JPH05307109A - Active optical device - Google Patents

Abstract

PURPOSE:To provide the active optical device which is reduced in the load on a control means by simplifying a deformation driving means. CONSTITUTION:This active optical device is equipped with a means 5 which measures the surface shape of an optical element 1 and a control circuit 4 which sends a driving signal to actuators 3 as the deformation driving means according to the measurement result of the measuring means 5, and the actuators 3 which have received the driving signal from the control circuit 4 expand or contract behind the photodetection surface 2 of the optical element 1 to deform the photodetection surface 2 of the optical element 1 into an ideal surface shape; and the actuators 3 are unevenly distributed more in the photodetection area of the optical element 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active optical device used as, for example, a large telescope.

[0002]

2. Description of the Related Art In order to construct a large telescope which is a huge structure, it is necessary to reduce the weight of the primary mirror. In order to compensate for the reduction in mirror rigidity that accompanies this weight reduction and to observe in the best condition, an active optical device monitors the mirror surface shape and tries to keep it on an ideal surface by computer control.

That is, the mirror surface of the telescope must be prevented from being deformed to the extent of the wavelength of light. When observing a celestial object, the telescope tilts in many different directions, so the direction in which its own weight is applied is not constant. If the mirror is easily supported, the mirror will be deformed. In order to reduce this self-weight deformation, it has been common knowledge that the glass material of the primary mirror is made sufficiently thick and rigid. However, in the case of a large telescope, the weight of the glass material becomes unrealistically large, and the structure for supporting the mirror becomes large and heavy, so the cost becomes an astronomical figure.

If the mirror can be made thin and lightweight, the whole body becomes lighter. That is, maintaining a thin and soft mirror in an ideal plane shape has always been the biggest challenge for realizing a large telescope. FIG. 5 is a schematic configuration of an active optical device that is made possible to substantially satisfy the above-mentioned demand.

In the figure, reference numeral 1 denotes an optical element which is a large-sized thin-walled main mirror, and the upper surface side in the figure is a light receiving surface, that is, a mirror surface 2. On the lower surface side which is a non-light receiving surface, a large number of actuators 3 ... Which are deformation driving means are arranged.

The actuators 3 ...
In contrast, the actuators 3a are arranged in order with a predetermined vertical and horizontal pitches, and the tips of the respective actuators 3a are directly connected to the lower surface of the optical element 1. The actuator 3a is designed to be capable of expanding and contracting, and the connecting portion for the optical element 1 is deformed accordingly. All the actuators 3 are electrically connected to the surface shape measuring means 5 via a control circuit 4 which is a control means.

The light received by the mirror surface 2 of the optical element 1 is reflected here and reaches the surface shape measuring means 5. Here, it is compared with a previously stored ideal surface shape, and the signal is sent to the control circuit 4. The control circuit 4 calculates the expansion / contraction control amount of the actuators 3a of the actuators 3 based on the comparison result, and sends a control signal that makes the mirror surface 2 have an ideal surface shape. In this way, the performance of the optical element 1 can be actively enhanced.

[0008]

The above-mentioned active optical device is intended to keep the surface shape of the optical element 1 in an ideal surface state by the actuator 3 which is the deformation driving means.
Therefore, the larger the number of actuators 3, the more precise the surface shape can be controlled. However, if the number of actuators 3 is increased, the calculation of the expansion / contraction control amount of the actuator 3a of each actuator 3 becomes enormous, resulting in poor efficiency. That is, it is required to reduce the number of actuators 3 without deteriorating the performance of the optical element 1. On the other hand, in the conventional device, the optical elements 1 having an extremely large diameter are arranged vertically and horizontally, and an extremely large number are provided.

However, it is impossible that the entire mirror surface 2 is used uniformly as the light receiving area, which is the use area where the optical element 1 actually receives light. Usually, a region in which the mirror surface 2 is partially limited is often used. And again, due to the shape structure of the optical element 1,
In particular, the deformation of the outer peripheral portion is large, and the deformation inside thereof is relatively small.

As described above, in the conventional active optical device, a large number of actuators are originally arranged even in a portion that does not need to be deformed, and the number of these actuators is increased to complicate the control.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an active optical device in which the deformation driving means is simplified and the load on the control means is reduced. Is.

