Abstract: An optical system capable of preventing degradation of the image quality and minimizing the effect of unwanted-order light even when a protective layer is provided on a diffraction surface, thereby obtaining an image of high quality. The optical system, on which band light is incident, has a relief type diffractive optical element (2), and a device (3) that limits a wavelength band of light entering or emerging from the diffractive optical element (2). The diffractive optical element (2) has an optical member (4) having a relief configuration on a surface thereof, and a protective layer (5) formed over the surface of the optical member (4) from a material different from a material constituting the optical member (4).

Abstract: An illumination optical system for cutting infrared light by a relief type optical element includes a light source and a relief type diffraction optical element having a rectangular sectional-shaped grating having an equal area of land and groove areas so that primarily zero order light can be used for illumination while higher order and infrared light may be filtered out. A relief pattern has characteristics such that a ratio .beta. of a width of a plurality of respective concave portions to a pitch of adjacent convex portions is in a range of 0.34.ltoreq..beta..ltoreq.0.66 and a groove depth d is in a range of 0.85 d.sub.0 .ltoreq.d.ltoreq.1.09 d.sub.0. Excessive heat from infrared light and higher order light may be eliminated without the use of an infrared cutter.

Abstract: A diffractive optical element including a first layer made of a first optical material having high refractive index and low dispersion, and a second layer made of a second optical material having low refractive index and high dispersion. The first and second layers are stacked together. The outer surfaces of the first and second layers are substantially smooth, while the connecting surfaces of the first and second layers are substantially contoured to follow a relief pattern. To satisfy a preferred operating wavelength range of 400 nm to 700 nm, a glass selected from the group consisting of BSM7, BSM81, BSL7, BAL5, BAL50, BAL22, LAL11, LAL12, LAL18, YGH51, LAH57 and LAH75 may be used as the first optical material, and a silicate glass containing certain amounts (e.g., 2 to 25 mol %) of Tl.sub.2 O may be used as the second optical material.

Abstract: Methods of manufacturing optical elements such as diffraction type lenses, aspherical lenses and diffraction gratings are disclosed. Deposited on a glass substrate is a workpiece film made of a material which can be machined much more easily than the substrate. Then the workpiece film is machined to form a predetermined shape or contour therein. After forming the predetermined shape or contour in the workpiece film, the workpiece film and substrate are subjected to etching to duplicate the predetermined shape or contour formed in the workpiece film into the substrate.