JPH04117636A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To facilitate the alignment of an optical axis in an optical system by converting an elliptical luminous flux to a circular luminous flux through the use of a pair of cylindrical lenses. CONSTITUTION:This device is equipped with an optical head optical system which irradiates an optical information recording medium 1 while converging a luminous flux from a semiconductor laser 21 on a minute spot and also detects a reflected light from the recording medium 1, and by the irradiation of the luminous flux of the optical head optical system, information is recorded or recorded information is reproduced on the medium 1. Also, in the optical head optical system, a pair of cylindrical lenses 11, 12, which convert the elliptical luminous flux to the circular luminous flux from the semiconductor laser 21, is disposed. Consequently, the alignment of the optical axis in the optical system is facilitated and the manufacturing is made easy.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an optical information recording and reproducing device that optically records information or reproduces recorded information by irradiating an optical information recording medium with a light beam. Regarding.

[Prior Art] Conventionally, various types of information media such as disk-shaped, card-shaped, tape-shaped, etc. are known for recording and reproducing information using light. These optical information recording media include those capable of recording and reproduction, and those capable of only reproduction. Information is recorded on a recordable medium by scanning an information track with a light beam that is modulated according to the recording information and focused into a minute spot, and the information is recorded as an optically detectable information bit string. Ru.

Furthermore, in order to reproduce information from a recording medium, the information bit string of the information track is scanned with a light beam spot of a certain power that does not cause recording on the medium, and the reflected light or transmitted light from the medium is detected. It is done by doing.

The optical head used for recording and reproducing information on the recording medium described above is movable relative to the recording medium in the direction of the information track and in a direction crossing the direction, and this movement changes the light beam spot. An information track scan is performed. For example, an objective lens is used as the lens for narrowing down the light beam spot in the optical head.

This objective lens is in its optical axis direction (focusing direction)
The optical head body is held in a direction perpendicular to both the optical axis direction and the information track direction of the recording medium (tracking direction) so as to be able to move independently in each direction. Such holding of the objective lens is generally achieved through an elastic member, and the movement of the objective lens in the above two directions is generally driven by an actuator that utilizes magnetic interaction.

By the way, among the above-mentioned optical information recording media, card-shaped optical information recording media (hereinafter referred to as optical cards) are
It is expected that there will be great demand in the future as a relatively large-capacity information recording medium that is small, lightweight, and convenient to carry.

FIG. 4 is a schematic plan view of the write-once optical card, and FIG. 5 is a partially enlarged view thereof.

In FIG. 4, on the information recording surface of the optical card 1, a large number of information tracks 2 are arranged in parallel in the LF direction.

Further, a home position 3 is provided on the information recording surface of the optical card 1, which serves as a reference position for accessing the information track 2. The information track 2 is arranged in order from the one closest to the home position 3 to 2-1.2-2.2-3. ..., and as shown in FIG. 5, tracking tracks are arranged adjacent to each of these information tracks in the order of 4-1.
3. They are set up sequentially like this. These tracking tracks 4 are used as guides for auto-tracking (hereinafter referred to as AT) that controls the beam spot so that it does not deviate from a predetermined information track when scanning the optical beam spot during information recording and reproduction. .

This AT servo detects the deviation of the optical beam spot from the information track (AT error) in the optical head,
This is performed by feeding back the detection signal negatively to the tracking actuator, moving the objective lens in the tracking direction (direction D) with respect to the optical head body, and causing the light beam spot to follow desired information tracking.

Additionally, when scanning an information track with a light beam spot during information recording and reproduction, autofocusing (hereinafter referred to as , AF) servo is performed. This AF servo detects the deviation of the light beam spot from the focused state (AFI difference) in the optical head, feeds the detection signal back to the focusing actuator negatively, and moves the objective lens in the focusing direction with respect to the optical head body. This is done by moving the light beam to focus the light beam spot on the surface of the optical card.

In addition, in FIG. 5, Sl, S2. S3 indicates a light beam spot, the light spots S1 and 83 are used for tracking, and the light spot S2 is used for focusing, creating information bits during recording, and reading information bits during playback. Furthermore, in each information track, 6-1, 6-2 and 7-1, 7-2 indicate the preformatted left side address field and right side address field, respectively, and by reading these address fields, the track can be identified. It is done. 5 (corresponding to 5-1 and 5-2 in the figure) is a data section in which predetermined information is recorded.

Here, a method for recording optical information will be explained using a schematic diagram of an optical head optical system shown in FIG.

In FIG. 6, 21 is a semiconductor laser serving as a light source;
In this example, light with a wavelength of 830 nm is emitted which is polarized in the direction in the plane of the paper. Further, 22 is a collimator lens, 23 is a beam shaping beam, 24 is a diffraction grating for splitting the beam, and 25 is a polarizing beam splitter. Furthermore, 26 is 1
27 is an objective lens, 29 is a cylindrical lens, and 30 is a photodetector.

