Optical data storage accessing apparatus
This application is a continuation of application Ser. No. 572,345 filed Aug. 27, 1990, abandoned, which is a continuation of application Ser. No. 344, 460 filed Apr. 28, 1989, abandoned, which is a continuation of application Ser. No. 094,745 filed Sep. 9, 1987, abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     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. 
     2. Discussion of the Related Art 
     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 SP 1  for data recording on a data storage area of the optical card. The reading light forms a second light spot SP 2  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 SP 1 . After the data recording operation, the second light spot SP 2  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 operation 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 SP 1  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 SP 1  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. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of this invention to provide an optical data storage accessing apparatus which has high recording efficiency. 
     It is another object of this invention to provide an optical data storage accessing apparatus which employs a laser diode with low power so as to reduce dramatically the cost thereof. 
     According to this invention, there is provided an optical data storage accessing apparatus for optically reading or recording data on a data storage medium which is moved relative to the apparatus. The apparatus includes (1) a first light projecting means including a laser diode for projecting data recording light onto a data storage medium, (2) a second light projecting means for projecting data reading light onto the data storage medium, (3) a light receiving means for receiving the data reading light reflected by the data storage medium to read data recorded thereon, and (4) an optical member for mixing the data recording and reading light and for separating the reflected data reading light from the data recording light. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other 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 a first embodiment of the invention; 
     FIG. 2 is a side view of a second embodiment of the invention; 
     FIG. 3 is a side view of a third 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 
     FIG. 1 shows an optical data storage accessing apparatus according to a first embodiment of the invention. This apparatus has a first light projecting system A 1  for projecting recording light L 1  on a data storage medium 10 to record data thereon, a second light projecting system A 2  for projecting reading light L 2  onto medium 10, and a light receiving system B for receiving the light reflected by medium 10. 
     The first light projecting system A 1  uses a laser diode 1 as its light source. Recording light L 1  emitted from laser diode 1 is collimated by a collimating lens 2 and propagated through a polarization beam splitter 3. The recording light L 1  is condensed by a condenser lens 4 to project a first light spot SP 1  with a diameter of about 1 micron on medium 10. Light spot SP 1  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 A 2  uses an LED 5 as its light source. Reading light L 2  emitted from LED 5 is collimated by a collimating lens 6 and propagated through a nonpolarization beam splitter 7 which separates the amplitude of light L 2  into two beams based on a difference in refractive indices. This type of beam splitter is exemplified by the conventional half mirror shown in FIG. 1 and will be referred to herein as a non-polarization, refractive beam splitter. Reading light L 2  further enters beam splitter 3. Beam splitter 3 is used not only to join the recording light L 1  and reading light L 2  but to separate reflected reading light L 3  from recording light L 1 . 
     Reading light L 2  reflected by the beam splitter 3 is condensed by condenser lens 4 to project a second light spot SP 2  with a diameter on the order of dozens of microns onto medium 10. Second light spot SP 2  is projected immediately after the projection of first light spot SP 1 . Second light spot SP 2  is used to check for pits or to detect pit lengths for identifying the contents of recorded data. 
     Reflected reading light L 3  from medium 10 propagates through lens 4 and is sequentially reflected by polarization beam splitter 3 and nonpolarization beam splitter 7. Reading light L 3 , reflected by beam splitter 7, is condensed by a condenser lens 8. Condensed light L 3  is received by a light detector 9 to check for pits or to detect pit lengths for identifying the contents of recorded data. 
     In this embodiment, since recording light L 1  does not propagate through nonpolarization beam splitter 7, the recording efficiency of light projecting system A 1  is about twice as high as in conventional systems. Therefore, the cost of the apparatus according to this invention is dramatically reduced because a low-power laser diode can be used for the recording operation. 
     FIG. 2 shows an optical data storage accessing apparatus according to a second embodiment of the invention. Reading light L 2  emitted form LED 5 is collimated by collimating lens 6 and reflected by polarization beam splitter 3 toward condenser lens 4. Then, light L 3  is condensed by condenser lens 4 to project a light spot onto medium 10. As shown in FIG. 2, reflected reading light L 3  propagates through a path different from the path at the time of the projection, because the optical axis of reflected light L 3  deviates from that of reading light L 2 . Light L 3  is further reflected by beam splitter 3 toward a reflecting mirror 11. Light L 3  reflected by reflecting mirror 11 is condensed by condenser lens 8 and received by the light detector 9. 
     In this second embodiment, since reflecting mirror 11 is used instead of a nonpolarization beam splitter 7, the reading efficiency of reading light L 2  is about twice as high as that of reading light L 2  according to the first embodiment and a third embodiment described below. In addition, the cost of the apparatus can be reduced because 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 the third embodiment of the invention. In the first and second embodiments, first light projecting system A 1  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. Although in this embodiment the paths for reading light L 2  and for reflected reading light L 3  are different from each other between beam splitters 3 and 7, the apparatus may be constructed such that light L 2  and light L 3  propagate through the same path. 
     In all the embodiments of FIGS. 1 to 5, like numerals designate like or corresponding components. The above description and the accompanying drawings are merely illustrative of the application of the principles of the present invention and are not limiting. Numerous other arrangements which employ the principles of the invention and which fall within its spirit and scope may be readily devised by those skilled in the art. Accordingly, the invention is not limited by the foregoing description, but is only limited by the scope of the appended claims.