Optical information recording/reproducing apparatus

Abstract: An optical information recording/reproducing apparatus is disclosed. The apparatus is provided with a device for irradiating a preheating light beam onto an information track of an optical information recording medium. Simultaneously, a recording/reproducing light beam is irradiated onto a light spot of the preheating light beam on the recording medium. The light intensity of the preheating light beam is varied in accordance with a detection result regarding an environmental temperature of the apparatus obtained by the detector. By such the construction, the recording/reproducing condition of information is kept constant irrespective of the environmental temperature.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an information recording and/or reproducing apparatus for recording information on an optical information recording medium and/or reproducing the information, and more particularly to an optical information recording and/or reproducing apparatus which is suitable for bit edge recording (which is also called pit edge recording). Related Background Art As the information is more and more utilized, a large capacity information recording and/or reproducing apparatus is required. An optical information recording and/or reproducing apparatus which optically records and/or reproduces information has been attracting a notice as one which meets the above requirement. An information recording mode in such an optical information recording and/or reproducing apparatus includes bit position recording (mark interval recording) in which the significance of the information is in the position of the center of the record bit, and bit edge recording (mark length recording) in which the significance of the information is in the position of the bit edge. The bit position recording has a characteristic of exactly recording the information while the bit edge recording has an advantage that a recording density is 1.5 times as high as that of the bit position recording. Accordingly, the bit edge recording is advantageous for higher density recording and the study on the bit edge recording has been actively done recently. However, the prior art bit edge recording has the following problem. In so-called heat mode recording in which a photo-energy is converted to a thermal energy which is used to record the information, edge positions of the beginning and the end of the record bit are determined by a critical temperature at the time of the recording. Accordingly, the edge position of the record bit is easily affected by a surrounding temperature of the apparatus and an internal temperature. Figs. 1A to 1C show changes of the record bit relative to a variation of temperature. Fig. 1A shows a record bit 40a in low temperature recording, Fig. 1B shows a record bit 40b in ordinary temperature recording, and Fig. 1C shows a record bit 40c in high temperature recording. Recording conditions other than the temperature are identical. As seen from Figs. 1A - 1C, the higher the temperature is, the larger is the area of the record bit and the more does the edge position of the record bit change. Patent abstracts of Japan vol.8, No. 6(P-247) 12/1/1984 & JP-A-58-169303 disclose a magneto-optic recording method in which information is written on the magneto-optic recording medium using a modulated magnetic field, whilst the recording area is heated by a preheating light beam, to enable the recording area of the medium to heat to a higher temperature if the illuminating laser beam has a low power to increase the speed of recording. Patent abstracts of Japan vol.8, No. 257 (P-316) 24/11/1984 & JP-A-59-127242 disclose an optical recording and/or reproducing apparatus in which data is written onto a metal film utilising a preheating light beam which preheats the recording region of the recording medium before writing the information to enable the recording time to be decreased. Patent abstracts of Japan, vol.11, No. 45 (P-546) [2492], 10/2/1987 & JP-A-61-214266 disclose a magneto-optic recording and/or reproducing apparatus in which the recording bits are recorded by application of a magnetic field pulse in the presence of an illuminating laser beam for raising the temperature of the film. The temperature of the recording medium is controlled by a laser drive section which also controls the intensity of laser light in response to the information signal. SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical information recording and/or reproducing apparatus which can exactly record information irrespective of the temperature change. A first aspect of the present invention provides an optical information recording apparatus as set out in claim 1. A second aspect of the present invention provides an optical information reproducing apparatus as set out in claim 3. A third aspect of the present invention provides a method of recording information as set out in claim 7. A fourth aspect of the present invention provides a method of reproducing information as set out in claim 8. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A to 1C illustrate that size and length of a record bit vary with an environmental temperature, Fig. 2 shows a configuration of one embodiment of the optical information recording and/or reproducing apparatus of the present invention, Fig. 3 shows a status in which a spot of a preheating light beam and a spot of a recording light beam are irradiated onto a medium surface, Fig. 4 shows a relation between a light intensity on the medium surface and a temperature, Fig. 5 shows a relation between a temperature of a magneto-optical recording medium and a coercive force, and Fig. 6 shows a block diagram of another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention is explained in detail with reference to the drawings. Fig. 2 shows a configuration of an optical head optical system in the optical information recording and/or reproducing apparatus of the present invention. In Fig. 2, numeral 1 denotes an optical disk which is an optical information recording medium, and numeral 2 denotes an objective lens for condensing a light beam of a light source. In the present embodiment, the light source includes a semiconductor laser 6 for irradiating a preheating light beam and a semiconductor laser 9 for irradiating a recording light beam. The light beam of the preheating semiconductor laser 6 is collimated by a collimator lens 5, reflected by