Optical memory and information processing apparatus

Abstract: The invention relates to an optical memory in which an optical recording medium (3) is built in a case (1), and also to a memory apparatus. Recording, reproducing and erasing operations are performed by irradiating light via a transparent portion of the case (1) onto the built-in optical recording medium (3). The optical recording medium (3) built in the case (1) has face vibrations with respect to the case (1), because it is moved within the case (1). The present invention is characterized by employing such a construction for optically mitigating irregular fluctuation in reflectivity caused by this face vibration. In the optical memory of the present invention, the reflectivity fluctuation caused by an interference effect made between reflection light from the case (1) and air, and also reflection light from the optical recording medium (3) and air due to the relative deviation in the face vibrations, may be reduced by antireflection films (2a, 2b) provided in the case (1) and the optical recording medium (3). In a memory apparatus of the present invention, the above-described memory is mounted, the fluctuation in the reflectivity is monitored and laser power is varied in order to further mitigate the reflection vibrations.

Description: BACKGROUND OF THE INVENTION (a) Field of the Invention The present invention relates to an optical memory such as an optical disk and an optical card for recording, reproducing and erasing information with employment of laser light or the like, and also to an information processing apparatus. Also, the present invention relates to an optical memory and an information processing apparatus used only for reproducing information previously stored therein. (b) Description of the Related Arts In an optical recording medium such as an optical disk, laser light or the like is focussed up to its diffraction limit in order to record, reproduce and erase information. As a result, the information can be recorded on such optical recording mediums at extremely high density. Thus, such large capacity-memories have been mainly developed as auxiliary memories for large-scale computers. On the other hand, small-sized portable computers such as for instance, lap-top computers have been marketed very recently. Floppy disks have been presently utilized as typical exchangeable medium memories for small-sized computers. However, the memory capacity of the typical floppy disk is rather small. A strong demand exists for such a high-density memory with an exchangeable recording medium having a higher recording density than the floppy disk. To meet such demands, various types of optical memories have been proposed. For instance, as to compactness, optical cards with higher portabilities have been proposed. Although an optical card has such merits that a higher portability may be expected with a compact size and a large memory capacity, there is a difficulty that the data transfer speed thereof is much slower than that of a rotation type optical disk, because both the data recording and reproducing operations are performed in a linear scanning. To solve the above-described difficulty belonging to the optical card, one invention has been made as JP-A-60-79581. This invention is directed to a card comprising a rotation type recording medium sheet, for instance, an optical disk having a thickness substantially equal to the thickness of a conventional cash card. Since data are recorded on the rotation type recording medium sheet in this optical card, there is a particular advantage that higher data transfer speed may be achieved, as compared with that of the conventional optical card. As a result, this invention can overcome the above-described problem inherent to the conventional optical card, i.e., low data transfer speed, while other merits such as better portability and easy handling of the typical optical cards are maintained. On the other hand, in the conventional optical disk, this optical disk is mounted within a cartridge case, a shutter which is opened/closed is provided on a portion of the case within the disk drive, and the laser light is irradiated onto the disk. The reason why such an optical disk is mounted within the cartridge case, is to prevent dust from being attached on the disk surface and also to facilitate mounting by this cartridge case. However, generally speaking, a hard cartridge case is rather thick and there is a drawback that the cartridge case becomes heavy. Therefore, there is a demand to make the cartridge case thinner and lighter. Nevertheless, to make a thinner cartridge case, an optical disk substrate having a typical thickness of 1.2 mm must be made thinner. In general, when the substrate is made thinner, the adverse influence of laser scattering (due to dust attached on the substrate surface) becomes greater. As a result, this may cause, in turn, other various drawbacks such as decreasing the laser power during the recording operation and causing read-out errors during the reproducing operation. Consequently, the presently available shutter type cartridge case can hardly prevent dust problem. As one of dust preventing methods, a mechanism has been proposed in JP-A-64-25378 that dust is collected by controlling air flows. However, there is no clear description that such a dust preventing method may be similarly applied to the above-described thinner optical disk substrate. In JP-A-64-30087, the following idea for preventing dust has been proposed: The optical disk is sealed within the cartridge case by way of the shutter and the laser light is irradiated through the cover glass formed on the cartridge case onto the surface of the optical disk. In accordance with the conventional ideas for preventing dust as described in JP-A-60-79581 and JP-A-64-30087, to achieve the sufficient dust protection with the thinner memory medium, the optical disk built in the cartridge case must be highly sealed, or sufficiently sealed within the cartridge case. To this end, the method of projecting the laser light via the case cover onto the disk surface, has a particular advantage distinguishing it from another conventional system in which the laser light is directly irradiated onto the disk surface. When, as described above, the optical disk is built in the cartridge case, this case is spatially separated from the optical disk so that a space is necessarily formed therebetween. Under normal use, there is air in this space. On the other hand, in case that a flexible thin optical disk as described in JP-A-60-79581 and JP-A-64-30087 is employed so as to be rotated within a case, space intervals between the optical disk and case are continuously varied due to face vibrations of this optical disk, while rotating the optical disk. In particular, since the face vibrations of the mechanically flexible optical disk become great, such great face vibrations may be suppressed by employing the stabilizer plate as described in JP-A-64-30087. It is very difficult to prevent the rotating optical disk from colliding with the stabilizer plate, but the rotating optical disk is set in close proximity to the stabilizer plate so that an air bearing effect may be established therebetween. SUMMARY OF THE INVENTION An object of the present invention is aimed not to mitigate a face vibration occurring in a built-in optical recording medium, particular to an optical disk as in the above-described