JP3323548B2 - Beam deflector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam deflecting device using an acousto-optic device, and more particularly to a beam deflecting device capable of obtaining a large deflection angle.

[0002]

2. Description of the Related Art In image forming apparatuses such as a laser microscope, a laser printer, a facsimile, and a scanner graph, a beam deflecting device having an acousto-optical element is widely used. In this beam deflecting device, a drive circuit for generating a deflection signal is connected to an acousto-optic element, and an ultrasonic wave whose frequency periodically changes is supplied to the acousto-optic element. Then, a periodically changing diffraction grating is formed in the acousto-optic element, and the incident beam is periodically deflected in a predetermined deflection direction by the formed diffraction grating. The beam polarizer using this acousto-optic element does not require a mechanical drive mechanism,
Moreover, there is a great advantage that high-speed scanning at a television rate is possible.

[0003]

In an optical device such as a laser microscope, for example, it is desired that the scanning length of a surface to be scanned by a light beam be as long as possible. However, since the deflection angle of the acousto-optic element is about several degrees, if the scanning length is to be increased, the optical path length from the acousto-optic element to the surface to be scanned must be increased, and the apparatus itself becomes large. Will occur.

Accordingly, an object of the present invention is to realize a beam deflecting device capable of obtaining a larger deflection angle while maintaining the specific effects of the acousto-optic element.

[0005]

SUMMARY OF THE INVENTION A beam deflecting device according to the present invention converts an incident beam polarized in one direction into a first beam.
An acousto-optic element that deflects light in the direction of deflection, an optical system that rotates the beam emitted from the acousto-optic element by 90 ° to re-enter the acousto-optic element, and re-enters the acousto-optic element 1 / placed between the optical system
A beam emitted from the optical system to be re-incident is re-incident on the acousto-optic element as a light beam polarized in the one direction, and passed through the acousto-optic element twice to obtain a larger combined deflection angle. Is emitted. As described above, if the beam is deflected in the first deflection direction and the second deflection direction orthogonal thereto by passing through the acousto-optic element twice, the deflection beam emitted from the beam deflection device becomes the first and second deflection directions. A resultant deflection beam is vector-combined in the direction. As a result, the deflection angle is further increased, and a longer scanning length on the surface to be scanned can be obtained.

When the first and second acousto-optical elements are driven by the same drive signal, the scanning length on the surface to be scanned can be increased by √2 times as compared with the case where deflection is performed by a single acousto-optical element. In addition, an inexpensive ordinary spherical lens can be used instead of an expensive cylindrical lens as a beam divergence correction unit after emission.

If at least one of the acousto-optic elements uses a drive signal whose drive frequency range is variable, the scan direction on the surface to be scanned can be adjusted. As a result, when applied to a laser microscope, it is necessary to electrically correct the tilt of the image of the object to be observed on the monitor without rotating the sample stage even when the object to be observed is displayed tilted on the monitor. Can be.

Further, one acousto-optic element and a deflection direction
When combined with an optical system that re-enters the acousto-optic element by rotating it by 90 °, the beam can be deflected in the first deflection direction and the second deflection direction orthogonal to this by using only one acousto-optic element. The deflection angle can be increased with a simple configuration.

[0009]

FIG. 1 is a diagram showing the configuration of an example of a beam deflecting device shown as a reference example. The light beam emitted from the laser light source 1 is made into an expanded beam by a beam expander optical system (not shown) and then is incident on the first acousto-optic element 2. Since the acousto-optic element has a deflecting action on P-polarized light due to its characteristics, the laser light source 1 emits a P-polarized light beam. The first acousto-optic element 2 is driven by a drive signal from a drive circuit 3. For example, in the case of the present example, high refractive index regions and low refractive index regions in stripes are alternately formed in the plane of the paper. A diffraction grating having a grating surface extending therein is formed. Therefore,
The incident beam is deflected at high speed at a predetermined frequency in the plane of the paper and is emitted. Since the light beam emitted from the first acousto-optic element 2 has been converted into S-polarized light, the λ / 2 plate 4
The light is converted into polarized light and then enters the second acousto-optic element 5. The second acousto-optic element 5 is driven by the drive signal from the drive circuit 3 and therefore by the same drive signal as that of the first acousto-optic element 2, in the direction orthogonal to the plane of the drawing, that is, in the first acousto-optic element 2. A diffraction grating having a grating plane orthogonal to the grating plane of the formed diffraction grating is formed, and thus the incident beam is rapidly deflected in a direction orthogonal to the plane of the paper, that is, in a direction orthogonal to the deflection direction of the first acousto-optic element. The acousto-optic element has a deflecting action only in its lattice plane,
In a plane perpendicular to the lattice plane, the light has no deflecting effect and acts only as a light passing medium. Therefore, a light beam oscillating in a plane orthogonal to the lattice plane is incident on the second acousto-optic element 5, but this incident light is maintained at its oscillating component and deflected at high speed only in the lattice plane. Emit. As a result, from the second acousto-optic element 5, a combined deflection beam deflected independently in the first and second directions orthogonal to each other is emitted.

