JPH01245439A - Information recording and reproducing optical system - Google Patents

Abstract

PURPOSE:To use the same lens used for a collimator lens (a first optical means) also for an objective lens (a second optical means) to image-form a small spot by composing the first optical means and the second optical means of the same optical element and specifying the relation between the thickness of an optical member for an emitting window and the thickness of a transparent substrate on a prescribed surface. CONSTITUTION:Flux emitted from a semiconductor laser chip 11 is passed through a plane-parallel plate 12 of a flux emitting window, made into parallel flux by a collimator lens (the first optical means) 2, transmitted through a beam splitter 3, and image-formed on an information recording medium 82 of an optical card 8 by an objective lens (the second optical means) 4 as the small spot. Further, the first optical means 2 and the second optical means 4 are composed of the same optical element, and the relation between thickness T1 of the optical member 12 for the light source flux emitting window and thickness T2 of a transparent substrate 81 provided on the prescribed surface is made into the one expressed by a shown expression. Thus, the same lens can be used, and the problem of correcting an aberration can be solved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an information recording/reproducing optical system including an optical information reproducing device for optically recording, reproducing, and/or erasing information and its recording medium. It is.

[Prior Art] In recent years, research and development have been actively conducted toward the practical application of optical information processing devices that perform recording and reproduction using semiconductor laser light as high-density recording memories.

FIG. 11 is a schematic diagram illustrating the configuration of an optical head used in an optical disk device. In FIG. 1t, 1 is a semiconductor laser, 1. is the laser chip of the semiconductor laser l,
1□ is a parallel plane plate with 94 windows for the light beam of semiconductor laser 1;
is a collimator lens.

3 is a beam splitter, 4 is an objective lens, 5 is an optical disk, 5. 5. is the transparent substrate of the optical disc 5, 5□ is the information recording surface of the optical disc 5, and 5. 6 is a support substrate for the optical disk 5, 6 is a condenser lens, and 7 is a photodetector.

The luminous flux emitted from the semiconductor laser chip l is.

The light beam passes through the parallel plane plate 12 of the light beam exit window, is made into a parallel light beam by the collimator lens 2, passes through the beam splitter 3, and is imaged by the objective lens 4 as a minute spot on the information recording surface 5□''2 of the optical disc 5. Generally, the focal length of the frimeter lens 2 and the objective lens 4 is 4 to b. Also, the reflected light from the information recording surface 52 of the optical disc 5 is
It becomes a parallel light beam again by the objective lens 4, is reflected by the beam splitter 3, passes through the condenser lens 6, and reaches the photodetector 7. Thereby, using a known method, R
Detection of F signal.

Focus control, tracking control, etc. are performed. Additionally, there are devices in which information is also recorded and erased using this system.

[Problems to be solved by the invention] The optical heads used in such conventional devices include:
It has the following drawbacks.

In an optical disk device, it is necessary to focus the laser beam emitted from the semiconductor laser 1 onto the information recording medium 5□'' to a diameter of about 1 μm. Therefore, the NA (numerical aperture) of the objective lens 4 is required to be about 0.5. In the optical disc 5, polycarbonate, polymethyl methacrylate, or glass is used for the 0;1 transparent substrate 5I, and its thickness is standardized to 1.2 mm. Further, the thickness of the parallel plane plate 1□ is generally 0.3 to 0.4 mm. Therefore, the collimator lens 2 and the objective lens 4
When using the same lens for 0.3
Various aberrations must be sufficiently corrected when a plane-parallel plate with a thickness of ~0.4+nm and a plane-parallel plate with a thickness of 1.2 mm are used. However, in reality, there is no lens that satisfies the conditions mentioned above and has an NA of about 0.5, and it has been impossible to realize the collimator lens 2 and the objective lens 4 with the same lens.

Therefore, in the conventional example, different lenses were used for the collimator lens 2 and the objective lens 4. For this reason, there was a drawback that the number of persimmons in the parts increased, leading to higher costs.

