Apparatus for optically recording and reproducing information

Abstract: An apparatus for optically recording and reproducing information in and from an optical information recording medium having a guide track. The apparatus uses an optical head having a diffraction grating, for recording and reproducing information. In recording information, a zero-order diffraction light beam from the diffraction grating is used for the information recording, and plus/minus first-order diffraction light beams from the diffraction grating are used for the tracking. In reproducing information, the zero-order diffraction light beam is used for the tracking, and higher- and odd-order diffraction light beams including at least plus/minus first-order diffraction light beams are used for information reproduction.

Description: BACKGROUND OF THE INVENTION The present invention relates to an apparatus for optically recording and reproducing information, and more particularly to an apparatus as above for use with a card type optical information recording medium. As an optical information recording medium of this type there is known a so-called write-once type optical card capable of recording information once and reproducing the recorded information plural times. In recording information in a write-once type optical card (hereinafter simply called an optical card), a light beam modulated by the information to be recorded is converged into a fine light spot by using a lens. The fine light spot (hereinafter simply called a light spot) is applied onto an information recording area of the optical card while scanning it along the information recording area. The information is accordingly recorded in the optical card as a pit train (information track) optically detectable, e.g., based on a difference of light reflectance between the pit area and the other area. In reproducing the recorded information, a light spot having less optical energy than that used for the recording is applied onto the information track while scanning it along the track. The reflected light from the information track is detected to reproduce the recorded information. An optical head is generally used for recording/reproducing information while applying a light spot onto an optical card. Either an optical head or an optical card is reciprocally moved in order to conduct light beam scanning. However, an optical head is a precision instrument constructed of a number of optical components and drive elements so that it has a poor resistance against impact motions such as rapid acceleration and deceleration. An optical card should be maintained so as to have no warp and held in position on a shuttle with as small a setting error as possible. Therefore, the shuttle is sufficiently strongly constructed to press an optical card and adjust warp or the like to some degree, resulting in a limit to making it light-weight. In view of the above, it is difficult to reciprocally move an optical head or an optical card (shuttle), whichever may be, at high speed. Thus, it has been difficult to realize high speed information recording/reproduction. Reproducing information in particular is carried out frequently and repeatedly so that there is much demand for high speed reproduction which the conventional background art cannot provide. The invention starts from a state of the art according to the precharacterizing portion of claim 1 which is described in FR-A-2575568. This document describes an apparatus for optically recording and reproducing information using an optical head having a diffraction grating and an optical information recording medium having guide tracks. In recording information a light beam located between two other light beams is used for information recording and one of the remaining beams is used for tracking. In reproducing information, the first mentioned light beam is used for tracking, and the other two beams are used for reproducing information. The light beam located between the two other light beams is a zero order light beam diffracted from the grating, whereas the other two beams located on each side of said light beams are the plus/minus first order diffraction light beams diffracted from the grating. Only one of the plus/minus first-order diffraction light beams is used for tracking, whereas the other plus/minus first-order diffraction light beam is used for synchronizing. SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus for optically recording and reproducing information, which apparatus records information on an optical card by using a well known three-beam method (or three-spot method), and reproduces the recorded information such that the recorded information can be reproduced optically at a first speed corresponding to a reciprocal motion of an optical head or an optical card and stored in a memory, and can be read from the memory at a second speed more than two times as fast as the first speed. The first speed may be the same as that conventionally used. In this specification, the term "reproducing information" is intended to mean picking up information from the information track by using a light spot, and the term "reading information" is intended to mean picking up the reproduced information from the memory into which the reproduced image has been stored. The above object can be achieved by the apparatus for optically recording and reproducing information according to claim 1. The apparatus uses an optical head having a diffraction grating