JPH08180493A - Minute displacement measuring instrument - Google Patents
Minute displacement measuring instrumentInfo
- Publication number
- JPH08180493A JPH08180493A JP32889294A JP32889294A JPH08180493A JP H08180493 A JPH08180493 A JP H08180493A JP 32889294 A JP32889294 A JP 32889294A JP 32889294 A JP32889294 A JP 32889294A JP H08180493 A JPH08180493 A JP H08180493A
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- JP
- Japan
- Prior art keywords
- diffraction grating
- light
- pitch
- diffracted
- grating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Optical Recording Or Reproduction (AREA)
- Automatic Focus Adjustment (AREA)
Abstract
Description
【０００１】[0001]
【０００２】[0002]
【従来の技術】従来、光磁気ディスク用の光学ヘッドに
使用されているフォーカスエラー信号を用いたフォーカ
スサーボ方式としては、非点収差法、臨界角法、ナイフ
エッジ法などが知られている。この中において、非点収
差法は光磁気ディスク用として用いられる他、コンパク
トディスク、レーザディスクを含む光ディスク全般に用
いられている。非点収差法に関する公知技術としては、
特公昭５３−３９１２３号公報に「自動焦点調整装
置」、特公昭５７−１２１８８号公報に「動いているデ
ータキャリア上に読取光ビームを集束させる装置」、特
公昭６０−４８９４９号公報に「光ビームで情報を読み
取る装置」、特公昭６１−６１１７８号公報に「自動焦
点調節法」としてそれぞれ開示されている。2. Description of the Related Art Conventionally, astigmatism method, critical angle method, knife edge method and the like are known as focus servo methods using a focus error signal used in optical heads for magneto-optical disks. Among them, the astigmatism method is used not only for magneto-optical discs but also for general optical discs including compact discs and laser discs. Known techniques relating to the astigmatism method include:
Japanese Patent Publication No. 53-39123 discloses an "automatic focus adjustment device", Japanese Patent Publication No. 57-12188 discloses "a device for focusing a reading light beam on a moving data carrier", and Japanese Patent Publication No. 60-48949 discloses "optical". An apparatus for reading information with a beam "and Japanese Patent Publication No. 61-61178 disclose" automatic focusing method ".
【０００３】図１０は、光ピックアップ装置における非
点収差法の動作原理を示したものである。半導体レーザ
（図示せず）から出射した光は、コリメートレンズ（図
示せず）によりコリメートされ、ビームスプリッタ１を
透過して対物レンズ２により集光されて光ディスク３の
面上に照射され、これにより情報の記録等が行われる。
また、光ディスク３からの反射光は、対物レンズ２を透
過し、ビームスプリッタ１により今度は反射され、集光
レンズ４、円筒レンズ５を順次透過して非点収差が発生
したビーム６となり、このビーム６は４分割受光面ａ，
ｂ，ｃ，ｄをもつ受光素子７に導かれる。そして、その
受光素子７の出力がアンプ８に送られることによりフォ
ーカスエラー信号Ｆｅが検出される。FIG. 10 shows the operating principle of the astigmatism method in an optical pickup device. Light emitted from a semiconductor laser (not shown) is collimated by a collimator lens (not shown), transmitted through the beam splitter 1, condensed by the objective lens 2 and irradiated onto the surface of the optical disc 3. Information is recorded.
Further, the reflected light from the optical disk 3 passes through the objective lens 2, is reflected by the beam splitter 1 this time, and is sequentially transmitted through the condenser lens 4 and the cylindrical lens 5 to become a beam 6 having astigmatism. The beam 6 is a 4-division light receiving surface a,
It is guided to the light receiving element 7 having b, c and d. Then, the output of the light receiving element 7 is sent to the amplifier 8 to detect the focus error signal Fe.
【０００４】この場合、光ディスク３の合焦時には、そ
の光ディスク３からの反射光のビーム６の形状は、受光
素子７の４分割受光面ａ，ｂ，ｃ，ｄにおいて円形とな
る。この時、差動出力｛（ａ＋ｃ）−（ｂ＋ｄ）｝の値
は零となり、フォーカスエラー信号Ｆｅの値は０となり
検出されない。また、光ディスク３が対物レンズ２から
遠くなったり近くなったりすると、ビーム６の形状は円
形から長円形状となり、差動出力は零とならず、これに
よりフォーカスエラー信号の値は正（遠い）或いは負
（近い）となって、対物レンズの位置調整が行われる。In this case, when the optical disc 3 is focused, the beam 6 of the reflected light from the optical disc 3 has a circular shape on the four-divided light receiving surfaces a, b, c, d of the light receiving element 7. At this time, the value of the differential output {(a + c)-(b + d)} becomes zero and the value of the focus error signal Fe becomes 0, which is not detected. Further, when the optical disk 3 becomes far from or near the objective lens 2, the shape of the beam 6 changes from a circular shape to an elliptical shape, and the differential output does not become zero, so that the value of the focus error signal is positive (far). Alternatively, the position of the objective lens is adjusted to be negative (close).
【０００５】[0005]
【発明が解決しようとする課題】近年、この種の光ディ
スク装置においては、アクセスタイムの高速化が要求さ
れており、このような目的を達成するためには、光ピッ
クアップ部の小型化、軽量化が必要不可欠となる。しか
し、前述したような非点収差法を用いたフォーカスサー
ボ方式では、ビームの形状変化を検出するために、受光
素子７までの距離（検出長）をある程度大きく（数ｃ
ｍ）しなければ十分な検出感度を得ることができない。
従って、従来の光ディスク装置においては小型化におの
ずと限界がある。また、受光素子７上のスポット径は数
ミクロンから数十ミクロンとかなり小さいため、調整が
難しく、環境によってはオフセットが生じることになる
ので、検出された信号が不安定となる。In recent years, there has been a demand for faster access times in this type of optical disk device, and in order to achieve such an object, the optical pickup unit is made smaller and lighter. Is essential. However, in the focus servo method using the astigmatism method as described above, the distance (detection length) to the light receiving element 7 is increased to some extent (a few c
If m) is not satisfied, sufficient detection sensitivity cannot be obtained.
Therefore, there is a limit to miniaturization in the conventional optical disk device. Further, since the spot diameter on the light receiving element 7 is as small as several microns to several tens of microns, it is difficult to adjust, and an offset occurs depending on the environment, so that the detected signal becomes unstable.
【０００６】[0006]
【課題を解決するための手段】請求項１記載の発明で
は、ｎ1 次光とｎ2 次光との第一回折光を発生する第一
回折格子と、前記第一回折光が入射することにより複数
の回折された第二回折光を発生する第二回折格子とから
なり、互いに干渉し合う前記第二回折光の位相が１／４
波長だけずれるような形状に各回折格子が形成された干
渉縞発生手段を設け、この干渉縞発生手段により生じた
前記第二回折光の間での干渉により干渉縞の位相の変化
を受光素子に検知することによって前記測定物の光軸方
向への移動量を測定するようにした。According to a first aspect of the invention, a first diffraction grating for generating first diffracted light of n 1 -order light and n 2 -order light, and the first diffracted light are incident. And a second diffraction grating that generates a plurality of diffracted second diffracted light beams, and the phases of the second diffracted light beams that interfere with each other are 1/4.
