JPH0432892A - Laser plotter - Google Patents

Abstract

PURPOSE:To inexpensively obtain an image of high horizontal resolution by deflecting a laser beam obtained by converting a pattern information signal into a pattern information signal having frequency higher than a prescribed frequency and modulating the converted signal in the horizontal direction. CONSTITUTION:The laser plotter is provided with a converting means 1 for reading out a pattern information signal Va with a prescribed frequency f1 sent at a fixed period T at a period ts faster than the period T and converting the read signal Va into a pattern information signal V having frequency f2 higher than the frequency f1 and a horizontally deflecting means 6 for horizontally deflecting the laser beam l modulated by the signal component of the signal V. Since the laser beam l modulated by the signal component of the signal V having the higher frequency, a horizontal blanking period can be extended without changing the prescribed one-horizontal scanning period and a margin can be applied to the fly-back line of the laser beam l. Consequently, the beam diameter D can be increased and an image of high resolution can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a laser drawing device that uses a laser beam to draw pattern information on a medium to be drawn, and particularly to a laser drawing device that uses a laser beam to display television images, etc. It is suitable for use in a laser drawing device.

[Summary of the invention]

The present invention provides a laser drawing device that draws pattern information on a medium to be drawn by raster scanning a laser beam. converting means for reading the pattern information signal at a faster period than the predetermined frequency and converting it into a pattern information signal having a frequency higher than the predetermined frequency; and a horizontal device for horizontally deflecting a laser beam modulated by the pattern information signal component from the converting means. By including the deflection means, even when high-speed horizontal raster scanning is required, images with high horizontal resolution can be obtained at low cost using almost the same optical system as conventional ones.

(Prior Art) Recently, there has been a laser drawing device that displays, for example, a television image by two-dimensionally raster scanning an intensity-modulated laser beam in the horizontal and vertical directions.

As a laser beam scanning method of this laser drawing apparatus, there is a mechanical method using a rotating polygon mirror, but this mechanical method using a rotating polygon mirror has the following drawbacks.

(i) Vibrations occur due to shaft vibration of the motor that rotationally drives the rotating polygon mirror.

(ii) Noise such as wind noise is generated due to the rotation of the rotating polygon mirror.

(iii) There is a problem with the durability of the rotating polygon mirror bearing.

(iv) Since the rotation of the above-mentioned rotary drive motor does not start up quickly, a quick start is difficult.

(v) There is a problem with the rotational stability of the rotary drive motor,
Time sinter occurs.

In contrast to the mechanical laser beam scanning method, which has the above-mentioned drawbacks, the acousto-optic scanning method uses an acousto-optic deflector without a mechanically driven part. type laser display device”
(Transactions of the Institute of Electronics and Communication Engineers Vol. 58, No. 4, C2, 1975, pp. 209 to 216).

A raster scanning laser display device using this acousto-optic deflector uses the acousto-optic deflector to perform raster scanning of a laser beam emitted from a laser light source to directly draw an image on a screen or the like.

This laser display device is free from vibration and noise, has excellent durability, is easy to quick start, and has no time jitter compared to mechanical devices. Also,
Miniaturization is also possible.

[Problem to be solved by the invention]

Generally, if the propagation mode of the laser beam is a Gaussian beam, the screen (3
1) The spot size (diameter at which the intensity is 1/e2) d is given by d-TλL/D (1). Here, T-4/π-1, 27, λ is the wavelength of the beam l, L is the distance between the deflection point in the acousto-optic deflector (32) and the screen (31), and D is the distance at the deflection point. It is the beam diameter.

Also, the number of resolution points (resolution) N on the screen (31)
can be estimated using the following equation (2), where φ is the deflection angle, and the resolution N is proportional to φD.

When the resolution N is expressed by the number of scanning lines N, N becomes the following equation N, =2N-1ζ2φD/rλ (3).

By the way, when high-speed Lasque scanning is required, such as in the HDTV (high-definition television/vision) system, conventional laser drawing devices have the disadvantage of decreasing horizontal resolution. The horizontal scanning frequency of 2 is about twice that of the NTSC system, and the horizontal blanking period is about 4 μsec, which is half of that, so if the beam diameter remains the same as before, the beam inside the acousto-optic deflector (32) There is no margin for the return line of
Horizontal resolution deteriorates.

