Abstract: A combination of an optical element and an antireflection film, the optical element being provided with a microlens array and configured to diverge a light beam, the maximum angle of a diverged ray to a reference axis being D, wherein in each microlens Z / P ? 0 . 8 is satisfied, where Z represents distance between the vertex and the bottom and P represents the diameter of the smallest circle enclosing the bottom and the antireflection film being designed such that { T ? ( 0 ) / T ? ( D ) } / { T ? ( 0 ) / T ? ( D ) } ? 0 . 8 ? 5 is satisfied, where T(0) and T(D) respectively represent transmittance of the film formed on a substrate made of the material of the optical element for incident rays at 0 and D, and T?(0) and T?(D) respectively represent transmittance of the substrate without an antireflection film for incident rays at 0 and D, wherein the combination is configured so as to realize a target intensity distribution of diverged rays.

Abstract: The diffusor has a microlens array including microlenses with the bases placed on a plane. Concerning a curved surface of each microlens, the following expressions are satisfied, where in a cross section perpendicular to the plane and containing a straight line passing through the projection point onto the plane of the vertex and maximizing a distance between two points of the straight line on the periphery of the base, coordinate along the straight line, coordinate of the curved surface of the microlens in the direction perpendicular to the plane, the maximum value of the first derivative of z? with respect to x?, the absolute value of the second derivative of z? with respect to x? at x? coordinate of the projection point and the absolute value at x? coordinate of an end of the straight line are represented respectively by x?, z?, d, D0 and D.

Abstract: A light-receiving optical system includes a rotating mirror configured to rotate around a rotation axis and having a reflection plane arranged at an angle with the rotation axis; an imaging optical system having an optical axis that coincides with the rotation axis; a multifocal Fresnel lens having sections formed concentrically around the optical axis; and light-receiving elements, wherein the imaging optical system is configured such that rays of light that enter the rotating mirror are converged onto one of the sections depending on an angle of the rays with the optical axis, and the multifocal Fresnel lens is configured such that the rays reach one of the light-receiving elements, which corresponds to the one of the sections so that a light-receiving element that the rays reach is determined depending on the angle of the rays with the optical axis independently of a rotational position of the rotating mirror.

Abstract: A light-receiving optical system includes a rotating mirror configured to rotate around a rotation axis and having a reflection plane arranged at an angle with the rotation axis; an imaging optical system having an optical axis that coincides with the rotation axis; a multifocal Fresnel lens having sections formed concentrically around the optical axis; and light-receiving elements, wherein the imaging optical system is configured such that rays of light that enter the rotating mirror are converged onto one of the sections depending on an angle of the rays with the optical axis, and the multifocal Fresnel lens is configured such that the rays reach one of the light-receiving elements, which corresponds to the one of the sections so that a light-receiving element that the rays reach is determined depending on the angle of the rays with the optical axis independently of a rotational position of the rotating mirror.

Abstract: A combination of a color image display device and a diffractive optical filter, the color image display device including dots arrayed two-dimensionally on a first surface, the diffractive optical filter including a diffraction grating provided on a second surface that is parallel to the first surface, and a cross section in each direction of the diffraction grating being of substantially sinusoidal shape, wherein the combination is configured such that it can restrain the screen-door effect and isolation of dots to a sufficient extent and/or such that it can restrain moiré that appears according to the pitches between pixels and the period of the diffraction grating of the diffractive optical filter.

Abstract: The method includes the steps of: obtaining lateral magnification of an optical scanning system; obtaining the maximum value of thickness in the optical axis direction of an scanner lens; obtaining allowance b on one side and beam diameter a in the vertical scanning direction in the lens; and obtaining width h in the vertical scanning direction of the lens by the following expression h=a+2b. The allowance b is a product of the maximum value of thickness in the optical axis direction of the lens and a coefficient, and the coefficient is determined according to the lateral magnification of the system in such a way that the maximum value of movement of the focal point of the lens due to moisture absorption is made smaller than or equal to a predetermined value.

Abstract: The method includes the steps of: obtaining lateral magnification of an optical scanning system; obtaining the maximum value of thickness in the optical axis direction of an scanner lens; obtaining allowance b on one side and beam diameter a in the vertical scanning direction in the lens; and obtaining width h in the vertical scanning direction of the lens by the following expression h=a+2b. The allowance b is a product of the maximum value of thickness in the optical axis direction of the lens and a coefficient, and the coefficient is determined according to the lateral magnification of the system in such a way that the maximum value of movement of the focal point of the lens due to moisture absorption is made smaller than or equal to a predetermined value.