SBS suppression – Yan Feng

Updates

It is the end of year again. I feel obligated to update this blog after a long hiatus. I have been busy as most of the men on the Chinese land do. I don’t have much time to blog, but I do spend some time on setting up a simple website for the research group and updating the new publications. The website has a nice domain name “laser.im“.

I wish to continue the guide star laser work. Therefore, we have researched ways to generate linearly polarized Yb doped fiber laser, and are now able to build 100 W class linearly polarized 1120 nm Yb-doped fiber laser with cross-axis-matched FBG pairs written in polarization maintaining fiber. We improved the SBS suppression technique further, and achieved a 44 W single frequency Raman fiber amplifier at 1178 nm with an optical efficiency of 52 %. Up to 25 W at 589 nm has been demonstrated with a home-built frequency doubling cavity, which is not yet optimized.

I feel mode locking of fiber laser fascinating, therefore, we have studied mode locking of Raman fiber laser with graphene absorber. The idea is simple: To achieve wavelength versatile mode locked fiber laser by combining the shared advantage of Raman gain and graphene saturable absorption, both of which is broadband. During the path, we have demonstrated passively Q-switched Yb-doped fiber laser by graphene, and the use of single-multi-single mode fiber structure as bandpass filter for building all fiber tunable dissipative soliton fiber laser.

The SBS suppression technique was applied to single frequency Yb doped fiber laser, and achieved 170 W linearly polarized laser with a 10 micron core PM fiber by 7 time increase of SBS threshold. We also find Yb doped fiber laser at the wing of gain spectrum interesting. One example is a demonstration of high power single frequency 1014.8 nm fiber amplifier working at room temperature for mercury cooling after frequency quadruplication. These works are not yet published.

The research works are on-going. Future update will be posted on the new group website.

Europhoton 2006, summer school

I am in Pisa, Italy right now for Europhoton 2006 conference. In the past two days, there are six summer school lectures. Among them the lecture on “high power fiber lasers” by Almantas Galvanauskas from Michigan University is of most interesting to me.

I learned something new from the lecture. For example, there are so called effective single mode fibers, which basically are multimode fibers but the high order modes are selectively coupled out of the core. It is an attractive way to design large mode area fibers that are desirable for scaling the fiber laser power and also for fiber delivery of narrow band lasers. Another interesting information from the lecture is that some people had demonstrated SBS suppression in a fiber with an acoustic waveguide outside the fiber optical core. This adds a new method on fighting SBS. I will check the technical details when back to work.

The summer school will be followed by a four-day main conference.

It is my second time being in Italy. But this is the first time being in ‘real’ Italy. (In my first visit, I stayed in the northest province, Suedtirol, which is a German speaking region.) I am remindered of China from time to time by somehow chaotic traffic, road sight, and also the size of people (which is similar to Chinese). It may be surpising and difficult to understand. But the feeling is true. There is something similar enough between China and Italy for me, a Chinese living in _Germany_, to be homesick a little bit.