JPH06215388A - Optical recording / reproducing device - Google Patents

Abstract

(57) [Abstract] [Purpose] The purpose of the present invention is to provide a device for recording or reproducing information on a tape-shaped recording medium by light, and particularly focusing suitable for a device in which an objective lens is provided in a rotary head. , For the purpose of providing a tracking method. A semiconductor laser 1, a collimator lens 2 provided so as to be movable in the optical axis direction or in a plane perpendicular to the optical axis, and a light beam incident from the collimator lens 2 is deflected outside the incident direction. A prism 6 for allowing the deflected light beam to form an image on the optical recording medium as a spot; and an objective lens 7 provided between the collimator lens 2 and the objective lens 7, and an exit pupil of the collimator lens 2 and the objective lens 7. Relay lenses 4, 5 that make the entrance pupil almost conjugate
Have and. The prism 6 and the objective lens 7 are arranged in a rotary head B that is rotatably provided about the direction of the incident light beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for recording and reproducing information on a recording medium by light,
The present invention relates to an optical recording / reproducing device suitable for a tape-shaped recording medium.

[0002]

2. Description of the Related Art A conventional optical recording / reproducing apparatus is generally one that records and reproduces information on a disk-shaped medium such as a compact disk, a video disk, or a magneto-optical disk.

In the above recording / reproducing apparatus, since the diameter of the light spot is narrowed down to the diffraction limit, further improvement in recording density cannot be expected. Therefore, the recording capacity of the medium depends on the recording area, but in the case of a disc-shaped recording medium, the size is also limited and the recording capacity is limited.

Therefore, it has been proposed to use a tape-shaped recording medium having a large recording area as a medium having a larger capacity.

When recording and reproducing information on a tape-shaped recording medium, as is the case with the VTR of magnetic recording,
A method of rotating the head so as to traverse the tape in its width direction is desirable for increasing the recording / reproducing speed.

In order to record and reproduce information, it is necessary to scan the light spot on the recording medium at high speed. Further, means for focusing the spot on the recording medium (focusing) and aligning it with the track (tracking) are also required.

In the conventional optical disk apparatus, since the disk is rotating, it is not necessary to move the objective lens to scan the spot, and it is easy to move the objective lens for focusing and tracking.

[0008]

However, when a tape-shaped recording medium is used, it is necessary to move the tape and move the spot across the tape, and the objective lens is used to scan the spot. Need to move at high speed. However, at this time, since the centrifugal force of the objective lens is applied, focusing by driving the objective lens like a conventional optical disk device,
Tracking is difficult.

Therefore, it is conceivable that focusing and tracking are performed by a lens provided at a place other than the objective lens, that is, a place other than the rotary head. However, for example, in the case of driving a collimator lens that collimates a light flux from a light source, if the following measures are not taken, the following problems will occur.

For example, when the collimator lens is moved in the optical axis direction for focusing, if the collimator lens is moved to the objective lens side, the light beam converges and the diameter of the light beam incident on the objective lens becomes thin, and the objective lens NA
Is substantially reduced, the spot size is increased and the recording density is reduced. On the contrary, when the collimator lens is moved to the light source side, the luminous flux is diverged and eclipsed, so that the amount of light used decreases.

Further, when the collimator lens is moved in a plane perpendicular to the optical axis for tracking, if the collimator lens moves and the emitted light beam is tilted with respect to the optical axis, it does not enter the objective lens. The luminous flux increases, and the utilization efficiency of light changes due to tracking. In order to prevent this change, the diameter of the light beam incident on the objective lens may be increased, but in this case, there is a problem that the utilization efficiency of the light beam from the light source is always low.

Therefore, especially when the distance between the collimator lens and the objective lens is large, there is a problem that the range in which focusing and tracking can be followed is narrowed.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide an apparatus for recording or reproducing information on a tape-shaped recording medium by light, and in particular, an objective lens. It is an object of the present invention to provide a focusing and tracking system suitable for a device provided in a rotary head.

