JPS6319944Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to an optical information recording and reproducing apparatus that can reproduce signals recorded on a signal recording medium such as a disk or additionally record a desired signal using one light source.

Recently, optical audio discs that optically record and reproduce audio signals and optical video discs that optically record and reproduce video signals along with audio signals have been introduced.
2. Description of the Related Art Devices for optically recording and reproducing signals on information recording media such as disks are being actively developed.

By the way, optical discs have various advantages, one of which is that new information can be additionally recorded in addition to the information already recorded on the disc. In this case, the new information must be recorded so as to maintain a constant interval with respect to the signal tracks already recorded on the disk as the signal recording medium. However, considering that the eccentricity of an optical disk is usually several tens of micrometers and the track pitch is several micrometers, the signal track to be newly added overlaps the already recorded signal track, making it difficult to record and reproduce accurately. This is because there is a risk that it may not be possible.

To solve this problem, a tracking beam is emitted in addition to the recording beam during recording, and the recording beam is used to record while tracking the signal track that has already been recorded or the pre-recorded tracking track (pre-group). Optical information recording and reproducing devices are being proposed. That is, as shown in FIG. 1 and FIG.
The light beam emitted from one light source 53 is separated into two light beams, a tracking light beam 54 and a recording light beam 55. However, this conventional mirror 52 not only has a complicated structure, but also requires accurate determination of the incident position 51A from the light source 53 onto the half mirror portion 51. For this reason, a diffused light source such as a semiconductor laser cannot be used. In addition, this structure uses one mirror 52 to function as a tracking mirror that corrects the optical path of the incident light or reflected light from the light source 53 in the tracking direction (that is, in the left-right direction with respect to the traveling direction of the disk). is almost impossible. Moreover, the reflectance of the half mirror section 51 must be made precise so as to prevent additional recording or re-recording of signals on the disk by the tracking beam. Moreover, the amount of recording light from the light source is reduced by the reflectance of the half mirror portion 51, and a light source with higher power is required accordingly.

The present invention was developed in view of the above points, and its purpose is to divide the light beam from one light source into a recording/reproducing light beam and a tracking light beam for track following using a simple configuration. To provide an optical information recording/reproducing device capable of recording desired information on recording tracks by separating the information by quantity and maintaining accurate track intervals.

A first embodiment of the present invention will be described below with reference to FIGS. 3 to 8.

Reference numeral 1 denotes a light source, and as the light source 1, in addition to using a diffused light source such as a semiconductor laser, a single light source such as a gas laser such as a He-Ne laser, or not only a light source that emits light rays can be used.

Reference numeral 2 denotes a collimator lens for sending a light ray I from the light source 1 to the rear optical system as a parallel light ray B. Reference numeral 3 denotes an optical means constituting this embodiment, which is configured by joining a wedge prism 5 with a refractive index n and an apex angle α to the side of a beam splitter 4 on the light source 1 side, which is made up of two prisms 4A and 4B joined together. Parallel light ray B from the light source 1 incident through the collimator lens 2 is divided into a first light ray 6 which is refracted at a constant refraction angle θ with respect to an axis X' parallel to the optical axis X by passing through the central wedge prism 5 and is used for track following, and a second light ray 7 which passes through the beam splitter 4 without passing through the wedge prism 5 and is used for tracking the disk.
A second light beam 8 is provided for recording and reproducing signals to the
and are separated into

The radius r of the wedge prism 5 is selected such that the ratio r/R to the pupil radius R of the objective lens 10 described later is approximately 0.3<r/R<0.6. When 0.3≧r/R, this is the NA of the first ray 6 that passed through the objective lens 10.
(opening degree) is too small. Further, when 0.6≦r/R, the shielding effect of the wedge prism 5 on the beam splitter 4 is too large, and the diffraction ring becomes too strong.

Reference numeral 9 represents a quarter-wave plate that causes a phase change in the incident light from the beam splitter 4 and the reflected light from the disk 7, which will be described later, and 10 represents an objective lens.
Reference numerals 15 and 16 denote two light receiving elements provided through a lens 17 at corresponding positions of the optical means 3, above or below the optical axis X, and one of these light receiving elements 15 is divided into two parts. The other light-receiving element 16 is for receiving the first light beam 6 for tracking the pit 12 formed on the disk 7, and the other light-receiving element 16 is for reproducing the signal recorded on the disk 7 or
This is for receiving the second light beam 8 for recording information.

One embodiment of the present invention has the above-described configuration, and when the light emitted from the light source 1 passes through the collimator lens 2, it becomes a parallel beam of light. Of the parallel rays B, the light that has passed through the wedge prism 5 of the optical means 3 remains a parallel ray with a parallel axis parallel to the optical axis X, as shown in FIG.
The first beam is refracted by a constant refraction angle θ with respect to
It becomes ray 6. This refraction angle θ is the apex angle α of the wedge prism 5 and its refractive index n, and θ≒α(n−
It is determined by the relationship 1). On the other hand, the peripheral parallel rays that do not pass through the wedge prism 5 are beam splitter 4.
Even after passing through, the second light ray 8 remains parallel to the optical axis X, and is separated from the first light ray 6.

