JP2004185737A - Near-field light probes and near-field light recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a near-field light probe by which recording/reproducing and erasing can be performed easily and to provide a near-field light recording and reproducing device which can record/reproduce and erase efficiently. <P>SOLUTION: This near-field light recording and reproducing device has a first laser beam source generating near-field light, a second laser beam source generating a second laser beam having a longer wavelength than the wavelength of a first laser beam generated from the first laser beam source, and an optical detecting unit introducing simultaneously the first laser beam and the second laser beam to the near-field light probe and detecting light reflecting recording information of an optical recording medium through the near-field light probe. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２４】
このようにして、近接場光のみではアモルファスマークの書き込みができなかった従来技術の欠点を克服した。このときのアモルファスマークが書き込まれる領域は、近接場光が照射される領域に限られる。従って、光の回折限界を超えた高密度な記録が可能となり、記録型大容量光記憶装置を可能とする。
【００２５】
次に、消去条件について説明すると、いわゆる書き換え型の記憶装置を実現するためには、記録層を結晶化に必要な温度まで加熱しなければいけない。既に記録されているアモルファスマークを消去するには、図４の（ｃ）のｅで示した時間にＥｌｂ（：消去に必要な青色レーザ光パワー）よりも強い近接場光を照射しなければいけないが、伝搬光から近接場光を再生する変換効率が著しく低いために、消去に必要なパワーを得るこことができない。図４の（ｃ）はそれを表している。Ｅｌｂに対して、実際の青色（遮光体を透過しない）の近接場光のパワーＥｂが小さく、消去ができない。これを改善するために、赤外のレーザを用いる。図４の（ｂ）では、図４の（ｃ）の青色レーザ光の消去時間にタイミングを合わせて、赤外レーザのパワーをＥｉに強くする。但しここで重要なことは、Ｅｌｉ（：消去に必要な赤外レーザ光パワー）よりもＥｉを小さくすることである。すなわちＥｉ＜Ｅｌｉとする。このようにしないと、図１での、青色の近接場光が照射されていなくてかつ赤外光のみが照射されている領域のアモルファスマークが消去されてしまい、記録されている情報が失われる。つまりマークを書き込もうとしている場所の周辺に記録されている情報が消えてしまうからである。さらに、図４の（ａ）に示すように赤外レーザ光と青色の近接場光の両方が照射されている領域では、消去に必要なレーザパワーを得る必要があるので、この時のトータルなレーザパワーＥｔはＥｌｔ（：消去に必要なレーザ光パワー）より大きくなければいけない。先に述べたように、説明しやすくするために、各波長のレーザパワーに対する相変化材料の感度は等しいとすると、Ｅｌｔ＜Ｅｔ＝Ｅｉ＋Ｅｂの条件を満たすように各レーザパワーを設定する。まとめると、下記の２つの条件を同時に満たすようにする。
【００２６】
【数２】

【００２７】
このようにして、近接場光のみではアモルファスマークの消去ができなかった従来技術の欠点を克服した。このときのアモルファスマークが消去される領域は、近接場光が照射される領域に限られる。従って、光の回折限界を超えた高密度な消去が可能となり、先の記録方法と相まって、書き換え型大容量光記憶装置を可能とする。
【００２８】
そして、再生を行うときには、赤外レーザ光は何ら効力を発揮することはできない。なぜならば光記録媒体から反射した赤外レーザ光は図１に示すダイクロイックミラー１７によりフォトダイオード２０側には伝搬しないので、再生に寄与できない。従って、再生時には青色の近接場光のみのパワーＲｂが、Ｒｌｂｍｉｎ（：再生に必要な青色レーザ光パワー）より大きくなければいけない。ここでは実際に再生を行っているわけではなく、記録時の急冷を行う時間のレーザパワーを言う。従って、バイアスパワーといった方がよいが、ここでの説明では再生時のパワーとバイアス時のパワーを等しくしているので、上記のような表現となる。よって、時間ｒでは赤外レーザを発光させなくても良い。ただし、赤外レーザ光を安定に発光させるためなど他の理由により時間ｒでもこれを発光せざるを得ない場合は、これにより近接場光のみが照射される領域で、既に記録されているアモルファスマークが消去されないように、以下の条件を満たす必要がある。
【００２９】
Ｅｌｔ＞Ｒｔ＝Ｒｉ＋Ｒｂ
【００３０】
なお、上記レーザ光源としては変調のしやすさなどから、半導体レーザが適している。波長１．２μｍ以下のレーザとしては、青色半導体レーザとして、ＧａＮ、ＺｎＯ、ＳＨＧなどの材料を用いたもので、赤色半導体レーザとして、Ｉｎ_{１ −ｘ}Ｇａ_ｘＰ、Ａｌ_ｘＧａ_{１ −ｘ}Ａｓ、ＧａＡｓ_{１ −ｘ}Ｐ_ｘなどが挙げられる。また、波長１．２から２．２μｍの半導体レーザとしては、Ｉｎ_ｘＧａ_{１ −ｘ}Ａｓ、ＩｎＡｓ_{１ −ｘ}Ｐ_ｘなどが挙げられる。また、波長２．５μｍ以下のレーザとしては、青色半導体レーザとしてＧａＮ、ＺｎＯ、ＳＨＧなどの材料を用いたもの、赤色レーザとして、Ｉｎ_{１ −ｘ}Ｇａ_ｘＰ、Ａｌ_ｘＧａ_{１ −ｘ}Ａｓ、ＧａＡｓ_{１ −ｘ}Ｐ_ｘ、Ｉｎ_ｘＧａ_{１ −ｘ}Ａｓ、ＩｎＡｓ_{１ −ｘ}Ｐ_ｘなどが挙げられる。また、波長２．５から５μｍの半導体レーザとしては、Ｉｎ_ｘＧａ_{１ −ｘ}Ａｓ、ＩｎＡｓ_{１ −ｘ}Ｐ_ｘ、ＩｎＡｓ_{１ −ｘ}Ｓｂ_ｘなどが挙げられる。更に、このようなレーザとしては、特に変調の方法が得られれば、ＹＡＧレーザ、ガラスレーザなどの固体レーザ、Ｈｅ−Ｎｅレーザやアルゴンレーザのような気体レーザ、Ｎ_２レーザのような分子レーザ、色素レーザなどでも良い。
【００３１】
また、ここでは遮光膜材料としてシリコンを示したが、特にこれに限定されることはなく、波長との組み合わせで、ＧａＡｓ、ＧａＰ、ＧａＮ、ＺｎＯ、ＺｎＳなどの化合物半導体や炭素材料、ＳｉＣなどでも良い。
【００３２】
図５は別の発明の第１の実施例に係る近接場光プローブの構成を示す断面図である。本実施例の近接場光プローブ２００は、プローブ基板２０１として透光性の石英を用いる。しかし、これに特に限定されるわけではなく、ガラスや樹脂であっても良い。これには斜面を持つ孔２０２が開いており、使用するレーザ波長以下の開口寸法を持つ微小開口２０３が開いている。ここでは、遮光体２０４の材料としてシリコンを用いる。なお、シリコンを製膜する方法としては、スパッタ、光ＣＶＤ、蒸着、熱ＣＶＤ、プラズマＣＶＤなどが挙げられる。また、ここでは遮光体２０４の材料としてシリコンを示したが、特にこれに限定されることはなく、波長との組み合わせで、ＧａＡｓ、ＧａＰ、ＧａＮ、ＺｎＯ、ＺｎＳなどの化合物半導体や炭素材料、ＳｉＣなどでも良い。
