JPH02292736A - Optical head - Google Patents

Abstract

PURPOSE:To improve reliability while increasing the degree of freedom of an adjusting position and facilitating an adjusting work by separating a converged luminous flux to two luminous fluxes close to each other, and receiving those two separated luminous fluxes at two sets of light receiving areas of a photodetector individually, respectively. CONSTITUTION:A prism 1 introduces the two luminous fluxes to the photodetector 2 after separating both the S- and P-polarized light of the luminous fluxes from a separator prism 13, and furthermore, generates astigmatism on those luminous fluxes. Therefore, each luminous flux of both the P- and S-polarized light emitted from the prism 1 is separated at a such a state where each optical axis is close in parallel, and the separated two luminous fluxes are received at the two sets of receiving areas 21 and 22 of the photodetector 2 individually, respectively. Thereby, the degree of freedom of the adjusting position can be increased, and the reliability can be improved while facilitating the adjusting work.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention is directed to separating a light beam obtained by condensing laser reflected light from a recording medium into two light beams, and receiving the separated light beams with a light-receiving element to control servo control. The present invention relates to an optical head that generates a signal, and particularly to an optical head suitable for use in a magneto-optical recording/reproducing device.

[Technical Background of the Invention and Problems Thereof] Conventionally, there is an optical head of this type as shown in FIG.

In the figure, 11 is a semiconductor laser as a laser light source;
12 is a condensing lens, l3 is a separation prism that transmits and reflects light, 14 is an objective lens, 15 is a magneto-optical disk as a recording medium, 16 is a cylindrical lens that focuses light in one direction, and 17 is a P , S, and 19 are a polarizing beam splitter that separates both polarized lights, and 19 are a first light receiving element and a second light receiving element that convert an optical signal into an electrical signal.

The laser beam from the semiconductor laser 11 is condensed by a condenser lens 12, reflected by a separation prism l3 toward an objective lens 14, condensed by the objective lens 14 to the diffraction limit, and irradiated onto a magneto-optical disk 15.

The reflected light from the magneto-optical disk 15 is made into a focused beam (a beam of light that travels to converge on one point) by the objective lens 14, passes through the separating prism 13, and is given astigmatism by the cylindrical lens 16 to become a polarized beam beam. Aimed at Britta 17. The P polarized light transmitted through the polarizing beam splitter 17 forms a spot on the light receiving surface of the first light receiving element 18, and the S polarized light reflected by the polarizing beam splitter 17 forms a spot on the light receiving surface of the first light receiving element 18.
A spot is formed on the light receiving surface of the light receiving element l9.

In the magneto-optical recording and reproducing system for this type of optical head, information signals are recorded by the magnetization direction of the perpendicular magnetic film of the disk, and the recorded signal is detected by detecting the rotation direction of the linearly polarized light of the laser beam reflected by the disk. Reproduce. In other words, the recording signal appears as a difference in the amount of light of both P and S polarizations separated by the polarization beam splitter l7, and magneto-optical reproduction is performed by the difference in the light reception output of the first light receiving element 18 and the second light receiving element 19. Signals are detected differentially.

Further, a force error signal and a tracking error signal (servo signal) are generated from the light receiving output of each light receiving element 18, 19. Note that in the above example, the focus error signal is generated by the astigmatism method.

However, in the conventional optical head as described above, the separated P and S polarized light beams are focused at a fixed position and received by two light receiving elements l8 and 19, respectively. It is necessary to adjust each light receiving element in three axial directions. Therefore, there were problems in terms of adjustment work and reliability.

Furthermore, there is a problem in that the number of parts increases and the optical head itself becomes large.

[Purpose of the invention]

The present invention makes it possible to reduce the number of parts and downsize the optical head itself in an optical head that separates and receives light beams, increases the degree of freedom in adjustment positions, and improves reliability while making adjustment work easier. The purpose is to improve

[Summary of the invention]

In an optical head that separates and receives a light beam, the present invention separates a condensed light beam into light beams that are close to each other, and each light-receiving surface is divided parallel to each other, and two sets of light-receiving devices are provided in which the dividing lines are orthogonal to each other. The regions are formed in an integrated light-receiving element, and the two separated beams of light are individually received by the two sets of light-receiving regions of the light-receiving element.

〔Example〕

FIG. 1 is a diagram showing an optical system of an optical head according to an embodiment of the present invention. Note that the same reference numerals as in FIG. 8 indicate the same elements, and the explanation thereof will be omitted.

In FIG. 1, 1 is a prism composed of two types of optical materials with different refractive indexes, 2 is a light receiving element for extracting a magneto-optical reproduction signal and a servo signal, and prism 1 is a prism composed of two types of optical materials with different refractive indexes. The P and S polarized lights are separated and two light beams are guided to the light receiving element 2, and astigmatism is generated in these light beams.

