Applications of collinear acousto-optic diffraction for optical frequency combs generation

Optical frequency combs (OFC) occupy an important place in modern optoelectronics. Plenty of OFC generation methods and practical application concepts were proposed in recent decade. Among the generation methods are several based on acousto-optic (AO) interaction application. In this paper we theoretically examine new OFC generation method based on joint use of collinear AO diffraction and frequency-shifting loop. This method gives two novel OFC generation schemes. The first one contains collinear AO cell driven by radio-frequency (RF) generator and optical loop connecting optical output and input of the AO cell. The second one includes not only the optical loop but also the optoelectronic feedback connecting the optical output of the system with the piezoelectric transducer of the AO cell. In this case the system operates above the self-excitation threshold without RF generator. Both systems were examined theoretically, it was discovered that they give the possibility to generate OFC’s in several ways. The switching between them is realized by mutual reorientation of a pair of polarizers placed before and behind the AO cell and achromatic half-wave plate included in the optical feedback loop. It is shown that the parameters OFCs obtained in the system with only optical feedback are determined by AO cell material, RF generator signal frequency and magnitude, optical loss and amplification. The system with both optic and electronic feedback gives the unique opportunity to obtain chirped OFCs.