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We demonstrate a technique to continuously tune center frequency and repetition rate of optical frequency combs generated in silicon microring modulators and bandwidth scale them. We utilize a drive frequency dependent, microwave power induced shifting of the microring modulator resonance. In this work, we demonstrate center frequency tunability of frequency combs generated in silicon microring modulators over a wide range (∼8nm) with fixed number of lines. We also demonstrate continuously tunable repetition rates from 7.5GHz to 15GHz. Further, we use this effect to demonstrate a proof-of-principle experiment to bandwidth scale an 8-line (20dB band) comb generated from a single ring modulator driven at 10GHz to a comb with 12 and 15 lines by cascading two and three ring modulators, respectively. This is accomplished by merging widely spaced ring modulator resonances to a common location, thus coupling light simultaneously into multiple cascaded ring modulators.

A transient, three‐dimensional mathematical model of a single‐pass laser surface alloying process has been developed to examine the macroscopic heat, momentum and species transport during the process. A numerical study is performed in a co‐ordinate system moving with the laser at a constant scanning speed. A fixed grid enthalpy‐porosity approach is used, which predicts the evolutionary development of the laser‐melted pool. It is observed that the melting of the added alloying element is not instantaneous in case its melting temperature is higher as compared to that of the base metal. As a result, the addition of alloying element at the top surface cannot be accurately modelled as a mass flux boundary condition at that surface. To resolve this situation, the addition of alloying elements is formulated by devising a species generation term for the solute transport equation. By employing a particle‐tracking algorithm and a simultaneous particle‐melting consideration, the species source term is estimated by the amount of fusion of a spherical particle as it passes through a particular control volume. Numerical simulations are performed for Ni as alloying element on Al base metal. It is revealed that the present model makes a distinctly different prediction of composition variation within the resolidified microstructure, as compared to a model that does not incorporate any considerations of distributed melting.