Optical information recording and reproduction apparatus

Abstract: The provision of an optical information recording and reproduction apparatus that correctly performs tracking control even if there is a step in the information recording surface in an apparatus that records and reproduces information to and from an information recording medium such as an optical card or the like. An optical information recording and reproduction apparatus which focusses a light spot from a laser (1), onto an optical information recording medium (7) which has a tracking track, and performs the recording and reproduction of information to required positions using said tracking track as a reference, said apparatus being characterized by reducing an optical output of said laser (1) when track jumping and seeking, to smaller than when there is information reproduction operation.

Description: The present invention relates to optical information recording and reproduction apparatus that perform discontinuous scanning of optical cards and the like, and that have an information recording medium as an object, and more particularly, relates to an apparatus in which an optical output of a laser source which performs optical scanning is increased and decreased. (Background Art) The following is a description of the conventional technology, with reference to FIGS. 2 through 6. Conventionally, when the recording and reproduction of information was performed using an optical information recording medium such as an optical card of the like, when it was necessary to have track jump or seek, tracking error signals were used as the basis for moving the optical head in the direction perpendicular to the tracks while the number of tracks crossed was counted, so that the light spot could be irradiated to a required track position. The method of taking the tracking signals is for example, the edge mirror method of the inventor of the invention of the present application and disclosed in Japanese Patent Laid Open Application No. 282167-1988. This method is configured as shown in FIG. 2, and is used for focus error detection and tracking error detection. In this configuration, the dispersed light from the laser is converted into parallel light beams by a collimator lens 2, passes through the diffraction grating 3, the beam splitter 4, the optical path change mirror 5 and the object lens 6 and a light spot is focussed to the surface of the optical information recording medium. As shown in FIG. 3, section (a), this light spot passes from the surface of the optical information recording medium and backwards along the optical path to the beam splitter 4 and reaches the photodetectors 10, 11 after passing through the collimator lens 8 and the edge mirror 9. Then, when the optical system is focussed, the light that is reflected from the optical information recording medium returns as parallel light in the same manner as the irradiated light. On the other hand, converging light beams are returned and when the object lens 6 and the optical information recording medium 7 are farther away such as when there is focussing or the like, and dispersing light beams are returned when they are closer. These light beams pass through the beam splitter 4 and become converging light at the collimator lens 8 for receiving light, half of the light has its optical path changed by the edge mirror 9 and the remaining light proceeds as it is in a straight line. This light that proceeds straight ahead is taken as focus error signals by the halving photodetector. This status is as shown in FIG. 3, section (b), and when the object lens 6 and the optical information recording medium 7 are close to each other, D1 - D2 > 0 and when they are apart from each other, D1 - D2 < 0. FIG. 3 (c) is a focus error signal. Tracking error detection is performed by the three-beam method shown in FIG. 4 (a). The diffraction grating 3 in FIG. 2 makes three beams, and after passing through the beam splitter 4, the mirror 5, and the object lens 6, are focussed as three spots to the optical information recording medium 7. This irradiated light is reflected by the optical information recording medium, and the zero-degree light that is included in this reflected light is used for focussing error detection, and in the same manner, the ±1 degree light is used for tracking error detection and so the spot which is hemispherical in section and which proceeds from the edge mirror 9 via the collimator lens for light receive becomes S2, and the spot which is hemispherical in section and which is reflected by the edge mirror 9 becomes S2. Taking the difference between both of these S1 and S2 gives the tracking error signal. FIG. 4 (b) is a track crossing error signal. The optical information recording medium for which such an apparatus performs focus error detection and tracking error detection is, as shown in FIG. 2, configured as shown in the enlarged view of FIG. 5. The two tracks of a tracking track and a data track are provided to the optical information recording medium and a photographic printing method is used to provide these tracks onto an acrylic card substrate surface to which an organic substance (a silver chloride) has been applied. The dimensions of the format are a tracking track width of 2.5 µm, an optical reflectivity of 20%, a track pitch of 12 µm, a data track width of 9.5 µm and a reflectivity ratio of 40%. (Problem to be Solved by the Invention) Such a format for an optical information recording medium has the following advantages and disadvantages. The advantage is that it is suited for mass production and can be provided at low cost, while the disadvantage is that there steps occur between the tracking track and the data track, and that these steps become a cause of tracking errors. This is described below, with reference to FIG. 6. The tracking track and the data track of the optical information recording medium having the configuration shown in FIG. 6 (a) has a step formed from the protrusion of the tracking track. The height a of this step is about 250nm, although there is a certain degree of