【００３３】
図６は別の発明の第２の実施例に係る近接場光プローブの構成を示す断面図である。本実施例の近接場光プローブ３００は、プローブ基板３０１としては透光性の石英を用いる。しかし、これに特に限定されるわけではなく、ガラスや樹脂であっても良い。これには斜面を持つ突起３０２が形成されており、突起先端の寸法は、使用するレーザ波長以下になっている。基板表面と突起斜面には遮光体３０３が形成されている。突起斜面のみに遮光体３０３が形成されているだけでも良い。ここでは、遮光体３０３の材料としてシリコンを用いる。波長１．２μｍ未満の波長の光をプローブ基板側から照射すると、突起先端に近接場光が生じる。なお、シリコンを製膜する方法としてはスパッタ、光ＣＶＤ、蒸着、熱ＣＶＤ、プラズマＣＶＤなどが挙げられる。また、ここでは遮光体３０３の材料としてシリコンを示したが、特にこれに限定されることはなく、波長との組み合わせで、ＧａＡｓ、ＧａＰ、ＧａＮ、ＺｎＯ、ＺｎＳなどの化合物半導体や炭素材料、ＳｉＣなどでも良い。なお、突起型プローブとしては図７の（ａ）〜（ｄ）に示したような構造のものでも良い。
【００３４】
なお、本発明は上記実施例に限定されるものではなく、特許請求の範囲内の記載であれば多種の変形や置換可能であることは言うまでもない。
【００３５】
【発明の効果】
以上説明したように、本発明の近接場光プローブは、光記録媒体を対向させて光記録媒体内に記録された情報を読み取りあるいは情報を光記録媒体内に書き込むために近接場光を発生する。そして、基板に、微小開口及び斜面を有する貫通孔を設けている。更に、特定波長の光を透過し、一方別の特定波長の光を透過しない遮光材料で形成された遮光体を少なくとも貫通孔の斜面に形成し、遮光体を透過しない光で近接場光を発生させるとともに、遮光体を透過する光を、貫通孔の斜面を通して光記録媒体に照射する。よって、記録・再生、消去が容易な近接場光プローブを提供できる。
【００３６】
また、本発明の近接場光プローブは、特定波長の光を透過し、一方別の特定波長の光を透過しない遮光材料で形成された平板の基板に貫通孔を設けたことに特徴がある。よって、記録・再生、消去が容易な近接場光プローブを提供できる。
【００３７】
更に、本発明の近接場光プローブは、基板に、微小開口及び斜面を有する突起を設け、特定波長の光を透過し、一方別の特定波長の光を透過しない遮光材料で形成された遮光体を少なくとも貫通孔の斜面に形成し、遮光体を透過しない光で近接場光を発生させるとともに、遮光体を透過する光を、突起の斜面を通して光記録媒体に照射する。よって、記録・再生、消去が容易な近接場光プローブを提供できる。
【００３８】
また、遮光材料は半導体材料であることが好ましい。更に、半導体材料をシリコンとし、遮光体を透過する光の波長を１．２〜２．２μｍとし、遮光体を透過しない光の波長を１．２μｍ未満とすることが好ましい。また、半導体材料をゲルマニュウムとし、遮光体を透過する光の波長を２．５〜５μｍとし、遮光体を透過しない光の波長を２．５μｍ未満とすることが好ましい。
【００３９】
更に、別の発明としての近接場光記録再生装置は、近接場光を発生させる第１のレーザ光源と、第１のレーザ光源から発生される第１のレーザ光の波長より長い波長の第２のレーザ光を発する第２のレーザ光源と、第１のレーザ光及び第２のレーザ光を同時に近接場光プローブに導入し、また光記録媒体の記録情報を反映した光を近接場光プローブを介して検出する光検出ユニットとを有することに特徴がある。よって、高効率に記録・再生、消去を行うことができる近接場光記録再生装置を提供できる。
【００４０】
また、光記録媒体の記録層に記録情報を書き込む場合、消去に必要な第２のレーザ光の光パワーをＥｌｉとし、記録情報書き込み時の第２のレーザ光の光パワーをＷｉとしたとき、条件Ｗｉ＜Ｅｌｉを満たすことにより、記録情報の記録を可能にするとともに既に記録されている情報を誤って消去されないようにすることができる。
【００４１】
更に、光記録媒体の記録層の記録情報を消去する場合、消去に必要な第２のレーザ光の光パワーをＥｌｉとし、記録情報消去時の第２のレーザ光の光パワーをＥｉとしたとき、条件Ｅｉ＜Ｅｌｉを満たすことにより、記録情報の消去を可能にするとともに既に記録されている情報を誤って消去されないようにすることができる。
【００４２】
また、第１のレーザ光は青色のレーザ光であり、また第２のレーザ光は赤外線レーザ光であることが好ましい。
【図面の簡単な説明】
【図１】本発明の一実施例に係る近接場光記録再生装置の構成を示す概略断面図である。
【図２】シリコンの吸収スペクトルの特性を示す図である。
【図３】ゲルマニュウムの吸収スペクトルの特性を示す図である。
【図４】全体のレーザパワー、赤外線レーザパワー、青色レーザパワーの各パワー特性を示す図である。
【図５】別の発明の第１の実施例に係る近接場光プローブの構成を示す断面図である。
【図６】別の発明の第２の実施例に係る近接場光プローブの構成を示す断面図である。
【図７】突起型プローブの一例を示す斜視図である。
【図８】従来の近接場光プローブの構成を示す断面図である。
【符号の説明】
１０；近接場光記録再生装置、１１；近接場光用レーザ、１２；赤外線レーザ、
１３〜１５；集光レンズ、１６；ハーフミラー、１７；ダイクロックミラー、
１８；対物レンズ、１９；近接場光プローブ、２０；フォトダイオード。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a near-field optical probe and a near-field optical recording / reproducing apparatus, and more particularly, to a near-field optical probe that generates and detects near-field light capable of high-density and large-capacity optical recording.
[0002]
[Prior art]
[Patent Document 1] JP-A-2000-164915
Optical memories currently in practical use record information by irradiating an optical recording medium with laser light focused to the diffraction limit and applying thermal or magnetic modulation to the recording layer. Reproduction of recorded information is performed by detecting a change in reflected light intensity or polarization state modulated by the light. In such information recording means, the recording density on the optical recording medium is almost determined by the laser wavelength and the numerical aperture (NA) of the objective lens. However, in order to cope with an increase in the amount of information surrounding information devices such as computers in recent years, a large-capacity optical memory that exceeds the limit of the recording density determined under the above conditions is required.
