光纤环形谐振腔的频率锁定及其特性

基于可调分束比的光纤分束器,制作了光纤环形谐振腔并通过调节分束比实现了对光纤环形谐振腔的欠耦合、临界耦合和过耦合的状态控制.实验测量了腔最小反射率与腔损耗之间的关系,获得光纤环形谐振腔的腔内衰减率为κ_0=2π×(1.60±0.03) MHz ,品质因子为Q=(1.10±0.02)×10.8.在此基础上,结合了压电陶瓷拉伸光纤以控制腔长和Pound-Drever-Hall锁频两大技术优势,克服了之前温度反馈控制等方法的反馈带宽窄、噪声大和稳定性差等问题,实现了对光纤环形谐振腔共振频率的快速、灵敏的控制和锁定.结果表明,锁频过程中相位调制功率与相位调制引起腔反射光的强度调制之间的关系为线性关系,进而通过降低相位调制信号的功率以减小相位调制对腔反射光强度调制的影响.当调制功率设定最低为–9 dBm时,光纤环形谐振腔仍能被稳定锁定.该光纤环形谐振腔为其与原子、金刚石色心等发光粒子相互作用的腔量子电动力学实验研究奠定了坚实的基础.

Characteristics and control of fiber ring resonator

Optical resonators play an active role in fundamental research and applications in atomic fine spectra, laser generation, precision measurements, and quantum information processing because of their high-resolution spectra and strong optical field enhancement. The fiber ring resonators, as a derivative of the resonant resonators, have the advantages of simple structure, small size, stable performance and easy integration. The fiber ring resonators are widely used in fiber lasers, optical communication devices, optical fiber sensing, etc. In this paper, we demonstrate the characteristics of a fiber ring resonator based on a tunable fiber beam splitter experimentally. Control of under-coupling, critical coupling and over-coupling state of the fiber ring resonator can be achieved by adjusting the splitting ratio of the tunable fiber beam splitter. The relationship between the minimum resonator reflectance and resonator loss is given. The intrinsic decay rate of the fiber ring resonator is \${\kappa _0}{\rm{=}}2{\text{π}} \times \left({1.60 \pm 0.03} \right){\rm{ MHz}}$\, and the quality factor is \$Q=\left({1.10 \pm 0.02} \right) \times {10.8}$\. The resonance frequency of the fiber ring resonator is controlled by stretching the fiber. The fiber resonator is kept straight and fixed on a self-made U-shaped holder by gluing two points. A piezoelectric transducer is used to change the distance between the two glued points. The fiber ring resonator length is changed and controlled when the fiber is stretched. The Pound-Drever-Hall technique is used to lock the resonator to resonance with the laser. The phase of the laser beam is modulated by using an electro-optical modulator, and two sidebands of the laser frequency are generated. Due to the phase sensitivity of the fiber resonator, the reflected light of the fiber resonator with an intensity modulation is observed when the fiber ring resonator is locked. The intensity modulation is caused by the interference between the resonance frequency and the sidebands of the fiber ring resonator. The reflected spectrum of the fiber ring resonator carries the same-frequency modulation as the phase modulation. This is a disadvantage for the usage of the fiber ring resonator. Thus, we reduce the phase modulation power to reduce the intensity modulation of the resonator reflectance. The linear relationship between the phase modulation power and the intensity modulation of the resonator reflectance caused by the phase modulation is obtained. The fiber ring resonator can be locked when the phase modulation power decreases to -9 dBm. The fiber ring resonator has laid a solid experimental foundation for experimental research on the interaction between the fiber ring resonator and quantum emitters such as atoms and color centers in diamond.