scattering. This value causes a problem due to its relationship with the wavelength of the light generated by the laser. Lasers for optical information recording medium recording and reproduction usually have a wavelength of 830nm and so one quarter of this wavelength is approximately 208 nm and is therefore a value in the vicinity of the height a of the step. More specifically, the modulation of a compact disc on the basis of the same principle as that of an optical information recording medium is known to use pits having a depth in the vicinity of λ/4. This is due to the nature of laser light, and a strong laser light having coherency becomes λ/4 + λ/4 = λ/2 between the light that is irradiated to the optical information recording medium by the step having a height of λ/4, and the light that is reflected from it, and becomes a status where there is a phase difference of 180°. Accordingly, as shown in (b) of the same figure, the interference light has a slightly smaller amplitude when compared to the irradiated light and the reflected light. In actuality, the ends of the step portion are not steep and so even though the irradiated light and the reflected light do not completely cancel each other out, there is still a large reduction in the amplitude. For example, of the three examples shown in FIG. 7 (a), examples 2 ○ and 3 ○ are equivalent to the case when the tracking spot of one side is at a track boundary, that is, where there is a reduction from the required light amount and dispersion to outside as the result of one of the two spots S1 and S2 generating interference striking the track boundary. More specifically, in the case shown in 1 ○ of FIG. 7 (a), the tracking spots S1 and S2 are both at positions of the boundaries between two tracks, that is, at steps, and the light amounts of both spots is reduced in the same manner and so there is no influence in the waveform 1 ○' shown in (c) of the same figure. With respect to this, in the case of 2 ○ shown in (a) of the same figure, only the spot S2' is at a boundary of both tracks and S1' is on the data track surface and so the error signal (S1' - S2') via the differential amplifier shown in (b) of the same figure has a shoulder generated in it as shown by the broken line of 2 ○ ' of (c) of the same figure. Then, the case shown by 3 ○ has the spot Sl" positioned at a boundary between both tracks and so receives the influence of the step, and the actual light as indicated by the solid line is less with respect to the reflected light of the ideal status indicated by the broken line of (b) of the same figure. Because of this, the difference signal (S1" - S2") has a smaller amplitude, and the output of the differential amplifier has a negative shoulder as indicated by the broken line in 3 ○ '. These shoulders overlap the ideal waveform shown by the solid line of (c) of the same figure when there is track jump and seek in the vicinity of data write start and data write end, that is, at both side portions of the card, and the peaks of shoulders 2 ○ ' and 3 ○ ' shown by the broken line have single tracking error signals, and there is miscount and so there is an error in the tracking control. Furthermore, from document JP-A-62 009 535 is known a focus control circuit for an optical disc reproducing device which reduces the power consumption by lowering a laser output during searching operation. Prior art document EP-A-0 407 573 discloses a disc recording apparatus for recording data which reacts to unexpected track jumping by dropping the laser power of the optical head to the reproduction power level of the laser, track jumping control and resuming the recording operation. Document JP-A-59 011 546 shows a device for detecting and controlling track jump. The device also reduces the optical power from the recording state into the reproducing state to prevent mis-recording and double recording caused by an unexpected track jump. The aim of the present invention as defined in claim 1 is to prevent unexpected track jumping by eliminating the interference effects at the steps between tracking track and data track of an optical information recording and reproduction apparatus. BRIEF EXPLANATION OF THE DRAWINGS FIG. 1 shows an output switching circuit of a laser diode used in an embodiment of the present invention, FIG. 2 shows an optical system of the edge mirror type and which is used in the present embodiment, FIG. 3 shows an outline configuration of the edge mirror method, FIG. 4 is a view describing the tracking error detection method of the edge mirror three-beam method used in FIG. 2 and FIG. 3, FIG. 5 is a view for describing the tracking error detection method in an optical information recording medium, FIG. 6 is a view describing the interference of laser light in an optical information recording medium, FIG. 7 is a view for describing the problems in tracking error detection in an optical information recording medium, FIG. 8 is a view for describing the operation modes of the laser diode in the present invention, and FIG. 9 is a view describing the relationship between the operating characteristics and the operating modes in FIG. 8. PREFERRED EMBODIMENT FIG. 1 shows an output switching circuit of a laser diode used in an embodiment of the present invention. In this circuit, the photodiode PD that receives the light generated by the laser diode LD uses the comparator AMP1 to compare the monitor signals with the reference signals and form the error signals, and these error signals are amplified by the power amplifier AMP2 and the amplified output is supplied to the anode of the laser diode. The reference signals are obtained by the variable resistors VR1, VR2 that are connected in series with the photodiode PD. The variable resistor VR1 is for applying the reference signals when there is a reading mode, and the variable resistor VR2 is for applying the reference signals when there is a writing mode, and these variable resistors are connected in series with the photodiode PD between the reference voltage +V and -V and form the reference voltage to the comparator AMP1. When reading, the