a beam splitter 4, passes through a beam splitter 3 and is directed to the objective lens 2. The incident light beam is condensed by the objective lens 2 and irradiated onto a recording layer of the optical disk 1 as a light spot 22 as shown in Fig. 3. On the other hand, the light beam of the recording semiconductor laser 9 which has a different wavelength from that of the preheating semiconductor laser 6 is collimated by a collimator lens 8 and converted to a circular beam by a beam shaping prism 7. The converted light beam passes through the beam splitters 4 and 3 and is directed to the objective lens 2. The incident light beam is condensed by the objective lens 2 and irradiated onto the recording layer of the optical disk 1 as a light spot 23 as shown in Fig. 3. In this case, the recording light spot 23 is irradiated such that it is located on an information track between tracking tracks 21. The preheating light spot 22 is sufficiently larger in size than the light spot 23 so that it irradiates the light spot 23 and its peripheral region. A light intensity of the recording light beam is modulated by a modulator (not shown) in accordance with a record signal. The recording layer is preheated by the preheating light beam to a temperature which does not cause the recording of information, and the intensity-modulated recording light beam is irradiated thereon to record the information. When the recorded information is to be reproduced, the light intensity of the recording semiconductor laser 9 is lowered to a reproducing power, and the reproducing light beam is irradiated to the optical disk 1 like the recording mode. The irradiated light beam is reflected by the optical disk 1, passes through the objective lens 2 and is directed to the beam splitter 3. The beam splitter 3 reflects the incident light beam to the reproducing light beam detection optical system. In the detection optical system, only the light beam of the semiconductor laser 9 is transmitted through a wavelength filter 10 and the light beam of the semiconductor laser 6 is blocked. The reproducing light beam transmitted through the wavelength filter 10 passes through an analyzer 13 and a focusing lens 11 and is detected by a photo-detector 12. The analyzer 13 is arranged because a polarized light is utilized when the optical disk 1 is a magneto-optical recording medium. A temperature sensor 14 shown in Fig. 2 senses an internal or external temperature of the apparatus, that is, an environmental temperature. A temperature detector 15 supplies a control signal which varies with the sensed output of the temperature sensor 14, to a light intensity control circuit 16, which controls the light intensity of the preheating semiconductor laser 6 in accordance with the control signal. It controls such that when the environmental temperature sensed by the temperature sensor 14 rises, the light intensity is lowered, and when the environmental temperature drops, the light intensity is increased. In this manner, the temperature of the recording layer in the irradiation area of the preheating light spot 22 is maintained constant without regard to the environmental temperature. Fig. 4 shows a relation between the light intensity of the light beam and the temperature of the recording layer of the optical disk. In Fig. 4, T B denotes a steady temperature by the preheating light beam and T o denotes the environmental temperature. As described above, the steady temperature T B is always constant irrespective of the environmental temperature T o . The steady temperature T B is set to a temperature which does not cause the recording of of the information. Tw denotes the recording temperature and Tr denotes the reproducing temperature. The light intensity of the recording semiconductor laser 9 is modulated within the temperature range. In the present embodiment, even if the environmental temperature varies, the recording spot irradiation area on the optical disk 1 can be maintained at the predetermined reproducing temperature Tr or recording temperature T w . Accordingly, the recording condition of the information is kept constant irrespective of the temperature. Thus, the problem of variation of the edge position of the record bit which was encountered in the prior art apparatus is solved and the information can be exactly recorded. An embodiment which uses a magneto-optical recording medium as the optical information recording medium is now explained. Fig. 5 shows a relation between a coercive force of the magneto-optical recording medium and a temperature. A coercive force Hc at a room temperature gradually decreases as the temperature rises and reaches zero at Curie point Tc. A material having such a characteristic is an amorphous film of TbFeCo. It is also known that a Kerr effect decreases as the temperature rises, as the coercive force does. Accordingly, the temperature of the medium may be indirectly detected from an amplitude of a signal reproduced by using the Kerr effect. Fig. 6 shows the embodiment based on the above finding. Numeral 17 denotes a reproduced signal amplitude detector for detecting the amplitude of the reproduced signal of the photo-detector 12. Numeral 16 denotes a light intensity control circuit which is identical to that shown in Fig. 2 and which controls the light intensity of the preheating semiconductor laser 6 in accordance with the reproduced signal amplitude. In the present embodiment, the medium temperature can be kept constant as it is in the previous embodiment. The present invention is not limited to the above embodiments. For example, data recorded under a predetermined temperature environment may be recorded in a monitor area of the medium as a medium temperature reference and the light intensity of the preheating light beam may be corrected prior to the recording. In accordance with the present invention, the light intensity of the preheating light beam is varied in accordance with the environmental temperature so that the medium temperature can be maintained at the predetermined temperature even if the environmental temperature changes. Accordingly, the information can always be recorded under the constant temperature condition and the change of the size or length of the record bit due to the temperature change is reduced and the information can be exactly recorded. The effect is particularly great in the bit edge recording in which the significance of information is in the edge position of the record bit.

