JP2744448B2 - Optical information recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording / reproducing information using an optical information recording medium.

2. Description of the Related Art Conventionally, as an optical information recording / reproducing apparatus using a diffraction grating (grating), there is a first conventional example disclosed in JP-A-61-230634.
That is, as shown in FIG. 6, the laser light emitted from the semiconductor laser 1 is collimated by the collimator lens 2,
The light enters the polarization beam splitter 3. In this case, the polarization direction of the incident light is set to be in a state parallel to the groove of the polarization beam splitter 3, so that the light is diffracted and enters the quarter-wave plate 4 to become a circularly polarized wave. The light is condensed and applied to an optical disk 6 as an optical information recording medium, whereby information is recorded. In addition, the optical disk 6
The reflected light is converted into a linearly polarized wave by the 波長 wavelength plate 4, thereby transmitting through the polarization beam splitter 3, guided to the optical information detection optical system 7 and incident on the critical angle diffraction grating 8. Here, the incident light undergoes two critical angle diffractions and total reflection to form a diffracted light and is incident on the light receiving element 9 divided into four parts. The detection of a spill error signal and the detection of a track error signal are performed.

As a second conventional example, as shown in FIG. 7, there is one using a dual grating 10. That is, the light emitted from the semiconductor laser 11 is
After being collimated, the light is reflected by the beam splitter 14 via the two shaping prisms 13 and condensed by the objective lens 15 to irradiate the magneto-optical disk 16, whereby information is recorded. The reflected light from the magneto-optical disk 16 passes through the beam splitter 14 and is guided to the optical information detection optical system 17, where it is collected by the condenser lens 18 and formed on the front and back surfaces of the dual grating 10 respectively. Is transmitted or diffracted. Of these, the zero-order light T that has passed through and travels straight as it is is guided to the four-divided light receiving element 20, and the diffracted first-order light K is guided to the two-divided light receiving element 21. The magneto-optical signal is detected based on the difference in light amount between the 0th-order light T and the 1st-order light K, the focus error signal is detected by the astigmatism method using the 0th-order light T, and the track error signal is detected by the 1st-order light. It is detected by the push-pull method using light K.

Problems to be Solved by the Invention First, in the first conventional example, a write-once optical disc and a CD
However, it cannot be applied to signal detection of magneto-optical disks, and the conventional configuration solves the problem that the diffraction angle fluctuates according to the wavelength fluctuation accompanying the grating. Can not do it. Further, in the second conventional example, the accuracy of the beam interval between the 0th-order light and the 1st-order light transmitted and diffracted through the dual grating is poor, so that the spot position is likely to shift, and as a result, an error is likely to occur in signal detection. That is, the arrangement of the optical information signal detector must be performed with strict dimensional accuracy.

Means for Solving the Problems A laser beam emitted from a semiconductor laser is irradiated on an optical information recording medium to record information, and reflected light from the optical information recording medium is condensed by a condensing lens to generate light. In an optical information recording / reproducing apparatus for guiding information to an information detection optical system and reproducing information, and detecting a track error signal and a focus error signal, an optical information recording / reproducing apparatus is provided on an optical path of light reflected by the optical information recording medium and condensed by the condenser lens. A dual grating in which a first diffraction grating having an equal pitch linear shape is formed on one surface, and a concentric second diffraction grating having a different pitch is formed on a surface opposite to this surface, Due to this dual grating, at least three divided first light receiving elements arranged on the optical path of the primary light diffracted and traveling are arranged on the optical path of the zero-order light traveling straight without being diffracted. And an optical information signal detector having at least three divided second light receiving elements.

The concentrating pitch of one of the diffraction gratings formed on both surfaces of the dual grating is made different from that of the concentric pitch so that the zeroth-order light and the first-order light can be obtained. Can be widened in the direction of the optical axis, and the optical information recording / reproducing device can be easily arranged.

