JPS6128173B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal recording method for recording signals using an optical modulator that utilizes an acousto-optic effect.

Optical modulators that utilize the acousto-optic effect (hereinafter referred to as AO elements) utilize the photoelastic effect in which the refractive index changes in a medium due to sound waves. Compression and expansion occur, and light is modulated by refraction or diffraction of light due to periodic layers with a temporally varying refractive index.

FIGS. 1A and 1B are principle diagrams showing the function of the AO element. In Fig. 1A and B, high frequency oscillator 1
The high frequency signal from the AO element 3 is input to a transformer 2 made of a material such as a piezoelectric element fixed to the AO element 3. Transducer 2 is oscillator 1
generates an ultrasonic wave corresponding to a high frequency signal from the AO element 3, and this ultrasonic wave propagates in the direction of arrow A within the AO element 3, and is absorbed by an absorber 4 provided on the end face of the AO element facing the transducer 2. Ru. In the AO element 3, when an ultrasonic wave propagates, a layer having a refractive index corresponding to the frequency of the ultrasonic wave is generated, and this layer functions as a kind of phase diffraction grating. When such an ultrasonic wave propagates within the AO element 3 and a certain region within the AO element forms a layer with a different refractive index than other regions, when a light beam enters the AO element, the light beam becomes Partly affected by diffraction, the light flux emitted from the AO element is divided into a zero-order light flux that is not affected by diffraction and a diffracted light flux.

The width of the transducer 2 is W, the wavelength of the light incident on the AO element 3 is λ, the frequency of the ultrasonic wave propagating inside the AO element is f, the refractive index of the AO element is n, and the sound speed inside the AO element is ν. Then, define the value Q=2πWλ ₀ f ² /Nν ² . When the value of Q is O<Q<π, the diffraction state of the light beam within the AO element 3 is as shown in FIG. +1st order diffracted light 7, -1st order diffracted light 7', +2nd order diffracted light 8, -2nd order diffracted light 8',
This is the so-called Ramannus diffraction, which separates into... or,
When 4.pi. Although each type of AO element shown in FIGS. 1A and 1B can be used depending on the purpose of use, hereinafter, in this specification, the AO element of the type shown in FIG. 1B will be exemplified and explained.

Conventionally, facsimiles and laser beam printers are known as information recording devices using the above-mentioned AO elements. Facsimile or laser beam printers require clear contrast when writing, so they record using diffracted light emitted from an AO element. In other words, if we take advantage of the fact that the diffracted light emitted from the AO element changes depending on the intensity of the high-frequency signal applied to the transducer fixed to the AO element, the intensity of the diffracted light will change when no high-frequency signal is applied to the AO element. can be made zero, and the ratio of brightness and darkness of the modulated diffracted light, that is, the extinction ratio, can be made very large, and an image with high contrast can be obtained.

In the AO element, as shown in FIG. 1B, the incident light beam 9 is diffracted by the refractive index layer in the AO element 3 and split into zero-order light 10 and diffracted light 11, so this is natural. However, as the diffracted light 11 is generated, the intensity of the zero-order light 10 changes. The intensity of the diffracted light 11 depends on the diffraction efficiency of the refractive index layer, and is at most about 60% of the intensity of the normal incident light 9, so the diffracted light 11 is the strongest. The zero-order light 10 also has an intensity of about 30% of the intensity of the incident light 9. In other words, the intensity of the zero-order diffracted light emitted from the AO element is about 30% of the intensity of the light beam incident on the AO element, even at its weakest. FIG. 2 is a diagram for explaining the relationship between the intensity of the diffracted light 11 and the zero-order light 10, in which the vertical axis shows the intensity I and the horizontal axis shows the time t. FIG. 2A shows the intensity of diffracted light, and FIG. 2B shows the intensity of zero-order light. The time t ₀ to _{t 1} and t ₂ to _{t 3} during which the diffracted light 11 does not occur is the zero-order light 1
An intensity of 0 is equal to an intensity of 1 of the incident light 9. However, in this case, the loss of light intensity within the AO element is ignored. At t ₁ to t ₂ and t ₃ to _{t 4} where the diffracted light 11 occurs, the intensity of the zero-order light 10 is higher than that of the incident light 9.
is reduced by the intensity of . Therefore, as described above, the extinction ratio of the zero-order light is small compared to that of the diffracted light, but the zero-order light is also modulated by a high-frequency signal like the diffracted light.

The present invention effectively uses zero-order light from an AO element, which has not been used conventionally due to its small extinction ratio, as a signal recording light beam. If this zero-order light is used, unlike diffracted light, the zero-order light travels in the same direction as the light beam incident on the AO element, which facilitates alignment of the optical system including the AO element. Furthermore, as mentioned above, diffracted light uses its intensity in two stages, zero and a certain value, to obtain the extinction ratio, but zero-order light has a certain level of intensity as mentioned above even when its intensity is the minimum. have. Therefore, a signal recording method using zero-order light always uses the light flux of the minimum intensity contained in the zero-order light as bias light, and a light flux by a modulation signal can be added to this bias light. It is suitable for recording signals on video discs, etc. Furthermore, by using zero-order light
The loss in the amount of light beam incident on the AO element can be suppressed to the extent that it is absorbed within the AO element by reducing the amount of diffracted light to a minute amount, so that the light beam can be used effectively.