prior art, but to mitigate an irregular fluctuation in an optical characteristic such as reflectivity of the optical recording medium, which is caused by the face vibration during recording, reproducing, or erasing operation. The present invention is to provide an optical memory, an information processing apparatus and an information recording and reproducing method in which while, as previously described, a memory is made thin, a case is tightly sealed in order to sufficiently realize dust-proof property, and laser light is irradiated through the case to a surface of an optical recording medium such as an optical disk which is relatively moved with respect to the case, for instance, in a rotating form, whereby optical recording operations such as data recording, reproducing, or data erasing are stably performed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically represents a construction of an optical memory according to the present invention; Figs. 2A and 2B are illustrations for showing principle of fluctuation in reflectivity caused by face vibrations; Figs. 3, 4 and 22 represent the fluctuation in reflectivity caused by face vibrations; Figs. 5 to 11 are schematic diagrams for showing constructions of an optical memory according to the present invention; Figs. 12 to 18 are schematic diagram for representing constructions of antireflection films; Fig. 19 is a graphic representation for showing spectral reflectivity of a case having mixed antireflection films; Figs. 20, 21, 23A, and 23B are schematic diagrams for showing a construction of a card-shaped optical memory; Fig. 22 is a characteristic diagram of the card-shaped optical memory according to the present invention; Figs. 24A and 24B are schematic diagrms of the optical head and optical disk, and also a control diagram thereof, and, Fig. 25 is a shcematic block diagram of an information procesing apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical memory according to the present invention is characterized by comprising a case, an optical recording medium disposed within the case, and an antireflection film. This optical recording medium is movable within the case, and more specifically is preferable to be rotatably stored within the case. Also, the antireflection film is preferable to be employed on at least one of the case and recording medium. As represented in Fig. 1, features of the present invention are as follows. In principle, the optical memory has a supereme self-holding characteristic and a better portability, and further environment resistance, oilproof characteristic, chemical resistance. A construction of the optical memory is made such that an optical recording medium 3 is built in a paired case 1 (including a cartridge form and a card shape) having a transparent portion, so as to be relatively movable with respect to this case 1, and an antireflection film or coating 2. It should be noted that reference numeral 4 shown in Fig. 1 denotes a substrate of the optical recording medium; reference numeral 5 indicates an optical path; and reference numeral 6 represents an air layer formed by the card and optical recording medium. Although the antireflection films 2 have been formed on both of an interior of the card and the optical recording medium, this antireflection film may be formed on only one member thereof. Alternatively, this antireflection film may be formed on an exterior of the card. An optical memory according to the present invention, comprises: a case having a transparent portion and made of a material having a self-holding charactristic; an optical recording medium stored within this case, for recording, reproducing and erasing information by light illuminated through the transparent portion of the case; and, an antireflection film provided on at least one of the above-described case and optical recording medium along a light path of the light, and made of a material through which the light can easily pass from the case and optical recording medium. The optical recording medium records information on a substrate having a holding characteristic and plasticity by way of physical or chemical changes by the light. At least one of a dielectric film or metal reflecting film is preferably formed on the optical recording medium. The optical recording medium may preferably record, reproduce and erase information thereon in such a manner that irradiating light thereto causes a phase change in an amorphous-crystal. As the optical recording medium, a recording medium capable of recording, reproducing and erasing information thereon by utilizing a photo-electro-magnetic effect, may be employed. The optical recording medium may be relatively moved with respect to the case within the case. Furthermore, it is preferable to rotate the optical recording medium with a substantially constant center axis inside the case. The optical recording medium may be such a disk as a compact disk only reproducing information which has previously been recorded. Assuming now that a refractive index of the transparent portion of the case is "n₁", a refractive index of a space between the case and the optical recording medium built in this case is "n₀", and a refractive index of a first layer constituting the optical recording medium with respect to an incident direction of the light, a refractive index "n₃" of the antireflection film employed in the case of the optical memory may be preferably n 1 n 0 , whereas a refractive index "n₄" of the anti-reflection film provided on the first layer of the optical recording medium may be n 2 n 0 . As for the antireflection film, a condition of: nh = (2m + 1)λ/4 may be preferable, assuming now that the wavelength of light used for recording or reproducing information is "λ", the refractive index of the antireflection film is "n", the film thickness is "h", and "m" is an integer. Also, the antireflection film may be formed by at least two layers having different refraction indexes, made of dielectric films selected from one of oxide, fluoride, sulfide and calcogen compounds. Further, the antireflection film may be preferably constructed of a dielectric film made by mixing at elast two sorts of oxide, fluoride, sulfide, chloride and calcogen compounds having different refractive indexes. This antireflection film may be preferably made of a material having higher transmittance than that of the above-described case and optical recording medium. Also, the light transmittance may be selected to be more than 80%. The optical memory may employ therein at least two recording media. The optical memory may be preferably shaped as a card, and an outer size thereof is smaller than 110 mm in a lateral direction thereof and smaller than 80 mm in a transverse direction thereof. A thickness of the optical memory may be preferably smaller than 3 mm. An optical memory according to the present invention comprises a case having a transparent portion and made of a material having a self-holding characteristic; and an optical recording medium stored in this case, for recording, reproducing and erasing information by irradiating light via the transparent portion of the case thereon; the transparent portion of the case being made of a material through which the light can easily pass from the optical recording medium. Transmittance of this transparent portion is preferably higher than 80 %. A description will now be made of this antireflection film. The antireflection film