and an optical information recording medium having guide tracks in accordance with the precharacterizing portion of claim 1. The inventional apparatus is characterized in that in recording information, both the plus/minus first-order diffraction beams are used for tracking and that in reproducing information, odd-order diffraction light beams of higher order than one are used for reproducing information from at least the pair of tracks. Focussing (claim 2) is carried out using a zero-order light beam both for the information recording and reproduction. A semiconductor laser of the optical head is activated at high optical output power for the information recording, and at low optical output power for the information reproduction. A plurality of information signals obtained from the reproduced information by using the higher order diffraction light beams containing at least plus/minus first order diffraction light beams are temporarily stored in a plurality of memories. Thereafter, the information signals stored in the memories are sequentially read at a speed faster than that of storing the information signals. Since a high energy light beam is used in recording information in an optical information recording medium, the zero-order diffraction light beam obtained from a diffraction grating is applied onto the recording medium. The zero-order diffraction light beam has the highest energy among diffraction light beams from a diffraction grating. Tracking is carried out using both plus/minus first-order diffraction light beams having lower energy than the zero-order diffraction light beam, whereas focussing is carried out using the zero-order diffraction light beams reflected from the surface of the recording medium. In reproducing the information recorded in the optical information recording medium as above, information is read from a plurality of recording tracks of the recording medium at the same time. To this end, a plurality of higher- and odd-order diffraction light beams including at least the plus/minus first-order diffraction light beams are applied onto the surface of the recording medium. The more the higher-order diffraction light beams are used, the more information can be reproduced from a plurality of information tracks, thus allowing a higher reading speed. According to the apparatus for optically recording and reproducing information of this invention, the three-beam method using zero-order and plus/minus first-order diffraction light beams from a diffraction grating is employed in recording information while carrying out tracking. In reproducing information, tracking is carried out using the zero-order diffraction light beam from the diffraction grating in a push-pull manner, whereas the information is reproduced using odd-order diffraction light beams of higher order than one. Therefore, after recording information by using a highly stable tracking method, the information can be read at high speed, without changing the scan speed of a light spot applied to and scanned on an optical information recording medium, by providing a simple switching circuitry. Therefore, the performance of information read can be improved and a compact and cost effective apparatus can be realized. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, advantages of this invention will become apparent to those skilled in the art from the following detailed description of the drawings in which Fig. 8-12 relate to a preferred embodiment of the invention Fig. 1 is a schematic plan view showing an optical card and light spots on the card while information is recorded therein; Fig. 2 shows an example of the structure of an optical head for applying a plurality of light spots on an optical card to record and reproduce information; Fig. 3 is a schematic plan view showing an optical card and light spots on the card while information is read at a speed twice as fast as the reproducing,; Fig. 4 shows an example of the arrangement of photodiodes, and three light spots received thereon; Fig. 5 is a block diagram showing a circuit for picking up a focussing signal and tracking signal from the photodiodes shown in Fig. 4; Fig. 6 is a block diagram showing a circuit for picking up a focussing signal, tracking signal, and two reproduced information signals from the photodiodes shown in Fig. 4; Fig. 7 is a schematic diagram conceptually illustrating the reproduction speed and reading speed twice as fast as the former; Fig. 8 is a schematic plan view showing an optical card and light spots on the card while information is read at a speed four times as fast as the reproducing speed by using the apparatus of this invention; Fig. 9 shows an example of the arrangement of photodiodes, and five spots received on the photodiodes; Fig. 10 is a block diagram showing a circuit for picking up a focussing signal, tracking signal, and four reproduced information signals from the photodiodes shown in Fig. 9; Fig. 11 is a schematic diagram conceptually illustrating the reproduction speed and reading speed four times faster than the former; Fig. 12 is a block diagram showing a signal output circuit for switching between the information recording and information reproducing following high speed information reading; Figs. 13(a) and 13(b) illustrate a change of angle between a line interconnecting light spots and the guide track, respectively, for information recording and information reproduction following high speed information reading; and Figs. 14(a) and 14(b) illustrate a method of changing the angle shown in Figs. 13(a) and 13(b). