The subject of a Nobel prize, femtosecond frequency combs have pushed the limits of high resolution spectroscopy and high precision astronomical observations in the past decade. However, for the many applications requiring a single precise frequency, it is difficult to use directly a single comb line due to the limited power per mode. To resolve this issue, I locked a cw laser to a single comb line, thus effectively producing a single frequency laser line with high power that inherits the stability and precision of the comb. Moreover, I demonstrated that offset locking can be implemented to tune the cw laser. The tuning range, however, is limited to frep (repetition rate of the laser) in this basic scheme because of difficulties in tracking the error beat note signal as it sweeps through background noise. We are in the process of adopting a scheme based on Schibli et al. that enables continuous tuning coverage across the entire bandwidth of the laser based on an electronic servo. By implementing it on a fiber (and eventually a monolithically integrated) platform, we aim to realize a compact and robust widely-tunable single-frequency synthesizer with carrier frequency in the optical regime.