JP2002040368A - Optically driven type wave front correction video method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform wave front correction for preventing an obtained image from becoming unclear by phase fluctuation such as the fluctuation of a medium in an optical path in video equipment such as a microscope, a telescope and a camera in real time by an optical write type liquid crystal space phase modulation element. SOLUTION: A laser beam passing through a disturbance medium between an object to be measured and an observation surface is made incident on the phase modulation surface 3 of the phase modulation element 2 as a laser for driving a compensation optical system. The reflected light is image-formed on a virtual plane F1 through a beam splitter BS3, the image is led to an interference optical system and an interference fringe reflecting the phase distribution of the disturbance medium is formed on the virtual plane F2. The image is image-formed on the write surface 4 of the phase modulation element 2. Thus, the phase modulation surface 3 is turned to the phase distribution for canceling the phase fluctuation of the disturbance medium and the compensation optical system is formed. When the image of the object to be measured is radiated to the phase modulation surface 3 in this state, the reflected light is turned to the image without the influence of the disturbance medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microscope, a telescope, a camera, and other imaging devices used for industrial measurement and medical equipment, which prevents an obtained image from being blurred due to phase fluctuation of a medium in an optical path. -Related wavefront correction imaging method and apparatus for implementing the method, and in particular, an optically driven wavefront correction imaging method and an apparatus for implementing the method, wherein the wavefront correction is performed in real time by a light-writing type liquid crystal spatial phase modulator. About.

[0002]

2. Description of the Related Art Imaging devices such as microscopes, telescopes, and cameras used as industrial instruments and medical equipment are often limited in resolution by phase fluctuations of a medium in an optical path that is inherently difficult to remove. Are known. For example, in the field of machining technology, when monitoring a workpiece on-site, it is caused by the fluctuation of air caused by the vibration of the machine tool or generated heat, and in the case of a medical fundus camera, by the effect of eye aberration (astigmatism). It is known that the obtained image becomes unclear.

That is, various image systems represented by a microscope, a telescope, a camera, and the like have a remarkable resolution due to phase fluctuation of a medium existing in an optical path connecting an object (subject) and an imaging plane (observation plane). descend. A technique for correcting the effect of the phase fluctuation in real time is called adaptive optics (or adaptive optics), and its effectiveness has already been confirmed in large astronomical telescopes and the like.

FIG. 6 shows the configuration of a system that has been widely used in the past. Basically, the wavefront 60 disturbed by the influence of the phase fluctuation of the medium in the optical path is reflected by the deformable mirror 61, and a part of the reflected light is split by the beam splitter (B).
S) Take it out by 62 and make it incident on the wavefront sensor 63. Here, the deformable mirror 61 is a thin mirror 64
This is a device in which a large number of electrostrictive elements 65 are attached to the back of the mirror and the shape of the mirror can be arbitrarily changed according to the voltage applied to each electrostrictive element 65.

[0005] The wavefront sensor 63 measures the disturbance of the wavefront, and the data is guided to the control device 66. The controller 66 calculates the shape of the mirror required to correct the wavefront based on the data, that is, the voltage applied to each electrostrictive element 65, and changes the shape of the deformable mirror based on the calculated voltage. By performing this series of operations quickly, the wavefront of the reflected light can be corrected in real time. By incorporating the deformable mirror 61 into an image system, it is possible to improve the resolution of the image system which has been reduced due to the disturbance of the wavefront.

In order to incorporate this into an astronomical telescope which is an example of an image system, the reflecting mirror inside the telescope is replaced by this deformable mirror 61, and a part of the reflected light therefrom is introduced into a wavefront sensor 63 to be used as a mirror. A control signal is generated, and the shape of the mirror is controlled based on the control signal. In fact, bright stars (reference stars)
By observing the wavefront, the wavefront of the light disturbed by the fluctuation of the atmosphere is detected, and the deformable mirror is deformed so that the wavefront disturbed in the reflection process is corrected. In this state, when a target star near the reference star is observed, the fluctuation of the atmosphere is corrected and a clear astronomical image is obtained.

