JP4297999B2 - Optical information recording medium and information reading method - Google Patents
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Description
【0001】
【発明の属する技術分野】
本発明は、光線の照射による出射光(透過光または反射光)のパターンを受光することによって、記録情報を光学的に読み取ることを目的とする光情報記録媒体に関する。
【0002】
【従来の技術】
上記のような光情報記録媒体として、バーコード,カルラコード,CD−ROM,近年ではDVDが公知である。
CD−ROMやDVD(記録情報の構成要素がピット)に比較して、記録情報の容量の向上を図った提案として、本出願人による特開平6−76365号公報が公知である。
【0003】
上記提案は、n個に領域分割された回折格子セルに、読み取り光(ビーム)を照射し、前記セルの各分割領域からの回折光を、領域分割数nに見合った個数で配置された受光素子により受光し、各分割領域からの再生情報和を、セル毎に記録されたコードとして認識するものである。(図1(a)参照)
図1(b)に示す回折格子セルは、領域分割数nが(縦方向3×横方向3=9個)の例である。
【0004】
各分割領域が表すのは、ON/OFFの2値データであるが、それらの集まりからなる各セルは、nに応じて多彩な種類のコードを表し得る。
【0005】
すなわち、CD−ROMやDVDでは、読み取り光(ビーム)の照射により、ピットの有無によるON/OFFの2値データのみしか表現できないが、上記提案によれば、1箇所のみの照射で、ON/OFF以上の多彩な表現を実現し、記録媒体の容量が飛躍的に向上することになる。
【0006】
上記提案では、各分割領域からの回折光と受光素子とが1:1の関係であり、下記の問題が潜在する。
【0007】
回折格子セル平面の任意の軸(方向)については、回折格子セルの直後では、出射する1次回折光の強度分布は、矩形関数で表せるように設計するのが一般的であり、記録情報の構成要素である回折格子セルからの1次回折光の分布は、セル直後では矩形関数で表される。
セル(回折格子に限らない)からの出射光の強度分布がセル内では一様な、従来の光情報記録媒体を図2に示す。
【0008】
しかし、1次回折光を、セル直後から距離が離れた「フレネル領域」および「フラウンホーファー領域」で受光する場合には、受光素子上での分布は、不均一で拡がったものとなる。
矩形関数による振幅分布を図3(a)に、受光素子上での1次回折光の分布を図3(b)に示す。
【0009】
図3(b)のような分布を持つ各分割領域からの1次回折光を受光すると、本来対応するべき受光素子以外の素子が1次回折光を検出してしまい、ノイズによる読み取りエラーが生じてしまう。
【0010】
また、各受光素子が、各分割領域からの1次回折光の強度を、ON/OFFの2値データのみならず、多値データ(段階的な強度)の検出も可能な場合には、本来受光するべき分割領域からの1次回折光の中心部か、隣接する分割領域からの1次回折光の周辺部(ノイズ)かの判別が困難であり、正確な情報読み取りの上で一層影響が大きい。これらの不都合を、クロストークと呼ぶこととする。
【0011】
【発明が解決しようとする課題】
本発明は、受光位置でのクロストークの惧れのない出射光を発生するようなセルから構成される光情報記録媒体とその情報読み取り方法を提供することを目的とする。
【0012】
【課題を解決するための手段】
本発明の請求項1の光情報記録媒体は、
光線の照射による出射光のパターンを、多値データを検出する受光素子群を複数備えた受光素子アレイから受光することによって、記録情報を光学的に読み取ることを目的とする光情報記録媒体において、記録情報の構成要素としてセルを備え、前記セルは隣合う2以上の分割領域を含むものであり、
前記セルが回折格子からなり、前記出射光が回折格子セルからの1次回折光であり、
記録情報の構成要素であるセルの分割領域からの出射光の持つ振幅分布が、セルの直後で、セルの中心部から周辺部へ向かって小さくなっていることを特徴とする。
【0013】
(削除)
【0014】
請求項2の発明は、回折格子セルからの出射光である1次回折光が、球面波の位相を持つことを特徴とする。
【0015】
上記光情報記録媒体の読み取りにあたっては、
請求項1〜3の何れかに記載の光情報記録媒体の情報記録部に光線を照射し、
情報記録部からの出射光を、マトリクス状に配置された前記受光素子群を備えた前記受光素子アレイによって、フレネル領域で受光することを特徴とする。
【0016】
<作用>