Therefore, there is an example in which a special acousto-optic deflector that supports high-speed access is used as the acousto-optic deflector (32) to avoid the above disadvantage, but in the case of this acousto-optic deflector, the propagation speed of the ultrasonic wave is Since it is very fast, the deflection angle φ becomes smaller than that of the conventional one, and the horizontal resolution does not improve as much as expected. As shown in FIG. 6, the deflection angle φ increases as the Bragg band (sweep width of ultrasonic frequency) Δf becomes wider. It is necessary to widen f, raise the sweep frequency (center frequency f.), and use a phase synchronization type (longitudinal wave type), etc., and the structure of the acousto-optic deflector itself becomes complicated and large. Since beam shaping is also troublesome, there is an inconvenience that the price of the laser drawing apparatus increases. In FIG. 6, the curve I shows the diffraction efficiency distribution of the sweep frequency f supplied to the acousto-optic deflector, and the curve ■ shows the frequency distribution of the diffraction angle θ.

Further, fC is the center frequency of the Bragg band Δf, f.

and f2 are the frequencies at points A and B at which the diffraction efficiency is 50% in curve I.

The present invention has been made in view of these points, and its purpose is to provide a laser drawing method that can inexpensively obtain images with high horizontal resolution even when high-speed horizontal raster scanning is required. The goal is to provide equipment.

[Means for Solving the Problems] The present invention provides a laser beam! In a laser drawing device (A) that draws pattern information on a drawing medium (11) by raster scanning, a pattern information signal (3) having a predetermined frequency f sent at a constant period T is transmitted. a converting means (1) for reading at a period t5 faster than the above-mentioned constant period T and converting it into a pattern information signal (1) having a frequency of 12 higher than the above-mentioned predetermined frequency f1;
A laser beam modulated by the signal component of the pattern information signal ■ from! horizontal deflection means (
6).

[Effect]

According to the configuration of the present invention described above, the pattern information signal 1 having a predetermined frequency f1 sent at a constant period T is read out at a high speed second cycle Mts and converted into a pattern information signal V having a high frequency. And a laser beam modulated by the signal component of this pattern information signal ■! Since the laser beam is deflected horizontally, it is possible to lengthen the horizontal blanking period without changing one predetermined horizontal scanning period. It is possible to provide some leeway regarding the return line. Therefore, it is possible to increase the beam diameter and obtain a high resolution image. In addition, it does not require the use of special horizontal scanning means (2) because almost the same configuration as the conventional optical system can be adopted, (5) the structure of the laser drawing device with high resolution (8) can be simplified, and manufacturing costs can be reduced. can be achieved at the same time.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to FIGS. 1 to 4.

FIG. 1 is a configuration diagram showing a laser drawing apparatus (A) according to this embodiment. In this figure, (]) is a constant period T
Video signal ■1 having a predetermined frequency f, sent at
This is a frequency conversion circuit that converts the signal into a video signal (2) having a frequency f2 higher than the frequency f1. This circuit (1)
The configuration and operation of will be described later.

The laser beam emitted from the laser light source (2) is narrowed down through a beam narrowing lens (3) and supplied to an acousto-optic light intensity modulator (4).

This light intensity modulator (4) modulates the intensity of the diffracted laser beam by changing the intensity of the ultrasound applied to the acousto-optic medium and changing the efficiency with which the laser beam is diffracted by the ultrasound. It is something.

The light intensity modulator (4) is supplied with the video signal (2) from the frequency conversion circuit (2), and the laser beam (1) is modulated in light intensity according to the luminance signal component of the video signal (2). The intensity-modulated laser beam 2 emitted from the light intensity modulator (4) is converted into a laser beam l of a predetermined thickness via a beam expansion lens (5), and then
It is supplied to an acousto-optic deflector (6) for horizontal scanning.

This acousto-optic deflector (6) has a structure in which an ultrasonic generator (6b) utilizing a piezoelectric effect is attached to the negative side of an acousto-optic medium (6a).
), a traveling wave of ultrasonic vibration is created in the acousto-optic medium (6a) by applying a voltage from the high frequency generator (6c) to the acousto-optic medium (6a). At this time, when the oscillation frequency of the high frequency oscillator (6c) is low, a traveling wave with a long wavelength is created, and when the oscillation frequency is high, a traveling wave with a short wavelength is created.