An interference fringe generating means is provided in which each diffraction grating is formed in a shape that is shifted by the wavelength, and a change in the phase of the interference fringe is caused in the light receiving element by the interference between the second diffracted light generated by the interference fringe generating means. The amount of movement of the measurement object in the optical axis direction is measured by detecting the amount.
【０００７】請求項２記載の発明では、請求項１記載の
発明において、第一回折格子と第二回折格子との相対的
な位相を、回折格子の４分の１ピッチを（ｎ1 −ｎ2 ）
で割った値、又は、その値にさらに１ピッチを（ｎ1 −
ｎ2 ）で割った値を１個ないしは複数個加算又は減算し
た値に設定した。According to a second aspect of the present invention, in the first aspect of the invention, the relative phase between the first diffraction grating and the second diffraction grating is set to a quarter pitch of the diffraction grating (n 1 -n 2 )
Divided by, or 1 pitch is added to that value (n 1 −
The value divided by n 2 ) is set to a value obtained by adding or subtracting one or a plurality of values.
【０００８】請求項３記載の発明では、請求項１記載の
発明において、第一回折格子と第二回折格子とを等ピッ
チとし、±１次光の第二回折光を用いて干渉縞を発生さ
せる場合、第一回折格子と第二回折格子との相対的な位
相を、回折格子の８分の１ピッチ、又は、８分の５ピッ
チの値に設定した。According to a third aspect of the present invention, in the first aspect of the present invention, the first diffraction grating and the second diffraction grating have an equal pitch, and interference fringes are generated by using the second diffracted light of ± first-order light. In this case, the relative phase between the first diffraction grating and the second diffraction grating was set to a value of 1/8 pitch or 5/8 pitch of the diffraction grating.
【０００９】請求項４記載の発明では、請求項１記載の
発明において、ピッチがΛ1 の第一回折格子により得ら
れる第一回折光をｎ1 次光とｎ2 次光とし、ピッチがΛ
2 の第二回折格子により得られる第二回折光をｍ1 次光
とｍ2 次光としたとき、各回折格子のピッチと回折光の
次数とを、 Λ2 ｎ1 ＋Λ1 ｍ1 ＝Λ2 ｎ2 ＋Λ1 ｍ2 の関係式を満たすように設定した。According to a fourth aspect of the invention, in the first aspect of the invention, the first diffracted light obtained by the first diffraction grating having a pitch of Λ 1 is n 1 -order light and n 2 -order light, and the pitch is Λ.
When the second diffracted light obtained by the second diffractive grating of 2 is m 1 -order light and m 2 -order light, the pitch of each diffraction grating and the order of diffracted light are Λ 2 n 1 + Λ 1 m 1 = Λ It was set so as to satisfy the relational expression of 2 n 2 + Λ 1 m 2 .
【００１０】[0010]
【作用】請求項１記載の発明においては、第二回折光の
位相が１／４波長だけずれるような形状に干渉縞発生手
段の各回折格子を形成したことによって、第二回折光の
干渉縞分布から求められるフォーカスエラー信号のＳ字
曲線を最大にすることができ、この最大とされたＳ字曲
線からデフォーカス量を容易に求めることができる。According to the first aspect of the invention, the diffraction fringes of the second diffracted light are formed by forming the diffraction gratings of the interference fringe generating means in a shape such that the phase of the second diffracted light is shifted by ¼ wavelength. The S-shaped curve of the focus error signal obtained from the distribution can be maximized, and the defocus amount can be easily obtained from this maximized S-shaped curve.
【００１１】請求項２記載の発明においては、４分の１
ピッチを（ｎ1 −ｎ2 ）で割った値か、又は、その４分
の１ピッチを（ｎ1 −ｎ2 ）で割った値に、１ピッチを
（ｎ1 −ｎ2 ）で割った値を１個ないしは複数個加算又
は減算した値に設定することによって、互いに干渉し合
う第二回折光の位相を１／４波長だけ正確にずらすこと
ができる。According to the second aspect of the invention, a quarter
The value obtained by dividing the pitch by (n 1 −n 2 ), or the value obtained by dividing the quarter pitch by (n 1 −n 2 ) by 1 pitch divided by (n 1 −n 2 ). By setting the value to one or to a value obtained by adding or subtracting a plurality of values, the phases of the second diffracted lights that interfere with each other can be accurately shifted by ¼ wavelength.
【００１２】請求項３記載の発明においては、第一回折
格子と第二回折格子との相対的な位相を、８分の１ピッ
チ、又は、８分の５ピッチの値に設定したことによっ
て、互いに干渉し合う第二回折光の位相を１／４波長だ
け正確にしかも容易にずらすことができる。また、第一
回折格子と第二回折格子とを等ピッチすなわち同一の格
子ピッチとし、±１次光の第二回折光を用いて干渉縞を
発生させることによって、回折格子の作成を容易に行う
ことができ、しかも、これにより干渉縞を受光する受光
素子側の形状も簡易化させることができる。According to the third aspect of the present invention, the relative phase between the first diffraction grating and the second diffraction grating is set to a value of 1/8 pitch or 5/8 pitch. The phases of the second diffracted lights that interfere with each other can be accurately and easily shifted by a quarter wavelength. Further, the first diffraction grating and the second diffraction grating have an equal pitch, that is, the same grating pitch, and the interference fringes are generated by using the second diffraction light of the ± first-order light, thereby facilitating the creation of the diffraction grating. In addition, the shape on the side of the light receiving element that receives the interference fringes can be simplified.
【００１３】請求項４記載の発明においては、第一回折
格子と第二回折格子とのピッチを異ならせ、各回折格子
のピッチと回折光の次数との間で一定の条件式を満足さ
せることによって、干渉縞となる第二回折光の位相を１
／４波長だけずらすことができる。In the invention of claim 4, the pitches of the first diffraction grating and the second diffraction grating are made different, and a constant conditional expression is satisfied between the pitch of each diffraction grating and the order of the diffracted light. To set the phase of the second diffracted light that becomes the interference fringe to 1
It can be shifted by / 4 wavelength.
【００１４】[0014]
【実施例】本発明の第一の実施例を図１〜図３に基づい
て説明する（請求項１記載の発明に対応する）。まず、
微小変位測定装置の全体構成を図２に基づいて述べる。
光源としての半導体レーザ９（以下、ＬＤという）から
の出射光はコリメートレンズ１０により平行光とされた
後、ビームスプリッタ１１により反射され、対物レンズ
１２により集光されたビームとなって測定物としての光
ディスク１３の面上に照射される。そして、その光ディ
スク１３からの反射光は、再び対物レンズ１２を通過し
た後、今度はビームスプリッタ１１を透過し受光素子１
４（以下、ＰＤという）に向かう。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. 1 to 3 (corresponding to the invention described in claim 1). First,
The overall configuration of the micro displacement measuring device will be described with reference to FIG.
Light emitted from a semiconductor laser 9 (hereinafter, referred to as LD) as a light source is collimated by a collimator lens 10 and then reflected by a beam splitter 11 to be a beam condensed by an objective lens 12 to be a measurement object. The surface of the optical disk 13 is irradiated. Then, the reflected light from the optical disc 13 passes through the objective lens 12 again, and then passes through the beam splitter 11 to receive the light receiving element 1.
Go to 4 (hereinafter referred to as PD).
