.[.An optical disc apparatus for recording, reproducing or erasing an
information signal by converging a light flux onto a recording layer
through a transparent substrate. The apparatus includes one or a
plurality of optical heads having a plurality of objective lenses whose
aberations have respectivley been corrected for a plurality of disc
substrates of different thicknesses, a cartridge for enclosing the
optical disc, a discrimination hole which is formed on the cartridge, and
a sensor for detecting the opening/ closing state of the discrimination
hole and for generating a discrimination signal. In accordance with the
result of the discrimination as to the thickness of the loaded optical
disc, the objective lens, in which the occurrence of the aberration is
smallest, is used, so that the information signal can preferably be
recorded, reproduced or erased onto/from the optical discs having
different substrate thicknesses. Instead of an optical head having
objective lenses, an optical head having a waveguide and a plurality of
converging grating couplers whose aberrations have respectively been
corrected for a plurality of converging grating couplers whose
aberrations have respectively been corrected for a plurality of disc
substrates of different thicknesses is provided to achieve the same
object..]. .Iadd.An optical recording/reproducing apparatus for
recording, reproducing or erasing an information signal onto/from an
optical disc having at least a transparent substrate and an information
layer by converging a light flux on the information layer through the
transparent substrate. The apparatus includes optical converging devices,
with different numerical apertures, focal distances or working distances,
such as objective lenses or grating lenses, for performing aberration
correction over a plurality of transparent substrates of different
thicknesses of optical discs and a device for discriminating the type of
optical disc based on the thicknesses of the transparent substrates. One
of the optical converging devices that generates the least aberration is
used according to a result of the discrimination of the thickness of the
optical disk loaded in the apparatus to cause the information signal to
be suitably recorded, reproduced or erased onto/from the optical discs
having the different substrate thicknesses..Iaddend.