FIG. 2 is an enlarged view of the optical system including the prism 1 and the light receiving element 2.

Prism 1 has a refractive index na -t. A flat first optical member IA made of optical material s1 and a refractive index nB=1.7
It is constructed by bonding together a flat second optical member IB made of optical material No. 6, and has five working surfaces 11 to 15. 11 is an incident side transmission surface that transmits the incident light; 1
2 is a polarization separation film surface formed on the bonding surface of the optical members IA and 1B, 13 and 14 are reflective surfaces, 1s is an output side transmission surface that transmits light, and the incident side transmission surface 11 and the reflection surface 1
4. The polarization separation film surface 12 and the exit-side transmission surface 15 are formed on the same surface.

Further, each of the working surfaces 11 to 15 is set substantially parallel to each other, and the prism 1 is connected to the normal line of the incident side transmission surface 11 and the objective lens I4.
The light flux (focused light flux) incident from
1 and the optical axis L (incident surface) is inclined at 45 degrees with respect to the track direction of the magneto-optical disk 15.

The light beam focused by the objective lens 14 and transmitted through the separation prism 13 is transmitted and refracted through the incident-side transmission surface 11 and reaches the polarization separation film surface 12. At this polarization separation film surface 12, the S-polarized light (solid line) is reflected. and P-polarized light (dashed line) is transmitted. Then, the reflected S-polarized light is directed toward the reflective surface l4, and the transmitted P-polarized light is reflected by the reflective surface l3, passes through the polarization separation film surface 12 again, and is directed toward the reflective surface 14.

In this way, the thickness of the second optical member IB (polarization separation film surface 1
2 and the reflecting surface 13), the P and S polarized light beams are separated in parallel, reflected by the reflecting surface 14 in this separated state, and guided to the light-receiving element 2 from the output-side transmitting surface 15.

Further, the light beam from the objective lens 14 is a condensed light beam, and is further transmitted through the entrance side transmission surface 11 and the output side transmission surface 15 tilted with respect to the optical axis L, so that P,
Astigmatism occurs in each of the light beams separated into S-polarized light.

In this way, the P and S polarized light beams emitted from the prism 1 are separated with their respective optical axes being parallel and close to each other, so that they can be received by one light receiving element 2. Moreover, since the direction is substantially parallel to the light beam from the objective lens l4, the optical system becomes compact. Furthermore, astigmatism can be imparted without arranging a cylindrical lens or the like. In this embodiment, the refractive indexes nA, n. is set as described above, and the light focusing position on the light receiving element 2 is set.

In addition, the substantially parallel working surfaces 11 to 15 are set at approximately 55 degrees with respect to the optical axis L, but the optical axis L of each working surface 11 to 15 is
By changing the setting of the relative angle between the working surfaces and the relative angle between the working surfaces, it is possible to adjust the amount of astigmatism generated, reduce coma aberration, adjust the spacing between the spots on the light receiving element 2, or adjust the size of the prism itself. etc.

FIG. 3 is a diagram showing the light-receiving surface of the light-receiving element 2. As shown in FIG.

As shown in the figure, two light-receiving areas 21 and 22, each divided into three in parallel, are formed on the light-receiving surface facing the prism 1 side, and the light-receiving element 2 is divided into three parts in parallel. They are arranged so that the direction of arrow A coincides with the vertical direction parallel to the paper planes of FIGS. 1 and 2.

The dividing line 21 of the first light-receiving head area 210 and the dividing line 22 of the second light-receiving area 22 are orthogonal to each other, and each dividing line 21.22
is oriented at 45° with respect to the track direction. That is, as described above, since the incident surface of the incident side transmission surface 11 and the track direction are inclined at 45 degrees, the track direction with respect to the light receiving surface is in the direction of arrow B in the figure. In addition,
Each area divided into strips (a*byc*dtetf)
outputs independent signals depending on the amount of light received.

Astigmatism is generated by the prism 1 in the two light beams guided to the light receiving element 2, and the shape of the spot formed on the light receiving element 2 is as shown in FIG. When the spot diameter of the laser beam on the magneto-optical disk 15 becomes the minimum, that is, at the best focus position, a circular spot is formed in each light receiving area 21, 22 as shown in the same figure. (a) shows a spot when the objective lens 14 is near the best focus position, and in the second light-receiving area 22, an elliptical spot included in the central area e is formed, and the first light-receiving area In No. 21, an elliptical spot is formed spanning a region b at the center and regions a and c at both outer sides thereof. The same figure (C) shows the spot when the objective lens 14 is located at a far point from the best focus position, and each light receiving area 211
The direction of the elliptical spot at 22 is opposite to that at the periapsis in FIG. Now, each light reception output in the area a % f is expressed by the code of the corresponding head area, and the addition of the output signals is expressed as "
+", and subtraction is represented by ". In the first light receiving area 21, the signal obtained by }'1 = a + c-b becomes a signal as shown in FIG. 5(a) depending on the focus position, and in the second light receiving area 22, the signal obtained by F2
The signal obtained by =e− (d+f) is as shown in Figure 5 (b). These signals can be used as they are as focus error signals, but since they are asymmetrical, in this embodiment, the summed output of both signals is extracted as a focus error signal.

