JP3401288B2 - Light detection unit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetection unit which separates a light beam by a grating surface and receives the separated light beams in separate light receiving regions.

[0002]

2. Description of the Related Art A photodetection unit in which a grating of this kind and a light receiving element are combined is disclosed in, for example, Japanese Patent Laid-Open No. 3-15.
No. 2428, etc. This publication discloses a polarization detecting device in which a grating and a light receiving element are integrally configured.

[0003]

However, since the above-described conventional photodetection unit uses the plate-shaped grating element, the angle between the separated light beams is large, and the light receiving area is secured on the same plane. Therefore, the distance between the grating surface and the light receiving region is set to be quite small, which makes it difficult to perform alignment during manufacturing or assembly.

In addition, it is necessary to incline the light receiving element with respect to the optical axis by a certain angle, which makes positioning difficult.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to reduce the angle between the separated light fluxes, the distance between the grating surface and the light receiving region, and An object of the present invention is to provide a photodetection unit capable of arbitrarily setting the angle of the light receiving element with respect to the optical axis.

[0006]

In order to achieve the above object, a photo-detecting unit according to the present invention is provided with an incident end face and an emitting end face which are non-parallel to each other, and is of a transmissive type having periodicity on the incident end face. A grating prism which has a grating surface, separates a light beam, which is reflected from the magneto-optical disk and is rotated by 45 ° in the polarization direction, from the incident end surface into 0th-order diffracted light and 1st-order diffracted light, and emits the light from the emission end surface. And a light-receiving element having at least two light-receiving regions for respectively receiving the two separated light fluxes are arranged in close proximity to each other, and the spot size of the two light fluxes received by the light-receiving element is determined by the tangency of the magneto-optical disk.
Is divided into three parallel dividing lines corresponding to the vertical direction.
Characterized in that divided into four strip-shaped region and a light detector for detecting a focus state by comparing the.

[0007]

EXAMPLES Examples of the photodetection unit will be described below.

[0008]

[Embodiment 1] FIG. 1 shows an optical system of a magneto-optical disk device in which a photodetection unit according to Embodiment 1 is incorporated.

The divergent luminous flux emitted from the semiconductor laser 1 is
The collimator lens 2 collimates the light into a parallel light flux, and the two anamorphic prisms 3 and 4 shape the light into a circular cross section. A rectangular prism 5 is joined to the anamorphic prism 4, and the joining surface is a half mirror surface 5a. The light flux reflected by the half mirror surface 5 a is condensed by the condenser lens 6 on the light receiving element 7 for automatic output adjustment of the semiconductor laser 1.

The light flux transmitted through the half mirror surface 5a is reflected by the mirror 8 and is converged on the signal recording surface of the magneto-optical disk 20 via the objective lens 9. The objective lens 9 and the mirror 8 are provided in a head (not shown) that slides in the radial direction x of the magneto-optical disk 20. The objective lens 9 is provided on an actuator provided in the head, and is driven in the optical axis direction z and the radial direction x of the disk.

On the other hand, the light flux reflected from the magneto-optical disk 20 is reflected by the half mirror surface 5a, the polarization direction is rotated by 45 ° by the λ / 2 plate 10, and the light is converged by the condenser lens 11 to form a grating and the grating. Prism 12
Incident on. The light flux incident on the grating prism 12 is reduced to 0 by the grating surface formed on the incident end surface.
The light is separated into the second-order diffracted light and the first-order diffracted light and reaches the two light-receiving regions formed on the light-receiving element 13. The light receiving element 13 is
It is provided perpendicularly to the optical axis of the reflected light from the disk, and its positioning is easier compared to the conventional device.

As shown in FIG. 2, the photodetection unit of the embodiment includes a grating prism 12 for separating a light beam incident through a λ / 2 plate 10 and a condenser lens 11 into a 1st-order diffracted light and a 0th-order diffracted light. , This grating prism 12
Two light receiving regions 13 for receiving the light flux separated by
The light receiving element 13 having a and 13b is integrally formed. 2, (a) is an explanatory view in the xy plane in FIG. 1, (b) is an explanatory view in the yz plane, and (c) is an explanatory view in the xz plane.

The grating prism 12 is shown in FIG.
As shown in, the grating surface formed on the incident end face separates the vibration component parallel to the groove of the grating of the light beam incident at the Bragg angle and the vibration component as the 0th-order diffracted light and the 1st-order diffracted light, and separates them. One of the 0th-order diffracted lights is emitted from the exit end face as it is, and the other 1st-order diffracted light is internally reflected and then emitted from the exit end face in parallel with the 0th-order diffracted light.

