Optical frequency comb generator using phase modulation in amplified circulating loop

A method to generate a comb of precisely spaced optical frequencies over a terahertz span is presented. This scheme uses a sinusoidally driven phase modulator and an optical amplifier placed within an optical fiber loop, so that the modulation is enhanced by multiple passes through the loop. By maintaining the loop round-trip gain slightly below unity, a comb of tens to hundreds of frequencies can be generated. If the loop input is derived from a laser locked to an absolute frequency reference, then each of the output frequencies has an absolute accuracy approaching that of the input.>