must be designed based upon a material of the case on which the antireflection film is provided, and a material of the optical recording medium. Accordingly, although various materials may be selected, the large light transmittance of the material in proximity to a wavelength of laser light used for recording/reproducing information is necessarily required. Preferably, the light transmittance may be selected be higher than 80 percents, or more than 90 percents. As this antireflection film, both a single layer antireflection film and a multi layer antireflection film may be employed. Materials capable of being used as the antireflection film are represented in a list 1. List 1: Materials usable as an antireflection film fluoride Ge F 3, LaF₃, MgF₂, Na₃AlF₈, BaF₂, SrF₂, ThF₄, LiF₂, CaF₂ nitride SiN, AlN oxide CeO₂, Fe₂O₃, Cr₂O₃, Al₂O₃, In₂O₃, La₂O₃, SiO, TiO₂, Y₂O₃, ZrO₂, Ta₂O₅ sulfide ZnS Calcogemide compounds ZnSe, PbTe organic resin ultraviolet curable resin, epoxy, acrylic polycarbon There are mainly inorganic compounds such as fluoride, nitride, oxide, sulfide, calcogens compounds, and organic coating materials such as an ultraviolet curable resin (UV resin). These materials may be employed as a monolayer or a multilayer. A method for manufacturing this antireflection film will now be explained. Various sorts of materials listed in the list 1 are formed on the case and optical recording medium. As the manufacturing methods, there are vacuum vapor deposition process, sputtering process, applicating process, chemical plating process, electric casting process, printing process and the like. Other manufacturing methods used for normal thin film materials may be utilized. The antireflection film must be designed so as to be fitted to the refractive indexes of the case and optical recording medium, as previously explained. To this end, materials having a suitable reflection index are required to be employed as the antireflection film. Although the refractive indexes of the materials listed in the list 1 may be fitted to that of the antireflection film to some extent, the refractive index of the antireflection film must be freely controlled in order to precisely suppress the above-described reflection fluctuations. In order to control the refractive index of the antireflection film, it is desirable to mix more than two different sorts of materials each having different refractive indexes with each other so as to obtain a predetermined refractive index. As the mixture method, there are a method for setting a multi-simultaneous vapor deposition or sputtering process, a vapor deposition source and a sputter target as a mixture, and further a method for mixing in a solution. In general, a refractive index "n" of a mixed antireflection film is given by Lorentz-Lorentz's formula: n 2 = Σa i n i 2 c i /ρ i Σa i c i /ρ i where a i = l/(n i 2 + 2) "n i " indicates the refractive index of a mixed material "i"; "c i " is its weight rate; and "ρ i " represents its density. In Fig. 5, there is shown a construction of an optical memory in which an antireflection film 2 is provided only inside a case. Similarly, fluctuation of reflectivity could be suppressed within 8 percents by highly adjusting the refractive index of the antireflection film in this construction. It should be noted that reference numeral 1 denotes a transparent case; reference numeral 3 indicates a recording layer; reference numeral 4 represents a substrate; reference numeral 5 denotes an optical path; and reference numeral 6 represents a space. Fig. 6 represents a construction of an optical memory having of an opaque case 7. In this construction, there is formed a window 8 (transparent portion) in a portion of the case, upon which laser light is incident, and an antireflection film 2 is provided only on the transparent portion of the case. It should be noted that reference numerals 3 to 6 are similar to those of Fig. 5. A design of a monolayer antireflection film will now be described. Assuming now that the refractive index of the antireflection film is "n"; the thickness of this film is "h" (µm); the refractive index of the case or the window (transparent portion of the case) on which the antireflection film is formed is "n₁"; and the refractive index of a space between the case and optical recording medium built in the case is "n₀", n = n 0 n 1 is satisfied based upon an amplitude condition of interference, or nh = (2m + 1)1/4 is satisfied based on a phase condition, where "m" denotes an integer, and "λ" represents the wavelength (µm) of laser light used for recording/reproducing operations. A similar designing idea may be applied to the antireflection film employed in the optical recording medium. Although a complex design is required for a multilayer antireflection film a generic designing policy for two layers and three layers will now be explained. The following two typical models are available for a two-layer antireflection film having refractive indexes of n₂ and n₃. 1 ○ λ/4(n₃) - λ/4(n₂)/case (n₁) model. Symbol "λ" represents the wavelength of laser light. In this case, optical film thicknesses n₂h₂ and n₃h₃ of the two-layer antireflection film are preferably equal to λ/4. Symbols "h₂" and "h₃" are film thicknesses of the antireflection film. 2 ○ λ/4(n₃) - λ/2(n₂)/case (n₁) model. In this case, optical film thicknesses n₂h₂ and n₃h₃ of the two-layer antireflection film are equal to λ/4 and λ/2, respectively. In the three-layer antireflection film having the refractive indexes n₂, n₃ and n₄. 3 ○ λ/4(n₃) - λ/2(n₂) - λ/4(n₄)/case It should be noted that n₂ > n₄ > n₃. In this case, n₃n₁ = n 4 2 must be satisfied and these refractive indexes are equal to λ/4 = n₃h₃ and λ/4 = n₄h₄. As the materials for the recording film of the optical recording medium, materials such as metal films, organic colors, calcogenide compounds, magnetic thin films and inorganic chloride are preferable which respond to light or heat produced by light irradiation. In particular, a material where an amorphous-crystal phase change may happen to occur, and another material having a rewritable capability by way of the photo-electro-magnetic effect may be preferable. As previously described, the optical memories provided with the antireflection film are advantageous for achieving the object of the present invention. An apparatus for mitigating the fluctuation in the reflectivity caused by the face vibrations of the relevant optical recording medium, according to a system of the present invention, will now be described. In an optical memory, both a focusing operation for correctly focussing a laser beam onto a medium plane and a tracking operation for precisely tracing the laser beam onto a recording track are required while recording, reproducing or erasing data. To this end, the light reflected from the medium plane is returned to a detector and then a servo control is performed that a condenser lens is fine-moved by an actuator or the like in response to output values of the detectors. Accordingly, if, as previously described, the fluctuation in the reflectivity of the medium happens to occur, a normal servo control can be hardly expected. Therefore, there is a necessity to monitor such a reflectivity fluctuation in order to suppress this fluctuation in the system. In an optical memory according to the present invention, there are employed: a case having a transparent portion and made of a material with a self-holding