Indirect photonic transitions for light control in integrated photonics

本研究计画的目标是让光脉冲在具有相对论性移动折射率波前的矽慢光波导中产生强烈的交互作用。正确选择慢光波导和前速度可以允许一个调色板的鼓舞人心的物理实验。也就是说，光脉冲可以在频率上移动，存储一定的时间，压缩和展宽。除了所列出的效应之外，光子带跃迁的间接性质使其在本质上是非互易的。因此，也可以研究诸如光学隔离之类的物理现象。除了科学上的兴趣，成功的实验实现这一建议可以导致几个新的方法，光脉冲操纵在光通信系统和其他领域。直接跃迁中的频移仅由动态变化的折射率阶跃（即产生自由载流子的功率）确定。这种折射率变化通常在10-3的量级，因此对于1.5 µm波长的信号，导致约100 GHz的频率变化。间接过渡通过选择前速度为频率控制创造了额外的方式。首先，设想使用两个反向传播信号来证明非互易频移，其中前向传播信号与后向传播信号相比经历不同的频移。这个概念可以用于光学隔离，这是当前高度感兴趣的科学和技术主题。此外，通过色散曲线和波前速度的正确组合，对于小的折射率阶跃可以获得非常大的频移。在这里，我们设想的频率移动1太赫兹和更多。可调的时间延迟是很难实现的直接过渡。通常，信号的频率被移动，但群速度保持不变。在光子晶体波导中的间接跃迁的情况下，前群速度的选择可以允许跃迁到任何群速度的状态或甚至到零群速度的状态。因此，我们计划展示一个可调的时间延迟，通过改变前端速度。间接跃迁也可以用来压缩或扩大从移动的光子晶体前端反射的光脉冲。这种方法有几个优点。首先，可以实现数量级为1-10的压缩和加宽因子。即使在很小的折射率调制下，也可以实现几乎100%的转换效率。同时，中心频率在该过渡中保持不变，这是一个非常重要的优点。

The goal of this research project is to let optical pulses strongly interact in silicon slow light waveguides with relativistically moving refractive index fronts. The right choice of a slow light waveguide and front velocity can allow a palette of inspiring physical experiments. Namely, the optical pulses can be shifted in frequency, stored for certain time, compressed and broadened. Apart from the listed effects the indirect quality of the photonic band transition causes it to be nonreciprocal in nature. Thus, physical phenomena such as optical isolation can be investigated as well. Apart from scientific interest the successful experimental realization of this proposal can lead to several new approaches for optical pulse manipulation in optical communication systems and other fields. The frequency shift in the direct transition is determined by just the refractive index step (namely the power that generates the free carriers) of the dynamic change. Such refractive index changes are usually in the order of 10-3 and thus lead to frequency changes of approximately 100 GHz for a signal at 1.5 µm wavelength. The indirect transition creates an additional way for frequency control via the choice of the front velocity. First of all, it is envisaged to demonstrate a non-reciprocal frequency shift using two counter propagating signals where the forward propagating signal experiences a different frequency shift as compared to the backward propagating signal. This concept can be used for optical isolation, which is a current scientific and technical topic of high interest. Also, by the right combination of the dispersion curve and the front velocity, very large frequency shifts can be obtained for small refractive index steps. Here we envisage frequency shifts of 1 THz and more.Tunable time delays are difficult to realise with direct transitions. Usually, the frequency of the signal is shifted but the group velocity stays the same. In case of an indirect transition in photonic crystal waveguides the choice of the front group velocity can allow transitions to states of any group velocity or even to a state of zero group velocity. Thus, we plan to demonstrate a tunable time delay by varying the front velocity.The indirect transition can be also used to compress or broaden optical pulses upon reflection from a moving photonic crystal front. There are several advantages of this approach. First of all, compression and broadening factors of the order of 1-10 can be realised. Almost 100% conversion efficiency can be achieved even with a small refractive index modulation. At the same time the center frequency stays the same in this transition, which is a very important advantage.