The light beam emitted from the semiconductor laser 21 becomes a diverging light beam and enters the collimator lens 22. The lens converts the light into a parallel light beam, and the beam shaping prism 23 shapes the light into a beam having a predetermined light intensity distribution, that is, a circular intensity distribution. Thereafter, the light flux enters the diffraction grating 24, and is split by the diffraction grating 24 into three effective light beams (0th-order diffraction light and ±1st-order diffraction light). These three light beams are sent to the polarizing beam splitter 25
The light is incident as a P-polarized light beam. Polarizing beam splitter 2
5 has spectral characteristics as shown in FIG. 7, and nearly 100% of the incident light is transmitted according to the characteristics.

Next, the three light beams are converted into circularly polarized light as they pass through the quarter-wave plate 26, and are focused onto the optical card 1 by the objective lens 27. As shown in Figure 5, this focused light forms three minute beam spots Sl (+1st order diffracted light), S2 (Oth order diffracted light), and S3 (-1st order diffracted light).
It is. The light beam S2 is used as recording, reproduction, and AF sub-control signal light, and the light beams S1 and S3 are used as AT sub-control signal light. As shown in FIG. 5, the spot position on the optical card 1 is the light beam spot Sl.
, S3 are located on the adjacent tracking track 4,
The light beam spot S2 is located on the information track 2 between the tracking tracks. Thus, optical card 1
The reflected light from the light beam spot formed above passes through the objective lens 27 again to become a parallel beam of light, and passes through the 174-wave plate 26, so that the polarization direction is 90" different from that at the time of incidence.
converted into a rotated beam of light. The light then enters the polarization beam splitter 25 as an S-polarized beam, is reflected by nearly 100% due to the spectral characteristics shown in FIG. 7, and is guided to the detection optical system.

The detection optical system is constructed by combining a spherical lens 28 and a cylindrical lens 29, and this combination performs AF sub-control using the astigmatism method. Furthermore, the three light beams reflected from the optical card 1 are condensed by the detection optical system and are incident on the photodetector 30. As shown in FIG. 8, the photodetector 30 includes two light receiving elements 30a,
30c and a light receiving element 30b divided into four parts. The light receiving elements 30a and 30c receive the reflected light from the aforementioned optical spots Sl and S3, and tracking control is performed using this light reception signal. Further, the four-divided light receiving element 30b receives reflected light from the optical spot S2, and focus control is performed based on this light reception signal, and recorded information is reproduced.

[Problems to be Solved by the Invention] However, in the conventional optical head optical system described above, since the light intensity distribution of the semiconductor laser is shaped into a predetermined intensity distribution by a beam shaping prism, alignment of the optical axis of the optical system is complicated. It is. That is, there is a problem in that the adjustment work for aligning the optical axes of the beam shaping prism and the subsequent optical system is complicated and that the adjustment takes a long time.

The present invention has been made to solve these problems, and its purpose is to provide an optical information recording/reproducing device that is easy to manufacture.

[Means for Solving the Problems] In order to achieve the above object, an optical head optical system is provided which irradiates an optical information recording medium with a light beam of a semiconductor laser focused on a minute spot and detects reflected light from the recording medium. In the optical information recording and reproducing apparatus that records information on the medium or reproduces recorded information by irradiation with a light beam of the optical head optical system, the elliptical light beam of the semiconductor laser is applied to the optical head optical system. An optical information recording and reproducing device is provided, which is characterized by having a pair of cylindrical lenses that shape a light beam.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the optical information recording/reproducing apparatus of the present invention. In FIG. 1, the same parts as those of the conventional device are given the same reference numerals.

In FIG. 1, 21 is a semiconductor laser used as a light source, and its light beam has an elliptical cross section. This elliptical light beam is corrected by a pair of cylindrical lenses 11 and 12 into a light beam having a predetermined intensity distribution, that is, a circular cross-section, as will be described in detail later. Furthermore, since the light beam of the semiconductor laser 21 is a diverging light beam, it is corrected into a parallel light beam by the collimator lens 22 . The cylindrical lens 11 has a concave shape and is arranged between the collimator lens 22 and the diffraction grating 24. Also, the other cylindrical lens 1
2 has a convex shape, and polarizing beam splitters 25 and 17
It is arranged between the four wavelength plates 26.

Here, the function of the cylindrical lenses 11 and 12 is explained as follows.
This will be explained using figures. Figure 2 shows cylindrical lens 1
1.12, and other optical systems are omitted. 2(a) is a front view of FIG. 1, and FIG. 2(b) is a side view thereof. In the example shown in FIG. 2, the ratio of the long axis to the short axis of the elliptical light beam is 2:1, and this is converted into a circular light beam having the same diameter as the long axis of the elliptical light beam. That is, the major axis direction of the elliptical light beam remains unchanged as shown in FIG. 2(b), and the minor axis direction is expanded twice (as shown in FIG. 2(a)).