The laser beam E supplied to the acousto-optic deflector (6) is guided through an acousto-optic medium (6aH), encounters a traveling wave of ultrasonic vibration, is diffracted by this traveling wave, and is deflected. At this time, the shorter the wavelength of the traveling wave of ultrasonic vibration, the greater the deflection, so the high frequency oscillator (6c)
By repeatedly sweeping the oscillation frequency from a low frequency to a high frequency in a sawtooth pattern, the laser beam emitted from the acousto-optic deflector (6) becomes a horizontal scanning laser beam l that undergoes deflection and repeats deflection scanning.

Here, in order to project a high-resolution image, it is necessary to increase the diameter of the laser beam l that is incident on the acousto-optic deflector (6). However, when the beam diameter is large, the propagation speed of the traveling wave of ultrasonic vibration in the acousto-optic medium (6a) is finite.
) The frequencies of the ultrasonic waves encountered differ between the parts near and far from the beam, and the deflection angle differs depending on the position of the beam diameter.

In other words, the part close to the ultrasonic generator (6b) encounters high-frequency ultrasound and receives a large deflection, and the part far away encounters low-frequency ultrasound and receives a small deflection, so it is as if it were a cylindrical lens. As if transmitted, the laser beam β does not become a parallel beam, but is condensed and deflected. This is called the cylindrical lens effect.

The laser beam l, which is emitted from the acousto-optic deflector (6) and becomes a horizontal scanning laser beam that repeats deflection and scanning, is supplied to the correction cylindrical lens (7).

This correction cylindrical lens C7) is for correcting the above-mentioned cylindrical lens effect, and the laser beam transmitted through it becomes a parallel laser beam l again and repeats horizontal deflection scanning.

And the horizontally deflected laser beam transmitted through this correction cylindrical lens (7)! is supplied to a vertical scanning acousto-optic deflector (8). This acousto-optic deflector [8] is
It has the same structure as the horizontal scanning acousto-optic deflector (6), in which an ultrasonic generator (8b) using a piezoelectric effect is attached to the negative side of the acousto-optic medium (8a), and a high-frequency oscillator (8c) ) by applying a voltage from the optical medium (8a)
A traveling wave of ultrasonic vibration is created, and the oscillation frequency of the high-frequency oscillator (8c) is repeatedly swept in a sawtooth pattern from a low frequency to a high frequency, thereby repeatedly deflecting the incident laser beam l in the vertical direction.

Note that the number of repetitions of vertical deflection scanning is, for example, 60 per second.
The cylindrical lens effect in the acousto-optic deflector (8) can be ignored because the deflection is slower than the horizontal deflection described above.

A laser beam l emitted from this acousto-optic deflector (8) repeats horizontal and vertical two-dimensional deflection scanning.
is projected onto the screen (11) via magnifying projection lenses (9) and (10). This magnifying projection lens (9
) and (10), the deflection angle with the deflector is only about 2 degrees, which is extremely small and the screen size on the screen (11) will not increase as it is, so the purpose of this is to increase the drawing size to a practical screen size. I am using it.

In this way, the laser beam is raster scanned on the screen (1), and the video signal V is given to the light intensity modulator (4) in synchronization with this horizontal and vertical deflection, thereby displaying a television image. It becomes possible.

Next, the configuration and operation of the frequency conversion circuit (1) according to this example will be explained based on FIGS. 2 and 3.

As shown in FIG. 2, this frequency conversion circuit (1) continuously transmits signals at a constant period T (for example, in the case of a high-definition television system, the horizontal scanning period is 29.63 μsec and the horizontal blanking period is 3.77 μsec). An A/D converter (21) that converts the incoming analog video signal ■, into a digital video signal ■6, and the analog video signal ■3
A synchronization separation circuit (22) that separates the horizontal synchronization signal sh from
), first and second line memories (23a) and (23b) that temporarily store the video signal (2) from the A/D converter (21), and each line memory (23a) or (
23b) video signal from ■゛4 is an analog video signal■
a D/A converter (24) for converting into
5). In addition, (26) is an acousto-optic deflector (6
), and (27) is a delay circuit that delays the output timing of the sweep signal f output from the sweep signal generator (26) by a predetermined time.

