Progress in integrated electro-optic frequency combs (Invited)

Optical frequency comb (OFC) is the spectrum structure composed of a set of discrete and equally spaced frequency components, which has been widely used in many areas such as spectroscopy, precision measurement, optical communication and sensing as the natural scale for spectral analysis. According to its generation methods, OFC can be generated in three ways, including mode-locked laser based OFC, Kerr microresonator OFC and electro-optic frequency comb (EOFC). EOFC has been greatly developed because of its advantages including remarkable tunability of frequency spacing, high comb line power, as well as the accessible conversion from microwave to optical wave. However, there are some drawbacks in conventional EOFC generator, for instance, the bulk size and required high power, which limit its further development. As the micro/nanofabrication technology gradually grows, more and more materials are applied into integrated chip-scale optical devices, including Si, Silicon Nitride, Aluminum Nitride, Indium Phosphide, Lithium Niobate and Aluminium Gallium Arsenide. Integrated EOFC possesses the excellent characteristics, such as small volume and low power consumption, which is an important device for optoelectronic integrated chip. The research status of the integrated EOFC is reviewed in this paper. First, the classification of optical frequency comb, as well as detailed content about generation mechanism of EOFC are introduced. Next, the information comprising various material platforms, corresponding devices performance metrics and applications about EOFC is presented. Finally, the future research directions are prospected in view of the existing problems of integrated EOFC.