Arbitrary free spectral range control of optical frequency combs based on an optical tapped delay line structure cascaded with a phase modulator

We propose and demonstrate a simple method to accomplish arbitrary free spectral range (FSR) control of optical frequency combs (OFC). The approach is based on the combination of an optical tapped delay line (OTDL) structure and a phase modulator (PM). The OTDL structure is utilized to multiply the FSR of input OFC, and the PM is used to divide the FSR of the consequent OFC. We illustrate that the proposed method allows one to divide or multiply the FSR of original OFC by any anticipated integer or fractional factor. Numerical simulation results match well with our theoretical analysis.