An optical device includes a copper plate, light receiving elements mounted on the copper plate, a light emitting element mounted on the light receiving elements, a flexible substrate bent to cover portions of upper and side surfaces of the copper plate, and a positioning frame of metal for fixing the flexible substrate and the copper plate to each other. The assembly comprises a set of superconducting coils within a cryostat, located about a bore, and arranged to generate a substantially uniform magnetic field in a primary working volume within the bore, and to generate a substantially uniform magnetic field in a secondary working volume within the coil structure and separate from the bore. The front- and back sections have laser-drilled tapered vias that are filled with conductive material and that are coupled to the plated through hole. The calibration system also include calibration data corresponding to the surgical instrument.