In order to satisfy such conditions, the cylindrical lenses 11 and 12 may be set as follows. First, if the focal length of the cylindrical lens 11 is f3, and the focal length of the cylindrical lens 12 is f8, then f2=-2
The conditions for each lens are set so as to satisfy the relationship f.

In other words, the virtual image point of the cylindrical lens 11 and the focal position of the cylindrical lens 12 are set to match. Note that a diffraction grating 24 and a polarizing beam splitter 25 are interposed between the cylindrical lenses 11 and 12, but since these have no curvature, the relationship f+ = -2tyo can be maintained.

In this case, two cylintrile lens elements.

The distance in 12 can be converted into air equivalent distance.

In this way, the light beam of the semiconductor laser 21 is converted into a circular intensity distribution and exits the cylindrical lens 12.

This emitted light flux passes through a 174-wavelength plate 26 and an objective lens 27, and is irradiated onto the optical card 1 as a minute light spot. Further, the reflected light returns to the cylindrical lens 12 again through the same path. In this case, the returned light beam is focused by the cylindrical lens 12 by the in-plane component. Further, after being reflected by the polarizing beam splitter 25, omnidirectional components of the light beam are focused by the spherical lens 28. At this time, since the in-plane direction component of the light beam becomes focused light in advance by the cylindrical lens 12, the in-plane direction component of the light forms an image in front of the light component orthogonal to it, and therefore, as in the conventional case, the astigmatism occurs. AF control can be performed using the aberration method.

Furthermore, in this embodiment, the cylindrical lens 12
has the same function as the conventional cylindrical lens 29 shown in FIG. 6, so there is no need to provide a cylindrical lens in the detection optical system. Therefore, there is an advantage that the length of the detection optical system in the optical axis direction can be shortened.

The cylindrical lens 11 may be placed anywhere between the collimator lens 22 and the polarizing beam splitter 25, and the cylindrical lens 12 may be placed anywhere between the polarizing beam splitter 25 and the objective lens 27. good. Furthermore, in the above embodiment, the short axis direction of the elliptical light beam is widened and shaped, but it may be conversely reduced, that is, the cylindrical lenses 11 and 12
Even if the position of is reversed, it can be converted into a circular light beam. Furthermore, as shown in FIG. 3, a convex cylindrical lens 31 is used instead of the concave cylindrical lens 11, and even if both lenses are convex, the same effect as in the embodiment described above can be obtained. However, in this embodiment, the optical path length becomes long to suppress the aberrations to the same level, so this is disadvantageous in terms of space. Further, both may be constructed of double-sided cylindrical lenses, but in this case, although the aberration is good, there is a disadvantage of high cost.

[Effects of the Invention] As explained above, according to the present invention, a pair of cylindrical lenses are used to convert an elliptical beam into a circular beam, so the optical axis of the optical system can be easily aligned. The complicated adjustment work of optical axis alignment when using a conventional beam shaping prism can be completely eliminated. Therefore, it is possible to easily manufacture the device and reduce manufacturing costs.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the optical head optical system in the optical information recording/reproducing apparatus of the present invention, FIG. 2 is an explanatory diagram showing the beam shaping effect of the cylindrical lens, and FIG. 3 is another embodiment. FIG. 4 is a plan view of the optical card, FIG. 5 is a partially enlarged view of the optical card, FIG. 6 is a configuration diagram showing a conventional optical head optical system, and FIG. 7 is a polarizing beam splitter. FIG. 8 is an explanatory diagram showing the light receiving surface of the photodetector. 1... Optical card 11... Cylindrical lens (concave) 12... Cylindrical lens (convex) 21... Semiconductor laser 22... Collimator lens 25... Polarizing beam splitter 27... Objective Lens 30... Photodetector agent Patent attorney Seki Taira Yamashita Figure 6 Figure 6

Claims (4)

[Claims] (1) An optical head optical system that irradiates an optical information recording medium with a light beam from a semiconductor laser focused on a minute spot and detects reflected light from the recording medium, and irradiates the light beam of the optical head optical system. In the optical information recording and reproducing apparatus for recording information on the medium or reproducing recorded information, the optical head optical system is provided with a pair of cylindrical lenses that shape an elliptical beam of the semiconductor laser into a circular beam. An optical information recording/reproducing device characterized by: (2) The optical information recording/reproducing apparatus according to claim 1, wherein one of the pair of cylindrical lenses is a concave cylindrical lens and the other is a convex cylindrical lens. (3) The optical information recording/reproducing apparatus according to claim 1, wherein the pair of cylindrical lenses are both convex cylindrical lenses. (4) Between a polarizing beam splitter that separates light incident on the recording medium and light reflected from the medium and guides the reflected light to a detection optical system, and an objective lens that focuses the light beam into a minute spot, the pair of 2. One of the cylindrical lenses is arranged as a convex cylindrical lens, and the convex cylindrical lens is also used as a cylindrical lens used for focusing control by an astigmatism method in the detection optical system. optical information recording and reproducing device.