An erbium-doped fiber (EDF) laser was configured with a fiber grating, a fiber ring resonator, and a saturable absorber by using un-pumped EDF as mode selection element. The laser showed single mode operation with a narrow linewidth of 5 kHz. The mode selection mechanisms of the un-pumped EDF and the ring resonator are theoretically and experimentally analyzed.

从理论上设计并从实验上实现了一种简单易行的环形谐振腔结构，它仅由两个耦合器连接成一个环形谐振腔，可以使得逆时针运行光的增益高于顺时针运行光的增益，其比值取决于两个耦合器耦合比的选取。将此作为掺铒光纤激光器的谐振腔，由于两个相反方向具有不同的损耗，因而可以实现在不需要隔离器的情况下也能保证激光的单向运行，从而简化了器件结构，消除隔离器的插入损耗，降低了成本。在实验的过程中使用两个3 dB耦合器，结果表明，在阈值及其以上抽运功率下，两个相反方向的输出功率差始终大于17 dBm，基本实现了激光的单向运行。

A simplified ring cavity for achieving a unidirectional room temperature multi-wavelength erbium-doped fiber ring laser without optical isolator is demonstrated. The fiber ring cavity is built in such a way that the optical fields propagating in two directions suffer different losses caused by one sampled fiber Bragg grating. Furthermore, simultaneous multi-wavelength lasing with 0.8-nm intervals is demonstrated with sinusoidal phase modulation just before the sampled fiber Bragg grating to prevent single-wavelength lasing and unstable wavelength oscillation.