[0003]
As a promising next-generation large-capacity optical memory, a so-called near-field optical recording / reproducing apparatus for recording / reproducing information using near-field light has been proposed. As an optical recording / reproducing apparatus using near-field light, a near-field optical probe described in Patent Document 1 has been proposed. This conventional near-field optical probe will be described below with reference to the drawings.
[0004]
FIG. 8 is a sectional view showing a configuration of a conventional near-field optical probe. The conventional near-field optical probe 80 shown in FIG. 1 includes a high-concentration impurity layer 81 of the first conductivity type, a low-concentration impurity layer 82 of the first conductivity type, and an impurity introduction region 83 of the second conductivity type. This is a structure in which a through hole 85 having a minute opening 84 is provided in a substrate on which a detector is formed, and a second conductivity type impurity introduction region 83 serving as a light receiving region of a semiconductor photodetector is provided only in the vicinity of the minute opening 84. Is provided. In the conventional near-field light probe 80 having such a structure, near-field light is generated in the minute aperture 84, and writing, reading, and erasing are performed using only the near-field light.
[0005]
In such a conventional near-field optical probe, a mark is written on a recording medium using only near-field light in order to record information. In general, a dye-based organic material or a phase change material is used as a recording material of a recording medium. (Refractive index and shape) are changed for recording.
[0006]
[Problems to be solved by the invention]
However, since the near-field light uses only a very small percentage of the light applied to the minute aperture, its optical power is very small. Therefore, sufficient power required for recording cannot be obtained, and recording is difficult. Another drawback is that sufficient power required for erasing cannot be obtained for the same reason.
[0007]
The present invention has been made to solve these problems, and provides a near-field optical probe in which recording / reproduction and erasing are easy, and a near-field optical recording / reproducing apparatus capable of recording / reproducing / erasing with high efficiency. The purpose is to provide.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a near-field optical probe according to the present invention includes a near-field optical probe for reading information recorded in an optical recording medium or writing information in the optical recording medium with an optical recording medium facing the optical recording medium. Occurs. Then, a through hole having a minute opening and a slope is provided in the substrate. Furthermore, a light-shielding body formed of a light-shielding material that transmits light of a specific wavelength and does not transmit light of another specific wavelength is formed on at least the slope of the through-hole, and generates near-field light with light that does not transmit through the light-shielding body. At the same time, the light transmitted through the light shield is irradiated to the optical recording medium through the slope of the through hole. Therefore, it is possible to provide a near-field optical probe in which recording / reproducing and erasing are easy.
