JPS62239338A - Optical information reproducer - Google Patents

Abstract

PURPOSE:To attain the satisfactory reproduction output by forming a grid within a unit information area and also specifying the form of the grid. CONSTITUTION:A phase grid of pitch (p) and piece number (m) is formed with a unit information area. Here the wavelength of the reproduced light is referred to as lambda and therefore lambda/mp<=NA<=lambda/p is satisfied for the numerical aperture NA of the optical system of an optical information reproducer. For instance, the recording pits 12 do not mean just the level differences of a recess/projection part but contain a grid of a cyclic structure. In such a constitution, the optical information reproducer can detect the satisfactory reproduction signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a news playback device that plays back information on an optical information recording medium such as an optical disk, an X-card, or an optical tape.

[Prior art]

Conventionally, various types of media such as optical disks, original cards, and original tapes are known as media for recording and reading information using a single source. The principles of recording or reading information on these media vary depending on the type of media material used, the optical system used for recording or continuous reading, and the type of system, and several methods have been put into practice. A typical example is to change the direction of magnetization of the medium using the original magnetic recording medium, and to detect the signal by changing the Kerr rotation angle that occurs when the reading source is irradiated to light intensity + g. method, or a method of recording and reproducing by changing the light transmittance, reflectance, and absorption spectrum of the medium only in the portion corresponding to information;
Also, a method of detecting a change in light intensity corresponding to a signal by changing the refractive index and shape of the information recording part of the medium and utilizing phenomena such as (B) refraction and interference of the reproduction light irradiated to the recording part. There is.

In all of these conventional methods, information is detected as changes in light intensity, so improving the S/N of the reproduced signal as much as possible is an important technical issue required for media or systems. There is.

Among these conventional optical information recording media, the unit recording area is recorded in the form of pits, and it is possible to obtain a good 8/N ratio of the reproduced signal with a relatively simple groove formation. There is.

The present applicant has proposed in Japanese Patent Application No. 59-250287 to obtain an even better S/N ratio of the reproduced signal by changing the shape of the wind level 11# signal area from a pit shape to a grid shape.

[Summary of the invention]

It is an object of the present invention to detect a good reproduced signal 44 from an optical information recording medium in which the format of recording in a unit information area is a lattice. The object of the present invention is to provide an optical information reproducing device.

〔Example〕

Prior to a detailed explanation of the present invention, the structure of an optical information recording medium in which the unit information area is a lattice, which has already been proposed by the applicant, and the benefit of information detection will be explained using Figure 1 + AI (Bl). Figure 1 (In Al, 11 is an optical information recording carrier, 12 is a posture information area which is the smallest courier for recording information (hereinafter, 12 is called a bit), 13 is a transparent protection 1 Firewood, 14 is a light reflecting film, and 15 is a substrate.

In the present invention,! The pits 12 are not simply uneven steps, but have a periodic lattice structure within the pits 12. Such a lattice structure can be formed by various means other than embossing. The f# information reproducing light 17 is assumed to be light from a dimensional source with a wide range such as an LED, and the reproduced light illuminates the pit 12 and its surrounding area almost uniformly through the lens 16. When the pit is illuminated, the light is reflected intensified in a specific direction determined by the pitch of the grating and the wave width of the illumination light due to the diffraction effect of the grating within the pit. Therefore, for example, if the pitch of the grating is selected so that at least the first-order diffracted light 18 does not enter the lens 16, all the diffracted light will be deflected outside the lens, and the old reflected light from the part where the pit 12 does not exist will be reflected from the lens 16. There is a clear difference in element f# from the case of returning through 16. Therefore, a reproduced signal with a good S/N ratio can be obtained. FIG. 1(B) is a diagram showing the optical output corresponding to the recording pit shown in FIG. 8g1(A). , as is clear from Figure 1 (B)! I.C.

5'e returning to the lens 16 from the part where the pit 12 is present
The amount of light that returns to the lens 16 from a portion where no pit exists is extremely small compared to the amount of light that returns to the lens 16 from a portion where no pit exists, and the difference in amount of light between the bit portion and the non-bit portion boundary area is also noticeable. This optical information riC
In recording media, it is a grid.

If the pitch is constant, the diffraction angle is always constant regardless of the length and size of the pit, so it is stable (g-number reproduction is possible).