However, if the same lens is used for the collimator lens 2 and the n;j objective lens 4, the following means can be considered. Usually, the thickness of the transparent substrate 51 is thicker than the thickness of the parallel plane plate I□, so a lens is designed according to the thickness of the transparent substrate 51 and used as the objective lens 4. On the other hand, the collimator lens 2 includes the transparent substrate 51 and the parallel plane plate 12 between the semiconductor laser l and the collimator lens 2.
The objective lens 4 is used by arranging a thickness correction plate that corrects the difference in thickness.

However, even if such a method is used, in reality, the thickness of the thickness correction plate is very thin, making it difficult to manufacture.
This method has the drawback of increasing the number of persimmons in the parts, leading to higher production costs.

Furthermore, the above-mentioned problems occur not only in optical discs but also in optical cards. That is, the outer diameter dimension of the optical card,
Although the thickness and structure have not yet been standardized, the outer diameter is set to 85.6 mm to match the size of magnetic cards used in cash cards, credit cards, etc.
X 54. In many cases, the thickness is approximately 0.8 mm. The basic structure of the optical card is as shown in FIG. 2, with a transparent substrate 83. Many of them have a sandwich structure consisting of an information recording medium 8g and a support substrate 82. The thickness of the eight support substrates must be at least 0.2 mm from the viewpoint of structural stability of the optical card. On the other hand, the thickness of the transparent substrate 8I needs to be 0.3 mm or more, considering the influence of dust and scratches during both recording and recording of information, and the same situation applies. In particular, since optical cards are required to be less expensive than optical discs due to their intended use, it has been desired to solve the problems mentioned above.

[Means for Solving the Problems] An object of the present invention is to solve the problems mentioned in 111J and to provide a low-cost optical information recording/reproducing device.
The object of the present invention is to provide a highly capable information recording/reproducing optical system.

The purpose of ``-'' is to provide a light source, an optical section (a) for the luminous flux of the light source (9) functioning as a window, and a first optical means (i) that converts the luminous flux emitted from the light source into a parallel luminous flux. , Firi
ai2 second optical means for condensing the parallel light beam onto a predetermined surface; iii. a transparent substrate provided at a predetermined location;
1. A means for detecting a reflected light beam from a predetermined surface; wherein the first optical means and 11?1. the second optical means are constituted by the same optical element; The relationship between the thickness T of the optical member for the light source beam exit window and the thickness T2 of the transparent substrate provided on the predetermined surface is 1.

The information record IIl Ikuko Silk Science System is achieved.

[Operation] By configuring the thickness of the optical member and the thickness of the transparent substrate so as to have the above relationship, the same lens can be used and the problem of aberration compensation IE can be solved.

[Example] Hereinafter, an information recording/reproducing optical system according to the present invention will be explained in detail based on the drawings.In addition, as an example below, an example in which an optical card is adopted as a recording medium will be described. .

FIG. 1 is a schematic diagram showing an embodiment of an optical head of an optical card recording/reproducing apparatus n using the information recording/reproducing optical system of the present invention. In FIG. 1, l is a semiconductor laser, Il is a laser chip of semiconductor laser 1, 18 is a plane parallel plate of a light beam exit window of semiconductor laser l, 2 is a collimator lens, 3 is a beam splitter, 4 is an objective lens, and 8 is a optical card, 81
8 is a transparent substrate of the optical card 8, 8□ is an information recording surface of the optical card 8, 83 is a supporting substrate of the optical card 5, 6 is a condensing lens, and 7
is a photodetector.

The light beam emitted from the semiconductor laser chip 11 passes through the parallel plane plate l of the light beam exit window, is made into a parallel light beam by the collimator lens 2, passes through the beam splitter 3, and is sent to the information recording medium 821 of the optical card 8 by the objective lens 4. ．． imaged as a minute spot. Information recording medium 8 of optical card 8. The reflected light from (q and Detection, ) orcus it'l+ control, tracking control, etc. are performed. Furthermore, information can be recorded and erased in the same way using this system.

The configuration of the optical card 8 according to this embodiment is the same as that shown in FIG. 2 described in 11.