[0012]

In order to achieve the above object, the first invention is an optical element, a means for measuring the surface shape of the optical element, and a deformation driving based on the measurement result of the measuring means. A control means for issuing a drive signal to the means,
In the active optical device, the deformation driving means receiving the drive signal from the control means expands and contracts on the surface on the back side of the light receiving surface of the optical element to deform the light receiving surface of the optical element into an ideal surface shape. Is an active optical device characterized in that it is arranged so as to be unevenly distributed in the light receiving region of the optical element.

A second aspect of the present invention is the active optical device according to the first aspect, wherein the deformation driving means is arranged so as to face the outer peripheral portion of the optical element having a large error from the ideal surface shape.

According to a third aspect of the present invention, the deformation driving means comprises a plurality of slit-shaped grooves provided on the surface on the back side of the light-receiving surface of the optical element, and a liquid actuator that penetrates into the grooves and deforms. The active optical device according to claim 1, wherein:

[0015]

According to the present invention, the deformation driving means is arranged in a particularly distributed manner in a particularly required place, so that the deformation driving means is simplified and the calculation amount of the control amount in the control means is reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In the figure, reference numeral 1 denotes an optical element which is a large-sized thin-walled main mirror, and in the figure, an upper surface side is a mirror surface 2 which is a light receiving surface, and has the same shape structure as that conventionally used. On the lower surface side of the optical element 1 which is a non-light receiving surface, actuators 3 ... Which are deformation driving means are arranged as described later.

That is, these actuators 3 ...
The optical elements 1 are arranged in a concentrated manner at positions facing the outer peripheral portion 1a. The other parts are arranged with the minimum required number being aligned. Therefore, the number of actuators 3 as a whole is much smaller than that of the conventional one.

The actuator 3 of each actuator 3 is directly connected to the lower surface of the optical element 1. It is the same as the conventional one in that the actuator 3a is driven to extend and contract, and the connecting portion of the optical element 1 is deformed accordingly. All of the above-mentioned actuators 3 are electrically connected to the surface shape measuring means 5 via a control circuit 4 which is a control means not shown here, as in the conventional case.

The light received by the mirror surface 2 of the optical element 1 is reflected here and reaches the surface shape measuring means 5. Here, it is compared with a previously stored ideal surface shape, and the signal is sent to the control circuit 4. The control circuit 4 calculates the expansion / contraction control amount of the actuator 3a of each actuator 3 based on the comparison result, and sends a control signal for causing the mirror surface 2 to have an ideal surface shape.

In the case of a large workpiece such as the optical element 1 used here, an error due to bending or distortion becomes large especially in the outer peripheral portion 1a. Further, even when the optical element 1 is tilted and used, it is expected that the error in the outer peripheral portion 1a becomes large.

If a large number of actuators 3 are arranged in the outer peripheral portion 1a of the optical element 1 in a concentrated manner as in the above embodiment, the degree of freedom of deformation, which is the error correction capability in the outer peripheral portion 1a, is increased. Further, since the number of actuators 3 is reduced, the amount of calculation in the surface shape measuring means 5 and the control circuit 4 can be reduced. As shown in FIG. 2, in the light receiving area S which is a usage area of the optical element 10, many actuators 3 ... Which are deformation driving means are eccentrically arranged.

That is, when the optical system is constructed by using a part of the mirror surface 11 which is the light receiving surface, it is not necessary for the entire mirror surface 11 to have high shape accuracy. A large number of actuators 3 ... Can be arranged in the required light receiving area S so as to face each other, and the degree of freedom of deformation of the optical element 10, which is the error correction capability in that area, can be increased.

In any of the embodiments, the actuators 3 are placed in the optical elements 1, 1 as the arrangement state.
They may be arranged concentrically with respect to 0, or may be arranged in a matrix. It may be an active optical device as shown in FIG. In the figure, reference numeral 20 denotes an optical element whose upper surface side is a mirror surface 21 which is a light receiving surface, and the deformation driving means 22 is integrally embedded in the lower surface side.

That is, a large number of slits 23 having a wedge-shaped cross section are provided on the lower surface side of the optical element 20. The intervals between the upper ends (pointed ends) of the slits 23 and the mirror surface 21 are uniform in all the slits 23 and are formed to have the same sectional angle. Each slit 23
The magnetic fluid 25 that constitutes the deformation driving means is collected in the inside of the storage tank 24 and in the storage portion 24 that communicates therewith.

The magnetic fluid 25 is a kind of colloidal solid-liquid mixed phase fluid obtained by distributing a large amount of fine particles of a magnetic material (diameter of about 100 Å) in a liquid as a dispersion medium.