FIG. 2 is a diagram showing an example of a reproducing apparatus for an optical information recording medium as shown in FIG. 1. ``The optical information recording carrier 11 is f
Although a reflective type record carrier as shown in Figure 1 may be used, here, for ease of understanding, a transmissive type record carrier is adopted and an apparatus is shown. The emission flux emitted from the semiconductor laser P is collimated by the objective lens 22, becomes a parallel light flux 23, and enters the recording medium 11. If the recording bit 12 does not exist at this incident position, the incident light beam passes through the recording medium as a parallel light beam, and the condenser lens 25
As a result, most of the light flux 27 is focused on the light receiving sensor 26 and detected. Recording pit 12 at the incident position on the recording medium
exists, the incident light beam 23 is diffracted by the recording pit 12, and most of the light beam 24 falls outside the aperture of the condenser lens 25, so that the light beam reaching the light receiving sensor 26 is caused by extremely small amounts of interference. be. By detecting the signal from the light receiving sensor 26, it can be determined whether or not a recording bit exists. Note: @
If the target is a reflective type, the objective lens 22 can also function as the condensing lens 25! t5
Not even.

At this time, in order to improve the BIN of the output signal and improve the reliability of the reading device, it is desirable that the difference in the original amount of the two types of signal lights (24, 27), that is, the contrast, be as large as possible.

By the way, in an information reading device such as the example mentioned above, if you try to carry out a succession without using an autofocus mechanism in order to reduce costs and make it more compact, the size of the posture information area is limited to around 10 μm. becomes. The grid formed within the nine unit information areas can be relatively easily formed with a width of about 1 μm using ordinary photorin technology. The present invention provides a multiplication table reproduction system configuration particularly suitable for obtaining the best contrast under such conditions.

FIG. 3 is a diagram illustrating the image intensity distribution of a unit information area having a grid appearing on the one-dimensional sensor light-receiving surface in the arrangement shown in FIG. 2.

The image intensity technique is the image portion 3 of the unit information area having the grid.
1, it is low, and it becomes high in the part 32 where there is no grid. The procedure for calculating the image intensity distribution will be briefly explained below.

For calculation purposes, the light flux emitted from the LED, which is the light source, is converted into a plane wave f0, which is assumed to be 9, and the plane wave passes through the aperture A of the illumination system and is focused onto the card surface by the condensing lens. The complex amplitude distribution is the Fourier transform F of A, f.
It is represented by (A, fo). If the translation of this distribution on the card surface is defined as mt, +, then the translated amplitude distribution is expressed as m(1)(F(A-fo)).

If the phase modulation by the card is 0 and the conversion of the imaging system is D, the image intensity distribution on the sensor plane is I D (C, mtx
l(F(A, fo ))) 12. Therefore, the image intensity distribution Et on the sensor surface of the information unit having the grid
,teeth! t, -710(C,011(1)(P(A-fo)
)) 12a! is required. The graph in Figure 3 can be obtained by performing numerical calculations using curve construction, but it is difficult to understand.

The shape of the grating depends on the shape and depth of the grating, the pitch, and the NA of the imaging lens.
It changes variously depending on the parameters such as. It is desirable to have this intensity as high as possible using a one-dimensional sensor such as a COD, and to have as high a resolution as possible.

In order to find a combination of the above-mentioned parameters suitable for the present invention, the inventor of the present invention investigated a rectangular lattice with a line space ratio of 1:1, a symmetrical triangular lattice, and a reflective type by adjusting the pitch of the lattice and the height of the lattice. In the case of a phase grating, the strong IW distribution was calculated when changing the phase difference (equivalent to 1/2 of one phase difference), and the contrast C was also determined. At this time, the MA of the imaging system is 0
．． 18. The wavelength of the illumination light is 0.88 μm.

The results are shown graphically in FIGS. 4 and 5.

As can be seen from the graph, in both the rectangular and triangular grids, the contrast is best when the grid height is approximately constant, regardless of the grid pitch. For rectangular grid, approximately 0.25μ
A contrast of approximately 0.8 or more is obtained within a range of approximately ±0.05μffl centered on the height of
．． A contrast of 0.95 or more can be obtained in a range of 45 μm±0.05 μm.

When converted into wavelength units, a rectangular grating has a wavelength of 0.28λ±0.
06λ, 0.51λ±0.06λ for triangular lattice (λ=
0.88 μm).

