JPS5922291B2 - Kogaku Tekikiki Rokusai Seisouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for optically recording and reproducing information, and when reading out information recorded at high density using a convergent light beam, a device with a diameter slightly larger than the diameter of the recording light beam is used. An object of the present invention is to provide a device in which a reproduction light beam accurately traces an information track by using a light beam.

A device that records and reproduces information by focusing a light beam into a minute spot and irradiating it onto a recording material has a great advantage in that it can significantly increase the recording density of information. For example, if information is recorded bit-by-bit using a light spot with a diameter of 1 μm, a recording density of 108 bits/Cd can theoretically be obtained. Various materials have been studied as high-density optical recording and reproducing materials as described above, but most of them utilize changes in the transmission density or reflection density of the recording material. When recording and reproducing information using a light spot with a diameter of 1 μm as described above, in order to obtain a certain S/L of the reproduced signal, the reproducing light must follow the information track with an accuracy of about ±0.3 μm. need to be irradiated. The present invention provides that the above-mentioned recording material stores information as changes in transmission or reflection density,
An object of the present invention is to provide a device for recording and reproducing by optical means, in which reproducing light accurately tracks an information track.

The details of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the optical recording/reproducing apparatus of the present invention. In FIG. 1, a light source 11 such as a laser generates a light beam a. Reference numeral 12 denotes an optical modulator that modulates the optical beam a in accordance with the electrical signal input to the terminal I.

13 is a projection lens that magnifies the light beam a and passes it through the objective lens 1.
Project to 6.

A total reflection mirror 14 changes the optical path of the light beam a.

This total reflection mirror rotates slightly around the axis X in the direction of the arrow. This keeps the light beam irradiated onto the information track 18. A beam splitter 15 changes the direction of the optical path of the light b reflected on the information track 18.

Reference numeral 16 denotes an objective lens, and an objective lens of a microscope or the like is used.

The light a incident on the objective lens 16 is focused to a minute light spot (for example, 1 μm in diameter) and is irradiated onto the information track 18 at point P. 17 is P on the objective lens 16 and the information track 18.
This is an objective lens driving device for maintaining a constant distance from a point, and moves the objective lens 16 up and down using a driving principle similar to the voice coil of a speaker.

Reference numerals 19 and 20 indicate a pair of photoelectric converters placed on the opposite side of the objective lens 16 with respect to the recording material.

The photoelectric converters 19 and 20 detect the transmitted light c of the information track 18 and reproduce the recorded signal.
, 20, it has a function of determining whether or not the minute light spot P is accurately irradiated onto the information track 18. 21,2
Amplifiers 2 amplify the output signals of the photodetectors 19 and 20, respectively.

A differential amplifier 23 calculates and amplifies the difference between the outputs of the amplifiers 21 and 22.

Therefore, a signal is generated at the terminal 1 indicating in which direction and by how much the minute light P has shifted with respect to the information track 18. This signal causes the total reflection mirror 14 to rotate slightly around the axis X, and is controlled so that minute light spots P are irradiated onto the information track. Information track 18
The light b reflected above is directed upward to the beam splitter 15.
The light is reflected and irradiated onto a pair of photodetectors 24 and 25.

The irradiation position of this reflected light is determined by the distance between the objective lens 16 and the point P on the information track 18 between the photoelectric converters 24 and 2.
5 in the directions of the arrows K and L. For example, in the configuration shown in FIG. 1, as the distance between the objective lens and point P approaches, the irradiation position of the reflected light moves toward the detector 25, as indicated by the dotted line b'. 26 is the pair of photoelectric converters 24, 2
5 in the direction of the arrow.

Thereby, when the distance between the objective lens 16 and the point P is at a desired value, the amount of light received by the photodetectors 24 and 25 can be set to be equal. 27 and 28 are amplifiers for amplifying the outputs of the photodetectors 24 and 25, respectively;
A differential amplifier 9 takes the difference between the outputs of the amplifiers 27 and 28 and amplifies it.

Therefore, when the distance between the objective lens 16 and point P is at a desired value, the output of the differential amplifier 29 can be made zero. 30 is a drive circuit for driving the objective lens drive device 17.

As described above, by using the reflected light b, the distance between the objective lens 16 and the point P can be kept constant regardless of deviations due to unevenness or warpage of the recording material, that is, the focus can be controlled. In addition, by slightly moving the photodetectors 24 and 25 in the direction of the arrow with the fine movement device 26, the focus control system is operated at a position where the irradiation position of the reflected light is unbalanced, and the distance between the objective lens 16 and the point P can be set arbitrarily. It is also possible to hold the value at Note that in FIG. 1, only the optical axis of light is shown for ease of explanation. In the optical recording and reproducing apparatus shown in FIG. 1, when information is optically recorded and reproduced as a change in the light transmittance or reflection density of the recording material, the quality of the reproduced signal is determined by the fact that the light spot P at the time of reproduction is on the information track 18. How to track accurately is an important factor.