Embodiment A basic structure of an embodiment of the present invention will be described with reference to FIGS. 1 to 4 (a), (b) and (c). Here, only the optical information detection optical system according to the present invention will be described.

The dual grating 22 has a parallel plate shape, and a first diffraction grating 24 having a straight line of equal pitch is formed on a surface on the side located on the condenser lens 23, and a similar surface is formed on a surface on the side opposite to this. A second diffraction grating 25 having a substantially equal pitch linear shape is formed. The dual grating 22 is provided on an optical path where light reflected from a not-shown magneto-optical disc as an optical information recording medium is condensed by the condenser lens 23 of the optical information detection optical system 26. . Further, of the 0th-order light T and the 1st-order light K that have passed through the dual grating 22 having the first diffraction grating 24 and the second diffraction grating 25, they are located on the optical path of the 1st-order light K. Light receiving surface a,
An optical information signal detector 29 in which a first light receiving element 27 having b, c is disposed, and a second light receiving element 28 having light receiving surfaces d, e, f positioned on the optical path of the zero-order light T is disposed. Is provided. In this case, the optical information signal detector 29 is located behind the converging point P of the primary light K and is located in front of the converging point Q of the 0th-order light T and is sandwiched between PQs. It has become.

In such a configuration, the reflected light from the magneto-optical disk is converged by the converging lens 23 in the optical information detection optical system 26 to become convergent light. In this state, the dual grating 22
Incident on the first diffraction grating 24, and is separated for each polarization direction component thereof.
It is split into two lights, the next light K. Further, the zero-order light T travels straight without being diffracted by the second diffraction grating 25, and the first-order light K is further diffracted by the second diffraction grating 25 and proceeds. Since the first and second diffraction gratings 24 and 25 do not have a convergence function, the condensing positions of the zero-order light T and the first-order light K are determined by the converging lens 23,
An image is formed at each of the positions P and Q. In this case, since the primary light K is diffracted, the optical path length is slightly longer than that of the zero-order light T,
As a result, the position of the converging point P is forward. Then, the 0th-order light T and the 1st-order light K are applied to the first light receiving element 27 and the second light receiving element 28 of the optical information signal detector 29 located between these two converging points P and Q. 3, the first light receiving element 27 is irradiated with a beam in a state after the primary light K is converged, and the second light receiving element 28 is converged with the zero order light T. The beam in the previous state will be irradiated.

Therefore, a method for detecting a focus error signal, a track error signal, and a magneto-optical signal will now be described. First, when a focus error signal is detected, the first light receiving element 27 and the second light receiving element
The spot diameters of the 0th-order light T and the 1st-order light K applied to each of the light-emitting elements 28 are equal to each other as shown in FIG. 4 (b). When the camera is out of focus as shown in FIG.
The spot diameter of the next-order light T becomes smaller and the spot diameter of the first-order light K becomes larger. On the contrary, as shown in FIG. The diameter increases and the spot diameter of the primary light K decreases. By utilizing the relationship that the two spot diameters change so as to be contradictory when the focal position of the magneto-optical disc shifts,
By calculating (a + c−b) − (d + fe), a focus error signal can be detected. Also,
The track error signal can be detected by obtaining (a + d)-(c + f) using the light quantity difference between both sides of the light receiving elements 27 and 28 divided into three. Further, a magneto-optical signal can be detected by obtaining a light amount difference between the light receiving elements 27 and 28, that is, a light amount difference (a + b + c)-(d + e + f) between the zero-order light and the primary light.

Next, an embodiment of the present invention formed based on the above-described structure will be described with reference to FIGS. 5 (a), (b) and (c).
This is an example in which the surface shape of one diffraction grating formed on the dual grating 22 is changed. That is, in the dual grating 22, the first diffraction grating 24 on the side located on the condenser lens 23 has the same pitch linear shape as in the above case, but the second diffraction grating located on the opposite side is The grating 30 is formed so as to form a part of a concentric circle having different pitches. Therefore, in addition to the condenser lens 23, such a concentric second diffraction grating 30 having a different pitch is used.
The primary light K diffracted by providing the light condensing function has the light converging point P at a position further in front, and accordingly, the light receiving elements 27 and 28 divided into three parts are provided. The optical information signal detector 29 can be provided with a margin.