[0007]

As described above, in the deformable mirror, a large number (about several tens to several hundreds) of electrostrictive elements are attached to the back of a thin mirror, and a high voltage is applied to each electrostrictive element. This is a device that changes the shape of the mirror by applying it. Therefore, the adaptive optics system using the deformable mirror not only makes the entire system expensive, but also consumes enormous power and requires a drive power supply for the device by the number of electrostrictive elements. There is a disadvantage that it becomes large. In addition, it is difficult to increase the resolution of the wavefront correction due to the physical limitation of the mirror shape change, and even if the number of electrostrictive elements is increased and the resolution of the wavefront correction is increased, With the increase in the number of calculations, the computation for generating the signals for driving the respective elements becomes enormous, and the wavefront correction in real time becomes impossible.

In a conventional adaptive optics system using a deformable mirror as described above, 1) the apparatus becomes expensive. 2) The power consumption increases. 3) The scale of the device increases. 4) It is difficult to increase the resolution of wavefront correction. 5) The wavefront correction in real time becomes difficult as the resolution of the wavefront correction increases. And so on. These problems make it extremely difficult to apply this device to various industrial measurements and medical equipment.

Accordingly, the present invention is an optically driven wavefront which is a small and inexpensive device, consumes little power, can easily increase the resolution of wavefront correction, and can perform wavefront correction in real time. It is an object of the present invention to provide a corrected image method and apparatus.

[0010]

The present invention provides the above-mentioned 1) to
In order to solve the problem 4), a high-resolution liquid crystal spatial phase modulation device is introduced as a device for correcting the wavefront, and in order to solve the problem 5), optics that does not require any operation for driving the device. An optically driven adaptive optics system based on dynamic feedback interferometer was introduced. In other words, a high-resolution optically-written liquid crystal spatial phase modulator is used as a wavefront correction device, and it is built into an optical feedback interferometer to construct an optically driven adaptive optics system, which is used in an image system It has been incorporated. In addition, since the main purpose of this device is to use it in various industrial measurement and medical equipment, the light for illuminating the object to be measured and the light for driving the adaptive optics system have high brightness and coherence. Uses excellent laser light.

Based on the above concept, the invention according to claim 1 depends on the intensity of light applied to the writing surface,
Using a liquid crystal spatial phase modulation element in which the modulation phase of the phase modulation surface on the back side changes, a reference light is incident on the phase modulation surface through a disturbance medium in the space between the measured object and the observation surface, and the phase modulation surface is Obtain interference fringes reflecting the phase distribution of the disturbing medium from the reference light reflected in the above, form a phase modulation surface so as to cancel the phase distribution of the disturbing medium by irradiating the writing surface with the interference fringes, and And observing the light to be measured reflected from the phase modulation surface after passing through the disturbing medium from above.

Further, the invention according to claim 2 provides a liquid crystal spatial phase modulation element in which the modulation phase of the phase modulation surface on the back side changes depending on the intensity of light irradiated on the writing surface; Reference light irradiation means for passing reference light through the disturbance medium in the space between the observation surfaces and entering the reference light into the phase modulation surface, and obtaining interference fringes reflecting the phase distribution of the disturbance medium from the reference light reflected by the phase modulation surface. Irradiating the writing surface with this to form a phase modulation surface so as to cancel the phase distribution of the disturbing medium; and inputting and reflecting the object from the measured object through the disturbing medium to the phase modulation surface. And an object to be measured observing means for observing the measured light.

According to a third aspect of the present invention, there is provided an optically driven wavefront correction image apparatus according to the second aspect, wherein the object to be measured is a surface of a workpiece.

According to a fourth aspect of the present invention, there is provided the optically driven wavefront correction image apparatus according to the second aspect, wherein the object to be measured is an object in a shielded space.

According to a fifth aspect of the present invention, there is provided an optically-driven wavefront correction image apparatus according to the second aspect, wherein an image obtained by imaging the interference fringe is projected on a writing surface of the liquid crystal spatial light modulator by a projection device. It was done.