[0014]

In order to achieve the above-mentioned object, an optical recording / reproducing apparatus according to the present invention is provided with a light source, a deflecting member for deflecting a light beam incident from the light source to the outside of the incident direction, and a deflecting member. An objective lens that forms an image of a light flux as a spot on an optical recording medium, a rotary head that is rotatably provided about the direction of the incident light flux, and is provided in an optical path between the light source and the rotary head, An exit pupil of the movable lens and an entrance pupil of the objective lens, which is provided between the movable lens and the objective lens, and is provided so as to be movable in the optical axis direction or in a plane perpendicular to the optical axis. And a relay lens that substantially conjugates and.

[0015]

Embodiments of the present invention will be described below. Figure 1
[Fig. 3] shows an outline of an optical system of the optical tape system of the embodiment.

A magnetic film is formed on the surface of the optical tape, and the recording / reproducing apparatus records information by heat and magnetic field of light and reflects the same as in a generally used magneto-optical disk apparatus. The recorded information is reproduced by using the magnetic Kerr effect of time.

A beam emitted from a semiconductor laser 1 as a light source is collimated by a collimator lens 2,
It passes through the first beam splitter 3.

In the embodiment, the collimator lens 2 is a movable lens, and is provided so as to be movable in the optical axis direction for focusing and movable in a plane perpendicular to the optical axis for tracking. There is.

The luminous flux transmitted through the beam splitter 3 is
It is relayed by relay lenses 4 and 5. The optical elements from the semiconductor laser 1 to the relay lens 5 are provided in the fixed portion A.

The light beam emitted from the relay lens 5 is reflected off the optical axis of the incident light beam by the first reflecting surface 6a of the prism 6 as a deflecting member provided in the rotary head B, and the second light beam is reflected.
The reflection surface 6b again reflects the light in a direction parallel to the incident light beam. The rotary head B has its optical axis Ax with respect to the fixed portion A.
Rotate around. R is the radius of gyration.

The reflected light beam from the prism 6 enters the objective lens 7 and forms a spot on the optical tape 8 which is a recording medium. The spot moves in a circle in a plane perpendicular to the rotation axis of the rotary head.

The relay lenses 4 and 5 have a function of making the exit pupil of the collimator lens 2 and the entrance pupil of the objective lens 7 substantially conjugate with each other. By inserting the relay lens in between, the image of the exit pupil of the collimator lens is projected onto the entrance pupil of the objective lens, the collimator lens 2 moves in the optical axis direction for focusing, or the optical axis for tracking. When moving in a plane perpendicular to,
Light is transmitted without waste.

The reflected light beam from the optical tape 8 becomes a parallel light beam again via the objective lens 7 and enters the first beam splitter 3 via the relay lenses 4 and 5. The light beam reflected by the first beam splitter 3 has its polarization direction rotated by 45 degrees by the ½ wavelength plate 9, and is separated into both P and S polarization components by the polarization beam splitter 10.

P transmitted through the polarization beam splitter 10
The polarized component is converted into the first light receiving element 12 by the condenser lens 11.
Focused on top. The S-polarized component reflected by the polarization beam splitter 10 is condensed by the condenser lens 13 on the second light receiving element 14.

Since the magnitude of the intensity of the polarization component changes depending on the direction of the magnetic field in the area where the spot is located on the optical tape, the reproduction signal from the optical tape is received by each light receiving element 1.
It is obtained by subtracting the outputs of 2, 14 by the subtracter 15. The signals of the track error and the focus error are detected by using the output of at least one of the light receiving elements, and the collimator lens 2 is driven by an actuator (not shown) so as to eliminate these errors. In order to detect the error signal, it is necessary to divide the light receiving area of the light receiving element into a plurality of areas. However, since these are generally known as the technology of the magneto-optical disk device, detailed description thereof will be omitted here.

In the embodiment, the focusing and tracking operations are performed by the collimator lens 2. Further, the relay lenses 4 and 5 are configured such that positive lenses having the same power are arranged so as to face each other so that their focal positions coincide with each other, and they have no power and have an angular magnification of −1. d is a constant of d = 4f + 2HH, where f is the focal length of the positive lens and HH is the distance between the principal points of the positive lens.