The specific numerical configuration of the grating prism 12 is as shown in Table 1 (a). In the table,
The angle of the apex facing the grating surface of the prism is θ
c, the angles of the remaining vertices are θa and θb, the refractive index of the prism is n, and the incident angle of the light beam on the grating surface is θ.
in, the pitch of the grating pattern is p, and the wavelength used is λ. Both the incident angle and the exit angle are angles with respect to the normal line of the surface.

[0015]

[Table 1]

When the incident angle of the light beam on the grating is set to the Bragg angle and the ratio λ / p between the wavelength λ and the grating pitch p is set to about 1.6, the vibration component parallel to the groove of the grating is parallel. The oscillating component is distributed to the 0th-order diffracted light and the 1st-order diffracted light, and the polarization separation characteristic by the grating becomes the best. By satisfying this condition, the grating prism 12 separates the incident light flux into two polarized light components of P component and S component and emits them.

Since the polarization direction of the laser light reflected by the magneto-optical disk 20 is rotated by the magnetic Kerr effect in accordance with the magnetization direction of the disk at the position where the spot is imaged, it is rotated by 45 ° to be 2 °. The magneto-optical recording signal can be read out by separating the two linearly polarized light components, detecting them by respective light receiving regions, and taking the difference.

The light receiving areas 13a and 13b are arranged at positions which are optically equidistant from the focal position of the reflected light when the objective lens 9 is focused on the magneto-optical disk 20, By comparing the spot sizes on both the light receiving areas, the focus state (focusing error) of the objective lens 9 with respect to the magneto-optical disk 20 can be detected.

Light receiving regions 13a, 13b of the light receiving element 13
3 are parallel to the direction corresponding to the tangential direction of the magneto-optical disk 20 as shown in FIG.
Four strip-shaped areas A divided by one dividing line
To D and E to H. Then, the light receiving area 13
The P-polarized light flux (0th-order diffracted light) and the S-polarized light flux (1st-order diffracted light) separated by the grating prism 12 are incident on a and 13b, respectively.

The signals from the respective light receiving areas are calculated by a calculation circuit (not shown) and recorded on the disk as a magneto-optical recording signal MO, a preformat signal RO recorded by physical unevenness, a focus error signal FE, The track error signal TE is output to a reproducing circuit and a servo circuit (not shown).

Each signal can be obtained by the following equations when the output of each light receiving area is represented by the same symbol as the light receiving area.

[0022]

[Equation 1] MO = (A + B + C + D)-(E + F + G + H) RO = (A + B + C + D) + (E + F + G + H) FE = (A + D-B-C)-(E + H-F-G) TE = (B-C) + (G-F)

According to this embodiment, the information signal and the error signal can be detected by using the common light-receiving region, the structure of the light-receiving element can be simplified and the cost can be reduced, and other later-described Compared to the embodiment, the single condensed light path makes it possible to occupy a small space and downsize the entire apparatus.

[0024]

[Embodiment 2] FIG. 5 shows an optical system of a magneto-optical disk device using a photodetection unit according to Embodiment 2 of the present invention. The elements from the semiconductor laser 1 to the objective lens 9 are the same as those in the first embodiment described above.

Of the reflected light from the magneto-optical disk 20, the component reflected by the half mirror surface 5a of the rectangular prism 5 is incident on the grating plate 14 as shown in FIG. The light is separated into the first-order diffracted light and is condensed on the light receiving element 15 via the condenser lens 11.

As shown in FIG. 6 (d), the grating plate 14 has unequal circular arcs of concentric circles whose pitch gradually decreases from one side on the left side in the figure to the other side on the right side in the figure. A pitch grating is formed.
By transmitting through this grating plate, the 0th-order diffracted light is transmitted as it is, and the + 1st-order diffracted light is diverged,
The −1st order diffracted light converges.

The 0th-order diffracted light which has passed through the grating plate 14 as it is is condensed along the optical axis, enters the grating prism 12 ', is separated into respective polarized components, and reaches the light receiving regions 15a and 15b. In this embodiment, instead of providing the λ / 2 plate as in the first embodiment, the light receiving element 15 is rotated with the grating prism 12 ′ rotated by 45 °.
It is provided in the center of. Grating prism 12 '
Is a similar shape of the grating prism 12 shown in Example 1, and the apex angle, diffraction angle, etc. are as shown in (a) of Table 1.