記録情報の構成要素であるセルからの出射光の持つ振幅分布が、セルの直後で、セルの平面における1方向については、中心部から周辺部へ向かって小さくなるように振幅変調が施されることにより、セルから離れて配置された受光素子上での出射光の分布の周辺の成分を減少することができるため、出射光と受光素子とを1:1の関係で維持する上で好適であり、クロストークが回避された正確な記録情報が検出できる。(請求項1)
【0017】
また、前記セルを回折格子により構成することにより、記録情報の容量の向上が図れると共に、振幅分布の変調の厳密な制御も可能である。(請求項1)
【0018】
上記の作用について、以下に詳述する。
回折格子により振幅変調を施す場合には、回折格子の周期に対する格子幅の比や、回折格子の位相変調量の変化など、多くの方法から選択できる。
尚、回折格子(位相型あるいは振幅型)においては、局所的な回折格子の周期に対する格子幅の比は1/2のときが最も回折効率が高く(すなわち1次回折光の振幅が大きく)、この値から増減することにより1次回折光の振幅は小さくなる。
【0019】
薄い位相型回折格子では、局所的な位相変調量(光が格子部とそうでない部分を通過する際にできる位相の差)がπのときが、1次回折光について最大の回折効率となり、これから離れるにつれて回折効率が小さくなる。
厚い位相型回折格子の場合は、格子の断面形状や材質や入射光の偏光状態などにより、回折効率が変化する。
【0020】
また、セルから出射した光は、中心からなだらかに減少させても良いが、中心付近では一定(最大値)であり、中心からある程度離れた位置から周辺部へ向かって減少させるようにした方が、入射光に対する利用効率が上がる。
【0021】
セルから出射する1次回折光が、球面波状の位相分布を有するようにすることで、セルのサイズに依存せず、出射する1次回折光を任意の範囲に拡げることができる。(請求項2)
【0022】
1次回折光に、球面波状の位相分布を持たせる手段としては、
(1)回折格子を曲線で構成する。(例えば、ゾーンプレートの一部を回折格子として用いる)
(2)1次回折光を発生させるための照明光を、平行光ではなく球面波状の位相分布を持つ光(例えば、点光源からの発散光)とする。
などがある。
【0023】
情報読み取りにあたり、受光素子が回折格子セルに対してフレネル領域である場合、1次回折光の強度分布のピーク中心の幅を狭くすることも可能であり、読み取り精度が向上する。(請求項3)
【0024】
【発明の実施の形態】
光情報記録媒体からの出射光の持つ振幅分布が、セル面における少なくとも1方向について、中心部から周辺部へ向かって小さくなるように振幅変調を施す上で、以下に挙げる数学的な表現(関数)が有効である。
【0025】
【数1】
【0026】
【数2】
【0027】
【数3】
【0028】
上式において、セルの外形が矩形の場合、xは矩形の任意の辺に垂直な軸をとり、素子中心を0とした座標である。
尚、Tは素子の大きさ(矩形形状の場合は1辺の長さ)であり、−T/2≦x≦T/2の範囲の値をとる。
【0029】
一般化Hamming関数においては、αにより関数の形を最適化できるが、α=0.5や0.54が一般的である。
【0030】
中心部の振幅分布を一定にし、中心から離れた位置から周辺部へ向かって減少するようにした場合は、台形関数に相当する。
ただし、本発明においては、台形関数として斜辺部は直線とは限らないものとする。(すなわち、中心付近で一定値をとり、その両側でなだらかに減少するような関数を台形関数と呼ぶ)
【0031】
振幅分布が台形関数で表されるようにすると、出射光の周辺部の強度の減少を伴ったまま、中心部の強度を上げることができ、入射光の利用効率を上げることになる。
ただし、台形の斜辺部を小さくし過ぎると、出射光の周辺部の強度が上がり、その効果が小さくなる。
例えば、素子の大きさが50μmのとき、台形の斜辺部が10μm程度(上辺が30μm程度の台形)なら十分な効果がある。
【0032】
回折格子からなるセルに対して、上記の振幅分布関数による振幅変調を施した場合の、セルの直後での1次回折光の振幅分布波形と回折光の強度分布を図4に示す。
Hamming関数による振幅分布が図4(a)、三角波関数による振幅分布を図4(b)、台形関数による振幅分布を図4(c)(d)であり、回折光の強度分布は図4(e)のようになる。
尚、ここでは振幅分布関数として、代表的ないくつかの関数を挙げたが、これらに限るものではない。
【0033】
図5は、回折格子セルにより記録情報を構成した光情報記録媒体に係る説明図である。同図で、各セルからの出射光の持つ振幅分布が、左右方向(x軸)および上下方向(y軸)で、中心部から周辺部へ向かって小さくなるように、各セルについて振幅変調が施されている。
【0034】
図5の回折格子は、バイナリー回折格子に振幅変調フィルターが貼り合わされたものとして捉えても良いが、白の部分を回折効率が最大となる位相変調量、黒の部分が回折効率が最小となる位相変調量を表す位相型回折格子として捉えても良い。