In the case of the embodiment, since the conjugate distance is constant regardless of the distance between the collimator lens 2 and the relay lens 4, the distance between the exit end face of the collimator lens 2 and the entrance end face of the objective lens 7 is equal to the relay lens. The relay lens may be arranged at any position between them as long as it is substantially equal to the conjugate distance d of 4 and 5.

[0028]

Embodiment 1 FIG. 2 is an explanatory diagram showing the optical system of the embodiment in more detail, and its specific numerical configuration is shown in the table below. The surface numbers in the table are given from the semiconductor laser 1 side, the symbol r is the radius of curvature, d is the lens thickness or the air gap, nd is the refractive index at d-line (588 nm), ν is the Abbe number, n780 is the refractive index at a wavelength of 780 nm.

Further, in this embodiment, since the deflecting means is composed of a prism, the thickness of the prism is calculated as the thickness in air when calculating the conjugate distance.

Table 1 shows the structure of the collimator lens 2. The collimating lens is composed of five lenses.
The second lens and the third lens are cemented together. The symbol d0 in the table indicates the laser diode 1 to the collimator lens 2
Is the distance to the first surface of.

[0031]

[Table 1] d0 = 4.861 Surface number rd nd ν n780 1 -7.871 1.900 1.88300 40.8 1.86888 2 -6.230 1.970 3 16.830 1.900 1.61800 63.4 1.61139 4 -7.241 1.200 1.84666 23.8 1.82484 5 -15.563 6.280 6 36.250 1.300 1.84666 23.8 1.82484 7 14.372 0.450 8 116.842 1.600 1.72916 54.7 1.72007 9 -17.350

Table 2 shows the configuration of the beam splitter 3. The symbol d0 in the table is the distance from the final surface of the collimator lens 2 to the first surface of the beam splitter 3. In addition, the air equivalent thickness of the beam splitter is 3.972 mm.

[0033]

[Table 2] d0 = 4.000 Surface number r d nd ν n780 1 ∞ 6.000 1.51633 64.1 1.51072 2 ∞

Table 3 shows the construction of the relay lenses 4 and 5. Each of the relay lenses 4 and 5 is configured as a lens having a positive power in which a positive lens and a negative lens are bonded together, and their focal lengths are the same. Conjugate distance is 1
It is 99.984 mm. The symbol d0 is the distance from the final surface of the beam splitter 3 to the first surface of the relay lens 4.

[0035]

[Table 3] d0 = 5.028 Surface number r d nd ν n780 1 34.000 2.000 1.69350 53.2 1.68468 2 -24.500 1.500 1.80518 25.4 1.78565 3 -180.770 94.841 4 180.770 1.500 1.80518 25.4 1.78565 5 24.500 2.000 1.69350 53.2 1.68468 6 -34.000

Table 4 shows the structure of the deflecting prism 6. The air-equivalent thickness is 37.068 mm. The symbol d0 is the distance from the final surface of the relay lens 5 to the first surface of the prism 6.

[0037]

[Table 4] d0 = 38.075 Surface number r d nd ν n780 1 ∞ 56.000 1.51633 64.1 1.51072 2 ∞

Table 5 shows the structure of the objective lens 7. symbol
d0 is the distance from the final surface of the prism 6 to the first surface of the objective lens 7.

[0039]

[Table 5] d0 = 10.000 Surface number rd nd ν n780 1 7.056 1.170 1.77250 49.6 1.76203 2 -80.922 0.430 3 -6.667 0.800 1.84666 23.8 1.82484 4 4.194 1.420 1.77250 49.6 1.76203 5 -65.760 0.780 6 16.720 1.220 1.77250 49.6 1.76203 7 -8.327 0.050 8 3.300 1.150 1.77250 49.6 1.76203 9 6.818 1.783 10 ∞ 1.200 1.51633 64.1 1.51072 11 ∞

In this embodiment, the distance from the exit end surface of the collimator lens to the entrance end surface of the objective lens is 199.984 mm when the beam splitter 3 and the prism 6 are converted into air, which is the same as the conjugate distance of the relay lens.

