JPH0346130A - Optical recording and reproducing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical recording and reproducing apparatus that uses a light beam to record, reproduce, and erase signals on an information recording carrier.

BACKGROUND OF THE INVENTION In recent years, there have been remarkable technological developments in optical memory, such as optical discs and optical cards. In this optical disk, a light beam is converged and recorded as a diffraction-limited light beam on a recording film on an information recording carrier, and the information is reproduced or erased by changing the amount of light or the attributes of the light. The same thing is possible with optical cards. Optical memories are divided into write-once types and erasable types that can be repeatedly recorded and erased, but the optical systems are considered to have almost the same configuration.

The basic structure of an optical system of a conventional optical disk, optical card, etc. will be explained with reference to FIG.

Semiconductor lasers are usually used as radiation light sources, but
This is used to make the optical system compact. Furthermore, since semiconductor lasers can be directly modulated with electric current, they are most often used as simple optical modulation light sources. The light beam emitted from the semiconductor laser 1 is made into almost parallel light by a collimator lens 2, and passes through a wedge prism 13 for light beam distribution and wavefront correction, and a beam splitter 3, and an objective lens 4 to converge the light beam. incident on . The light beam emitted from the objective lens 4 is converged to form a light spot on the information recording carrier 6. The full width at half maximum W of the light spot is expressed as W=0.53λ/NA. Here, λ is the wavelength of the light source being used, and NA is the aperture ratio of the objective lens 4. The light beam modulated by the signal element on the information record carrier is reflected, passes through the objective lens 4 again, is reflected by the beam splitter 3, and enters the optical signal detector 14. When the information recording carrier 6 rotates,
Due to surface deflection of the information recording carrier, the convergence point of the light beam exiting the objective lens 4 is the information recording 1! It becomes a different point from the top of the i-body 6, and is in a defocused state. This defocus state is detected by the optical signal detector 14 and the objective lens 4 is moved to bring the convergence point of the light beam onto the information recording carrier 6. Many methods have already been proposed for this focusing method, and for example, the method shown in US Pat. No. 4,724,533 can be used. Using the signal detected by this method, the actuator m mechanism for moving the objective lens 4 in the optical axis direction can be moved, and the information recording carrier 6 can be positioned at the focal position of the objective lens 4.

Problems to be Solved by the Invention As mentioned above, in the past, it has been common to use an actuator to focus a light beam onto an information recording carrier. In the method using this actuator, 0.1 to 0
．． In order to move an objective lens weighing about 3 grams, a coil is attached to a mover weighing several grams, and the actuator that can move the objective lens by passing a t-current through the coil weighs about 20 grams. As a result, optical disk recording and reproducing devices have become larger and heavier. Furthermore, due to the mechanical characteristics, the frequency response characteristics are low, and there is a problem in that focusing cannot be performed sufficiently for information recording FFI bodies that change rapidly.

The present invention solves the above-mentioned conventional problems, and aims to provide an optical recording/reproducing device that eliminates a mechanical focusing mechanism and can realize sufficient focusing with good response characteristics.

Means for Solving the Problems In order to solve the above problems, the optical recording and reproducing apparatus of the present invention uses a method that changes the refractive index to converge the light beam emitted from the objective lens, instead of using the mechanical actuator as described above. The first beam receives the light beam emitted from the synchrotron radiation source and focuses it on the information recording carrier.
A transparent lens plate or parallel plate is provided as a second optical means with a variable refractive index between the optical means and the information recording carrier, and between the information recording carrier and the light converging portion of the first optical means. The refractive index of the plate is changed according to an electric signal corresponding to a change in the distance of
×N is changed to change the working path M of the first optical means to the information recording carrier or the working distance along the surface of the information recording carrier.

Effects With the above configuration, it is possible to maintain a constant focusing state of the convergent beam point on the information recording carrier and at the same time correct track deviation, etc., eliminating the need for mechanical focusing and tracking actuators that require high acceleration and high frequency characteristics. Resonance in the frequency domain can be reduced, accuracy can be improved, and a compact, high-capacity optical disk system can be realized. That is, by being small, access time can be shortened, and by having a high capacity, a high transfer rate can be achieved.

Example An embodiment of the present invention will be described below based on the drawings.

FIG. 1 shows a basic configuration diagram of an optical recording/reproducing apparatus according to an embodiment of the present invention. In FIG. The beam passes through the beam splitter 3 and enters the objective lens 4. The light beam that has passed through the objective lens 4 passes through a parallel plate-like refractive index change plate 5 and enters an information recording carrier 6 . The light beam reflected by the information recording carrier 6 enters the objective lens 4 again, is reflected by the beam splitter 3, passes through the detection lens 7, and enters the photodetector 8. The electrical signal detected by the photodetector 8 is sent to a differential circuit 9,
A feedback electric signal is supplied to the refractive index change plate 5 via the drive circuit 10. For the photodetector, differential circuit, etc., conventionally well-known systems can be used. The refractive index change plate 5 changes its refractive index according to the applied voltage.
A type proportional to the applied voltage, a type proportional to the square of the applied voltage, etc. can be used. Efficiency decreases when the voltage is proportional to the third power of the applied voltage or more.

