Implantable illuminating device intended to be implanted in a living being with a view to locally illuminating a region of said living being, said device comprising a probe having an architecture that is elongate along an axis between a near end and a far end, said probe taking the form of a rod of circular section of constant diameter over all its length, said probe comprising: - a stimulating optical fibre that comprises a core, a cladding and a protective coating, - a jacket (13, 130), and a tube, - said architecture comprising: - a plurality of successive segments along its longitudinal axis, each segment having a section (Sc to S4 or Sc to S30) containing a plurality of concentrically superposed layers, in which each segment comprises a section containing a plurality of superposed layers that is different from the section of each adjacent segment, - at least a first segment along which said stimulating optical fibre is jacketed by the jacket (13, 130), - at least a second segment extending said first segment, in which said stimulating optical fibre is stripped to remove its protective coating so as to leave behind only its core and its optical cladding jacketed by the jacket, - at least a terminal segment the section (S4, S30) of which comprises only said jacket, said terminal segment comprising the far end of the probe and in that this far end is configured so as to be atraumatic, - the section of the first segment comprising a first layer comprising the optical-fibre core, a second layer comprising the optical-fibre cladding, a third layer comprising the protective optical-fibre coating, a fourth layer comprising the jacket and an external fifth layer composed of the tube, - the section of the second segment comprising a first layer comprising the core of said optical fibre, a second layer formed from the cladding of the optical fibre, a third layer comprising said jacket and a fourth layer comprising said tube, - the device comprising a third segment extending said second segment and the section of which comprises a first layer comprising said jacket and a second layer comprising said tube. - a stimulating optical fibre that comprises a core, a cladding and a protective coating, - a jacket (13, 130), and a tube, - said architecture comprising: - a plurality of successive segments along its longitudinal axis, each segment having a section (Sc to S4 or Sc to S30) containing a plurality of concentrically superposed layers, in which each segment comprises a section containing a plurality of superposed layers that is different from the section of each adjacent segment, - at least a first segment along which said stimulating optical fibre is jacketed by the jacket (13, 130), - at least a second segment extending said first segment, in which said stimulating optical fibre is stripped to remove its protective coating so as to leave behind only its core and its optical cladding jacketed by the jacket, - at least a terminal segment the section (S4, S30) of which comprises only said jacket, said terminal segment comprising the far end of the probe and in that this far end is configured so as to be atraumatic, - the section of the first segment comprising a first layer comprising the optical-fibre core, a second layer comprising the optical-fibre cladding, a third layer comprising the protective optical-fibre coating, a fourth layer comprising the jacket and an external fifth layer composed of the tube, - the section of the second segment comprising a first layer comprising the core of said optical fibre, a second layer formed from the cladding of the optical fibre, a third layer comprising said jacket and a fourth layer comprising said tube, - the device comprising a third segment extending said second segment and the section of which comprises a first layer comprising said jacket and a second layer comprising said tube.