A method of designing an freeform surface off-axial three-mirror imaging system is provided. The method includes: establishing an initial system and T (T2) object-image relationships according to a design goal, and selecting M feature fields for each object-image relationship; using feature rays of the T object-image relationships to construct a freeform surface system by using the initial system; step (S3), the freeform surface system obtained in step (S2) is used as another initial system, using iterative process to reduce a deviation between actual intersection points and ideal target points of the feature rays and feature surfaces, iteratively reconstructing free-form surfaces in the free-form surface system.

A Bi-spectral Korsch-type anastigmat telescope having an optical axis and includes a visible channel comprising three mirrors, a concave first mirror, a convex second mirror and a concave third mirror and a visible detector that is sensitive in a visible band, the mirrors being arranged so that the first mirror and the second mirror form, of an object at infinity, an intermediate image located between the second mirror and the third mirror, the third mirror forming, from this intermediate image, a final image in the visible focal plane of the telescope, wherein the visible detector is placed, an infrared channel comprising first and second mirrors in common with the visible channel, a third IR mirror, a fourth IR mirror, and an IR detector that is sensitive in an infrared band, the third and fourth IR mirrors being configured to form, from said intermediate image, a final image in an IR focal plane of the telescope, wherein the IR detector is placed, the forms and positions of the third and fourth IR mirrors being defined using Korsch equations generalized to 4 mirrors with the constraint of the first and second mirrors common with the visible channel.

According to certain examples a spectrometer module for use in an imaging spectrometer includes a monolithic spectrometer body component made of an immersion material and including three mirrored surfaces configured to form a reflective triplet having an optical path immersed within the immersion material, the reflective triplet configured to receive incident optical radiation from an entrance face of the monolithic spectrometer body component and reflect the incident optical radiation along the optical path, and a dispersive element configured to receive and disperse the incident optical radiation reflected from the reflective triplet to provide dispersed optical radiation. The reflective triplet is configured to receive the dispersed optical radiation from the dispersive element and to reflect the dispersed optical radiation along the optical path to an exit face of the monolithic spectrometer body component.

A head-up display device reflects a display light on a projection member to display a virtual image. A light condensing unit causes condensation and collimates an illumination light from a light source unit. A liquid crystal element includes forms an image illuminated with the illumination light. The liquid crystal element emits the display light of the image in a light flux form in an emission direction corresponding to an incident direction of the illumination light. A positive optical element has a positive refractive power. A negative optical element has a negative refractive power. Both of the optical elements are located on the optical path and guide the display light from the liquid crystal element toward the projection member to enlarge a virtual image. The negative optical element on the optical path is located closer to the liquid crystal element than the positive optical element.

A point-by-point design method for off-axis aspheric optical system, in which feature light rays from different field angles and aperture coordinates are considered. Some of the feature data points are calculated first and surface fitted into an initial aspheric surface. Then, intermediate point calculations, feature data point calculations, and aspheric surface fitting were repeated continuously to calculate remaining feature data points and the desired aspheric surface are repeated continuously to calculate remaining feature data points and a desired aspheric surface. A least-squares method with a local search algorithm is used for aspheric surface fitting and deviations in both the coordinates and normals are used to reduce error.

An off-axis hybrid surface three-mirror optical system comprises a primary mirror, a secondary mirror, a tertiary mirror, and an image sensor. A reflective surface of the primary mirror is a sixth-order polynomial freeform surface of xy. A reflective surface of the secondary mirror is a sixth-order polynomial aspheric surface of xy. A reflective surface of the a tertiary mirror is a spherical surface of xy.

A method for designing an off-axis three-mirror imaging system with freeform surfaces is provided. A primary mirror initial structure, a secondary mirror initial structure, and a tertiary mirror initial structure are established. A number of first feature rays are selected, while the primary mirror initial structure and the secondary mirror initial structure unchanged. The first feature rays are forward ray tracked from an object space to an image detector. A number of first feature data points are calculated to obtain a tertiary mirror. A number of fields and a number of second feature rays are selected, while the secondary mirror initial structure and the tertiary mirror unchanged. The second feature rays are reverse ray tracked from the image detector to the object space. A number of second feature data points are calculated to obtain the primary mirror.

An imaging optical system including three mirrors has a configuration adapted to block stray rays which could otherwise reach an image sensor of the system, while permitting large fields, high apertures, and good system compactness. The system may also incorporate two entrance baffles which are arranged one on either side of an optical entrance of the system. Functions of the two entrance baffles may be limited to intercepting rays originating from fields which are angularly distant from the entrance field useful to each captured image. The two entrance baffles can thus have reduced lengths upstream, so that the system has a small size.

An optical element includes a substrate, a first resin portion provided on a first main surface of the substrate and having a linear expansion coefficient larger than a linear expansion coefficient of the substrate, a reflection portion provided on the first resin portion, and a second resin portion provided on a second main surface of the substrate opposite to the first main surface and having a linear expansion coefficient larger than the linear expansion coefficient of the substrate.

A method for designing off-axial three-mirror optical system with freeform surfaces is provided. A first initial surface, a second initial surface, and a third initial surface are established. A plurality of feature rays are selected, while the first initial surface and the third initial surface remain unchanged; a plurality of first feature data points are calculated to obtain a third freeform surface equation by surface fitting the plurality of first feature data points. A third freeform surface and the second initial surface are remained unchanged; a plurality of second feature data points are calculated to obtain a first freeform surface equation by surface fitting the plurality of second feature data points. The third freeform surface and a first freeform surface are remained unchanged; a plurality of third feature data points are calculated to obtain a second freeform surface equation by surface fitting the plurality of third feature data points.