提出了一种基于保偏光纤(PMF)中布拉格光栅的波长间隔可调的可开关双波长掺铒光纤激光器(EDFL)。由于和光纤布拉格光栅(FBG)两个反射峰对应的不同波长的两纵模在偏振态上是正交的,从而在均匀展宽的掺铒光纤中增强了偏振烧孔(PHB)效应。这种偏振烧孔效应大大减小了不同模式之间的竞争,因此可在室温下得到稳定的双波长振荡。另一方面,通过调整偏振控制器的状态,即改变腔内的双折射状态,光纤光栅的两个反射峰强度会发生变化。基于以上原理,便形成了对激光振荡模式的选择,即通过调整偏振控制器的状态可使激光器工作在稳定的双波长状态或在两波长之间转换。通过改变加在光纤光栅上侧向应力的大小和方向,可有效控制双波长激射的波长间隔,实验中得到了0.2～1.1 nm的可调间隔。

A switchable and spacing-tunable dual-wavelength linear cavity erbium-doped fiber (EDF) laser based on a polarization-maintaining fiber Bragg grating (PM-FBG) is demonstrated experimentally. Feedback from the FBG results in the laser operating on two longitudinal modes that are separated in both wavelength and polarization. The birefringence induced by the FBG is beneficial to diversify the polarization states of different wavelength in the EDF and enhance the polarization hole burning (PHB) effect. This PHB greatly increased the inhomogeneous gain broadening of EDF and accordingly reduced the wavelength competition. Then, it was possible to achieve stable dual-wavelength oscillations at room temperature. On the other hand, through adjusting the state of the polarization controller (PC), the transmission characteristic of the FBG is changed. When the eigenaxe of one mode is more populated than the other, it will oscillate stably in that mode. Especially, when the eigenaxes of both modes are equally populated, the two modes can co-exist with equal amplitudes. Thus mode selection is achieved in laser oscillation and the laser can be designed to operate in wavelength switching modes, only by simple adjustment of the PC. Applying strain in line with the fast axis reduces the birefringence of the fiber grating and causes the wavelength separation of the two modes to be decreased. On the other hand, strain applied in line with the slow axis increases the birefringence and a concomitant increase in wavelength spacing is produced. Then, transverse strain loading on the FBG allows the wavelength spacing to be controlled and a tunable wavelength separation from 0.2 to 1.1 nm was demonstrated.