[0009]
Further, the near-field optical probe of the present invention is characterized in that a through-hole is provided in a flat substrate formed of a light shielding material that transmits light of a specific wavelength and does not transmit light of another specific wavelength. Therefore, it is possible to provide a near-field optical probe in which recording / reproducing and erasing are easy.
[0010]
Further, the near-field light probe of the present invention is provided with a projection having a minute opening and a slope on a substrate, and a light-shielding body formed of a light-shielding material that transmits light of a specific wavelength but does not transmit light of another specific wavelength. Is formed on at least the slope of the through-hole, and near-field light is generated by light that does not pass through the light shield, and light transmitted through the light shield is irradiated onto the optical recording medium through the slope of the protrusion. Therefore, it is possible to provide a near-field optical probe in which recording / reproducing and erasing are easy.
[0011]
Further, the light shielding material is preferably a semiconductor material. Further, it is preferable that the semiconductor material is silicon, the wavelength of light transmitted through the light shield is 1.2 to 2.2 μm, and the wavelength of light not transmitted through the light shield is less than 1.2 μm. Preferably, the semiconductor material is germanium, the wavelength of light passing through the light shield is 2.5 to 5 μm, and the wavelength of light not passing through the light shield is less than 2.5 μm.
[0012]
Further, a near-field optical recording / reproducing apparatus as another invention includes a first laser light source for generating near-field light, and a second laser light having a wavelength longer than the wavelength of the first laser light generated from the first laser light source. A second laser light source that emits a laser beam, a first laser beam and a second laser beam are simultaneously introduced into a near-field optical probe, and light reflecting information recorded on an optical recording medium is transmitted through the near-field optical probe. And a light detection unit that detects the light through the light source. Therefore, it is possible to provide a near-field optical recording / reproducing apparatus capable of performing recording / reproducing / erasing with high efficiency.
[0013]
Further, when recording information is written on the recording layer of the optical recording medium, when the optical power of the second laser light required for erasing is Eli and the optical power of the second laser light at the time of writing the recording information is Wi, By satisfying the condition Wi <Eli, the recording information can be recorded and the already recorded information can be prevented from being accidentally erased.
[0014]
Further, when erasing the recording information of the recording layer of the optical recording medium, the optical power of the second laser light required for erasing is Eli, and the optical power of the second laser light at the time of erasing the recording information is Ei. By satisfying the condition Ei <Eli, it is possible to erase recorded information and prevent information already recorded from being accidentally erased.
[0015]
Preferably, the first laser light is a blue laser light, and the second laser light is an infrared laser light.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The near-field optical recording / reproducing device includes a first laser light source for generating near-field light, and a second laser light for emitting a second laser light having a wavelength longer than the wavelength of the first laser light generated from the first laser light source. A laser light source, a first laser beam and a second laser beam are simultaneously introduced into a near-field optical probe, and a light detection unit that detects light reflecting information recorded on an optical recording medium via the near-field optical probe And
[0017]
【Example】
FIG. 1 is a schematic sectional view showing a configuration of a near-field optical recording / reproducing apparatus according to one embodiment of the present invention. In FIG. 1, a near-field optical recording / reproducing apparatus 10 according to the present embodiment includes a near-field light laser 11, an infrared laser 12, condensing lenses 13 to 15, a half mirror 16, a dichroic mirror 17, an objective lens 18, a near-field It is configured to include an optical probe 19 and a photodiode 20. The near-field optical recording / reproducing apparatus 10 according to the present embodiment having such a configuration uses the converging lens 13, the half mirror 16, the dichroic mirror 17, and the objective lens 18 to apply blue laser light from the near-field light laser 11 to the converging lens 13. The infrared laser beam from the infrared laser 12 is introduced into the near-field optical probe 19 through the condenser lens 14, the dichroic mirror 17, and the objective lens 18. Then, the light intensity of the light reflecting the recording information of the recording layer 102 of the optical recording medium 100 is transmitted to the photodiode 20 via the near-field optical probe 19, the objective lens 18, the dichroic mirror 17, the half mirror 16, and the condenser lens 15. An optical system for detecting by means of is provided as a basic unit. The optical recording medium 100 has the form of a disk, and the recording data is arranged such that information that is continuous in the circumferential direction of concentric circles is arranged. Further, in the near-field optical recording / reproducing apparatus 10, a central portion thereof is coupled to a rotating shaft and is rotated by a motor (not shown).
[0018]
Here, the near-field light probe 19 for generating near-field light is formed of a flat plate having a hole having an inclined surface, and a small opening having a wavelength equal to or less than the wavelength of the light for generating near-field light is formed on the surface on the optical recording medium 100 side. is open. The near-field light probe 19 functions as a light shield for the emission wavelength of the near-field light laser 11, and uses a semiconductor as a material of the light shield.