characteristic; and an optical recording medium stored within the case, in which a recording layer for recording, reproducing and erasing information by receiving light irradiated through the transparent portion of the case has been formed on a transparent substrate, the transparent substrate is made of a material through which the above-described light can more easily pass rather than the transparent portion of the case. Transmittance of this transparent portion of the case is preferably higher than 80 percents. In an optical memory according to the present invention, there are employed: a case having a transparent portion and made of a material with a self-holding characteristic; and an optical recording medium stored within the case via an internal plane of this case and an air layer, for recording, reproducing and erasing information by receiving light irradiated through the transparent portion of the case, at least one of antireflection means, the reflectivity of which at a boundary plane between the optical recording medium and air layer becomes below 4%, and anti-reflection means, the reflectivity of which at a boundary plane between the transparent portion of the case and air layer becomes lower than 4 % is employed within the optical path. An information processing apparatus, according to the present invention, is characterized by comprising an optical head, a memory which includes an optical recording medium rotatably disposed within a case having a transparent portion, and an antireflection film formed on at least one of said case and said optical recording medium; recording information on said optical recording medium by irradiating light thereon through the transparent portion of the case; reproducing the information which has been recorded on said optical recording medium; and, erasing the information which has been recorded on said optical recording medium. A variation in reflectivity of light reflected from the above-described optical recording medium is preferably selected to be smaller than 5%. Furthermore, it is preferable to employ a circuit for correcting the variation in the reflectivity of the light reflected from the optical recording medium. An information processing apparatus according to the present invention comprises: an optical memory in which an optical recording medium for optically recording, reproducing and erasing information is movably storedwithin a case having a transparent portion; an optical head for recording the information on the optical recording medium, for reproducing the information from the optical recording medium and for erasing the information recorded on the optical recording medium; means for setting a variation in a reflecting amount of light reflected from the optical recording medium to lower than 5 %; means for driving the optical recording medium; and, a drive circuit for controlling the operation of the optical head and the rotation number of the drive means. This drive means corresponds to a spindle motor, flat motor, linear motor and ultrasonic actuator for rotating or performing a parallel motion of the optical recording medium with respect to the case. The optical head preferably includes a semiconductor laser; a collimation lens, an object lens, a focusing actuator, a photodiode, prisms, a mirror, a tracking actuator, a 1/4λ plate and an opto-acoustic element. Both of the optical head and optical memory employed in the information processing apparatus according to the present invention may be used only for reproducing operation. Also, the information processing apparatus according to the present invention may include a circuit for correcting fluctuation in reflectivity of the light reflected from the optical recording medium, instead of the means for lowering an amount of reflectivity of the light reflected from the optical recording medium. In an information recording method according to the present invention, light is irradiated onto an optical recording medium movably stored within a case having a transparent portion and made of a material with a self-holding characteristic via a transparent portion of the case, whereby information is recorded, reproduced and erased on and from the optical recording medium, and also the light is irradiated through an antireflection film on a light path of the light, which is formed on at least one of the above-described case and optical recording medium, and is made of a material the transmittance of which is higher than 80 percents. In an information reproducing method according to the present invention, light is irradiated onto an optical recording medium movably stored within a case having a transparent portion and made of a material with a self-holding characteristic via a transparent portion of the case, whereby the formation previously recorded on this optical recording medium is reproduced, the light is irradiated on a light path of the light via an antireflection film which is formed on at least one of the case and optical recording medium and is made of a material the transmittance of.which is higher than 80 percents. The antireflection film employed in the information processing apparatus according to the present invention, is to prevent or suppress interference of light caused by the air layer. The light interference caused by this air layer becomes a noise with respect to a signal. Accordingly, this antireflection film may also be referred to as "a light interference suppressing film". Furthermore, this antireflection film may be preferably formed on both of the case and recording medium. Also, this antireflection film may be made of a transparent material, and may have a refractive index different from that of the case and optical recording medium. Then, the case may be relatively moved with respect to the optical recording medium in accordance with the present invention. More specifically, the optical recording medium may be rotatable within the case. Also, an optical memory according to the present invention comprises: a case having a transparent portion and made of a material with a self-holding characteristic; and, an optical recording medium rotatably stored within the case via an internal plane of the case and an air layer, for performing at least one of recording, reproducing and erasing operations for information by light irradiated through the transparent portion of the case, characterized in that a light interference suppressing film for suppressing interference of said light at the air layer is provided in a light path of the light in at least one of the internal plane of the case and a plane in contact with the air layer of the optical recording medium. In an optical memory according to the present invention, comprising a case having a transparent portion and made of a material with a self-holding characteristic; and an optical recording medium stored whithin the case, and relatively moved with respect to the case, for reproducing and recording/reproducing information, or recording/reproducing/erasing the information by light irradiated through the transparent portion of the case, a thin film having a refractive index different from that of said case is formed on at least a side plane of the case in a light path of said light of both said case and optical recording medium, and also a thin film having a refractive index different from that of a transparent substrate to constitute said optical recording medium or that of a transparent thin