FIG. 3 is a diagram for explaining the effects of the optical system that can be achieved by this embodiment, in which 100 is an aspherical single lens with one surface being flat, and +01 is a parallel plane plate. Hereinafter, the extent to which various aberrations due to the thickness of the n;1 descending plane plate +01 can be corrected by the aspheric single lens 100 will be described using two examples (Example 1 and Example 2).

Example 1 Example 2 Here, in Examples 11 and 2, f is the focal length of the aspheric single lens 100, r is the radius of curvature near the optical axis of the first surface of the lens 100, and 8 is the diameter of the lens 100. 100 second
The radius of curvature of the surface, d, is 11; Also, the lens 100 has a refractive index of 6
The aspherical shape of the first surface of has its origin at its vertex, the optical axis as the X axis, and the height from the optical axis as 11. When , rotational symmetry 2
Based on the following surface, 11. is expressed by the following equation including terms up to the 10th power (see the equation below); however, this restriction on the order is for convenience and is not limited to this. Note that 1 is a conic constant.

+ 8 + ・Hr'+ CI' H18+ DI
・1118+ E + ・HI" + A +'
・H+'+B+°・H, +t+C1゛・H+'+D+°
・Hl” In the diagrams shown below, the object distance is set to infinity.

4 to 9 are spherical aberration diagrams, astigmatism diagrams, and lateral aberration diagrams of the above two examples, M is a meridional image diagram,
S indicates the sagittal image plane.

FIG. 4 is an aberration diagram due to the optical system of the aspherical single lens 100 and the parallel plane plate 101 shown in Example 1.

FIG. 5 shows that in the mj destination optical system shown in Example 1, 0; 12
The thickness of the parallel plane plate 101 is multiplied by 0.7, that is, t, =
It is an aberration diagram when it is 0.06521 mm.

FIG. 6 shows that in the optical system shown in Example 1, the thickness t of the fiil writing plane plate +01 is 1.5 times that is, t =
It is an aberration diagram when it is 0.13973 mm.

Here, the hand plane plate 101 is replaced with the transparent substrate 81 of the optical card.
If the focal length i@if of Example 1 is 4.5 mm, then the parallel plane plate! The wall thickness of 01 is 0.42mm in Figure 4.
, 0.29 mm in FIG. 5 and 0.63 mm in FIG.

FIG. 7 is an aberration diagram due to the optical system of the aspherical LIT lens 100 and the parallel plane plate LOT shown in Example 2.

FIG. 8 shows that in the optical system shown in Example 2, 1j; 12
The thickness of the parallel plane plate 101 is multiplied by 0.7, that is, t =
It is an aberration diagram when it is set to 0.0FI2511111.

FIG. 9 shows that in the optical system shown in Example 2, 1);
The thickness of the parallel plane plate 101 is 1.5 times, that is, 20,
It is an aberration diagram when l is set to 125 mm.

Here, the hand plane plate 101 is the hand plane plate l of the light beam exit window of the semiconductor laser, and the focal length Mf in Example 2 is 4.5 m.
m, the thickness of the parallel plane plate 101 is 0.34 mm in FIG. 7, 0.24 mm in FIG. 8, and 0.51 mm in FIG. 9.

The above is based on the aberration diagrams shown in FIGS. 4 to 9.

It can be seen that aberrations can be sufficiently corrected for the parallel plane of the light beam exit window of the semiconductor laser and the transparent substrate of the optical card with the same lens. Considering the relationship between the thickness of the transparent substrate, the thickness of the hand-held flat plate is T1. Till the thickness of the transparent substrate is 1゛2
Then, from the examples shown in Figures 4 to 6.

1′.

From the examples shown in Figures 7 to 9, 1゛.

becomes.

Here, how to derive equation (a) is shown below.

(1) The thickness of the semiconductor laser window is usually 0.3 to 0.4 m.
It is m. (See pages 4 and 15) (2) Thickness of the transparent protective layer of the optical card - The thickness of the entire optical card is approximately 0.8 mm, and the supporting base must be at least 0.2n+l++ - Scratches on the surface of the protective layer. Considering dust, I would like something with a diameter of 0.3 mm or more (see page 5) (3) Normally, the collimator and objective are used at f=4 to 6 (page 3)
Reference) Here, Example 19 Example 2 (see plo, +1) has f=1
In this case, if f=4.5mn+, t is p I 3 ~ p I
The value shown in 4 is obtained.

