Observation device comprising free-form mirrors and a curved detector

Abstract

This scene observation device comprises a detector (2) and first, second, third, and fourth mirrors (4, 6, 8, 10), each of freeform and non-axisymmetric shape. The detector (2) includes a pixel matrix (12) with a curved surface. (See Figure 1 for abbreviations.)

Description

Title of the invention: Observation device comprising free-form mirrors and a curved detector technical field

[0001] The invention has as its technical field observation devices, in particular for space or ground observation with an ultra large field of observation and high angular resolution. Previous techniques

[0002] It is common, when designing an optical system, to make a compromise between a high field of view and a high angular resolution.

[0003] It is known that avoiding such a compromise involves using multiple optical systems so that each optical system images a different field of view, with the different fields of view then being recombined. Such a solution is generally complex, expensive, and bulky.

[0004] Prior art is known from US patent 5,331,470, which describes an observation device equipped with a plane mirror, three aspherical mirrors, and a focal plane grating. Such an observation device has a field of view of at least 13.5 degrees vertically and 27 degrees horizontally. Description of the invention

[0005] The present invention therefore aims to provide a compact observation system having a high field of observation and angular resolution.

[0006] The present invention relates to a scene observation device comprising a detector and first, second, third and fourth mirrors arranged such that:

[0007] - the first mirror is configured to direct towards the second mirror a electromagnetic radiation emanating from the stage;

[0008] - the second mirror is configured to direct towards the third mirror the electromagnetic radiation reflected by the first mirror;

[0009] - the third mirror is configured to direct towards the fourth mirror the electromagnetic radiation reflected by the second mirror; and

[0010] - the fourth mirror is configured to direct the radiation towards the detector electromagnetic reflected by the third mirror.

[0011] The first, second, third and fourth mirrors are each of free form and of non-axisymmetric shape.

[0012] The detector comprises a pixel matrix whose surface is curved.

[0013] In other words, the first, second, third and fourth mirrors are each of the "freeform" type according to the English term.

[0014] The use of the first, second, third and fourth mirrors, each of free form and non-axisymmetric shape, and of the pixel matrix whose surface is curved, makes it possible to increase the number of degrees of freedom for the design of the optical system, and thus to obtain an observation device with a high field of observation and angular resolution.

[0015] In addition, the use of the first, second, third and fourth mirrors makes it possible to avoid chromatic aberrations and to reduce costs compared to an optical system equipped with a lens.

[0016] The use of the pixel matrix whose surface is curved makes it possible to reduce the complexity of the shape of the first, second, third and fourth mirrors.

[0017] Preferably, the detector is a curved focal plane grating.

[0018] In a particular embodiment, the detector is an infrared detector or visible.

[0019] Preferably, the first mirror is convex, the second mirror is convex, the third mirror is concave, the fourth mirror is concave.

[0020] According to a particular design, the surface of the pixel matrix is ​​strictly concave along a first direction and strictly convex along a second direction which is secant to the first direction.

[0021] The first and second directions can be perpendicular. Such a shape is said to be "saddle-shaped", which corresponds to a form of hyperbolic paraboloid.

[0022] Advantageously, the observation device further comprises at least one part which is disposed on a path of parasitic electromagnetic radiation between the detector and the first mirror, and which is configured to interrupt said parasitic radiation.

[0023] The use of the first, second, third, and fourth mirrors, each free-form and non-axisymmetric, and of the pixel matrix with a curved surface, provides sufficient spacing between the first, second, third, and fourth mirrors to position the component without blocking useful electromagnetic radiation. Useful electromagnetic radiation is the electromagnetic radiation from the scene that travels along the optical path from the first mirror to the detector, passing successively through the second, third, and fourth mirrors. Stray electromagnetic radiation represents any electromagnetic radiation other than useful electromagnetic radiation.

[0024] Optionally, said part is provided with an absorbing surface, said part being arranged so that said absorbing surface is on the path of parasitic electromagnetic radiation between the detector and the first mirror.

[0025] According to a particular design, said part comprises a plate painted black.

[0026] Advantageously, the detector and the first, second, third and fourth mirrors are designed so that the observation device has an aperture number less than or equal to 2.8, in particular less than or equal to 1.5.

[0027] In other words, the detector and the first, second, third and fourth mirrors are designed so that the observation device has a numerical aperture greater than or equal to f / 2.8, in particular greater than or equal to f / 1.5.

[0028] Advantageously, the aperture diaphragm is carried by one of the first, second, third and fourth mirrors, in particular by the third mirror.

[0029] In other words, the amount of light received by the observation device is limited by one of the first, second, third and fourth mirrors, in particular by the third mirror, this mirror determining the size and position of the apparent opening of the observation device.

[0030] The aperture diaphragm carried by one of the first, second, third and fourth mirrors makes it possible not to add a diaphragm or other optical element to limit the electromagnetic radiation that enters the observation device.

[0031] When the aperture diaphragm is carried by the third mirror, the optical performance of the observation device is improved.

