# Brief Review of Recent Developments in Fiber Lasers
## 7 Conclusions  
The present work gives a brief overview of the latest achievements in fiber lasers including RE-doped fiber lasers, Raman fiber lasers, and Brillouin fiber lasers. In comparison to conventional bulk lasers, fiber lasers have a number of advantages.  
* The inherently flexible structure of fibers enables the use of much longer (up to several kilometers) gain distances, which provides higher optical gains, compared to other lasers.
* The optical feedback in fiber lasers is usually provided by fiber Bragg gratings imprinted in the fiber. This integrated design provides a stable optical cavity.  
* In fiber lasers, single-mode fibers typically offer the best beam performance, which is very important in a number of applications.
* In fiber lasers, the optical path is enclosed within protective cladding layers, and as a result, the laser beam is less susceptible to exterior disturbance compared to traditional lasers.  
It has been shown that the Er\({}^{3+}\)- and Tm\({}^{3+}\)-doped lasers are significantly limited in power and efficiency compared to Yb\({}^{3+}\)-doped fiber lasers, which can reach output powers of tens or hundreds of watts. Heat generation in traditional high-power fiber lasers is a serious problem.  
* One solution to the heat generation problem is the development of radiation-balanced lasers based on cooling with anti-Stokes fluorescence. The efficiency of the laser cooling process can be improved by applying novel low-phonon fiber materials. The recent achievements in implementing new materials in high-power fiber lasers have been presented in ref. [109], where adverse interactions between the laser light and the host are discussed, and novel composition glass fiber designs and fabrication methodologies are presented.
* The alternative approach to mitigating heat dissipation in Raman lasers is based on an ultralow quantum defect.  
As of now, the development of multiwavelength Brillouin fiber lasers with an increased number of Stokes channels that present high flatness and reasonable optical-to-signal ratio is a challenge that fiber laser technology still faces. Multiwavelength Brillouin fiber lasers operating at optical communication wavebands such as 1.5 \(\upmu\)m have been widely reported. However, there is still a lot of room for further development of multiwavelength Brillouin fiber lasers in the 1.0 \(\upmu\)m, 1.3 \(\upmu\)m, and 2.0 \(\upmu\)m spectral regions. In these spectral regions, multiwavelength Brillouin fiber lasers show a low optical-to-signal ratio and poor flatness. Finding the best setup parameters for such lasers can considerably improve their performance in these promising spectral ranges.  
Although fiber lasers have already revolutionized the laser industry, they continue to be a very promising technique for different applications, including industrial material processing, in military and medical sectors, and quantum physics. Considerable room remains for their improvement.  
* As already noted, the optimization of fiber materials is very important for the future development of high-power lasers. The absorption and radiation characteristics of fiber materials can be improved.
* Widely used pump technology such as laser diode pumps and fiber laser pumps can be improved in terms of pump efficiency and fiber absorption efficiency.
* The optical design of fiber lasers can be improved too. For example, specially designed fibers can be developed to achieve brightness enhancement in Raman lasers.  
This research received no external funding.  
Not applicable.  
The author declares no conflicts of interests.