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a positional relationship between an optical card and light spots while information is recorded in the card. Referring to Fig. 1, an optical card 1 is formed with guide tracks 2 (2a, 2b, 2c, ...) having, e.g., a smaller light reflectance, and information recording areas 3 (3a, 3b, 3c, ...) interposed between guide tracks 2. By using the well known three-beam method, an optical head applies three light spots onto the optical card 1. Namely, a light spot 4 is applied onto the information area 3a, a light spot 5a onto both the information area 3a and guide track 2a, and a light spot 5b onto both the information area 3a and guide track 2b. The light spot 4 uses the zero-order diffraction light beam from a diffraction grating for performing information recording and focussing. Information pits 6 are formed using the zero-order diffraction beam having the highest light energy among respective order diffraction light beams. Automatic focussing control is conducted by the well known astigmatism method using light reflected from the optical card. The light spots 5a and 5b use the plus/minus first order diffraction light beams from the diffraction grating. The light spots 5a and 5b having the light energy smaller than the light spot 4 scan parts of the guide tracks 2a and 2b, respectively, to thus conduct tracking control in such a manner that the light spot 4 correctly scans the center of the information recording area 3a. Fig. 2 shows an example of the structure of an optical head for applying a plurality of light spots onto an optical card 1 to record and reproduce information. In the optical head shown in Fig. 2, a divergent laser beam radiated from a semiconductor laser 7 is made parallel by a collimator lens 8 and thereafter, applied to a diffraction grating 9 to generate a plurality of diffraction light beams including those of the zero order, plus/minus first order, and higher order diffraction light beams. These plural diffraction light beams pass through a beam splitter 10 and are applied to a focussing lens 11 to produce light spots 4, 5a and 5b which are applied onto the optical card 1. The focussing lens 11 is adapted to move in two directions, one being the direction perpendicular to the surface of the optical card 1, and the other being the direction orthogonal to the guide track 2. A plurality of laser beams applied to the optical card 1 are reflected therefrom in accordance with the reflectance of the surface of the optical card 1, reversely applied to the focussing lens 11, reflected by the beam splitter 10 to be directed to the right side, focussed by a light receiving lens 12, imparted with astigmatism by a cylindrical lens 13, and applied to a photodiode 14 which converts optical information contained in the laser beam reflected from the optical card, into electric information. Fig. 3 is a schematic plan view showing an optical card and light spots on the card while information is read at a speed twice as fast as the reproducing speed. Referring to Fig. 3, an optical card 1 is formed with guide tracks 2 (2a, 2b, 2c, ...) and information tracks 15 (15a, 15b, 15c, ...) composed of information pits 6. An optical head applies a light spot 4 onto the guide track 2b, a light spot 5a onto the information track 15a, and a light spot 5b onto the information track 15b. The light spot 4 is used for picking up focussing and tracking control signals, the former being by means of the astigmatism method or the like and the latter by means of the push-pull method or the like, respectively of well known in the art. The light spots 5a and 5b are used for picking up information signals. For instance, the optical card 1 is moved from the right to the left in the direction indicated by an arrow S to thus relatively scan the light spots 5a and 5b and reproduce the information signals on the information tracks 15a and 15b, respectively. Fig. 4 shows an example of the arrangement of photodiodes 14, and three light spots received thereon. Photodiode elements 14A, 14B, 14C and 14D are disposed at the central area in the form of 2 × 2 matrix, and photodiode elements 14E and 14F are disposed at the upper and lower sides. Three laser beams reflected from the optical card 1 pass through the light receiving lens 12 and cylindrical lens 13 and focussed on the photodiodes 14 as light spots 16, 17a and 17b. The electric outputs from the photodiode elements 14A to 14F are represented by VA to VF as shown in Fig. 5. In recording information in the optical card 1, VFO = (VA + VB) - (VC + VD) and VTR = VE - VF are obtained by adders 18 and 19, and subtracters 20 and 21. The signals VFO and VTR are used as the focussing and tracking control signals, as is well known in the art. Next, in reproducing information from the optical card 1, VFO = (VA + VB) - (VC + VD) and VTR = (VA + VD) - (VB + VC) are obtained by adders 18, 19, 22, and subtracters 20 and 21, as shown in Fig. 6. The signals VFO and VTR are used as the focussing and tracking control signals, as is well known in the art. The electric outputs VE and VF from the photodiode elements 14E and 14F are the reproduced signals from the information tracks 15a and 15b which are read at a higher speed than the reproducing speed as in the following. Namely, as shown in Fig. 7, the reproduced signals VE and VF (during a period T) are temporarily stored