For this purpose, it is necessary to generate a highly sensitive tracking signal at terminal 1 in FIG. Second
FIG. 1A shows the relationship between the information track, the irradiation light beam, and the tracking detection photodetector in FIG. 1. 100 indicates an irradiation light beam, and 101 indicates an information track.

The information track is oriented perpendicular to the page. Tw indicates the width of the information track. Reference numerals 103 and 104 indicate a pair of photoelectric converters, which receive the transmitted light of the information track.

Reference numeral 102 indicates the end recording portion of the recording material.

FIG. 2b shows a signal representing the difference between the outputs of the two photoelectric converters 103 and 104 (FIG. 1) when the light beam 100 crosses the information track 101 in the x direction in FIG. Now, we will show an ideal case of the output of the differential amplifier 23 appearing at terminal 1. That is, when the light beam 100 approaches the information track from the negative direction of X, the photoelectric converter 1 first
The output of 03 gradually becomes larger than the output of 104 and shows a peak at the point where the light beam starts to hit the information track.
Next, when the information track is completely ridden (x=0), the outputs of both detectors become equal and the differential output voltage becomes zero. As x continues to move in the positive direction, the differential output voltage becomes negative and exhibits a characteristic curve as shown in FIG. 2b. This characteristic curve actually changes slightly depending on the mutual relationship between the diameter of the irradiated light beam and the width Tw of the information track.
The characteristics shown in Fig. 2b cannot be obtained under any conditions, and the track detection sensitivity near the origin (x = 0) (the slope near x = 0 in Fig. 2b) is as described above. It varies significantly depending on the irradiation light beam diameter and the width of the information track. Figure 3 shows some examples. FIG. 3a shows a case where the diameter of the light beam 100 irradiating the information track 101 is the same as the width of the information track.

In this case, when the light beam 100 is slightly deviated from the information track, the diffraction effect of the light is extremely large, and the I light that deviates from the information track is transmitted to the photodetector 103,
104, and the difference in light amount between the two becomes significantly small. Therefore, the gradient of the differential output voltage in the vicinity of x=O is also small, and the track detection sensitivity is significantly reduced. FIG. 3b shows that the diameter of the light beam 100 that illuminates the information track 101 is
This shows the case where it is smaller than the information track. In this case, as in the case of FIG. 3a, sufficient differential output cannot be obtained at the portion where the light beam begins to deviate from the track due to the diffraction effect, resulting in the characteristic curve shown at the bottom of FIG. 3b. Therefore, the third
In both cases of figures A and b, it is difficult to perform tracking control with high accuracy. FIG. 3c shows a case where the diameter of the light beam irradiating the information track is wider than the width of the information track. In this case, the above-mentioned diffraction effect is small, and track deviation detection is performed with high sensitivity even to a slight positional deviation on the information track. The characteristic curve is also shown in Figure 3c.
As shown in , a large gradient near x-0 and a large amplitude can be obtained. However, it is clear that increasing the irradiation light beam diameter too much will adversely affect detection sensitivity.
In our experiments, we obtained the best detection sensitivity by setting the irradiation beam diameter to a range of 1.1 to 1.4 times the 1μ information track. As a result of the above, in order to improve the tracking accuracy and reproduce high-quality signals in the optical recording/reproducing apparatus shown in Fig. 1, the diameter of the light beam irradiating the recording material during recording should be determined by the diameter of the irradiation beam during reproduction. It is necessary to increase the diameter.

FIG. 4a shows the relationship between the irradiating light beam and the information track when recording information. In other words, the diameter of the light beam and the width of the information track recorded thereby have approximately the same value. FIGS. 4B and 4C show an example in which the recorded information track is read out using an irradiation light beam having a larger diameter.
FIG. 4b shows a method of increasing the diameter of the irradiated light beam by making the distance between the objective lens 16 and the information track 18 shown in FIG. 1 larger than during recording. In FIG. 4c, the projection lens 13 in FIG. 1 is moved in the optical axis direction to make the diameter of the light incident on the objective lens 16 smaller than that during recording, thereby increasing the diameter of the light beam irradiated onto the information track itself. Show how. Generally, there is a relationship between λf and dα-, where f is the focal length of the objective lens, D is the diameter of the incident light, d is the diameter of a minute light spot focused by the objective lens, and λ is the wavelength of the light.