Next, set the height of the grid to the above central value, that is, 0 for a rectangular grid.
The contrast was determined by the same calculation while keeping the diameter at 25 μm and 0.45 μm for the triangular grating, and changing the NA of the imaging system. The results are shown graphically in FIGS. 6 and 7. When using the NA of the imaging system as a parameter, as the NA decreases, the absolute amount of light that reaches the sensor surface decreases, so it is necessary to pay attention not only to the contrast but also to the amount of light. Therefore, the figure also shows the relative ratio of the amount of light reaching the sensor surface from the nest position information area when there is no grid. (Dotted line) From FIG. 6, it can be seen that in the case of a rectangular lattice, the contrast is best near NA O,2, and a sufficient amount of 51t can be obtained from a portion without a lattice. In the case of the triangular grid in Figure 6, the contrast is approximately NA O, in the range of 20 to 0.25.
It is a good break in both light quantity. In either case, if the NA becomes too large, the contrast will decrease, and conversely, if the HA is too small, the absolute light amount will be insufficient. The range of NA that can be practically used differs depending on the snowmaking specifications, but by adding the following interpretation to the above graph, the approximately usable range can be determined.

First, if we consider the case of increasing the NA of the reproduction optical system, we will see that in general [as the NA increases, the resolving power of the optical system increases, and it becomes possible to resolve fine grids within the unit information area. goes down. This is because even high-order diffracted light out of the light diffracted by the grating is taken into the optical system and contributes to the resolution. On the contrary, NA
As the value becomes smaller, the zero-order diffracted light finally begins to be traced, and the absolute amount of light reaching the sensor surface reaches its peak. Therefore, in the case of a potential information area having a grating, one guideline can be a range in which at least the O dimension is included and diffracted light of the first order or higher is not included. Next, a unit without a lattice? '# Think about the news area. Since the unit information area can be attached to an aperture having a certain finite width, it is only necessary to consider how much of the diffracted light by the position information area should be taken into the imaging system.

In order to prevent a decrease in the absolute light amount, it is necessary to filter out at least the 0th order light. - Even if the diffracted light of the highest order is extracted, since there is no grating in this case, the contrast of the unit information area will not deteriorate. Therefore, in this case, the MA that injects at least the 0th order or more of the diffracted light determined by the aperture
The range of fI can be used as a guideline for obtaining a good output signal fI.

Let the fundamental period of the grating be p, the grating length aeffl, the wavelength of the reproduced light be λ, and the diffraction angle of the diffracted light be θ.

As is well known, for vertically incident light, the first-order diffracted light has a maximum value in the θ direction of λ θInl w − . In the case of a unit information area without a grating, the width of the aperture is given by mp, so if θ' is the angle at which the amount of light becomes minimum between the 0th-order light and the 1st-order light, then λ sinθ' = □ mp. , N and A of the optical system have refractive indexes of 1 before and after the optical system.
In the case of , there is a relationship of N, A = sin θ.

Therefore, it provides a range of N and A for the optical system that provides good contrast and does not reduce the amount of light.

As explained above, in the present invention, a good reproduction output can be achieved by forming a grid within a unit information area and setting the shape of the grid as described above.

In the above-mentioned embodiments, a light-reflecting phase object was particularly used for the explanation, but according to the gist of the present invention, it can also be applied to a transmission-type phase object and an amplitude grating type object. It is. Furthermore, although the present invention is particularly suitable for optical cards, it is not limited thereto and can be applied to various forms of information recording media such as optical disk source tapes.

[Brief explanation of drawings]

4X 1 Figures (A) and (B) are diagrams showing the structure of an optical information recording medium in which the unit information area is a lattice and the principle of information detection.
The figure shows the schematic configuration of the optical t# information reproducing device according to the present invention.The third country shows the image intensity IJ1' distribution of the information unit area appearing on the light receiving sensor in the arrangement shown in Figure 8g2. The explanatory drawings, FIG. 4, FIG. 5, FIG. 6, and FIG. 7 are diagrams for explaining preferred embodiments of the apparatus according to the present invention. 11... Optical information recording medium 12... Unit information area P,... Semiconductor laser 22... Objective lens 25... Condensing lens 26... Light receiving sensor

Claims (1)

[Scope of Claims] (1) An apparatus for reproducing information from an optical information recording medium that forms a grid in a unit information area in which information is to be recorded, and records information depending on the presence or absence of the grid, the apparatus comprising: is a phase grating with pitch P and number m, and the wavelength of the reproduction light is λ, then
Numerical aperture N. of the optical system of the device. A. is λ/mP≦N. A. An optical information reproducing device characterized by satisfying the relationship: ≦λ/P. (2) The optical information reproducing device according to claim 1, wherein the phase grating has a rectangular cross-sectional shape, and the phase difference Δn is in the range of 0.22λ≦Δn≦0.34λ. (3) The optical information reproducing device according to claim 1, wherein the phase grating has a triangular cross-sectional shape, and the phase difference Δn is in the range of 0.4λ≦Δn≦0.5λ.