There are many kinds of fiber lasers in the 1.5 mm band using erbium-doped fiber amplifiers. Our group has been studying and developing advanced fiber lasers, such as 1) 10–40 GHz harmonically mode-locked fiber lasers, 2) femtosecond fiber lasers that use single-wall carbon nanotube (CNT)-doped polymers as a saturable absorber, and 3) frequency-stabilized fiber lasers that employ acetylene C2H2. We will describe recent progress on these fiber lasers and their applications in this article.