JPH04105225A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To surely perform recording by the light spot of a fundamental wave and to perform reproduction with high sensitivity by the light spot of a second higher harmonic by irradiating the prescribed area of a recording medium with the light spots of both the fundamental wave and the second higher harmonic by using dedicated stop-down lenses, respectively. CONSTITUTION:An optical system 4 which emits both waves of the fundamental wave and the second higher harmonic by controlling the transmittance factor and reflectivity of the light wavelength conversion optical systems 1-3 and also, separates the fundamental wave from the second higher harmonic is provided, and optical systems 5, 6, 16, 26, and 18 which irradiate the prescribed area of the recording medium with the light spots of both the fundamental wave and the second higher harmonic independently are provided. Therefore, the diameters of two light spots stopped down on the recording medium 3 can be set almost equally by making incident both the fundamental wave and the second higher harmonic on the stop-down lenses 6, 18 with different numerical aperture. Thereby, it is possible to surely perform the recording by the light spot of the fundamental wave and to perform the reproduction with high sensitivity by the second higher harmonic.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an apparatus for recording, reproducing, and erasing information by irradiating a recording medium with a laser beam.

[Prior art 1] As described in Japanese Patent Application Laid-Open No. 1-271932, a conventional device focuses both the fundamental wave and the second harmonic into almost the same area on the recording medium, and effectively records the By improving the intensity of light, it became possible to achieve high-density and high-speed optical recording. Problems to be Solved by the Invention In the above-mentioned prior art, both the fundamental wave and the second harmonic are narrowed down to almost the same area on the recording medium using one focusing lens, but the fundamental wave and the second harmonic are Due to conditions such as the twofold difference in wavelength and the wavelength dispersion of the aperture lens, the optical spot diameter of the fundamental wave is more than twice as large as the optical spot diameter of the second harmonic. Therefore, the optical energy of the fundamental wave is irradiated onto the information areas on the front, rear, left and right sides of the area to be recorded, resulting in a problem of lowering the reliability of information and causing destruction of the information. An object of the present invention is to emit both the fundamental wave and the second harmonic wave, and to transmit both the fundamental wave and the second harmonic wave independently to a predetermined area of the recording medium, and to adjust the optical spot diameter of the fundamental wave to a predetermined area of the recording medium. By irradiating the light spot close to the diameter of the light spot caused by the second harmonic, it prevents a decrease in the reliability of information during recording and the occurrence of information destruction, resulting in highly reliable, high-density, high-sensitivity optical recording and playback. The goal is to provide equipment. Another object of the present invention is to perform reliable recording and reproduction by using a fundamental wave with sufficient light intensity for recording and using a second harmonic wave with low light intensity for reproduction. Another object of the present invention is to improve the light utilization efficiency of the reproduction optical system and reproduce signals with high sensitivity by using the second harmonic only for reproduction. Another object of the present invention is to double the data transfer speed during playback by independently controlling the two light spots. [Means for Solving the Problems] In the present invention, in order to achieve the above-mentioned object, both the fundamental wave and the second harmonic are focused using dedicated aperture lenses, respectively.
A light spot is irradiated onto a predetermined area of the recording medium. At this time, the numerical aperture of the diaphragm lens that narrows down the fundamental wave is made larger than the numerical aperture of the diaphragm lens that narrows down the second harmonic. In order to achieve the other objectives mentioned above, in the optical characteristics of the final output surface of the optical wavelength conversion optical system, the reflectance of the fundamental wave is increased to 10.
By setting the transmittance of the second harmonic to less than 0% and making the transmittance of the second harmonic almost 100%, in an optical system that extracts light with two different wavelengths from one light source and separates the fundamental wave and the second harmonic, the fundamental wave By using optical components that have the characteristics of reflecting almost 100% of the light and transmitting almost 100% of the second harmonic, the low light intensity of the second harmonic due to the low light wavelength conversion efficiency can be used for reproduction, and the light intensity can be increased. A modulator is used to modulate the light intensity of the fundamental wave, which has ample margin, and is used for recording. In order to achieve the other objectives mentioned above, a polarizing beam splitter for guiding the reproduction signal and a position control signal of the optical spot is placed on the optical path guiding the second harmonic to the recording medium, and the P-polarized light of the polarizing beam splitter is The reflectance is equal to or greater than the P-polarized light transmittance, and the S-polarized light reflectance is approximately 100%. In order to achieve the other objectives mentioned above, an optical system that independently irradiates a light spot on a predetermined area of a recording medium with both the fundamental wave and the second harmonic wave is equipped with two aperture lenses that form a light spot. However, it is equipped with an optical system that detects a focus error signal and a tracking error signal for independently controlling the position of each optical spot, and is also equipped with a differential detection system that can also detect a magneto-optical signal. [Operation 1] By making both the fundamental wave and the second harmonic wave incident on a focusing lens having different numerical apertures, the diameters of the two light spots focused on the recording medium can be made to be approximately the same size. This enables reliable recording using the optical spot of the fundamental wave, and highly sensitive reproduction using the second harmonic. In addition, since the light spot can be formed independently and the position of the light spot can be controlled independently,