film provided on an outermost layer is formed on said substrate or outermost layer thin film. Further, in an optical memory according to the present invention, comprising a case having a transparent portion and made of a material with a self-holding characteristic; and an optical recording medium stored within the case, and relatively moved with respect to the case, for reproducing and recording/reproducing information, or recording/reproducing/erasing the information by light irradiated through the transparent portion of the case, a thin film having transmittance greater than that of said case is formed on at least one side plane of the case in an optical path of the light of both the case and optical recording medium, and also a thin film having transmittance greater than that of a transparent substrate to constitute said optical recording medium, or that of a thin film provided on an outermost layer is formed on said transparent substrate or thin film of the outermost layer. In the optical memory according to the present invention, comprising a case having a transparent portion and made of a material with a self-holding characteristic; and an optical recording medium stored via an air layer within the case, and relatively moved with respect to the case, for reproducing and recording/reproducing information, or recording/reproducing/erasing the information by light irradiated through the transparent portion of the case, a thin film having a refractive index different from that of said case is formed on at least a side plane of the case in a light path of said light of both said case and optical recording medium so as to set reflectivity at a boundary plane with said air layer to be lower than 4%, and also a thin film having a refractive index different from that of a transparent substrate of said optical recording medium or that a transparent thin film provided on an outermost layer of said optical recording medium is formed on said substrate or outermost layer thin film. An information processing apparatus according to the present invention comprises: an optical memory in which an optical recording medium for optically recording, reproducing, or erasing information is movably stored within a case having a transparent portion; an optical head for recording, reproducing, or erasing the information on said recording medium; means for setting a variation in a reflection amount of light to be lower than 5%, which is projected from said optical head and reflected from said optical recording medium; means for driving said optical recording medium; and, a drive circuit for controlling both operations of said optical head and a rotation number of said drive means. An information processing apparatus according to the present invention comprises: an optical memory in which an optical recording medium for optically recording, reproducing, or erasing information is movably stored within a case having a transparent portion; an optical head for recording, reproducing, or erasing the information on said recording medium; correcting means for correcting a variation in a reflection amount of light to be lower than 5%, which is projected from said optical head and reflected from said optical recording medium; means for driving said optical recording medium; and, a drive circuit for controlling both operations of said optical head and a rotation number of said drive means. Also, an optical memory, according to the present invention, comprises an optical recording medium rotatably disposed within a case; and, a film for suppressing interference of light occurring in an air layer formed between the case and the optical recording medium. In this optical memory, the interference suppressing film is preferable to be provided on at least one of a plane between the air layer of the case and this suppressing film, and also another plane between the air layer of the recording medium and this suppressing film. Also, the refraction index of the case is preferably different from that of the optical recording medium. In accordance with the present invention, the antireflection films provided in the case and optical recording medium have effects to reduce the variation in the reflectivity which is caused by the optical recording medium built in the case when being relatively moved with respect to the case. Further, the information is recorded, reproduced and erased by the information processing apparatus including the correcting circuit for monitoring the variations in the reflectivity of the medium, so that the stable recording and reproducing operations with the small variation of the reflectivity can be realized. Irregular variations in the optical characteristics such as reflectivity caused by the face vibrations of the optical recording medium movable within the case during the recording, reproducing, or erasing operations will now be described. In Figs. 2a and 2b, there are shown the variations in the reflectivity caused by the face vibrations. To achieve a better data transfer speed than that of the presently available floppy disk, an optical memory must be designed such that assuming now that a diameter of an optical disk 4 built in the optical memory is selected to be 2 inches (approximately 50 mm), for instance, this optical disk 4 must be rotated at a rotating speed on the order of 3600 rpm. When the optical disk 4 is rotated at such a high speed within the case 1 under substantially sealed condition, a pressure difference may occur within the case 1 due to the face that a velocity difference may exist between an inner periphery and an outer periphery of the disk 4. Then this pressure difference may induce the face vibrations of the optical disk. There are other face vibrations caused by center vibrations of the spindle for driving the optical disk. As described above, when the optical disk is rotated within the case, the face vibrations may occur. Accordingly, this may cause an interval between the case and optical disk to be continuously, irregularly varied. Fig. 2a shows such a condition that the optical disk 4 is positioned in close proximity to the case 1, whereas Fig. 2b shows such a condition that the optical disk 4 is most separated from the case 1. Laser light 5 incident on the case perpendicular to the case (note that in Fig. 2, its angle of incidence has been changed for the sake of convenience) produces one reflected beam 5a which has been reflected at a boundary plane between the case and a space 6 within the case, and the other reflected beam 5b which has been reflected at a boundary plane between the optical disk 4 and the space 6. In the figures, both the light reflected at the surface of the case 1 and the light reflected from the inside of the optical disk 4 containing the data have been omitted. Considering now the case shown in Fig. 2a where the reflected beams 5a and 5b interfere constructively, and the case shown in Fig. 2b where the reflected beams 5a and 5b interfere destructively, since the interference condition is continuously changed due to the face vibrations of the optical disk, the reflected beam 5a may be strengthened, or weakened by the reflected beam 5b. This fact may cause noise when a variation in the reflectivity during the recording and reproducing operations of the optical disk is detected. Accordingly, if both reflected beams 5a and 5b are reduced, the overall variation of the reflectivity may be lowered. In Fig. 3, there is shown