FIG. 2 is a schematic diagram showing the trajectory of the combined deflection beam emitted from the second acousto-optic element 5, and the light of the light beam projected on a plane orthogonal to the optical axis (on the surface to be scanned). The trajectory of a point is shown. Line a shows the trajectory of the light spot of the deflection beam in the case of the first acousto-optic element alone, line b shows the trajectory of the light spot of the deflection beam in the case of the second acousto-optic element alone, and line c shows the trajectory of the deflecting beam. FIG. 4 shows the trajectories of the light spots of the combined deflection beam subjected to the deflection action of both the first and second acousto-optic elements. First
And the second acousto-optical element is driven by the same drive signal, so that it performs a beam deflecting action synchronously,
Since the deflection actions of the first and second acousto-optic elements are independent of each other, the trajectory of the light spot of the combined deflection beam is equivalent to the vector synthesis of the deflection amounts of the first and second acousto-optic elements. As a result, as shown in FIG. 2, the scanning length of the combined deflection beam in the scanning direction becomes √2 times longer than the scanning length of each of the acousto-optic elements alone.

When the beam is deflected using an acousto-optic element, a deflection beam having divergence only in the deflection direction is formed due to the characteristics of the acousto-optic element. For this reason, in the conventional beam deflecting device, an expensive cylindrical lens is arranged on the emission side of the acousto-optic element to perform beam correction. On the other hand, in the present invention, since two acousto-optic elements whose deflection surfaces are orthogonal to each other are used, the divergence generated by the acousto-optic element is formed symmetrically with respect to the optical axis. The unique advantage that the beam can be corrected using a normal spherical lens without using a simple cylindrical lens is also achieved.

FIG. 3 is a diagram showing a modification of the beam deflecting device of the reference example. In this example, the first and second acousto-optical elements 2 and 5 are driven by different driving circuits 3 and 6, respectively, and the driving frequency range of the first acousto-optical element 2 is set to a fixed frequency range, and the second The drive frequency of the optical element 5 is set to a variable frequency range that can be adjusted. The deflection angle of the acousto-optic element, that is, the scanning length on the surface to be scanned is defined by the drive frequency range of the drive signal. The scanning line formed on the surface to be scanned by the combined deflection beam emitted from the beam deflecting device is obtained by vector combining the scanning line formed on the surface to be scanned by each acousto-optic element. An angle formed by a scanning line formed on the surface to be scanned by the beam with respect to a reference line on the surface to be scanned (for example, the x-axis or the y-axis of the surface to be scanned) changes according to the driving frequency range of the driving signal. I do. This state will be described with reference to FIG.

FIG. 4 shows a scanning line formed by the combined deflection beam on the surface to be scanned defined by the x-axis and the y-axis. Now, the first acousto-optic device 2 deflects the light beam in the x-axis direction on the surface to be scanned, and the second acousto-optic device 5 deflects the light beam in the y-axis direction. When the first and second acousto-optical elements are driven by drive signals in the same frequency range, an angle of 45 ° with respect to the scanning line indicated by the arrow a, that is, the x-axis and the y-axis, on the surface to be scanned. A scanning line is formed. On the other hand, when the driving frequency range of the first acousto-optical element is fixed and the driving frequency range of the second acousto-optical element becomes gradually smaller than the driving frequency range of the first acousto-optical element, the y-axis of the combined scanning line Since the components gradually decrease, as shown by arrows b and c, a scanning line is formed in which the inclination angle with respect to the reference coordinate axis, for example, the x-axis gradually decreases. As a result, when the beam deflecting device of the present example is applied to, for example, a laser microscope, as shown in FIG. 5, the image of the observed object displayed on the display screen of the monitor is inclined with respect to the reference axis of the display screen. Even if you have a second
By adjusting the driving frequency range of the acousto-optic element, the image can be displayed as an erect image. Therefore, the tilted sample line can be displayed as an erect image on the monitor by adjusting the electric signal without rotating the sample stage, and the operability in sample observation can be further improved.

FIG. 6 is a circuit diagram showing an example of the configuration of a drive circuit used in the beam deflector shown in FIG. A sawtooth wave generating circuit 10 generates a sawtooth wave having a horizontal scanning frequency of, for example, a television rate, and supplies the sawtooth wave to a first voltage control circuit (VCO) 11 for forming a first acousto-optical element drive signal. Then, the output signal from the first VCO is supplied to the first acousto-optical element 2 via the amplifier 12 as a drive signal in a fixed frequency range. Further, the output signal from the sawtooth wave generation circuit 10 is also supplied to the voltage control circuit 13. This voltage control circuit 13
It functions to control the peak value and the base value of the voltage signal to be supplied to the second VCO 14 for the second acousto-optic element at the subsequent stage. Therefore, for example, the operator can appropriately adjust the supply voltage to the second VCO by operating an operation switch or the like (not shown) connected to the voltage control circuit 14. The output signal from the voltage control circuit 14 is supplied to the second VCO
15 to the second acousto-optic element 5 via the amplifier 16 to supply a drive signal whose drive frequency range is adjusted. FIG. 7 shows drive signals supplied to the first and second acousto-optical elements 2 and 5, respectively. In FIG. 7, the vertical axis indicates frequency, and the horizontal axis indicates time. As shown in FIG. 7, the first and second acousto-optical elements are supplied with drive signals which are synchronized with each other and have different drive frequency ranges.