[0019]
As the near-field light laser 11, a blue semiconductor laser using GaN or SHG is used. Here, a GaN semiconductor laser with a wavelength of 405 nm is used. On the other hand, as the infrared laser 12 as another laser light source, an infrared laser having a wavelength of 1.5 μm is used. In both cases, the emitted light is collimated by the condenser lenses 13 and 14. The collimated light from the near-field light laser 11 passes through the half mirror 16 and is incident on the prism type dichroic mirror 17, and the collimated light from the infrared laser 12 is incident on the dichroic mirror 17. The dichroic mirror 17 is manufactured such that light on the short wavelength side near 400 nm is transmitted, and light on the long wavelength side near 1.5 μm is reflected. Thereby, the infrared laser light and the blue laser light pass through the same optical path. Both light beams are applied to the minute aperture by the objective lens 18 in front of the near-field light probe 19. Since the objective lens 18 is optimally designed for a wavelength of 405 nm, the focused spot of the infrared laser beam is larger than that of the blue laser beam. In addition, since the wavelength of the infrared laser light is longer than that of the blue laser light, the diffraction limit also causes the infrared laser light to have a larger focused spot than the blue laser light. Although the absorption spectrum of silicon changes depending on its resistance value (which can be controlled by the doping amount), one having a resistance value as low as possible (doping amount is small) is selected. This is because there is less absorption on the long wavelength side. As an example, a case of a specific resistance of 0.5 Ω · cm will be described. The absorption spectrum of silicon is shown in Fig. 2 (HY Fan and M. Becker, ed. When the wavelength is between 1.2 μm and 2.2 μm, the absorption coefficient is extremely low. In particular, at 1.5 μm, the absorption is the lowest, and it can be said that it is almost transparent at this wavelength. On the other hand, although not shown in FIG. 2, it can function as a light-shielding material that does not transmit light of almost 405 nm even in an experiment, even if it is considered as an extension of the graph on the short wavelength side. Accordingly, the light of the infrared laser light (wavelength: 1.5 μm) is transmitted through the silicon probe with the spot diameter larger than the minute aperture, and is irradiated on the optical recording medium 100 with the same spot diameter. On the other hand, since the blue laser light cannot pass through the silicon probe, near-field light of the blue laser light is generated on the optical recording medium 100 side with a minute opening. Since the spot diameter at this time is near-field light and is limited by the size of the minute aperture, it can be made 100 nm or less. Therefore, the spot becomes smaller than the infrared laser beam. Then, the blue near-field light and the infrared light are reflected by the optical recording medium 100, the blue light passes through the minute aperture, and the infrared light passes through the light shield and enters the objective lens 18 again. Conversely, follow the light path. The infrared light is reflected by the dichroic mirror 17 toward the infrared laser, while the blue laser light passes through and is reflected by the half mirror 16 toward the photodiode 20. Generally, half is reflected. This light is focused on the photodiode 20 by the focusing lens 15. Thus, information recorded on the recording layer can be read.
[0020]
As another near-field light laser 11, a red to near-infrared semiconductor laser using GaAsP or the like is used. Here, a near-infrared semiconductor laser having an emission wavelength of 780 nm is used. On the other hand, the infrared laser 12 serving as another laser light source has an emission wavelength of 2.5 to 3.5 μm._xGa_{1 -X}As and InAs_{1 -X}P_xAn infrared laser is used. As an embodiment, a semiconductor laser having a wavelength of 3.5 μm is used. The constituent optical system is the same as in FIG. However, the emission wavelength of the infrared laser is 3.5 μm. Further, the dichroic mirror is manufactured so that light on the short wavelength side near 780 nm is transmitted, and light on the long wavelength side near 3.5 μm is reflected. Other operations are the same as those described with reference to FIG. However, germanium is used as the material of the light shield. Although the absorption spectrum of germanium changes depending on its resistance value (which can be controlled by the doping amount), one having as low a resistance value as possible (with a small doping amount) is selected. This is because there is less absorption on the long wavelength side. As an example, a case of a specific resistance of 0.5 Ω · cm will be described. FIG. 3 shows the absorption spectrum of germanium. The source is the same as in FIG. When the wavelength is between 2.5 μm and 5 μm, the absorption coefficient is extremely low. In particular, at 3.5 μm, the absorption is the lowest, and it can be said that it is almost transparent at this wavelength. On the other hand, although not shown in FIG. 3, it can be considered as an extension of the graph on the short wavelength side, and in our experiments, it functions as a light shielding material that does not transmit light of almost 780 nm. Accordingly, in the case of the near-field light probe 19 shown in FIG. 1, the light of the infrared laser light (wavelength: 3.5 μm) is transmitted through the germanium probe with the spot diameter being larger than the minute aperture, and optical recording is performed with the spot diameter as it is. The medium 100 is irradiated. On the other hand, near-infrared laser light (wavelength 780 nm) cannot pass through the silicon probe, so that near-field light of near-infrared laser light is generated on the optical recording medium 100 side with a minute aperture. Since the spot diameter at this time is near-field light and is limited by the size of the minute aperture, it can be made 100 nm or less. Therefore, the spot becomes smaller than the infrared laser beam (wavelength: 3.5 μm). The near-infrared near-field light and the infrared light are reflected by the optical recording medium 100, the near-infrared light passes through the minute aperture, and the infrared light passes through the light shield and enters the objective lens 18 again. , On the contrary, along the light path. The infrared light is reflected by the dichroic mirror 17 toward the infrared laser 12, while the near infrared laser light passes through and is reflected by the half mirror 16 toward the photodiode 20. Generally, half is reflected. This light is focused on the photodiode 20 by the focusing lens 15. Thus, information recorded on the recording layer can be read.