[0016]

Embodiments of the present invention will be described with reference to the drawings. 1 and 2 show a basic configuration of the present invention. In addition, due to space limitations, one device is divided into two and displayed. FIG. 1 mainly shows a part of an image system, and FIG. 2 shows a part of an adaptive optics system for driving an element for correcting a wavefront in a partially overlapped manner.

In FIG. 1, a plane wave is created from a linearly polarized laser beam, and thereby the object to be measured 1 is illuminated. The light wave transmitted through the measured object 1 passes through the lens L1, the beam splitter BS1, the lenses L2 and L3, is reflected by the phase modulation surface 3 of the optical writing type liquid crystal spatial phase modulation element 2, and the reflected light is the beam splitter BS2. Through the lens L4 to form an image on an imaging surface 6 as an observation surface.

The above-mentioned optical writing type liquid crystal spatial phase modulation element 2
Is an element in which the modulation phase of the phase modulation surface 3 on the back side changes depending on the intensity of light applied to the writing surface 4.
However, phase modulation has polarization dependence, and modulates only the phase of a light wave of a polarization component parallel to the alignment direction of liquid crystal molecules. Further, since this element can arbitrarily perform phase modulation according to the intensity pattern applied to the writing surface 4,
Has high resolution wavefront correction capability. Disturbing medium 5 that disturbs the wavefront
Is disposed between the beam splitter BS1 and the lens L2 and on the phase modulation surface 3 so as to form an image plane by the lenses L2 and L3. The focal length of each lens is equal for the lenses L1 and L4 and for the lenses L2 and L3. These arrangements are of an afocal system in which the focal points of the lenses match.

In this optical system, when the phase of the phase modulating surface of the liquid crystal spatial phase modulating element 2 is opposite to the phase of the disturbance medium 5 and has a distribution of half the size, the two cancel each other out in the reflection process. The effect of the disturbing medium in this imaging system is eliminated. At this time, the image on the imaging surface 6 (directly looking into this portion or installing a camera, a microscope, or the like), which has been blurred due to the influence of the disturbance medium, changes to a clear image. However, since the phase modulation characteristic of the liquid crystal spatial phase modulation element 2 has polarization dependency, the polarization direction of the incident light is adjusted so that the phase of the reflected light wave is sufficiently modulated with respect to the orientation direction of the liquid crystal molecules (in FIG. Vertical direction)
Must be parallel to

In order to make the phase distribution of the phase modulation surface 3 of the liquid crystal spatial phase modulation element 2 a distribution that cancels out the phase fluctuation of the disturbance medium 5, an adaptive optical system shown in FIG. 2 is used. First,
As shown in FIG. 1, the turbulent medium is illuminated via a beam splitter BS1 with a plane wave (corresponding to the “reference star” in the above-mentioned astronomical observation) created from linearly polarized laser light, and the lenses L2 and L3 are illuminated. An image is formed on the phase modulating surface 3 of the phase modulating element via the optical modulator. The reflected light from the phase modulation surface 3 is
The light is guided to the lens L5 via the beam splitter BS3 (see FIG. 2). The light wave distribution on the phase modulation surface 3 is incident on the virtual plane F1 via the lenses L5 and L6, and further incident on the polarization beam splitter 7. This virtual plane F1 is the entrance of the Mach-Zehnder interferometer.

In this interferometer, the vertical polarization component of the light wave is reflected by the polarization beam splitter 7, and the lenses L7 and L7
8, a half-wave plate 8, and then enter another virtual plane F2 via a beam splitter BS4. On the other hand, the horizontal polarization component passes through the polarization beam splitter 7 and passes through the lens L9.
And L10, a reference plane wave is simulated from the distorted wavefront and formed on the virtual plane F2. As a result, an interference fringe is formed on F2 that faithfully reflects the phase distribution of the disturbing medium present in the video system.

In order to form interference fringes, it is necessary to align the polarization directions of the two light waves to be superimposed. Therefore, by introducing a half-wave plate, the polarization direction of one light wave is rotated by 90 degrees, and the two light waves are rotated. The polarization directions are aligned. The polarization direction of the laser for driving this system is adjusted so that the intensities of the two superimposed light waves are equal.

