Generation and cancellation of second-order harmonic distortion in analog optical systems by interferometric FM-AM conversion

The generation of strong harmonic distortion from interferometric FM-AM conversion in analog lightwave systems is demonstrated both theoretically and experimentally. The effect results from the combined effects of wavelength chirping of the laser coupled with the nonlinear transmission characteristics of a dispersive element in the optical beam path. It is shown that reflections as small as 2-10/sup -4/ will result in second-order distortion as large as -65 dBc. The effect can also be used to cancel any laser- or detector-induced harmonic distortion. In one example, the -36 dBc second-order distortion in a distributed-feedback (DFB) laser is improved to better than -70 dBc.<
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