On the other hand, the + 1st order diffracted light diverged by the grating plate 14 is received by the light receiving region 15c in front of the converging point located behind the converging point by the condensing lens 11. Further, the −1st-order diffracted light converged by the grating plate 14 is received by the light receiving region 15d behind the condensing point located in front of the condensing point by the condensing lens 11.

FIG. 7 is an enlarged view of the light receiving area of the light receiving element 15. The light receiving areas 15c and 15d are shown in FIG.
It is similar to the first embodiment shown in FIG. 3 and is composed of strip-shaped regions indicated by A to H. In addition, the light receiving area 15a,
Reference numeral 15b is composed of single regions I and J that are not divided, and receives the P-polarized light flux and the S-polarized light flux that are polarized and separated by the grating prism 12 ', respectively.

The magneto-optical recording signal MO, the preformat signal RO, the focus error signal FE, and the track error signal TE can be obtained by the following equations when the output of each light receiving area is represented by the same symbol as the light receiving area.

[0031]

[Equation 2] MO = I−J RO = (A + B + C + D) + (E + F + G + H) + (I + J) FE = (A + D-B-C)-(E + H-F-G) TE = (B-C) + (G-F)

According to this embodiment, since the information signal and the error signal can be detected by the independent light receiving regions, the influence of the interference between the respective signals is small and an accurate signal can be obtained. Further, when compared with the light receiving element 13 of Example 1,
A light receiving region 15a for detecting the magneto-optical recording signal MO,
The area of 15b can be reduced. Since the response speed of the light receiving element becomes higher as the area of the light receiving region becomes smaller, the configuration of the second embodiment makes it possible to detect a signal having a higher frequency.

[0033]

[Third Embodiment] FIG. 8 shows an optical system of a magneto-optical disk apparatus using a photodetecting unit according to a third embodiment of the present invention. The third embodiment is different only in the configuration of the grating prism 16 provided in front of the light receiving element 15, and the other configurations are similar to those of the device of the second embodiment.

The grating prism 16 is shown in FIG.
As shown in (b), a grating for polarization separation is formed on the end face from which light is emitted. The light receiving element 15 for receiving the separated light flux is arranged at a predetermined distance from the grating prism 16 as shown in FIG.

The specific numerical configuration of the grating prism 16 is as shown in column (b) of Table 1 above. The arrangement of the light receiving area of the light receiving element 15 and the method of detecting each signal are the same as those in the second embodiment.

[0036]

[Fourth Embodiment] FIG. 10 shows an optical system of a magneto-optical disk apparatus using a photodetecting unit according to a second embodiment of the present invention.

The optical system of the fourth embodiment comprises a magneto-optical disk 20.
Reflected light from the 0th order and ± 1 by the grating plate 14
The light is separated into the following three diffracted lights and is condensed by the condenser lens 11. Then, the 0th-order diffracted light is vertically reflected toward the outside of the optical path by the minute deflection prism 17 provided in the optical path as shown in FIG.
Is received by the light receiving element 18 for detecting the magneto-optical signal. The structure of the grating prism 12 'is the same as that of the second embodiment. The first light receiving element 18 for detecting a magneto-optical signal has two adjacent light receiving regions 18a, 18a.
b, and these light receiving regions 18a and 18b are
As shown in FIG. 12, it is composed of single regions I and J which are not divided.

On the other hand, the ± first-order diffracted light is received by the second light receiving element 19 for detecting an error signal provided behind the minute deflection prism 17. The light receiving element 19 for error signal detection includes two light receiving areas 19a and 19b,
Each of the light-receiving regions has four strip-shaped light-receiving regions A to H similarly to the light-receiving element of the first embodiment shown in FIG.
The method of detecting each signal is the same as that in the second embodiment.

According to the configuration of the fourth embodiment, since the error signal and the magneto-optical signal can be detected by separate light receiving elements, there is little influence of leakage of light flux and stray light, and each of them is different from those of the first to third embodiments. It is possible to prevent the influence due to the interference of the photocurrent which is smaller than that in the light receiving region in the same package.

Further, the optical path to the light receiving element for detecting the magneto-optical signal and the optical path to the light receiving element for detecting the error signal can be made orthogonal to each other, so that the degree of freedom in optical design and mechanical design is improved, and the entire apparatus is improved. You can make effective use of the available space.

Further, since the 0th-order diffracted light is separated from the optical paths of the ± 1st-order diffracted lights, it is possible to separate the respective light fluxes even if the diffraction angle by the grating plate 14 is relatively small, and the diffraction angle by the grating plate 14 is small. By setting it, the aberration of the spot image of the ± 1st-order diffracted light can be reduced, and stable error signal detection can be performed.