According to the configuration of the first embodiment, the focusing sensitivity is 0.17 in the change of the back focus of the objective lens with respect to the movement 1 of the collimating lens in the optical axis direction, and the tracking sensitivity is the same as that of the collimating lens. The ratio of the spot movement is 0.41 with respect to the movement 1 in the plane perpendicular to the optical axis direction.

FIG. 3 is a diagram showing a state of light rays when the collimator lens 2 is moved by 180 μm along the optical axis from the reference state shown in FIG. This movement changes the back focus of the objective lens by -30 μm. As for the sign, the optical tape side is positive.

FIG. 4 is a diagram showing a state of light rays when the collimator lens 2 is moved by −180 μm along the optical axis from the reference state shown in FIG. This movement changes the back focus of the objective lens by 30 μm. In any case, the light flux can be made incident on the objective lens without changing the light flux diameter.

FIG. 5 is a diagram showing a state of light rays when the collimator lens 2 is moved by 150 μm in a plane perpendicular to the optical axis from the reference state shown in FIG. This movement changes the position of the spot by 61 μm, but the light beam is incident on the objective lens without being eclipsed.

6 and 7, for comparison, a collimator lens is provided in the direction of the optical axis without providing a relay lens.
An example is shown in which 0 μm and −180 μm are moved. The diameter of the light beam incident on the objective lens changes considerably, resulting in an increase in the spot diameter due to a decrease in NA and eclipse of the light beam.

FIG. 8 is a diagram showing a state of light rays when the collimator lens is moved by 150 μm in a plane perpendicular to the optical axis without providing the relay lens. More than half of the light flux is lost without entering the objective lens.

[0047]

Second Embodiment FIG. 9 shows a second embodiment of the optical information recording / reproducing apparatus according to the present invention. In the second embodiment, one mirror 20 is used as the deflecting member, and the spot scans the inner surface of the cylinder centered on the rotation axis of the rotary head B. Since other configurations are similar to those of the first embodiment, the same members are designated by the same reference numerals and the description thereof will be omitted.

In the second embodiment, one relay lens 4 is provided on the fixed portion, and the other relay lens is provided close to the objective lens 7 in the rotary head.

Since the structure of the collimator lens 2 is the same as that of the first embodiment shown in Table 1, its explanation is omitted. Tables 6 and 7 show numerical configurations of the relay lens and the objective lens 7 of Example 2. D0 in Table 6 is the distance between the final surface of the collimator lens 2 and the first surface of the relay lens 4, and d0 in Table 7
Is the distance between the final surface of the relay lens 5 and the first surface of the objective lens 7.

[0050]

[Table 6] d0 = 98.043 Surface number r d nd ν n780 1 34.000 2.000 1.69350 53.2 1.68468 2 -24.500 1.500 1.80518 25.4 1.78565 3 -180.770 94.841 4 180.770 1.500 1.80518 25.4 1.78565 5 24.500 2.000 1.69350 53.2 1.68468 6 -34.000

[0051]

[Table 7] d0 = 0.100 Surface number rd nd ν n780 1 9.763 1.700 1.77250 49.6 1.76203 2 -212.222 0.650 3 -11.336 1.100 1.84666 23.8 1.82484 4 7.040 2.100 1.72916 54.7 1.72007 5 -69.476 2.000 6 26.500 1.830 1.77250 49.6 1.76203 7 -12.800 0.080 8 4.161 2.000 1.77250 49.6 1.76203 9 6.530 2.340 10 ∞ 1.200 1.51633 64.1 1.51072 11 ∞

In this embodiment, the distance from the exit end surface of the collimator lens to the entrance end surface of the objective lens is 199.984 mm, which is equal to the conjugate distance of the relay lens.

The second embodiment also has a configuration in which focusing and tracking are performed by a collimator lens, and the sensitivity of focusing is such that a change in the back focus of the objective lens is 0.3 with respect to 1 movement of the collimator lens in the optical axis direction.
The ratio of 6 and the tracking sensitivity are such that the movement of the spot is 0.60 with respect to the movement 1 in the plane perpendicular to the optical axis of the collimator lens.