Two light spots can be independently controlled in different information areas to improve the transfer speed during playback. Example 1 An example of the present invention will be described below with reference to FIG. The recording medium is formed from a substrate 30 and a perpendicular magnetization film 31, and the perpendicular magnetization film is attached to the surface of the substrate 2 by a method such as sputtering. This recording medium is rotated by a rotation mechanism such as a motor (not shown). A fundamental wave emitted from a light source 1 is guided to a nonlinear optical element 3 by a condensing lens 2. Here, the optical wavelength conversion optical system in this case is. It is formed by optical components 1 to 3. As for the optical characteristics of the output end face 3a of the nonlinear optical element, the reflectance of the fundamental wave is less than 100%, and the transmittance of the second harmonic wave is approximately 100%. This optical characteristic allows light of two different wavelengths, the fundamental wave and the second harmonic, to be extracted. The wavelength separation prism 4 transmits the second harmonic of the light having two different wavelengths and reflects the fundamental wave. The transmitted second harmonic is guided to the polarizing prism 5. The second harmonic transmitted through the polarizing prism 5 is. The aperture lens 6 focuses the light onto the perpendicularly magnetized film 31 . The second harmonic reflected from the perpendicular magnetization film 31 is reflected again by the polarizing prism 5, passes through the half-wave plate 8, and is guided by the lens 9 and the polarizing prism 10 to the light receiver 11.12. The light receiver 11 is arranged in front of the focal position of the lens 9, and the light receiver 12 is arranged behind the focal position of the lens 9. Furthermore, due to the characteristics of the 1/2 wavelength plate 8 and the polarizing prism 10, the amount of light guided to the light receivers 11 and 12 is approximately equal, and the rotational component of the polarization plane can be converted into the intensity of the light. Error signals and track error signals can also be detected (for detailed signal detection methods, see Japanese Patent Application No. 60-63578).
. The focus error signal and the tracking error signal from the light receivers 11 and 12 are fed back to the actuator and used to control the position of the second harmonic light spot. Also,
By taking the difference between the outputs of the photoreceivers 11 and 12, a magneto-optical signal can be obtained. Furthermore, the receiver 11.12
By summing the outputs of , it is also possible to obtain signals of phase pits and grayscale pits. The second harmonic reflected by the polarizing prism 5 is transmitted to the lens 13
is guided to the light receiver 14 by. The output of the light receiver 14 is
Since the second harmonic changes depending on the output fluctuation of the second harmonic, stable second harmonic can be guided onto the recording medium by feeding it back to the light source 1. The fundamental wave reflected by the polarizing prism 4 passes through the modulator 15 and enters the polarizing prism 16. The fundamental wave reflected by the polarizing prism 16 passes through the polarizing prism 26 and is focused onto the perpendicularly magnetized film 31 by the focusing lens 18 . The fundamental wave reflected from the perpendicular magnetization film 31 is reflected again by the polarizing prism 26, passes through the 172 wavelength plate 17, and is sent to the light receiver 25 by the lens 22 and the polarizing prism 23.
I am led to ゜26. Obtained in two steps. Focus error signal 2 Track error signal,
The reproduction signal is the same as the second harmonic. The fundamental wave transmitted through the polarizing prism 16 is guided to a light receiver 21 by a lens 20. In the light receiver 21, the modulator 1
Monitoring the light intensity of the fundamental wave modulated by 5,
The signal is fed back to the modulator 15. During recording, a recording signal is input to the modulator 15, and the polarization state of the fundamental wave is controlled so that the intensity of light reflected by the polarizing prism 16 is increased. At this time, recording becomes possible by applying a constant current to the electromagnetic coil 32 to generate a predetermined recording magnetic field in the recording medium. Erasing is performed by reversing the direction of the current applied to the electromagnetic coil 32. Furthermore, the numerical aperture of the diaphragm lens 18 is made larger than the numerical aperture of the diaphragm lens 6 so that the optical spot diameters of the fundamental wave and the second harmonic are approximately the same. As a result, it does not matter whether the fundamental wave light spot or the second harmonic light spot is in the first position. For example, it is also possible to perform recording with the fundamental wave light spot first, and then immediately reproduce the recorded information using the second harmonic light spot. Furthermore, when two optical spots are used for reproduction, different tracks or different information areas can be reproduced independently, so the information transfer speed can be doubled. FIG. 2 shows another embodiment of the light wavelength conversion optical system shown in FIG. 1. Light emitted from the first light source 40 is focused by a lens 41 into a solid-state laser 42 . The solid-state laser 42 is excited by the optical energy from the first light source 40, and a fundamental wave is generated from the solid-state laser 42. This fundamental wave passes through the nonlinear optical element 3 and is guided to the lens 44. mirror 4
4a and the solid-state laser end face 42a form a resonator. This accumulates the energy of the fundamental wave, increases the energy contributing to second harmonic generation, and enables highly efficient optical wavelength conversion. Here, the optical characteristics of the mirror 44a are that the reflectance of the fundamental wave is less than 100%, and the transmittance of the second harmonic is approximately 100%.