in memories 24 and 25, respectively. Thereafter, the reproduced and stored information signal VE in the memory 24 is first read at a clock speed twice as fast as the clocks contained in the reproduced information signal VE, and then the reproduced and stored information signal VF in the memory 25 is read at a clock speed twice as fast as the clocks contained in the reproduced information signal VF. Therefore, the information signal V(E+F) is obtained (during the period T). As described above, the information reading speed is twice as fast as the information reproducing speed per one information track. Fig. 8 is a schematic plan view showing an optical card and light spots on the card while information is read at a speed four times faster than the reproducing speed by using the apparatus of this invention. In this embodiment, the diffraction grating 9 of the optical head shown in Fig. 2 produces five diffraction light beams including zeroth order, plus/minus first order, and plus/minus third order diffraction light beams. These five light beams are focussed onto the surface of the optical card 1 as light spots 4, 5a, 5b, 5c and 5d by means of the focussing lens 11 which is adapted to be movable in the direction perpendicular to the surface of the optical card 1 and in the direction orthogonal to the guide track 2. In this case, light spots 5m and 5n of the plus/minus second order diffraction light beams are also produced. However, these light spots are not relevant to this invention, and so their description is omitted. Referring again to Fig. 8, the light spot 4 applied to the guide track 2b of the optical card 1 is reflected therefrom with the focussing information and tracking information being supplied. The light spots 5a, 5b, 5c and 5d applied to the information tracks 15a, 15b, 15c and 15d are reflected therefrom with the information recorded on the tracks being supplied. The five laser beams reflected from the optical card 1 are applied to the photodiodes 14 and converted into electric information signals corresponding to the optical information contained in the laser beams. Fig. 9 shows an example of the arrangement of photodiodes 14, and five spots received on the photodiodes, to be used in the embodiment shown in Fig. 8. The arrangement of photodiodes 14 has additional photodiode elements 14G and 14H at the upper and lower sides, as compared with the photodiodes 14 shown in Fig. 4. The five laser beams reflected from the optical card 1 are focussed onto the surface of the photodiodes 14 as light spots 16, 17a, 17b, 17c and 17d as shown in Fig. 9. The focussing and tracking control signals VFO and VTR shown in Fig. 10 similar to those shown in Fig. 5 are picked up from the photodiodes 14. The reproduced information signals VE, VF, VG and VH are picked up from the photodiode elements 14E, 14F, 14G and 14H, respectively. The electric information signals VE, VF, VG and VH are the reproduced information signals from the information tracks 15a, 15b, 15d and 15c, respectively, which are read at a higher speed than the reproducing speed as in the following. Namely, as shown in Fig. 11, the reproduced signals VE, VF, VG and VH (during a period T) are temporarily stored in memories 24, 25, 26 and 27, respectively. Thereafter, the reproduced and stored information signals VG, VE, VF and VH are read sequentially in this order from the memories 26, 24, 25 and 27 at a clock speed four times as fast as the clocks contained in the reproduced information signals VG, VE, VF and VH, respectively. Therefore, the information signal V(G+E+F+H) is obtained (during the period T). As described above, the information reading speed is four times as fast as the information reproduction speed per information track. As can be readily understood from the foregoing description, higher- and odd-order diffraction light beams including plus/minus fifth-order, seventh-order diffraction light beams and so on, from the diffraction grating may be used to obtain still higher read speeds. In the above description, light spots 5 applied to the optical card 1 are obliquely aligned relative to the guide track 2 and information track 15 as shown in Figs. 1, 3 and 8. However, light spots 5 may be aligned perpendicular to the guide track 2 and information track 15 on the condition that adjacent light spots are not superposed in part one upon another. Furthermore, higher- and even-order diffraction light beams including plus/minus second-order, fourth-order diffraction light beams from the diffraction grating are not needed, so that it is desirable to design the diffraction grating 9 such that the diffraction light beams of even order have as small an intensity as possible. With the described apparatus for optically recording and reproducing information, light spots 5 are applied to the optical card 1 while sequentially and reciprocally scanning the tracks 15. Information is stored in a memory at the forward scan, whereas for backward scan, the stored information is read at a speed four or more times faster than the reproducing speed and at the same time, information on the new information tracks is stored in the memory. In recording information in the optical card 1, a single light spot is generally used while reciprocally scanning it. Therefore, use of a plurality of light spots in reproducing information as in the case of the present invention results in reversed time sequence for adjacent information tracks. Whether the reproduced information