[0032] Advantageously, the detector and the first, second, third and fourth mirrors are designed so that the field of observation of the detector of the observation device is at least 10 degrees vertically and at least 50 degrees horizontally.

[0033] Optionally, the detector and the first, second, third and fourth mirrors are designed so that the field of view of the detector of the observation device is at least 13.5 degrees vertically and at least 65 degrees horizontally.

[0034] Advantageously, the detector and the first, second, third and fourth mirrors are designed so that the angular resolution of the detector of the observation device is less than or equal to 10 arcseconds.

[0035] Such angular resolution is superior to that of the human eye.

[0036] In other words, the detector and the first, second, third and fourth mirrors are designed so that the angular resolution of the detector of the observation device is less than 10 / 3600 degrees.

[0037] Optionally, the detector and the first, second, third and fourth mirrors are designed so that the percussion response of the observation device is less than 15 pm on root mean square, in particular less than 10 pm on root mean square, and more particularly less than or equal to 5 pm on root mean square.

[0038] According to a particular design, each of the first, second, third and fourth mirrors is designed so as to have a strictly positive conicity constant.

[0039] According to a particular design, the detector is designed so that the surface of the pixel matrix has a zero taper constant.

[0040] Thus, the detector is defined on a spherical basis. Such a detector is easier to produce. Brief description of the drawings

[0041] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which:

[0042] [Fig. 1] illustrates an observation device according to a first example of an embodiment of the invention;

[0043] [Fig.2] is a perspective representation of the observation device of [Fig. 1]

[0044] [Fig.3] is a perspective representation of a detector of the device observation of [Fig. 1]; and

[0045] [Fig.4] illustrates an observation device according to a second embodiment of the invention. Detailed description

[0046] Fig. 1 schematically represents an observation device which includes a detector 2 and first, second, third and fourth mirrors 4, 6, 8, 10.

[0047] Detector 2 is, for example, an infrared or visible detector 2, so that the observation device is capable of imaging infrared or visible electromagnetic radiation from a scene observed by the observation device.

[0048] The first mirror 4 is arranged so as to reflect the electromagnetic radiation from the scene towards the second mirror 6. The first mirror 4 is freeform and non-axisymmetric.

[0049] The second mirror 6 is arranged so as to reflect the electromagnetic radiation coming from the first mirror 4, that is to say the electromagnetic radiation coming from the scene and then reflected by the first mirror 4, towards the third mirror 8. The second mirror 6 is freeform and non-axisymmetric.

[0050] The third mirror 8 is arranged so as to reflect the electromagnetic radiation from the second mirror 6, that is to say the electromagnetic radiation from the scene then reflected successively by the first mirror 4 and by the second mirror 6, towards the fourth mirror 10. The third mirror 8 is of free form and of non-axisymmetric shape.

[0051] The fourth mirror 10 is arranged so as to reflect the electromagnetic radiation from the third mirror 8, i.e. the electromagnetic radiation from the scene then reflected successively by the first mirror 4, by the second mirror 6 and by the third mirror 8, towards the detector 2. The fourth mirror 10 is freeform and non-axisymmetric.

[0052] As more clearly illustrated in [Fig. 2], the first mirror 4 is convex, the second mirror 6 is convex, the third mirror 8 is concave, and the fourth mirror 10 is concave. In particular, none of the mirrors 4, 6, 8, or 10 of the observation device are flat.

[0053] As more clearly illustrated in [Fig. 3], the detector 2, for example a focal plane grating, comprises a pixel matrix 12 whose surface is curved. More precisely, the surface of the pixel matrix 12 is strictly concave along a first direction and strictly convex along a second direction which is orthogonal to the first direction.

[0054] For designing detector 2 and the first, second, third and fourth mirrors 4, 6, 8, 10, at least one of the following criteria may be considered:

[0055] - an observation field of detector 2 of the observation device of at least 10 degrees vertically and at least 50 degrees horizontally;

[0056] - an image spot or percussion response of the observation device less than 15 pm on root mean square;

[0057] - an opening number of the observation device less than or equal to 1.5;

[0058] - an angular resolution of detector 2 of the observation device of less than 10 arcseconds; and

[0059] - an aperture diaphragm of the observation device carried by one of the first, second, third and fourth mirrors 4, 6, 8, 10.

[0060] For example, the following criteria are selected:

[0061] - an observation field of detector 2 of the observation device of 13.5 degrees vertically and 65 degrees horizontally;

[0062] - a percussion response of 5 pm;

[0063] - a focal length of the observation device of approximately 100 mm;

[0064] - a numerical aperture of f / 1.5;

[0065] - an angular resolution of detector 2 of the observation device of 10 seconds of the bow; and

[0066] - an aperture diaphragm of the observation device carried by the third mirror 8.

[0067] For this example, detector 2 and the first, second, third and fourth mirrors 4, 6, 8, 10 are designed in the manner summarized in the following Table 1, in which:

[0068] - R is the osculating radius;

[0069] - Rnorm is the normalization radius of Zemike polynomials;

[0070] - K is the tapering constant; and

[0071] - ZFn is the coefficient of the Zernike polynomial n according to the Fringe convention.