The interference fringes formed on the virtual plane F2 as described above are imaged by the lenses L11 and L12 on the writing surface 4 (behind the phase modulation surface 3) of the optical writing type liquid crystal spatial light modulator 2. Is done. However, since the image is inverted as it is, the image rotation prism 9 is used to compensate for this.
Is inserted. For the focal length of each lens,
The lenses L5 and L12, L6 and L11, L7 and L8 are made equal, and the lenses are arranged so as to form an afocal system in which the focal points of the lenses match.

The lenses L9 and L10 are determined in accordance with the magnification for producing the reference plane wave (for example, in order to obtain a magnification of 5 times, the lenses L9 and L10 are required).
Is set to 1 to 5). If you realize the above,
Due to the polarization dependence of the optical writing type liquid crystal spatial phase modulation device 2, the phase of only the light wave of the vertical polarization component of the incident light is modulated on the phase modulation surface of the device. The group implements a feedback interferometer whose principle has been created. As a result, the phase distribution of the phase modulation surface 3 of the liquid crystal spatial phase modulation element 2 becomes a distribution that cancels out the phase fluctuation of the disturbance medium 5, and operates as an adaptive optical system.

When this optical system is correctly assembled, light (laser for illuminating an object) used for an image enters the writing surface of the liquid crystal spatial light modulator through the adaptive optics system shown in FIG. Will interfere with its normal operation. This phenomenon is avoided by slightly tilting the incident direction of the light illuminating the object. On the other hand, light for driving the adaptive optics system (laser for driving the adaptive optics system)
Although the light enters the image plane of the image system via the beam splitter BS2, the light becomes a small spot on the image plane, and thus does not significantly affect the operation of the image system.

Since the above-described embodiment shows an example in which the present invention is used for various types of industrial measurement and medical equipment, a laser beam having high luminance and good coherence is used as reference light and illumination light for an object to be measured. .

An optically driven adaptive optics system has been
Although reports have been made on the proposal of its own concept and the verification experiment of its operation, no specific proposal has been made on the entire device incorporating the concept into a specific video system. This is considered to be mainly because the light used for driving the adaptive optics system and the light used for the video system affect each other, so that the entire device does not operate normally. In that regard, in the device of the present invention, the light wave used for the image and the light wave used for driving the adaptive optics system are made so as not to affect each other. It can now be fully demonstrated.

The present invention based on the above basic principle can be used for various techniques. Representative examples among them will be described. FIG. 3 shows a system for monitoring a workpiece in a factory on the spot as an embodiment of the present invention. Since it is difficult to observe most of the workpieces by transmitting light, a workpiece 10 which is an object to be measured is irradiated with a laser from the front using a beam splitter BS0 here. Generally, when the workpiece 10 is observed in this state, the air between the object to be measured and the observation surface fluctuates due to the vibration of the operating machine and the generated heat, and the image on the observation surface deteriorates. The system of FIG. 3 is used to compensate for it. This system functions basically as shown in FIG. However, in the arrangement of the devices in this system, the arrangement is such that the air fluctuation 11 to be corrected comes between the beam splitter BS1 and the lens L2. The system shown in FIG. 2 is used for the adaptive optics system.

As another embodiment of the present invention, FIG. 4 shows a system for monitoring an object in a shielded space 15. Since microfabricated products such as high-density integrated circuits are easily affected by minute dust, work in a clean room is often required. In order to observe the processed object, photographing through an observation window is indispensable. In addition, there is a situation in which precision equipment such as a camera cannot be brought into the inside of a nuclear reactor or the like, and the inside state is observed through a window from outside the shielded space. At this time, the thickness of the window,
Phase fluctuations due to non-uniform density and disturbances of light waves at the interface due to differences in environment between the inside and outside (temperature difference, pressure difference, etc.) induce image disturbance on the observation surface. . In the arrangement of FIG. 4, the position of the observation window 16 in the shielded space 15 is exactly the same as the beam splitter BS1 and the lens L.
2, the use of the adaptive optics system described above corrects the phase disturbance occurring near the window, and recovers the image disturbance.