is at the forward or backward scan can be easily detected on the basis of the address signal recorded on the end portion of each information track. Therefore, the reversed time sequence can be corrected at the time the information is read from the memory. The same optical head is used for both information recording and information reproduction following high speed information read. Therefore, it is necessary to switch the electric circuits and optical systems between both cases. For the electric circuits during the information recording, a large current near the rated value is supplied to the semiconductor laser 7 shown in Fig. 2 to radiate a laser beam of high power, and the three-beam method is employed for tracking. Therefore, the relationship between light spots and tracks on an optical card becomes as shown in Fig. 1, and the tracking control signal VTR is picked up using the circuit arrangement shown in Fig. 5. In reproducing information following high speed information reading, a current supplied to the semiconductor laser 7 shown in Fig. 2 is reduced to radiate a laser beam of low power, and the push-pull method is employed for tracking. Therefore, the relationship among light spots and tracks on an optical card becomes as shown in Figs. 3 and 8, and the tracking control signal VTR is picked up using the circuit arrangement shown in Figs. 6 and 10. An example of a circuit for switching between the information reading and information reproducing following high speed information reading is shown in Fig. 12. The circuit shown in Fig. 12 is a combined circuit of those shown in Figs. 5 and 6. In recording information, switches 28 and 29 are turned to the contacts (1) to select the electric output VE - VF = VTR from the photodiode elements 14E and 14F as the tracking control signal. In reproducing information following high-speed information read, the switches 28 and 29 are turned to the contacts (2) to select the electric output signal (VA + VD) - (VB + VC) = VTR from the photodiode elements 14A, 14B, 14C and 14D as the tracking signal, and the electric output signals VE and VF from the photodiode elements 14E and 14F as the reproduced information signal. Figs. 13(a) and 13(b) illustrate a change of angle between a line interconnecting light spots 5a, 4 and 5d and the guide track 2, respectively for the information recording and information reproducing following high speed information reading. An angle between a straight line 30 interconnecting the light spots 5a, 4 and 5b and the center line of the guide track 2a is represented by ϑW and ϑR which are represented by ϑW = sin⁻¹(W₃/W₁) and ϑR = sin⁻¹[(W₂ + W₃)/W₁] , where ϑW is smaller than ϑR, W₁ is a space between light spots 5a and 5b, W₂ is a width of the guide track 2, and W₃ is the width of the information track 3. Since W₁, W₂ and W₃ take a constant value if the same optical head and optical card are used, it is necessary to change the mounting angle of the optical head itself or the optical elements thereof such that the angle ϑW is used for the information recording, and ϑR for the information reproducing following high speed information reading. Particularly, an optical head housing 32 may be finely rotated around the optical axis 33 of the focussing lens 11 in the direction indicated by an arrow 34. Alternatively, the diffraction grating 9 may be finely rotated around an optical axis 35 in the direction indicated by an arrow 36. Such fine rotation may be effected by employing various known methods using electromagnetic force. In the foregoing description of the apparatus of this invention, although a write-once type optical card has been used as an optical information recording medium, the apparatus is also applicable to erase/re-recording type optical cards, optical disks and the like.

Claims: An apparatus for optically recording information and reproducing information from an optical information recording medium (1) having information tracks (15) and guide tracks (2), said apparatus comprising an optical head having a diffraction grating (9), wherein in recording information, a zero-order diffraction light beam is used for information recording and a first-order diffraction light beam is used for tracking; and in reproducing information, said zero-order diffraction light beam (4) is used for tracking and the plus/minus first-order diffraction light beams are used for reproducing information from a pair of information tracks (15), characterized in that in recording information, both the plus/minus first order diffraction beams are used for tracking and in reproducing information, also odd-order diffraction light beams of higher order than one are used for reproducing information from said information tracks (15). An apparatus according to claim 1, wherein said zero-order diffraction light beam is used for focussing both for the information recording and information reproducing. An apparatus according to claim 1, wherein in reproducing information a plurality of information signals reproduced by using said odd-order diffraction light beams including said plus/minus first-order diffraction light beams are stored in a plurality of memories and thereafter, said information signals are read from said plurality of memories in time sequence.

Inventors: NODA KAZUO, YAMAZAKI KOICHI, NODA, KAZUO, YAMAZAKI, KOICHI
Applicants: NIPPON CONLUX CO LTD, NIPPON CONLUX CO., LTD.
Application year: 1989
Main classification: G06K7
IPC codes: G11B7, G06K7, G06K17