FIG. 8 is a diagram showing another modification of the beam deflecting device of the reference example. In this example, an example is shown in which the first acousto-optic element and the second acousto-optic element are coupled with a long optical path length. The P-polarized light beam is made incident on the first acousto-optic element 20 and deflected at high speed in the plane of the drawing. The output beam is converted into P-polarized light by the λ / 2 plate 21, and the first, second, and third
The image of the luminescent spot is formed at the pupil position of the third relay lens 24 via the relay lenses 22, 23 and 24. At this pupil position, the first
A second acousto-optic element 25 that synchronizes with the acousto-optic element 20 and deflects the incident beam in a direction orthogonal to the paper surface is arranged. With this configuration, since the deflected beam in a stationary state enters the second acousto-optic element 25, the light beam can be deflected twice without any trouble.

FIG. 9 is a diagram showing a beam deflecting device according to the present invention. In this example, an example is shown in which beam deflection is performed twice using one acousto-optic element. The P-polarized light beam to be deflected is incident on the acousto-optic device 30. The incident surface of the acousto-optic element 30 is a plane parallel to the xy plane of the illustrated coordinate system xyz, and the acousto-optic element 30 deflects the incident beam in the y-axis direction. The light beam deflected by this acousto-optic element passes through the λ / 4 plate 31 and enters the re-entry optical system 32. This re-incident optical system 32 is composed of two total reflection mirrors 32a and 32b which are at right angles to each other, and the ridge line 32c of the two total reflection mirrors is parallel to the xy plane and 45 ° with respect to the x axis and the y axis.
At an angle of. Re-entry optical system mirror 32
The deflected beam incident on a is deflected in a direction forming an angle of 45 ° with respect to the ridgeline 32c, is reflected on the mirror surface 32a, and the reflected light is reflected on the mirror surface 32b to pass through the λ / 4 plate 31. The light passes through and reenters the acousto-optic element 30. Since the light beam re-entering the acousto-optic element is reflected twice on the mirror surface forming an angle of 45 ° with respect to the y-axis, a deflected beam deflected along the x-axis direction orthogonal to the y-axis, ie, deflection 90 ° face
It becomes a rotated deflection beam. Further, since the light has passed through the λ / 4 plate 31 twice, it is converted into P-polarized light again.
Incident on. The re-entered deflected beam is deflected again along the y-axis direction and exits the acousto-optic element 30. As a result,
From the acousto-optic element 30, a combined deflection beam deflected in the x-axis direction and the y-axis direction orthogonal thereto is emitted. With this configuration, a combined deflection beam can be generated by using only one acousto-optic element.

[0017]

As described above, according to the present invention, the beam is deflected in the first deflection direction and the second deflection direction orthogonal to the first deflection direction by passing through the acousto-optic element twice.
A combined deflection beam formed by vector synthesis is formed. As a result, the deflection angle is further increased, and a scanning line having a longer scanning length can be formed on the surface to be scanned.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an example of a beam deflecting device of a reference example.

FIG. 2 is a diagram showing scanning lines formed by a deflection beam on a surface to be scanned.

FIG. 3 is a diagram showing a modified example of the beam deflecting device of the reference example of FIG. 3;

FIG. 4 is a diagram showing scanning lines formed on a surface to be scanned of the beam deflecting device shown in FIG. 3;

FIG. 5 is a diagram showing an image displayed on a monitor.

FIG. 6 is a circuit diagram showing a drive circuit of the beam deflector shown in FIG.

FIG. 7 is a diagram illustrating an example of a drive signal output from the drive circuit illustrated in FIG. 6;

FIG. 8 is a diagram showing another modified example of the beam deflecting device of the reference example.

FIG. 9 is a perspective view showing another modified example of the beam deflecting device according to the present invention.

Claims (1)

(57) [Claims] 1. An acousto-optic device for deflecting an incident beam polarized in one direction in a first deflection direction, and a beam emitted from the acousto-optic device is rotated by 90 ° to the acousto-optic device. An optical system to be re-entered, and the acoustic light
Quarter wave placed between the optical element and the optical system to be re-entered
A beam emitted from the re-entering optical system.
Acousto-optic element as a light beam polarized
A beam deflector that re-enters the beam and passes through the acousto-optic element twice to emit a light beam having a larger combined deflection angle.