Then, as shown in FIG. 3, the video signal {
3, for example, the video signal ■, 1(
(see FIG. 3A) during the first display period t1, the A/D clock pulse pa from the control clock generator (25)
d, the A/D converter (21) converts it into a digital video signal Vdl, and the control clock generator (25
) with a frequency of, for example, 70 MH2, the digital video signal Vdl
For example, write in the first line memo') (23a) (
(See Figure 3C). Next, the video signal for the second scanning line ■
, 2 (see FIG. 3A) in the second display period t2,
The A/D converter (21) converts the video signal Vd2 into a digital video signal Vd□, and the video signal Vd2 is converted into a second digital video signal Vd2 based on a write clock pulse pw□ whose frequency is, for example, 70 MHz from the control clock generator (25). line memory (2
3b) (see third diagram). In addition, during this second display period t2, based on the read clock pulse Pr+ whose frequency is, for example, 100 MH2 from the control clock generator (25), the video signal 1 for the first scanning line is sent from the first line memory (23a).゛4. Figure 3 C
Based on the D/A clock pulse pd from the control clock generator (25), the D/A converter (24) generates an analog video signal V (V
1), the analog video signal V (V, ) is supplied to the subsequent light intensity modulator (4), and the laser light source (2)
The laser beam l emitted from the video signal V (V,
) is modulated by the luminance signal component.

That is, on the upper side, after the video signal (1) regarding the first scanning line is once converted into a digital video signal (2),1, the write clock pulse P having a higher frequency than the video signal (VII) is applied.
w+, the digital video signal V□ is written to the first line memory (23a), and then, based on the read clock pulse Pr+ having a higher frequency than the write clock pulse pw+, the digital video signal Vdl is written to the input video. The input video signal 81 for the first scanning line is read out at a cycle t5 faster than the display period t1 of the signal 1, and is converted into a high-frequency video signal 2 (1). Therefore, in this example, the period t5 becomes the display period.

On the other hand, the delay circuit (27) operates for a certain period of time td based on the input of the horizontal synchronization signal sh from the synchronization separation circuit (22).
Output one pulse Pd after the elapsed time (see Figure 3C)
. Then, based on this pulse Pd, a sweep signal generator (
26) outputs a sweep signal f to the acousto-optic deflector (6) (see FIG. 3C). 20 The sweep signal f has a sawtooth waveform whose frequency is swept from a low frequency to a high frequency,
The output period Tf is set to be the same as the repetition period Td of the pulse Pd, that is, the same as the reference period T of the input video signal Va (the total period of the horizontal scanning period t and the horizontal blanking period tII). Especially in this example, laser beam! According to the emission of the ultrasonic wave, the spatial distribution of the ultrasonic wavelength in the acousto-optic medium (6a) in the acousto-optic deflector (6) always follows the linear equation,
The frequency change amount Δf of the sweep signal f is set so as to be in a so-called linear access mode (LAM). That is,
In the above example, the linear access mode (LAM) is set when the laser beam 2 related to the first scanning line is emitted, and the laser beam ! can be horizontally deflected uniformly, and at the same time the sweep ends at the rise of the next pulse Pd, the next scan vA! Sweep to the relevant laser beam p is started. Therefore, in this example,
The horizontal blanking period T is a period from the end of reading until the next horizontal scan, and is longer by (t ts) than the normal horizontal blanking period tg&.

Then, in the next third display period t3, the digital video signal Vd3 regarding the third scanning line is written into the first line memory (23δ) (see FIG. 3C), and the digital video signal Vd3 regarding the third scanning line is written into the second line memory (23b). The video signal ゛, 2 related to the second scanning line is read out at a period ts based on a readout clock pulse Pr2 having a frequency of, for example, 100 MH2, and converted into an analog video signal V (vz) via a D/A converter (24). After conversion, the signal V(vz;+) is sent to an optical intensity modulator (4).
supply to. Of course, this continues, and even in period t5, the acousto-optic deflector (6) is in the linear access mode 1".
(LAM) It is made to fit 4 pieces.

Then, by sequentially repeating the above operations, the laser beam! are sequentially raster scanned on the screen (11), and each time this raster scan is performed, the screen (11)
1) An image based on the input video signal Va is drawn.

Next, a comparison of the horizontal resolution Nr according to the Rayleigh limit between the example and the comparative example will be explained based on the table below and FIG. 4. Here, the horizontal resolution Nr based on the Rayleigh limit is the number of resolved lines determined by the following equation, and TV lines are used as a unit.