[0021]
Next, an optical recording medium as another invention will be described. A phase change material is used for a recording layer in the optical recording medium. Typical examples of the phase-change material include a quaternary system of Ag-In-Sb-Te and a ternary system of In-Sb-Te, all of which have a broad absorption spectrum and absorb light in a wide range of 300 to 2 μm. I do. Therefore, in the near-field optical recording / reproducing apparatus 10 of FIG. 1, the recording layer is heated by both the blue laser light and the infrared laser light. Examples of phase-changeable non-crystalline / crystalline reversible recording materials include Ge-Te-Sb-S and Te-TeO.₂-Ge-Sn, Te-Ge-Sn-Au, Ge-Te-Sn, Sn-Se-Te, Sb-Se-Te, Sb-Se, Ga-Se-Te, Ga-Se-Te-Ge, In -Se, In-SeTl-Co, Ga-Se-Te, In-Se-Te and the like. For irreversible changes (write-once optical disks), Te-TeO₂, TeO₂-Pb, Sb₂Se₃/ Bi₂Te₃and so on. Here, a mark is recorded (written), reproduced (read), and erased on a recording medium by emitting an infrared laser and a blue laser. Hereinafter, the light emission conditions will be described with reference to FIG. 4 showing respective power characteristics of the entire laser power, infrared laser power, and blue laser power. In order to facilitate the description of the concept of the present invention, the description will be made assuming that the sensitivity of the phase change material to the laser power of each wavelength is equal.
[0022]
First, the writing conditions will be described. The recording layer (phase change material) on the recording medium is initialized and polycrystallized. In order to record an amorphous mark in this crystal field, the laser power to be irradiated is increased (rapid heat) at the time indicated by w in FIG. 4 (c), and then it is rapidly reduced at time r. As a result, the recording layer is rapidly cooled. For that purpose, strong laser light must first be irradiated, but the conversion efficiency for reproducing near-field light from propagating light is extremely low, so that the power required for writing cannot be obtained. FIG. 4C shows this. The power Wb of the near-field light of the actual blue light (which does not pass through the light-shielding body) is smaller than Wlb (the blue laser light power required for recording), and writing cannot be performed. In order to improve this, an infrared laser is used. In FIG. 4B, the power of the infrared laser is increased to Wi in synchronization with the rapid heating time w of the blue laser light in FIG. 4C. However, what is important here is to make Wi smaller than Eli (: infrared laser light power required for erasing). That is, Wi <Eli. If this is not done, the amorphous mark in the area where the blue near-field light is not irradiated and the infrared light alone is irradiated in FIG. 1 will be erased, and the recorded information will be lost. . That is, the information recorded around the place where the mark is to be written is lost. Further, as shown in FIG. 4A, in a region where both the infrared laser light and the blue near-field light are irradiated, it is necessary to obtain the laser power required for writing, so that the total The laser power Wt must be larger than Wlt (: laser light power required for writing). As described above, for ease of explanation, assuming that the sensitivity of the phase change material to the laser power of each wavelength is equal, each laser power is set so as to satisfy the condition of Wlt <Wt = Wi + Wb. In summary, the following two conditions should be satisfied at the same time.
[0023]
(Equation 1)

[0024]
In this way, the disadvantage of the prior art, in which an amorphous mark could not be written only by near-field light, was overcome. At this time, the area where the amorphous mark is written is limited to the area irradiated with the near-field light. Therefore, high-density recording exceeding the diffraction limit of light becomes possible, and a recordable large-capacity optical storage device is made possible.
[0025]
Next, an erasing condition will be described. In order to realize a so-called rewritable storage device, the recording layer must be heated to a temperature required for crystallization. In order to erase an already recorded amorphous mark, near-field light stronger than Elb (: blue laser light power required for erasure) must be applied at the time indicated by e in FIG. However, since the conversion efficiency for reproducing the near-field light from the propagating light is extremely low, the power required for erasing cannot be obtained. FIG. 4C shows this. The power Eb of the actual near-field light of blue (which does not pass through the light-shielding body) is smaller than that of Elb, and erasing cannot be performed. In order to improve this, an infrared laser is used. In FIG. 4B, the power of the infrared laser is increased to Ei in synchronization with the erasing time of the blue laser light in FIG. 4C. However, what is important here is to make Ei smaller than Eli (: infrared laser light power required for erasing). That is, Ei <Eli. If this is not done, the amorphous mark in the area where the blue near-field light is not irradiated and the infrared light alone is irradiated in FIG. 1 will be erased, and the recorded information will be lost. . That is, the information recorded around the place where the mark is to be written is lost. Further, as shown in FIG. 4A, in a region irradiated with both the infrared laser light and the blue near-field light, it is necessary to obtain a laser power required for erasing. The laser power Et must be larger than Elt (: laser light power required for erasing). As described above, for ease of explanation, assuming that the sensitivity of the phase change material to the laser power of each wavelength is equal, each laser power is set so as to satisfy the condition of Elt <Et = Ei + Eb. In summary, the following two conditions should be satisfied at the same time.
[0026]
(Equation 2)

[0027]
In this way, the disadvantage of the prior art, in which the amorphous mark could not be erased only by the near-field light, was overcome. The area where the amorphous mark is erased at this time is limited to the area irradiated with near-field light. Therefore, high-density erasing exceeding the diffraction limit of light becomes possible, and a rewritable large-capacity optical storage device becomes possible in combination with the above-mentioned recording method.
[0028]
When performing reproduction, the infrared laser beam cannot exert any effect. This is because the infrared laser light reflected from the optical recording medium does not propagate to the photodiode 20 side by the dichroic mirror 17 shown in FIG. Therefore, at the time of reproduction, the power Rb of only the blue near-field light must be larger than Rlbmin (: blue laser light power required for reproduction). Here, it does not mean that the reproduction is actually performed, but refers to the laser power at the time of performing rapid cooling during recording. Therefore, it is better to use the bias power. However, in the description here, the power at the time of reproduction is equal to the power at the time of bias. Therefore, it is not necessary to emit the infrared laser at the time r. However, if it is inevitable to emit light even at time r for other reasons, such as to stably emit infrared laser light, the area where only near-field light is irradiated is used. The following conditions must be satisfied so that the mark is not erased.