A method for realizing the case D in FIG. 4b will be explained with reference to FIG.

First, when recording information, the focus detection photodetector 24, 2
5 in the direction of the arrow with the fine movement device 26, the waist part of the narrowed light beam (the concave part of the line indicating the light beam) is irradiated onto the recording material as shown in FIG. 4a. Make it. This is important in increasing the recording density of recorded information. It is also important for effectively and efficiently utilizing the optical power of the light source 11. In this way, information is recorded on the recording material with a track width approximately equal to the waist of the irradiated light beam. Next, when reproducing information, the focus detection photodetector 2 at the time of recording is used.
4 and 25 in the direction of arrow K using the fine movement device 26, the balance between the outputs of both photodetectors is lost, and the differential amplifier 2
9 causes the objective lens driving device 17 to move the objective lens 16 in a direction away from the information track 18, and equilibrium is reached at a point corresponding to the amount of minute movement. The value of this distance is the reflected light b1 photodetector 24, 25, amplifier 27, 2
8, a focus control system consisting of a differential amplifier 29, a drive circuit 30, an objective lens drive device 17, and an objective lens 16 keeps the focus constant. As described above, the relationship between the information track 101 and the irradiation light beam 100 shown in FIG. 4b can be obtained. Further, in the above, the distance between the objective lens 16 and the information track 18 is brought closer by slightly moving the focus detection photodetector in the direction of the arrow L using the fine movement device 26 shown in FIG. The relationship between the information track 101 and the irradiated light beam 100 shown in FIG. In the case of FIG. 4b and the case of d, the polarity of the differential voltage output to the differential amplifier 23 of FIG. 1 is reversed, as is clear optically. Further, as shown in FIG. 4C, the waist portion of the focused light beam is irradiated onto the recording material, but if the diameter of the waist itself is to be increased, the focus control system may be left as it is during recording. The position of the projection lens 13 in FIG. 1 may be moved along the optical axis. In this way, in a device that optically records and reproduces information, the tracking accuracy of information tracks can be improved by making the diameter of the light beam irradiated onto the recording material during playback larger than the diameter of the light beam irradiated onto the recording material during recording. A device that can record and reproduce signals of high quality can be obtained. In FIG. 1, the total reflection mirror 14 is constituted by a vibrating mirror used in, for example, a galvanometer, and is controlled and driven by the differential output appearing at the terminal 1. 31 indicates this drive circuit.

Further, an embodiment of the objective lens driving device shown in FIG. 1 is shown in FIG. FIG. 5 shows an example in which the objective lens is driven up and down by electromagnetic force. The objective lens 50 and the cylindrical coil 51 are connected to the leaf spring 5
2, and the coil 51 is inserted between the cylindrical magnets 53. Therefore, when a current is passed between terminals A and B of the coil 51, an electromagnetic force acts on the coil, and the objective lens moves up and down according to the direction of the current through the leaf spring. In the above embodiments, a case has been described in which information is reproduced from a recording material using transmitted light, but the same applies to a case where information is reproduced using reflected light.

As described above, in the present invention, a highly sensitive tracking detection signal is obtained by increasing the diameter of the irradiated light beam during optical information recording and reproduction.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical recording and reproducing apparatus according to an embodiment of the present invention, and FIGS. FIG. 5 is a diagram showing the relationship between the irradiation light beam and the information track and the output of the detection circuit. FIG. 5 is a diagram showing an example of the configuration of the objective lens driving device in the optical recording/reproducing apparatus of the present invention. 11... Light source such as a router, 12... Light modulator, 13... Projection lens, 14...
A vibrating mirror consisting of a total reflection mirror, 15...
Beam splitter, 16...Objective lens, 17
...Objective lens drive device, 18...Information track, 19, 20...Photoelectric conversion element for detecting track deviation of irradiated light beam, 24, 25...
-Photoelectric conversion element for focus detection control, 26...Photoelectric conversion element drive device.

Claims (1)

[Claims] 1. In an apparatus for sequentially recording and reproducing information signals on information tracks by irradiating a light beam onto a recording material, a light beam irradiation means for irradiating the light beam onto the recording material, and an irradiation light irradiated onto the recording material. The recording method includes means for switching the beam diameter between recording and reproduction, and means for detecting deviation from the information track using reflected light or transmitted light of the irradiated light beam from the recording material. 1. An optical recording and reproducing apparatus characterized in that the diameter of a light beam irradiated onto a recording material during reproduction is made larger than the time of reproduction.