基于石墨烯的宽带全光空间调制器

提出了单层石墨烯包裹微纳光纤的全光空间调制.石墨烯作为可饱和吸收体包裹在通过二氧化碳激光器加热制备的微纳光纤上，当信号光沿着微纳光纤传输时部分光将以倏逝场的形式沿着微纳光纤表面传递，并与石墨烯产生作用被吸收.同时将波长为808 nm的抽运光从空间垂直入射到石墨烯包裹的微纳光纤处，依据石墨烯的优先吸收特性，通过抽运光控制石墨烯对信号光的吸收，实现了宽带全光空间调制.在1095 nm波长处获得最大调制深度约为6 dB，调制带宽约为50 nm，调制速率约为1.5 kHz.空间全光调制器具有输出信号光“干净”的特点.与传统石墨烯微纳光纤全光调制器相比，输出端不需要对抽运光进行光学滤波而直接获得已调信号.该复合波导全光空间调制器以更为灵活、高效的方式打开了微纳超快信号处理的大门.

Graphene-based broadband all-optical spatial modulator

In this paper, the all-optical spatial modulation of monolayer graphene-coated microfiber is proposed. Graphene is used as a saturable absorber wrapped on the microfiber produced by heating the carbon dioxide laser. When the signal light travels along the microfiber, part of the light will pass along the surface of the microfiber in the form of an evanescent field, and it will be absorbed by the graphene. Simultaneously we shoot the 808 nm pump light into the micro-nanofiber wrapped by the graphene vertically from the space. According to graphene characteristic of preferential absorption, the absorption of the signal light is controlled by the pump light, thus the broadband all-optical space modulation is realized. In a conventional graphene microfiber all-optical modulator, signal light and pump light are generally input into a microfiber via a coupler. However, the mode of operation of pump light and graphene in all-optical spatial modulation are different from those of the traditional modulation, the pump light works on the graphene outside the microfiber, which realizes the separation of the pump light and the signal light. The output signal does not need to be optically filtered for the pump light to obtain the modulated signal. The output signal light of the spatial all-optical modulator has the characteristics of “clean”. We also verify this in experiment. In addition, the pump light is vertically incident from space, the effect of the graphene length on the modulation is not considered and the modulation time is only related to the relaxation time of graphene, which is helpful in improving the response time. Modulation experiments include static spectral modulation and dynamic frequency modulation. In the static spectral modulation, the broad spectrum signal has a maximum modulation depth of 6 dB at 1095 nm when the pump power is 569 mW. The relationship among pump power, wavelength and modulation depth is also analyzed. The higher the pump power, the higher the modulation depth will be; with the same pump power, the modulation depth of long wave length is higher than that of short wave. In the dynamic modulation experiment with the modulation bandwidth~50 nm and the modulation rate~1.5 kHz, the influence of pump light and signal light on output dynamic signal are studied, the feasibility of all-optical space modulation based on graphene is verified experimentally. The composite waveguide of all-optical spatial modulator opens the door to micro-nano ultrafast signal, processing in a more flexible and efficient way.