplification of raw laser light into a laser beam
To prepare the raw laser light emitted from the doped fiber for practical applications, a strengthening process is necessary. In fiber lasers, this is accomplished through the utilization of Fibre Bragg Gratings (FBGs). These gratings serve as reflective mirrors with varying reflectivity, replacing conventional dielectric mirrors.
The laser light within the fiber cavity undergoes a back-and-forth process, interacting with the Bragg Grating. A portion of the light infiltrates the grating in one direction, while the remaining light is reflected back into the laser cavity. The transmitted light that passes through the grating becomes the laser beam. This beam then proceeds through an oscillator, sometimes accompanied by a combiner, to enhance coherence before being delivered as the final output.
Laser light of a specific wavelength is created
The wavelength generated by the doped fiber relies on the choice of a doping element within the laser cavity. This aspect holds significant importance since different applications necessitate different wavelengths. Common doping elements include erbium, ytterbium, neodymium, and thulium, among others. For instance, ytterbium-doped fiber lasers produce a wavelength of 1064 nm, which finds application in laser marking and laser cleaning.
The laser beam is shaped and released
The laser beam formed by the exiting photons from the resonant cavity exhibits exceptional collimation owing to the light-guiding properties of the fiber. However, this high level of collimation may not be suitable for most laser applications. So to achieve the desired beam shape, various components like lenses and beam expanders are employed. Different types of lenses offer distinct advantages, and laser experts carefully select them to optimize the laser for specific applications.
What to Look for in a fiber laser?
Laser source
Fiber lasers exhibit variations based on the material mixed with the laser source. Several examples include ytterbium-doped fiber lasers, thulium-doped fiber lasers, and erbium-doped fiber lasers. These distinct types of fiber lasers are employed for diverse applications due to their ability to generate different wavelengths.
Mode of operation
Various types of lasers emit laser beams in different ways. Laser beams can be generated through pulsed fiber lasers, which operate by pulsing at a specific repetition rate to achieve high-peak powers. This is commonly observed in lasers known as "q-switched," "gain-switched," and "mode-locked" lasers. On the other hand, laser beams can also be continuous, meaning they continuously emit a consistent amount of energy. This continuous emission is typically seen in lasers called "continuous-wave fiber lasers."
Laser power
The power of a laser is measured in watts and indicates the average power of the laser beam. For instance, there are 20W fiber lasers, 60W fiber lasers, and various other power options available. A high-power laser has the capability to generate energy at a faster rate compared to low-power lasers.
Mode
The mode of an optical fiber refers to the size of the core through which light travels. There are two categories of modes: single-mode fiber lasers and multi-mode fiber lasers. In single-mode lasers, the core diameter is smaller, typically ranging between 8 and 9 micrometers. Conversely, multi-mode lasers have a larger core diameter, usually between 50 and 100 micrometers. As a general guideline, single-mode lasers are more efficient in conveying laser light and exhibit superior beam quality compared to multi-mode lasers.
Why use fiber lasers?
With the advancements in fiber laser technology, the range of applications for these lasers continues to expand along with their practicality.
Stable
Typically, when we intend to transmit a laser beam, we often rely on optical fibers to ensure its safe and reliable movement. Another option is to reflect the beam between mirrors, but this method necessitates precise alignment. Achieving efficient coupling of a laser beam into the minuscule core of a fiber is challenging and requires meticulous adjustments. Consequently, conventional lasers are highly susceptible to disruptions from impacts or jolts, and realigning the optics requires the expertise of a specialist. In contrast, fiber lasers generate the beam internally within the fiber itself, eliminating the need for intricate and delicate optics during beam delivery. This inherent characteristic renders fiber lasers highly stable and user-friendly.
High beam quality
The fiber laser generates and confines the beam within the compact core of the fiber. As a result, the beam remains exceptionally straight and can be focused into a minute dot. This quality proves particularly advantageous in applications such as precision fiber laser cutting, where a smaller dot size enhances laser effectiveness. In numerous laser applications, achieving such a focused beam is highly desirable.
Powerful laser
Laser devices can pose a threat to the skin even at relatively low power levels, typically starting at around 1 Watt. Although this amount of power may seem insignificant when compared to everyday appliances like kettles or toasters, the concentrated focus of a laser beam on a single point amplifies its impact significantly. Fiber lasers, in particular, have been advancing in terms of power and can now exceed 1,000 Watts (1kW). This level of power is more than sufficient to penetrate through an inch of steel, highlighting the impressive cutting capabilities of fiber lasers.
Efficient and cools easily
Unlike other types of lasers that have lower power conversion efficiency, a fiber laser has the ability to convert approximately 70-80% of the input power from the pump source. This high efficiency is not only beneficial for power consumption but also results in less power being transformed into heat. In fiber lasers, the heat is distributed along the length of the fiber, which helps prevent excessive heating that could lead to fiber breakage. It's worth noting that the optical properties of most materials undergo changes as they heat up, and these changes can have an impact on the quality of the laser beam.
Applications of fiber lasers
Fiber lasers find extensive application across a diverse range of power outputs, enabling their effectiveness in various fields. Here are several examples of that a fiber laser cut machine can do:
Laser marking
Ytterbium-doped fiber lasers emitting at a wavelength of 1064 nm are widely regarded as ideal for laser marking purposes. These lasers excel in creating permanent, high-contrast marks on various materials including plastics and metals. Both original equipment manufacturers (OEMs) and suppliers rely on laser marking machines for part identification needs, such as barcodes, logos, and other textual information.
Laser marking machines can be categorized as either manual or automated, providing flexibility to accommodate different production cycles, whether they are short or extended. These machines are highly customizable to meet specific requirements. Beyond marking applications, a fiber laser cut machine is also capable of performing tasks such as annealing, etching, and laser engraving, further expanding their versatility.
Laser cleaning
Laser cleaning, a process performed by fiber lasers, proves highly efficient in removing various contaminants like paint, oxide, and rust from metal surfaces. This automated process can be customized to match the specific parameters of different production lines, enhancing its adaptability and effectiveness in diverse industrial settings.
Laser welding
Fiber lasers are extensively used in welding services, making them one of the most promising and rapidly growing technologies in the field. Fiber laser welding offers numerous advantages, leading to its increasing market share. This advanced process enables faster welding speeds, enhanced precision, reduced deformation, superior quality, and improved overall efficiency when compared to traditional welding methods.
Laser cutting
The application of fiber laser cutting is a highly researched area within the realm of fiber lasers. It exhibits remarkable capabilities in handling intricate cuts while maintaining impressive edge quality. As a result, a fiber laser cut machine is particularly well-suited for parts that require close tolerances. The adoption of laser cutting is steadily growing across various industries, as fabricators recognize its extensive list of benefits.
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