OPTICAL FIBER LASERS
What are fiber lasers?
Fiber lasers or optical fiber lasers use the principle of total internal reflection with the help of optical fibers for transmitting light. These lasers are used for transmitting light over long lengths and also helps in reducing the thermal distortion of the laser beam. Optical fiber lasers are generally doped with rare-Earth with like ytterbium, erbium, neodymium, praseodymium, holmium, dysprosium, and thulium. These lasers used doped fiber amplifiers that do not use lasing action for providing light amplification. The gain in these lasers is provided by fiber nonlinearities like four-wave mixing or stimulated Raman scattering. In fiber lasers, the laser cavity is generated by the method of fusion splicing with different optical fibers.
What are the advantages of Optical fiber lasers?
Fiber lasers have significant advantages over other lasers:
- In fiber lasers, the laser light is both produced and directed by an integrally flexible medium allowing better and easier conveyance of laser light to the targeted location.
- Optical Fiber-based lasers provide high output power compared to the other different types of lasers.
- Optical fiber-based lasers provide very high optical gain and have active regions ranging over several kilometers.
- Optical fibers have a high surface area to volume ratio that allows continuous output power of kilowatt level with efficient cooling.
- The waveguide of an optical fiber reduces the distortion in the optical path due to thermal issues.
- Optical fiber-based lasers are comparatively more compact than solid-state or gas lasers (of the same power output) and generate a diffraction-limited, high-quality laser beam.
- Optical fiber-based lasers provide vibrational stability, high-temperature tolerance, and an extended lifespan at lower costs.
What are the applications of fiber lasers?
Optical fiber-based lasers provide high power continual laser beams that can be effective for several industrial applications like welding and cutting materials like polymer or metal or glass. Medium and low power fiber optics lasers are used for engraving on materials.
Apart from industrial applications, optical fiber-based lasers are also used in medicine, telecommunications, spectroscopy. lasers are well suited in medical field on delicate and soft tissues where using a scalpel might be difficult. Optical fiber-based lasers are often used in spectroscopy for studying and observing the interaction between electromagnetic radiations and matter.
What are optical fiber disk lasers?
Fiber disk laser is a form of optical fiber laser in which the pump is not restricted within the cladding of the optical fiber. The pump in these lasers is coiled in order to direct the pump light multiple times across the core. These types of lasers are effective for power scaling that requires several pump sources around the periphery of the coil.
How are optical fiber lasers mode-locked?
Optical fiber-based lasers are generally mode-locked with the help of birefringence of the fiber. Due to the optical non-linear Kerr effect, the amount of change in polarization varies with the intensity of light. Therefore, the polarizer present in the laser cavity absorbs or blocks the lower intensity laser light and allows high-intensity light to pass with negligible attenuation. This supports mode-locked pulses.
At times, Semiconductor saturable-absorber mirrors (SESAMs) are also used for mode-locking optical fiber lasers. Semiconductor saturable-absorber mirrors (SESAMs) have some saturable absorber techniques that allow customizing the absorber limits according to the laser type. In recent times, Graphene saturable absorbers are incorporated in optical fiber-based (especially in tunable lasers) for mode-locking.
What are dark soliton fiber lasers?
Dark soliton lasers were built from all-normal dispersion erbium-doped fiber laser that has a polarizer present in the laser cavity. These lasers belong to the non-mode locking regime. Even though the bright pulse emission is common for these lasers, under suitable conditions dark soliton fiber lasers are capable of emitting single or multiple dark pulses. The dark pulse generation by these lasers can be attributed to the dark soliton shaping according to numerical simulations.
What are Multi-wavelength optical fiber lasers?
Multi-wavelength fiber lasers are types of optical fiber based lasers that generate multiple wavelengths of laser light simultaneously. ZBLAN optical fiber-based laser demonstrated the emission of blue and green coherent light simultaneously. The ZBLAN end-pumped laser was grounded on an upconversion optical gain media that used semiconductor lasers of longer wavelengths for pumping a Pr3+/Yb3+ doped fluoride fiber. This fluoride fiber had coated dielectric mirrors present on either end of the optical fiber for forming a cavity.
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