基于调Q锁模激光束缚态的多波长光纤激光器波长间隔调控技术研究

Wavelength spacing tunable, multi-wavelength fiber lasers have important applications in microwave generation, Terahertz generation, optical frequency metrology and fiber multiplexing technology. However, conventional tuning methods, which are mainly based on controlling the optical path difference or polarization mechanically, suffer drawbacks of low resolution and poor repeatability. For the next generation of all optical networks, it urgently requires the light-dependent controlling fiber laser to advance the integration. Compared with the integrated circuit, the high integration of fiber system can bring the benefits as much as stability, low power and small size etc. In our laboratory, we experimentally observed the bound state of Q-switched mode-locked laser in a fiber cavity , with specific dispersion, nonlinearity and loss adjustment. Once the bound state formed, it is obviously noticed that each of those output pulses contains several Q-switched lasers with temporal spacing varying with pump intensity. The wavelength number of the multi-wavelength laser is ultrasensitive to the pump power. This phenomenon prompts us to do further research about tunable fiber laser for it is might be a promising light-dependent controlling laser source. We propose to study the method of wavelength spacing tunable, multi-wavelength fiber laser after the conditions and physical mechanism of the bound state of Q-switched mode-locked laser is finished. When this research program executes successfully, it will offer a convenient, low-cost and wavelength spacing tunable fiber laser technique. It is expected that we can provide a new technical approach for the field of tunable wavelength spacing multi-wavelength optical source, which has scientific significance and application potentials.

波长间隔可调的多波长光纤激光器在微波信号源、太赫兹波源、光学频率梳和光纤波分复用技术中有重要应用。通过机械调节激光系统中干涉仪的光程差或者偏振特性来实现间隔调控的方法比较普遍，而光控方式的全光纤可调激光器是下一代高集成全光网络的迫切需求。课题组在实验中观察到在强非线性激光条件下可形成调Q锁模激光束缚态，形成该束缚态时每一个输出激光脉冲包含一系列的调Q锁模脉冲，且这些调Q锁模脉冲所具有的时序差随激光器的泵浦功率变化而变化，利用该激光器光谱中波长数目对泵浦功率变化极为敏感的特性，可快速、准确地进行波长间隔调谐。这为光控可调光纤激光器提供了一种新的方法，我们将探索调Q锁模束缚态形成的条件和物理机制，并在此基础上研究一种新的波长间隔可调谐的多波长光纤激光器的制作原理和技术。通过本项目的研究能够为激光束缚态和波长间隔光控可调谐多波长光纤激光器研究提供新的内容，因此该项目具有重要的学术意义和应用价值。

开展波长间隔可调控的光纤激光器的研究具有非常重要的学术意义和工业价值。传统的波长调谐方法直接利用掺铒光纤的增益特性，结合多反射峰布拉格光栅、光纤干涉仪等对激光器进行多波长选择和调控，这类方法受增益谱局限，调谐范围只能在增益谱内；且调谐方式多为机械或电流，响应速度难以低于毫秒级别。利用光纤激光器的非线性特性输出多波长激光器，如四波混频效应、受激拉曼、光学参量震荡等，突破了增益局限，且响应速度远远大于机械方式。本项目研究了利用锁模激光的束缚态这种非线性特性来实现波长间隔调节机制及其相关支撑元器件和技术。在本项目中，我们提出一种新类型的波长间隔可调谐的多波长光纤激光器。其物理基础是激光腔内形成调Q锁模激光的束缚态。与直流锁模激光不同，调Q锁模激光被认为是由于在传统锁模激光腔内引入周期性强损耗所形成的，它同时对色散、非线性和泵浦能量敏感，其包络宽度、周期均随泵浦变化而变化。因此，在适当条件下，当调Q锁模激光腔内由色散、非线性、损耗和泵浦等引起的吸引和排斥力能够像在连续锁模激光腔内一样达到平衡时，不同阶次的调Q锁模的束缚态可以在超低的泵浦范围内出现。我们通过实验研究了该类激光的演变过程及调谐技术，我们观察到在100mW的泵浦强度变化范围内，从低阶到超高阶的束缚态的连续变化。在相关支撑技术方面，做了大量研究，如利用石墨烯包裹啁啾光纤布拉格光栅，并且通过不同的包裹方式实现了灵敏度为1.5pm/mw的中心波长漂移的光控光栅，实现了灵敏度分别为0.77pm/mw或1.5pm/mw的反射光谱压缩或展宽的光控光栅，光控波长脉宽可调谐光纤超快激光器系统，实现了锁模激光输出脉冲中心波长从1551.026nm到1552.346nm总共1.32nm的全光控调谐，其调谐灵敏度为2.9pm/mw；实现了锁模激光输出脉冲时域宽度从40.2ps到27.3ps的全光控调谐，其调谐灵敏度为645fs/mw。本项目研究可以加深人们对光纤激光器内脉冲相互作用机理的理解，而该光纤激光器还可以为超高频微波源、雷达信号源、超密集光纤通信等提供一种优质新激光光源。