【００１５】そのビームスプリッタ１１とＰＤ１４との
間の光路上には、干渉縞発生手段としての二重回折格子
１５が配置されている。この二重回折格子１５は、ｎ1
次光とｎ2 次光との第一回折光Ｋ1 を発生する第一回折
格子１５ａと、第一回折光Ｋ1 が入射することにより複
数の回折された第二回折光Ｋ2 を発生する第二回折格子
１５ｂとからなっている。そして、光ディスク１３から
の反射光がそのような二重回折格子１５を通過すること
によって第二回折光Ｋ2 の干渉縞が発生し、この干渉縞
の位相の変化がＰＤ１４に検出され、光ディスク１３の
光軸方向への移動量の測定が行われる。On the optical path between the beam splitter 11 and the PD 14, a double diffraction grating 15 as an interference fringe generating means is arranged. This double diffraction grating 15 has n 1
The first diffraction grating 15a that generates the first diffracted light K 1 of the second light and the n 2 -order light and the plurality of diffracted second diffracted lights K 2 are generated by the incidence of the first diffracted light K 1. It is composed of the second diffraction grating 15b. Then, the reflected light from the optical disc 13 passes through such a double diffraction grating 15 to generate an interference fringe of the second diffracted light K 2 , and a change in the phase of this interference fringe is detected by the PD 14, and the optical disc is detected. The amount of movement of 13 in the optical axis direction is measured.
【００１６】本実施例では、二重回折格子１５を構成す
る第一回折格子１５ａと第二回折格子１５ｂとが、干渉
縞となる第二回折光Ｋ2 の位相が１／４波長（λ）だけ
ずれるような格子形状に形成されている。以下、これら
２つの回折光Ｋ1 ，Ｋ2 の位相がλ／４だけずれる理由
について述べる。図１は、ＰＤ１４面上の中心を座標Ｏ
とした座標軸ｘ，ｙ，ｚを示す。今、ＰＤ１４面に対し
て２つの点光源Ｐ1 ，Ｐ2 からの距離をＬ1 ，Ｌ2 と
し、これら点光源間のｘ方向の距離をｌ1 とし、点光源
Ｐ1 ，Ｐ2 の中心の（ｙ，ｚ）座標を（ｙ0 ，ｚ0 ）と
する。このとき、Ｌ1 2，Ｌ2 2の値は、 Ｌ1 2＝（ ｌ1 ／２＋ｘ）2＋ｙ0 2＋ｚ2 …（１） Ｌ2 2＝（−ｌ1 ／２＋ｘ）2＋ｙ0 2＋ｚ2 …（２） として表わされる。これにより、二重回折格子１５によ
る位相差を付与していないときの光路長差ｄＬは、 ｄＬ＝Ｌ1 −Ｌ2 ＝（Ｌ1 2−Ｌ2 2）／（Ｌ1 −Ｌ2 ） ≒〔（ｌ1 ／２＋ｘ）2−（−ｌ1 ／２＋ｘ）2〕／２ｙ0 ＝ｌ1 ｘ／ｙ0 …（３） となる。ここで、二重回折格子１５による位相差を位相
差をπ／２＋δ0 としたとき、光路長の位相差δは、 δ＝２πｄＬ／λ＋π／２＋δ0 ＝２πｌ1 ｘ／λｙ0＋π／２＋δ0 …（４） として表わされる。そして、２つの点光源Ｐ1 ，Ｐ2 に
よる干渉縞の強度Ｉは、 Ｉ∝ｃｏｓ2（δ／２） …（５） として表わされる。さらに、（４）式を（５）式に代入
すると、干渉縞強度分布Ｉ（ｘ）は、 Ｉ（ｘ）∝ｃｏｓ2（πｌ1 ｘ／λｙ0＋π／４＋δ0／２） ＝〔−ｓｉｎ（２πｌ1 ｘ／λｙ0＋δ0）＋１〕／２ …（６） として表わされる。In the present embodiment, the first diffraction grating 15a and the second diffraction grating 15b constituting the double diffraction grating 15 have the phase of the second diffracted light K 2 which becomes interference fringes of ¼ wavelength (λ ) It is formed in a grid shape that is displaced. The reason why the phases of these two diffracted lights K 1 and K 2 deviate by λ / 4 will be described below. In FIG. 1, the center on the PD14 surface is coordinate O.
The coordinate axes x, y, and z are shown. Now, let L 1 and L 2 be the distances from the two point light sources P 1 and P 2 with respect to the PD 14 surface, and let the distance in the x direction between these point light sources be l 1 and define the centers of the point light sources P 1 and P 2 . Let (y, z) coordinates of (y 0 , z 0 ). At this time, L 1 2, L 2 2 values, L 1 2 = (l 1 /2 + x) 2 + y 0 2 + z 2 ... (1) L 2 2 = (- l 1/2 + x) 2 + y 0 2 + z 2 is represented as (2). Accordingly, the optical path length difference dL when the phase difference is not given by the double diffraction grating 15 is dL = L 1 −L 2 = (L 1 2 −L 2 2 ) / (L 1 −L 2 ). ≒ becomes [(l 1/2 + x) 2 - - (l 1/2 + x) 2 ] / 2y 0 = l 1 x / y 0 ... (3). Here, when the phase difference due to the double diffraction grating 15 is π / 2 + δ 0 , the phase difference δ of the optical path length is δ = 2πdL / λ + π / 2 + δ 0 = 2πl 1 x / λy 0 + π / 2 + δ It is represented as 0 (4). The intensity I of the interference fringe due to the two point light sources P 1 and P 2 is expressed as I∝cos 2 (δ / 2) (5). Further, (4) Substituting equation in the equation (5), the interference fringe intensity distribution I (x) is, I (x) αcos 2 ( πl 1 x / λy 0 + π / 4 + δ 0/2) = [- sin (2πl 1 x / λy 0 + δ 0 ) +1] / 2 (6)
【００１７】次に、光ディスク１３にデフォーカスが生
じた場合におけるｙ0 の値を求める。今、対物レンズ１
２の焦点距離をｆ0 とし、対物レンズ１２からの反射光
の検出光路側の焦点位置をｙ1 とすると、 １／（ｆ0 ＋ｄ）＋１／ｙ1 ＝１／ｆ0 …（７） の関係が成立する。これにより、ｙ1 は、 ｙ1 ≒ｆ0 2／ｄ …（８） として表わされる。そして、ｙ0 ＝ｙ1 −ｙ2 とし、
（８）式を（６）式に代入すると、 Ｉ（ｘ，ｄ）∝−ｓｉｎ〔２πｌ1 ｘ／λ（ｆ0 2／ｄ−ｙ2）＋δ0〕 ＋１ …（９） を得る。このＩ（ｘ，ｄ）が干渉縞分布を示す基本式で
ある。そして、（９）式中、ｙ2 が小さいとし、ｙ2 ＝
０を（９）式に代入すると、 Ｉ（ｘ，ｄ）∝−ｓｉｎ〔２πｌ1 ｘｄ／λｆ0 2＋δ0〕＋１ …（１０） となる。これにより、干渉縞分布Ｉ（ｘ，ｄ）は、ｘ，
ｄに対して対称であり、二重回折格子１５に位相差をも
たせた効果を得ることができ、波長変動の影響によりそ
の干渉縞分布も対称的に変化する。なお、デフォーカス
がないときは波長に拘らず干渉縞分布は平坦になり、ジ
ャストオンフォーカス時には影響がない。Next, the value of y 0 when the optical disk 13 is defocused is obtained. Now the objective lens 1
When the focal length of 2 is f 0 and the focal position of the reflected light from the objective lens 12 on the detection optical path side is y 1 , 1 / (f 0 + d) + 1 / y 1 = 1 / f 0 (7) The relationship is established. Accordingly, y 1 is expressed as y 1 ≈f 0 2 / d (8) Then, y 0 = y 1 −y 2, and
By substituting the equation (8) into the equation (6), I (x, d) ∝-sin [2πl 1 x / λ (f 0 2 / d−y 2 ) + δ 0 ] +1 (9) is obtained. This I (x, d) is a basic equation showing the interference fringe distribution. Then, in the equation (9), y 2 is small, and y 2 =
Substituting 0 into equation (9) yields I (x, d) ∝-sin [2πl 1 xd / λf 0 2 + δ 0 ] +1 (10). As a result, the interference fringe distribution I (x, d) becomes x,
It is symmetric with respect to d, and the effect of giving a phase difference to the double diffraction grating 15 can be obtained, and its interference fringe distribution also changes symmetrically due to the influence of wavelength fluctuation. When there is no defocus, the interference fringe distribution becomes flat regardless of the wavelength, and there is no influence during just-on-focus.
