  The linear polarisation of the Crab pulsar and its close environment was
derived from observations with the high-speed photo-polarimeter OPTIMA at the
2.56-m Nordic Optical Telescope in the optical spectral range (400 - 750 nm).
Time resolution as short as 11 microseconds, which corresponds to a phase
interval of 1/3000 of the pulsar rotation, and high statistics allow the
derivation of polarisation details never achieved before. The degree of optical
polarisation and the position angle correlate in surprising details with the
light curves at optical wavelengths and at radio frequencies of 610 and 1400
MHz. Our observations show that there exists a subtle connection between
presumed non-coherent (optical) and coherent (radio) emissions. This finding
supports previously detected correlations between the optical intensity of the
Crab and the occurrence of giant radio pulses. Interpretation of our
observations require more elaborate theoretical models than those currently
available in the literature.
