JP2001318300A - Catoptric system for optical antenna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catoptric system maintaining high accuracy even if there are temperature changes. SOLUTION: A main mirror 1 is an aspherical mirror near a paraboloid, having an aperture of 300 mm and consisting of material such as glass ceramic, whose thermal expansion coefficient is <=5×10-8[/K], so that the change of curvature and profile irregularity caused by temperature is minimum. Shallow grooves for injecting an adhesive 5, having a depth of several tens micrometers are formed at 12 spots at every 30 deg. at the outer periphery part of the base part 1a of the mirror 1 by grinding and etching, and the groove 5 is provided with an injection port for pressuring and injecting an adhesive and a suction port for vacuum sucking the adhesive. Since the adhesive is accumulated only in the recessed groove 5, the thickness of an adhesive layer will not be interposed on the contact surface of a lens barrel 2 which consists of the same glass ceramic as the mirror 1 with the base part 1a of the mirror 1, so that the space will not change at all due to adhesion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telescope optical system mounted on an artificial satellite requiring particularly high imaging performance, and a reflection optical system for an optical antenna for performing optical inter-satellite communication in outer space. .

[0002]

2. Description of the Related Art In a telescope optical system intended to be mounted on an artificial satellite, a small and light-weight and high imaging performance is required. Therefore, in many cases, a reflection optical system is employed.
In addition, even in optical systems for optical antennas required to perform optical inter-satellite communication in outer space, transmitted wavefront accuracy close to the diffraction limit and small size and light weight are required despite large diameter, so in many cases, A Cassegrain type reflection optical system is employed.

[0003] Since the reflection optical system has a high degree of sensitivity that the displacement of the optical element affects the imaging performance, a focus adjustment mechanism for correcting a focus variation due to a temperature change or the like is often required. However, the provision of the focus adjustment mechanism complicates the structure and leads to an increase in weight.

In order to reduce performance deterioration such as focus change due to temperature change, a material having a small coefficient of thermal expansion may be used. However, in a space environment where a temperature change is large, a temperature difference close to 100 ° [K] is used. When a metal material having a small coefficient of thermal expansion, such as invar or a titanium alloy, is used for a lens barrel or a spider, a dimensional change exceeding an allowable range cannot be avoided. Furthermore, in optical systems for satellites that are exposed to a strong vibration environment during launch, even if a load smaller than the yield stress is applied to metallic materials, permanent dimensional changes on the order of μm will occur, degrading optical performance. There is.

In order to solve this problem, for example, Japanese Patent Laid-Open No. 7-239442 discloses a mirror optical device in which all the constituent elements are made of the same brittle material having a small coefficient of thermal expansion.

[0006]

However, in the above-mentioned Japanese Patent Application Laid-Open No. Hei 7-239442, an optical system which can maintain high optical performance even when exposed to a large temperature change and strong vibration despite its extremely light weight is achieved. However, since the three columns for supporting the secondary mirror are independent, there is a problem that it is very difficult to adjust the optical axis and join the columns, resulting in poor productivity. In particular, it is dangerous to directly join a brittle material such as glass with bolts or pins, but it is difficult to bond and harden the column with the adhesive alone while maintaining the positioned state.

An object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide a reflection optical system for an optical antenna that can maintain a highly accurate structure even when a temperature change is large.

[0008]

According to the present invention, there is provided a reflection optical system for an optical antenna, comprising: a primary mirror; a secondary mirror facing the primary mirror; and a support mirror for supporting the secondary mirror. In a reflection optical system including a spider and a lens barrel interposed between the primary mirror and the spider for maintaining a relative position of the secondary mirror with respect to the primary mirror, the primary mirror, the secondary mirror, the spider, The lens barrel is made of a brittle material having a coefficient of thermal expansion of 5 × 10 ⁻⁶ [/ K] or less, and the main mirror and the lens barrel, the lens barrel and the spider, and the spider and the sub-mirror are respectively bonded by bonding flat portions. It is characterized by having done.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the illustrated embodiment. FIG. 1 is a cross-sectional view of the reflection optical system in the present embodiment, and FIG. 2 is a cross-sectional view taken along line AA of FIG. A flange portion 2a of a lens barrel 2 made of the same material is fixed to a main mirror 1 made of glass ceramics (Zerodur: manufactured by Shot Co., Ltd.) having a coefficient of thermal expansion of 5 × 10 ⁻⁸ [/ K] or less. 2 has a flange portion 2b at the other end.
Titanium silicate glass (ULE: having a number of columns and having a coefficient of thermal expansion of 5 × 10 ⁻⁸ [/ K] or less and transmitting ultraviolet rays.
A spider 3 made of Corning Inc.) is attached by bonding. On the central plane portion of the spider 3, a sub-mirror 4 made of a glass-ceramic made of the same material as the main mirror 1 and the lens barrel 2 and made of an aspherical mirror close to a hyperboloid of 50 mm in diameter.
Are arranged by bonding. A Cassegrain telescope having an F value of about 6 is configured as a whole.

The primary mirror 1 and the secondary mirror 4 are added with higher order aspherical coefficients in order to correct spherical aberration and off-axis aberration. A silver reflective film has been deposited on the surface to enhance it. The front surface of the primary mirror 1 is a mirror portion 1b, and a central hole 1c is formed in the center.