もちろん、この図のような回折格子に限らず、回折格子の周期に対する格子幅の比を変調した振幅型あるいは位相型回折格子であっても良い。
【0035】
図5の光情報記録媒体による情報読み取りの状態を、図6・図7に示す。
図6は「透過型」の読み取りを示す説明図であり、図7は「反射型」の読み取りを示す説明図である。
【0036】
図6では、左側から読み取り光線が記録媒体に入射し、媒体上の各セルで前記光線が透過回折され、同図の右側に配置された受光素子アレイ(受光素子の集まり)によって受光されて、記録情報が検出される。
【0037】
図7では、右側から読み取り光線が記録媒体に入射し、媒体上の各セルで前記光線が反射回折され、同図の右側に配置された受光素子アレイ(受光素子の集まり)によって受光されて、記録情報が検出される。
【0038】
何れの場合でも、受光素子アレイは、回折格子セルに対してフレネル領域に配置することが、本発明の作用・効果を奏する上で一層望ましい。
【0039】
【発明の効果】
光情報記録媒体からの記録情報を検出する受光素子には、ノイズやクロストークの少ない情報光が達することになるため、高密度(容量)な光情報記録媒体について、正確な情報読み取りが実現される。
【0040】
【図面の簡単な説明】
【図1】領域分割された回折格子セルからの再生情報和により、記録情報を検出する従来技術に係る説明図であり、図1(a)は読み取る様子を示す概要図、図1(b)は領域分割された回折格子セルの一例を示す説明図である。
【図2】従来の光情報記録媒体を示す説明図。
【図3】矩形関数による振幅分布図3(a)と、出射光の強度分布図3(b)を示す説明図。
【図4】各種の振幅分布関数と、それらの振幅変調を施した場合の波長選択素子からの1次回折光の強度分布を示す説明図。図7(a)はHamming関数による振幅分布、図7(b)は三角波関数による振幅分布、図7(c)(d)は台形関数による振幅分布であり、図7(e)は回折光の強度分布。
【図5】回折格子セルにより記録情報を構成した光情報記録媒体の説明図。
【図6】本発明の透過型での情報読み取りを示す説明図。
【図7】本発明の反射型での情報読み取りを示す説明図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical information recording medium intended to optically read recorded information by receiving a pattern of emitted light (transmitted light or reflected light) by irradiation of light rays.
[0002]
[Prior art]
As such an optical information recording medium, a bar code, a carla code, a CD-ROM, and recently a DVD are known.
Japanese Patent Laid-Open No. 6-76365 by the present applicant is known as a proposal for improving the capacity of recorded information as compared with CD-ROM and DVD (the component of recorded information is a pit).
[0003]
In the above proposal, a diffraction grating cell divided into n regions is irradiated with reading light (beam), and diffracted light from each divided region of the cell is received in a number corresponding to the number of divided regions n. Light is received by the element, and the reproduction information sum from each divided area is recognized as a code recorded for each cell. (See Fig. 1 (a))
The diffraction grating cell shown in FIG. 1B is an example in which the number of area divisions n is (vertical direction 3 × horizontal direction 3 = 9).