【００１８】図３は、その干渉縞分布Ｉ（ｘ，ｄ）をｘ
方向に積分することにより得られるデフォーカス量に対
するフォーカスエラー信号ＦｅのＳ字曲線Ｓ（ｄ）を示
す。Ｓ字曲線Ｓ（ｄ）の波形Ａ（実線）は実験値を示
し、波形Ｂ（破線）は理論的な計算値を示す。この場
合、ＰＤ１４の面をｘ座標にして、−ａから０、そし
て、０からａの２つの領域に分けられるため、その場の
干渉縞分布Ｉ（ｘ，ｄ）を平坦な光量分布を仮定してそ
れぞれを積分してその差をとると、Ｓ（ｄ）は、 Ｓ（ｄ）∝λｆ0 2・ ｃｏｓδ0〔−１＋ｃｏｓ（２πｌ1 ｘｄ／λｆ0 2〕／πｌ1 ｄ …（１１） として表わすことができる。この（１１）式中には、ｃ
ｏｓδ0の項があり、δ0＝０のときには、ｃｏｓδ0＝
１となり、δ0 ＝πのときにはｃｏｓδ0＝−１とな
り、これによりＳ（ｄ）の絶対値は最大となる。FIG. 3 shows the interference fringe distribution I (x, d) as x.
The S-shaped curve S (d) of the focus error signal Fe with respect to the defocus amount obtained by integrating in the direction is shown. A waveform A (solid line) of the S-shaped curve S (d) shows an experimental value, and a waveform B (broken line) shows a theoretical calculated value. In this case, since the surface of the PD 14 is set to the x-coordinate, it can be divided into two regions from −a to 0 and 0 to a. Therefore, the interference fringe distribution I (x, d) at that place is assumed to be a flat light amount distribution. Then, integrating each and taking the difference, S (d) ∝λf 0 2 · cos δ 0 [−1 + cos (2πl 1 xd / λf 0 2 ] / πl 1 d (11) In this equation (11), c can be expressed as
some sections of osδ 0, when [delta] 0 = 0 is, cos [delta] 0 =
1 becomes, δ 0 = π cosδ 0 = -1 becomes when the, thereby an absolute value of S (d) is maximized.
【００１９】従って、δ0 ＝０のとき、すなわち、干渉
する２つの第二回折光Ｋ2 の位相がλ／４だけずれるよ
うに、第一回折格子１５ａと第二回折格子１５ｂとの格
子形状を形成することによって、フォーカスエラー信号
ＦｅのＳ字曲線を最大にすることができ、これにより、
デフォーカス量を容易に求めることができ、信号の検出
感度を向上させることができる。Therefore, when δ 0 = 0, that is, the phases of the two interfering second diffracted lights K 2 are shifted by λ / 4, the grating shapes of the first diffraction grating 15a and the second diffraction grating 15b. The S-shaped curve of the focus error signal Fe can be maximized by forming
The defocus amount can be easily obtained, and the signal detection sensitivity can be improved.
【００２０】次に、本発明の第二の実施例を図４〜図６
に基づいて説明する（請求項２，３記載の発明に対応す
る）。なお、前述した第一の実施例と同一部分について
の説明は省略し、その同一部分については同一符号を用
いる。Next, a second embodiment of the present invention will be described with reference to FIGS.
(Corresponding to the invention described in claims 2 and 3). The description of the same parts as those in the first embodiment described above will be omitted, and the same reference numerals will be used for the same parts.
【００２１】本実施例では、第一回折格子１５ａと第二
回折格子１５ｂとの相対的な位相は、その回折格子の１
／４ピッチを（ｎ1 −ｎ2 ）で割った値、又は、その値
にさらに１ピッチを（ｎ1 −ｎ2 ）で割った値を１個な
いしは複数個加算又は減算した値に設定されている。こ
の場合、特に、第一回折格子１５ａと第二回折格子１５
ｂとの相対的な位相を、その回折格子の１／８ピッチ、
又は、５／８ピッチの値に設定するようにしてもよい。In this embodiment, the relative phase between the first diffraction grating 15a and the second diffraction grating 15b is 1 of that diffraction grating.
/ 4 pitch divided by (n 1 −n 2 ), or 1 pitch divided by (n 1 −n 2 ), or 1 or more added or subtracted. ing. In this case, in particular, the first diffraction grating 15a and the second diffraction grating 15a
The relative phase with b is 1/8 pitch of the diffraction grating,
Alternatively, it may be set to a value of 5/8 pitch.
【００２２】以下、回折格子１５ａ，１５ｂの相対的な
位相関係を、上記条件に設定することにより、フォーカ
スエラー信号ＦｅのＳ字曲線を最大にすることができる
理由について述べる。図４は、単一の回折格子１６に光
を入射させ、その回折格子１６が移動するときに回折光
の波面も移動することを示す例である。今、回折格子１
６が１ピッチ移動し、その移動方向に回折する光をｎ1
次光とし、反対方向に回折する光をｎ2 次光とする。こ
の場合、回折格子１６の移動方向に対して同一方向に進
む光は波面１７ａも同一方向に進み、次数のｎ1 に対し
て１ピッチ当たり波長のｎ1 倍進む。一方、回折格子１
６の移動方向に対して反対方向に進む光は波面１７ｂが
後退し、次数のｎ2 に対して１ピッチ当たり波長のｎ2
倍後退する（ｎ2 が負の数とすると、−ｎ2 倍進む）。
また、図５に示すように、２枚の回折格子、例えば第
一、第二回折格子１５ａ，１５ｂからなる二重回折格子
１５の場合、一方の第一回折格子１５ａを１ピッチ移動
させ、他方の第二回折格子１５ｂを固定したとすると、
ｎ1 次光の波面１７ａとｎ2 次光の波面１７ｂとの進行
が逆になるため、（ｎ1 −ｎ2 ）倍×２πの位相変化と
なり、この変化分だけ波面１７ａ，１７ｂが重なること
になる。例として、ｎ1 ＝１、ｎ2 ＝−１とすると、
（ｎ1 −（−ｎ2 ））×２π＝（１−（−１））×２π
＝２×２πなる位相変化を生じる。The reason why the S-shaped curve of the focus error signal Fe can be maximized by setting the relative phase relationship between the diffraction gratings 15a and 15b under the above conditions will be described below. FIG. 4 is an example showing that light is incident on a single diffraction grating 16 and the wavefront of the diffracted light also moves when the diffraction grating 16 moves. Now diffraction grating 1
6 moves 1 pitch and the light diffracted in the moving direction is n 1
The second light and the light diffracted in the opposite direction are the n 2 -order light. In this case, light traveling in the same direction to the moving direction of the diffraction grating 16 is wavefront 17a also proceeds in the same direction, the process proceeds 1 times n of one pitch per wavelength with respect to n 1 in order. On the other hand, the diffraction grating 1
6 light wavefront 17b is retracted traveling in the opposite direction to the moving direction of, n 2 of one pitch per wavelength with respect to n 2 orders
Double backwards (advance −n 2 times when n 2 is a negative number).