FIG. 2 is a schematic diagram showing how the focal position is changed by changing the refractive index. The permissible range of change in the refractive index is determined from the aberrations of the flat plate. The thickness T of the parallel plate of the refractive index change plate 5, the refractive index N, and the aperture ratio NA of the objective lens are Na, pj! The wavefront aberration W caused by passing through a parallel plate is expressed as follows. A certain refractive index NO and plate thickness T.

If the optical system is corrected for The range in which the refractive index can be changed under the condition that the wavefront aberration is over-corrected or under-corrected by 0.01 in an optical system corrected for 1.5 is 1.43<N<1.62. Even if the wavefront aberration changes by 0.01λ, the effect on the entire optical system is small, resulting in a sufficiently good optical system.When the refractive index of the parallel plate changes, the convergence position of the light beam exiting the objective lens changes. can be changed.If the change in refractive index is ΔN, then the amount of change in focal position ΔZ can be approximately expressed as follows.The plate thickness is 1.2 rm, and the average refractive index is 1.5.
Then, by changing the refractive index by 0.01, it is possible to change the focal position by about 5.3 μm. here,
6a shows the information recording carrier surface.

Figure 3 shows a method of scanning a light beam by changing the refractive index. In order to change the focal position as shown in Figure 2, it is necessary to change the refractive index mainly in the optical axis direction. When scanning a light beam, it is necessary to change the refractive index in a direction perpendicular to the optical axis. The refractive index changing plate 15 shown in FIG. 3 is arranged so as to change the refractive index in a direction perpendicular to the optical axis. In order to increase the scanning speed of light, it is better to make the part through which the light beam passes as small as possible. Although the cross-sectional area of the light beam is relatively large, high-speed tracking is possible by bringing the refractive index change plate 15 close to the information recording carrier 6. A method of detecting a servo signal for following a track on the information recording carrier 6 can be obtained by using a known method.

FIG. 4 shows a configuration that is a combination of those shown in FIGS. 2 and 3. In FIG. 4, the light beam reflected from the information recording carrier surface 6a is focused on a photodetector 8 by a detection lens 7,
A focus servo signal and a tracking servo signal are obtained by the circuit 16, and the first refractive index variable plate 5 and the second refractive index variable plate 15 are driven by the focus drive circuit 17 and the tracking drive circuit 18, respectively. Therefore, even if the information carrier surface 6a moves, focus servo and tracking servo that detect and correct deviations in the focal position and track position become possible. It is also possible to integrate the first refractive index change plate 5 and the second refractive index change plate 15 together.

These embodiments can of course be applied to a removable medium in which the information recording carrier has a protective film, but the information recording carrier does not have a protective film or is very thin, and the refractive index change plate can be approached to the information recording carrier. advantageous to That is, in order to change the refractive index at a fairly high speed, it is necessary to keep the voltage applied to the refractive index change plate as low as possible.

For this reason, it is desirable that the refractive index change plate be as small as possible, and the refractive index change plate can be given a little power and have a lens-like configuration. In addition, crystals, glass doped with impurities,
Ceramic materials are available, and in addition to crystal materials, liquid crystal inserted between glass plates can also be used as the refractive index change plate.

Effects of the Invention According to the present invention, compared to the conventional method in which the objective lens is mechanically driven to perform focusing servo or tracking servo, the number of mechanical parts can be significantly reduced. In addition to making the device smaller, it also enables high-speed access, which was not possible with conventional mechanical methods.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of an optical recording and reproducing device according to an embodiment of the present invention, and FIG. 2 is a schematic diagram illustrating focusing servo in the optical axis direction by a refractive index change plate of the same optical recording and reproducing device. Figure 3 is a schematic diagram explaining the tracking servo in the direction perpendicular to the optical axis using the refractive index change plate of the same optical recording/reproducing device, Figure 4 is a configuration diagram of a combination of focusing servo and tracking servo, and Figure 5 is a conventional diagram. FIG. 2 is a configuration diagram of an optical recording and reproducing apparatus that performs servo by driving an objective lens in the direction of an arrow as an example of an optical system of the method. 1... Semiconductor laser, 2... Collimator lens, 3
...beam splitter-14...objective lens,5.
15... refractive index change plate, 6... information recording carrier, 8...
...Photodetector, 9...Differential circuit, 10...Drive circuit, 17...Focus drive circuit, 18...Tracking drive circuit.

Claims (1)

[Claims] 1. A first optical means that receives a light beam emitted from a radiation light source and focuses it on an information recording carrier, and a second optical means that is located between the information recording carrier and the first optical means and has a variable refractive index. The first optical means device includes an optical means, a light converging part for condensing a light beam, a branching part for branching the light beam from the information recording carrier, and receiving the light beam branched by the branching part. , at least an optical-to-electrical converter that outputs an electrical signal corresponding to a change in the distance between the information recording carrier and the light converging section, and the second optical means includes a transparent lens plate or a parallel plate. and changes the optical path length T×N multiplied by the thickness T of the plate and the refractive index N in accordance with the electric signal, and changes the working distance of the first optical means to the information recording carrier or the surface of the information recording carrier. An optical recording/reproducing device configured to change the working distance along the .