[0004]
Each divided area represents binary data of ON / OFF, but each cell formed by the collection can represent various types of codes according to n.
[0005]
That is, in CD-ROM and DVD, only binary data of ON / OFF depending on the presence or absence of pits can be expressed by irradiation of reading light (beam), but according to the above proposal, ON / OFF can be expressed by irradiation of only one place. Various expressions beyond OFF are realized, and the capacity of the recording medium is dramatically improved.
[0006]
In the above proposal, the diffracted light from each divided region and the light receiving element have a 1: 1 relationship, and the following problems are latent.
[0007]
For an arbitrary axis (direction) of the diffraction grating cell plane, the intensity distribution of the emitted first-order diffracted light is generally designed to be expressed by a rectangular function immediately after the diffraction grating cell. The distribution of the first-order diffracted light from the diffraction grating cell as an element is represented by a rectangular function immediately after the cell.
FIG. 2 shows a conventional optical information recording medium in which the intensity distribution of emitted light from a cell (not limited to a diffraction grating) is uniform in the cell.
[0008]
However, when the first-order diffracted light is received by the “Fresnel region” and the “Fraunhofer region” that are separated from each other immediately after the cell, the distribution on the light receiving element is uneven and widened.
FIG. 3A shows the amplitude distribution by the rectangular function, and FIG. 3B shows the distribution of the first-order diffracted light on the light receiving element.
[0009]
When the first-order diffracted light from each divided region having the distribution as shown in FIG. 3B is received, elements other than the light-receiving element that should originally correspond detect the first-order diffracted light, resulting in a reading error due to noise. .
[0010]
If each light receiving element can detect the intensity of the first-order diffracted light from each divided area as well as ON / OFF binary data as well as multi-valued data (stepwise intensity), it will receive light originally. It is difficult to discriminate between the central portion of the first-order diffracted light from the divided region to be performed and the peripheral portion (noise) of the first-order diffracted light from the adjacent divided region, and this has a greater influence on accurate information reading. These inconveniences are called crosstalk.
[0011]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical information recording medium composed of cells that generate outgoing light that does not cause crosstalk at a light receiving position, and an information reading method thereof.
[0012]
[Means for Solving the Problems]
The optical information recording medium of claim 1 of the present invention comprises:
In an optical information recording medium intended to optically read recorded information by receiving a pattern of emitted light by irradiation of light from a light receiving element array having a plurality of light receiving element groups for detecting multi-value data , A cell is provided as a component of the recording information, and the cell includes two or more adjacent divided regions,
The cell comprises a diffraction grating, and the emitted light is a first-order diffracted light from the diffraction grating cell;
The amplitude distribution of the emitted light from the divided area of the cell, which is a component of the recorded information, is characterized by decreasing from the central part of the cell to the peripheral part immediately after the cell.
[0013]
(Delete)
[0014]
The invention of claim 2 is characterized in that the first-order diffracted light that is emitted from the diffraction grating cell has a spherical wave phase.
[0015]
In reading the optical information recording medium,
Irradiating light to the information recording part of the optical information recording medium according to any one of claims 1 to 3,
The emitted light from the information recording unit, by the light receiving element array having a light receiving element group arranged in a matrix, characterized in that it received in the Fresnel region.
[0016]
<Action>
Amplitude modulation is performed so that the amplitude distribution of the light emitted from the cell, which is a component of the recorded information, decreases immediately from the center to the periphery in one direction on the plane of the cell immediately after the cell. As a result, it is possible to reduce the components around the distribution of the emitted light on the light receiving elements arranged away from the cell, which is suitable for maintaining the emitted light and the light receiving elements in a 1: 1 relationship. Yes, it is possible to detect accurate recording information in which crosstalk is avoided. (Claim 1)
[0017]
Further, by constituting the cell with a diffraction grating, it is possible to improve the capacity of recorded information and to strictly control the modulation of the amplitude distribution. (Claim 1 )
[0018]
The above action will be described in detail below.
When amplitude modulation is performed using a diffraction grating, a number of methods can be selected, such as the ratio of the grating width to the period of the diffraction grating and the change in the phase modulation amount of the diffraction grating.
