OPTICAL DATA STORAGE ACCESSING APPARATUS

Abstract: An optical data storage accessing apparatus which in­ cludes a first light projecting unit (A1) including a laser diode (1) for projecting data recording light (L1) onto a data storage medium (10), a second light projecting unit (A2) for projecting data reading light (L2) onto the data storage medium (10), and a light receiving unit (B). The light receiving unit (B) receives the data reading light (L2) after it is reflected by the data storage medium (10) to read data recorded on the data storage medium. An optical unit (3) joins the data recording light (L1) and the data reading light (L2) and separates data reading light reflected from the data storage medium (10) from the data recording light (L1).

Description: This invention relates to an optical data storage accessing apparatus which employs a head for reading or writing data on an optical data storage medium, and more particularly, to an improved optical data storage accessing apparatus which employs two optical systems, one for data recording and the other for data reading. An optical card accessing apparatus which employs a laser diode for data recording and a light emitting diode (LED) for data reading is well known. Data recording light (hereinafter referred to as recording light) which is linearly polarized and emitted from the laser diode of a recording optical system is collimated by a collimating lens. Data reading light (hereinafter referred to as reading light) emitted from the LED of a reading optical system is collimated by another collimating lens. The recording and reading light are projected through a polarization beam splitter. The polarization direction of the recording light is set such that all of the recording light propagates through the polarization beam splitter. About fifty percent of the reading light emitted from the LED joins the recording light in the polarization beam splitter and reflects off the splitter. The joined recording and reading light propagate through a non-polarization beam splitter and further through a condenser lens to reach the optical card. The nonpolarization beam splitter is used to separate the reading light reflected by the optical card from the recording light. The recording light forms a first light spot SP₁ for data recording on a data storage area of the optical card. The reading light forms a second light spot SP₂ for data reading, which follows the first optical spot on the data storage area. In this apparatus, the optical card is moved in a given direction relative to the optical head and data (a data unit is called a pit) are thermally irreversibly recorded on the data storage area using the first light spot SP₁. After the data recording operation, the second light spot SP₂ is projected onto the data storage area. A light receiving system, which includes a condenser lens and a light detector, receives the reading light reflected by the data storage area to check for pits or to detect pit lengths. Thus, the data recording and monitoring of the data can be done during a one-directional movement of the card. The data are sometimes incorrectly recorded because a laser diode for the recording operaiton often deteriorates with time or due to changes of temperature, and the data storage area of the card often collects dust. An apparatus with two optical systems can quickly check for incorrect data because the apparatus monitors the recorded data immediately after the recording. The first light spot SP₁ for data recording is required to have at least a predetermined energy density to form thermally irreversible pits on the data storage area of the optical card. In the conventional systems, however, the energy density of the first light spot SP₁ often becomes lower than the predetermined density because only about fifty percent of the recording light can pass through the nonpolarization beam splitter. Consequently, the data are often incorrectly recorded. If a second polarization beam splitter is used instead of a nonpolarization beam splitter, the energy density of the recording light is increased. In this case, however, since about fifty percent of the reading light is reflected by the first polarization beam splitter and almost all of the remaining reading light is further reflected by the second splitter, almost all of the reading light is hindered from reaching the optical card. Therefore, no data can be read. Thus, use of a nonpolarization beam splitter for separating the reflected reading light lowers the recording efficiency. Moreover, a laser diode with higher power is required to offset the lowered recording efficiency. However, since the price of a laser diode exponentially increases as the rated power thereof increases, the cost of the apparatus dramatically increases even with only a slight increase in the power of the laser diode. An optical data storage according apparatus according to the preamble of claim 1 is known from JP-A-60-224131. In this known apparatus the beam of data reading light reflected from the data storage medium leaves the optical means coaxially with the beam of data reading light impinging on the optical means. The invention is as claimed in claim 1. The objects, advantages and features of this invention will be more fully understood when considered in conjunction with the following figures, of which: Fig. 1 is a side view of an optical data storage accessing apparatus; Fig. 2 is a side view of a first embodiment of the invention; Fig. 3 is a side view of a second embodiment of the invention; Fig. 4 is a view taken along a line IV-IV in Fig. 3; and Fig. 5 is a perspective view of Fig. 3. Detailed Description of the Invention Prior art which is depicted by Fig. 1 shows an optical data storage accessing apparatus. This apparatus has a first light projecting system A₁ for projecting recording light L₁ on a data storage medium 10 to record data thereon, a second light projecting system A₂ for projecting reading light L₂ onto medium 10, and a light receiving system B for receiving the light reflected by medium 10. The first light projecting system A₁ uses a laser diode 1 as its light source. Recording light L₁ emitted from laser diode 1 is collimated by a collimating lens 2 and propagated through a polarization beam splitter 3. The recording light L₁ is condensed by a condenser lens 4 to project a first light spot SP₁ with a diameter of about 1 micron on medium 10. Light spot SP₁ is used to form thermally irreversible pits on medium 10. The reflectivity of a pit is lower than that of the surrounding area. Second light projecting system A₂ uses an LED 5 as its light source. Reading light L₂ emitted from LED 5 is collimated by a collimating lens 6 and propagated through a nonpolarization beam splitter 7. Reading light L₂ further enters beam splitter 3. Beam splitter 3 is used not only to join the recording light L₁ and reading light L₂ but to separate reflected reading light L₃ from recording light L₁. Reading light L₂ reflected by the beam splitter 3 is condensed by condenser lens 4 to project a second light spot SP₂ with a diameter on the order of dozens of microns onto medium 10. Second light spot SP₂ is projected immediately after the projection of first light spot SP₁. Second light spot SP₂ is used to check for pits or to detect pit lengths for identifying the contents of recorded data. Reflected reading light L₃ from medium 10 propagates through lens 4 and is sequentially reflected by polarizatrion beam splitter 3 and nonpolarization beam splitter 7. Reading light L₃, reflected by beam splitter 7, is condensed by a condenser lens 8. Condensed light L₃ is received by a light detector 9 to check for pits or to detect pit lengths for identifying the contents of recorded data. Fig. 2 shows an optical data storage accessing apparatus according to a first embodiment of the invention. Reading light L₂ emitted form LED 5 is collimated by collimating lens 6 and reflected by polarization beam splitter 3 toward condenser lens 4. Then, light L₃ is condensed by condenser lens 4 to project a light spot onto medium 10. As shown in Fig. 2, reflected reading light L₃ propagates through a path different from the path at the time of the projection, because the optical axis of reflected light L₃ deviates from that of reading light L₂. Light L₃ is further reflected by beam splitter 3 toward a reflecting mirror 11. Light L₃ reflected by reflecting mirror 11 is condensed by condenser lens 8 and received by the light detector 9. In this first embodiment, since reflecting mirror 11 is used instead of a nonpolarization beam splitter 7, the reading efficiency of reading light L₂ is about twice as high as that of reading light L₂ according to the apparatus described above and a second embodiment described below. In addition, the cost of the apparatus can be reduced because a mirror like mirror 11 is inexpensive. The other elements of the Fig. 2 embodiment are the same as those of the Fig. 1 apparatus so that description thereof is omitted with respect to Fig. 2. Figs. 3-5 show an optical data storage accessing apparatus according to a second embodiment of the invention. In the apparatuses described above, first light projecting system A₁ and light receiving system B are disposed perpendicularly to the surface of medium 10. In the Figs. 3-5 embodiment, however, light receiving system B is disposed parallel to the surface of medium 10. Therefore, the apparatus can be made thinner.

