High Pulse Energy Erbium-Doped Fiber Laser-an Ideal Eye-Safe Laser Radar Light Source
High pulse energy fiber lasers can have great application potential, especially for various lidar applications. In the past few decades, scientists have been trying to solve many challenges in pulsed fiber lasers. One of the most important technical challenges is how to obtain high enough single pulse energy and peak power from an all-fiber laser system for long-distance lidar measurements.
High-pulse energy Erbium-doped (Er) pulsed fiber laser is an ideal eye-safe laser light source, especially suitable for long-range lidar applications in the atmosphere, including, for example, atmospheric wind speed remote sensing measurement, observation of atmospheric chemical small molecules, and remote targets Ranging/recognition etc.
All Fiber Pulsed Laser
The all-fiber pulse laser adopts the same fiber laser system design structure (MOPA), and uses different seed laser pulse formats, which can generate narrow linewidth laser pulses for coherent lidar or direct time-of-flight (TOF) The short-pulse laser required for detection of lidar.
However, the existing all-fiber pulsed lasers cannot be widely used in lidar applications. The main obstacle lies in its limited pulse output energy and peak power, which is limited by various nonlinear optical effects in fiber lasers. . In the past decade, there have been a lot of efforts to meet this challenge-that is, how to obtain high-energy laser pulses from an all-fiber laser system. At present, the existing high-power pulsed all-fiber lasers/amplifiers on the market usually use large-mode field gain fibers based on the step refractive index of quartz glass. For this reason, a gain fiber of several meters is required to construct the last-stage fiber power amplifier. Generate the required pulse output energy.
In such fiber amplifiers, the use of such a long gain fiber greatly limits their maximum output energy. For example, for laser pulses with limited linewidth of Fourier transform (~100 ns pulse width), if you want to have a fairly good The beam quality, the maximum single pulse energy is only <200 μJ, which is mainly affected by the stimulated Brillouin scattering (SBS) effect in the gain fiber. Although in rod-shaped photonic crystal fibers with ultra-large core diameters, the ability to generate maximum pulse energy up to mJ level has been demonstrated for a long time, photonic crystal fibers have not been widely used in commercial pulsed fiber laser systems, mainly because It lacks an all-fiber solution for signal laser and pumping processing coupling, and has to still use a fragile free-space optical coupling solution similar to solid-state lasers. This completely loses the greatest advantage of fiber laser/amplifier itself, those are, its compactness and reliability of its height.
High Pulse Energy Erbium (Er) Fiber Laser
In the past few years, AdValue Photonics of the United States has developed a multi-component glass fiber laser technology with independent intellectual property rights, which can output a single pulse energy greater than 1 in multiple spectral regions (1 μm, 1.55 μm and 2 μm bands). mJ, Fourier transform limited line width, pulse duration is about 100 ns laser pulse. This technology can be applied to an all-fiber laser system to generate laser pulses with the same high single pulse energy but shorter pulse duration (2~5 ns), which is suitable for TOF lidar detection.
The uniqueness of this glass fiber lies in its very high rare earth ion doping, which enables it to produce high optical gain in a short large-mode field gain fiber and output high-energy laser pulses in a single-mode field. The fiber laser amplifier composed of this special gain fiber, large fiber core diameter (30-50 μm) and short gain fiber (tens of centimeters) greatly improves the threshold of nonlinear optical effects and maintains high beam quality.
Among the three commonly used spectral bands of the above-mentioned fiber lasers, the erbium-doped fiber pulse laser operating in the 1.55 μm band is particularly beneficial to the application of lidar. Compared with the other two bands, the 1.55 μm band lidar has more advantages, including eye safety, atmospheric transparency, and ready-made high-speed and high-sensitivity signal detectors for the optical communications industry, or low-cost, high-speed , High resolution, high sensitivity, two-dimensional imaging device without active cooling, suitable for three-dimensional coherent radar imaging applications.