In the diffraction grating (phase type or amplitude type), the diffraction efficiency is highest when the ratio of the grating width to the local diffraction grating period is 1/2 (that is, the amplitude of the first-order diffracted light is large). By increasing / decreasing from the value, the amplitude of the first-order diffracted light becomes smaller.
[0019]
In a thin phase diffraction grating, when the amount of local phase modulation (the difference in phase that occurs when light passes through a grating portion and a portion that does not) is π, the maximum diffraction efficiency is obtained for the first-order diffracted light, and the distance is far from this. As the diffraction efficiency decreases.
In the case of a thick phase diffraction grating, the diffraction efficiency varies depending on the cross-sectional shape and material of the grating, the polarization state of incident light, and the like.
[0020]
In addition, the light emitted from the cell may be reduced gradually from the center, but it is constant (maximum value) near the center, and should be reduced from a position somewhat away from the center toward the periphery. , Use efficiency with respect to incident light increases.
[0021]
By allowing the first-order diffracted light emitted from the cell to have a spherical wave-like phase distribution, the emitted first-order diffracted light can be expanded to an arbitrary range without depending on the cell size. (Claim 2 )
[0022]
As means for giving the first-order diffracted light a spherical wave-like phase distribution,
(1) The diffraction grating is configured by a curve. (For example, a part of the zone plate is used as a diffraction grating)
(2) Illumination light for generating the first-order diffracted light is not parallel light but light having a spherical wave phase distribution (for example, divergent light from a point light source).
and so on.
[0023]
In reading information, when the light receiving element is a Fresnel region with respect to the diffraction grating cell, the width of the peak center of the intensity distribution of the first-order diffracted light can be narrowed, and the reading accuracy is improved. (Claim 3 )
[0024]
DETAILED DESCRIPTION OF THE INVENTION
When performing amplitude modulation so that the amplitude distribution of the emitted light from the optical information recording medium becomes smaller from the center to the periphery in at least one direction on the cell surface, the following mathematical expression (function ) Is effective.
[0025]
[Expression 1]
[0026]
[Expression 2]
[0027]
[Equation 3]
[0028]
In the above equation, when the outer shape of the cell is a rectangle, x is a coordinate having an axis perpendicular to an arbitrary side of the rectangle and the element center being zero.
Note that T is the size of the element (the length of one side in the case of a rectangular shape), and takes a value in the range of −T / 2 ≦ x ≦ T / 2.
[0029]
In the generalized Hamming function, the shape of the function can be optimized by α, but α = 0.5 or 0.54 is general.
[0030]
A case where the amplitude distribution in the center is constant and decreases from a position away from the center toward the periphery corresponds to a trapezoid function.
However, in the present invention, the hypotenuse as a trapezoidal function is not necessarily a straight line. (That is, a function that takes a constant value near the center and decreases gently on both sides is called a trapezoidal function.)
[0031]
If the amplitude distribution is represented by a trapezoidal function, the intensity of the central part can be increased while the intensity of the peripheral part of the emitted light is decreased, and the utilization efficiency of incident light is increased.
However, if the hypotenuse of the trapezoid is made too small, the intensity of the peripheral portion of the emitted light is increased and the effect is reduced.
For example, when the element size is 50 μm, it is sufficient if the trapezoidal hypotenuse is about 10 μm (the upper side is about 30 μm).
[0032]
FIG. 4 shows the amplitude distribution waveform of the first-order diffracted light and the intensity distribution of the diffracted light immediately after the cell when amplitude modulation by the above-described amplitude distribution function is performed on the cell composed of the diffraction grating.
The amplitude distribution by the Hamming function is shown in FIG. 4A, the amplitude distribution by the triangular wave function is shown in FIG. 4B, the amplitude distribution by the trapezoid function is shown in FIGS. 4C and 4D, and the intensity distribution of the diffracted light is shown in FIG. e).
In addition, although some typical functions were mentioned here as an amplitude distribution function, it is not restricted to these.
[0033]
FIG. 5 is an explanatory diagram relating to an optical information recording medium in which recording information is constituted by diffraction grating cells. In the figure, amplitude modulation is performed for each cell so that the amplitude distribution of the light emitted from each cell decreases from the center to the periphery in the left-right direction (x-axis) and the up-down direction (y-axis). It has been subjected.
