PROJECT TITLE :
Long-term stable 60 GHz optical two-tone signal by destructive optical interference obtained from RF phase adjustment
An optical 2-tone signal with 60 GHz frequency spacing is experimentally demonstrated, by sinusoidally modulating two lightwaves with completely different modulation indices and RF phases. By superposing two modulation lightwaves with orthogonal polarisation, polarisation orthogonality is achieved between undesired low-order optical sidebands and the desired high-order optical sidebands together with the incident light-weight-wave. This permits us to suppress the undesired sidebands using polarisers rather than optical filter. Such operation has been implemented using optical modulator possessing RF ports for external termination, that is nested in one mode of polarisation-maintaining Sagnac interferometer (PMSI). This implementation is resembling optical single-sideband modulator, but required nested Mach–Zehnder structure is simply one. Owing to the current reduction along with use of 1 mode in PMSI, long-term stable operation more than half-dozen h has been successfully obtained, with 29 dB suppression ratio of undesired initial-order sidebands against desired third-order optical sidebands.
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