[0042]

As described above, according to the present invention, the angle between the two light beams incident on the light receiving element is arbitrarily set by using the prism having the grating and the light receiving element in combination. Therefore, it is possible to arbitrarily set the distance to the light receiving element and the angle of the light receiving element with respect to the optical axis. Particularly, when the light receiving element is set perpendicularly to the optical axis, positioning, adjustment, etc. of the light receiving element become easy. In addition, the spot size on the light receiving area
Focused state for magneto-optical disk by comparing
(Focusing error) can be detected.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a magneto-optical disk device that uses a light detection unit according to a first embodiment.

2A and 2B are explanatory views of a light receiving system of the apparatus of FIG. 1, where FIG. 2A is an explanatory view in the xy plane in FIG. 1, FIG. 2B is an explanatory view in the yz plane, and FIG. Is an explanatory diagram in the xz plane.

FIG. 3 is an explanatory diagram of a single grating prism used in an example.

FIG. 4 is a plan view showing a light receiving region of the light receiving element of the first embodiment.

FIG. 5 is an explanatory diagram of a magneto-optical disk device using the photodetection unit according to the second embodiment.

6A and 6B are explanatory views of a light receiving system of the apparatus of FIG. 5, where FIG. 6A is an explanatory view in the xy plane in FIG. 5, FIG. 6B is an explanatory view in the yz plane, and FIG. Is an explanatory diagram in the xz plane.

FIG. 7 is a plan view showing a light receiving region of a light receiving element according to a second embodiment.

FIG. 8 is an explanatory diagram of a magneto-optical disk device using the photodetection unit according to the third embodiment.

9A and 9B are explanatory views of a light receiving system of the apparatus of FIG. 8, where FIG. 9A is an explanatory view in the xy plane in FIG. 8, FIG. 9B is an explanatory view in the yz plane, and FIG. Is an explanatory diagram in the xz plane.

FIG. 10 is an explanatory diagram of a magneto-optical disk device using the photodetection unit according to the fourth embodiment.

11 is an explanatory diagram of a light receiving system of the apparatus of FIG.
10A is an explanatory view in the xy plane in FIG. 10, FIG. 9B is an explanatory view in the yz plane, and FIG. 11C is an explanatory view in the xz plane.

FIG. 12 is a plan view showing a light receiving region of a light receiving element for detecting a magneto-optical signal according to a fourth embodiment.

[Explanation of symbols]

1 ... Semiconductor laser 5a ... Half mirror surface 9 ... Objective lens 11 ... Condensing lens 12, 12 ', 16 ... Grating prism 13, 15, 18, 19 ... Light receiving element 14 ... Grating plate 17 ... Micro deflection prism 20 ... Magneto-optical disk

Front page continued (72) Inventor Koichi Maruyama 2-36 Maenocho, Itabashi-ku, Tokyo Asahi Kogaku Kogyo Co., Ltd. (72) Inventor Masahiro Ono 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Asahi Kogaku Within Kogyo Co., Ltd. (56) Reference JP-A 1-184639 (JP, A) JP-A 5-242496 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 27 / 42 G02B 5/18 G11B 7/13

Claims (5)

(57) [Claims] 1. A transmission-type grating surface having an incident end surface and an exit end surface which are non-parallel to each other and having a periodicity is formed on the incident end surface, and the polarization direction is reflected by a magneto-optical disk incident from the incident end surface. Is a 45 ° rotated light beam and is separated into a 0th-order diffracted light and a 1st-order diffracted light and emitted from the exit end face.
A light-receiving element having at least two light-receiving regions for receiving two light fluxes is arranged close to each other, and the spot size of the two light fluxes received by the light-receiving element is determined by a magneto-optical method.
3 parallels corresponding to the tangential direction of the disc
Divide into four strip-shaped areas divided into
Photodetector unit, characterized in that a photodetector for detecting a focus state by Te comparisons. 2. The grating prism internally reflects one of the 0th-order diffracted light and the 1st-order diffracted light separated by the grating surface by a reflecting surface that is not parallel to the incident end surface, The light detection unit according to claim 1, wherein the light is emitted from the emission end surface in a substantially parallel state. 3. The grating prism and the light receiving element are integrally joined together.
The light detection unit described in. 4. The light detection unit according to claim 1, wherein the grating prism and the light receiving element are adjacent to each other with a slight air gap therebetween. 5. The light detection unit according to claim 1, wherein the light receiving element is provided perpendicularly to a light beam incident on the light receiving element.