[0034]
The diffraction grating shown in FIG. 5 may be regarded as an amplitude modulation filter bonded to a binary diffraction grating, but the white portion has the maximum phase modulation amount and the black portion has the minimum diffraction efficiency. It may be understood as a phase type diffraction grating representing the amount of phase modulation.
Of course, it is not limited to the diffraction grating as shown in this figure, and may be an amplitude type or phase type diffraction grating in which the ratio of the grating width to the period of the diffraction grating is modulated.
[0035]
The state of information reading by the optical information recording medium of FIG. 5 is shown in FIGS.
FIG. 6 is an explanatory diagram showing “transmission type” reading, and FIG. 7 is an explanatory diagram showing “reflection type” reading.
[0036]
In FIG. 6, the reading light beam enters the recording medium from the left side, the light beam is transmitted and diffracted by each cell on the medium, and is received by the light receiving element array (collection of light receiving elements) arranged on the right side of FIG. Record information is detected.
[0037]
In FIG. 7, the reading light beam enters the recording medium from the right side, the light beam is reflected and diffracted by each cell on the medium, and is received by the light receiving element array (collection of light receiving elements) arranged on the right side of FIG. Record information is detected.
[0038]
In any case, it is more desirable to arrange the light receiving element array in the Fresnel region with respect to the diffraction grating cell in order to achieve the function and effect of the present invention.
[0039]
【The invention's effect】
Information light with less noise and crosstalk reaches the light receiving element that detects the recorded information from the optical information recording medium, so accurate information reading can be realized for high-density (capacity) optical information recording media. The
[0040]
[Brief description of the drawings]
1A and 1B are explanatory diagrams according to a conventional technique for detecting recorded information based on a sum of reproduction information from a region-divided diffraction grating cell. FIG. 1A is a schematic diagram showing a state of reading, and FIG. FIG. 4 is an explanatory view showing an example of a region-divided diffraction grating cell.
FIG. 2 is an explanatory view showing a conventional optical information recording medium.
FIG. 3 is an explanatory diagram showing an amplitude distribution diagram 3 (a) by a rectangular function and an intensity distribution diagram 3 (b) of emitted light.
FIG. 4 is an explanatory diagram showing various amplitude distribution functions and the intensity distribution of the first-order diffracted light from the wavelength selection element when the amplitude modulation is performed. 7A shows the amplitude distribution by the Hamming function, FIG. 7B shows the amplitude distribution by the triangular wave function, FIGS. 7C and 7D show the amplitude distribution by the trapezoid function, and FIG. 7E shows the diffracted light. Intensity distribution.
FIG. 5 is an explanatory diagram of an optical information recording medium in which recording information is constituted by diffraction grating cells.
FIG. 6 is an explanatory diagram showing information reading in a transmission type according to the present invention.
FIG. 7 is an explanatory view showing information reading by the reflection type of the present invention.
Claims (3)
前記セルが回折格子からなり、前記出射光が回折格子セルからの1次回折光であり、
記録情報の構成要素であるセルの分割領域からの出射光の持つ振幅分布が、セルの直後で、セルの中心部から周辺部へ向かって小さくなっていることを特徴とする光情報記録媒体。In an optical information recording medium intended to optically read recorded information by receiving a pattern of emitted light by irradiation of light from a light receiving element array having a plurality of light receiving element groups for detecting multi-value data , A cell is included as a component of the recorded information, and the cell includes two or more adjacent divided areas.
The cell comprises a diffraction grating, and the emitted light is a first-order diffracted light from the diffraction grating cell;
An optical information recording medium characterized in that an amplitude distribution of light emitted from a divided region of a cell, which is a component of recorded information, decreases from the central portion of the cell toward the peripheral portion immediately after the cell.
情報記録部からの出射光を、マトリクス状に配置された前記受光素子群を備えた前記受光素子アレイによって、フレネル領域で受光することを特徴とする光情報記録媒体の情報読み取り方法。Irradiating a light beam to the information recording portion of the optical information recording medium according to any one of claims 1-2,
An information reading method for an optical information recording medium, wherein light emitted from an information recording unit is received in a Fresnel region by the light receiving element array including the light receiving element groups arranged in a matrix.
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