  Electro-optical modulation of a continuous wave laser is a highly stable way
to generate frequency combs, gaining popularity in telecommunication and
spectroscopic applications. These combs are generated by modulating non-linear
electro-optic crystals with radio frequencies, creating equally spaced
side-bands centered around the single-frequency seed laser. Electro-optic
frequency comb architectures often choose between optical bandwidth (cascaded
GHz combs) or higher mode density (chirped RF generation). This work
demonstrates an electro-optic frequency comb with > 120 GHz of bandwidth and a
75 MHz repetition rate. The comb has three cascaded electro-optic modulators
driven at sequentially lower harmonics, the last megahertz modulation dictating
the repetition rate. This architecture can modulate at any individual harmonic
and repetition rate without changes to the components. This comb can be used in
any applications where a stable and tunable repetition rate is needed.