Claims: An optical information recording apparatus comprising: means (6, 2) for irradiating an information track of an optical information recording medium (1) with a preheating light beam; and means (9) for irradiating said information track of the optical information recording medium (1) with a recording light beam; the apparatus being characterised by further comprising: detection means (14, 15) for detecting the environmental temperature of the apparatus; and means (16) for varying the light intensity of the preheating light beam in accordance with the detection result of said detection means (14,15). An optical information recording apparatus according to Claim 1, including means for reproducing information from the recording medium (1). An optical information reproducing apparatus comprising: means (6, 2) for irradiating an information track of a magneto-optical information recording medium (1) with a preheating light beam during reproduction; means for irradiating said information track of the magneto-optical information recording medium (1) with a reproducing light beam; the apparatus being characterised by further comprising: detection means (14, 15) for detecting the environmental temperature of the apparatus; and means (16) for varying the light intensity of the preheating light beam in accordance with the detection result of said detection means (14,15). An apparatus according to claim 1 or claim 2, wherein said optical information recording medium (1) is a magneto-optical recording medium. An apparatus according to any one of the preceding claims in which the preheating light beam and the recording light beam are of different wavelengths. An apparatus according to any one of the preceding claims when dependent upon claims 2 or claim 3, in which the preheating light beam and the reproducing light beam are of different wavelengths. A method of recording information using an optical information recording apparatus, said method comprising the steps of: irradiating an information track of an optical information recording medium (1) with a preheating light beam; and irradiating said information track of the optical information recording medium (1) with a recording light beam; the method being characterised by comprising the further steps of: detecting the environmental temperature of the apparatus; and varying the light intensity of the preheating light beam in accordance with the detection result. A method of reproducing information using an optical information reproducing apparatus, said method comprising the steps of: irradiating an information track of a magneto-optical information recording medium (1) with a preheating light beam; and irradiating said information track of the magneto-optical information recording medium with a reproducing light beam; the method being characterised by comprising the further steps of: detecting the environmental temperature of the apparatus; and varying the light intensity of the preheating light beam in accordance with the detection result. A method according to Claims 7, in which the recording medium (1) is a magneto-optical recording medium. A method according to any one of Claims 7 to 9, in which the preheating light beam and recording light beam are of different wavelengths.

Inventors: HOSHI HIROAKI, MATSUMURA SUSUMU, MORISHIMA HIDEKI, YAMAGUCHI EIJI, YAMAMOTO MASAKUNI, HOSHI, HIROAKI, MATSUMURA, SUSUMU, MORISHIMA, HIDEKI, YAMAGUCHI, EIJI, YAMAMOTO, MASAKUNI, HOSHI, HIROAKI, C/O CANON KABUSHIKI KAISHA, MATSUMURA, SUSUMU, C/O CANON KABUSHIKI KAISHA, MORISHIMA, HIDEKI, C/O CANON KABUSHIKI KAISHA, YAMAGUCHI, EIJI, C/O CANON KABUSHIKI KAISHA, YAMAMOTO, MASAKUNI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: G11B7
IPC codes: G11B7, G11B11