Further, as shown in FIG. 5, in the case of a double diffraction grating 15 including two diffraction gratings, for example, first and second diffraction gratings 15a and 15b, one first diffraction grating 15a is moved by one pitch, If the other second diffraction grating 15b is fixed,
Since the wavefront 17a of the n 1st- order light and the wavefront 17b of the n 2nd- order light are in opposite directions, the phase change is (n 1 −n 2 ) times × 2π, and the wavefronts 17a and 17b overlap by this change. become. As an example, if n 1 = 1 and n 2 = -1,
(N 1 − (− n 2 )) × 2π = (1 − (− 1)) × 2π
A phase change of 2 × 2π occurs.
【００２３】また、図６に示すように、第一、第二回折
格子１５ａ，１５ｂの相対的な位相がピッタリ合ってい
ると波面１７ａ，１７ｂも揃う。このような状態から、
一方の第一回折格子１５ａが移動して、波面１７ａを波
面１７ｂに対してλ／４だけ異ならせるためには、回折
格子の４分の１ピッチを（ｎ1 −ｎ2 ）で割った距離だ
け移動させることによってその目的を達成できる。例と
して、ｎ1 ＝１、ｎ2＝−１の場合は、４分の１ピッチ
を（１−（−１））＝２で割った１／８ピッチだけ回折
格子を相対的に移動させることによって、λ／４だけ波
面の位相を異ならせることができる。なお、回折格子を
移動させる方向は左右どちらでもよい。Further, as shown in FIG. 6, if the relative phases of the first and second diffraction gratings 15a and 15b are exactly matched, the wavefronts 17a and 17b are also aligned. From this state,
To move the first diffraction grating 15a on one side to make the wavefront 17a different from the wavefront 17b by λ / 4, a distance obtained by dividing a quarter pitch of the diffraction grating by (n 1 −n 2 ). You can achieve the purpose by moving only. As an example, in the case of n 1 = 1 and n 2 = -1, the diffraction grating is relatively moved by a 1/8 pitch obtained by dividing a quarter pitch by (1-(-1)) = 2. The phase of the wavefront can be changed by λ / 4. The diffraction grating may be moved in either the left or right direction.
【００２４】さらに、第一、第二回折格子１５ａ，１５
ｂのうちの一方を１ピッチ移動させると、（ｎ1 −ｎ
2 ）倍×２πの位相変化となることから、２つの波面１
７ａ，１７ｂの位相差は回折格子の１ピッチの移動の間
に（ｎ1 −ｎ2 ）回の同じ位相となり、これにより１ピ
ッチを（ｎ1 −ｎ2 ）で割った位相分だけ回折格子を移
動させることで同一の位相となる。例として、ｎ1 ＝
１、ｎ2 ＝−１の場合は、１ピッチを（１−（−１））
＝２で割った値、すなわち、１／２ピッチの移動で２つ
の波面１７ａ，１７ｂの位相関係が同一となる。従っ
て、波面１７ａを波面１７ｂに対してλ／４だけ異なら
せるためには、１ピッチを（ｎ1 −ｎ2 ）で割った値
に、回折格子の４分の１ピッチを（ｎ1 −ｎ2 ）で割っ
た距離（ｎ1 −ｎ2 ）で割った値を加算又は減算させる
ようにすればよい。この例では、１／２ピッチと１／８
ピッチとを加算して５／８ピッチだけ移動させることに
よって、λ／４だけ波面の位相を異ならせることができ
る。Furthermore, the first and second diffraction gratings 15a, 15
When one of b is moved by one pitch, (n 1 −n
2 ) x 2π phase change, so two wavefronts 1
The phase difference between 7a and 17b becomes the same phase of (n 1 −n 2 ) times during the movement of 1 pitch of the diffraction grating, and thus the pitch of 1 pitch divided by (n 1 −n 2 ) It becomes the same phase by moving. As an example, n 1 =
When 1, n 2 = -1, 1 pitch is (1-(-1))
= 2, that is, the phase relationship between the two wavefronts 17a and 17b becomes the same by moving by 1/2 pitch. Therefore, in order to vary the wavefront 17a only lambda / 4 with respect to the wavefront 17b is 1 divided by the pitch (n 1 -n 2), a ¼ pitch of the diffraction grating (n 1 -n The value divided by the distance (n 1 −n 2 ) divided by 2 ) may be added or subtracted. In this example, 1/2 pitch and 1/8
By adding the pitch and moving by 5/8 pitch, the phase of the wavefront can be changed by λ / 4.
【００２５】この他の高次数を例にとると、ｎ1 ＝２、
ｎ2 ＝−３の場合は、１／４ピッチを（２−（−３））
＝５で割って、１／２０ピッチの分だけ回折格子の位相
変化をもたせることによって、λ／４だけ波面の位相を
異ならせることができる。さらにこのことは、１ピッチ
を（２−（−３））＝５で割った１／５ピッチの値と、
１／２０ピッチとを加算した１／４ピッチだけ移動させ
ることによって、λ／４だけ波面の位相を異ならせるこ
とができる。Taking another high order as an example, n 1 = 2,
In the case of n 2 = -3, the 1/4 pitch is (2-(-3))
It is possible to change the phase of the wavefront by λ / 4 by dividing by 5 and giving the phase change of the diffraction grating by 1/20 pitch. Furthermore, this means that a value of 1/5 pitch obtained by dividing 1 pitch by (2-(-3)) = 5,
The phase of the wavefront can be changed by λ / 4 by moving by 1/4 pitch, which is the sum of 1/20 pitch.
【００２６】上述したように、第一回折格子１５ａと第
二回折格子１５ｂとの相対的な位相を、１／４ピッチを
（ｎ1 −ｎ2 ）で割った値か、又は、その１／４ピッチ
を（ｎ1 −ｎ2 ）で割った値に、１ピッチを（ｎ1 −ｎ
2 ）で割った値を１個ないしは複数個加算又は減算した
値に設定したので、干渉縞となる第二回折光の位相を１
／４波長だけ正確にしかも容易にずらすことができ、こ
れにより、フォーカスエラー信号ＦｅのＳ字曲線を最大
にして、デフォーカス量を正確に求めることができる。
特に、±１次光を用い、１／８ピッチ、５／８ピッチの
値に設定することによって、第一，第二回折格子１５
ａ，１５ｂや受光素子１４の形状が単純化されて作成が
容易となり、生産コストを低減することができる。As described above, the relative phase between the first diffraction grating 15a and the second diffraction grating 15b is a value obtained by dividing the quarter pitch by (n 1 -n 2 ), or 1 / pitch thereof. The value obtained by dividing 4 pitches by (n 1 −n 2 ) is 1 pitch (n 1 −n 2
Since the value divided by 2 ) is set to one or a value obtained by adding or subtracting a plurality of values, the phase of the second diffracted light that becomes the interference fringe is set to 1
It can be accurately and easily shifted by / 4 wavelength, whereby the defocus amount can be accurately obtained by maximizing the S-shaped curve of the focus error signal Fe.
