The museum has a photograph of a 500 Series Optical Spectrum Analyzer concept.  This analyzer was never produced but in 1975 the 7000 Series Rapid Scan Optical Spectrometer was introduced.

Note that the plugin spelling is "Analyser" and the optical probe unit is "Analyzer".  The optical probe unit is less than half the volume of the Rapid Scan Optical Spectrometer so it is possible this was not brought to market due to the complexity of the required optics at the time.