FIG. 3 is a diagram showing an embodiment of a signal recording device using zero-order light of an AO element according to the present invention. Third
As shown in the figure, a beam 16 emitted from a light source 15 such as a laser is separated into zero-order light 18 and diffracted light 19 by an AO modulation element 17 as described above. The electrical signal to be recorded from the signal source 20 is transmitted to the high frequency generator 2
1 converts the voltage into a modulated high frequency signal, which is input to a transducer fixed to the AO element 17 to generate ultrasonic waves. The ultrasound is AO
The beam 16 is propagated through the element, forming a layer with a different refractive index than the rest of the AO element, and diffracting the beam 16. Since the strength of the high frequency signal is varied by the recording signal from the signal source 20, the strength of the ultrasound generated by the transducer varies with the strength of the recording signal. Therefore, the zero-order light 18 or the diffracted light 19 emitted from the AO element 17 is intensity-modulated according to the recording signal.

The diffracted light 19 is reflected by the reflecting mirror 22 and received by the photodetector 23, and by monitoring the signal from the photodetector 23, the modulation signal can be monitored. The zero-order light 18 passes through an optical system 24, such as a beam expander, and is converted into a beam 25 with a suitable spatial intensity distribution before entering the recording head 26. The beam 25 is reflected downward by a mirror 27 in the recording head, and is reflected by a lens 29 built into a lens mount 28 onto the recording material 3.
Focus the light on 0. The lens mount 28 is attached to the recording head 26 via a spring 31, and the recording material 3 is passed through a pipe 32 from a nozzle 33.
For example, the beam 25 is adjusted so that it is floated by a gas such as air, and the beam 25 always forms an image on the recording material 30. The recording material 30 is rotationally driven by a motor 34, and the recording head 26 is sent in the direction of arrow B while being guided by a guide rod 35. Therefore, signals are recorded on the recording material 30 in a concentric circle or a spiral shape.

FIG. 4A shows an example of the electrical signal from the signal source 20 shown in FIG. 3, in which the vertical axis represents voltage and the horizontal axis represents time. The signal shown in FIG. 4A is, for example, a waveform obtained by FM modulating a television signal and shaping it into a rectangular wave. FIG. 4B shows changes in the intensity of the zero-order light 18 with respect to the signal shown in FIG. 4A, with the vertical axis representing the intensity and the horizontal axis representing time. As shown in FIG. 4B, the zero-order light has an intensity of I ₁ when it is maximum, and has a certain intensity I ₂ even when it is weak. Assuming that the recording material 30 is a recording material such as a positive type photoresist, and recording is performed with a beam having an intensity as shown in FIG. 4B, the shape of the signal recorded on the photoresist will be as shown in FIG. 5. , the place 40 where no light is irradiated is not dug at all,
Locations 41 irradiated with intensity I ₁ are dug deeply, and locations 42 irradiated with intensity I are dug shallowly. The signal shape recorded on the photoresist, as shown in FIG. 5, is very convenient for reproduction using a stylus, which is one method of reproducing video discs, for example. In other words, the non-illuminated portion 40 guides the needle to illuminate and excavate locations 41 and 42 with the zero-order light.
This is because it corresponds to a signal of 0 or 1.

As described above, in the present invention, the zero-order light from the AO element, which was conventionally not used due to its small extinction ratio, is used as a light beam for signal recording by taking advantage of its characteristics, and is used in the writing optical system. Easy alignment;
It has a low loss of light quantity and can add a light flux of intensity corresponding to a modulation signal on top of a certain bias light. For example, it is used for writing on a video desk that records with a two-level signal of 0 and 1. It has particularly excellent effects on, etc.

[Brief explanation of the drawing]

Figures 1A and 1B are diagrams for explaining the AO element.
FIG. 1A shows the case of Ramannus diffraction, and FIG. 1B shows the case of black diffraction. Figures 2A and 2B are diagrams for explaining the intensity of the diffracted light and the zero-order light that are black diffracted within the AO element. Figure 2A is the intensity of the diffracted light, and Figure 2B is the zero-order light. Indicates the strength of FIG. 3 is a diagram showing an example of the configuration of a recording device using the method of the present invention;
4A and 4B are diagrams for explaining the modulation signal and the intensity of zero-order light according to the present invention, and FIG. 5 is a diagram showing an example of a state recorded according to the present invention. 2...Transducer, 3...AO element,
6, 10...Zero-order light, 7, 7', 8, 8', 11...
...Diffracted light.

Claims (1)

[Claims] 1. A modulator that modulates the intensity of light by an acousto-optic effect is provided, and the zero-order light emitted from the modulator is irradiated onto a recording material whose shape changes depending on the light intensity, and the bias light contained in the zero-order light is A signal recording method using an acousto-optic modulator, in which recording is performed for guidance during playback using an acousto-optic modulator, and a recording signal is recorded using a modulated light beam added to this bias light.