Energy is provided by laser diodes, whose light (ordinarily 915nm or 977nm) is passed through optical fibers to reach the doped glass fiber. There are typically no clear beam routes for laser or pump light, resulting in the fiber laser being moderately indifferent to pollution and fluctuations. The overall lifespan of the pump diodes is high, primarily due to them having their own heat sink and being evenly distributed. The lifespan of the laser can last several tens of thousands of hours if the max power of the laser pulses is maintained below 10 – 20kW. There are two types of fiber lasers: continuously emitting, or continuous wave, and pulsed. Pulsed fiber lasers are typically better for engraving and marking applications, so they will be the only type discussed below. Pulse durations of about 100 nanoseconds are normal, though it is possible to achieve shorter pulses of a few nanoseconds at lower pulse energy.
The design of the MOPA fiber laser systems includes a master oscillator, otherwise known as a seed laser, as well as a fiber-coupled power amplifier. The power amplifier is either a diode laser or a “laser on a chip.” This has an average power ranging from just a few milliwatts to about 150mW. The laser has a specific pulse shape while the “laser on a chip” contains a laser on a single chip where the laser-active medium, reflectors, and additional optical components are usually combined, or sometimes even constructed from a single piece of material. The amplifier contains a ytterbium-doped glass fiber, which is provided energy through fiber-coupled pump diodes. To generate a laser pulse, the pump diodes charge the amplifier fiber through population inversion. Before it releases by random emission, the seed laser releases a pulse that is increased exponentially as it moves through the fiber. The amplification is completed in just one pass. The fiber is usually coiled allowing for higher gain in a small volume with a high amplifier range.