CW Fiber Lasers
Frequently Asked Questions
In fiber lasers the active gain medium is an optical fiber doped with rare elements. A pump source, typically a laser diode is coupled into the core of a doped optical fiber where stimulated emission occurs. Doping the optical fiber with rare earth element such as ytterbium, erbium, holmium, etc. creates the medium where population inversion is enabled and where light amplification by stimulated emission occurs. The light generated is then amplified upon thousands of reflections off the nodes of a fiber Bragg grating which acts as the “cavity mirrors” similar to that of a traditional free-space laser. Fiber Bragg grating acts as the optical filter allowing reflection of only specific modes in the laser cavity.
Fiber Bragg grating (FBG) is a periodic structure (segment of periodic variation of optical index) created inside the fiber core that causes the light to diffract, reflect or transmit based on the phase and wavelength. These periodic structures applied to the core of the optical fibers are typically a few millimeters or centimeters long with a period that is on the order of a wavelength or hundreds of nanometers. FBG acts as an effective optical filter in fiber optic devices including fiber lasers.
Single-mode and multimode fibers are both used in designing and producing fiber lasers. However, single-mode fiber lasers tend to be more efficient and have a higher beam quality. Not to mention that single-mode fiber lasers do not suffer from mode hopping. In particular, ultra-narrow linewidth fiber lasers are constructed of single mode fibers doped with rare elements.
Supercontinuum generation exploits the nonlinear effects of certain optical media. Therefore, the fibers used in supercontinuum lasers are made of strongly nonlinear materials. These fibers will also need to provide good transmission throughout the entire amplification bandwidth. Fluoride based optical fibers are often used in supercontinuum fiber lasers.
While free-space lasers can last up to 15 years, fiber lasers enjoy a much longer lifespan which could reach 45 years or the equivalent of 100,000 hours of operation. This longevity is thanks to the compact sealed design that has fully integrated cavity without any free space intracavity optics that exists in other DPSS lasers.
Owing to their strong power output, CW fiber lasers are widely used in laser machining applications such as laser cutting, drilling, marking, and welding. They are also used in many research areas to perform precision measurements, spectroscopy, laser pumping, and optical testing.
You are probably referring to the external fiber that couples the laser output to other devices. Typically, the fiber length ranges between 0.5 and 1m in fiber lasers. However, the fiber end is attached to a connector which makes it very easy and simple to connect to other fibers if needed. The length of the optical fiber inside the cavity is fixed and determines the amplification gain.
Some units offer a tunable wavelength feature which allows the user to select a wavelength out of a few options. Supercontinuum fiber lasers can be used along with a bandpass filter to filter out the desired wavelength as well.
Many suppliers of CW fiber lasers offer models with both linear and random polarization. Less frequently, circular polarization is also an available option on market from many suppliers.
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