[0072] [Tables 1] Mirror 4 Mirror 6 Mirror 8 Mirror 10 Detector 2 R 1715.1 -376.6 -335.1 366.2 226.4 Rnorm 150 108 95 90 68 K 1.50 3.82 0.14 1.50 0 ZF5 -2.51 0.69 0.15 -6.39 -12.75 ZF8 0.63 0.11 0.17 -1.82 -2.73 ZF9 -0.02 -0.06 0.00 0.10 -0.01 ZF11 1.68 0.49 -0.02 1.00 2.54 ZF12 0.30 0.11 0.00 -0.27 -0.16 ZF15 -0.07 -0.01 0.01 -0.04 0 ZF17 -0.68 -0.07 0.00 0.14 0 ZF20 0.07 -0.01 0.00 0.02 0 ZF27 -0.08 0.01 0.00 -0.01 0

[0073] Here, each of the first, second, third and fourth mirrors 4, 6, 8, 10 has been designed so that each of the first, second, third and fourth mirrors 4, 6, 8, 10 has a strictly positive conicity constant.

[0074] Detector 2 has been designed here so that detector 2 has a conicity constant of zero.

[0075] Furthermore, detector 2 is designed here with fewer Zernike polynomials than the first, second, third, and fourth mirrors 4, 6, 8, 10, so that the curvature of detector 2 is simpler to achieve. In particular, we have limited ourselves here to the first 12 Zernike polynomials for the design of detector 2 and the first 27 Zernike polynomials to design the first, second, third and fourth mirrors 4, 6, 8, 10. Detector 2 is also designed here so that its pixel matrix retains at least one plane of symmetry.

[0076] The second embodiment illustrated in [Fig. 4] differs from the first embodiment illustrated in Figures 1 to 3 in that the observation device further comprises parts 14 arranged along a path of stray electromagnetic radiation between the detector 2 and the first mirror 4. In particular, each part 14 is provided with an absorbing surface arranged along the path of stray electromagnetic radiation. More precisely, the observation device here comprises parts 14 arranged along a direct path of electromagnetic radiation between the detector 2 and the first mirror 4.

[0077] Each part 14 is here arranged in a gap in the observation device. In particular, the addition of the parts 14 does not modify the arrangement of the detector 2 and the first, second, third and fourth mirrors 4, 6, 8, 10 compared to the observation device without parts 14

[0078] The observation device here comprises two parts. Alternatively, the observation device could comprise one part or more than two parts.

Claims

Demands

1. A scene observation device comprising a detector (2) and first, second, third and fourth mirrors (4, 6, 8, 10) arranged such that: - the first mirror (4) is configured to direct electromagnetic radiation from the scene towards the second mirror (6); - the second mirror (6) is configured to direct the electromagnetic radiation reflected by the first mirror (4) towards the third mirror (8); - the third mirror (8) is configured to direct the electromagnetic radiation reflected by the second mirror (6) towards the fourth mirror (10); and - the fourth mirror (10) is configured to direct the electromagnetic radiation reflected by the third mirror (8) towards the detector (2), characterized in that: - the first, second, third and fourth mirrors (4, 6, 8, 10) are each freeform and non-axisymmetric;and - the detector (2) comprises a pixel matrix (12) whose surface is curved.;

2. Observation device according to claim 1, wherein the first mirror (4) is convex, the second mirror (6) is convex, the third mirror (8) is concave, the fourth mirror (10) is concave.

3. Observation device according to claim 1 or 2, wherein the surface of the pixel matrix (12) is strictly concave along a first direction and strictly convex along a second direction which is secant to the first direction.

4. Observation device according to any one of claims 1 to 3, further comprising at least one part (14) which is disposed on a path of parasitic electromagnetic radiation between the detector (2) and the first mirror (4), and which is configured to interrupt said parasitic radiation.

5. An observation device according to any one of claims 1 to 4, wherein the detector (2) and the first, second, third and fourth mirrors (4, 6, 8, 10) are designed such that the device observation has an aperture number less than or equal to 2.8, in particular less than or equal to 1.

5.

6. Observation device according to any one of claims 1 to 5, wherein the aperture diaphragm of the observation device is carried by one of the first, second, third and fourth mirrors (4, 6, 8, 10), in particular by the third mirror (8).

7. Observation device according to any one of claims 1 to 6, wherein the detector (2) and the first, second, third and fourth mirrors (4, 6, 8, 10) are designed so that the field of view of the detector (2) of the observation device is at least 10 degrees vertically and at least 50 degrees horizontally.

8. Observation device according to any one of claims 1 to 7, wherein the detector (2) and the first, second, third and fourth mirrors (4, 6, 8, 10) are designed so that the angular resolution of the detector (2) of the observation device is less than or equal to 10 arcseconds.

9. Observation device according to any one of claims 1 to 8, wherein each of the first, second, third and fourth mirrors (4, 6, 8, 10) is designed to have a strictly positive taper constant.

10. Observation device according to any one of claims 1 to 9, wherein the detector (2) is designed such that the surface of the pixel matrix (12) has a zero taper constant.

Images