%. This optical characteristic allows light of two different wavelengths, the fundamental wave and the second harmonic, to be extracted. The curvature 44b focuses the light emitted from the mirror 44a. The light emitted from the curvature 44b is the same as the light that enters the wavelength separation prism 4 in FIG. From then on, the first
As explained in the figures, an optical recording/reproducing device can be formed. Solid-state lasers include, for example, Nd:YAG, and
A fundamental wave and a second harmonic can be generated by using a crystal such as KTiOPO for the nonlinear optical element. FIG. 3 shows another embodiment of the light wavelength conversion optical system shown in FIG. Light emitted from the first light source 40 is focused into the waveguide 50 by the lens 41. As for the optical characteristics of the waveguide end face 50a, the reflectance of the fundamental wave is less than 100%, and the transmittance of the second harmonic wave is approximately 0%. Due to this optical characteristic, the fundamental wave can be extracted from the waveguide end face 5Oa. The fundamental wave emitted from the waveguide end face 50a is focused by the lens 52. Further, the second harmonic is emitted to the substrate 51 at a certain angle (for details of second harmonic generation, see Japanese Patent Laid-Open No. 61-72
222). The optical characteristic of the substrate end face 51a is that the second harmonic transmittance is approximately 100%. The second harmonic wave emitted from the substrate end surface 51a passes through the beam shaping plate 53, enters the lens 54, and is focused. As described above, the fundamental wave and the second harmonic can be extracted independently, and an optical recording/reproducing device can be formed as explained below with reference to FIG. The fundamental wave and the second harmonic can be generated by forming the substrate 51 using, for example, a lithium niobate single crystal, and by forming the waveguide by diffusing titanium onto the surface of the substrate 51. . [Effects of the Invention] According to the present invention, since the fundamental wave and the second harmonic can be generated simultaneously and each optical sponode is formed independently, the optical spot of the fundamental wave is recorded in advance. Since the recorded information can be immediately reproduced using the optical spot of the second harmonic, the reliability of the information during recording can be improved. Further, when both of the two optical spots are used for reproduction, different tracks or different information areas can be reproduced independently, which has the effect of doubling the information transfer speed.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of an optical recording/reproducing apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of an optical wavelength conversion optical system according to an embodiment of the present invention, and FIG. 3 is a diagram of another embodiment of the present invention. FIG. 2 is an explanatory diagram of a light wavelength conversion optical system in an example. Explanation of symbols 1 Light source, 3... Nonlinear optical element 6.18... Stop lens 31... Perpendicular magnetization film, 15... Modulator 50... Waveguide

Claims (1)

[Scope of Claims] 1. A laser light source serving as a fundamental wave, a light wavelength conversion optical system that converts the wavelength of the fundamental wave to 1/2, a recording medium, and an optical system that irradiates a light spot onto a predetermined area of the recording medium. In an optical recording/reproducing device consisting of a 1. An optical recording and reproducing apparatus, comprising an optical system that separates the fundamental wave and the second harmonic wave, and independently irradiates a light spot onto a predetermined area of the recording medium. 2. Regarding the transmittance and reflectance of the last exit surface of the optical wavelength conversion optical system according to claim 1, the reflectance of the fundamental wave is less than 100%, and the transmittance of the second harmonic is approximately 100%. %. 3. The optical system for separating the fundamental wave and the second harmonic as set forth in claim 1 includes an optical component having a characteristic of reflecting almost 100% of the fundamental wave and transmitting almost 100% of the second harmonic. An optical recording/reproducing device comprising: 4. In the optical system that independently irradiates a light spot on a predetermined area of a recording medium with both the fundamental wave and the second harmonic wave as described in claim 1, there are two diaphragm lenses that form the light spot. What is claimed is: 1. An optical recording/reproducing device comprising: an optical system for detecting a focus error signal and a tracking error signal for independently controlling the position of each optical spot. 5. An optical recording and reproducing device characterized in that, in the two diaphragm lenses according to claim 4, the numerical aperture of the lens that diaphragms the fundamental wave is larger than the numerical aperture that diaphragms the second harmonic. 6. The optical system for detecting a focus error signal and a tracking error signal for independently controlling the position of each optical spot as described in claim 4, comprising a differential detection system capable of detecting a magneto-optical signal as well. An optical recording/reproducing device characterized by: 7. In the optical recording and reproducing device capable of recording and reproducing according to claim 1, the optical intensity of the fundamental wave is set on the optical path that guides the fundamental wave after separating the fundamental wave and the second harmonic to the recording medium. An optical recording/reproducing device characterized by comprising a modulator that modulates. 8. In the optical recording and reproducing device capable of recording and reproducing according to claim 1, a reproduction signal and A polarizing beam splitter is disposed for guiding a position control signal of a light spot, and the polarizing beam splitter has a P-polarized light reflectance equal to or greater than a P-polarized light transmittance, and an S-polarized light reflectance of approximately 100%. An optical recording and reproducing device.