[0029]
Elt> Rt = Ri + Rb
[0030]
Note that a semiconductor laser is suitable as the laser light source because of its ease of modulation. As a laser having a wavelength of 1.2 μm or less, a blue semiconductor laser using a material such as GaN, ZnO, or SHG is used._{1 -X}Ga_xP, Al_xGa_{1 -X}As, GaAs_{1 -X}P_xAnd the like. As a semiconductor laser having a wavelength of 1.2 to 2.2 μm, In_xGa_{1 -X}As, InAs_{1 -X}P_xAnd the like. Further, as a laser having a wavelength of 2.5 μm or less, a blue semiconductor laser using a material such as GaN, ZnO, or SHG, and a red laser using In_{1 -X}Ga_xP, Al_xGa_{1 -X}As, GaAs_{1 -X}P_x, In_xGa_{1 -X}As, InAs_{1 -X}P_xAnd the like. As a semiconductor laser having a wavelength of 2.5 to 5 μm, In_xGa_{1 -X}As, InAs_{1 -X}P_x, InAs_{1 -X}Sb_xAnd the like. Further, as such a laser, solid-state lasers such as a YAG laser and a glass laser, gas lasers such as a He-Ne laser and an argon laser,₂A molecular laser such as a laser or a dye laser may be used.
[0031]
Although silicon is shown as the light-shielding film material here, the present invention is not particularly limited to this, and compound semiconductors such as GaAs, GaP, GaN, ZnO, ZnS, and the like, carbon materials, SiC, and the like may be used in combination with wavelengths. good.
[0032]
FIG. 5 is a sectional view showing the configuration of the near-field optical probe according to the first embodiment of another invention. The near-field optical probe 200 of this embodiment uses translucent quartz as the probe substrate 201. However, the present invention is not particularly limited to this, and may be glass or resin. In this, a hole 202 having a slope is opened, and a minute opening 203 having an opening size smaller than the laser wavelength to be used is opened. Here, silicon is used as a material of the light shielding body 204. In addition, as a method of forming a silicon film, sputtering, optical CVD, vapor deposition, thermal CVD, plasma CVD, or the like can be given. Although silicon is shown here as the material of the light-shielding body 204, the material is not particularly limited thereto, and a compound semiconductor such as GaAs, GaP, GaN, ZnO, ZnS, a carbon material, SiC And so on.
[0033]
FIG. 6 is a sectional view showing the configuration of a near-field optical probe according to a second embodiment of another invention. In the near-field optical probe 300 of this embodiment, translucent quartz is used as the probe substrate 301. However, the present invention is not particularly limited to this, and may be glass or resin. A projection 302 having a slope is formed on this, and the dimension of the tip of the projection is smaller than the laser wavelength to be used. A light shielding body 303 is formed on the surface of the substrate and the slope of the projection. The light shielding body 303 may be formed only on the projection slope. Here, silicon is used as a material of the light shielding body 303. When light having a wavelength of less than 1.2 μm is irradiated from the probe substrate side, near-field light is generated at the tip of the protrusion. In addition, as a method of forming a silicon film, sputtering, optical CVD, vapor deposition, thermal CVD, plasma CVD, or the like can be given. Although silicon is shown as a material of the light shielding body 303 here, the material is not particularly limited thereto, and a compound semiconductor such as GaAs, GaP, GaN, ZnO, ZnS, a carbon material, SiC And so on. The projection type probe may have a structure as shown in FIGS. 7A to 7D.
[0034]
It should be noted that the present invention is not limited to the above embodiment, and it goes without saying that various modifications and substitutions can be made within the scope of the claims.
[0035]
【The invention's effect】
As described above, the near-field optical probe of the present invention generates near-field light for reading information recorded in an optical recording medium or writing information in the optical recording medium with the optical recording medium facing the optical recording medium. . Then, a through hole having a minute opening and a slope is provided in the substrate. Furthermore, a light-shielding body formed of a light-shielding material that transmits light of a specific wavelength and does not transmit light of another specific wavelength is formed on at least the slope of the through-hole, and generates near-field light with light that does not transmit through the light-shielding body. At the same time, the light transmitted through the light shield is irradiated to the optical recording medium through the slope of the through hole. Therefore, it is possible to provide a near-field optical probe in which recording / reproducing and erasing are easy.
[0036]
Further, the near-field optical probe of the present invention is characterized in that a through-hole is provided in a flat substrate formed of a light shielding material that transmits light of a specific wavelength and does not transmit light of another specific wavelength. Therefore, it is possible to provide a near-field optical probe in which recording / reproducing and erasing are easy.
[0037]
Further, the near-field light probe of the present invention is provided with a projection having a minute opening and a slope on a substrate, and a light-shielding body formed of a light-shielding material that transmits light of a specific wavelength but does not transmit light of another specific wavelength. Is formed on at least the slope of the through-hole, and near-field light is generated by light that does not pass through the light shield, and light transmitted through the light shield is irradiated onto the optical recording medium through the slope of the protrusion. Therefore, it is possible to provide a near-field optical probe in which recording / reproducing and erasing are easy.
[0038]
Further, the light shielding material is preferably a semiconductor material. Further, it is preferable that the semiconductor material is silicon, the wavelength of light transmitted through the light shield is 1.2 to 2.2 μm, and the wavelength of light not transmitted through the light shield is less than 1.2 μm. Preferably, the semiconductor material is germanium, the wavelength of light passing through the light shield is 2.5 to 5 μm, and the wavelength of light not passing through the light shield is less than 2.5 μm.