As an application of this embodiment, when the focal length of the condenser lens 23 is to be shortened to reduce the overall configuration of the optical information detection optical system 26, the zero-order light T In this case, astigmatism may occur, which may have a considerable effect on signal detection. In such a case, the second diffraction grating 30 on one side may be formed into a curved shape having a different pitch. Astigmatism is also generated in the next light K, and an adverse effect on a signal detected by canceling out the astigmatism is removed, thereby making it possible to reduce the size. However, in this case, the primary light K
If only the light condensing function is provided, the convergence state will be zero-order light T
Unlike this, the way of changing the spot diameter is not the same, so that electrical correction after signal detection must be considered.

As described above, the present invention irradiates laser light emitted from a semiconductor laser onto an optical information recording medium to record information, and collects reflected light from the optical information recording medium by a condenser lens. It shines to the optical information detection optical system and reproduces information,
In an optical information recording / reproducing apparatus for detecting a track error signal and a focus error signal, an equal pitch linear shape is formed on an optical path of light reflected by the optical information recording medium and condensed by the condenser lens. A dual grating in which a first diffraction grating is formed and a concentric second diffraction grating having a different pitch is formed on a surface opposite to this surface is arranged, and the dual grating is diffracted by the dual grating. At least 3 arranged on the optical path of the next light
Since the optical information signal detector having the divided first light receiving element and at least three divided second light receiving elements disposed on the optical path of the zero-order light that travels straight without being diffracted is provided, The function of condensing one-sided light with curved surfaces having different pitches on one side enables the zero-order light and the
The distance between the condensing points of the next light in the optical axis direction can be widened, so that an optical information signal detector having a light receiving element divided into three can be easily arranged. It is.

[Brief description of the drawings]

FIG. 1 is a plan view of an optical information detecting optical system showing a basic structure of one embodiment of the present invention, FIG. 2 (a) is a front view of a first diffraction grating, and FIG. 2 (b) is a dual gray. FIG. 2 (c) is a front view of the second diffraction grating, FIG. 3 is a front view of the optical information signal detector, and FIGS. 4 (a), (b) and (c) are focus error signals. FIG. 5 (a) is a front view of a first diffraction grating showing an embodiment of the present invention, FIG. 5 (b) is a side view of the dual grating, and FIG. c) is a front view of the second diffraction grating, FIG. 6 is a plan view showing a first conventional example, FIG. 7 (a) is a plan view showing a second conventional example, and FIG. FIG. 3 is a circuit diagram showing a detection circuit for various signals. 22 ... Dual grating, 23 ... Condenser lens, 24
... first diffraction grating, 27 ... first light receiving element, 28 ... second light receiving element, 29 ... optical information signal detector, 30 ... second diffraction grating, K ... primary light, T ... 0th order light

Claims (1)

(57) [Claims] An optical information recording medium is recorded by irradiating a laser beam emitted from a semiconductor laser onto an optical information recording medium, and light reflected from the optical information recording medium is collected by a condenser lens to detect optical information. In an optical information recording / reproducing apparatus for guiding information to an optical system and reproducing information, and detecting a track error signal and a focus error signal, an optical path of light reflected by the optical information recording medium and condensed by the condenser lens is provided on the optical path. A dual grating in which a first diffraction grating having an equal pitch linear shape is formed on one surface, and a concentric second diffraction grating having a different pitch is formed on a surface opposite to this surface is provided. Due to the grating, at least three divided first light receiving elements disposed on the optical path of the primary light diffracted and traveling at least are disposed on the optical path of the zero-order light traveling straight without being diffracted. 3 divided optical information recording and reproducing apparatus characterized by comprising an optical information signal detector and a second light receiving element.