That is, the focus error signal (F) is F= (a
+c+e)-(b+d+f)-(1), and is symmetrical as shown in FIG. 6, and the signal level is larger than that in FIG. Further, as is clear from the above equation (1), there is a difference in the track direction, and cross-track noise with respect to the focus error signal is reduced. Furthermore, since the directions at 45 degrees with respect to the track direction are summed, the influence of disturbances due to disk polarization, etc., is reduced. Further, the tracking error signal (T) and the magneto-optical reproduction signal (R) are generated by T= (a+f) - (d+c) R= (a+b+c) = (d+e+f), and this tracking error signal has a central area. Since the received light outputs of b and e are not included, the signal has good sensitivity. Note that in a device that generates a repeat signal based on the amount of laser reflected light, the reproduced signal (R') can be generated as follows: R' = a + b + c + d + e + f. Furthermore, the sensitivity of the above-mentioned reproduced signal (R') can be increased by not including the light receiving outputs of the regions b and e in the central portion, but by setting R' = a + c + d + f. Furthermore, for the magneto-optical reproduction signal (R), by setting R=be, it is possible to eliminate the influence of unevenness in the intensity distribution at the peripheral part of the light flux caused by the birefringence of the disk, and improve the C/N. can.

In the above embodiment, the dividing line 21 of the light receiving area 21.22
．． Since the directions of 22 are orthogonal to each other,
Even if the interval between the two separated beams changes due to component errors or assembly errors, the change in the interval between the two beams can be absorbed by the degree of freedom of the light receiving area 22 in the direction of arrow A (FIG. 3). can.

In the above example, light reception? ■ Areas 21 and 22 are divided into three parts, but the central areas b and e are divided into two parts parallel to the other areas.
Reliability can be further improved by dividing the area and obtaining a push-pull tracking error signal based on the difference in the received light output of the two divided areas.

In addition, by configuring the light receiving area 2122' as shown in FIG. 7 and arranging it so that the elongated direction of the spot due to astigmatism is in the track direction and in a direction perpendicular to the track direction, the focus error signal can be transmitted to one side. The tracking error signal can be generated from the light receiving outputs of the light receiving area or both light receiving areas, and the tracking error signal can be obtained from the light receiving outputs of the areas located on both sides of the line in the track direction.

〔Effect of the invention〕

As explained above, according to the optical head of the present invention, in an optical head that separates and receives light beams, the condensed light beam is separated into light beams that are close to each other, and each light receiving surface is divided in parallel. Two sets of light-receiving areas whose dividing lines are perpendicular to each other are formed in an integrated light-receiving element, and the two separated beams are individually received by the two sets of light-receiving areas of the above-mentioned light-receiving element. The degree of freedom is increased, making adjustment work easier and improving reliability.

Furthermore, according to the embodiment, the degree of confusion of the signal is improved, and the influence of disturbances is reduced.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the optical system of the optical head according to the embodiment of the present invention, Fig. 2 is a partially enlarged view of Fig. 1, Fig. 3 is a diagram showing the light receiving surface of the light receiving element in the embodiment, and Fig. 4. 5 is a diagram showing an example of a signal obtained from the light receiving area in the example. FIG. 6 is a diagram showing a focus error signal in the example. Fig. 7 is a diagram showing another example of the light receiving surface in the embodiment, and Fig. 8 is a diagram showing an example of a conventional optical head.
- Prism, 2... Light receiving element, 21*22... Light receiving area, 21.22... Division line. Figure 4 Figure 4 (0》 (b) Figure 4

Claims (2)

[Claims] (1) In an optical head that separates a light beam condensing laser reflected light from a recording medium into two light beams, and receives the separated light beams with a light receiving element to generate a servo signal, the above-mentioned light focusing a light-receiving element that has two sets of parallel-divided light-receiving areas, with dividing lines of the light-receiving areas perpendicular to each other; An optical head characterized in that the two light beams separated by the separating means are individually received by two sets of light receiving areas of the light receiving element. (2) The two light beams have astigmatism in the same shape and direction,
Each light-receiving area of the light-receiving element is divided into at least three parallel areas, a central part and both sides thereof, and the spot at the time of astigmatism of 1 is defined by the dividing line of one of the light-receiving areas. Light is received in the central area of the light receiving area parallel to the area, and the sum of the light receiving outputs of the central area of one light receiving area and the outside area of the other light receiving area, and the light receiving output of all other areas. 2. The optical head according to claim 1, wherein the focus servo signal is generated based on the difference between the sum and the sum.