In particular, by using ± 1st order light and setting the values of 1/8 pitch and 5/8 pitch, the first and second diffraction gratings 15
The shapes of a and 15b and the light-receiving element 14 are simplified to facilitate the production, and the production cost can be reduced.
【００２７】次に、本発明の第三の実施例を図７〜図９
に基づいて説明する（請求項４記載の発明に対応す
る）。なお、前記各実施例と同一部分についての説明は
省略し、その同一部分については同一符号を用いる。Next, a third embodiment of the present invention will be described with reference to FIGS.
(Corresponding to the invention of claim 4). It should be noted that the description of the same parts as those in the above-mentioned respective embodiments is omitted, and the same reference numerals are used for the same parts.
【００２８】本実施例では、二重回折格子１５における
第一回折格子１５ａのピッチはΛ1とされ、第二回折格
子１５ｂのピッチはΛ2 とされている。そして、第一回
折格子１５ａにより回折される第一回折光Ｋ1 はｎ1 次
光とｎ2 次光とされ、また、第二回折格子１５ｂにより
得られる第二回折光Ｋ2 はｍ1 次光とｍ2 次光とされて
いる。この場合、各回折格子のピッチと回折光の次数と
の間は、 Λ2 ｎ1 ＋Λ1 ｍ1 ＝Λ2 ｎ2 ＋Λ1 ｍ2 …（１２） の関係式に設定されている。In this embodiment, the pitch of the first diffraction grating 15a in the double diffraction grating 15 is Λ 1 and the pitch of the second diffraction grating 15b is Λ 2 . The first diffracted light K 1 diffracted by the first diffraction grating 15a is an n 1 -order light and an n 2 -order light, and the second diffracted light K 2 obtained by the second diffraction grating 15b is an m 1 -order light. Light and m 2 light. In this case, the relation between the pitch of each diffraction grating and the order of the diffracted light is set to a relational expression of Λ 2 n 1 + Λ 1 m 1 = Λ 2 n 2 + Λ 1 m 2 (12).
【００２９】以下、回折格子１５ａ，１５ｂの相対的な
位相関係を、上記（１２）式の条件に設定することによ
り、フォーカスエラー信号ＦｅのＳ字曲線を最大にする
ことができる理由について述べる。図７は、ピッチΛ1
の第一回折格子１５ａとピッチΛ2 の第二回折格子１５
ｂとが形成された二重回折格子１５での回折条件を示
す。今、光ディスク１３からの反射光が入射角θ0 で二
重回折格子１５に入射し、第一回折格子１５ａ側で出射
角θ1 のｎ1 次光，出射角θ3 のｎ2 次光が発生し、第
二回折格子１５ｂ側で出射角θ2 のｍ1 次光，出射角θ
4 のｍ2 次光が発生するものとする。この場合、第一回
折格子１５ａ側では、 ｓｉｎθ0 ＋ｓｉｎθ1 ＝ｎ1 λ／Λ1 …（１３） ｓｉｎθ0 ＋ｓｉｎθ3 ＝ｎ2 λ／Λ1 …（１４） が成り立つ。一方、第二回折格子１５ｂ側では、 ｓｉｎθ1 ＋ｓｉｎθ2 ＝−ｍ1 λ／Λ2 …（１５） ｓｉｎθ3 ＋ｓｉｎθ4 ＝−ｍ2 λ／Λ2 …（１６） が成り立つ。これにより、二重回折格子１５から出射し
たｍ1 次光、ｍ2 次光の２つの回折光を平行にするため
に、θ2 ＝θ4 とすると、 Λ2 ｎ1 ＋Λ1 ｍ1 ＝Λ2 ｎ2 ＋Λ1 ｍ2 …（１７） の関係が得られる。The reason why the S-shaped curve of the focus error signal Fe can be maximized by setting the relative phase relationship of the diffraction gratings 15a and 15b to the condition of the above expression (12) will be described below. FIG. 7 shows the pitch Λ 1
Of the first diffraction grating 15a and the second diffraction grating 15 of the pitch Λ 2
The diffraction condition in the double diffraction grating 15 in which b and b are formed is shown. Now, the reflected light incident on the incident angle theta 0 double diffraction grating 15 from the optical disk 13, the emission angle theta 1 of n 1-order light in the first diffraction grating 15a side, n 2 order light emission angle theta 3 Occurs, and the m 1 -order light with the emission angle θ 2 and the emission angle θ are generated on the second diffraction grating 15b side.
It is assumed that 4 m 2 order light is generated. In this case, on the first diffraction grating 15a side, sin θ 0 + sin θ 1 = n 1 λ / Λ 1 (13) sin θ 0 + sin θ 3 = n 2 λ / Λ 1 (14) holds. On the other hand, on the second diffraction grating 15b side, sin θ 1 + sin θ 2 = −m 1 λ / Λ 2 (15) sin θ 3 + sin θ 4 = −m 2 λ / Λ 2 (16) holds. Accordingly, in order to make the two diffracted lights of the m 1 -order light and the m 2 -order light emitted from the double diffraction grating 15 parallel to each other, if θ 2 = θ 4 , then Λ 2 n 1 + Λ 1 m 1 = The relationship of Λ 2 n 2 + Λ 1 m 2 (17) is obtained.
【００３０】例として、図８に示すように、第一回折格
子１５ａのΛ1 ＝１μｍ、第二回折格子１５ｂのΛ2 ＝
２μｍ、ｎ1 ＝２、ｎ2 ＝−１として、（１７）式に代
入すると、 ２・２＋１・ｍ1 ＝２・（−１）＋１・ｍ2 すなわち、 ｍ1 −ｍ2 ＝−６ …（１８） の関係式を得る。この（１８）式から、例えば、図９に
示すように、ｍ1 ＝−２、ｍ2 ＝４とすると、第一回折
格子１５ａにより２次光と−１次光が発生し、第二回折
格子１５ｂにより−２次光と４次光が発生する。これに
より、回折されたｍ1 ，ｍ2 次光の位相をλ／４だけず
らすことが可能となる。[0030] As an example, as shown in FIG. 8, lambda 1 = 1 [mu] m of the first diffraction grating 15a, the second diffraction grating 15b lambda 2 =
Substituting into equation (17) assuming 2 μm, n 1 = 2, n 2 = −1, 2 · 2 + 1 · m 1 = 2 · (−1) + 1 · m 2, that is, m 1 −m 2 = −6 ... The relational expression of (18) is obtained. From Equation (18), for example, if m 1 = -2 and m 2 = 4 as shown in FIG. 9, the first diffraction grating 15a generates second-order light and -1st-order light, and the second diffraction The grating 15b generates −2nd order light and 4th order light. This makes it possible to shift the phases of the diffracted m 1 and m 2 -order lights by λ / 4.