a variation in reflectivity when an optical memory is read. An amount of face vibrations produced while the optical recording medium (in this case, an optical disk) built in the optical memory was rotated within 1 rotation, was 10 µm at maximum. At this time, the variation in the reflectivity became 22% at maximum, under which normal recording and reproducing operations could not be realized. Accordingly, to achieve stable recording and reproducing operations by irradiating the laser light via the case onto the optical recording medium built in the case, the fluctuation in the reflectivity caused by the face vibration of the optical recording medium must be solved. To this end, the optical memory according to the present invention includes such a construction capable of mitigating the fluctuation in the reflectivity. Fig. 4 represents fluctuation in reflectivity when an antireflection film has is provided in the optical memory of Fig. 3. The fluctuation in the reflectivity could be suppressed below 5%, as compared with that of Fig. 3. This implies that since the antireflection films are provided with the case and optical recording medium at a side of a laser incident reflection, the reflection light 5a and 5b shown in Figs. 2a and 2b are attenuated. Precisely speaking, to attenuate the reflection light reflected from a surface of the case, which is not represented in Figs. 2a and 2b, another antireflection film may also be provided on the case surface. However, even if no such an antireflection film is provided on the case surface, there is no practical problem. In other words, according to the optical memory of the present invention, providing the antireflection films or coatings enables' the reflectivity fluctuation during the recording/reproducing operations to be mitigated even when the face vibrations of the optical recording medium may happen to occur. An information processing apparatus according to the present invention can achieve stable recording and reproducing operations by correcting the reflectivity fluctuation by a correcting circuit and the like. By the optical memory and information processing apparatus according to the present invention, the fluctuation in the reflectivity caused by the face vibrations due to movement of the optical recording medium built in the case may be mitigated, and a stable optical recording characteristic of the optical memory may be realized. In accordance within preferred embodiments, the present invention has been embodied as an optical disk which is a typical example of the optical recording medium. (Embodiment 1) Fig. 7 represents such a construction that antireflection films 2a and 2b are provided on a case and an optical recording medium. Inside the case 1 having a thickness of 2 mm and made of an acrylic resin, the antireflection film 2a made of MgF₂, having a thickness of 16 mm, was formed by a sputtering process. Furthermore, the antireflection film 2b made of CeO₂, having a thickness of 100 nm, was formed by a sputtering process on a naphthacyanine organic dye recording film 3 which has been coated on a glass substrate 4 bearing an Au reflection film 10. In accordance with this preferred embodiments, fluctuation in reflectivity was within 5% while the optical disk built in the optical memory was rotated, and the stable recording/reproducing characteristic could be achieved by utilizing a semiconductor laser having a wavelength of 830 nm. Also, as a secondary effect, near ultraviolet radiation was shielded by the case and therefore the environment resistance of the organic recording medium could be improved. It should be noted that reference numeral 5 indicates a light path and reference numeral 6 denotes a space. (Embodiment 2) In Fig. 8, there is shown a construction in which the antireflection films 2a and 2b are provided on a case and an optical recording medium. A transparent acrylic resin window 8 upon which laser light is incident was formed in a case 7 made of an opaque polystyrene resin and having a thickness of 2 mm, and then the antireflection film 2a made of MaF₂, having a thickness of 160 nm was formed by the sputtering process. The optical disk built in the optical memory was so constructed that an Au reflection film 10 having a thickness of 100 nm, a ZnS dielectric film 11 having a thickness of 70 nm, the above-described In₃SbTe₂ ternary compound recording film 12 having a thickness of 30 nm, a ZnS dielectric film having a thickness of 70 nm, and also an SiO₂ antireflection film 2b having a thickness of 140 nm were successively formed on the glass substrate 4 by way of the sputtering process. In accordance with this preferred embodiment, while rotating the optical disk built in the optical memory at a rotation speed of 3600 rpm by employing a semiconductor laser having a wavelength of 830 nm, the fluctuation in the reflectivity was within 5%, stable recording/reproducing/erasing characteristics with higher C/N could be realized, and furthermore, the overwrite could be achieved. It should be noted that reference numeral 5 indicates a light path and reference numeral 6 denotes a space. (Embodiment 3) Fig. 9 shows such a construction in which the anti-reflection films 2a and 2b are formed on a case and an optical recording medium. Inside a case 1 having a thickness of 2 mm and made of a transparent acrylic resin, the antireflection film 2a made of MgF₂, having a thickness of 160 nm was formed by the sputtering process. An optical disk built in the optical memory was so constructed that an Al dielectric film 11 having a thickness of 100 nm, a TbFeCo Magneto-optical recording film 13 having a thickness of 50 nm, an AlN dielectric film having a thickness of 100 nm, an SiO₂ antireflection film 2b having a thickenss of 140 nm were successively formed on the glass substrate 4 by the sputtering process. By using a semiconductor laser 5c having a wavelength of 830 nm, which has been linear-polarized by an analyzer, the photo-electro-magnetic disk built-in the optical memory according to this preferred embodiment is rotated a rotating speed of 3600 rpm, so that the fluctuation in the reflectivity was within 1% and the stable recording, reproducing and erasing characteristics could be realized. From these conditions, it could be recognized that the present invention also has a particular advantage in an optical memory with employment of a Magneto-optical recording disk the reflectivity of which is not directly detected. It should be noted that reference numeral 6 indicates a space. (Embodiment 4) In Fig. 10, there is shown an optical memory according to another preferred embodiment, in which an Na₃AlF₆ antireflection film 2a having a thickness of 160 nm has been formed by vacuum vapor deposition on a transparent acrylic resin window 8 which was formed at a portion of a polystyrene resin case 7 having a thickness of 2 mm. Reference numeral 14 indicates an Al layer (compact disk layer) having a thickness of 100 nm on which data have been previously recorded; reference numeral 4 indicates a glass substrate; and reference numeral 2b denotes a ZnS antireflection film having a thickness of 150 nm. When the optical disk built in this optical memory was rotated at a rotation number of 600 rpm, the stably reproduced signal with small fluctuation could be produced. It should be noted that reference numeral 5 indicates a light path and reference numeral 6 represents a space. (Embodiment 5) Figs. 11a and 11b