Ferromagnetic materials such as magnetite, iron and cobalt are used as fine particles, and water is used as a dispersion medium.
A solution of kerosene, diester, eicosylnaphthalene or the like is used.

The magnetic fluid 25 is a substance that has the two properties of being a magnetic substance and being a fluid at the same time. In order to have such properties, the surface of the magnetic fine powder is coated with a surfactant.

That is, the magnetic fluid 25 is made to maintain a uniform dispersed state of the magnetic particles by the effect of the finely divided magnetic particles and the surfactant coated on each of the magnetic particles. The reason is that it has both properties of being a fluid and being a magnetic substance.

The magnetic fluid 25 in each slit 23 provided in the optical element 20 is stored in the reservoir 24 of the optical element 20.
It corresponds to the actuator drive coil 26 arranged in the lower part. The drive coil 26 is controlled by the control circuit 27.
It is electrically connected to the surface shape measuring means 28 via.

Since it is an active optical device constructed in this way, the light reflected by the mirror surface 21 of the optical element 20 goes to the surface shape measuring means 28, where it is compared with the previously stored ideal surface shape. It

The control circuit 27 receives the measurement result of the surface shape measuring means 28 and sends a control signal to the necessary actuator drive coil 26. The actuator drive coil 26 receiving the control signal applies a magnetic field to the magnetic fluid 25 in the corresponding slit 23. As shown in FIG. 4 (A), the magnetic fluid 25 in the slit 23 does not exert any action on the wall of the slit 23 in the state where the magnetic field is not applied.

When a magnetic field is applied to the magnetic fluid 25 in the slit 23, this applies pressure to the upper wall of the slit 23, as shown in FIG. The slit 23 wall is pushed and expanded in the direction in which the width of the slit 23 is expanded by receiving this force.

As a result, the light receiving surface of the optical element 20, that is, the mirror surface 21 is deformed. By forming a feedback control system with such a function together with the surface shape measuring means 28 and the control circuit 27, the performance of the optical element 20 can be actively enhanced.

In FIG. 3, a large number of slits 23 for causing the magnetic fluid 25 to act are provided at equal intervals, but the number of slits 23 is not limited to this, and as described above, an ideal surface shape is formed. Light receiving element 2 which is expected to have a large error
You may provide many slits 23 so that it may oppose the outer peripheral part of 0.

Further, the slits 23 may be arranged so as to face the light receiving region which is the use region and be unevenly distributed. In short, the position and the number of the slits 23 can be set freely, and the degree of freedom of deformation of the optical element 20 can be increased.

In any case, since it is the deformation driving means 22 provided with the magnetic fluid 25, the supporting and fixing structure can be simplified and the wiring labor can be saved as compared with the actuator 3 described above.

[0038]

As described above, according to the present invention, the deformation driving means for the optical element is arranged in a more unevenly distributed manner in the light receiving area. Therefore, the deformation driving means can be simplified to reduce the cost and control. The effect of reducing the burden on the means and the running cost is achieved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention with a part of an active optical device omitted.

FIG. 2 is a block diagram of an active optical device according to another embodiment with a part thereof omitted.

FIG. 3 is a block diagram of an active optical device according to still another embodiment with a part thereof omitted.

4 (A) and 4 (B) are views for explaining a modification action of the embodiment.

FIG. 5 is a configuration diagram of an active optical device showing a conventional example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical element, 2 ... Light receiving surface (mirror surface), 5 ... Surface shape measuring means, 4 ... Control means (control circuit), 3 ... Deformation drive means (actuator), 1a ... (Optical element) outer peripheral part, S ...
Light receiving region (of optical element), 23 ... Slit, 25 ... Magnetic fluid.

Claims (3)

[Claims] 1. An optical element, means for measuring the surface shape of the optical element, and control means for issuing a drive signal to the deformation driving means based on the measurement result of the measuring means. In the active optical device in which the deformation driving means that receives the signal expands and contracts on the surface on the back side of the light receiving surface of the optical element to deform the light receiving surface of the optical element into an ideal surface shape, the deformation driving means includes the optical element. The active optical device is characterized in that it is arranged so as to be unevenly distributed in the light receiving region of the. 2. The active optical device according to claim 1, wherein the deformation driving means is arranged so as to face the outer peripheral portion of the optical element having a large error from the ideal surface shape. 3. The deformation driving means comprises a plurality of slit-shaped grooves provided on the surface on the back side of the light-receiving surface of the optical element, and a liquid actuator which penetrates into the grooves and deforms. The active optical device according to claim 1.