In Figures 4, 5, and 6, L = 0.42.0
．． 29°063 is shown. Since the aberration is good for any of these three values, these three values are used as a collimator.
You may use any of the following, but considering f1), 1'
, 0.42.

You can use any of these three forces as your object.

0.29≦T2≦0.63 In general, the thickness of the parallel deck of the beam exit window of a conductor laser is 0.3 to 0.4 mm, as described above, and is suitable for recording and reproducing information. 0; 1 transparent substrate 1 at time
- Considering the effects of dirt and scratches on the surface.

O1i The thickness of the transparent substrate needs to be 0.3 mm or more.

For this reason, it is necessary that the relationship between the thickness T1 of the parallel plate and the thickness ''' of the transparent substrate is T2≧T1. Therefore, the following condition is ultimately preferable as the relationship. 6 In addition, 1
) In Embodiment 11, an example is shown in which the optical system is composed of an aspherical single lens and a Hertagonist surface plate. However, the present invention is not limited to this configuration only; For example, 1 instead of 19 lenses.

Various applications are possible, such as a lens configuration consisting of a plurality of lJi lenses.

Further, FIG. 10 is a schematic diagram (cross-sectional view) showing the structure of a destination card 8 which is another embodiment of the present invention.

In FIG. 10, 84 is an air gap, and the present invention can be implemented in the same way in an optical card having such an air gap 84. Furthermore, the 10th
In the figure, the same parts as those in FIG. By configuring the plate thickness so that the thickness of the transparent substrate (transparent protective layer) of the recording medium and the light beam exit window of the light source (semiconductor laser) are parallel to each other as described above, the distance from the light source of the optical head can be reduced. It is now possible to use the same lens for the collimator lens to collimate the emitted light beam and the objective lens to image the collimated light beam as a minute spot on the information recording medium of the optical card. It has become possible to reduce the types of parts that make up the head.Also, since twice as many of the same parts as in the past have to be manufactured, costs can also be reduced due to production at a later date.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an optical head for an optical card recording/amplifying device that can be achieved according to the present invention. FIG. 2 is a schematic diagram showing the configuration of an optical card that is an embodiment of the present invention.6 FIG. 3 is a diagram for explaining an optical system that can be achieved by the present invention. 4 to 9 are aberration diagrams for explaining the present invention. 10M is a schematic diagram showing the configuration of an optical card according to another embodiment of the present invention. FIG. 11 is a schematic diagram showing an optical head of a conventional optical disk recording/reproducing device. 1... Semiconductor laser 2... Collimator lens 3... Beam splitter 4... Objective lens 6... Collection Optical lens 7... Photodetector 8... Optical card 100... Photospheric single lens 101... Parallel plane plate Agent Patent attorney Jo Taira Yamashita Figure 1 Figure 2 Figure 4 #i Aberration Fig. 5 Fig. 6 Closed aberration Fig. 8 Fig. 8 Bar convergence Fig. 9 Ladder convergence left Fig. 10 Fig. 11 Fig. □53

Claims (2)

[Claims] (1) A light source, an optical member functioning as a light beam exit window of the light source, a first optical means that converts the light beam emitted from the light source into a parallel light beam, and a first optical means that focuses the parallel light beam onto a predetermined surface. 2; a transparent substrate provided on the predetermined surface; and a means for detecting a reflected light beam from the predetermined surface; and the means are constituted by the same optical element, and the thickness T_1 of the optical member for the exit window and the thickness T_2 of the transparent substrate provided on the predetermined surface are 1.0≦T_2/T_1≦2.1 An information recording/reproducing optical system characterized by having the following relationship. (2) Claim 1, wherein the predetermined surface is an information recording surface of an optical card or an optical disc, and the transparent substrate is a transparent protective layer provided on a side of the information recording surface on which a light flux enters. Information recording/reproducing optical system described in Section 1.