In the above equation (1), τ is the horizontal blanking period, T is the horizontal scanning period, Δf is the Bragg band, and 9/16 is the aspect ratio.

The horizontal blanking period τ of the normal high-definition system, that is, the comparative example, is as shown in Table ■ below and Figure 4 A.
Because it is very short at 3.77 μsec, an acousto-optic deflector (
6) It is necessary to reduce the diameter of the laser beam l by reducing the aperture, and the horizontal resolution Nr is as low as 26 OTV lines.

On the other hand, in this embodiment, as shown in Table 3 above and FIG. Since we made it as long as 14.5μsec,
Since the aperture of the acousto-optic deflector (6) can be made larger and the beam diameter of the laser beam l can be made larger accordingly, the horizontal resolution Nr can take a high value of 590 TV lines.

As described above, according to this example, the video signal Va sent at a constant period T is transmitted at a period t5 faster than the above-mentioned constant period T.
Since the laser beam l modulated by the luminance signal component of this video signal is horizontally deflected, the horizontal blanking period TI is changed without changing one horizontal scanning period T. This allows for a longer return line of the laser beam l within the acousto-optic deflector (6). Therefore, it becomes possible to enlarge the aperture of the acousto-optic deflector (6), and accordingly,
Laser beam! The beam diameter can be increased and high-resolution images can be obtained. In addition, because the beam diameter can be increased, a conventional acousto-optic deflector with a simple structure, that is, a commercially available acousto-optic deflector, can be used, although it is relatively inaccessible, and a laser drawing device with high resolution can be used. The structure of (A) can be simplified and the manufacturing cost can be reduced at the same time.

In the above embodiment, a laser diode may be used instead of the laser light source (2) and the light intensity modulator (4). In this case, the video signal ■ from the frequency conversion circuit (1) is directly supplied to the laser diode, and the laser diode emits a laser beam modulated by the luminance signal component of the video signal ■! emit.

Further, in the above embodiment, a vertical acousto-optic deflector (8) is used as the vertical deflection means, but a galvanometer mirror, a polygon mirror, etc. may also be used.

(Effects of the Invention) According to the laser drawing device of the present invention, even in cases where high-speed horizontal raster scanning is required, such as in high-definition television systems, horizontal resolution can be achieved at low cost using almost the same optical system as conventional ones. You can get high quality images.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing a laser drawing device according to this embodiment,
FIG. 2 is a block diagram showing the frequency conversion circuit according to this example, FIG. 3 is a time chart showing its operation, FIG. 4 is an explanatory diagram showing differences in parameters related to horizontal scanning, and FIG.
The figure is an explanatory diagram showing the principle of an acousto-optic deflector, and FIG. 6 is a characteristic diagram showing the relationship between the Blang band and the deflection angle. (A) is a laser drawing device, (1) is a frequency conversion circuit, (
2) is a laser light source, (3) is a beam reduction lens, (4)
is a light intensity modulator, (5) is a beam expansion lens, (6) is an acousto-optic deflector for horizontal scanning, (7) is a correction cylindrical lens, (8) is an acousto-optic deflector for vertical scanning, (9)
, (10) is a magnifying projection lens, and (11) is a screen. Agent Hidemori Matsukuma T h 3a Iku ln'f'fl Ii Fubhen 1 East Times Kyo Izumi 1 Flo.
7 ridges Fig. 2 #4 Male l\l Shihai number book East Ro stem of the middle eye 11 Keji Δmunaito 31 again □, ゛-n Fig. 5 Fra 77 Ear Chaos Bi 4斤笥 ryo 0 Zia Taoun Quan 1st Year 11th Box No. 6, Figure 7, 乎疎语、-7vIiz Island ``Kumeg's 12'', book 1 box B111 distribution Figure 4

Claims (1)

[Claims] In a laser drawing device that draws pattern information on a medium to be drawn by raster scanning a laser beam, a pattern information signal having a predetermined frequency sent at a certain period is used as a pattern information signal having a predetermined frequency. converting means for reading the pattern information signal at a frequency faster than the predetermined frequency and converting the pattern information signal into a pattern information signal having a frequency higher than the predetermined frequency; and horizontally deflecting a laser beam modulated by the pattern information signal component from the converting means. A laser drawing device comprising horizontal deflection means.