The method of manufacturing an optical disc related to the invention first forms warp prevention layer on one surface or the other surface of the disc substrate where information is recorded on one surface, and then, recording film covering the surface opposite from the surface having warp prevention layer or beam reflection film covering the information-recorded surface, and finally protection layer covering either the beam reflection film or the recording film, in this order. Thus the optical disc related to this invention can prevent damage and dust from incurring and adhering to the other surface of the disc substrate when forming these films on one surface so that the warp prevention layer can be perfectly level by suppressing swell of the layer itself. Since the warp prevention layer is formed on one surface before forming those films mentioned above on the other surface, the one surface maintains satisfactory wetness, and as a result, foam is rarely generated between the warp prevention layer and the disc substrate. Furthermore, the method of manufacturing an optical disc related to the invention introduces a system which measures the warp of the disc substrate coated with warp prevention layer before coating protection film, and then properly adjusts the thickness of the protection film to a specific thickness enough to fully cancel the warp. This effectively minimizes warping of the disc substrate itself.

An optical unit as used for an optical sensor, including a substrate, one or more optical elements fixedly supported by the substrate, and an protecting arrangement associated with the substrate and at least one of the optical elements, for protecting each associated optical element from thermal stresses exerted thereto due to a difference in thermal expansion coefficient between the substrate and the associated optical element. The protecting arrangement may consist of at least one intermediate body interposed between the substrate and the associated optical element. Each intermediate body has a thermal expansion coefficient close to that of the associated optical element. Alternatively, the protecting arrangement may consist of a constricted protecting portion such as protrusions or slots formed on one of the associated optical elements and the substrate, such that the protecting portion defines an adjoining interface between the optical element and the substrate, or is located adjacent to the adjoining interface.

An optical device having a lens substrate and a microlens portion formed thereon, wherein the microlens has its lens portion formed on the part of the optical device that has substantially the same coefficient of expansion as that of the lens substrate.

Transmission spectrometers require low levels of background light so that the signal to noise ratio is increased, and also require stable performance over wide temperature ranges. Light reflected by the transmission grating can result in increased background levels. One approach to reducing the background level is to orient the transmissive diffraction grating so that light reflected by the grating is reflected out of the diffraction plane. The temperature-induced wavelength drift of a transmission spectrometer can be due to the frame upon which the transmission grating is mounted. The wavelength drift is reduced by allowing the thermal expansion of the grating to be independent of the frame.