Both the first light beam 6 and the second light beam 8 pass through a quarter-wave plate 9 to have their phases changed by 1/4 wavelength, and then pass through an objective lens 10 so that they are printed on the disk 7 at regular intervals. The light is focused at a constant angle of displacement, and individual spots A and B are irradiated onto the disk 7 as shown in FIG. and the first
Spot A of ray 6 is located on disk 7 as described later.
Spot B of the second light beam 8 is used for reproducing or recording pits 12 already recorded on the disk 7. In this case, if the deviation amount P of spot A and spot B is the focal length of the objective lens 10, then
Since the first light ray 6 is refracted by the refraction angle θ with respect to the X' axis parallel to the optical axis X, P=
tanθ...the formula () is obtained. Further, when the pickup rotates about the optical axis X, the respective spots A and B of the first light beam 6 and the second light beam
The angle β between the line H connecting the center of the spot B of the second light ray 8 and the line segment H' extending in the radial direction through the center of the spot B of the second light ray 8 also rotates in the same way.

Therefore, there are pits 12 for reproducing already recorded signals and pits 12' for recording new information.
The track pitch T _P of the wedge prism 5 can be arbitrarily determined by T _P =tan{α-(n-1)}·cosβ...(), if the apex angle α and the wedge angle β of the wedge prism 5 are known.

Spot A of the first light ray 6 refracted by the wedge prism 5 and spot B of the second light ray 8 that does not pass through the wedge prism 5 are each located on the disk 7.
The respective reflected lights pass through the objective lens 10 again, have their phases changed by the quarter-wave plate 9, and are then separated from the incident light by the beam splitter 4 and reflected. Then, the reflected light is focused by a lens 17 provided at a corresponding position of the optical means 3, and the light receiving element 15,
The light beams are individually received by the light beams 16 and converted into electrical signals according to the modulation rate of the light irradiated onto the disk 7 .

In this way, the spot A of the first ray 6 hits the pit 12.
While following the track (or a pre-group recorded in advance for tracking during recording), the pit 12 recorded on the disk 7 is played back with a constant track pitch T _P at spot B of the second beam 8. or record the pit 12' as new information on the disk 7. Of course, during reproduction, at least the energy of spot B is reduced by, for example, reducing the power of the light source 1 compared to during recording.

The first light ray 6 for tracking is refracted by the wedge prism 5 and passes only a part of the way around the optical axis X of the objective lens 10, so the NA is
(opening degree) is small and the cutoff frequency is low. Therefore, the spot A on the disk 7 is expanded and the energy density is lowered, so it is suitable for use for tracking purposes.

On the other hand, the spot B of the second light beam 8, which has passed through the beam splitters 4A and 4B without passing through the wedge prism 5, is sandwiched in shape and has sufficient energy density, so it can be used as a light beam for reproduction or recording. Can be used as a light beam.

FIG. 8 is a graph showing calculated values of the energy intensity I _P of the first light ray 6 that passes through the wedge prism 5 and the energy intensity of the second light ray 8 in the periphery that does not pass through the wedge prism 5.

In this case, the vertical axis shows the intensity I when the center intensity of the optical axis X is set to 1, and the horizontal axis shows the distance from the optical axis X.

The calculation formula is I _(uv) = |A _(uv) | ² |∫∫ _x ² _+y ² <1 _(xy)・exp(−2πλ(ux+vy))dxdy| ² ...(). Here, u, v are infinite coordinates showing the image plane coordinates in diffraction units (λ/NA),
x, y are dimensionless coordinates normalized with the pupil radius of the objective lens 10 as 1, _(xy) is a pupil function consisting of the lens aberration of the objective lens 10 and the amplitude distribution of the beam of the light source 1, and A _{(uv )} indicates the amplitude distribution at the coordinates (u, v), and I _(uv) indicates the intensity distribution. Moreover, in order to simplify calculations, the lens is aberration-free, the laser beam is uniformly distributed, and the ratio r/R of the radius R of the objective lens 10 and the radius r of the wedge prism 5 is set to 0.5. In other words, pupil function (R) = 0 (R < 0.5), 1 (0.5≦R≦1), 0 (1
<R).

As can be seen from FIG. 8, the first light ray 6 that passes through the wedge prism 5 has a low energy density and is suitable for tracking, while the peripheral second light ray 8 that does not pass through the wedge prism 5 has a high energy density and is suitable for tracking. It can be seen that it is suitable for use or reproduction.

Next, other embodiments of the present invention will be described with reference to FIGS. 9 to 12.

In this embodiment, the MTF of the pickup during reproduction is increased by forming an insensitive member 18 with a radius r' or a shield at the center of the light receiving element 16 that receives the second light beam 8 for recording and reproduction.
(Modulation Transfer Function) can be improved. In this case, when the radius of the beam on the light receiving element 16 at the time of in-focus is R', r/R=r'/R' for the ratio of the pupil radius R of the objective lens 10 and the radius r of the wedge prism 5. Form to maintain relationships. In this case, the far field pattern of the light reflected by the disk 7
Pattern) is a _(xyt) = ∫∫∞A _(uv)・R _(uvt)・e
xp
(2πi(ux+vy))dudy...It can be found from formula (). In the above equation (), R _(uvt) is the complex reflectance of the spot irradiation position on the disk 7 at time t.