【００３１】上述したように、（１２）式の関係を満た
すように設定することによって、干渉縞となる第二回折
光Ｋ2 の位相をλ／４だけずらすことができ、これによ
り、フォーカスエラー信号ＦｅのＳ字曲線を最大にし
て、デフォーカス量を正確に求めることができる。な
お、ここでは、回折格子に入射する光が垂直であること
を前提としているが、垂直に入射しない場合にも、２つ
の回折光の位相がλ／４だけずれるように調整すればよ
い。As described above, the phase of the second diffracted light K 2 which becomes interference fringes can be shifted by λ / 4 by setting so as to satisfy the relationship of the expression (12). The defocus amount can be accurately obtained by maximizing the S-shaped curve of the signal Fe. Although it is assumed here that the light incident on the diffraction grating is vertical, it may be adjusted so that the phases of the two diffracted lights are shifted by λ / 4 even when the light does not enter vertically.
【００３２】[0032]
【発明の効果】請求項１記載の発明は、互いに干渉し合
う第二回折光の位相が１／４波長だけずれるように、干
渉縞発生手段の各回折格子を形成したので、フォーカス
エラー信号のＳ字曲線を最大にしてデフォーカス量を容
易に求めることができ、これにより、従来のナイフエッ
ジ法や非点収差法に比べて、信号の検出感度を格段に向
上させて微小変位の測定を正確に行うことができる。ま
た、このような干渉縞を用いた測定方式においては、検
出光路長を従来よりも短くとることができるため、光ピ
ックアップ部の小型化を図ることができる。さらに、こ
のような干渉縞による検出においてはビーム形状を比較
的大きくとれるため、光学素子の位置調整を極めてラフ
に行うことができ、耐環境性を向上させ、常に安定した
信号検出を行うことができる。According to the first aspect of the present invention, since the diffraction gratings of the interference fringe generating means are formed so that the phases of the second diffracted lights that interfere with each other are shifted by ¼ wavelength, the focus error signal The defocus amount can be easily obtained by maximizing the S-curve, which significantly improves the signal detection sensitivity as compared with the conventional knife edge method and astigmatism method, and can measure minute displacements. Can be done accurately. Further, in the measurement method using such interference fringes, the detection optical path length can be made shorter than before, so that the optical pickup unit can be downsized. Further, since the beam shape can be made relatively large in the detection by such interference fringes, the position of the optical element can be adjusted extremely roughly, the environment resistance can be improved, and stable signal detection can always be performed. it can.
【００３３】請求項２記載の発明は、第一回折格子と第
二回折格子との相対的な位相を、４分の１ピッチを（ｎ
1 −ｎ2 ）で割った値か、又は、その４分の１ピッチを
（ｎ1 −ｎ2 ）で割った値に、１ピッチを（ｎ1 −ｎ
2 ）で割った値を１個ないしは複数個加算又は減算した
値に設定したので、干渉縞となる第二回折光の位相を１
／４波長だけ正確にずらすことができ、これにより、フ
ォーカスエラー信号のＳ字曲線を最大にして、デフォー
カス量を正確に求めることができる。According to a second aspect of the present invention, the relative phase of the first diffraction grating and the second diffraction grating is set to a quarter pitch (n
1 -n 2) at or divided by, or divided by the one pitch of the quarter (n 1 -n 2), and 1 pitch (n 1 -n
Since the value divided by 2 ) is set to one or a value obtained by adding or subtracting a plurality of values, the phase of the second diffracted light that becomes the interference fringe is set to 1
It can be accurately shifted by / 4 wavelength, and by doing so, the defocus amount can be accurately obtained by maximizing the S-shaped curve of the focus error signal.
【００３４】請求項３記載の発明は、第一回折格子と第
二回折格子との相対的な位相を、８分の１ピッチ、又
は、８分の５ピッチの値に設定したので、干渉縞となる
第二回折光の位相を１／４波長だけ正確にしかも容易に
ずらすことができ、これにより、フォーカスエラー信号
のＳ字曲線を最大にして、デフォーカス量を一段と正確
に求めることができる。また、第一回折格子と第二回折
格子とを等ピッチすなわち同一の格子ピッチとし、±１
次光の第二回折光を用いて干渉縞を発生させるようにし
たので、回折格子や受光素子の作成が容易となり、生産
コストを一段と削減することができる。According to the third aspect of the present invention, the relative phase between the first diffraction grating and the second diffraction grating is set to a value of 1/8 pitch or 5/8 pitch. It is possible to accurately and easily shift the phase of the second diffracted light by 1/4 wavelength, thereby maximizing the S-shaped curve of the focus error signal and more accurately obtaining the defocus amount. . Further, the first diffraction grating and the second diffraction grating have an equal pitch, that is, the same grating pitch, and ± 1
Since the interference fringes are generated by using the second diffracted light of the next light, the diffraction grating and the light receiving element can be easily manufactured, and the production cost can be further reduced.
【００３５】請求項４記載の発明は、ピッチがΛ1 の第
一回折格子により得られる第一回折光をｎ1 次光とｎ2
次光とし、ピッチがΛ2 の第二回折格子により得られる
第二回折光をｍ1 次光とｍ2 次光としたとき、各回折格
子のピッチと回折光の次数とを、 Λ2 ｎ1 ＋Λ1 ｍ1 ＝Λ2 ｎ2 ＋Λ1 ｍ2 の関係式を満たすように設定したので、干渉縞となる第
二回折光の位相を１／４波長だけずらし、フォーカスエ
ラー信号のＳ字曲線を最大にしてデフォーカス量を一段
と正確に求めることができる。According to a fourth aspect of the present invention, the first diffracted light obtained by the first diffraction grating having a pitch of Λ 1 is converted into n 1 -order light and n 2
When the second diffracted light obtained by the second diffraction grating having a pitch of Λ 2 is the m 1 -order light and the m 2 -order light, the pitch of each diffraction grating and the order of the diffracted light are Λ 2 n Since the relational expression of 1 + Λ 1 m 1 = Λ 2 n 2 + Λ 1 m 2 is set, the phase of the second diffracted light that becomes the interference fringes is shifted by ¼ wavelength, and the S-shaped curve of the focus error signal is obtained. Can be maximized to more accurately obtain the defocus amount.
【図１】本発明の第一の実施例として２つの回折光によ
り１／４波長の位相差が生じた場合の理論的解析の等価
光学系を示す模式図である。FIG. 1 is a schematic diagram showing an equivalent optical system for theoretical analysis in the case where a phase difference of ¼ wavelength is generated by two diffracted lights as a first embodiment of the present invention.
【図２】微小変位測定装置の全体構成を示す光路図であ
る。FIG. 2 is an optical path diagram showing an overall configuration of a micro displacement measuring device.
【図３】デフォーカス量に対するフォーカスエラー信号
のＳ字曲線を示す波形図である。FIG. 3 is a waveform diagram showing an S-shaped curve of a focus error signal with respect to a defocus amount.
【図４】本発明の第二の実施例として回折格子の移動に
より回折光の波面も移動することを示す側面図である。FIG. 4 is a side view showing that, as a second embodiment of the present invention, the wavefront of diffracted light also moves due to the movement of the diffraction grating.