Although the basic configuration of the optically driven adaptive optics system is shown in FIG. 2, the configuration can be modified and used. One of them is shown in FIG. In the figure, the interference fringes formed on the virtual plane F2 are photographed by the CCD camera 20 or the like. This is imaged on the writing surface 4 of the phase modulation element 2 in real time using a projection device such as a video projector 21. At this time, it is necessary to enlarge or reduce the interference fringes on the projection device side so that the light wave on the phase modulation surface 3 and the light wave on the writing surface 4 correspond one to one. Basically, since the interference fringes formed on the virtual plane F2 are imaged on the writing surface 4 of the phase modulation element 3, this optical system performs exactly the same operation as the optical system of FIG.

[0031]

As described above, the present invention is constructed as described above, and by utilizing a high-resolution liquid crystal spatial phase modulator,
Compared to adaptive optics systems that use deformable mirrors,
There is the effect of having a small, inexpensive, low power consumption, and high resolution correction capability. Further, since no electronic arithmetic processing is required for controlling the phase modulation element, there is an advantage that the real-time control is not lost even if the resolution of the phase modulation element is further dramatically increased in the future.

[Brief description of the drawings]

FIG. 1 is an optical device configuration diagram mainly showing a video system portion in a basic configuration of the present invention.

FIG. 2 is an optical device configuration diagram mainly showing an adaptive optics system portion in the basic configuration of the present invention.

FIG. 3 is an optical device configuration diagram of a part of an image system showing an example in which the present invention is used for monitoring a workpiece in a factory on the spot.

FIG. 4 is an optical device configuration diagram of a portion of an image system showing an example in which the present invention is used for observing an object to be measured in a shielded space.

FIG. 5 is a configuration diagram of an optical apparatus showing another embodiment of an optically driven adaptive optics system.

FIG. 6 is a conceptual diagram of a conventional adaptive optics system using a deformable mirror.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Object to be measured 2 Optical writing type liquid crystal spatial phase modulation element 3 Phase modulation surface 4 Writing surface 5 Disturbing medium 6 Imaging surface 7 Polarization beam splitter 8 Half-wave plate 9 Image rotation prism

Claims (5)

[Claims] 1. A liquid crystal spatial phase modulation element in which the modulation phase of a phase modulation surface on the back side changes depending on the intensity of light applied to a writing surface, and a disturbance in a space between an object to be measured and an observation surface. By passing a reference light into the phase modulation surface through a medium, obtaining an interference fringe reflecting the phase distribution of the disturbing medium from the reference light reflected by the phase modulation surface, and irradiating the writing surface with the interference fringe. Forming a phase modulation surface so as to cancel the phase distribution of the disturbing medium, and observing the light to be measured reflected from the object to be measured, which is incident on the phase modulation surface through the disturbing medium and reflected. Correction video method. 2. A liquid crystal spatial phase modulation element in which the modulation phase of a phase modulation surface on the back side changes depending on the intensity of light applied to a writing surface, and a disturbance medium in a space between an object to be measured and an observation surface. Reference light irradiating means for passing the reference light to the phase modulation surface after passing through, and obtaining interference fringes reflecting the phase distribution of the disturbance medium from the reference light reflected by the phase modulation surface, and applying the interference fringes to the writing surface. An adaptive optics means for forming a phase modulation surface so as to cancel the phase distribution of the disturbing medium by irradiating the object; and an object for observing light to be measured reflected from the object to be measured incident on the phase modulation surface through the disturbing medium through the disturbance medium. An optically driven wavefront correction image apparatus, comprising: a measurement object observation unit. 3. The optically driven wavefront correction imaging apparatus according to claim 2, wherein the object to be measured is a surface of a workpiece. 4. The light-driven wavefront correction image apparatus according to claim 2, wherein the object to be measured is an object in a shielded space. 5. The light-driven wavefront correction image apparatus according to claim 2, wherein an image obtained by imaging the interference fringes by a projection device is applied to a writing surface of the liquid crystal spatial light modulator.