[0039]
Further, a near-field optical recording / reproducing apparatus as another invention includes a first laser light source for generating near-field light, and a second laser light having a wavelength longer than the wavelength of the first laser light generated from the first laser light source. A second laser light source that emits a laser beam, a first laser beam and a second laser beam are simultaneously introduced into a near-field optical probe, and light reflecting information recorded on an optical recording medium is transmitted through the near-field optical probe. And a light detection unit that detects the light through the light source. Therefore, it is possible to provide a near-field optical recording / reproducing apparatus capable of performing recording / reproducing / erasing with high efficiency.
[0040]
Further, when recording information is written on the recording layer of the optical recording medium, when the optical power of the second laser light required for erasing is Eli and the optical power of the second laser light at the time of writing the recording information is Wi, By satisfying the condition Wi <Eli, the recording information can be recorded and the already recorded information can be prevented from being accidentally erased.
[0041]
Further, when erasing the recording information of the recording layer of the optical recording medium, the optical power of the second laser light required for erasing is Eli, and the optical power of the second laser light at the time of erasing the recording information is Ei. By satisfying the condition Ei <Eli, it is possible to erase recorded information and prevent information already recorded from being accidentally erased.
[0042]
Preferably, the first laser light is a blue laser light, and the second laser light is an infrared laser light.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a configuration of a near-field optical recording / reproducing apparatus according to one embodiment of the present invention.
FIG. 2 is a diagram illustrating characteristics of an absorption spectrum of silicon.
FIG. 3 is a diagram showing characteristics of an absorption spectrum of germanium.
FIG. 4 is a diagram showing power characteristics of the entire laser power, infrared laser power, and blue laser power.
FIG. 5 is a cross-sectional view illustrating a configuration of a near-field optical probe according to a first embodiment of another invention.
FIG. 6 is a sectional view showing a configuration of a near-field optical probe according to a second embodiment of another invention.
FIG. 7 is a perspective view showing an example of a projection type probe.
FIG. 8 is a cross-sectional view showing a configuration of a conventional near-field optical probe.
[Explanation of symbols]
10: near-field optical recording / reproducing device, 11: laser for near-field light, 12: infrared laser,
13 to 15; condenser lens, 16; half mirror, 17; dichroic mirror,
18; objective lens; 19; near-field optical probe; 20; photodiode.

Claims (10)

In a near-field optical probe that generates near-field light for reading information recorded in the optical recording medium or writing information in the optical recording medium with the optical recording medium facing,
A through-hole having a minute opening and a slope is provided in the substrate, and a light-shielding body formed of a light-shielding material that transmits light of a specific wavelength and does not transmit light of another specific wavelength is formed on at least the slope of the through-hole. A near-field light probe that generates near-field light with light that does not pass through the light-shielding body, and irradiates the optical recording medium with light that passes through the light-shielding body through a slope of the through-hole. In a near-field optical probe that generates near-field light for reading information recorded in the optical recording medium or writing information in the optical recording medium with the optical recording medium facing,
A near-field optical probe characterized in that a through-hole is provided in a flat substrate formed of a light-shielding material that transmits light of a specific wavelength and does not transmit light of another specific wavelength. In a near-field optical probe that generates near-field light for reading information recorded in the optical recording medium or writing information in the optical recording medium with the optical recording medium facing,
On the substrate, a projection having a minute opening and a slope is provided, and a light-shielding body formed of a light-shielding material that transmits light of a specific wavelength and does not transmit light of another specific wavelength is formed on at least the slope of the through-hole, A near-field optical probe, wherein near-field light is generated by light that does not pass through the light-shielding body, and light that passes through the light-shielding body is irradiated on an optical recording medium through an inclined surface of the protrusion. The near-field optical probe according to claim 1, wherein the light shielding material is a semiconductor material. 5. The near-field light according to claim 4, wherein the semiconductor material is silicon, the wavelength of light transmitted through the light shield is 1.2 to 2.2 [mu] m, and the wavelength of light not transmitted through the light shield is less than 1.2 [mu] m. probe. The near-field optical probe according to claim 4, wherein the semiconductor material is germanium, the wavelength of light passing through the light shield is 2.5 to 5 m, and the wavelength of light not transmitting through the light shield is less than 2.5 m. A first laser light source that generates near-field light, a second laser light source that emits a second laser light having a wavelength longer than the wavelength of the first laser light generated from the first laser light source, A light detection unit that simultaneously introduces the first laser light and the second laser light into the near-field optical probe and detects light reflecting information recorded on an optical recording medium via the near-field optical probe. A near-field optical recording / reproducing apparatus characterized by the above-mentioned. When recording information is written on the recording layer of the optical recording medium, when the optical power of the second laser light required for erasing is Eli and the optical power of the second laser light at the time of writing the recording information is Wi, The near-field optical recording / reproducing apparatus according to claim 7, wherein the condition Wi <Eli is satisfied. When erasing the recording information of the recording layer of the optical recording medium, the light power of the second laser light required for erasing is Eli, and the light power of the second laser light at the time of erasing the recording information is Ei. 8. The near-field optical recording / reproducing apparatus according to claim 7, wherein the condition Ei <Eli is satisfied. The near-field optical recording / reproducing apparatus according to any one of claims 7 to 9, wherein the first laser light is a blue laser light, and the second laser light is an infrared laser light.

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