represent a construction of an optical memory according to one preferred embodiment of the present invention, in which a card-shaped memory is built in a polystyrene resin case 7 having a thickness of 0.2 mm. Fig. 11b is a cross-sectional view taken along a line A - A' shown in Fig. 11a. As the construction of the built optical card, the constructions described in Embodiments 1 to 4 may be employed. A feature of this preferred embodiment is such that a card-shaped memory 15 is driven within the case in a translation mode 18. This translation drive may be realized by magnetically connecting a magnet hub 16 (not shown) employed therein to a drive apparatus. Laser light 5 is irradiated onto a surface of the card-shaped memory 15 via a transparent acrylic window 8 which has been formed on a portion of the case, so as to record/ reproduce data thereon/therefrom. A high speed data accessing operation may be realized by the translation movement according to this preferred embodiment. Also in this translation movement, both an MgF₂ antireflection film 2a and a CeO₂ antireflection film 2b have an effect to mitigate the reflectivity fluctuation. It should be noted that reference numeral 4 indicates a substrate; reference numeral 3 denotes a recording film; reference numeral 17 represents a recording unit; and reference numeral 19 shows a cadmium layer. (Embodiment 6) Figs. 12 to 15 represent structures of antireflection films according to preferred embodiments provided on the optical recording mediums. The antireflection film 2 was provided at an incidence side of laser light 5 for the optical recording medium. In the structure shown in Fig. 12, ZnS, ZrO₂ and TaO₅ monolayer antireflection layers represent particular advantages. Similarly, in the structure shown in Fig. 13, SiO₂/ZnS, and CeO₂/Y₂O₃ two-layer antireflection films own particular advantages. In the structure shown in Fig. 14, a ZnS/MgF₂/SiO three-layer antireflection film has a particular advantage. In a construction of a multilayer antireflection film larger than the three-layer antireflection film, as shown in Fig. 15, such a construction that a 3-layer period of ZnS/MgF₂/SiO is stacked by 10 periods represents a particular advantage. (Embodiment 7) Figs. 16 to 18 represent structures of antireflection films 2 according to preferred embodiments of the present invention, employed in the case 1. In the structure shown in Fig. 16, MgF₂, CaF₂, BaF₂, ThF₄ and LiF monolayer antireflection films own particular advantages. In the structure shown in Fig. 17, MgF₂/ZnS and CaF₂/Y₂O₃ two-layer antireflection films have particular advantages. In the structure of the multilayer antireflection film higher than the two-layer antireflection film such a construction that an LaF₂/MgF₂/SiO three-layer period is stacked by 5 periods has a particular advantage. (Embodiment 8) As represented in Embodiments 6 to 7, the structures of the antireflection films own particular effects by stacking substances each having a different refractive index. In accordance with this preferred embodiment, a mixture film is made of substances whose refractive indexes are different from each other as an antireflection film. The antireflection film to be formed on an acrylic resin case was fabricated by the vacuum vapor deposition process with employment of a vapor source by mixing ZrO₂ with MgF₂. Fig. 19 graphically represents an antireflection effect achieved by this preferred embodiment. Fig. 19(a) represents spectral reflectivity of a surface of an acrylic resin case having no antireflection film; Fig. 19(b) indicates spectral reflectivity of a case having ZrO₂ and MgF₂ two-layer antireflection films; and, Fig. 19(c) denotes spectral reflectivity of a case employing the mixed antireflection film according to this preferred embodiment. From the reflectivity characteristics shown in Fig. 19, it may be understood that the mixed antireflection film according to this preferred embodiment has the best advantages. (Embodiment 9) Figs. 20A and 20B represent application examples of the optical memory according to the present invention. As shown in Fig. 20A, this application example is constructed of a transparent card-shaped case 20 having a thickness of 0.5 mm and made of polysulfone; an optical disk 21 built therein having a diameter of 130 mm; a stainless hub 22 fixed with an external drive apparatus for rotating the optical disk 21; a laser projection window 23 made of polycarbon, for projecting the laser light so as to externally record, erase and reproduce; and a stainless sliding type shutter 24 for dust-proofing the laser projection window 23 and fixing hub 22. This card has a thickness of 1.5 mm, a lateral length of 85 mm and a transverse length of 53 mm. Fig. 20B is a sectional view, take along a line A-A' shown in Fig. 20A. As represented in this sectional view, the optical disk 22 has a space defined between the card-shaped case 20 and this disk 22. However, the optical disk 22 may be in contact with the case face during the rotation of the optical disk 22. In Fig. 21, there are shown a detailed construction of the optical disk built in the card-shaped case and also a positional relationship of this optical disk in the sectional direction. Reference numeral 20 shown in Fig. 21 indicates a card-shaped case; reference numeral 21 indicates an optical disk; reference numeral 23 represents a laser projection window; reference numerals 2a and 2b indicate an MgF₂ antireflection film having a thickness of 160 nm which has been formed on the card-shaped case and laser projection window, and another ZrO₂ antireflection film 2b having a thickness of 100 nm provided on the disk 21 in the laser projection direction, respectively, reference numeral 3 indicates an In₃SbTe₂ ternary compound recording film having a thickness of 30 nm (note that this film may be selected from not only In₃SbTe₂, but also other materials laid open in JP-A-No. 63-251290) capable of recording/erasing information by irradiating laser light therein, whereby amorphous-crystal phase change occurs; reference numeral 4 denotes a stainless circular substrate having a thickness of 0.03 mm; reference numeral 25 indicates an optical system such as an object lens for collecting the laser light 5 onto the optical disk 21; and reference numeral 6 denotes an air layer necessarily formed between the card shaped case and optical disk. In Fig. 22, there is shown fluctuation in reproduced signals (corresponding to the reflectivity of the card) derived from a mirror unit for focus-controlling the laser beam and servo-controlling the tracking operation when the optical disk employed within the card is rotated at a rotation speed 3600 rpm. As apparent from Fig. 22, it can be seen that the reflectivity fluctuation in the card according to the present invention is considerably reduced. To achieve the stable focusing and tracking operations of the laser light on the optical recording medium, it may be easily understood that the fluctuation in the reflectivity of the mirror unit is reduced as much as possible. Also, in the card according to the present invention, the recorded signal could be reproduced under condition that C/N corresponds to 50 dB. As previously stated, it could be proved that setting the antireflection films 2a and 2b must be required in the card in which the rotation type optical disk has been formed. Furthermore, as shown in Fig. 23, in accordance with the present application