【図５】回折格子を２枚重ねて構成し、回折格子を１ピ
ッチだけ移動した場合における回折光に位相差が生じて
いる様子を示す側面図である。FIG. 5 is a side view showing a state in which a phase difference is generated in diffracted light when two diffraction gratings are stacked and the diffraction grating is moved by one pitch.
【図６】回折格子の相対的な位相が一致している場合に
回折光の波面も一致する場合の様子を示す側面図であ
る。FIG. 6 is a side view showing a state where the wavefronts of diffracted light also match when the relative phases of the diffraction grating match.
【図７】本発明の第三の実施例である回折格子のピッチ
が異なっている場合の回折光の発生の様子を示す側面図
である。FIG. 7 is a side view showing how the diffracted light is generated when the pitch of the diffraction grating according to the third embodiment of the present invention is different.
【図８】ピッチが異なっている回折格子を用いた場合に
回折光に位相差が生じている様子を示す側面図である。FIG. 8 is a side view showing how a phase difference occurs in diffracted light when diffraction gratings having different pitches are used.
【図９】高次の回折光が発生した場合の様子を示す側面
図である。FIG. 9 is a side view showing a state where high-order diffracted light is generated.
【図１０】従来の装置におけるフォーカスエラー信号の
検出方式を示す光路図である。FIG. 10 is an optical path diagram showing a detection method of a focus error signal in a conventional device.
９ 光源 １２ 対物レンズ １３ 測定物 １４ 受光素子 １５ 干渉縞発生手段 １５ａ 第一回折格子 １５ｂ 第二回折格子 Ｋ1 第一回折光 Ｋ2 第二回折光9 light sources 12 objective lens 13 measured 14 receiving element 15 interference fringe generating means 15a first diffraction grating 15b second diffraction grating K 1 first diffracted beam K 2 second diffracted light
Claims (4)
て測定物に照射しその測定物により反射され前記対物レ
ンズを再び通過した光が入射することによりｎ1 次光と
ｎ2 次光との第一回折光を発生する第一回折格子と、前
記第一回折光が入射することにより複数の回折された第
二回折光を発生する第二回折格子とからなり、互いに干
渉し合う前記第二回折光の位相が１／４波長だけずれる
ような形状に各回折格子が形成された干渉縞発生手段を
設け、この干渉縞発生手段により生じた前記第二回折光
の間での干渉により干渉縞の位相の変化を受光素子で検
知することによって前記測定物の光軸方向への移動量を
測定するようにしたことを特徴とする微小変位測定装
置。1. An n 1st- order light and an n 2nd- order light are obtained by collecting light from a light source with an objective lens, irradiating the object to be measured, and reflecting light reflected by the object and passing through the objective lens again. And a first diffraction grating that generates a first diffracted light, and a second diffraction grating that generates a plurality of diffracted second diffracted lights by the incidence of the first diffracted light, and the two interfere with each other. By providing interference fringe generating means in which each diffraction grating is formed in a shape such that the phase of the second diffracted light is shifted by ¼ wavelength, the interference between the second diffracted light caused by the interference fringe generating means A micro-displacement measuring device characterized in that the amount of movement of the measured object in the optical axis direction is measured by detecting a change in the phase of the interference fringes with a light receiving element.
な位相を、回折格子の４分の１ピッチを（ｎ1 −ｎ2 ）
で割った値、又は、その値にさらに１ピッチを（ｎ1 −
ｎ2 ）で割った値を１個ないしは複数個加算又は減算し
た値に設定したことを特徴とする請求項１記載の微小変
位測定装置。2. The relative phase between the first diffraction grating and the second diffraction grating is set to a quarter pitch of the diffraction grating (n 1 −n 2 ).
Divided by, or 1 pitch is added to that value (n 1 −
The small displacement measuring device according to claim 1, wherein the value divided by n 2 ) is set to one or a plurality of values added or subtracted.
格子と第二回折格子とを等ピッチとし、第一回折格子と
第二回折格子との相対的な位相を、回折格子の８分の１
ピッチ、又は、８分の５ピッチの値に設定したことを特
徴とする請求項１記載の微小変位測定装置。3. A first diffraction grating and a second diffraction grating for generating interference fringes of ± first-order light are arranged at an equal pitch, and a relative phase between the first diffraction grating and the second diffraction grating 1 / 8th
The minute displacement measuring device according to claim 1, wherein the value is set to a pitch or a value of 5/8 pitch.
れる第一回折光をｎ1 次光とｎ2 次光とし、ピッチがΛ
2 の第二回折格子により得られる第二回折光をｍ1 次光
とｍ2 次光としたとき、各回折格子のピッチと回折光の
次数とを、 Λ2 ｎ1 ＋Λ1 ｍ1 ＝Λ2 ｎ2 ＋Λ1 ｍ2 の関係式を満たすように設定したことを特徴とする請求
項１記載の微小変位測定装置。4. The first diffracted light obtained by the first diffraction grating having a pitch of Λ 1 is n 1 -order light and n 2 -order light, and the pitch is Λ
When the second diffracted light obtained by the second diffractive grating of 2 is m 1 -order light and m 2 -order light, the pitch of each diffraction grating and the order of diffracted light are Λ 2 n 1 + Λ 1 m 1 = Λ The micro displacement measuring device according to claim 1, wherein the micro displacement measuring device is set so as to satisfy the relational expression of 2 n 2 + Λ 1 m 2 .
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32889294A JP3573367B2 (en) | 1994-12-28 | 1994-12-28 | Micro displacement measuring device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32889294A JP3573367B2 (en) | 1994-12-28 | 1994-12-28 | Micro displacement measuring device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH08180493A true JPH08180493A (en) | 1996-07-12 |
| JP3573367B2 JP3573367B2 (en) | 2004-10-06 |
Family
ID=18215266
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP32889294A Expired - Lifetime JP3573367B2 (en) | 1994-12-28 | 1994-12-28 | Micro displacement measuring device |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3573367B2 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH11328713A (en) * | 1998-05-14 | 1999-11-30 | Hideo Maeda | Directional diffraction grating |
| US6733939B2 (en) * | 2000-09-28 | 2004-05-11 | Ricoh Company, Ltd. | Toner, developer and container for the developer, and method of and apparatus for forming an image |
| KR100444913B1 (en) * | 2002-01-28 | 2004-08-21 | 한국과학기술원 | Displacement Measurement Sensor |
| CN103759656A (en) * | 2014-01-23 | 2014-04-30 | 清华大学 | Two-degree-of-freedom heterodyne grating interferometer displacement measurement system |
-
1994
- 1994-12-28 JP JP32889294A patent/JP3573367B2/en not_active Expired - Lifetime
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH11328713A (en) * | 1998-05-14 | 1999-11-30 | Hideo Maeda | Directional diffraction grating |
| US6733939B2 (en) * | 2000-09-28 | 2004-05-11 | Ricoh Company, Ltd. | Toner, developer and container for the developer, and method of and apparatus for forming an image |
| KR100444913B1 (en) * | 2002-01-28 | 2004-08-21 | 한국과학기술원 | Displacement Measurement Sensor |
| CN103759656A (en) * | 2014-01-23 | 2014-04-30 | 清华大学 | Two-degree-of-freedom heterodyne grating interferometer displacement measurement system |
| CN103759656B (en) * | 2014-01-23 | 2017-01-18 | 清华大学 | Two-degree-of-freedom heterodyne grating interferometer displacement measurement system |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3573367B2 (en) | 2004-10-06 |
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