Claims: An optical data storage accessing apparatus for optically reading and recording data on a data storage medium (10) which is moved relative to said apparatus, said apparatus comprising: first light projecting means including a laser diode (1)for projecting data recording light onto said data storage medium (10); second light projecting means for projecting data reading light onto said data storage medium (10); light receiving means (9) for receiving said data reading light after it is reflected by said data storage medium to read data recorded on said data storage medium; and an optical means (3) for joining said data recording light and said data reading light and for separating data reading light reflected from said data storage medium from said data recording light, characterized in that the axis of the beam of data reading light impinging on said optical means (3) is offset with respect to the axis of the beam of reflected data reading light emanating from said optical means (3) after separation from said data recording light. An optical data storage accessing apparatus according to claim 1, characterized by comprising a mirror (11) disposed in the path of the beam of data reading light reflected from said data storage medium (10) and emanating from said optical means, for fully reflecting said beam into said light receiving means (9). An optical data storage accessing apparatus according to claim 1 or 2, characterized by a condenser lens (4) disposed between said optical means (3) and said recording medium (10) such that the optical axis of said condenser lens (4) is offset with respect to the axis the beam of data reading light has when impinging on said condenser lens (4) after passing said optical means (3). An optical data storage accessing apparatus according to anyone of claims 1 to 3, characterized by said second light projecting means including a light emitting diode (5).

Inventors: TSUBOI, KAZUO C/O OMRON TATEISI ELECTRONICS CO., YODA, SHIGERU C/O OMRON TATEISI ELECTRONICS CO.
Applicants: OMRON TATEISI ELECTRONICS CO.
Application year: 1987
Main classification: G11B7
IPC codes: G11B7