example, the data transfer speed can be easily improved by employing two sheets of the built-in optical disk and by over-writing the data in the parallel and simultaneous fashion, and recording/reproducing the data in the parallel form. It should be noted that reference numerals employed in Fig. 23 are the same as those employed in Fig. 20. Figs. 24A, 24B and 25 represent an information processing apparatus according to a preferred embodiment of the present invention. As described in the specification, a feature of this information processing apparatus is to employ a mechanism for mitigating the fluctuation in the reflectivity of the optical memory caused when the recording and reproducing operations are carried out. Fig. 24A represents a construction of an optical head employed in this information processing apparatus. This optical head is arranged by an object lens 25 with an actuator for focusing the laser light onto the optical recording medium and also for tracking this laser light; a 1/4 wavelength plate 27; a polarized beam splitter 28; an opto-acoustic element 29; a Foucault prism 30; a condenser lens 31; a position sensor 32; a beam shaping prism 33; a collimator lens 34; a laser diode 35; and an operational amplifier 36. When the light returned from the optical memory medium 26 is returned to the polarized beam splitter 28, an opto-acoustic voltage proportional to an amount of the returning light is outputted from the opto-acoustic element 29. This output voltage is differential-detected by the operational amplifier 36 so as to control the laser power output of the laser diode 35 via a servo loop 37. It is so designed that the reflectivity fluctuation caused from the optical memory is continuously mitigated by the servo control loop defined by 29 to 35. It should be, however, designed that the laser power control servo system is not operative during the recording and reproducing operations of the optical memory, as shown in Fig. 24B. This is because the reflectivity fluctuation during the data reproducing operation is distinguishable from the change in the reflection amount caused when the laser power is increased during the recording operation. As a consequence, as represented in Fig. 24B, the laser power control servo system is operated only when both the focusing and tracking servo systems are in an operative condition. As the opto-acoustic element, a pyroelectric substance such as PZT, LiNbO₃ and ZnO may be used. Fig. 25 shows a schematic block diagram of one arrangement of the information processing apparatus is constructed of an optical memory 38 including an optical disk 3; an optical head 39; a motor 40 for rotating the optical disk; a drive circuit 41 for driving both the optical head and motor; a processor 43 for recording the data, for processing the reproduced data, and for managing output/input of the data; input means 44 such as a keyboard; and, output means 42 such as a CRT. It should be noted that the optical memory 38 is provided within this information processing apparatus and has flexibility.

Claims: An optical memory comprising: a case (1) having an upper wall and a lower wall, said upper wall having at least a portion (8) which is transparent to light; an optical recording medium (3) movably disposed within said case (1) so as to receive light which is transmitted through said transparent portion for purpose of recording or reproducing information on or from said medium; characterized in that an antireflection film (2) is formed on at least one of a surface of said transparent portion (8), and a surface of said optical recording medium (3) which faces said upper wall of said case. An optical memory as claimed in claim 1, characterized in that said antireflection film (2) is made of a material through which light can easily pass, as compared with said case (1) and said optical recording medium (3). An optical memory as claimed in one of the preceding claims, characterized in that the light transmittance of said antireflection film (2) is higher than that of said case (1) and said optical recording medium (3). An optical memory as claimed in one of the preceding claims, characterized in that the light transmittance of said antireflection film (2) is higher than 80 %. An optical memory as claimed in one of the preceding claims, characterized in that the light transmittance of said transparent portion (8) is higher than 80 %. An optical memory as claimed in one of the preceding claims, characterized in that the said optical recording medium (3) is constructed by forming a recording layer on a substrate having light transmittance higher than 80 %. An optical memory as claimed in any one of claims 1 to 6, characterized in that an air layer is formed between said transparent portion and said optical recording medium (3), said antireflection film (2) is formed on the surface of said optical recording medium (3) which faces said upper wall of said case, and the reflectivity of the boundary plane between said optical recording medium (3) and said air layer is lower than 4 %. An information processing apparatus comprising an optical head (39); a memory which includes an optical recording medium (3) movably disposed within a case having an upper wall, a lower wall and a portion (8) in said upper wall which is transparent to the light from said optical head; means for recording information (44) on said optical recording medium by irradiating light thereon from said optical head through the transparent portion of said case; means for reproducing information (42) which has been recorded on said optical recording medium; means for erasing the information which has been recorded on said optical recording medium using light from said optical head, characterized in that an antireflection film (2) is formed on at least one of a surface of said transparent portion (8), and a surface of said optical recording medium (3) which faces said upper wall of said case. An information processing apparatus as claimed in claim 8, characterized in that the variation in reflectivity of light reflected from said optical recording medium (3) is less than 5 %. An information processing apparatus as claimed in claim 8 or 9, characterized by further comprising: a circuit for correcting a variation in light reflected from said optical recording medium (3). An information recording and reproducing method for performing at least one of information recording, reproducing and erasing operations with respect to an optical recording medium (3) rotatably disposed within a case (1) having an upper wall, a lower wall and a transparent portion disposed in said upper wall by irradiating light thereon through the transparent portion onto the recording medium (3), characterized in that light is irradiated onto said optical recording medium (3) through an antireflection film (2) formed on at least one of a surface of said transparent portion (8), and a surface of said optical recording medium (3) which faces said upper wall of said case.

Inventors: ANDOH HISASHI, IKUTA ISAO, KATO YOSHIMI, MAEDA YOSHIHITO, MINEMURA HIROYUKI, NAGAI MASAICHI, SATO YOSHIO, SUGITA TATSUYA, SUGITA YUTAKA, TSUBOI NOBUYOSHI, ANDOH, HISASHI, IKUTA, ISAO, KATO, YOSHIMI, MAEDA, YOSHIHITO, MINEMURA, HIROYUKI, NAGAI, MASAICHI, SATO, YOSHIO, SUGITA, TATSUYA, SUGITA, YUTAKA, TSUBOI, NOBUYOSHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1990
Main classification: G11B7
IPC codes: G11B11, G11B23, G11B7