switch SW2 is open since there is no write signal WT, and the set voltage of the variable resistor becomes the reference voltage. With respect to this, when writing, the write signal WT is applied and the switch SW2 is closed and so both of the variable resistors VR1 and VR2 have the combined set voltage become the reference signal. The anode of the laser diode LD operates the laser diode LD in the duty cycle when there is grounding through the resistor R2 and the switch SW1. The switch SW1 opens and closes in accordance with the output of the AND gate G1, and has applied to it the three inputs of a pulse that is high at 90% duty, a WT input that is high when not writing, and a SEEK input that is high when seeking or track jumping, and when the AND conditions are established, generates output so that the switch SW1 is turned on. The series circuit of the resistor R1 and the condenser C2 which is inserted between the inverted input terminal of the comparator AMP1 and the power amplifier AMP2 has the two purposes of feed forward action so as to cancel the floating capacitance C2 of the photodiode PD, and smoothing operation for the optical output and switching when reading. The circuit of FIG. 1 configured in this manner becomes an intermediate mode or a single mode when there is continuous operation of the laser diode LD in the opened state of the switch SW1, and the intermittent on-off operation of the switch SW1 causes the laser diode LD to turn on intermittently and to become the multi-mode. More specifically, when the switch SW1 is open, there is either recording or reproduction, and when there is recording, the switch SW2 is closed and a large negative voltage from the reference power - V is applied to the inverted input terminal of the comparator AMP1 and so the laser diode LD operates in the single mode, and when there is reproduction, the switch SW2 is open and the input to the inverted input terminal of the comparator AMP1 is made smaller and so the laser diode LD operates in the light multi-mode. In addition, when the switch SW1 is intermittently closed, there is seek or track jump and the laser diode LD has 10% operation in the duty cycle and so the average power is extremely small, and the laser diode LD operates in the multi-mode. FIG. 8 shows the light generated by the laser diode (FIG. 1) in each of the operating modes. In the single mode when there is the maximum input, the switch SW1 in FIG. 1 is opened and the switch SW2 is closed and this mode is used for recording, and there is output of 10 mW for only light of the wavelength λ p . The intermediate mode is used as the reproduction mode and so in this figure, the two outputs of 1mW and 0.5 mW are shown but here, the 1mW output is used in the reproduction mode. The set value of the variable resistor of FIG. 1 changes so that 0.5 mW is selected. Then, the intermittent closing of the switch SW1 in FIG. 1 enables the reduction of the power supplied to the laser diode LD in accordance with the duty cycle, and the case shown in FIG. 1 has a duty cycle of 10% and so the output changes from 1mW to one tenth of this which is 0.1mW. The wavelength of this generated light becomes a spectrum which is characteristic of multi-mode and which includes many wavelengths around the central wavelength of λ p . In this multi mode, the absolute amount of return light from the optical information recording medium to the laser diode is small when seeking and so it is possible to prevent unstable operation due to resonance between the laser diode and the medium, and as a result, it is possible to prevent fluctuation of the amplitude of the tracking error signals. In addition, the return light is the multi mode and so it is possible to obtain stable tracking error signals that have little interference due to return light in which is close to incoherence. FIG. 9 shows the operating characteristics of the laser diode and so a light output of 10 mW is generated in the single mode which is used when writing, and a light output of 0.1 mW is used in the multi mode which is used when track jumping and seeking. There is a light output of 1mw generated for the intermediate mode which is used for read. As has been described above, a laser diode operates in a multi-mode and has a small output for when track jumping and seeking, and therefore errors in tracking control for when track jumping and seeking and which are caused by optical interference resulting from steps in the information recording surface of the optical information recording medium when there is large output in the single mode, are prevented and it is possible to have correct control.

Claims: An optical information recording and reproduction apparatus using a three-beam method for tracking a focussed recording and reading laser beam on an optical information recording medium along a data track using a tracking track forming a step transition with regard to the data track as a reference for the pair of tracking beams, said apparatus being characterized by means for cycling a laser generating said beam on and off intermittently to cause said laser to operate in a multi-mode when a track jump and seek operation is performed, such that in said multi-mode the effective laser output is smaller than during reproduction and the laser energy spectrum includes a plurality of wavelengths each having similar but reduced energy peaks to substantially eliminate the effects of interference. An optical information recording and reproduction apparatus according to claim 1, wherein the step of reducing the output of said laser includes reducing the effective laser output to be about one tenth of the output of the first reproduction level. An optical information recording and reproduction apparatus according to claim 1, wherein the means of reducing the output of said laser intermittently switch on the laser power applied during reproduction.

Inventors: NAKAMARUA EIICHI, YAMAZAKI KOICHI, NAKAMARUA, EIICHI, YAMAZAKI, KOICHI
Applicants: NIPPON CONLUX CO LTD, NIPPON CONLUX CO., LTD.
Application year: 1992
Main classification: G11B7
IPC codes: G11B7