A light beam arriving from a distant light source is reflected and condensed by the mirror portion 1b of the primary mirror 1, and after being reflected again by the secondary mirror 4,
The light passes through the central hole 1c of the primary mirror 1 and forms an image on a detector surface (not shown).

The primary mirror 1 is an aspherical mirror close to a parabolic surface having a diameter of 300 mm and made of a material whose coefficient of thermal expansion is selected so that changes in curvature and surface accuracy due to temperature are minimized. The weight has been reduced. As shown in FIG. 2, adhesive injection grooves 5 are provided at twelve locations at intervals of 30 ° on the outer surface of the base 1 a supporting the main mirror 1. The groove 5 for injecting the adhesive is a shallow groove having a depth of several tens of μm, formed by grinding and etching, and an inlet 5a for injecting the adhesive by pressing, and a suction for sucking the adhesive in vacuum. An opening 5b and an adhesive groove 5c are provided. Since the adhesive is accumulated only in the recessed adhesive groove 5c, the thickness of the adhesive layer does not intervene on the contact surface between the base 1a of the main mirror 1 and the flange 2a of the lens barrel 2. By using the same glass ceramic as the material of the main mirror 1 as the material of the lens barrel 2, a change in the distance between the main mirror 1 and the sub mirror 4 due to a temperature change on the orbit is suppressed to 1 micron or less.

For bonding the spider 3 and the lens barrel 2, both the flanges 3a and 2b, which are bonding surfaces, have a surface accuracy of 1 μmP.
The surface is optically polished so as to have a flat surface within V, and an epoxy-based adhesive is applied to the entire bonding surface, and the surface is bonded and hardened. This epoxy adhesive is selected to have a very small outgassing in vacuum.

The joint surface of the secondary mirror 4 and the spider 3 is optically polished so that both surfaces have a surface accuracy of 1 μmPV or less, and an ultraviolet curing adhesive is applied to the entire joint surface and irradiated with ultraviolet rays. In this way, the adhesive is cured. This UV-curable adhesive is selected so as not to cause distortion of the mirror surface of the sub-mirror 4 at the time of curing, and to release gas very little in a vacuum.

All surfaces other than the polished surfaces of the primary mirror 1, the lens barrel 2, the spider 3, and the secondary mirror 4 have their latent scratches removed by etching, and the structure has sufficient strength.

After the coupling of the sub-mirror 4, the spider 3, and the lens barrel 2 is completed, fine adjustment of the alignment between the main mirror 1 and the lens barrel 2 is performed while confirming the transmitted wave front with an interferometer. Then, the primary mirror 1 and the lens barrel 2 are connected. The base part 1a of the above-mentioned main mirror 1 optically polished so that the surface accuracy becomes a plane within 1 μmPV is used for coupling the main mirror 1 and the lens barrel 2.
And the flange 2a of the lens barrel 2. With the above configuration, the transmitted wavefront accuracy of the entire telescope optical system is λ /
Very high imaging performance of 20 rms or less can be achieved.

If the optical system is smaller than this embodiment or if the required imaging performance is not so high,
As a constituent material of the primary mirror 1, the secondary mirror 4, and the spider 3, it is possible to use synthetic quartz or a ceramic material instead of glass ceramics or titanium silicate glass.

In the present embodiment, since the procedure for joining the main mirror 1 and the lens barrel 2 is performed last, the groove 5 for injecting the adhesive is formed in the main mirror 1. Depending on the case, it is also possible to form a similar adhesive injection groove 5 in another joint. However, in any case, it is necessary to form the groove 5a for injecting the adhesive at the last part to be joined.

By arranging a collimator near the image plane of the telescope optical system to re-parallel the light beam, a highly accurate optical antenna optical system for optical inter-satellite communication or an optical system for a coherent laser radar is provided. It is also possible to get

[0020]

As described above, the reflection optical system for an optical antenna according to the present invention can be used in a telescope optical system requiring high imaging performance or an optical antenna optical system for optical inter-satellite communication.
The focus adjustment mechanism is not required, and an optical system with high productivity can be obtained with high accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment.

FIG. 2 is a sectional view taken along line AA of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Primary mirror 2 Lens barrel 3 Spider 4 Secondary mirror 5 Adhesive injection groove

Claims (3)

[Claims] 1. A primary mirror, a secondary mirror facing the primary mirror, a spider for supporting the secondary mirror, and a relative position of the secondary mirror interposed between the primary mirror and the spider with respect to the primary mirror. In the reflection optical system including the lens barrel for maintaining the following, the primary mirror, the secondary mirror, the spider, and the lens barrel are made of a brittle material having a thermal expansion coefficient of 5 × 10 ⁻⁶ [/ K] or less. A reflection optical system for an optical antenna, wherein the main mirror and the lens barrel, the lens barrel and the spider, and the spider and the sub-mirror are respectively bonded by bonding flat portions. 2. The main mirror and a lens barrel, the lens barrel and a spider,
At least one of the bonding between the spider and the flat portion of the secondary mirror
2. The method according to claim 1, wherein a groove for injecting an adhesive is provided in any one of the flat portions so that a gap between the primary mirror and the secondary mirror does not change due to a layer thickness of the adhesive during bonding. 3. The reflection optical system for an optical antenna according to 1. 3. The plurality of grooves at one location.
3. The reflection optical system for an optical antenna according to 1.