In each of the above-described embodiments, only the structure for moving the collimating lens for focusing and tracking is described, but it is moved between the relay lens and the collimating lens for focusing and tracking. The lens may be provided separately. Further, focusing and tracking functions may be independently provided in different lenses.

In the present embodiment, an example of a relay lens having an angular magnification of -1 times, which makes the conjugate distance a constant, is shown. However, an afocal lens having an angular magnification of a relay lens system other than -1 times, a focal length It is sufficient to satisfy the conjugate relation of the pupil, even if is a finite size.

[0056]

As described above, according to the present invention, since it is possible to realize a structure in which a movable lens provided outside the rotary head is moved for focusing or tracking, the rotary head can be made light and small. can do.

That is, since the exit pupil of the movable lens and the entrance pupil of the objective lens are made substantially conjugate by providing the relay lens, even if the movable lens is moved, the diameter and position of the light beam incident on the objective lens hardly change. , An optical recording / reproducing apparatus having good and stable characteristics can be configured without causing an increase in spot diameter due to a decrease in NA and a loss of light amount due to beam eclipse.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of an embodiment of an optical recording / reproducing apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a specific configuration of the optical system of Example 1.

FIG. 3 is an explanatory diagram showing a state where the collimator lens is moved 180 μm in the optical axis direction in the optical system of Example 1.

FIG. 4 is an explanatory diagram showing a state where the collimator lens is moved by −180 μm in the optical axis direction in the optical system of Example 1.

FIG. 5 is an explanatory diagram showing a state in which the collimator lens is moved by 150 μm in a plane perpendicular to the optical axis in the optical system of Example 1.

FIG. 6 is an explanatory diagram showing a state in which a collimator lens is moved by 180 μm in the optical axis direction in an optical system having no relay lens in the comparative example of Example 1.

FIG. 7 is an explanatory diagram showing a state in which a collimator lens is moved by −180 μm in the optical axis direction in an optical system having no relay lens in the comparative example of Example 1.

FIG. 8 is a comparative example of Example 1 in which an optical system having no relay lens has a collimator lens of 150 in a plane perpendicular to the optical axis.
It is explanatory drawing which shows the state moved by μm.

FIG. 9 is an explanatory diagram showing a specific configuration of the optical system of Example 2.

[Explanation of symbols]

 1 ... Semiconductor laser 2 ... Collimating lens 3 ... Beam splitter 4, 5 ... Relay lens 6 ... Prism 6a ... 1st reflective surface 6b ... 2nd reflective surface 7 ... Objective lens 8 ... Optical tape

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunichiro Wakamiya 2-36-9 Maenocho, Itabashi-ku, Tokyo Asahi Optical Co., Ltd.

Claims (4)

[Claims] 1. A light source, a deflecting member for deflecting a light beam incident from the light source out of its incident direction, and an objective lens for forming an image of the deflected light beam as a spot on an optical recording medium. A rotary head provided rotatably around the direction of the light flux, and provided in an optical path between the light source and the rotary head,
A movable lens that is provided so as to be movable at least in the optical axis direction, and a relay lens that is provided between the movable lens and the objective lens and that makes the exit pupil of the movable lens and the entrance pupil of the objective lens substantially conjugate. An optical recording / reproducing apparatus having: 2. The optical recording / reproducing apparatus according to claim 1, wherein the movable lens is provided so as to be movable in a plane perpendicular to the optical axis. 3. A light source, a deflecting member for deflecting a light beam incident from the light source out of its incident direction, and an objective lens for forming the deflected light beam as a spot on an optical recording medium. A rotary head provided rotatably around the direction of the light flux, and provided in an optical path between the light source and the rotary head,
A movable lens that is provided so as to be movable at least in a plane perpendicular to the optical axis, and an exit pupil of the movable lens and an entrance pupil of the objective lens that are provided between the movable lens and the objective lens. An optical recording / reproducing apparatus having a substantially conjugated relay lens. 4. The optical recording / reproducing apparatus according to claim 3, wherein the movable lens is provided so as to be movable also in the optical axis direction.