Integrated frequency combs for flexible optical networks

Optical frequency comb (OFC) sources have proven to be useful in applications such as frequency metrology [1], spectroscopy [2], millimetre wave generation [3] and dense/ultra-dense wavelength division multiplexed high speed optical communications [4]. These applications require highly coherent, stable and cost efficient optical comb sources. Other important comb parameters include a flexible free spectral range (FSR) and uniform power distribution amongst the frequency components. Typical OFC sources generate multiple optical carriers offering low power consumption and complexity by replacing multiple independent lasers with a single subsystem. Therefore, OFCs ensure constant and stable frequency spacing between the carriers enabling the reduction or elimination of guard bands in advanced multicarrier modulation techniques. In order to enable/enhance the practical use of comb sources in >100G next generation optical transport networks, a key issue to be considered is the footprint/compactness of the device as this directly relates to the ease of manufacturing (cost), power consumption, and reliability. Therefore, monolithically integrated comb sources [5, 6] with simple and compact designs could be highly beneficial. In this work, the authors present the optimum features of an integrated externally injected master slave laser [7] used to generate a gain switched optical frequency comb [8]. In addition, the employment of this comb in a flexible optical networking environment will be reviewed and experimental results presented.