Then, the intensity i(t) of the reflected light from the disk 7
is i(t)=∫∫g _(xy) ｜a _(xyt) ｜ ² dx・dy……(
)
It can be calculated from

In this case, g _(xy) is the sensitivity distribution of the light receiving element 16,
Again, in order to simplify the calculation, the complex reflectance R _(uv) of the pit depth λ/4 and the part without pits is
=1, complex reflectance R _(uv) of the part with pits =-
1, and if the shape of the pit 12 is rectangular as shown in Fig. 10, then the width P' of the pit 12 is
The MTF when set to 0.3μm or 0.4μm is the 11th
and FIG. 12, respectively.

In FIGS. 11 and 12, the horizontal axis S indicates the normalized spatial frequency expressed as S=(diffraction unit)/2d, where d is the pit length, and in addition, in the conventional usage state where the wedge prism S is not used, It is normalized to the value of S=0.

A shows the MTF characteristics in a conventional usage state without using the wedge prism 5 and the insensitive body 18;
B shows the sensitivity distribution of the light receiving element 16 when the wedge prism 5 is used and the light receiving element 16 is provided with an insensitive body 18.
The MTF characteristics of this second embodiment when g _(xy) is 0 (r'<0.5) and 1 (r'>0.5), and C is the insensitive body 1
When the sensitivity distribution g _(xy) of the light receiving element 16 is set to 1 and the wedge prism 5 is used without providing the prism 8 (in the first embodiment)
D shows the MTF characteristics of each of the first light beams 6 for tracking.

From FIG. 11 and FIG. 12, the second
The insensitive body 1 is attached to the light receiving element 16 for receiving the light beam 8.
It can be seen that the MTF is improved when 8 or a light shield is provided.

As mentioned above, the present invention can separate the light beam from one light source into the recording/reproducing light beam and the tracking light beam for track following on the information recording medium by a certain amount of displacement, so the track spacing can be accurately determined. desired information can be recorded on the recording track while maintaining the In addition, the simple structure of simply joining a wedge prism to the light source side of a beam splitter that forms part of a conventional optical system allows the tracking light beam and the recording or reproducing light beam to be separated without major design changes. Light rays can be separated without requiring precise setting of the incident position and reflection position as in conventional half mirrors. Therefore, materials and costs are low, and a diffused light source such as a semiconductor laser can be used as the light source. In addition, unlike conventional half mirrors, there is no need to take precautions such as making the reflectance precise to prevent recording during playback, so recording can be performed without using a high-power light source, and MTF during playback This can contribute to the miniaturization of the device.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing an example of a polarizer of a conventional optical information recording/reproducing device, Figure 2 is a front view, and Figure 3 is a front view.
The figure is a cross-sectional view showing one embodiment of the optical information recording/reproducing device of the present invention, FIG. 4 is a cross-sectional view showing an example of optical means constituting this embodiment, and FIG. FIG. 6 is a plan view showing an example of the light receiving element constituting this embodiment, and FIG. 7 is a front view showing the radius ratio of the wedge-shaped prism and the objective lens. FIG. 8 is a plan view showing the state in which the disk is irradiated with the beam spot of the light ray; FIG.
The figure is a plan view showing an example of a light receiving element in another embodiment of the present invention, FIG. 10 is a plan view showing the pit shape of the disk, and FIG. 11 is a plan view showing the pit width.
Figure 12 is a graph comparing the MTF characteristics when the pit width is 0.3 μm.
A graph comparing TF characteristics is shown. DESCRIPTION OF SYMBOLS 1... Light source, 3... Optical means, 4... Beam splitter, 5... Wedge prism, 6... First light ray, 7... Disc, 8... Second light ray, 10...
Objective lens, 12, 12'... Pit, 18...
Insensitive body, 19...Sensitive body, A, B...Spot, 1
5, 16... Light receiving element, R... Radius of objective lens 10, r... Radius of wedge prism 5, R'... Radius of sensitive body 19, r'... Radius of insensitive body 18.

Claims (1)

[Claims for Utility Model Registration] (1) In an optical information recording and reproducing device that optically records and reproduces predetermined signal information on a recording medium such as a disk using a single light source, the light beam from the light source is separating into a first light beam around the optical axis and a second light beam around the optical axis using optical means, and receiving the first light beam by a first light receiving element for tracking a track recorded on the recording medium; An optical recording and reproducing method characterized in that the second light beam is focused at a position a certain distance away from the spot of the first light beam and is received by a second light receiving element for recording and reproducing signals on the recording medium. Device. (2) The optical information recording and reproducing apparatus according to claim 1, wherein the optical means is formed by joining a wedge prism to the light source side of a beam splitter. (3) Optical information according to claim 1 or 2 of the utility model registration claim, characterized in that the central part of the light receiver of the second light receiving element is shielded or the central part is made into a dead zone. Recording and playback device.